Patent Application
20070173787
1. Field of the Invention
The present invention relates to the administration of therapeutic agents for the prevention and treatment of vascular disease, and more particularly to intraluminal medical devices in combination with therapeutic agents for the prevention and treatment of vascular disease.
2. Discussion of the Related Art
Many individuals suffer from circulatory disease caused by a progressive blockage of the blood vessels that perfuse the heart and other major organs. More severe blockage of blood vessels in such individuals often leads to hypertension, ischemic injury, stroke, or myocardial infarction. Atherosclerotic lesions, which limit or obstruct coronary blood flow, are the. major cause of ischemic heart disease. Percutaneous transluminal coronary angioplasty is a medical procedure whose purpose is to increase blood flow through an artery. Percutaneous transluminal coronary angioplasty is the predominant treatment for coronary vessel stenosis. The increasing use of this procedure is attributable to its relatively high success rate and its minimal invasiveness compared with coronary bypass surgery. A limitation associated with percutaneous transluminal coronary angioplasty is the abrupt closure of the vessel, which may occur immediately after the procedure and restenosis, which occurs gradually following the procedure. Additionally, restenosis is a chronic problem in patients who have undergone saphenous vein bypass grafting. The mechanism of acute occlusion appears to involve several factors and may result from vascular recoil with resultant closure of the artery and/or deposition of blood platelets and fibrin along the damaged length of the newly opened blood vessel.
Restenosis after percutaneous transluminal coronary angioplasty is a more gradual process initiated by vascular injury. Multiple processes, including thrombosis, inflammation, growth factor and cytokine release, cell proliferation, cell migration and extracellular matrix synthesis each contribute to the restenotic process.
While the exact mechanism of restenosis is not completely understood, the general aspects of the restenosis process have been identified. In the normal arterial wall, smooth muscle cells proliferate at a low rate, approximately less than 0.1 percent per day. Smooth muscle cells in the vessel walls exist in a contractile phenotype characterized by eighty to ninety percent of the cell cytoplasmic volume occupied with the contractile apparatus. Endoplasmic reticulum, Golgi, and free ribosomes are few and are located in the perinuclear region. Extracellular matrix surrounds the smooth muscle cells and is rich in heparin-like glycosylaminoglycans, which are believed to be responsible for maintaining smooth muscle cells in the contractile phenotypic state (Campbell and Campbell, 1985).
Upon pressure expansion of an intracoronary balloon catheter during angioplasty, smooth muscle cells and endothelial cells within the vessel wall become injured, initiating a thrombotic and inflammatory response. Cell derived growth factors such as platelet derived growth factor, basic fibroblast growth factor, epidermal growth factor, thrombin, etc., released from platelets, invading macrophages and/or leukocytes, or directly from the smooth muscle cells provoke a proliferative and migratory response in medial smooth muscle cells. These cells undergo a change from the contractile phenotype to a synthetic phenotype characterized by only a few contractile filament bundles, extensive rough endoplasmic reticulum, Golgi and free ribosomes. Proliferation/migration usually begins within one to two days' post-injury and peaks several days thereafter (Campbell and Campbell, 1987; Clowes and Schwartz, 1985).
Daughter cells migrate to the intimal layer of arterial smooth muscle and continue to proliferate and secrete significant amounts of extracellular matrix proteins. Proliferation, migration and extracellular matrix synthesis continue until the damaged endothelial layer is repaired at which time proliferation slows within the intima, usually within seven to fourteen days post-injury. The newly formed tissue is called neointima. The further vascular narrowing that occurs over the next three to six months is due primarily to negative or constrictive remodeling.
Simultaneous with local proliferation and migration, inflammatory cells adhere to the site of vascular injury. Within three to seven days post-injury, inflammatory cells have migrated to the deeper layers of the vessel wall. In animal models employing either balloon injury or stent implantation, inflammatory cells may persist at the site of vascular injury for at least thirty days (Tanaka et al., 1993; Edelman et al., 1998). Inflammatory cells therefore are present and may contribute to both the acute and chronic phases of restenosis.
Numerous agents have been examined for presumed anti-proliferative actions in restenosis and have shown some activity in experimental animal models. Some of the agents which have been shown to successfully reduce the extent of intimal hyperplasia in animal models include: heparin and heparin fragments (Clowes, A. W. and Karnovsky M., Nature 265: 25-26, 1977; Guyton, J. R. et al., Circ. Res., 46: 625-634, 1980; Clowes, A. W. and Clowes, M. M., Lab. Invest. 52: 611-616, 1985; Clowes, A. W. and Clowes, M. M., Circ. Res. 58: 839-845, 1986; Majesky et al., Circ. Res. 61: 296-300, 1987; Snow et al., Am. J. Pathol. 137: 313-330, 1990; Okada, T. et al., Neurosurgery 25: 92-98, 1989), colchicine (Currier, J. W. et al., Circ. 80: 11-66, 1989), taxol (Sollot, S. J. et al., J. Clin. Invest. 95: 1869-1876, 1995), angiotensin converting enzyme (ACE) inhibitors (Powell, J. S. et al., Science, 245: 186-188, 1989), angiopeptin (Lundergan, C. F. et al. Am. J. Cardiol. 17 (Suppl. B):132B-136B, 1991), cyclosporin A (Jonasson, L. et al., Proc. Natl., Acad. Sci., 85: 2303, 1988), goat-anti-rabbit PDGF antibody (Ferns, G. A. A., et al., Science 253: 1129-1132, 1991), terbinafine (Nemecek, G. M. et al., J. Pharmacol. Exp. Thera. 248: 1167-1174, 1989), trapidil (Liu, M. W. et al., Circ. 81: 1089-1093, 1990), tranilast (Fukuyama, J. et al., Eur. J. Pharmacol. 318: 327-332, 1996), interferon-gamma (Hansson, G. K. and Holm, J., Circ. 84: 1266-1272, 1991), rapamycin (Marx, S. O. et al., Circ. Res. 76: 412-417, 1995), steroids (Colburn, M. D. et al., J. Vasc. Surg. 15: 510-518, 1992), see also Berk, B. C. et al., J. Am. Coll. Cardiol. 17: 111B-117B, 1991), ionizing radiation (Weinberger, J. et al., lnt. J. Rad. Onc. Biol. Phys. 36: 767-775, 1996), fusion toxins (Farb, A. et al., Circ. Res. 80: 542-550, 1997) antisense oligionucleotides (Simons, M. et al., Nature 359: 67-70, 1992) and gene vectors (Chang, M. W. et al., J. Clin. Invest. 96: 2260-2268, 1995). Anti-proliferative action on smooth muscle cells in vitro has been demonstrated for many of these agents, including heparin and heparin conjugates, taxol, tranilast,. colchicine, ACE inhibitors, fusion toxins, antisense oligionucleotides, rapamycin and ionizing radiation. Thus, agents with diverse mechanisms of smooth muscle cell inhibition may have therapeutic utility in reducing intimal hyperplasia.
However, in contrast to animal models, attempts in human angioplasty patients to prevent restenosis by systemic pharmacologic means have thus far been unsuccessful. Neither aspirin-dipyridamole, ticlopidine, anti-coagulant therapy (acute heparin, chronic warfarin, hirudin or hirulog), thromboxane receptor antagonism nor steroids have been effective in preventing restenosis, although platelet inhibitors have been effective in preventing acute reocclusion after angioplasty (Mak and Topol, 1997; Lang et al., 1991; Popma et al., 1991). The platelet GP Ilb/IIIa receptor, antagonist, Reopro® is still under study but Reopro® has not shown definitive results for the reduction in restenosis following angioplasty and stenting. Other agents, which have also been unsuccessful in the prevention of restenosis, include the calcium channel antagonists, prostacyclin mimetics, angiotensin converting enzyme inhibitors, serotonin receptor antagonists, and anti-proliferative agents. These agents must be given systemically, however, and attainment of a therapeutically effective dose may not be possible; anti-proliferative (or anti-restenosis) concentrations may exceed the known toxic concentrations of these agents so that levels sufficient to produce smooth muscle inhibition may not be reached (Mak and Topol, 1997; Lang et al., 1991; Popma et al., 1991).
Additional clinical trials in which the effectiveness for preventing restenosis utilizing dietary fish oil supplements or cholesterol lowering agents has been examined showing either conflicting or negative results so that no pharmacological agents are as yet clinically available to prevent post-angioplasty restenosis (Mak and Topol, 1997; Franklin and Faxon, 1993: Serruys, P. W. et al., 1993). Recent observations suggest that the antilipid/antioxident agent, probucol, may be useful in preventing restenosis but this work requires confirmation (Tardif et al., 1997; Yokoi, et al., 1997). Probucol is presently not approved for use in the United States and a thirty-day pretreatment period would preclude its use in emergency angioplasty. Additionally, the application of ionizing radiation has shown significant promise in reducing or preventing restenosis after angioplasty in patients with stents (Teirstein et al., 1997). Currently, however, the most effective treatments for restenosis are repeat angioplasty, atherectomy or coronary artery bypass grafting, because no therapeutic agents currently have Food and Drug Administration approval for use for the prevention of post-angioplasty restenosis.
Unlike systemic pharmacologic therapy, stents have proven useful in significantly reducing restenosis. Typically, stents are balloon-expandable slotted metal tubes (usually, but not limited to, stainless steel), which, when expanded within the lumen of an angioplastied coronary artery, provide structural support through rigid scaffolding to the arterial wall. This support is helpful in maintaining vessel lumen patency. In two randomized clinical trials, stents increased angiographic success after percutaneous transluminal coronary angioplasty, by increasing minimal lumen diameter and reducing, but not eliminating, the incidence of restenosis at six months (Serruys et al., 1994; Fischman et al., 1994).
Additionally, the heparin coating of stents appears to have the added benefit of producing a reduction in sub-acute thrombosis after stent implantation (Serruys et al., 1996). Thus, sustained mechanical expansion of a steriosed coronary artery with a stent has been shown to provide some measure of restenosis prevention, and the coating of stents with heparin has demonstrated both the feasibility and the clinical usefulness of delivering drugs locally, at the site of injured tissue.
As stated above, the use of heparin coated stents demonstrates the feasibility and clinical usefulness of local drug delivery; however, the manner in which the particular drug or drug combination is affixed to the local delivery device will play a role in the efficacy of this type of treatment. For example, the processes and materials utilized to affix the drug/drug combinations to the local delivery device should not interfere with the operations of the drug/drug combinations. In addition, the processes and materials utilized should be biocompatible and maintain the drug/drug combinations on the local device through delivery and over a given period of time. For example, removal of the drug/drug combination during delivery of the local delivery device may potentially cause failure of the device.
Accordingly, there exists a need for drug/drug combinations and associated local delivery devices for the prevention and treatment of vascular injury causing intimal thickening which is either biologically induced, for example, atherosclerosis, or mechanically induced, for example, through percutaneous transluminal coronary angioplasty. In addition, there exists a need for maintaining the drug/drug combinations on the local delivery device through delivery and positioning as well as ensuring that the drug/drug combination is released in therapeutic dosages over a given period of time.
A variety of stent coatings and compositions have been proposed for the prevention and treatment of injury causing intimal thickening. The coatings may be capable themselves of reducing the stimulus the stent provides to the injured lumen wall, thus reducing the tendency towards thrombosis or restenosis. Alternately, the coating may deliver a pharmaceutical/therapeutic agent or drug to the lumen that reduces smooth muscle tissue proliferation or restenosis. The mechanism for delivery of the agent is through diffusion of the agent through either a bulk polymer or through pores that are created in the polymer structure, or by erosion of a biodegradable coating.
Both bioabsorbable and biostable compositions have been reported as coatings for stents. They generally have been polymeric coatings that either encapsulate a pharmaceutical/therapeutic agent or drug, e.g. rapamycin, taxol etc., or bind such an agent to the surface, e.g. heparin-coated stents. These coatings are applied to the stent in a number of ways, including, though not limited to, dip, spray, or spin coating processes.
One class of biostable materials that has been reported as coatings for stents is polyfluoro homopolymers. Polytetrafluoroethylene (PTFE) homopolymers have been used as implants for many years. These homopolymers are not soluble in any solvent at reasonable temperatures and therefore are difficult to coat onto small medical devices while maintaining important features of the devices (e.g. slots in stents).
Stents with coatings made from polyvinylidenefluoride homopolymers and containing pharmaceutical/therapeutic agents or drugs for release have been suggested. However, like most crystalline polyfluoro homopolymers, they are difficult to apply as high quality films onto surfaces without subjecting them to relatively high temperatures that correspond to the melting temperature of the polymer.
It would be advantageous to develop coatings for implantable medical devices that will reduce thrombosis, restenosis, or other adverse reactions, that may include, but do not require, the use of pharmaceutical or therapeutic agents or drugs to achieve such affects, and that possess physical and mechanical properties effective for use in such devices even when such coated devices are subjected to relatively low maximum temperatures. It would also be advantageous to develop implantable medical devices in combination with various drugs, agents and/or compounds which treat disease and minimize or substantially eliminate a living organisms'reaction to the implantation of the medical device. In certain circumstances, it may be advantageous to develop implantable medical devices in combination with various drugs, agents and/or compounds which promote wound healing and endothelialization of the medical device.
It would also be advantageous to develop delivery devices that provide for the delivery of the coated implantable medical devices without adversely affecting the coating or the medical device itself. In addition, such delivery devices should provide the physician with a means for easily and accurately. positioning the medical device in the target area.
It would also be advantageous to develop coatings for implantable medical devices that allow for the precise control of the elution rate of drugs, agents and/or compounds from the implantable medical devices.
It would also be advantageous to develop delivery devices that provide for the release of one or more agents that act through different molecular mechanisms affecting cell proliferation.
It would also be advantageous to develop delivery devices that provide for the regional administration of one or more agents for the treatment of atherosclerotic plaque.
It would also be advantageous to develop liquid formulations of the drugs to increase the efficacy and deliverability thereof. Specifically, liquid solution dosage forms of water insoluble and lipohilic drugs are difficult to create without resorting to substantial quantities of surfactants, co-solvents and the like.
Another type of vascular disease of considerable concern is atherosclerosis. Atherosclerosis is a thickening and hardening of the arteries and is generally believed to be caused by the progressive buildup of fatty substances, e.g. cholesterol, inflammatory cells, cellular waste products, calcium and other substances in the inner lining or intima of the arteries. The buildup of these irritating substances may in turn stimulate cells in the walls of the affected arteries to produce additional substances that result in the further buildup of cells leading to the growth of a lesion. This buildup or lesion is generally referred to as plaque.
Recent studies have lead to a shift in the understanding of atherosclerosis and uncovered another major vascular problem not yet well treated. Scientists theorize that at least some coronary disease is an inflammatory process, in which inflammation causes plaque to destabilize and rupture. This inflamed plaque is known as atherosclerotic vulnerable plaque.
Vulnerable plaque consists of a lipid-rich core covered by a thin layer of smooth muscle cells. These vulnerable plaques are prone to rupture and erosion, and can cause significant infarcts if the thin cellular layer ruptures or ulcerates. When the inflammatory cells erode or rupture, the lipid core is exposed to the blood flow, forming thrombi in the artery. These thrombi may grow rapidly and block the artery, or detach and travel downstream, leading to embolic events, unstable angina, myocardial infarction, and/or sudden death. In fact, some recent studies have suggested that plaque rupture may trigger sixty to seventy percent of all fatal myocardial infarctions. See U.S. Pat. No. 5,924,997 issued to Campbell and U.S. Pat. No. 6,245,026 issued to Campbell et al. for further descriptions of vulnerable plaques.
Early methods used to detect atherosclerosis lacked the diagnostic tools to visualize and identify vulnerable plaque in cardiac patients. However, new diagnostic technologies are under development to identify the location of vulnerable plaques in the coronary arteries. These new devices include refined magnetic resonance imaging (MRI), thermal sensors that measure the temperature of the arterial wall on the premise that the inflammatory process generates heat, elasticity sensors, intravascular ultrasound, optical coherence tomography (OCT), contrast agents, and near-infrared and infrared light. What is not currently clear, however, is how to treat these vulnerable plaque lesions once they are found.
Treating vulnerable plaque by using balloon angioplasty followed by traditional stenting would provide less than satisfactory results. Balloon angioplasty by itself may rupture the vulnerable plaque exposing the underlying fresh tissue cells, collagen or damaged endothelium, to the blood flow. This condition ultimately leads to the formation of a thrombi or blood clot that may partially or completely occlude the vessel. In addition, while bare or uncoated stents will induce neointimal hyperplasia that will provide a protective cover over the vulnerable plaque, restenosis remains a major problem that may create more risk to the patient than the original vulnerable plaque.
Accordingly, it would be advantageous to develop a drug eluting stent or other medical device that effectively treats vulnerable plaque and related vascular disease.
As described above, any number of drugs, agents and/or compounds may be locally delivered via any number of medical devices. For example, stents and anastomosis devices may incorporate coatings comprising drugs, agents and/or compounds to treat various disease states and reactions by the body as described in detail above. Other devices which may be coated with or otherwise incorporate therapeutic dosages of drugs, agents and/or compounds include stent-grafts and devices utilizing stent-grafts, such as devices for treating abdominal aortic aneurysms as well as other aneurysms, e.g. thoracic aorta aneurysms.
Stent-grafts may be utilized to treat aneurysms. An aneurysm is an abnormal dilation of a layer or layers of an arterial wall, usually caused by a systemic collagen synthetic or structural defect. An abdominal aortic aneurysm is an aneurysm in the abdominal portion of the aorta, usually located in or near one or both of the two iliac arteries or near the renal arteries. The aneurysm often arises in the infrarenal portion of the diseased aorta, for example, below the kidneys. A thoracic aortic aneurysm is an aneurysm in the thoracic portion of the aorta. When left untreated, the aneurysm may rupture, usually causing rapid fatal hemorrhaging.
Accordingly, it would be advantageous to develop drugs and drug delivery devices for the treatment of abdominal aortic aneurysms and inflammation.
For all drug eluting medical devices there are a number of characteristics or features that are beneficial. For example, precise control over dosing while maintaining a low profile, uniformity of drug distribution over the coated areas of the device, precise dosing over specific regions of the device and the minimization of the creation of embolic material during implantation or if required, explantation are all desirable features.
The medical devices in combination with therapeutic dosages of one or more drugs, agents, and/or compounds of the present invention provide a means for overcoming the difficulties associated with the methods and devices currently in use for the treatment of occluded blood vessels, restenosis and other related vascular disease, as briefly described above.
In accordance with one aspect, the present invention is directed to a medical device. The medical device comprises an implantable structure having at least one surface, a thin film mesh affixed to the at least one surface of the implantable structure, and at least one agent, in therapeutic dosage, releasably affixed to the thin film mesh, the thin film mesh being configured to increase the surface area available for the at least one agent and release the at least one agent for a predetermined period of time.
In accordance with another aspect, the present invention is directed to a medical device. The medical device comprises an implantable structure having at least one surface, a thin film layer affixed to the at least one surface of the implantable structure, and at least one agent, in therapeutic dosage, releasably affixed to the thin film, the thin film being configured as a substrate for the controlled release of the at least one agent.
In accordance with another aspect, the present invention is directed to a medical device. The medical device comprises an implantable structure having at least one surface, a thin film affixed to the at least one surface of the implantable structure, the thin film having a predetermined pattern of micro features in the surface thereof, and at least one agent, in therapeutic dosage, releasably affixed to at least one of the surface of the thin film and the predetermined pattern of micro features, in the surface thereof.
In accordance with another aspect, the present invention is directed to a medical device. The medical device comprises an implantable structure having at least one surface, a radiopaque material layer affixed to the at least one surface of the implantable structure, a thin film affixed to the radiopaque material layer; and at least one agent, in therapeutic dosage, releasably affixed to the thin film.
In accordance with another aspect, the present invention is directed to a medical device. The medical device comprises an implantable structure having at least one surface, a radiopaque material layer affixed to the at least one surface of the implantable structure, a thin film mesh affixed to the radiopaque material layer, and at least one agent, in therapeutic dosage, releasably affixed to the thin film mesh.
In accordance with another aspect, the present invention is directed to a medical device. The medical device comprises an implantable structure having at least one surface, a thin film mesh affixed to the at least one surface of the implantable structure, the thin film mesh having a textured surface, and at least one agent, in therapeutic dosage, releasably affixed to the thin film mesh, the thin film mesh being configured to increase the surface area available for the at least one agent and release the at least one agent for a predetermined period of time.
In accordance with another aspect, the present invention is directed to a medical device. The medical device comprises an implantable structure having at least one surface, a thin film layer affixed to the at least one surface of the implantable structure, the thin film layer having a textured surface, and at least one agent, in therapeutic dosage, releasably affixed to the thin film, the thin film being configured as a substrate for the controlled release of the at least one agent.
The medical devices, drug coatings, delivery devices and methods for maintaining the drug coatings or vehicles thereon of the present invention utilizes a combination of materials to treat disease, and reactions by living organisms due to the implantation of medical devices for the treatment of disease or other conditions. The local delivery of drugs, agents or compounds generally substantially reduces the potential toxicity of the drugs, agents or compounds when compared to systemic delivery while increasing their efficacy.
Drugs, agents or compounds may be affixed to any number of medical devices to treat various diseases. The drugs, agents or compounds may also be affixed to minimize or substantially eliminate the biological organism's reaction to the introduction of the medical device utilized to treat a separate condition. For example, stents may be introduced to open coronary arteries or other body lumens such as biliary ducts. The introduction of these stents cause a smooth muscle cell proliferation effect as well as inflammation. Accordingly, the stents may be coated with drugs, agents or compounds to combat these reactions. Anastomosis devices, routinely utilized in certain types of surgery, may also cause a smooth muscle cell proliferation effect as well as inflammation. Stent-grafts and systems utilizing stent-grafts, for example, aneurysm bypass systems may be coated with drugs, agents and/or compounds which prevent adverse affects caused by the introduction of these devices as well as to promote healing and incorporation. Therefore, the devices may also be coated with drugs, agents and/or compounds to combat these reactions. In addition, devices such as aneurysm bypass systems may be coated with drugs, agents and/or compounds that promote would healing and endothelialization, thereby reducing the risk of endoleaks or other similar phenomena.
The drugs, agents or compounds will vary depending upon the type of medical device, the reaction to the introduction of the medical device and/or the disease sought to be treated. The type of coating or vehicle utilized to immobilize the drugs, agents or compounds to the medical device may also vary depending on a number of factors, including the type of medical device, the type of drug, agent or compound and the rate of release thereof.
In order to be effective, the drugs, agents or compounds should preferably remain on the medical devices during delivery and implantation. Accordingly, various coating techniques for creating strong bonds between the drugs, agents or compounds may be utilized. In addition, various materials may be utilized as surface modifications to prevent the drugs, agents or compounds from coming off prematurely.
Microneedles or other catheter-based delivery systems such as perfusion balloons may be utilized to deliver one or more drugs, agents and/or compounds, including rapamycin, to the site of atherosclerotic plaque. This type of regional delivery may be utilized alone or in combination with an implantable medical device with the same or different drugs affixed thereto. The one or more drugs, agents and/or compounds are preferably delivered to the adventitial space proximate the lesion.
A locally or regionally delivered solution of a potent therapeutic agent, such as rapamycin, offers a number of advantages over a systemically delivered agent or an agent delivered via an implantable medical device. For example, a relatively high tissue concentration may be achieved by the direct deposition of the pharmaceutical agent in the arterial wall. Depending on the location of the deposition, a different drug concentration profile may be achieved than through that of a drug eluting stent. In addition, with a locally or regionally delivered solution, there is no need for a permanently. implanted device such as a stent, thereby eliminating the potential side affects associated therewith, such as inflammatory reaction and long term tissue damage. It is, however, important to note that the locally or regionally delivered solution may be utilized in combination with drug eluting stents or other coated implantable medical devices. Another advantage of solution or liquid formulations lies in the fact that the adjustment of the excipients in the liquid formulation would readily change the drug distribution and retention profiles. In addition, the liquid formulation may be mixed immediately prior to the injection through a pre-packaged multi-chamber injection device to improve the storage and shelf life of the dosage forms.
Stent-grafts may be utilized to treat aneurysms. An aneurysm is an abnormal dilation of a layer or layers of an arterial wall, usually caused by a systemic collagen synthetic or structural defect. An abdominal aortic aneurysm is an aneurysm in the abdominal portion of the aorta, usually located in or near one or both of the two iliac arteries or near the renal arteries. The aneurysm often arises in the infrarenal portion of the diseased aorta, for example, below the kidneys. A thoracic aortic aneurysm is an aneurysm in the thoracic portion of the aorta. When left untreated, the aneurysm may rupture, usually causing rapid fatal hemorrhaging.
Aneurysms may be classified or typed by their position as well as by the number of aneurysms in a cluster. Typically, abdominal aortic aneurysms may be classified into five types. A Type I aneurysm is a single dilation located between the renal arteries and the iliac arteries. Typically, in a Type 1 aneurysm, the aorta is healthy between the renal arteries and the aneurysm and between the aneurysm and the iliac arteries.
A Type II A aneurysm is a single dilation located between the renal arteries and the iliac arteries. In a Type II A aneurysm, the aorta is healthy between the renal arteries and the aneurysm, but not healthy between the aneurysm and the iliac arteries. In other words, the dilation extends to the aortic bifurcation. A Type II B aneurysm comprises three dilations. One dilation is located between the renal arteries and the iliac arteries. Like a Type II A aneurysm, the aorta is healthy between the aneurysm and the renal arteries, but not healthy between the aneurysm and the iliac arteries. The other two dilations are located in the iliac arteries between the aortic bifurcation and the bifurcations between the external iliacs and the internal iliacs. The iliac arteries are healthy between the iliac bifurcation and the aneurysms. A Type II C aneurysm also comprises three dilations. However, in a Type II C aneurysm, the dilations in the iliac arteries extend to the iliac bifurcation.
A Type III aneurysm is a single dilation located between the renal arteries and the iliac arteries. In a Type III aneurysm, the aorta is not healthy between the renal arteries and the aneurysm. In other words, the dilation extends to the renal arteries.
Stent-grafts or endoprostheses are now FDA approved and commercially available. The delivery procedure typically involves advanced angiographic techniques performed through vascular accesses gained via surgical cutdown of a remote artery, such as the common femoral or brachial arteries. Over a guidewire, the appropriate size introducer will be placed. The catheter and guidewire are passed through the aneurysm, and, with the appropriate size introducer housing a stent-graft, the stent-graft will be advanced along the guidewire to the appropriate position. Typical deployment of the stent-graft device requires withdrawal of an outer sheath while maintaining the position of the stent-graft with an inner-stabilizing device. Most stent-grafts are self-expanding; however, an additional angioplasty procedure, e.g., balloon angioplasty, may be required to secure the position of the stent-graft. Following the placement of the stent-graft, standard angiographic views may be obtained.
Any number of aneurysmal repair systems comprising stent-grafts may be coated with the appropriate drugs, agents and/or compounds, as well as combinations thereof. Regardless of the type of aneurysm or its position within the living organism, the components comprising the repair system may be coated with the appropriate drug, agent and/or compound as described above with respect to stent-grafts. For example, rapamycin may be utilized as an anti-inflammatory. In addition, rapamycin may also be utilized in controlling the vascular remodeling phenomenon. Rapamycin may also affect the translation of key proteins involved in collagen formation or metabolism. In addition, rapamycin may be combined with another therapeutic agent with a different mechanism of action, thereby producing a synergistic effect. Alternately, rather than a rapomycin, analogs, derivatives and congeners that bind a high infinity cytosolic protein, FKBP12 may be utilized in combination with another therapeutic agent.
The foregoing and other features and advantages of the invention will be apparent from the following, more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.
The drug/drug combinations and delivery devices of the present invention may be utilized to effectively prevent and treat vascular disease, and in particular, vascular disease caused by injury. Various medical treatment devices utilized in the treatment of vascular disease may ultimately induce further complications. For example, balloon angioplasty is a procedure utilized to increase blood flow through an artery and is the predominant treatment for coronary vessel stenosis. However, as stated above, the procedure typically causes a certain degree of damage to the vessel wall, thereby potentially exacerbating the problem at a point later in time. Although other procedures and diseases may cause similar injury, exemplary embodiments of the present invention will be described with respect to the treatment of restenosis and related complications following percutaneous transluminal coronary angioplasty and other similar arterial/venous procedures, including the joining of arteries, veins and other fluid carrying conduits. In addition, various methods and devices will be described for the effective delivery of the coated medical devices.
While exemplary embodiments of the invention will be described with respect to the treatment of restenosis and related complications following percutaneous transluminal coronary angioplasty, it is important to note that the local delivery of drug/drug combinations may be utilized to treat a wide variety of conditions utilizing any number of medical devices, or to enhance the function and/or life of the device. For example, intraocular lenses, placed to restore vision after cataract surgery is often compromised by the formation of a secondary cataract. The latter is often a result of cellular overgrowth on the lens surface and can be potentially minimized by combining a drug or drugs with the device. Other medical devices which often fail due to tissue in-growth or accumulation of proteinaceous material in, on and around the device, such as shunts for hydrocephalus, dialysis grafts, colostomy bag attachment devices, ear drainage tubes, leads for pace makers and implantable defibrillators can also benefit from the device-drug combination approach. Devices which serve to improve the structure and function of tissue or organ may also show benefits when combined with the appropriate agent or agents. For example, improved osteointegration of orthopedic devices to enhance stabilization of the implanted device could potentially be achieved by combining it with agents such as bone-morphogenic protein. Similarly other surgical devices, sutures, staples, anastomosis devices, vertebral disks, bone pins, suture anchors, hemostatic barriers, clamps, screws, plates, clips, vascular implants, tissue adhesives and sealants, tissue scaffolds, various types of dressings, bone substitutes, intraluminal devices, and vascular supports could also provide enhanced patient benefit using this drug-device combination approach. Perivascular wraps may be particularly advantageous, alone or in combination with other medical devices. The perivascular wraps may supply additional drugs to a treatment site. Essentially, any type of medical device may be coated in some fashion with a drug or drug combination which enhances treatment over use of the singular use of the device or pharmaceutical agent.
In addition to various medical devices, the coatings on these devices may be used to deliver therapeutic and pharmaceutic agents including: anti-proliferative/antimitotic agents including natural products such as vinca alkaloids (i.e. vinblastine, vincristine, and vinorelbine), paclitaxel, epidipodophyllotoxins (i.e. etoposide, teniposide), antibiotics (dactinomycin (actinomycin D) daunorubicin, doxorubicin and idarubicin), anthracyclines, mitoxantrone, bleomycins, plicamycin (mithramycin) and mitomycin, enzymes (L-asparaginase which systemically metabolizes L-asparagine and deprives cells which do not have the capacity to synthesize their own asparagine);
antiplatelet agents such as G(GP) IIb/IIIa inhibitors and vitronectin receptor antagonists; anti-proliferative/antimitotic alkylating agents such as nitrogen mustards (mechlorethamine, cyclophosphamide and analogs, melphalan, chlorambucil), ethylenimines and methylmelamines (hexamethylmelamine and thiotepa), alkyl sulfonates-busulfan, nirtosoureas (carmustine (BCNU) and analogs, streptozocin), trazenes—dacarbazinine (DTIC); anti-proliferative/antimitotic antimetabolites such as folic acid analogs (methotrexate), pyrimidine analogs (fluorouracil, floxuridine, and cytarabine), purine analogs and related inhibitors (mercaptopurine, thioguanine, pentostatin and 2-chlorodeoxyadenosine {cladribine}); platinum coordination complexes (cisplatin, carboplatin), procarbazine, hydroxyurea, mitotane, aminoglutethimide; hormones (i.e. estrogen); anti-coagulants (heparin, synthetic heparin salts and other inhibitors of thrombin); fibrinolytic agents (such as tissue plasminogen activator, streptokinase and urokinase), aspirin, dipyridamole, ticlopidine, clopidogrel, abciximab; antimigratory; antisecretory (breveldin); anti-inflammatory: such as adrenocortical steroids (cortisol, cortisone, fludrocortisone, prednisone, prednisolone, 6α-methylprednisolone, triamcinolone, betamethasone, and dexamethasone), non-steroidal agents (salicylic acid derivatives i.e. aspirin; para-aminophenol derivatives i.e. acetaminophen; indole and indene acetic acids (indomethacin, sulindac, and etodalac), heteroaryl acetic acids (tolmetin, diclofenac, and ketorolac), arylpropionic acids (ibuprofen and derivatives), anthranilic acids (mefenamic acid, and meclofenamic acid), enolic acids (piroxicam, tenoxicam, phenylbutazone, and oxyphenthatrazone), nabumetone, gold compounds (auranofin, aurothioglucose, gold sodium thiomalate); immunosuppressives: (cyclosporine, tacrolimus (FK-506), sirolimus (rapamycin), azathioprine, mycophenolate mofetil); angiogenic agents: vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF); angiotensin receptor blockers; nitric oxide donors; antisense oligionucleotides and combinations thereof; cell cycle inhibitors, mTOR inhibitors, and growth factor receptor signal transduction kinase inhibitors; retenoids; cyclin/CDK inhibitors; HMG co-enzyme reductase inhibitors (statins); and protease inhibitors.
As stated previously, the implantation of a coronary stent in conjunction with balloon angioplasty is highly effective in treating acute vessel closure and may reduce the risk of restenosis. Intravascular ultrasound studies (Mintz et al., 1996) suggest that coronary stenting effectively prevents vessel constriction and that most of the late luminal loss after stent implantation is due to plaque growth, probably related to neointimal hyperplasia. The late luminal loss after coronary stenting is almost two times higher than that observed after conventional balloon angioplasty. Thus, inasmuch as stents prevent at least a portion of the restenosis process, a combination of drugs, agents or compounds which prevents smooth muscle cell proliferation, reduces inflammation and reduces coagulation or prevents smooth muscle cell proliferation by multiple mechanisms, reduces inflammation and reduces coagulation combined with a stent may provide the most efficacious treatment for post-angioplasty restenosis. The systemic use of drugs, agents or compounds in combination with the local delivery of the same or different drug/drug combinations may also provide a beneficial treatment option.
The local delivery of drug/drug combinations from a stent has the following advantages; namely, the prevention of vessel recoil and remodeling through the scaffolding action of the stent and the prevention of multiple components of neointimal hyperplasia or restenosis as well as a reduction in inflammation and thrombosis. This local administration of drugs, agents or compounds to stented coronary arteries may also have additional therapeutic benefit. For example, higher tissue concentrations of the drugs, agents or compounds may be achieved utilizing local delivery, rather than systemic administration. In addition, reduced systemic toxicity may be achieved utilizing local delivery rather than systemic administration while maintaining higher tissue concentrations. Also in utilizing local delivery from a stent rather than systemic administration, a single procedure may suffice with better patient compliance. An additional benefit of combination drug, agent, and/or compound therapy may be to reduce the dose of each of the therapeutic drugs, agents or compounds, thereby limiting their toxicity, while still achieving a reduction in restenosis, inflammation and thrombosis. Local stent-based therapy is therefore a means of improving the therapeutic ratio (efficacy/toxicity) of anti-restenosis, anti-inflammatory, anti-thrombotic drugs, agents or compounds.
There are a multiplicity of different stents that may be utilized following percutaneous transluminal, coronary angioplasty. Although any number of stents may be utilized in accordance with the present invention, for simplicity, a limited number of stents will be described in exemplary embodiments of the present invention. The skilled artisan will recognize that any number of stents may be utilized in connection with the present invention. In addition, as stated above, other medical devices may be utilized.
A stent is commonly used as a tubular structure left inside the lumen of a duct to relieve an obstruction. Commonly, stents are inserted into the lumen in a non-expanded form and are then expanded autonomously, or with the aid of a second device in situ. A typical method of expansion occurs through the use of a catheter-mounted angioplasty balloon which is inflated within the stenosed vessel or body passageway in order to shear and disrupt the obstructions associated with the wall components of the vessel and to obtain an enlarged lumen.
The stent 100 generally comprises first and second ends with an intermediate section therebetween. The stent 100 has a longitudinal axis and comprises a plurality of longitudinally disposed bands 102, wherein each band 102 defines a generally continuous wave along a line segment parallel to the longitudinal axis. A plurality of circumferentially arranged links 104 maintain the bands 102 in a substantially tubular structure. Essentially, each longitudinally disposed band 102 is connected at a plurality of periodic locations, by a short circumferentially arranged link 104 to an adjacent band 102. The wave associated with each of the bands 102 has approximately the same fundamental spatial frequency in the intermediate section, and the bands 102 are so disposed that the wave associated with them are generally aligned so as to be generally in phase with one another. As illustrated in the figure, each longitudinally arranged band 102 undulates through approximately two cycles before there is a link to an adjacent band 102.
The stent 100 may be fabricated utilizing any number of methods. For example, the stent 100 may be fabricated from a hollow or formed stainless steel tube that may be machined using lasers, electric discharge milling, chemical etching or other means. The stent 100 is inserted into the body and placed at the desired site in an unexpanded form. In one exemplary embodiment, expansion may be effected in a blood vessel by a balloon catheter, where the final diameter of the stent 100 is a function of the diameter of the balloon catheter used.
It should be appreciated that a stent 100 in accordance with the present invention may be embodied in a shape-memory material, including, for example, an appropriate alloy of nickel and titanium or stainless steel. Structures formed from stainless steel may be made self-expanding by configuring the stainless steel in a predetermined manner, for example, by twisting it into a braided configuration. In this embodiment after the stent 100 has been formed it may be compressed so as to occupy a space sufficiently small as to permit its insertion in a blood vessel or other tissue by insertion means, wherein the insertion means include a suitable catheter, or flexible rod. On emerging from the catheter, the stent 100 may be configured to expand into the desired configuration where the expansion is automatic or triggered by a change in pressure, temperature or electrical stimulation.
In an alternate exemplary embodiment, the entire inner and outer surface of the stent 100 may be coated with drug/drug combinations in therapeutic dosage amounts. A detailed description of a drug for treating restenosis, as well as exemplary coating techniques, is described below. It is, however, important to note that the coating techniques may vary depending on the drug/drug combinations. Also, the coating techniques may vary depending on the material comprising the stent or other intraluminal medical device.
Rapamycin is a macrocyclic triene antibiotic produced by Streptomyces hygroscopicus as disclosed in U.S. Pat. No. 3,929,992. It has been found that rapamycin among other things inhibits the proliferation of vascular smooth muscle cells in vivo. Accordingly, rapamycin may be utilized in treating intimal smooth muscle cell hyperplasia, restenosis, and vascular occlusion in a mammal, particularly following either biologically or mechanically mediated vascular injury, or under conditions that would predispose a mammal to suffering such a vascular injury. Rapamycin functions to inhibit smooth muscle cell proliferation and does not interfere with the re-endothelialization of the vessel walls.
Rapamycin reduces vascular hyperplasia by antagonizing smooth muscle proliferation in response to mitogenic signals that are released during an angioplasty induced injury. Inhibition of growth factor and cytokine mediated smooth muscle proliferation at the late G1 phase of the cell cycle is believed to be the dominant mechanism of action of rapamycin. However, rapamycin is also known to prevent T-cell proliferation and differentiation when administered systemically. This is the basis for its immunosuppressive activity and its ability to prevent graft rejection.
As used herein, rapamycin includes rapamycin and all analogs, derivatives and conjugates that bind to FKBP12, and other immunophilins and possesses the same pharmacologic properties as rapamycin including inhibition of TOR.
Although the anti-proliferative effects of rapamycin may be achieved through systemic use, superior results may be achieved through the local delivery of the compound. Essentially, rapamycin works in the tissues, which are in proximity to the compound, and has diminished effect as the distance from the delivery device increases. In order to take advantage of this effect, one would want the rapamycin in direct contact with the lumen walls. Accordingly, in a preferred embodiment, the rapamycin is incorporated onto the surface of the stent or portions thereof. Essentially, the rapamycin is preferably incorporated into the stent 100, illustrated in
Rapamycin may be incorporated onto or affixed to the stent in a number of ways. In the exemplary embodiment, the rapamycin is directly incorporated into a polymeric matrix and sprayed onto the outer surface of the stent. The rapamycin elutes from the polymeric matrix over time and enters the surrounding tissue. The rapamycin preferably remains on the stent for at least three days up to approximately six months, and more preferably between seven and thirty days.
Any number of non-erodible polymers may be utilized in conjunction with rapamycin. In one exemplary embodiment, the rapamycin or other therapeutic agent may be incorporated into a film-forming polyfluoro copolymer comprising an amount of a first moiety selected from the group consisting of polymerized vinylidenefluoride and polymerized tetrafluoroethylene, and an amount of a second moiety other than the first moiety and which is copolymerized with the first moiety, thereby producing the polyfluoro copolymer, the second moiety being capable of providing toughness or elastomeric properties to the polyfluoro copolymer, wherein the relative amounts of the first moiety and the second moiety are effective to provide the coating and film produced therefrom with properties effective for use in treating implantable medical devices.
The present invention provides polymeric coatings comprising a polyfluoro copolymer and implantable medical devices, for example, stents coated with a film of the polymeric coating in amounts effective to reduce thrombosis and/or restenosis when such stents are used in, for example, angioplasty procedures. As used herein, polyfluoro copolymers means those copolymers comprising an amount of a first moiety selected from the group consisting of polymerized vinylidenefluoride and polymerized tetrafluoroethylene, and an amount of a second moiety other than the first moiety and which is copolymerized with the first moiety to produce the polyfluoro copolymer, the second moiety being capable of providing toughness or elastomeric properties to the polyfluoro copolymer, wherein the relative amounts of the first moiety and the second moiety are effective to provide coatings and film made from such polyfluoro copolymers with properties effective for use in coating implantable medical devices.
The coatings may comprise pharmaceutical or therapeutic agents for reducing restenosis, inflammation, and/or thrombosis, and stents coated with such coatings may provide sustained release of the agents. Films prepared from certain polyfluoro copolymer coatings of the present invention provide the physical and mechanical properties required of conventional coated medical devices, even where maximum temperature, to which the device coatings and films are exposed, are limited to relatively low temperatures. This is particularly important when using the coating/film to deliver pharmaceutical/therapeutic agents or drugs that are heat sensitive, or when applying the coating onto temperature-sensitive devices such as catheters. When maximum exposure temperature is not an issue, for example, where heat-stable agents such as itraconazole are incorporated into the coatings, higher melting thermoplastic polyfluoro copolymers may be used and, if very high elongation and adhesion is required, elastomers may be used. If desired or required, the polyfluoro elastomers may be crosslinked by standard methods. described in, e.g., Modern Fluoropolymers, (J. Shires ed.), John Wiley & Sons, New York, 1997, pp. 77-87.
The present invention comprises polyfluoro copolymers that provide improved biocompatible coatings or vehicles for medical devices. These coatings provide inert biocompatible surfaces to be in contact with body tissue of a mammal, for example, a human, sufficient to reduce restenosis, or thrombosis, or other undesirable reactions. While many reported coatings made from polyfluoro homopolymers are insoluble and/or require high heat, for example, greater than about one hundred twenty-five degrees centigrade, to obtain films with adequate physical and mechanical properties for use on implantable devices, for example, stents, or are not particularly tough or elastomeric, films prepared from the polyfluoro copolymers of the present invention provide adequate adhesion, toughness or elasticity, and resistance to cracking when formed on medical devices. In certain exemplary embodiments, this is the case even where the devices are subjected to relatively low maximum temperatures.
The polyfluoro copolymers used for coatings according to the present invention are preferably film-forming polymers that have molecular weight high enough so as not to be waxy or tacky. The polymers and films formed therefrom should preferably adhere to the stent and not be readily deformable after deposition on the stent as to be able to be displaced by hemodynamic stresses. The polymer molecular weight should preferably be high enough to provide sufficient toughness so that films comprising the polymers will not be rubbed off during handling or deployment of the stent. In certain exemplary embodiments the coating will not crack where expansion of the stent or other medical devices occurs.
Coatings of the present invention comprise polyfluoro copolymers, as defined hereinabove. The second moiety polymerized with the first moiety to prepare the polyfluoro copolymer may be selected from those polymerized, biocompatible monomers that would provide biocompatible polymers acceptable for implantation in a mammal, while maintaining sufficient elastomeric film properties for use on medical devices claimed herein. Such monomers include, without limitation, hexafluoropropylene (HFP), tetrafluoroethylene (TFE), vinylidenefluoride, 1-hydropentafluoropropylene, perfluoro(methyl vinyl ether), chlorotrifluoroethylene (CTFE), pentafluoropropene, trifluoroethylene, hexafluoroacetone and hexafluoroisobutylene.
Polyfluoro copolymers used in the present invention typically comprise vinylidinefluoride copolymerized with hexafluoropropylene, in the weight ratio in the range of from about fifty to about ninety-two weight percent vinylidinefluoride to about fifty to about eight weight percent HFP. Preferably, polyfluoro copolymers used in the present invention comprise from about fifty to about eighty-five weight percent vinylidinefluoride copolymerized with from about fifty to about fifteen weight percent HFP. More preferably, the polyfluoro copolymers will comprise from about fifty-five to about seventy weight percent vinylidinefluoride copolymerized with from about forty-five to about thirty weight percent HFP. Even more preferably, polyfluoro copolymers comprise from about fifty-five to about sixty-five weight percent vinylidinefluoride copolymerized with from about forty-five to about thirty-five weight percent HFP. Such polyfluoro copolymers are soluble, in varying degrees, in solvents such as dimethylacetamide (DMAc), tetrahydrofuran, dimethyl formamide, dimethyl sulfoxide and n-methyl pyrrolidone. Some are soluble in methylethylketone (MEK), acetone, methanol and other solvents commonly used in applying coatings to conventional implantable medical devices.
Conventional polyfluoro homopolymers are crystalline and difficult to apply as high quality films onto metal surfaces without exposing the coatings to relatively high temperatures that correspond to the melting temperature (Tm) of the polymer. The elevated temperature serves to provide films prepared from such PVDF homopolymer coatings that exhibit sufficient adhesion of the film to the device, while preferably maintaining sufficient flexibility to resist film cracking upon expansion/contraction of the coated medical device. Certain films and coatings according to the present invention provide these same physical and mechanical properties, or essentially the same properties, even when the maximum temperatures to which the coatings and films are exposed is less than about a maximum predetermined temperature. This is particularly important when the coatings/films comprise pharmaceutical or therapeutic agents or drugs that are heat sensitive, for example, subject to chemical or physical degradation or other heat-induced negative affects, or when coating heat sensitive substrates of medical devices, for example, subject to heat-induced compositional or structural degradation.
Depending on the particular device upon which the coatings and films of the present invention are to be applied and the particular use/result required of the device, polyfluoro copolymers used to prepare such devices may be crystalline, semi-crystalline or amorphous.
Where devices have no restrictions or limitations with respect to exposure of same to elevated temperatures, crystalline polyfluoro copolymers may be employed. Crystalline polyfluoro copolymers tend to resist the tendency to flow under applied stress or gravity when exposed to temperatures above their glass transition (Tg) temperatures. Crystalline polyfluoro copolymers provide tougher coatings and films than their fully amorphous counterparts. In addition, crystalline polymers are more lubricious and more easily handled through crimping and transfer processes used to mount self-expanding stents, for example, nitinol stents.
Semi-crystalline and amorphous polyfluoro copolymers are advantageous where exposure to elevated temperatures is an issue, for example, where heat-sensitive pharmaceutical or therapeutic agents are incorporated into the coatings and films, or where device design, structure and/or use preclude exposure to such elevated temperatures. Semi-crystalline polyfluoro copolymer elastomers comprising relatively high levels, for example, from about thirty to about forty-five weight percent of the second moiety, for example, HFP, copolymerized with the first moiety, for example, VDF, have the advantage of reduced coefficient of friction and self-blocking relative to amorphous polyfluoro copolymer elastomers. Such characteristics may be of significant value when processing, packaging and delivering medical devices coated with such polyfluoro copolymers. In addition, such polyfluoro copolymer elastomers comprising such relatively high content of the second moiety serves to control the solubility of certain agents, for example, rapamycin, in the polymer and therefore controls permeability of the agent through the matrix.
Polyfluoro copolymers utilized in the present inventions may be prepared by various known polymerization methods. For example, high pressure, free-radical, semi-continuous emulsion polymerization techniques such as those disclosed in Fluoroelastomers-dependence of relaxation phenomena on compositions, POLYMER 30, 2180, 1989, by Ajroldi, et al., may be employed to prepare amorphous polyfluoro copolymers, some of which may be elastomers. In addition, free-radical batch emulsion polymerization techniques disclosed herein may be used to obtain polymers that are semi-crystalline, even where relatively high levels of the second moiety are included.
As described above, stents may comprise a wide variety of materials and a wide variety of geometrics. Stents may be made of biocomptible materials, including biostable and bioabsorbable materials. Suitable biocompatible metals include, but are not limited to, stainless steel, tantalum, titanium alloys (including nitinol), and cobalt alloys (including cobalt-chromium nickel alloys). Suitable nonmetallic biocompatible materials include, but are not limited to, polyamides, polyolefins (i.e. polypropylene, polyethylene etc.), nonabsorbable polyesters (i.e. polyethylene terephthalate), and bioabsorbable aliphatic polyesters (i.e. homopolymers and copolymers of lactic acid, glycolic acid, lactide, glycolide, para-dioxanone, trimethylene carbonate, ε-caprolactone, and blends thereof).
The film-forming biocompatible polymer coatings generally are applied to the stent in order to reduce local turbulence in blood flow through the stent, as well as adverse tissue reactions. The coatings and films formed therefrom also may be used to administer a pharmaceutically active material to the site of the stent placement. Generally, the amount of polymer coating to be applied to the stent will vary depending on, among other possible parameters, the particular polyfluoro copolymer used to prepare the coating, the stent design and the desired effect of the coating. Generally, the coated stent will comprise from about 0.1 to about fifteen weight percent of the coating, preferably from about 0.4 to about ten weight percent. The polyfluoro copolymer coatings may be applied in one or more coating steps, depending on the amount of polyfluoro copolymer to be applied. Different polyfluoro copolymers may be used for different layers in the stent coating. In fact, in certain exemplary embodiments, it is highly advantageous to use a diluted first coating solution comprising a polyfluoro copolymer as a primer to promote adhesion of a subsequent polyfluoro copolymer coating layer that may include pharmaceutically active materials. The individual coatings may be prepared from different polyfluoro copolymers.
Additionally, a top coating may be applied to delay release of the pharmaceutical agent, or they could be used as the matrix for the delivery of a different pharmaceutically active material. Layering of coatings may be used to stage release of the drug or to control release of different agents placed in different layers.
Blends of polyfluoro copolymers may also be used to control the release rate of different agents or to provide a desirable balance of coating properties, i.e. elasticity, toughness, etc., and drug delivery characteristics, for example, release profile. Polyfluoro copolymers with different solubilities in solvents may be used to build up different polymer layers that may be used to deliver different drugs or to control the release profile of a drug. For example, polyfluoro copolymers comprising 85.5/14.5 (wt/wt) of poly(vinylidinefluoride/HFP) and 60.6/39.4 (wt/wt) of poly(vinylidinefluoride/HFP) are both soluble in DMAc. However, only the 60.6/39.4 PVDF polyfluoro copolymer is soluble in methanol. So, a first layer of the 85.5/14.5 PVDF polyfluoro copolymer comprising a drug could be over coated with a topcoat of the 60.6/39.4 PVDF polyfluoro copolymer made with the methanol solvent. The top coating may be used to delay the drug delivery of the drug contained in the first layer. Alternately, the second layer could comprise a different drug to provide for sequential drug delivery. Multiple layers of different drugs could be provided by alternating layers of first one polyfluoro copolymer, then the other. As will be readily appreciated by those skilled in the art, numerous layering approaches may be used to provide the desired drug delivery.
Coatings may be formulated by mixing one or more therapeutic agents with the coating polyfluoro copolymers in a coating mixture. The therapeutic agent may be present as a liquid, a finely divided solid, or any other appropriate physical form. Optionally, the coating mixture may include one or more additives, for example, nontoxic auxiliary substances such as diluents, carriers, excipients, stabilizers or the like. Other suitable additives may be formulated with the polymer and pharmaceutically active agent or compound. For example, a hydrophilic polymer may be added to a biocompatible hydrophobic coating to modify the release profile, or a hydrophobic polymer may be added to a hydrophilic coating to modify the release profile. One example would be adding a hydrophilic polymer selected from the group consisting of polyethylene oxide, polyvinyl pyrrolidone, polyethylene glycol, carboxylmethyl cellulose, and hydroxymethyl cellulose to a polyfluoro copolymer coating to modify the release profile. Appropriate relative amounts may be determined by monitoring the in vitro and/or in vivo release profiles for the therapeutic agents.
The best conditions for the coating application are when the polyfluoro copolymer and pharmaceutic agent have a common solvent. This provides a wet coating that is a true solution. Less desirable, yet still usable, are coatings that contain the pharmaceutical agent as a solid dispersion in a solution of the polymer in solvent. Under the dispersion conditions, care must be taken to ensure that the particle size of the dispersed pharmaceutical powder, both the primary powder size and its aggregates and agglomerates, is small enough not to cause an irregular coating surface or to clog the slots of the stent that need to remain essentially free of coating. In cases where a dispersion is applied to the stent and the smoothness of the coating film surface requires improvement, or to be ensured that all particles of the drug are fully encapsulated in the polymer, or in cases where the release rate of the drug is to be slowed, a clear (polyfluoro copolymer only) topcoat of the same polyfluoro copolymer used to provide sustained release of the drug or another polyfluoro copolymer that further restricts the diffusion of the drug out of the coating may be applied. The topcoat may be applied by dip coating with mandrel to clear the slots. This method is disclosed in U.S. Pat. No. 6,153,252. Other methods for applying the topcoat include spin coating and spray coating. Dip coating of the topcoat can be problematic if the drug is very soluble in the coating solvent, which swells the polyfluoro copolymer, and the clear coating solution acts as a zero concentration sink and redissolves previously deposited drug. The time spent in the dip bath may need to be limited so that the drug is not extracted out into the drug-free bath. Drying should be rapid so that the previously deposited drug does not completely diffuse into the topcoat. The amount of therapeutic agent will be dependent upon the particular drug employed and medical condition being treated. Typically, the amount of drug represents about 0.001 percent to about seventy percent of the total coating weight, more typically about 0.001 percent to about sixty percent of the total coating weight. It is possible that the drug may represent as little as 0.0001 percent to the total coating weight.
The quantity and type of polyfluoro copolymers employed in the coating film comprising the pharmaceutic agent will vary depending on the release profile desired and the amount of drug employed. The product may contain blends of the same or different polyfluoro copolymers having different molecular weights to provide the desired release profile or consistency to a given formulation.
Polyfluoro copolymers may release dispersed drug by diffusion. This can result in prolonged delivery (over, say approximately one to two-thousand hours, preferably two to eight-hundred hours) of effective amounts (0.001 μg/cm2-min to 1000 μg/cm2-min) of the drug. The dosage may be tailored to the subject being treated, the severity of the affliction, the judgment of the prescribing physician, and the like.
Individual formulations of drugs and polyfluoro copolymers may be tested in appropriate in vitro and in vivo models to achieve the desired drug release profiles. For example, a drug could be formulated with a polyfluoro copolymer, or blend of polyfluoro copolymers, coated onto a stent and placed in an agitated or circulating fluid system, for example, twenty-five percent ethanol in water. Samples of the circulating fluid could be taken to determine the release profile (such as by HPLC, UV analysis or use of radiotagged molecules). The release of a pharmaceutical compound from a stent coating into the interior wall of a lumen could be modeled in appropriate animal system. The drug release profile could then be monitored by appropriate means such as, by taking samples at specific times and assaying the samples for drug concentration (using HPLC to detect drug concentration). Thrombus formation can be modeled in animal models using the In-platelet imaging methods described by Hanson and Harker, Proc. Natl. Acad. Sci. USA 85:3184-3188 (1988). Following this or similar procedures, those skilled in the art will be able to formulate a variety of stent coating formulations.
While not a requirement of the present invention, the coatings and films may be crosslinked once applied to the medical devices. Crosslinking may be affected by any of the known crosslinking mechanisms, such as chemical, heat or light. In addition, crosslinking initiators and promoters may be used where applicable and appropriate. In those exemplary embodiments utilizing crosslinked films comprising pharmaceutical agents, curing may affect the rate at which the drug diffuses from the coating. Crosslinked polyfluoro copolymers films and coatings of the present invention also may be used without drug to modify the surface of implantable medical devices.
A PVDF homopolymer (Solef® 1008 from Solvay Advanced Polymers, Houston, Tex., Tm about 175° C.) and polyfluoro copolymers of poly(vinylidenefluoride/HFP), 92/8 and 91/9 weight percent vinylidenefluoride/HFP as determined by F19 NMR, respectively (eg: Solef® 11010 and 11008, Solvay Advanced Polymers, Houston, Tex., Tm about 159 degrees C. and 160 degrees C., respectively) were examined as potential coatings for stents. These polymers are soluble in solvents such as, but not limited to, DMAc, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), tetrahydrofuran (THF) and acetone. Polymer coatings were prepared by dissolving the polymers in acetone, at five weight percent as a primer, or by dissolving the polymer in 50/50 DMAc/acetone, at thirty weight percent as a topcoat. Coatings that were applied to the stents by dipping and dried at 60 degrees C. in air for several hours, followed by 60 degrees C. for three hours in a <100 mm Hg vacuum, resulted in white foamy films. As applied, these films adhered poorly to the stent and flaked off, indicating they were too brittle. When stents. coated in this manner were heated above 175 degrees C., i.e. above the melting temperature of the polymer, a clear, adherent film was formed. Since coatings require high temperatures, for example, above the melting temperature of the polymer, to achieve high quality films. As mentioned above, the high temperature heat treatment is unacceptable for the majority of drug compounds due to their thermal sensitivity.
A polyfluoro copolymer (Solef® 21508) comprising 85.5 weight percent vinylidenefluoride copolymerized with 14.5 weight percent HFP, as determined by F19 NMR, was evaluated. This copolymer is less crystalline than the polyfluoro homopolymer and copolymers described in Example 1. It also has a lower melting point reported to be about 133 degrees C. Once again, a coating comprising about twenty weight percent of the polyfluoro copolymer was applied from a polymer solution in 50/50 DMAc/MEK. After drying (in air) at 60 degrees C. for several hours, followed by 60 degrees C. for three hours in a <100 mtorr Hg vacuum, clear adherent films were obtained. This eliminated the need for a high temperature heat treatment to achieve high quality films. Coatings were smoother and more adherent than those of Example 1. Some coated stents that underwent expansion show some degree of adhesion loss and “tenting” as the film pulls away from the metal. Where necessary, modification of coatings containing such copolymers may be made, e.g. by addition of plasticizers or the like to the coating compositions. Films prepared from such coatings may be used to coat stents or other medical devices, particularly where those devices are not susceptible to expansion to the degree of the stents.
The coating process above was repeated, this time with a coating comprising the 85.5/14.6 (wt/wt) (vinylidenefluoride/HFP) and about thirty weight percent of rapamycin (Wyeth-Ayerst Laboratories, Philadelphia, Pa.), based on total weight of coating solids. Clear films that would occasionally crack or peel upon expansion of the coated stents resulted. It is believed that inclusion of plasticizers and the like in the coating composition will result in coatings and films for use on stents and other medical devices that are not susceptible to such cracking and peeling.
Polyfluoro copolymers of still higher HFP content were then examined. This series of polymers were not semicrystalline, but rather are marketed as elastomers. One such copolymer is Fluorel™ FC2261Q (from Dyneon, a 3M-Hoechst Enterprise, Oakdale, Minn.), a 60.6/39.4 (wt/wt) copolymer of vinylidenefluoride/HFP. Although this copolymer has a Tg well below room temperature (Tg about minus twenty degrees C.) it is not tacky at room temperature or even at sixty degrees C. This polymer has no detectable crystallinity when measured by Differential Scanning Calorimetry (DSC) or by wide angle X-ray diffraction. Films formed on stents as described above were non-tacky, clear, and expanded without incident when the stents were expanded.
The coating process above was repeated, this time with coatings comprising the 60.6/39.4 (wt/wt) (vinylidenefluoride/HFP) and about nine, thirty and fifty weight percent of rapamycin (Wyeth-Ayerst Laboratories, Philadelphia, Pa.), based on total weight of coating solids, respectively. Coatings comprising about nine and thirty weight percent rapamycin provided white, adherent, tough films that expanded without incident on the stent. Inclusion of fifty percent drug, in the same manner, resulted in some loss of adhesion upon expansion.
Changes in the comonomer composition of the polyfluoro copolymer also can affect the nature of the solid state coating, once dried. For example, the semicrystalline copolymer, Solef® 21508, containing 85.5 percent vinylidenefluoride polymerized with 14.5 percent by weight HFP forms homogeneous solutions with about 30 percent rapamycin (drug weight divided by total solids weight, for example, drug plus copolymer) in DMAc and 50/50 DMAc/MEK. When the film is dried (60 degrees C./16 hours followed by 60 degrees C./3 hours in vacuum of 100 mm Hg) a clear coating, indicating a solid solution of the drug in the polymer, is obtained. Conversely, when an amorphous copolymer, Fluorel™ FC2261Q, of PDVF/HFP at 60.6/39.5 (wt/wt) forms a similar thirty percent solution of rapamycin in DMAc/MEK and is similarly dried, a white film, indicating phase separation of the drug and the polymer, is obtained. This second drug containing film is much siower to release the drug into an in vitro test solution of twenty-five percent ethanol in water than is the former clear film of crystalline Solef® 21508. X-ray analysis of both films indicates that the drug is present in a non-crystalline form. Poor or very low solubility of the drug in the high HFP containing copolymer results in slow permeation of the drug through the thin coating film. Permeability is the product of diffusion rate of the diffusing species (in this case the drug) through the film (the copolymer) and the solubility of the drug in the film.
In Vitro Release Results of Rapamycin from Coating.
In Vivo Stent Release Kinetics of Rapamycin from Poly(VDF/HFP).
Nine New Zealand white rabbits (2.5-3.0 kg) on a normal diet were given aspirin twenty-four hours prior to surgery, again just prior to surgery and for the remainder of the study. At the time of surgery, animals were premedicated with Acepromazine (0.1-0.2 mg/kg) and anesthetized with a Ketamine/Xylazine mixture (40 mg/kg and 5 mg/kg, respectively). Animals were given a single intraprocedural dose of heparin (150 IU/kg, i.v.)
Arteriectomy of the right common carotid artery was performed and a 5 F catheter introducer (Cordis, Inc.) placed in the vessel and anchored with ligatures. Iodine contrast agent was injected to visualize the right common carotid artery, brachlocephalic trunk and aortic arch. A steerable guide wire (0.014 inch/180 cm, Cordis, Inc.) was inserted via the introducer and advanced sequentially into each iliac artery to a location where the artery possesses a diameter closest to 2 mm using the angiographic mapping done previously. Two stents coated with a film made of poly(VDF/HFP):(60.6/39.4) with thirty percent rapamycin were deployed in each animal where feasible, one in each iliac artery, using 3.0 mm balloon and inflation to 8-10 ATM for thirty seconds followed after a one minute interval by a second inflation to 8-10 ATM for thirty seconds. Follow-up angiographs visualizing both iliac arteries are obtained to confirm correct deployment position of the stent.
At the end of procedure, the carotid artery was ligated and the skin is closed with 3/0 vicryl suture using a one layered interrupted closure. Animals were given butoropanol (0.4 mg/kg, s.c.) and gentamycin (4 mg/kg, i.m.). Following recovery, the animals were returned to their cages and allowed free access to food and water.
Due to early deaths and surgical difficulties, two animals were not used in this analysis. Stented vessels were removed from the remaining seven animals at the following time points: one vessel (one animal) at ten minutes post implant; six vessels (three animals) between forty minutes and two hours post-implant (average, 1.2 hours); two vessels (two animals) at three days post implant; and two vessels (one animal) at seven days post-implant. In one animal at two hours, the stent was retrieved from the aorta rather than the iliac artery. Upon removal, arteries were carefully trimmed at both the proximal and distal ends of the stent. Vessels were then carefully dissected free of the stent, flushed to remove any residual blood, and both stent and vessel frozen immediately, wrapped separately in foil, labeled and kept frozen at minus eighty degrees C. When all samples had been collected, vessels and stents were frozen, transported and subsequently analyzed for rapamycin in tissue and results are illustrated in
Purifying the Polymer.
The FluorelTM FC2261Q copolymer was dissolved in MEK at about ten weight percent and was washed in a 50/50 mixture of ethanovwater at a 14:1 of ethanol/water to MEK solution ratio. The polymer precipitated out and was separated from the solvent phase by centrifugation. The polymer again was dissolved in MEK and the washing procedure repeated. The polymer was dried. after each washing step at sixty degrees C. in a vacuum oven (<200 mtorr) over night.
In Vivo Testing of Coated Stents in Porcine Coronary Arteries.
CrossFlex® stents (available from Cordis, a Johnson & Johnson Company) were coated with the “as received” Fluorel™ FC2261Q PVDF copolymer and with the purified polyfluoro copolymer of Example 6, using the dip and wipe approach. The coated stents were sterilized using ethylene oxide and a standard cycle. The coated stents and bare metal stents (controls) were implanted in porcine coronary arteries, where they remained for twenty-eight days.
Angiography was performed on the pigs at implantation and at twenty-eight days. Angiography indicated that the control uncoated stent exhibited about twenty-one percent restenosis. The polyfluoro copolymer “as received” exhibited about twenty-six percent restenosis(equivalent to the control) and the washed copolymer exhibited about 12.5 percent restenosis.
Histology results reported neointimal area at twenty-eight days to be 2.89±0.2, 3.57±0.4 and 2.75±0.3, respectively, for the bare metal control, the unpurified copolymer and the purified copolymer.
Since rapamycin acts by entering the surrounding tissue, it s preferably only affixed to the surface of the stent making contact with one tissue. Typically, only the outer surface of the stent makes contact with the tissue. Accordingly, in one exemplary embodiment, only the outer surface of the stent is coated with rapamycin.
The circulatory system, under normal conditions, has to be self-sealing, otherwise continued blood loss from an injury would be life threatening. Typically, all but the most catastrophic bleeding is rapidly stopped though a process known as hemostasis. Hemostasis occurs through a progression of steps. At high rates of flow, hemostasis is a combination of events involving platelet aggregation and fibrin formation. Platelet aggregation leads to a reduction in the blood flow due to the formation of a cellular plug while a cascade of biochemical steps leads to the formation of a fibrin clot.
Fibrin clots, as stated above, form in response to injury. There are certain circumstances where blood clotting or clotting in a specific area may pose a health risk. For example, during percutaneous transluminal coronary angioplasty, the endothelial cells of the arterial walls are typically injured, thereby exposing the sub-endothelial cells. Platelets adhere to these exposed cells. The aggregating platelets and the damaged tissue initiate further biochemical process resulting in blood coagulation. Platelet and fibrin blood clots may prevent the normal flow of blood to critical areas. Accordingly, there is a need to control blood clotting in various medical procedures. Compounds that do not allow blood to clot are called anti-coagulants. Essentially, an anti-coagulant is an inhibitor of thrombin formation or function. These compounds include drugs such as heparin and hirudin. As used herein, heparin includes all direct or indirect inhibitors of thrombin or Factor Xa.
In addition to being an effective anti-coagulant, heparin has also been demonstrated to inhibit smooth muscle cell growth in vivo. Thus, heparin may be effectively utilized in conjunction with rapamycin in the treatment of vascular disease. Essentially, the combination of rapamycin and heparin may inhibit smooth muscle cell growth via two different mechanisms in addition to the heparin acting as an anti-coagulant.
Because of its multifunctional chemistry, heparin may be immobilized or affixed to a stent in a number of ways. For example, heparin may be immobilized onto a variety of surfaces by various methods, including the photolink methods set forth in U.S. Pat. Nos. 3,959,078 and 4,722,906 to Guire et al. and U.S. Pat. Nos. 5,229,172; 5,308,641; 5,350,800 and 5,415,938 to Cahalan et al. Heparinized surfaces have also been achieved by controlled release from a polymer matrix, for example, silicone rubber, as set forth in U.S. Pat. Nos. 5,837,313; 6,099,562 and 6,120,536 to Ding et al.
Unlike rapamycin, heparin acts on circulating proteins in the blood and heparin need only make contact with blood to be effective. Accordingly, if used in conjunction with a medical device, such as a stent, it would preferably be only on the side that comes into contact with the blood. For example, if heparin were to be administered via a stent, it would only have to be on the inner surface of the stent to be effective.
In an exemplary embodiment of the invention, a stent may be utilized in combination with rapamycin and heparin to treat vascular disease. In this exemplary embodiment, the heparin is immobilized to the inner surface of the stent so that it is in contact with the blood and the rapamycin is immobilized to the outer surface of the stent so that it is in contact with the surrounding tissue.
In an alternate exemplary embodiment, the stent may comprise a heparin layer immobilized on its inner surface, and rapamycin and heparin on its outer surface. Utilizing current coating techniques, heparin tends to form a stronger bond with the surface it is immobilized to then does rapamycin. Accordingly, it may be possible to first immobilize the rapamycin to the outer surface of the stent and then immobilize a layer of heparin to the rapamycin layer. In this embodiment, the rapamycin may be more securely affixed to the stent while still effectively eluting from its polymeric matrix, through the heparin and into the surrounding tissue.
There are a number of possible ways to immobilize, i.e., entrapment or covalent linkage with an erodible bond, the heparin layer to the rapamycin layer. For example, heparin may be introduced into the top layer of the polymeric matrix. In other embodiments, different forms of heparin may. be directly immobilized onto the top coat of the polymeric matrix, for example, as illustrated in
As stated above, a rapamycin coating may be applied to stents by a dip, spray or spin coating method, and/or any combination of these methods. Various polymers may be utilized. For example, as described above, poly(ethylene-co-vinyl acetate) and polybutyl methacrylate blends may be utilized. Other polymers may also be utilized, but not limited to, for example, polyvinylidene fluoride-co-hexafluoropropylene and polyethylbutyl methacrylate-co-hexyl methacrylate. Also as described above, barrier or top coatings may also be applied to modulate the dissolution of rapamycin from the polymer matrix. In the exemplary embodiment described above, a thin layer of heparin is applied to the surface of the polymeric matrix. Because these polymer systems are hydrophobic and incompatible with the hydrophilic heparin, appropriate surface modifications may be required.
The application of heparin to the surface of the polymeric matrix may be performed in various ways and utilizing various biocompatible materials. For example, in one embodiment, in water or alcoholic solutions, polyethylene imine may be applied on the stents, with care not to degrade the rapamycin (e.g., pH<7, low temperature), followed by the application of sodium heparinate in aqueous or alcoholic solutions. As an extension of this surface modification, covalent heparin may be linked on polyethylene imine using amide-type chemistry (using a carbondiimide activator, e.g. EDC) or reductive amination chemistry (using CBAS-heparin and sodium cyanoborohydride for coupling). In another exemplary embodiment, heparin may be photolinked on the surface, if it is appropriately grafted with photo initiator moieties. Upon application of this modified heparin formulation on the covalent stent surface, light exposure causes cross-linking and immobilization of the heparin on the coating surface. In yet another exemplary embodiment, heparin may be complexed with hydrophobic quaternary ammonium salts, rendering the molecule soluble in organic solvents (e.g. benzalkonium heparinate, troidodecylmethylammonium heparinate). Such a formulation of heparin may be compatible with the hydrophobic rapamycin coating, and may be applied directly on the coating surface, or in the rapamycin/hydrophobic polymer formulation.
It is important to note that the stent, as described above, may be formed from any number of materials, including various metals, polymeric materials and ceramic materials. Accordingly, various technologies may be utilized to immobilize the various drugs, agent, compound combinations thereon. Specifically, in addition to the polymeric matricies described above biopolymers may be utilized. Biopolymers may be generally classified as natural polymers, while the above-described polymers may be described as synthetic polymers. Exemplary biopolymers, which may be utilized include, agarose, alginate, gelatin, collagen and elastin. In addition, the drugs, agents or compounds may be utilized in conjunction with other percutaneously delivered medical devices such as grafts and profusion balloons.
In addition to utilizing an anti-proliferative and anti-coagulant, anti-inflammatories may also be utilized in combination therewith. One example of such a combination would be the addition of an anti-inflammatory corticosteroid such as dexamethasone with an anti-proliferative, such as rapamycin, cladribine, vincristine, taxol, or a nitric oxide donor and an anti-coagulant, such as heparin. Such combination therapies might result in a better therapeutic effect, i.e., less proliferation as well as less inflammation, a stimulus for proliferation, than would occur with either agent alone. The delivery of a stent comprising an anti-proliferative, anti-coagulant, and an anti-inflammatory to an injured vessel would provide the added therapeutic benefit of limiting the degree of local smooth muscle cell proliferation, reducing a stimulus for proliferation, i.e., inflammation and reducing the effects of coagulation thus enhancing the restenosis-limiting action of the stent.
In other exemplary embodiments of the inventions, growth factor inhibitor or cytokine signal transduction inhibitor, such as the ras inhibitor, R115777, or P38 kinase inhibitor, RWJ67657, or a tyrosine kinase inhibitor, such as tyrphostin, might be combined with an anti-proliferative agent such as taxol, vincristine or rapamycin so that proliferation of smooth muscle cells could be inhibited by different mechanisms. Alternatively, an anti-proliferative agent such as taxol, vincristine or rapamycin could be combined with an inhibitor of extracellular matrix synthesis such as halofuginone. In the above cases, agents acting by different mechanisms could act synergistically to reduce smooth muscle cell proliferation and vascular hyperplasia. This invention is also intended to cover other combinations of two or more such drug agents. As mentioned above, such drugs, agents or compounds could be administered systemically, delivered locally via drug delivery catheter, or formulated for delivery from the surface of a stent, or given as a combination of systemic and local therapy.
In addition to anti-proliferatives, anti-inflammatories and anti-coagulants, other drugs, agents or compounds may be utilized in conjunction with the medical devices. For example, immunosuppressants may be utilized alone or in combination with these other drugs, agents or compounds. Also gene therapy delivery mechanisms such as modified genes (nucleic acids including recombinant DNA) in viral vectors and non-viral gene vectors such as plasmids may also be introduced locally via a medical device. In addition, the present invention may be utilized with cell based therapy.
In addition to all of the drugs, agents, compounds and modified genes described above, chemical agents that are not ordinarily therapeutically or biologically active may also be utilized in conjunction with the present invention. These chemical agents, commonly referred to as pro-drugs, are agents that become biologically active upon their introduction into the living organism by. one or more mechanisms. These mechanisms include the addition of compounds supplied by the organism or the cleavage of compounds from the agents caused by another agent supplied by the organism. Typically, pro-drugs are more absorbable by the organism. In addition, pro-drugs may also provide some additional measure of time release.
As stated above, rapamycin may be utilized alone or in combination with one or more drugs, agents and/or compounds for the prevention of restenosis following vascular injury.
Histone proteins are part of cellular chromatin that aid in the packaging of DNA and transcription of genes. Several histone proteins exist, each expressing net positive charges capable of interacting with anionic DNA. These histone proteins form nucleosome subunits around which DNA is wound. Chemical modification of the histones through acetylation/deacetylation by acetyltransferase and deacetylase enzymes as well as other post-translational modifications help regulate the shape of the histone proteins, and subsequently, the accessibility of DNA to transcription enzymes. In resting cells, gene transcription is, at least in part, regulated by a balance of acetylation (transcription ON) and deacetylation (transcription OFF) of histone proteins that bind to DNA. Therefore, affecting the balance between acetylation and deacetylation can ultimately impact gene transcription, and subsequently, cell proliferation as proliferative pathways depend to a significant degree on gene transcription. Histone deacetylase are of two general classes, RPd3-like and Hda1-like proteins.
Other drugs, agents and or compounds that may be utilized include other histone deacetylase inhibitors, which include trichostatin A, its analogs and derivatives as well as similar agents. These agents include short-chain fatty acids, such as butyrate, phenylbutyrate and valproate, hydroxamic acids, such as trichostatins, SAHA and its derivatives, oxamflatin, ABHA, scriptaid, pyroxamide, and propenamides, epoxyketone-containing cyclic tetrapeptides, such as trapoxins, HC-toxin, chlamydocin, diheteropeptin, WF-3161 and Cyl-1 and Cyl-2, non-epoxyketone-containing cyclic tetrapeptides such as, FR901228 and apicidin, benzamides, such as MS-275 (MS-27-275), Cl-994 and other benzamide analogs, and various miscellaneous structures, such as depudecin and organosulfur compounds.
Trichostatin A is a histone deacetylase inhibitor that arrests tumor cell proliferation predominantly in the G1 and G2 phases of the cell cycle. The G1 and G2 phases of the cell cycle are the phases characterized by gene transcription. The anti-proliferative activity and point of cell cycle arrest profile of trichostatin A have been characterized primarily in tumor cell lines with anti-proliferative IC50's in the low nM range (Woo et al., J. Med Chem, 45: 2877-2885, 2002). In addition, trichostatin A has been shown to have anti-angiogenic activity (Deroanne et al., Oncogene 21 (3): 427-436, 2002).
In in vitro cell culture studies, trichostatin A has been shown to completely inhibit human coronary artery smooth muscle cell proliferation and has an anti-proliferative IC50 of approximately 6 nM.
Rapamycin, as described above, is a macroyclic triene antibiotic produced by streptomyces hygroscopicus as disclosed in U.S. Pat. No. 3,929,992. It has been found that rapamycin inhibits the proliferation of vascular smooth muscle cells in vivo. Accordingly, rapamycin may be utilized in treating intimal smooth muscle cell hyperplasia, restenosis and vascular occlusion in a mammal, particularly following either biologically or mechanically mediated vascular injury, or under conditions that would predispose a mammal to suffering such a vascular injury. Rapamycin functions to inhibit smooth muscle cell proliferation and does not interfere with the re-endothelialization of the vessel walls.
Rapamycin functions to inhibit smooth muscle cell proliferation through a number of mechanisms. In addition, rapamycin reduces the other effects caused by vascular injury, for example, inflammation. The mechanisms of action and various functions of rapamycin are described in detail below. Rapamycin as used throughout this application shall include rapamycin, rapamycin analogs, derivatives and congeners that bind FKBP12 and possess the same pharmacologic properties as rapamycin, as described in detail below.
Rapamycin reduces vascular hyperplasia by antagonizing smooth muscle proliferation in response to mitogenic signals that are released during angioplasty. Inhibition of growth factor and cytokine mediated smooth muscle proliferation at the late G1 phase of the cell cycle is believed to be the dominant mechanism of action of rapamycin. However, rapamycin is also known to prevent T-cell proliferation and differentiation when administered systemically. This is the basis for its immunosuppressive activity and its ability to prevent graft rejection.
The molecular events that are responsible for the actions of rapamycin, a known anti-proliferative, which acts to reduce the magnitude and duration of neointimal hyperplasia, are still being elucidated. It is known, however, that rapamycin enters cells and binds to a high-affinity cytosolic protein called FKBP12. The complex of rapamycin and FKPB12 in turn binds to and inhibits a phosphoinositide (PI)-3 kinase called the “mammalian Target of Rapamycin” or TOR. TOR is a protein kinase that plays a key role in mediating the downstream signaling events associated with mitogenic growth factors and cytokines in smooth muscle cells and T lymphocytes. These events include phosphorylation of p27, phosphorylation of p70 s6 kinase and phosphorylation of 4BP-1, an important regulator of protein translation.
It is recognized that rapamycin reduces restenosis by inhibiting neointimal hyperplasia. However, there is evidence that rapamycin may also inhibit the other major component of restenosis, namely, negative remodeling. Remodeling is a process whose mechanism is not clearly understood but which results in shrinkage of the external elastic lamina and reduction in lumenal area over time, generally a period of approximately three to six months in humans.
Negative or constrictive vascular remodeling may be quantified angiographically as the percent diameter stenosis at the lesion site where there is no stent to obstruct the process. If late lumen loss is abolished in-lesion, it may be inferred that negative remodeling has been inhibited. Another method of determining the degree of remodeling involves measuring in-lesion external elastic lamina area using intravascular ultrasound (IVUS). Intravascular ultrasound is a technique that can image the external elastic lamina as well as the vascular lumen. Changes in the external elastic lamina proximal and distal to the stent from the post-procedural timepoint to four-month and twelve-month follow-ups are reflective of remodeling changes.
Evidence that rapamycin exerts an effect on remodeling comes from human implant studies with rapamycin coated stents showing a very low degree of restenosis in-lesion as well as in-stent. In-lesion parameters are usually measured approximately five millimeters on either side of the stent i.e. proximal and distal. Since the stent is not present to control remodeling in these zones which are still affected by balloon expansion, it may be inferred that rapamycin is preventing vascular remodeling.
The data in Table 1 below illustrate that in-lesion percent diameter stenosis remains low in the rapamycin treated groups, even at twelve months. Accordingly, these results support the hypothesis that rapamycin reduces remodeling.
Additional evidence supporting a reduction in negative remodeling with rapamycin comes from intravascular ultrasound data that was obtained from a first-in-man clinical program as illustrated in Table 2 below.
The data illustrated that there is minimal loss of vessel area proximally or distally which indicates that inhibition of negative remodeling has occurred in vessels treated with rapamycin-coated stents.
Other than the stent itself, there have been no effective solutions to the problem of vascular remodeling. Accordingly, rapamycin may represent a biological approach to controlling the vascular remodeling phenomenon.
It may be hypothesized that rapamycin acts to reduce negative remodeling in several ways. By specifically blocking the proliferation of fibroblasts in the vascular wall in response to injury, rapamycin may reduce the formation of vascular scar tissue. Rapamycin may also affect the translation of key proteins involved in collagen formation or metabolism.
Rapamycin used in this context includes rapamycin and all analogs, derivatives and congeners that bind FKBP12 and possess the same pharmacologic properties as rapamycin.
In a preferred embodiment, the rapamycin is delivered by a local delivery device to control negative remodeling of an arterial segment after balloon angioplasty as a means of reducing or preventing restenosis. While any delivery device may be utilized, it is preferred that the delivery device comprises a stent that includes a coating or sheath which elutes or releases rapamycin. The delivery system for such a device may comprise a local infusion catheter that delivers rapamycin at a rate controlled by the administrator. In other embodiments, an injection need may be utilized.
Rapamycin may also be delivered systemically using an oral dosage form or a chronic injectible depot form or a patch to deliver rapamycin for a period ranging from about seven to forty-five days to achieve vascular tissue levels that are sufficient to inhibit negative remodeling. Such treatment is to be used to reduce or prevent restenosis when administered several days. prior to elective angioplasty with or without a stent.
Data generated in porcine and rabbit models show that the release of rapamycin into the vascular wall from a nonerodible polymeric stent coating in a range of doses (35-430 ug/15-18 mm coronary stent) produces a peak fifty to fifty-five percent reduction in neointimal hyperplasia as set forth in Table 3 below. This reduction, which is maximal at about twenty-eight to thirty days, is typically not sustained in the range of ninety to one hundred eighty days in the porcine model as set forth in Table 4 below.
1Stent nomenclature: EVA/BMA 1X, 2X, and 3X signifies approx. 500 μg, 1000 μg, and 1500 μg total mass (polymer + drug), respectively. TC, top coat of 30 μg, 100 μg, or 300 μg drug-free BMA; Biphasic; 2 × 1X layers of rapamycin in EVA/BMA separated by a 100 μg drug-free BMA layer.
20.25 mg/kg/d × 14 d preceeded by a loading dose of 0.5 mg/kg/d × 3d prior to stent implantation.
*p < 0.05 from EVA/BMA control.
**p < 0.05 from Metal;
*Inflammation score: (0 = essentially no intimal involvement; 1 = <25% intima involved; 2 = ≧25% intima involved; 3 = >50% intima involved).
The release of rapamycin into the vascular wall of a human from a nonerodible polymeric stent coating provides superior results with respect to the magnitude and duration of the reduction in neointimal hyperplasia within the stent as compared to the vascular walls of animals as set forth above.
Humans implanted with a rapamycin coated stent comprising rapamycin in the same dose range as studied in animal models using the same polymeric matrix, as described above, reveal a much more profound reduction in neointimal hyperplasia than observed in animal models, based on the magnitude and duration of reduction in neointima. The human clinical response to rapamycin reveals essentially total abolition of neointimal hyperplasia inside the stent using both angiographic and intravascular ultrasound measurements. These results are sustained for at least one year as set forth in Table 5 below.
QCA = Quantitative Coronary Angiography
SD = Standard Deviation
IVUS = Intravascular Ultrasound
Rapamycin produces an unexpected benefit in humans when delivered from a stent by causing a profound reduction in in-stent neointimal hyperplasia that is sustained for at least one year. The magnitude and duration of this benefit in humans is not predicted from animal model data. Rapamycin used in this context includes rapamycin and all analogs, derivatives and congeners that bind FKBP12 and possess the same pharmacologic properties as rapamycin.
These results may be due to a number of factors. For example, the greater effectiveness of rapamycin in humans is due to greater sensitivity of its mechanism(s) of action toward the pathophysiology of human vascular lesions compared to the pathophysiology of animal models of angioplasty. In addition, the combination of the dose applied to the stent and the polymer coating that controls the release of the drug is important in the effectiveness of the drug.
As stated above, rapamycin reduces vascular hyperplasia by antagonizing smooth muscle proliferation in response to mitogenic signals that are released during angioplasty injury. Also, it is known that rapamycin prevents T-cell proliferation and differentiation when administered systemically. It has also been determined that rapamycin exerts a local inflammatory effect in the vessel wall when administered from a stent in low doses for a sustained period of time (approximately two to six weeks). The local anti-inflammatory benefit is profound and unexpected. In combination with the smooth muscle anti-proliferative effect, this dual mode of action of rapamycin may be responsible for its exceptional efficacy.
Accordingly, rapamycin delivered from a local device platform, reduces neointimal hyperplasia by a combination of anti-inflammatory and smooth muscle anti-proliferative effects. Rapamycin used in this context means rapamycin and all analogs, derivatives and congeners that bind FKBP12 and possess the same pharmacologic properties as rapamycin. Local device platforms include stent coatings, stent sheaths, grafts and local drug infusion catheters or porous balloons or any other suitable means for the in situ or local delivery of drugs, agents or compounds.
The anti-inflammatory effect of rapamycin is evident in data from an experiment, illustrated in Table 6, in which rapamycin delivered from a stent was compared with dexamethasone delivered from a stent. Dexamethasone, a potent steroidal anti-inflammatory agent, was used as a reference standard. Although dexamethasone is able to reduce inflammation scores, rapamycin is far more effective than dexamethasone in reducing inflammation scores. In addition, rapamycin significantly reduces neointimal hyperplasia, unlike dexamethasone.
*= significance level P < 0.05
Rapamycin has also been found to reduce cytokine levels in vascular tissue when delivered from a stent. The data in
Since rapamycin may be shown to inhibit local inflammatory events in the vessel it is believed that this could explain the unexpected superiority of rapamycin in inhibiting neointima.
As set forth above, rapamycin functions on a number of levels to produce such desired effects as the prevention of T-cell proliferation, the inhibition of negative remodeling, the reduction of inflammation, and the prevention of smooth muscle cell proliferation. While the exact mechanisms of these functions are not completely known, the mechanisms that have been identified may be expanded upon.
Studies with rapamycin suggest that the prevention of smooth muscle cell proliferation by blockade of the cell cycle is a valid strategy for reducing neointimal hyperplasia. Dramatic and sustained reductions in late lumen loss and neointimal plaque volume have been observed in patients receiving rapamycin delivered locally from a stent. The present invention expands upon the mechanism of rapamycin to include additional approaches to inhibit the cell cycle and reduce neointimal hyperplasia without producing toxicity.
The cell cycle is a tightly controlled biochemical cascade of events that regulate the process of cell replication. When cells are stimulated by appropriate growth factors, they move from G0 (quiescence) to the G1 phase of the cell cycle. Selective inhibition of the cell cycle in the G1 phase, prior to DNA replication (S phase), may offer therapeutic advantages of cell preservation and viability while retaining anti-proliferative efficacy when compared to therapeutics that act later in the cell cycle i.e. at S, G2 or M phase.
Accordingly, the prevention of intimal hyperplasia in blood vessels and other conduit vessels in the body may be achieved using cell cycle inhibitors that act selectively at the G1 phase of the cell cycle. These inhibitors of the G1 phase of the cell cycle may be small molecules, peptides, proteins, oligonucleotides or DNA sequences. More specifically, these drugs or agents include inhibitors of cyclin dependent kinases (cdk's) involved with the progression of the cell cycle through the G1 phase, in particular cdk2 and cdk4.
Examples of drugs, agents or compounds that act selectively at the G1 phase of the cell cycle include small molecules such as flavopiridol and its structural analogs that have been found to inhibit cell cycle in the late G1 phase by antagonism of cyclin dependent kinases. Therapeutic agents that elevate an endogenous kinase inhibitory proteinkip called P27, sometimes referred to as P27kip 1, that selectively inhibits cyclin dependent kinases may be utilized. This includes small molecules, peptides and proteins that either block the degradation of P27 or enhance the cellular production of P27, including gene vectors that can transfact the gene to produce P27. Staurosporin and related small molecules that block the cell cycle by inhibiting protein kinases may be utilized. Protein kinase inhibitors, including the class of tyrphostins that selectively inhibit protein kinases to antagonize signal transduction in smooth muscle in response to a broad range of growth factors such as PDGF and FGF may also be utilized.
Any of the drugs, agents or compounds discussed above may be administered either systemically, for example, orally, intravenously, intramuscularly, subcutaneously, nasally or intradermally, or locally, for example, stent coating, stent covering or local delivery catheter. In addition, the drugs or agents discussed above may be formulated for fast-release or slow release with the objective of maintaining the drugs or agents in contact with target tissues for a period ranging from three days to eight weeks.
As set forth above, the complex of rapamycin and FKPB12 binds to and inhibits a phosphoinositide (PI)-3 kinase called the mammalian Target of Rapamycin or TOR. An antagonist of the catalytic activity of TOR, functioning as either an active site inhibitor or as an allosteric modulator, i.e. an indirect inhibitor that allosterically modulates, would mimic the actions of rapamycin but bypass the requirement for FKBP12. The potential advantages of a direct inhibitor of TOR include better tissue penetration and better physical/chemical stability. In addition, other potential advantages include greater selectivity and specificity of action due to the specificity of an antagonist for one of multiple isoforms of TOR that may exist in different tissues, and a potentially different spectrum of downstream effects leading to greater drug efficacy and/or safety.
The inhibitor may be a small organic molecule (approximate mw<1000), which is either a synthetic or naturally derived product. Wortmanin may be an agent which inhibits the function of this class of proteins. It may also be a peptide or an oligonucleotide sequence. The inhibitor may be administered either sytemically (orally, intravenously, intramuscularly, subcutaneously, nasally, or intradermally) or locally (stent coating, stent covering, local drug delivery catheter). For example, the inhibitor may be released into the vascular wall of a human from a nonerodible polymeric stent coating. In addition, the inhibitor may be formulated for fast-release or slow release with the objective of maintaining the rapamycin or other drug, agent or compound in contact with target tissues for a period ranging from three days to eight weeks.
As stated previously, the implantation of a coronary stent in conjunction with balloon angioplasty is highly effective in treating acute vessel closure and may reduce the risk of restenosis. Intravascular ultrasound studies (Mintz et al., 1996) suggest that coronary stenting effectively prevents vessel constriction and that most of the late luminal loss after stent implantation is due to plaque growth, probably related to neointimal hyperplasia. The late luminal loss after coronary stenting is almost two times higher than that observed after conventional balloon angioplasty. Thus, inasmuch as stents prevent at least a portion of the restenosis process, the use of drugs, agents or compounds which prevent inflammation and proliferation, or prevent proliferation by multiple mechanisms, combined with a stent may provide the most efficacious treatment for post-angioplasty restenosis.
Further, insulin supplemented diabetic patients receiving rapamycin eluting vascular devices, such as stents, may exhibit a higher incidence of restenosis than their normal or non-insulin supplemented diabetic counterparts. Accordingly, combinations of drugs may be beneficial.
The local delivery of drugs, agents or compounds from a stent has the following advantages; namely, the prevention of vessel recoil and remodeling through the scaffolding action of the stent and the drugs, agents or compounds and the prevention of multiple components of neointimal hyperplasia. This local administration of drugs, agents or compounds to stented coronary arteries may also have additional therapeutic benefit. For example, higher tissue concentrations would be achievable than that which would occur with systemic administration, reduced systemic toxicity, and single treatment and ease of administration. An additional benefit of drug therapy may be to reduce the dose of the therapeutic compounds, thereby limiting their toxicity, while still achieving a reduction in restenosis.
As rapamycin and trichostatin A act through different molecular mechanisms affecting cell proliferation, it is possible that these agents, when combined on a medical device such as a drug eluting stent, may potentiate each other's anti-restenotic activity by downregulating both smooth muscle and immune cell proliferation (inflammatory cell proliferation) by distinct multiple mechanisms. This potentiation of rapamycin anti-proliferative activity by trichostatin A may translate to an enhancement in anti-restenotic efficacy following vascular injury during revascularization and other vascular surgical procedures and a reduction in the required amount of either agent to achieve the anti-restenotic effect.
Trichostatin A may be affixed to any of the medical devices described herein utilizing any of the techniques and materials described herein. For example, trichostatin A may be affixed to a stent, with or without polymers, or delivered locally via a catheter-based delivery system. The trichostatin A may substantially block neointimal formation by local vascular application by virtue of a substantially complete and potent blockade of human coronary artery smooth muscle cell proliferation. The combination of rapamycin and trichostatin A, as well as other agents within its pharmacologic class, represents a new therapeutic combination that may be more efficacious against restenosis/neointimal thickening then rapamycin alone. In addition, different doses of the combination may lead to additional gains of inhibition of the neointimal growth than the simple additive effects of rapamycin plus trichostatin A. The combination of rapamycin and trichostatin A may be efficacious towards other cardiovascular diseases such as vulnerable atherosclerotic plaque.
In yet another alternate exemplary embodiment, rapamycin may be utilized in combination with mycophenolic acid. Like rapamycin, mycophenolic acid is an antibiotic, an anti-inflammatory and an immunosuppressive agent. Rapamycin, as previously stated, acts to reduce lymphocyte proliferation by arresting cells in the G1 phase of the cell cycle through the inhibition of the mammalian target of rapamycin. The downstream effects of rapamycin on the mammalian target of rapamycin block subsequent activity of cell cycle associated protein kinases. In contrast, mycophenolic acid, inhibits immune cell proliferation in the S phase of the cell cycle through the inhibition of inosine monophosphate dehydrogenase, an enzyme necessary for purine biosynthesis. In addition to their immunosuppressive and anti-inflammatory effects, rapamycin and mycophenolic acid are each potent inhibitors of human coronary artery smooth muscle cell proliferation.
As rapamycin and mycophenolic acid act through different molecular mechanisms affecting cell proliferation at different phases of the cell cycle, it is possible that these agents, when combined on a drug eluting stent or any other medical device as defined herein, my potentiate each others anti-restenotic activity by down regulating both smooth muscle and immune cell proliferation by different mechanisms.
Referring to
Similarly to the rapamycin pharmacokinetics, the BMA topcoat does slow the release of mycophenolic acid from the basecoat, which in turn provides a mechanism for greater drug release control. However, mycophenolic acid elutes more completely over a shorter duration than the rapamycin.
In yet another alternate exemplary embodiment, rapamycin may be utilized in combination with cladribine. Cladribine (2-chlorodeoxyadenosine or 2-CdA) is the 2-chloro-2′-deoxy derivative of the purine nucleoside, adenosine. Cladribine is resistant to degradation by adenosine deaminase, one of two intracellular adenine nucleotide regulatory enzymes, found in most cells. The other enzyme, 5′-nucleotidase, is present in variable amounts in different cell types (Carson et al., 1983). After initial phosphorylation to its monophosphate derivative by the intracellular enzyme, deoxycytidine kinase, 2-CdA is converted to a 5′-triphosphate (2-CdATP) which accumulates in levels which may be fifty fold greater than normal dATP levels. Thus, in cells such as leukocytes, which contain a high ratio (<0.04) of deoxycytidine kinase to 5′-nucleotidase, 2-CdA and its subsequent metabolites will tend to accumulate in pharmacological concentrations (Carson et al., 1983). Such high levels of a nucleoside triphosphate are known to inhibit the enzyme ribonucleotide reductase in rapidly dividing cells, thus preventing synthesis of deoxynucleotides required for DNA synthesis.
In resting cells, 2-CdATP is incorporated into DNA which results in single strand breaks. Breaks in DNA results in the activation of poly (ADP-ribose) polymerase which in turn leads to a depletion of NAD, ATP and a disruption of cell metabolism (Carson et al., 1986; Seto et al., 1985). Further activation of a Ca2+/Mg2+-dependent endonuclease results in cleavage of the damaged DNA into fragments leading to programmed cell death (apoptosis). Thus, 2-CdA may be cytotoxic to both resting and dividing cells (Beutler, 1992). Cladribine has shown activity in other cell types known to play a role in the inflammatory process which accompanies restenosis. Additionally, data presented herein demonstrate that cladribine also possesses an ability to inhibit smooth muscle cell proliferation, an action previously unknown for cladribine (see Cladribine Example). Therefore, cladribine may possess a unique spectrum of therapeutic action, including the prevention of the leukocyte accumulation known to occur at sites of arterial injury and inflammation and the prevention of smooth muscle hyperplasia which results from angioplasty and stent implantation.
To assess the ability of cladribine to prevent cell proliferation, human smooth muscle or endothelial cells (Clonetics, Walkersville, Md.) were seeded at a density of 2000 cells/cm2 (approximately 3600 cells/well) into each well of 12-well plates and cultured with 1.5 ml of growth medium containing five percent fetal calf serum (FCS). After twenty-four hours, the growth medium was changed and fresh medium containing 10 ng/ml platelet-derived growth factor AB (PDGF AB; LIFE Technologies), as well as various concentrations of cladribine (0.001-10,000 nM) were added with triplicate wells. Medium was replaced with fresh cladribine-containing medium after three days. On day six, cells were detached by trypsinization to yield a cell suspension, lightly centrifuged to pellet and then counted manually using a Neubauer hemocytometer system. Cell viability was assessed by trypan blue exclusion.
Table 7 provides the percent inhibition of the various tested concentrations of cladribine on human smooth muscle and endothelial cells in culture. Cladribine produced a concentration-related decrease in the proliferation of both smooth muscle and endothelial cells in this model system. IC50 values (concentration required to produce a reduction in proliferation to 50 percent of the vehicle-treated cell count) for the inhibition of smooth muscle cell and endothelial cell growth were 23 nanomolar and 40 nanomolar, respectively. Cladribine was thus approximately twice as potent as an inhibitor of smooth muscle cells as it was as an inhibitor of endothelial cells. Both IC50 values are within the range of inhibitory concentrations reported for cladribine on human monocytes (Carrera et al., J. Clin. Invest. 86:1480-1488, 1990) and normal bone marrow, lymphocytic and lymphoblastic cell lines (Carson, D. A. et al., Blood 62: 737-743, 1983). Thus, concentrations of cladribine known to be effective at inhibiting peripheral leukemic blood cell proliferation and bone marrow cells are also effective at inhibiting proliferating vascular smooth muscle and endothelial cells. Cladribine may therefore be therapeutically useful for inhibition of the intimal smooth muscle cell proliferation which accompanies stent implantation.
Values represent % of PDGF-stimulated increase in cell count. Each % is the mean of triplicate determinations. SMC, smooth muscle cells; EC, endothelial cells.
Cladribine or 2-chlorodeoxyadenosine is a purine antimetabolite prodrug that undergoes intracellular phosphorylation and incorporation into the DNA of proliferating cells. This leads to DNA strand breaks and inhibition of DNA synthesis. Cladribine is-capable of arresting cells at the G1/S phase interface. Thus it is possible that cladribine may inhibit vascular smooth muscle cell proliferation and inhibit inflammatory cell function secondary to revascularization procedures.
As rapamycin and cladribine act through different molecular mechanisms affecting cell proliferation at different phases of the cell cycle, it is possible that these agents, when combined on a drug eluting stent or any other medical device as defined herein, may potentiate each other's anti-restenotic activity by downregulating both smooth muscle cell and immune cell proliferation by different mechanisms. In non-synchronized cultured human. coronary artery smooth muscle cells studies, the addition of cladribine to cells treated with rapamycin resulted in a leftward and upward shift of the anti-proliferative rapamycin dose response curves, as set forth in detail below, suggesting that cladribine does in fact potentiate the anti-proliferative activity of rapamycin in coronary artery smooth muscle cells. The combination of rapamycin and cladribine may be utilized to enhance the anti-restenotic efficacy following vascular injury and a reduction in the required amount of either agent to achieve the anti-restenotic effect. The combination may be particularly relevant to the subpopulations of patients that are resistant to single drugs regimens such as rapamycin or paclitaxel coated stents.
Referring to
In yet another alternate exemplary embodiment, topotecan in combination with rapamycin may be utilized to prevent restenosis following vascular injury. Rapamycin acts to reduce lymphocyte and smooth muscle cell proliferation by arresting cells in the G1 phase of the cell cycle through the inhibition of the mammalian target of rapamycin. Subsequent activity of cell cycle associated protein kinases is blocked by the downstream effects of rapamycin on the mammalian target of rapamycin. Topotecan is an analog of camptothecin that interfaces with DNA synthesis through the inhibition of topoisomerase I. This inhibition leads to an accumulation of DNA double strand breaks and an arrest of cell division at the S phase of the cell cycle. Topotecan has been shown to inhibit human coronary artery smooth muscle cell proliferation (Brehm et al., 2000).
Camptothecin is a quinoline-based alkaloid found in the barks of the Chinese camptotheca tree and the Asian nothapodytes tree. Camptothecin, aminocamptothecin, amerogentin, CPT-11 (irinotecan), DX-8951f and topotecan are all DNA topoisomerase I inhibitors. Topotecan, irinotecan and camptothecin belong to the group of medicines or agents generally referred to as anti-neoplastics and are utilized to treat various forms of cancer, including cancer of the ovaries and certain types of lung cancer. Camptothecin may be particularly advantageous in local delivery because of its high lipid solubility and poor water solubility. Poor water solubility may help retain the drug near the release site for a longer period of action time, potentially covering more cells as they cycle. High lipid solubility may lead to increased penetration of the drug through the lipid cellular membrane, resulting in better efficacy.
As rapamycin and topotecan (and the analogs camptothecin and irinotecan) act through different molecular mechanisms affecting cell proliferation at different phases of the cell cycle, it is possible that these agents, when combined on a drug eluting stent or any other medical device as defined herein, may potentiate each other's anti-restenotic activity by downregulating both smooth muscle cell and immune cell proliferation (inflammatory cell proliferation) by distinct multiple mechanisms. In synchronized cultured human coronary artery smooth muscle cells studies, the addition of topotecan to cells treated with rapamycin resulted in a leftward and upward shift of the anti-proliferative rapamycin dose response curves, as set forth in detail below, suggesting that topotecan, and by extension, other agents in the topoisomerase I inhibitor class, does in fact potentiate the anti-proliferative activity of rapamycin in coronary artery smooth muscle cells. The combination of rapamycin and topotecan may be utilized to enhance the anti-restenotic efficacy following vascular injury and a reduction in the required amount of either agent to achieve the anti-restenotic effect. The combination may be particularly relevant to the subpopulations of patients that are resistant to single drug regimens such as rapamycin or paclitaxel coated stents.
Referring to
The combination of rapamycin and topotecan, as well as other topoisomerase I inhibitors, may provide a new therapeutic combination that may be more efficacious against restenosis/neointimal thickening than rapamycin alone. Different doses of rapamycin and topotecan, as well as other topoisomerase I inhibitors, may lead to additional gains of inhibition of the neointimal growth than the simple additive effects of rapamycin and topotecan. In addition, the combination of topotecan, as well as other topoisomerase I inhibitors, may be efficacious in the treatment of other cardiovascular diseases such as vulnerable atherosclerotic plaque.
The combination of rapamycin and topotecan, as well as other topoisomerase I inhibitors, may be delivered to the target tissue through any number of means including stents and catheters. The delivery of the drug combination may be achieved at different dose rates to achieve the desired effect, and as explained in more detail subsequently, each drug may be loaded into different levels of the polymeric matrix.
In yet another alternate exemplary embodiment, etoposide in combination with rapamycin may be utilized to prevent restenosis following vascular injury. Rapamycin acts to reduce smooth muscle cell proliferation and lymphocyte proliferation by arresting cells in the G1 phase of the cell cycle through inhibition of the mammalian target of rapamycin. Subsequent activity of cell cycle associated protein kinases is blocked by the downstream effects of rapamycin on the mammalian target of rapamycin. Etoposide is a cytostatic glucoside derivative of podophyllotoxin that interferes with DNA synthesis through inhibition of topoisomerase II. This inhibition leads to DNA strand breaks and an accumulation of cells in the G2/M phase of the cell cycle, G2/M checkpoint dysregulation and subsequent apoptosis.
Podophyllotoxin (podofilox) and its derivatives, etoposide and teniposide, are all cytostatic (antimitotic) glucosides. Podofilox is an extract of the mayapple. Proliferating cells are particularly vulnerable to podofilox. Etoposide is utilized to treat cancer of the testicles, lungs and other kinds of cancer. Etoposide and teniposide both block the cell cycle in two specific places. Etoposide and teniposide block the phase between the last division and the start of DNA replication and also block the replication of DNA.
As rapamycin and etoposide act through different molecular mechanisms affecting cell proliferation at different phases of the cell cycle, it is likely that these agents, when combined on a drug eluting stent or any other medical device as defined herein may potentiate each other's anti-restenotic activity by downregulating both smooth muscle cell and immune cell proliferation (inflammatory cell proliferation) by distinct multiple mechanisms. In non-synchronized cultured human coronary artery smooth muscle cell studies, the addition of etoposide to cells treated with rapamycin resulted in a leftward and upward shift of the anti-proliferative rapamycin dose response curves, as set forth in detail below, suggesting that etoposide, and by extension, other agents in the topoisomerase II inhibitor class, potentiate the anti-proliferative activity of rapamycin in coronary artery srhooth muscle cells. The combination of rapamycin and etoposide may be utilized to enhance the anti-restenotic efficacy following vascular injury and a reduction in the required amount of either agent to achieve the anti-restenotic effect. The combination may be particularly relevant to the subpopulation of patients that are resistant to single drug regimens such as rapamycin or paclitaxel coated stents.
Referring to
The combination of rapamycin and etoposide, as well as other cytostatic glucosides, including podophyllotoxin, its derivatives and teniposide, may provide a new therapeutic combination that may be more efficacious against restenosis/neointimal thickening than rapamycin alone. Different doses of rapamycin and etoposide, as well as other cytostatic glucosides, including podophyllotoxin, its derivatives and teniposide, may lead to additional gains of inhibition of the neointimal growth than the simple additive effects of rapamycin and etoposide. In addition, the combination of etoposide, as well as other cytostatic glucosides, including podophyllotoxin, its derivatives and teniposide, may be efficacious in the treatment of other cardiovascular diseases such as vulnerable atherosclerotic plaque.
The combination of rapamycin and etoposide, as well as other cytostatic glucosides, including podophyllotoxin, its derivatives and teniposide, may be delivered to the target tissue through any number of means including stents and catheters. The delivery of the drug combination may be achieved at different dose rates to achieve the desired effect, and as explained in more detail subsequently, each drug may be loaded into different levels of the polymeric matrix.
In yet another alternate exemplary embodiment, Panzem® may be utilized alone or in combination with rapamycin to prevent restenosis following vascular injury. Rapamycin or sirolimus acts to reduce lymphocyte and smooth muscle cell proliferation by arresting cells in the G1 phase of the cell cycle through the inhibition of the mammalian target of rapamycin (mTOR). Rapamycin or sirolimus has shown excellent anti-restenotic effects when administered during revascularization procedures using drug eluting stents. In recent clinical trials, the Cypher® stent, available from Cordis Corporation, which contains rapamycin or sirolimus in a polymer coating, consistently demonstrated superior efficacy against restenosis after the implantation of the stent as compared to a bare metal stent. Although the local delivery of rapamycin from a drug eluting stent or other medical device is effective in reducing restenosis, further reductions in neointimal hyperplasia would benefit certain patient populations. Thus, the combination of rapamycin with another agent, for example, another anti-proliferative agent from a stent or other medical device may further reduce fibroproliferative vascular responses secondary to procedures involving vascular injury.
Panzem®, or 2-methoxyestradiol (2ME2) is a naturally occurring metabolite of endogenous estrogen. Its many properties provide for a wide range of potential formulations for drug delivery to treat numerous indications. Panzem® has been shown to exhibit anti-cancer activity in patients with breast cancer, prostate cancer and multiple myeloma. Panzem® is a by-product of the metabolism estrogen and is normally present in the body in small amounts. Panzem®; however, does not act like a hormone. Panzem® is a potent inhibitor of angiogenesis, which is what makes it such an effective anti-tumor agent. Essentially, Panzem® inhibits the formation of new blood vessels that supply oxygen and nutrients to tumor cells. Panzem® also appears to have multiple direct and indirect anti-myeloma effects as briefly described above.
Panzem®, 2-methoxyestradiol (2ME2) or methoxy-β-estradiol is, as described above, a product of estrogen metabolism and is currently being evaluated clinically for a variety of oncologic indications. Panzem® has anti-angiogenic activity, blocks the production of vascular endothelial growth factor and directly inhibits the growth of a number of tumor cell types. Panzem® is also proapoptotic (programmed cell death) to myeloma cells. Panzem® has been found to upregulate the DR-5 receptor (of the TNF receptor family) number responsible for TRAIL-mediated apoptosis (AACR, 2003) and has microtubule stabilizing properties and reduces hypoxia-inducible factor-1 (AACR, 2003). In addition, as illustrated in detail below, Panzem® reduces human coronary artery smooth muscle cell proliferation without negatively impacting coronary artery smooth muscle cell viability.
Referring to
As rapamycin or sirolimus and Panzem® or other estrogen receptor modulators act to inhibit cell proliferation through different molecular mechanisms, it is possible that these agents, when combined on a drug eluting stent or other medical device as defined herein, may potentiate each other's anti-restenotic activity by downregulating both smooth muscle and immune cell proliferation (inflammatory cell proliferation) by distinct multiple mechanisms.
Referring to
In vitro cytotoxicity tests or assays may be utilized to determine if drugs, agents and/or compounds are potentially toxic and the level of toxicity. Essentially, in vitro cytotoxicity assays determine acute necrotic effects by a drug causing direct cellular damage. The idea behind these assays is that toxic chemicals affect basic functions of cells which are common to all cells. Typically, a control is utilized to determine baseline toxicity. There are a number of different assays that may be utilized. In the present invention, the cytotoxicity assay utilized is based upon the measurement of cellular metabolic activity. A reduction in metabolic activity is an indication of cellular damage. Tests that can measure metabolic function measure cellular ATP levels or mitochondrial activity via MTS metabolism.
In yet another alternate exemplary embodiment, rapamycin may be utilized in combination with cilostazol. Cilostazol {6[4-(1-cyclohexyl-1H-tetrazol-5-yl)-butoxy]-3,4-dihydro-2-(1H)-quinolinone} is an inhibitor of type III (cyclic GMP-inhibited) phosphodiesterase and has anti-platelet and vasodilator properties. Cilostazol was originally developed as a selective inhibitor of cyclic nucleotide phosphodiesterase 3. Phosphodiesterase 3 inhibition in platelets and vascular smooth muscle cells was expected to provide an anti-platelet effect and vasodilation; however, recent preclinical studies have demonstrated that cilostazol also possesses the ability to inhibit adenosine uptake by various cells, a property that distinguishes cilastazol from other phosphodiesterase 3 inhibitors, such as milrinone. Accordingly, cilostazol has been shown to have unique antithrombotic and vasodilatory properties based upon a number of novel mechanisms of action.
Studies have also shown the efficacy of cilostazol in reducing restenosis after the implantation of a stent. See, for example, Matsutani M., Ueda H. et al.: “Effect of cilostazol in preventing restenosis after percutaneous transluminal coronary angioplasty, Am. J. Cardiol 1997, 79:1097-1099, Kunishima T., Musha H., Eto F., et al.: A randomized trial of aspirin versus cilostazol therapy after successful coronary stent implantation, Clin Thor 1997, 19:1058-1066, and Tsuchikane E. Fukuhara A., Kobayashi T., et al.: Impact of cilostazol on restenosis after percutaneous coronary balloon angioplasty, Circulation 1999, 100:21-26.
In accordance with the present invention, cilostazol may be configured for sustained release from a medical device or medical device coating to help reduce platelet deposition and thrombosis formation on the surface of the medical device. As described herein, such medical devices include any short and long term implant in constant contact with blood such as cardiovascular, peripheral and intracranial stents. Optionally, cilostazol may be incorporated in an appropriate polymeric coating or matrix in combination with a rapamycin or other potent anti-restenotic agents.
The incorporation and subsequent sustained release of cilostazol from a medical device or a medical device coating will preferably reduce platelet deposition and thrombosis formation on the surface of the medical device. There is, as described above, pre-clinical and clinical evidence that indicates that cilostazol also has anti-restenotic effects partly due to its vasodilating action. Accordingly, cilostazol is efficacious on at least two aspects of blood contacting devices such as drug eluting stents. Therefore, a combination of cilostazol with another potent anti-restenotic agent including a rapamycin, such as sirolimus, its analogs, derivatives, congeners and conjugates or paclitoxel, its analogs, derivatives, congeners and conjugates may be utilized for the local treatment of cardiovascular diseases and reducing platelet deposition and thrombosis formation on the surface of the medical device. Although described with respect to stents, it is important to note that the drug combinations described with respect to this exemplary embodiment may be utilized in connection with any number of medical devices, some of which are described herein.
As may be readily seen from a comparison of
The anti-thrombotic efficacy of the above-described three configurations is illustrated in
Another critical parameter for the performance of the thrombus resistance of a device coated with cilostazol is the duration of the drug release from the coating. This is of particular significance in the two weeks after device implantation. In the porcine drug elution PK studies of the dual drug eluting coating, both cilostazol and sirolius were slowly released from the coating, resulting in a sustained drug release profile. The purpose of the porcine PK study is to assess the local pharmacokinetics of a drug eluting stent at a given implantation time. Normally three stents are implanted in three different coronary arteries in a pig for a given time point and then retrieved for total drug recovery analysis. The stents are retrieved at predetermined time points; namely, 1, 3 and 8 days. The stents are extracted and the total amount of drug remaining on the stents is determined by analysis utilizing HPLC (high performance liquid chromatography) for total drug amount. The difference between the original amount of drug on the stent and the amount of drug retrieved at a given time represents the amount of drug released in that period. The continuous release of drug into surrounding arterial tissue is what prevents the neointimal growth and restenosis in the coronary artery. A normal plot represents the percentage of total drug released (%, y-axis) vs. time of implantation (day, x-axis). As illustrated in
The combination of a rapamycin, such as sirolimus, and cilostazol, as described above, may be more efficacious than either drug alone in reducing both smooth muscle cell proliferation and migration. In addition, as shown herein, cilostazol release from the combination coating may be controlled in a sustained fashion to achieve prolonged anti-platelet deposition and thrombosis formation on the stent surface or the surface of other blood contacting medical devices. The incorporation of cilostazol in the combination coating may be arranged in both a single layer with sirolimus or in a separate layer outside of the sirolimus containing layer. With its relatively low solubility in water, cilostazol has a potential to be retained in the coating for a relatively long period of time inside the body after deployment of the stent or other medical device. The relatively slow in vitro elution as compared to sirolimus in the inner layer suggests such a possibility. Cilostazol is stable, soluble in common organic solvents and is compatible with the various coating techniques described herein. It is also important to note that both sirolimus and cilostazol may be incorporated in a non-absorbable polymeric matrix or an absorbable matrix.
It is important to reiterate that as used herein, that rapamycin includes rapamycin and all analogs, derivatives, congeners and conjugates that bind to FK3P12 and other immunophilins and possesses the same pharmacologic properties as rapamycin inclding inhibition of mTOR.
As is explained in more detail subsequently, a combination of incompatible polymers may be utilized in combination with rapamycin and mycophenolic acid, rapamycin and trichostatin A, rapamycin and cladribine, rapamycin and topotecan, rapamycin and etoposide, rapamycin and Panzem and/or any of the drugs, agents and/or compounds described herein to provide for the controlled local delivery of these drugs, agents and/or compounds or combinations thereof from a medical device. In addition, these incompatible polymers may be utilized in various combinations to control the release rates of individual agents from combinations of agents. For example, from the tests described above, it is seen that mycophenolic acids elute more quickly than rapamycin. Accordingly, the correct combination of incompatible polymers may be utilized to ensure that both agents elute at the same rate if so desired.
The coatings and drugs, agents or compounds described above may be utilized in combination with any number of medical devices, and in particular, with implantable medical devices such as stents and stent-grafts. Other devices such as vena cava filters and anastomosis devices may be used with coatings having drugs, agents or compounds therein. The exemplary stent illustrated in
Surgical anastomosis is the surgical joining of structures, specifically the joining of tubular organs to create an intercommunication between them. Vascular surgery often involves creating an anastomosis between blood vessels or between a blood vessel and a vascular graft to create or restore a blood flow path to essential tissues. Coronary artery bypass graft surgery (CABG) is a surgical procedure to restore blood flow to ischemic heart muscle whose blood supply has been compromised by occlusion or stenosis of one or more of the coronary arteries. One method for performing CABG surgery involves harvesting a saphenous vein or other venous or arterial conduit from elsewhere in the body, or using an artificial conduit, such as one made of Dacron® or GoreTex® tubing, and connecting this conduit as a bypass graft from a viable artery, such as the aorta, to the coronary artery downstream of the blockage or narrowing. It is preferable to utilize natural grafts rather than synthetic grafts. A graft with both the proximal and distal ends of the graft detached is known as a “free graft.” A second method involves rerouting a less essential artery, such as the internal mammary artery, from its native location so that it may be connected to the coronary artery downstream of the blockage. The proximal end of the graft vessel remains attached in its native position. This type of graft is known as a “pedicled graft.” In the first case, the bypass graft must be attached to the native arteries by an end-to-side anastomosis at both the proximal and distal ends of the graft. In the second technique at least one end-to-side anastomosis must be made at the distal end of the artery used for the bypass. In the description of the exemplary embodiment given below reference will be made to the anastomoses on a free graft as the proximal anastomosis and the distal anastomosis. A proximal anastomosis is an anastomosis on the end of the graft vessel connected to a source of blood, for example, the aorta and a distal anastomosis is an anastomosis on the end of the graft vessel connected to the destination of the blood flowing through it, for example, a coronary artery. The anastomoses will also sometimes be called the first anastomosis or second anastomosis, which refers to the order in which the anastomoses are performed regardless of whether the anastomosis is on the proximal or distal end of the graft.
At present, essentially all vascular anastomoses are performed by conventional hand suturing. Suturing the anastomoses is a time-consuming and difficult task, requiring much skill and practice on the part of the surgeon. It is important that each anastomosis provide a smooth, open flow path for the blood and that the attachment be completely free of leaks. A completely leak-free seal is not always achieved on the very first try. Consequently, there is a frequent need for resuturing of the anastomosis to close any leaks that are detected.
The time consuming nature of hand sutured anastomoses is of special concern in CABG surgery for several reasons. Firstly, the patient is required to be supported on cardiopulmonary bypass (CPB) for most of the surgical procedure, the heart must be isolated from the systemic circulation (i.e. “cross-clamped”), and the heart must usually be stopped, typically by infusion of cold cardioplegia solution, so that the anastomosis site on the heart is still and blood-free during the suturing of the anastomosis. Cardiopulminary bypass, circulatory isolation and cardiac arrest are inherently very traumatic, and it has been found that the frequency of certain post-surgical complications varies directly with the duration for which the heart is under cardioplegic arrest (frequently referred to as the “crossclamp time”). Secondly, because of the high cost of cardiac operating room time, any prolongation of the surgical procedure can significantly increase the cost of the bypass operation to the hospital and to the patient. Thus, it is desirable to reduce the duration of the crossclamp time and of the entire surgery by expediting the anastomosis procedure without reducing the quality or effectiveness of the anastomoses.
The already high degree of manual skill required for conventional manually sutured anastomoses is even more elevated for closed-chest or port-access thoracoscopic bypass surgery, a newly developed surgical procedure designed to reduce the morbidity of CABG surgery as compared to the standard open-chest CABG procedure. In the closed-chest procedure, surgical access to the heart is made through narrow access ports made in the intercostal spaces of the patient's chest, and the procedure is performed under thoracoscopic observation. Because the patient's chest is not opened, the suturing of the anastomoses must be performed at some distance, using elongated instruments positioned through the access ports for approximating the tissues and for holding and manipulating the needles and sutures used to make the anastomoses. This requires even greater manual skill than the already difficult procedure of suturing anastomoses during open-chest CABG surgery.
In order to reduce the difficulty of creating the vascular anastomoses during either open or closed-chest CABG surgery, it would be desirable to provide a rapid means for making a reliable end-to-side anastomosis between a bypass graft or artery and the aorta or the native vessels of the heart. A first approach to expediting and improving anastomosis procedures has been through stapling technology. Stapling technology has been successfully employed in many different areas of surgery for making tissue attachments faster and more reliably. The greatest progress in stapling technology has been in the area of gastrointestinal surgery. Various surgical stapling instruments have been developed for end-to-end, side-to-side, and end-to-side anastomoses of hollow or tubular organs, such as the bowel. These instruments, unfortunately, are not easily adaptable for use in creating vascular anastomoses. This is partially due to the difficulty in miniaturizing the instruments to make them suitable for smaller organs such as blood vessels. Possibly even more important is the necessity of providing a smooth, open flow path for the blood. Known gastrointestinal stapling instruments for end-to-side or end-to-end anastomosis of tubular organs are designed to create an inverted anastomosis, that is, one where the tissue folds inward into the lumen of the organ that is being attached. This is acceptable in gastrointestinal surgery, where it is most important to approximate the outer layers of the intestinal tract (the serosa). This is the tissue which grows together to form a strong, permanent connection. However, in vascular surgery this geometry is unacceptable for several reasons. Firstly, the inverted vessel walls would cause a disruption in the blood flow. This could cause decreased flow and ischemia downstream of the disruption, or, worse yet, the flow disruption or eddies created could become a locus for thrombosis which could shed emboli or occlude the vessel at the anastomosis site. Secondly, unlike the intestinal tract, the outer surfaces of the blood vessels (the adventitia) will not grow together when approximated. The sutures, staples, or other joining device may therefore be needed permanently to maintain the structural integrity of the vascular anastomosis. Thirdly, to establish a permanent, nonthrombogenic vessel, the innermost layer (the endothelium) should grow together for a continuous, uninterrupted lining of the entire vessel. Thus, it would be. preferable to have a stapling instrument that would create vascular anastomoses that are everted, that is folded outward, or which create direct edge-to-edge coaptation without inversion.
At least one stapling instrument has been applied to performing vascular anastomoses during CABG surgery. This device, first adapted for use in CABG surgery by Dr. Vasilii I. Kolesov and later refined by Dr. Evgenii V. Kolesov (U.S. Pat. No. 4,350,160), was used to create an end-to-end anastomosis between the internal mammary artery (IMA) or a vein graft and one of the coronary arteries, primarily the left anterior descending coronary artery (LAD). Because the device could only perform end-to-end anastomoses, the coronary artery first had to be severed and dissected from the surrounding myocardium, and the exposed end everted for attachment. This technique limited the indications of the device to cases where the coronary artery was totally occluded, and therefore there was no loss of blood flow by completely severing the coronary artery downstream of the blockage to make the anastomosis. Consequently, this device is. not applicable where the coronary artery is only partially occluded and is not at all applicable to making the proximal side-to-end anastomosis between a bypass. graft and the aorta.
One attempt to provide a vascular stapling device for end-to-side vascular anastomoses is described in U.S. Pat. No. 5,234,447, issued to Kaster et al. for a Side-to-end Vascular Anastomotic Staple Apparatus. Kaster et al. provide a ring-shaped staple with staple legs extending from the proximal and distal ends of the ring to join two blood vessels together in an end-to-side anastomosis. However, Kaster et al. does not provide a complete system for quickly and automatically performing an anastomosis. The method of applying the anastomosis staple disclosed by Kaster et al. involves a great deal of manual manipulation of the staple, using hand operated tools to individually deform the distal tines of the staple after the graft has been attached and before it is inserted into the opening made in the aortic wall. One of the more difficult maneuvers in applying the Kaster et al. staple involves carefully everting the graft vessel over the sharpened ends of the staple legs, then piercing the evened edge of the vessel with the staple legs. Experimental attempts to apply this technique have proven to be very problematic because of difficulty in manipulating the graft vessel and the potential for damage to the graft vessel wall. For speed, reliability and convenience, it is preferable to avoid the need for complex maneuvers while performing the anastomosis. Further bending operations must then be performed on the staple legs. Once the distal tines of the staple have been deformed, it may be difficult to insert the staple through the aortotomy opening. Another disadvantage of the Kaster et al. device is that the distal tines of the staple pierce the wall of the graft vessel at the point where it is evened over the staple. Piercing the wall of the graft vessel potentially invites leaking of the anastomosis and may compromise the structural integrity of the graft vessel wall, serving as a locus for a dissection or even a tear, which could lead to catastrophic failure. Because the Kaster et al staple legs only apply pressure to the anastomosis at selected points, there is a potential for leaks between the staple legs. The distal tines of the staple are also exposed to the blood flow path at the anastomotic site where it is most critical to avoid the potential for thrombosis. There is also the potential that exposure of the medial layers of the graft vessel where the staple pierces the wall could be a site for the onset of intimal hyperplasia, which would compromise the long-term patency of the graft as described above. Because of these potential drawbacks, it is desirable to make the attachment to the graft vessel as atraumatic to the vessel wall as possible and to eliminate as much as possible the exposure of any foreign materials or any vessel layers other than a smooth uninterrupted intimal layer within the anastomosis site or within the graft vessel lumen.
A second approach to expediting and improving anastomosis procedures is through the use of anastomotic fittings for joining blood vessels together. One attempt to provide a vascular anastomotic fitting device for end-to-side vascular anastomoses is described in U.S. Pat. No. 4,366,819, issued to Kaster for an Anastomotic Fitting. This device is a four-part anastomotic fitting having a tubular member over which the graft vessel is evened, a ring flange which engages the aortic wall from within the aortic lumen, and a fixation ring and a locking ring which engage the exterior of the aortic wall. Another similar Anastomotic Fitting is described in U.S. Pat. No. 4,368,736, also issued to Kaster. This device is a tubular fitting with a flanged distal end that fastens to the aortic wall with an attachment ring, and a proximal end with a graft fixation collar for attaching to the graft vessel. These devices have a number of drawbacks. Firstly, the anastomotic fittings described expose the foreign material of the anastomotic device to the blood flow path within the arteries. This is undesirable because foreign materials within the blood flow path can have a tendency to cause hemolysis, platelet deposition and thrombosis. Immune responses to foreign material, such as rejection of the foreign material or auto-immune responses triggered by the presence of foreign material, tend to be stronger when the material is exposed to the bloodstream. As such, it is preferable that as much as possible of the interior surfaces of an anastomotic fitting that will be exposed to the blood flow path be covered with vascular tissue, either from the target vessel or from the graft vessel, so that a smooth, continuous, hemocompatible endothelial layer will be presented to the bloodstream. The anastomotic fitting described by Kaster in the '819 patent also has the potential drawback that the spikes that hold the graft vessel onto the anastomotic fitting are very close to the blood flow path, potentially causing trauma to the blood vessel that could lead to leaks in the anastomosis or compromise of the mechanical integrity of the vessels. Consequently, it is desirable to provide an anastomosis fitting that is as atraumatic to the graft vessel as possible. Any sharp features such as attachment spikes should be placed as far away from the blood flow path and the anastomosis site as possible so that there is no compromise of the anastomosis seal or the structural integrity of the vessels.
Another device, the 3M-Unilink device for end-to-end anastomosis (U.S. Pat. Nos. 4,624,257; 4,917,090; 4,917,091) is designed for use in microsurgery, such as for reattaching vessels severed in accidents. This device provides an anastomosis clamp that has two eversion rings which are locked together by a series of impaling spikes on their opposing faces. However, this device is awkward for use in end-to-side anastomosis and tends to deform the target vessel; therefore it is not currently used in CABG surgery. Due to the delicate process needed to insert the vessels into the device, it would also be unsuitable for port-access surgery.
In order to solve these and other problems, it is desirable to provide an anastomosis device which performs an end-to-side anastomosis between blood vessels or other hollow organs and vessels. It is also desirable to provide an anastomosis device which minimizes the trauma to the blood vessels while performing the anastomosis, which minimizes the amount of foreign materials exposed to the blood flow path within the blood vessels and which avoids leakage problems, and which promotes rapid endothelialization and healing. It is also desirable that the invention provide a complete system for quickly and automatically performing an anastomosis with a minimal amount of manual manipulation.
Anastomosis devices may be utilized to join biological tissues, and more particularly, joining tubular organs to create a fluid channel. The connections between the tubular organs or vessels may be made side to side, end to end and/or end to side. Typically, there is a graft vessel and a target vessel. The target vessel may be an artery, vein or any other conduit or fluid carrying vessel, for example, coronary arteries. The graft vessel may comprise a synthetic material, an autologus vessel, a homologus vessel or a xenograft. Anastomosis devices may comprise any suitable biocompatible materials, for example, metals, polymers and elastomers. In addition, there are a wide variety of designs and configurations for anastomosis devices depending on the type of connection to be made. Similarly to stents, anastomosis devices cause some injury to the target vessel, thereby provoking a response from the body. Therefore, as in the case with stents, there is the potential for smooth muscle cell proliferation which can lead to blocked connections. Accordingly, there is a need to minimize or substantially eliminate smooth muscle cell proliferation and inflammation at the anastomotic site. Rapamycin and/or other drugs, agents or compounds may be utilized in a manner analogous to stents as described above. In other words, at least a portion of the anastomosis device may be coated with rapamycin or other drug, agent and/or compound.
In the exemplary embodiment, the fastening flange 202 resides on the interior surface 206 of the target vessel wall 208 when the anastomosis is completed. In order to substantially reduce the risk of hemolysis, thrombogenesis or foreign body reactions, the total mass of the fastening flange 202 is preferably as small as possible to reduce the amount of foreign material within the target vessel lumen 210.
The fastening flange 202 is in the form of a wire ring with an internal diameter, which when fully expanded, is slightly greater than the outside diameter of the graft vessel wall 214 and of the opening 216 made in the target vessel wall 208. Initially, the wire ring of the fastening flange 202 has a rippled wave-like shape to reduce the diameter of the ring so that it will easily fit through the opening 216 in the target vessel wall 208. The plurality of staple members 204 extend substantially perpendicular from the wire ring in the proximal direction. In the illustrative exemplary embodiment, there are nine staple members 204 attached to the wire ring fastening flange 202. Other variations of the anastomosis device 200 might typically have from four to twelve staple members 204 depending on the size of the vessels to be joined and the security of attachment required in the particular application. The staple members 204 may be integrally formed with the wire ring fastening flange 202 or the staple members 204 may be attached to the fastening flange 202 by welding, brazing or any other suitable joining method. The proximal ends 218 of the staple members 204 are sharpened to easily pierce the target. vessel wall 208 and the graft vessel wall 214. Preferably, the proximal ends 218 of the staple members 204 have barbs 220 to improve the security of the attachment when the anastomosis device 200 is deployed. The anastomosis device 200 is prepared for use by mounting the device onto the distal end of an application instrument 222. The fastening flange 202 is mounted on an anvil 224 attached to the distal end of the elongated shaft 226 of the application instrument 222. The staple members 204 are compressed inward against a conical holder 228 attached to the instrument 222 proximal to the anvil 224. The staple members 204 are secured in this position by a cap 230 which is slidably mounted on the elongated shaft 226. The cap 230 moves distally to cover the sharpened, barbed proximal ends 218 of the staple members 204 and to hold them against the conical holder 228. The application instrument 222 is then inserted through the lumen 232 of the graft vessel 214. This may be done by inserting the application instrument 222 through the graft vessel lumen 232 from the proximal to the distal end of the graft vessel 214, or it may be done by back loading the elongated shaft 226 of the application instrument 222 into. the graft vessel lumen 232 from the distal end to the proximal end, whichever is most convenient in the case. The anvil 224 and conical holder 228 on the distal end of the application instrument 222 with the anastomosis device 200 attached is extended through the opening 216 into the lumen 210 of the target vessel.
Next, the distal end 234 of the graft vessel wall 214 is everted against the exterior surface 236 of the target vessel wall 208 with the graft vessel lumen 232 centered over the opening 216 in the target vessel wall 208. The cap 230 is withdrawn from the proximal ends 218 of the staple members 204, allowing the staple members 204 to spring outward to their expanded position. The application instrument 222 is then drawn in the proximal direction so that the staple members pierce the target vessel wall 208 surrounding the opening 216 and the everted distil end 234 of the graft vessel 214.
The application instrument 222 has an annular staple former 238 which surrounds the outside of the graft vessel 214. Slight pressure on the everted graft vessel wall from the annular staple former 238 during the piercing step assists in piercing the staple members 204 through the graft vessel wall 214. Care should be taken not to apply too much pressure with the annular staple former 238 at this point in the process because the staple members 204 could be prematurely deformed before they have fully traversed the vessel walls. If desired, an annular surface made of a softer material, such as an elastomer, can be provided on the application instrument 222 to back up the vessel walls as the staple members 204 pierce through them.
Once the staple members 204 have fully traversed the target vessel wall 208 and the graft vessel wall 214, the staple former 238 is brought down with greater force while supporting the fastening flange 202 with the anvil 224. The staple members 204 are deformed outward so that the sharpened, barbed ends 218 pierce back through the everted distil end 234 and into the target vessel wall 208 to form a permanent attachment. To complete the anastomosis, the anvil 224 is withdrawn through the graft vessel lumen 232. As the anvil 224 passes through the wire ring fastening flange 202, it straightens out the wave-like ripples so that the wire ring flange 202 assumes its full expanded diameter. Alternately, the wire ring fastening flange 202 may be made of a resilient material so that the flange 202 may be compressed and held in a rippled or folded position until it is released within the target vessel lumen 210, whereupon it will resume its full expanded diameter. Another alternate construction would be to move the anastomosis device of a shape-memory alloy so that the fastening flange may be compressed and inserted through the opening in the target vessel, whereupon it would be returned to its full expanded diameter by heating the device 200 to a temperature above the shape-memory transition temperature.
In the above-described exemplary embodiment, the staple members 204 and/or the wire ring fastening flange 202 may be coated with any of the above-described agents, drugs or compounds such as rapamycin to prevent or substantially reduce smooth muscle wall proliferation.
A needle 308 preferably is curved and is disposed at the first end 304 of the suture 302. A sharp tip 310 of needle 308 enables easy penetration of various anatomical structures and enables the needle 308 and the suture 302 to readily pass therethrough. The needle 308 may be attached to the suture 302 in various ways, for example, by swedging, preferably substantially matching the outer diameter of the needle 308 and the suture 302 as closely as possible.
Apparatus 300 also includes a holding device 312 disposed at the second end 306 of the suture 302. The holding device 312 includes first and second limbs 314, 316, according to the illustrated exemplary embodiment, and preferably is of greater stiffness than the suture 302. The first limb 314 may be connected to suture 302 in a number of ways, for example, by swedging, preferably substantially matching the outside diameter of the suture 302 and the holding device 312 as closely as possible. The holding device 312 includes a staple structure comprising a bendable material that preferably is soft and malleable enough to crimp and hold its crimped position on the outside of an anastomosis. Such materials may include titanium or stainless steel. The holding device 312 may be referred to as a staple, according to the illustrated embodiment, and the suture 302 and the needle 308 a delivery system for staple 312.
The holding device 312 preferably is substantially V-shaped or substantially U-shaped, as illustrated, but may assume a wide variety of shapes to suit particular surgical situations and/or surgeon preference. For example, one of limbs 314, 316 may be straight and the other curved, or limbs 314, 316 may be collinear. The holding device 312 preferably is as smooth and round in cross-section as the needle 308. Further, the diameters of the needle 308, the suture 302, and the holding device 312 preferably are substantially identical, especially the needle 308 and the holding device 312, to avoid creating holes in the anatomical structures that are larger than the diameter of the staple 312. Such holes likely would cause bleeding and/or leakage.
A method of using apparatus 300 is illustrated in
As illustrated in
Thus, the staple 312 holds vascular structures 318, 320 together from inside the vascular structures, as well as from outside, unlike the many prior art staples that secure opposed structures only externally. This achieves a number of advantages, as described above. Not only does a better approximation result, but crimping a staple is simpler than tying one or more knots and is also less likely traumatic on tissue. Staple closure with a single crimp provides less tension on an anastomosis, for example, than a knot requiring several throws. Embodiments of the invention are especially advantageous in minimally invasive surgical situations, as knot-tying with, for example, a knot pusher in a minimally invasive setting through a small port is particularly tedious, and can require up to four or five throws to prevent slippage. Crimping a staple through the port, as with embodiments of the invention, is far simpler and eliminates much of the difficulty.
According to one exemplary embodiment, the surgeon achieves a precise approximation of the vascular or other structures with preferably a limited number of staples or other holding devices, and then completes the anastomosis with biologic glue or laser techniques. The holding devices, for example, two or more in number, may be used to orient or line up the structures initially and thus used as a “pilot” for guiding the completion of the anastomosis.
In the above described exemplary embodiment, the holding device 312 may be coated with any of the above-described drugs, agents or compounds such as rapamycin to prevent or substantially reduce smooth muscle cell proliferation.
As described above, various drugs, agents or compounds may be locally delivered via medical devices. For example, rapamycin and heparin may be delivered by a stent to reduce restenosis, inflammation, and coagulation. Various techniques for immobilizing the drugs, agents or compounds are discussed above, however, maintaining the drugs, agents or compounds on the medical devices during delivery and positioning is critical to the success of the procedure or treatment. For example, removal of the drug, agent or compound coating during delivery of the stent can potentially cause failure of the device. For a self-expanding stent, the retraction of the restraining sheath may cause the drugs, agents or compounds to rub off the stent. For a balloon expandable stent, the expansion of the balloon may cause the drugs, agents or compounds to simply delaminate from the stent through contact with the balloon or via expansion. Therefore, prevention of this potential problem is important to have a successful therapeutic medical device, such as a stent.
There are a number of approaches that may be utilized to substantially reduce the above-described concern. In one exemplary embodiment, a lubricant or mold release agent may be utilized. The lubricant or mold release agent may comprise any suitable biocompatible lubricious coating. An exemplary lubricious coating may comprise silicone. In this exemplary embodiment, a solution of the silicone base coating may be introduced onto the balloon surface, onto the polymeric matrix, and/or onto the inner surface of the sheath of a self-expanding stent delivery apparatus and allowed to air cure. Alternately, the silicone based coating may be incorporated into the polymeric matrix. It is important to note, however, that any number of lubricious materials may be utilized, with the basic requirements being that the material be biocompatible, that the material not interfere with the actions/effectiveness of the drugs, agents or compounds and that the material not interfere with the materials utilized to immobilize the drugs, agents or compounds on the medical device. It is also important to note that one or more, or all of the above-described approaches may be utilized in combination.
Referring now to
Materials such as synthetic waxes, e.g. diethyleneglycol monostearate, hydrogenated castor oil, oleic acid, stearic acid, zinc stearate, calcium stearate, ethylenebis (stearamide), natural products such as paraffin wax, spermaceti wax, carnuba wax, sodium alginate, ascorbic acid and flour, fluorinated compounds such as perfluoroalkanes, perfluorofatty acids and alcohol, synthetic polymers such as silicones e.g. polydimethylsiloxane, polytetrafluoroethylene, polyfluoroethers, polyalkylglycol e.g. polyethylene glycol waxes, and inorganic materials such as talc, kaolin, mica, and silica may be used to prepare these coatings. Vapor deposition polymerization e.g. parylene-C deposition, or RF-plasma polymerization of perfluoroalkenes and perfluoroalkanes can also be used to prepare these lubricious coatings.
If a self-expanding stent is utilized, the lubricious coating may be affixed to the inner surface of the restraining sheath.
In an alternate approach, physical and/or chemical cross-linking methods may be applied to improve the bond strength between the polymeric coating containing the drugs, agents or compounds and the surface of the medical device or between the polymeric coating containing the drugs, agents or compounds and a primer. Alternately, other primers applied by either traditional coating methods such as dip, spray or spin coating, or by RF-plasma polymerization may also be used to improve bond strength. For example, as shown in
A related difficulty occurs in medical devices such as stents. In the drug-coated stents crimped state, some struts come into contact with each other and when the stent is expanded, the motion causes the polymeric coating comprising the drugs, agents or compounds to stick and stretch. This action may potentially cause the coating to separate from the stent in certain areas. The predominant mechanism of the coating self-adhesion is believed to be due to mechanical forces. When the polymer comes in contact with itself, its chains can tangle causing the mechanical bond, similar to Velcro®. Certain polymers do not bond with each other, for example, fluoropolymers. For other polymers, however, powders may be utilized. In other words, a powder may be applied to the one or more polymers incorporating the drugs, agents or other compounds on the surfaces of the medical device to reduce the mechanical bond. Any suitable biocompatible material which does not interfere with the drugs, agents, compounds or materials utilized to immobilize the drugs, agents or compounds onto the medical device may be utilized. For example, a dusting with a water soluble powder may reduce the tackiness of the coatings surface and this will prevent the polymer from sticking to itself thereby reducing the potential for delamination. The powder should be water-soluble so that it does not present an emboli risk. The powder may comprise an anti-oxidant, such as vitamin C, or it may comprise an anti-coagulant, such as aspirin or heparin. An advantage of utilizing an anti-oxidant may be in the fact that the anti-oxidant may preserve the other drugs, agents or compounds over longer periods of time.
It is important to note that crystalline polymers are generally not sticky or tacky. Accordingly, if crystalline polymers are utilized rather than amorphous polymers, then additional materials may not be necessary. It is also important to note that polymeric coatings without drugs, agents and/or compounds may improve the operating characteristics of the medical device. For example, the mechanical properties of the medical device may be improved by a polymeric coating, with or without drugs, agents and/or compounds. A coated stent may have improved flexibility and increased durability. In addition, the polymeric coating may substantially reduce or eliminate galvanic corrosion between the different metals comprising the medical device. The same holds true for anastomosis devices.
As stated above, for a self-expanding stent, the retraction of the restraining sheath may cause the drugs, agents or compounds to rub off the stent. Accordingly, in an alternate exemplary embodiment, the stent delivery device may be modified to reduce the potential of rubbing off the coating. This is especially important for long stents, for example, long rapamycin coated stents. In addition, there is also the potential of damaging the stent itself when the delivery sheath is retracted during stent deployment. Accordingly, the stent delivery device may be modified to substantially reduce the forces acting on certain areas of the stent by distributing the forces to more areas of the stent. The stent and stent delivery system described herein are intended to be merely illustrative in nature and those skilled in the art will recognize that the designs disclosed may be incorporated into any number of stents and stent delivery systems.
Shaft 5012 has proximal and distal ends 5016 and 5018 respectively. The proximal end 5016 of the shaft 5012 has a Luer guidewire hub 5020 attached thereto. As seen best from
As will be described in greater detail below, shaft 5012 has a body portion 5022, wherein at least a section thereof is made from a flexible coiled member 5024, looking very much like a compressed or closed coil spring. Shaft 5012 also includes a distal portion 5026, distal to body portion 5022, which is preferably made from a coextrusion of high-density polyethylene and Nylon®. The two portions 5022 and 5026 are joined together by any number of means known to those of ordinary skill in the art including heat fusing, adhesive bonding, chemical bonding or mechanical attachment.
As best seen from
The stent delivery apparatus 5010 glides over a guide wire 8000 (shown in
The guidewire lumen 5034 has a diameter that is matched to hug the recommended size guide wire so that there is a slight frictional engagement between the guidewire 8000 and the guidewire lumen 5034 of distal tip 5028. The distal tip 5028 has a rounded section 5036 between its distal portion 5032 and its proximal portion 5030. This helps prevent the sheath 5014 from slipping distally over the distal tip 5028, and thereby exposing the squared edges of the sheath 5014 to the vessel, which could cause damage thereto. This improves the device's “pushability.” As the distal tip 5028 encounters resistance it does not allow the sheath 5014 to ride over it thereby exposing the sheath's 5014 square cut edge. Instead the sheath 5014 contacts the rounded section 5036 of the distal tip 5028 and thus transmits the forces applied to the distal tip 5028. The distal tip 5028 also has a proximally tapered section 5038 which helps guide the distal tip 5028 through the deployed stent 7000 without providing a sharp edge that could grab or hang up on a stent strut end or other irregularity in the lumen inner diameter.
Attached to distal portion 5026 of shaft 5012 is a stop 5040, which is proximal to the distal tip 5028 and stent 7000. Stop 5040 may be made from any number of suitable materials known in the art, including stainless steel, and is even more preferably made from a highly radio-opaque material such as platinum, gold tantalum, or radio-opaque filled polymer. The stop 5040 may be attached to shaft 5012 by any suitable means, including mechanical or adhesive bonding, or by any other means known to those skilled in the art. Preferably, the diameter of stop 5040 is large enough to make sufficient contact with the loaded stent 7000 without making frictional contact with the sheath 5014. As will be explained subsequently, the stop 5040 helps to “push” the stent 7000 or maintain its relative position during deployment, by preventing the stent 7000 from migrating proximally within the sheath 5014 during retraction of the sheath 5014 for stent deployment. The radio-opaque stop 5040 also aides in positioning the stent 7000 within the target lesion area during deployment within a vessel, as is described below.
A stent bed 5042 is defined as being that portion of the shaft 5012 between the distal tip 5028 and the stop 5040 (
As seen from
The flexible coiled member 5024 further includes a covering 5046 that fits over the flexible coiled member 5024 to help resist buckling of the coiled member 5024 in both bending and compressive modes. The covering 5046 is an extruded polymer tube and is preferably a soft material that can elongate slightly to accommodate bending of the flexible coiled member 5024, but does not allow the coils to ride over each other. Covering 5046 may be made from any number of suitable materials including coextrusions of Nylon® and high-density polyethylene, polyurethane, polyamide, polytetrafluoroethylene, etc. The extrusion is also attached to the stop 5040. Flexible coiled member 5024 may be made of any number of materials known in the art including stainless steel, Nitinol, and rigid polymers. In one exemplary embodiment, flexible coiled member 5024 is made from a 0.003 inch thick by 0.010 inch wide stainless steel ribbon wire. The wire may be round, or more preferably flat to reduce the profile of the flexible coiled member 5024.
Sheath 5014 is preferably a polymeric catheter and has a proximal end 5048 terminating at a sheath hub 5050 (
As detailed in
A problem encountered with earlier self-expanding stent delivery systems is that of the stent becoming embedded within the sheath in which it is disposed. Referring to
The three layers 5060, 5062, and 5064 comprising the sheath 5014 collectively enhance stent deployment. The outer layer 5060 facilitates insertion and removal of the entire apparatus 5010. The inner layer 5062 and the wire reinforcement layer 5064 function to prevent the stent 7000 from becoming embedded in the sheath 5014. Self-expanding stents such as the stent 7000 of the present invention tend to expand to their programmed diameter at a given temperature. As the stent attempts to undergo expansion, it exerts a radially outward directed force and may become embedded in the sheath 5014 restraining it from expanding. Accordingly, the wire reinforcing layer 5064 provides radial or hoop strength to the inner layer 5062 thereby creating sufficient resistance to the outwardly directed radial force of the stent 7000 within the sheath 5014. The inner layer 5062, also as discussed above, provides a lower coefficient of friction surface to reduce the forces required to deploy the stent 7000 (typically in the range from about five to eight pounds). The wire reinforcement layer 5064 also provides tensile strength to the sheath 5014. In other words, the wire reinforcement layer 5064 provides the sheath 5014 with better pushability, i.e., the ability to transmit a force applied by the physician at a proximal location on the sheath 5014 to the distal tip 5028, which aids in navigation across tight stenotic lesions within the vasculature. Wire reinforcement layer 5064 also provides the sheath 5014 with better resistance to elongation and necking as a result of tensile loading during sheath retraction for stent deployment.
The sheath 5014 may comprise all three layers along its entire length or only in certain sections, for example, along the length of the stent 7000. In a preferred embodiment, the sheath 5014 comprises all three layers along its entire length.
Prior art self-expanding stent delivery systems did not utilize wire reinforcement layers. Because the size of typical self-expanding stents is relatively large, as compared to balloon expandable coronary stents, the diameter or profile of the delivery devices therefore had to be large as well. However, it is always advantageous to have delivery systems which are as small as possible. This is desirable so that the devices can reach into smaller vessels and so that less trauma is caused to the patient. However, as stated above, the advantages of a thin reinforcing layer in a stent delivery apparatus outweighs the disadvantages of slightly increased profile.
In order to minimize the impact of the wire reinforcement layer on the profile of the apparatus 5010, the configuration of the wire reinforcement layer 5064 may be modified. For example, this may be accomplished in a number of ways, including changing the pitch of the braid, changing the shape of the wire, changing the wire diameter and/or changing the number of wires utilized. In a preferred embodiment, the wire utilized to form the wire reinforcement layer comprises a substantially rectangular cross-section as illustrated in
In another alternate exemplary embodiment, the sheath of the delivery system may comprise an inner layer or coating on its inner surface which substantially prevents the stent from becoming embedded therein while increasing the lubricity thereof. This inner layer or coating may be utilized with the sheaths illustrated in
Essentially, in the exemplary embodiment, a hard and lubricious coating is applied to or affixed to the inner surface of the sheath of the self-expanding delivery system. The coating provides a number of advantages over currently utilized self-expanding stent delivery systems. For example, the coating provides a hard surface against which the stent exerts a radially outward directed force. As described above, self-expanding stents have a constant outward force of expansion when loaded into the delivery system. This constant and relatively high radially outward directed force can force the polymeric materials that comprise the sheath of the delivery system to creep and allow the stent to become embedded into the polymer surface. As stent platforms are developed with larger diameter stents and subsequently higher radially outward directed forces, the occurrence of this phenomenon will increase. Consequently, embedding increases the force required to deploy the stent because it causes mechanical resistance to the movement of the stent inside the delivery system, thereby preventing accurate deployment and causing potential damage to the stent. In addition, the coating is lubricious, i.e. it has a low coefficient of friction. A lubricious coating, as stated above, functions to further reduce the force required to deploy the stent, thereby increasing the facility by which the stents are delivered and deployed by physicians. This is especially important with respect to newer larger diameter stent designs and/or drug/polymer coated stent designs that have either increased radial forces, increased profile or increased overall diameter. A lubricious coating is particularly advantageous with respect to drug/polymer coated stents. Accordingly, the coating functions to prevent the stent from embedding in the sheath of the delivery system prior to deployment and reducing the friction between the sheath and the stent, both of which will reduce the deployment forces.
Various drugs, agents or compounds may be locally delivered via medical devices such as stents. For example, rapamycin and/or heparin may be delivered by a stent to reduce restenosis, inflammation and coagulation; Various techniques for immobilizing the drugs, agents or compounds onto the stent are known; however, maintaining the drugs, agents or compounds on the stent during delivery and positioning is critical to the success of the procedure or treatment. For example, removal of the drug, agent or compound during delivery of the stent can potentially cause failure of the device. For a self-expanding stent, the retraction of the restraining sheath may cause the drugs, agents or compounds to rub off the stent. Therefore, prevention of this potential problem is important to have successful therapeutic medical devices such as stents.
Pyrolytic carbon's usefulness in the implantable medical device area is a result of its unique combination of physical and chemical characteristics, including chemical inertness, isotrophy, low weight, compactness and elasticity. Pyrolytic carbon belongs to a specific family of turbostratic carbons which are similar to the structure of graphite. In graphite, the carbon atoms are covalently bonded in planar hexagonal arrays that are stacked in layers with relatively weak interlayer bonding. In turbostratic carbons, the stacking sequence is disordered and distortions may exist within each of the layers. These structural distortions in the layers are responsible for the superior ductility and durability of pyrolytic carbon. Essentially, the microstructure of pyrolytic carbon makes the material durable, strong and, wear resistant. In addition, pyrolytic carbon is highly thromboresistant and has inherent cellular. biocompatability with blood and soft tissue.
The pyrolytic carbon layer 5070 may be deposited along the entire length of the sheath 5014 or only in proximity to the stent bed 5042, illustrated in
As stated above, pyrolytic carbon surfaces are recognized as biocompatible, especially with respect to blood contact applications. This is, however, only a minor benefit in terms of stent delivery applications because the location of the pyrolytic carbon layer 5070 within the sheath 5014 is only minimally exposed to blood and is only within the body for a duration sufficient to deliver a stent.
The pyrolytic carbon layer 5070 may be affixed to the lumen of the sheath in any number of ways as mentioned above. In one exemplary embodiment, the pyrolytic carbon layer 5070 may be directly affixed to the lumen of the sheath 5014. In another exemplary embodiment, the pyrolytic carbon layer 5070 may be indirectly applied to the lumen of the sheath 5014 by first applying it to a variety of substrates, also utilizing any number of known techniques. Regardless of whether the pyrolytic carbon layer 5070 is deposited directly onto the sheath 5014 or first onto a substrate, any number of known techniques may be utilized, for example, chemical vapor deposition. In chemical vapor deposition, the carbon material is deposited from gaseous hydrocarbon compounds on suitable underlying substrates, e.g. carbon materials, metals, ceramics as well as other materials, at temperatures ranging from about 1000K to about 2500K. At these temperatures, one can understand the need to possibly utilize substrates. Any suitable biocompatible, durable and flexible substrate may be utilized and then affixed to the lumen of the sheath 5014 utilizing well-known techniques such as adhesives. As stated above, profile and flexibility are important design characteristics; accordingly, the type of substrate material chosen and/or its thickness should be considered. It is important to note that a wide range of microstructures, e.g. isotropic, lamellor, substrate-nucleated and a varied content of remaining hydrogen can occur in pyrolytic carbons, depending on the deposition conditions, including temperature, type, concentration and flow rates of the source gas and surface area of the underlying substrate.
Other techniques which may be utilized to affix the pyrolytic carbon layer 5070 directly onto the sheath 5014 or onto a substrate include pulsed laser ablation deposition, radio frequency plasma modification, physical vapor deposition as well as other known techniques. In addition to pyrolytic carbon, other materials that might be beneficial in providing similar properties include diamond-like carbon coatings, silane/silicon glass like surfaces and thin ceramic coatings such as alumina, hydroxyapatite and titania.
In an alternate exemplary embodiment, the pyrolytic carbon coating may be applied with a controlled finite porosity as briefly described above. This controlled finite porosity provides two distinct advantages. First, the porosity may serve to reduce the contact surface area if the stent with the pyrolytic carbon coating 5070, thereby reducing the friction between the stent and the inner lumen of the sheath 5014. Second, lubricious materials such as biocompatible oils, waxes and powders could be infused or impregnated within the porous surface of the coating thereby providing a reservoir of lubricious material further reducing the, frictional coefficient.
When being inserted into a patient, sheath 5014 and shaft 5012 are locked together at their proximal ends by a Tuohy Borst valve 5058. This prevents any sliding movement between the shaft 5012 and sheath 5014, which could result in a premature deployment or partial deployment of the stent 7000. When the stent 100 reaches its target site and is ready for deployment, the Tuohy Borst valve 5058 is opened so that the sheath 5014 and shaft 5012 are no longer locked together.
The method under which delivery apparatus 5010 deploys stent 7000 may best be described by referring to
Stent 7000 is a tubular member having front and back open ends a longitudinal axis extending there between. The tubular member has a first smaller diameter,
The above described geometry helps to better distribute strain throughout the stent, prevents metal to metal contact when the stent is bent, and minimizes the opening size between the features, struts, loops and bridges. The number of and nature of the design of the struts, loops and bridges are important factors when determining the working properties and fatigue life properties of the stent. Preferably, each hoop has between twenty-four to thirty-six or more struts. Preferably the stent has a ratio of number of struts per hoop to strut length (in inches) which is greater than two hundred. The length of a strut is measured in its compressed state parallel to the longitudinal axis of the stent.
In trying to minimize the maximum strain experienced by features, the stent utilizes structural geometries which distribute strain to areas of the stent which are less susceptible to failure than others. For example, one vulnerable area of the stent is the inside radius of the connecting loops. The connecting loops undergo the most deformation of all the stent features. The inside radius of the loop would normally be the area with the highest level of strain on the stent. This area is also critical in that it is usually the smallest radius on the stent. Stress concentrations are generally, controlled or minimized by maintaining the largest radii possible. Similarly, we want to minimize local strain concentrations on the bridge and bridge to loop connection points. One way to accomplish this is to utilize the largest possible radii while maintaining feature widths, which are consistent with applied forces. Another consideration is to minimize the maximum open area of the stent. Efficient utilization of the original tube from which the stent is cut increases stent strength and it's ability to trap embolic material.
As set forth above, stents coated with combinations of polymers and drugs, agents and/or compounds may potentially increase the forces acting on the stent during stent deployment. This increase in forces may in turn damage the stent. For example, as described above, during deployment, the stent is forced against a stop to overcome the force of sliding the outer sheath back. With a longer stent, e.g. greater than 200 mm, the forces exerted on the end of the stent during sheath retraction may be excessive and could potentially cause damage to the end of the stent or to other sections of the stent. Accordingly, a stent delivery device which distributes the forces over a greater area of the stent would be beneficial.
The raised sections 5200 may be formed in any number of ways. For example, the raised sections 5200 may be formed using a heated clamshell mold or a waffle iron heated die approach. Either method allows for the low cost mass production of inner shafts comprising protrusions.
The size, shape and pattern of the raised sections 5200 may be modified to accommodate any stent design. The height of each of the raised sections 5200 is preferably large enough to compensate for the slight gap that exists between the inner shaft 5012 and the outer sheath 5014. The height, H, of the raised sections or protrusions 5200 on the shaft 5012 should preferably be, at a minimum, greater than the difference in radius between the outside diameter of the shaft 5012, IM(r), and the inside diameter of the sheath 50i4, OM(r), minus the wall thickness of the device or stent 7000, WT. The equation representing this relationship is given by
H>(OM(r)−IM(r))−WT.
For example, if the shaft 5012 has an outside diameter of 0.08 inches, the sheath 5014 has an inside diameter of 0.1 inches, and the wall thickness of the stent 7000 is 0.008 inches, then the height of the raised sections or protrusions 5200 is
It is important to note that the height of the raised sections 5200 should preferably be less than the difference between the radius of the sheath and the radius of the shaft unless the protrusions 5200 are compressible.
Although each raised section 5200 is small, the number of raised sections 5200 may be large and each of the raised sections 5200 apply a small amount of force to different parts of the stent. 7002, thereby distributing the force to deploy the stent 7000 and preventing damage to the stent 7000 particularly at its proximal end. The raised sections 5200 also protect the stent 7000 during loading of the stent 7000 into the delivery system. Essentially, the same forces that act on the stent 7000 during deployment act on the stent 7000 during loading. The longitudinal flexibility of the stent necessitates that as little force as possible is placed on the stent as it is released or deployed to ensure repeatable foreshortening and accurate placement. Essentially, it is preferable that longitudinal movement of the stent 7000 be eliminated or substantially reduced during deployment thereby eliminating or substantially reducing compression of the stent. Without the raised sections 5200, as the stent 7000 is being deployed, the compressive forces will compress the delivery system as well as the stent 7000. This compressive energy will be released upon deployment, reducing the chances of accurate placement of the stent 7000 and contributing to the possibility of stent “jumping.” With the raised sections 5200, the stent 7000 is less likely to move, thereby eliminating or substantially reducing compression.
In an alternate exemplary embodiment, once the stent is positioned on the shaft of the delivery device, the stent may be heated and externally pressurized to make a mirror-like imprint in the inner shaft of the delivery system. The imprint provides a three-dimensional surface which allows the stent to maintain its position as the sheath is retracted. The three-dimensional imprint may be made using heat alone, pressure alone or with a separate device.
Any of the above-described medical devices may be utilized for the local delivery of drugs, agents and/or compounds to other areas, not immediately around the device itself. In order to avoid the potential complications associated with systemic drug delivery, the medical devices of the present invention may be utilized to deliver therapeutic agents to areas adjacent to the medical device. For example, a rapamycin coated stent may deliver the rapamycin to the tissues surrounding the stent as well as areas upstream of the stent and downstream of the stent. The degree of tissue penetration depends on a number of factors, including the drug, agent or compound, the concentrations of the drug and the release rate of the agent. The same holds true for coated anastomosis devices.
The drug, agent and/or compound/carrier or vehicle compositions described above may be formulated in a number of ways. For example, they may be formulated utilizing additional components or constituents, including a variety of excipient agents and/or formulary components to affect manufacturability, coating integrity, sterilizability, drug stability, and drug release rate. Within exemplary embodiments of the present invention, excipient agents and/or formulary components may be added to achieve both fast-release and sustained-release drug elution profiles. Such excipient agents may include salts and/or inorganic compounds such as acids/bases or buffer components, anti-oxidants, surfactants, polypeptides, proteins, carbohydrates including sucrose, glucose or dextrose, chelating agents such as EDTA, glutathione or other excipients or agents.
It is important to note that any of the above-described medical devices may be coated with coatings that comprise drugs, agents or compounds or simply with coatings that contain no drugs, agents or compounds. In addition, the entire medical device may be coated or only a portion of the device may be coated. The coating may be uniform or non-uniform. The coating may be discontinuous.
As described above, any number of drugs, agents and/or compounds may be locally delivered via any number of medical devices. For example, stents and anastomosis devices may incorporate coatings comprising drugs, agents and/or compounds to treat various disease states and reactions by the body as described in detail above. Other devices which may be coated with or otherwise incorporate therapeutic dosages of drugs, agents and/or compounds include stent-grafts, which are briefly described above, and devices utilizing stent-grafts, such as devices for treating abdominal aortic aneurysms as well as other aneurysms, e.g. thoracic aorta aneurysms.
Stent-grafts, as the name implies, comprise a stent and a graft material attached thereto.
In accordance with the present invention, the stent may be variously configured. For example, the stent may be configured with struts or the like that form repeating geometric shapes. One skilled in the art will readily recognize that a stent may be configured or adapted to include certain features and/or to perform a certain function(s), and that alternate designs may be used to promote that feature or function.
In the exemplary embodiment of the invention illustrated in
An inner or outer surface of the stent 802 may be covered by or support a graft material. Graft material 812 may be made from any number of materials known to those skilled in the art, including woven or other configurations of polyester, Dacron®, Teflon®, polyurethane porous polyurethane, silicone, polyethylene, terephthalate, expanded polytetrafluoroethylene (ePTFE) and blends of various materials.
The graft material 812 may be variously configured, preferably to achieve predetermined mechanical properties. For example, the graft material may incorporate a single or multiple weaving and/or pleating patterns, or may be pleated or unpleated. For example, the graft material may be configured into a plain weave, a satin weave, include longitudinal pleats, interrupted pleats, annular or helical pleats, radially oriented pleats, or combinations thereof. Alternately, the graft material may be knitted or braided. In the embodiments of the invention in which the graft material is pleated, the pleats may be continuous or discontinuous. Also, the pleats may be oriented longitudinally, circumferentially, or combinations thereof.
As illustrated in
In addition, the pleats 814 help facilitate stent-graft manufacture, in that they indicate the direction parallel to the longitudinal axis, allowing stent to graft attachment along these lines, and thereby inhibiting accidental twisting of the graft relative to the stent after attachment. The force required to push the stent-graft 800 out of the delivery system may also be reduced, in that only the pleated edges of the graft make frictional contact with the inner surface of the delivery system. One further advantage of the pleats 814 is that blood tends to coagulate generally uniformly in the troughs of the pleats 814, discouraging asymmetric or large clot formation on the graft surface, thereby reducing embolus risk.
As shown in
The foregoing graft materials may be braided, knitted or woven, and may be warp or weft knitted. If the material is warp knitted, it may be provided with a velour, or towel like surface; which is believed to speed the formation of blood clots, thereby promoting the integration of a stent-graft or stent-graft component into the surrounding cellular structure.
A graft material may be attached to a stent or to another graft material by any number of structures or methods known to those skilled in the art, including adhesives, such as polyurethane glue; a plurality of conventional sutures of polyvinylidene fluoride, polypropylene, Dacron®, or any other suitable material; ultrasonic welding; mechanical interference fit; and staples.
The stent 802 and/or graft material 812 may be coated with any of the above-described drugs, agents and/or compounds. In one exemplary embodiment, rapamycin may be affixed to at least a portion of the graft material 812 utilizing any of the materials and processes described above. In another exemplary embodiment, rapamycin may be affixed to at least a portion of the graft material 812 and heparin or other anti-thrombotics may be affixed to at least a portion of the stent 802. With this configuration, the rapamycin coated graft material 812 may be utilized to minimize or substantially eliminate smooth muscle cell hyperproliferation and the heparin coated stent may substantially reduce the chance of thrombosis.
The particular polymer(s) utilized depends on the particular material upon which it is affixed. In addition, the particular drug, agent and/or compound may also affect the selection of polymer(s). As set forth above, rapamycin may be affixed to at least a portion of the graft material 812 utilizing the polymer(s) and processes described above. In another alternate exemplary embodiment, the rapamycin or any other drug, agent and/or compound may be directly impregnated into the graft material 812 utilizing any number of known techniques.
In yet another alternate exemplary embodiment, the stent-graft may be formed from two stents with the graft material sandwiched therebetween.
In yet another alternate exemplary embodiment, the stent-graft design may be modified to include a graft cuff. As illustrated in
Stent-grafts may be utilized to treat aneurysms. An aneurysm is an abnormal dilation of a layer or layers of an arterial wall, usually caused by a systemic collagen synthetic or structural defect. An abdominal aortic aneurysm is an aneurysm in the abdominal portion of the aorta, usually located in or near one or both of the two iliac arteries or near the renal arteries. The aneurysm often arises in the infrarenal portion of the diseased aorta, for example, below the kidneys. A thoracic aortic aneurysm is an aneurysm in the thoracic portion of the aorta. When left untreated, the aneurysm may rupture, usually causing rapid fatal hemorrhaging.
Aneurysms may be classified or typed by their position as well as by the number of aneurysms in a cluster. Typically, abdominal aortic aneurysms may be classified into five types. A Type I aneurysm is a single dilation located between the renal arteries and the iliac arteries. Typically, in a Type 1 aneurysm, the aorta is healthy between the renal arteries and the aneurysm and between the aneurysm and the iliac arteries.
A Type II A aneurysm is a single dilation located between the renal arteries and the iliac arteries. In a Type II A aneurysm, the aorta is healthy between the renal arteries and the aneurysm, but not healthy between the aneurysm and the iliac arteries. In other words, the dilation extends to the aortic bifurcation. A Type II B aneurysm comprises three dilations. One dilation is located between the renal arteries and the iliac arteries. Like a Type II A aneurysm, the aorta is healthy between the aneurysm and the renal arteries, but not healthy between the aneurysm and the iliac arteries. The other two dilations are located in the iliac arteries between the aortic bifurcation and the bifurcations between the external iliacs and the internal iliacs. The iliac arteries are healthy between the iliac bifurcation and the aneurysms. A Type II C aneurysm also comprises three dilations. However, in a Type II C aneurysm, the dilations in the iliac arteries extend to the iliac bifurcation.
A Type III aneurysm is a single dilation located between the renal arteries and the iliac arteries. In a Type III aneurysm, the aorta is not healthy between the renal arteries and the aneurysm. In other words, the dilation extends to the renal arteries.
A ruptured abdominal aortic aneurysm is presently the thirteenth leading cause of death in the United States. The routine management of abdominal aortic aneurysms has been surgical bypass, with the placement of a graft in the involved or dilated segment. Although resection with a synthetic graft via transperitoneal or retroperitoneal approach has been the standard treatment, it is associated with significant risk. For example, complications include perioperative myocardial ischemia, renal failure, erectile impotence, intestinal ischemia, infection, lower limb ischemia, spinal cord injury with paralysis, aorta-enteric fistula, and death. Surgical treatment of abdominal aortic aneurysms is associated with an overall mortality rate of five percent in a symptomatic patients, sixteen to nineteen percent in symptomatic patients, and is as high as fifty percent in patients with ruptured abdominal aortic aneurysms.
Disadvantages associated with conventional surgery, in addition to the high mortality rate, include an extended recovery period associated with the large surgical incision and the opening of the abdominal cavity, difficulties in suturing the graft to the aorta, the loss of the existing thrombosis to support and reinforce the graft, the unsuitability of the surgery for many patients having abdominal aortic aneurysms, and the problems associated with performing the surgery on an emergency basis after the aneurysm has ruptured. Further, the typical recovery period is from one to two weeks in the hospital, and a convalescence period at home from two to three months or more, if complications ensue. Since many patients having abdominal aortic aneurysms. have other chronic illnesses, such as heart, lung, liver and/or kidney disease, coupled with the fact that many of these patients are older, they are less than ideal candidates for surgery.
The occurrence of aneurysms is not confined to the abdominal region. While abdominal aortic aneurysms are generally the most common, aneurysms in other regions of the aorta or one of its branches are possible. For example, aneurysms may occur in the thoracic aorta. As is the case with abdominal aortic aneurysms, the widely accepted approach to treating an aneurysm in the thoracic aorta is surgical repair, involving replacing the aneurysmal segment with a prosthetic device. This surgery, as described above, is a major undertaking, with associated high risks and with significant mortality and morbidity.
Over the past five years, there has been a great deal of research directed at developing less invasive, percutaneous, e.g., catheter directed, techniques for the treatment of aneurysms, specifically abdominal aortic aneurysms. This has been facilitated by the development of vascular stents, which can and have been used in conjunction with standard or thin-wall graft material in order to create a stent-graft or endograft. The potential advantages of less invasive treatments have included reduced surgical morbidity and mortality along with shorter hospital and intensive care unit stays.
Stent-grafts or endoprostheses are now FDA approved and commercially available. The delivery procedure typically involves advanced angiographic techniques performed through vascular accesses gained via surgical cutdown of a remote artery, such as the common femoral or brachial arteries. Over a guidewire, the appropriate size introducer will be placed. The catheter and guidewire are passed through the aneurysm, and, with the appropriate size introducer housing a stent-graft, the stent-graft will be advanced along the guidewire to the appropriate position. Typical deployment of the stent-graft device requires withdrawal of an outer sheath while maintaining the position of the stent-graft with an inner-stabilizing device. Most stent-grafts are self-expanding; however, an additional angioplasty procedure, e.g., balloon angioplasty, may be required to secure the position of the stent-graft. Following the placement of the stent-graft, standard angiographic views may be obtained.
Due to the large diameter of the above-described devices, typically greater than twenty French (3F=1 mm), arteriotomy closure requires surgical repair. Some procedures may require additional surgical techniques, such as hypogastric artery embolization, vessel ligation, or surgical bypass, in order to adequately treat the aneurysm or to maintain flow to both lower extremities. Likewise, some procedures will require additional, advanced catheter directed techniques, such as angioplasty, stent placement, and embolization, in order to successfully exclude the aneurysm and efficiently manage leaks.
While the above-described endoprostheses represent a significant improvement over conventional surgical techniques, there is a need to improve the endoprostheses, their method of use and their applicability to varied biological conditions. Accordingly, in order to provide a safe and effective alternate means for treating aneurysms, including abdominal aortic aneurysms and thoracic aortic aneurysms, a number of difficulties associated with currently known endoprostheses and their delivery systems must be overcome. One concern with the use of endoprostheses is the prevention of endo-leaks and the disruption of the normal fluid dynamics of the vasculature. Devices using any technology should preferably be simple to position and reposition as necessary, should preferably provide an acute fluid tight seal, and should preferably be anchored to prevent migration without interfering with normal blood flow in both the aneurysmal vessel as well as branching vessels. In addition, devices using the technology should preferably be able to be anchored, sealed, and maintained in bifurcated vessels, tortuous vessels, highly angulated vessels, partially diseased vessels, calcified vessels, odd shaped vessels, short vessels, and long vessels. In order to accomplish this, the endoprostheses should preferably be extendable and re-configurable while maintaining acute and long term fluid tight seals and anchoring positions.
The endoprostheses should also preferably be able to be delivered percutaneously utilizing catheters, guidewires and other devices which substantially eliminate the need for open surgical intervention. Accordingly, the diameter of the endoprostheses in the catheter is an important factor. This is especially true for aneurysms in the larger vessels, such as the thoracic aorta.
As stated above, one or more stent-grafts may be utilized to treat aneurysms. These stent-grafts or endoprostheses may comprise any number of materials and configurations.
A prosthesis used in a system in accordance with the present invention typically includes a support, stent or lattice of interconnected struts defining an interior space or lumen having an open proximal end and an open distal end. The lattice also defines an interior surface and an exterior surface. The interior and/or exterior surfaces of the lattice, or a portion of the lattice, may be covered by or support at least one gasket material or graft material.
In preferred embodiments of the invention, a prosthesis is moveable between an expanded or inflated position and an unexpanded or deflated position, and any position therebetween. In some exemplary embodiments of the invention, it may be desirable to provide a prosthesis that moves only from fully collapsed to fully expanded. In other exemplary embodiments of the invention, it may be desirable to expand the prosthesis, then collapse or partially collapse the prosthesis. Such capability is beneficial to the surgeon to properly position or re-position the prosthesis. In accordance with the present invention, the prosthesis may be self-expanding, or may be expandable using an inflatable device, such as a balloon or the like.
Referring back to
The first prosthesis includes a support matrix or stent that supports a sealing material or foam, at least a portion of which is positioned across a biological fluid flow path, e.g., across a blood flow path. In preferred embodiments of the invention, the first prosthesis, the stent, and the sealing material are radially expandable, and define a hollow space between a proximal portion of the prosthesis and a distal portion of the prosthesis. The first prosthesis may also include one or more structures for positioning and anchoring the prosthesis in the artery, and one or more structures for engaging and fixing at least one second prosthesis in place, e.g., a bypass prosthesis.
The support matrix or stent of the first prosthesis may be formed of a wide variety of materials, may be configured in a wide variety of shapes, and their shapes and uses are well known in the art. Exemplary prior art stents are disclosed in U.S. Pat. No. 4,733,665 (Palmaz); U.S. Pat. No. 4,739,762 (Palmaz); and U.S. Pat. No. 4,776,337 (Palmaz), each of the foregoing patents being incorporated herein by reference.
In preferred embodiments of the invention, the stent of the first prosthesis is a collapsible, flexible, and self-expanding lattice or matrix formed from a metal or metal alloy, such as nitinol or stainless steel. Structures formed from stainless steel may be made self-expanding by configuring the stainless steel in a predetermined manner, for example, by twisting it into a braided configuration. More preferably, the stent is a tubular frame that supports a sealing material. The term tubular, as used herein, refers to any shape having a sidewall or sidewalls defining a hollow space or lumen extending therebetween; the cross-sectional shape may be generally cylindrical, elliptic, oval, rectangular, triangular, or any other shape. Furthermore, the shape may change or be deformable as a consequence of various forces that may press against the stent or prosthesis.
The sealing material or gasket member supported by the stent may be formed of a wide variety of materials, may be configured in a wide variety of shapes, and their shapes and uses are well known in the art. Exemplary materials for use with this aspect of the invention are disclosed in U.S. Pat. No. 4,739,762 (Palmaz) and U.S. Pat. No. 4,776,337 (Palmaz), both incorporated herein by reference.
The sealing material or gasket member may comprise any suitable material. Exemplary materials preferably comprise a biodurable and biocompatible material, including but are not limited to, open cell foam materials and closed cell foam materials. Exemplary materials include polyurethane, polyethylene, polytetrafluoroethylene; and other various polymer materials, preferably woven or knitted, that provide a flexible structure, such as Dacron®. Highly compressible foams are particularly preferred, preferably to keep the crimped profile low for better delivery. The sealing material or foam is preferably substantially impervious to blood when in a compressed state.
The sealing material may cover one or more surfaces of the stent i.e., may be located along an interior or exterior wall, or both, and preferably extends across the proximal end or a proximal portion of the stent. The sealing material helps impede any blood trying to flow around the first prosthesis, e.g., between the first prosthesis and the arterial wall, and around one or more bypass prostheses after they have been deployed within the lumen of the first prosthesis (described in more detail below).
In preferred embodiments of the invention, the sealing material stretches or covers a portion of the proximal end of the stent and along at least a portion of the outside wall of the stent.
In some embodiments of the invention, it may be desirable for the portion of the sealing material covering the proximal portion of the stent to include one or more holes, apertures, points, slits, sleeves, flaps, weakened spots, guides, or the like for positioning a guidewire, for positioning a system component, such as a second prosthesis, and/or for engaging, preferably matingly engaging, one or more system components, such as a second prosthesis. For example, a sealing material configured as a cover or the like, and having a hole, may partially occlude the stent lumen.
These openings may be variously configured, primarily to conform to its use. These structures promote proper side by side placement of one or more, preferably multiple, prostheses within the first prosthesis, and, in some embodiments of the invention, the sealing material may be configured or adapted to assist in maintaining a certain shape of the fully deployed system or component. Further, these openings may exist prior to deployment of the prosthesis, or may be formed in the prosthesis as part of a deployment procedure. The various functions of the openings will be evident from the description below. In exemplary embodiments of the invention, the sealing material is a foam cover that has a single hole.
The sealing material may be attached to the stent by any of a variety of connectors, including a plurality of conventional sutures of polyvinylidene fluoride, polypropylene, Dacron®, or any other suitable material and attached thereto. Other methods of attaching the sealing material to the stent include adhesives, ultrasonic welding, mechanical interference fit and staples.
One or more markers may be optionally disposed in or on the stent between the proximal end and the distal end. Preferably, two or more markers are sized and/or positioned to identify a location on the prosthesis, or to identify the position of the prosthesis, or a portion thereof, in relation to an anatomical feature or another system component.
First prosthesis is typically deployed in an arterial passageway upstream of an aneurysm, and functions to open and/or expand the artery, to properly position and anchor the various components of the system, and, in combination with other components, seal the system or portions thereof from fluid leaks. For example, the sealing prosthesis may be deployed within the infrarenal neck, between an abdominal aortic aneurysm and the renal arteries of a patient, to assist in repairing an abdominal aortic aneurysm.
Stent 1016 may further include at least two but preferably eight (as shown in
The sealing material 1034 helps impede any blood trying to flow around bypass prostheses 1004 and 1006 after they have been deployed (as shown in
The second prostheses 1004 and 1006 may comprise stent-grafts such as described with respect to
It is important to note that the above-described system for repairing abdominal aortic aneurysms is one example of such a system. Any number of aneurysmal repair systems comprising stent-grafts may be coated with the appropriate drugs, agents and/or compounds, as well as combinations thereof. For example, thoracic aorta aneurysms may be repaired in a similar manner. Regardless of the type of aneurysm or its position within the living organism, the components comprising the repair system may be coated with the appropriate drug, agent and/or compound as described above with respect to stent-grafts.
A difficulty associated with the treatment of aneurysms, specifically abdominal aortic aneurysms, is endoleaks. An endoleak is generally defined as the persistence of blood flow outside of the lumen of the stent-graft, but within the aneurysmal sac or adjacent vascular segment being treated with the stent-graft. Essentially, endoleaks are caused by one of two primary mechanisms, wherein each mechanism has a number of possible modalities. The first mechanism involves the incomplete sealing or exclusion of the aneurysmal sac or vessel segment. The second mechanism involves retrograde flow. In this type of endoleak, blood-flow into the aneurysmal sac is reversed due to retrograde flow from patent collateral vessels, particularly the lumbar arteries or the inferior mesenteric artery. This type of endoleak may occur even when a complete seal has been achieved around the stent-grafts. It is also possible that an endoleak may develop due to stent-graft failure, for example, a tear in the graft fabric.
Endoleaks may be classified by type. A type I endoleak is a perigraft leak at the proximal or distal attachment sites of the stent-grafts. Essentially, this type of endoleak occurs when a persistent perigraft channel of blood flow develops due to an ineffective or inadequate seal at the ends of the stent-graft. There are a number of possible causes of a type I endoleak, including improper sizing of the stent-graft, migration of the stent-graft, incomplete stent-graft expansion and an irregular shape of the arterial lumen. A type II endoleak is persistent collateral blood flow into the aneurysmal sac from a patent branch of the aorta. Essentially, the pressure in the aneurysmal sac is lower than the collateral branches, thereby causing a retrograde blood flow. Sources of type II endoleaks include the accessory renal arteries, the testicular arteries, the lumbar arteries, the middle sacral artery, the inferior mesenteric artery and the spinal artery. A type III endoleak may be caused by a structural failure of the abdominal aortic aneurysm repair system or its components, for example, the stent-grafts. A type III endoleak may also be caused by a junction failure in systems employing modular components. Sources of type III endoleaks include tears, rips or holes in the fabric of the stent-graft, improper sizing of the modular components and limited overlap of the modular components. A type IV endoleak is blood flow through the graft material itself. The blood flow through the pores of the graft material or through small holes in the fabric caused by the staples or sutures attaching the graft material to the stent. Blood flow through the pores typically occurs with highly porous graft fabrics. A type V endoleak or endotension is a persistent or recurrent pressurization of the aneurysmal sac without any radiologically detectable endoleak. Possible causes of a type V endoleak include pressure transmission by thrombus, highly porous graft material, or the adjacent aortic lumen.
There are a number of possible treatment options for each type of endoleak described above. The particular treatment option depends mainly upon the cause of endoleak and the options are not always successful. The present invention is directed to a modification of existing endovascular abdominal aortic aneurysm repair systems or devices, such as the exemplary devices described herein, that is intended to eliminate or substantially reduce the incidence of endoleaks.
The modification comprises coating at least a portion of the various. components comprising an abdominal aortic aneurysm repair system with drugs, agents and/or compounds which promote wound healing as described below. For example, portions of the exemplary system 1000, illustrated in
Normal wound healing essentially occurs in three stages or phases, which have a certain degree of overlap. The first phase is cellular migration and inflammation. This phase lasts for several days. The second phase is the proliferation of fibroblasts for two to four weeks with new collagen synthesis. The third phase is remodeling of the scar and typically lasts from one month to a year. This third phase includes collagen cross linking and active collagen turnover.
As stated above, there are certain drugs, agents and/or compounds that may be delivered locally to the repair site, via the repair system, that promotes wound healing which in turn may eliminate or substantially reduce the incidence of endoleaks. For example, increased collagen production early in wound healing leads to greater wound strength. Accordingly, collagen may be combined with the repair system to increase wound strength and promote platelet aggregation and fibrin formation. In addition, certain growth factors may be combined with the repair system to promote platelet aggregation and fibrin formation as well as to increase wound strength.
Platelet-derived Growth Factor induces mitoses and is the major mitogen in serum for growth in connective tissue. Platelet Factor 4 is a platelet released protein that promotes blood clotting by neutralizing heparin. Platelet-derived Growth Factor and Platelet Factor 4 are important in inflammation and repair. They are active for human monocytes, neutrophils, smooth muscle cells, fibroblasts and inflammation cells. Transforming Growth Factor-β is a part of a complex family of polypeptide hormones or biological factors that are produced by the body to control growth, division and maturation of blood cells by the bone marrow. Transforming Growth Factor-β is found in tissues and platelets, and is known to stimulate total protein, collagen and DNA content in wound chambers implanted in vivo. Transforming Growth Factor-β in combination with collagen has been shown to be extremely effective in wound healing.
A series of reactions take place in the body whenever a blood clot begins to form. A major initiator of these reactions is an enzyme system called the Tissue Factor/VIIa complex. Accordingly, Tissue Factor/VIIa may be utilized to promote blood clot formation and thus enhance wound healing. Other agents which are known to initiate thrombus formation include thrombin, fibrin, plasminogin-activator initiator, adenosine diphosphate and collagen.
The use of these drugs, agents and/or compounds in conjunction with the various components of the repair system may be used to eliminate or substantially reduce the incidence of endoleaks through the formation of blood clots and wound healing.
The stent and/or graft material comprising the components of the system 1000 may be coated with any of the above-described drugs, agents and/or compounds. The above-described drugs, agents and/or compounds may be affixed to a portion of the components or to all of the components utilizing any of the materials and processes described above. For example, the drugs, agents and/or compounds may be incorporated into a polymeric matrix or affixed directly to various portions of the components of the system.
The particular polymer(s) utilized depends on the particular material upon which it is affixed. In addition, the particular drug, agent and/or compound may also affect the selection of polymer(s).
An aneurysm is an abnormal dilation of a section of an artery. An aneurysm may occur in an artery in any part of the body but typically occurs in the aorta, for example, an abdominal aortic aneurysm as described above, in the brain, for example, a cerebral aneurysm, in the legs, for example, a popliteal artery aneurysm, in the intestine, for example, a mesenteric artery aneurysm and a splenic artery aneurysm. Essentially, an aneurysm may occur when the pressure of blood passing through part of a weakened artery forces the vessel to balloon or otherwise expand. Any condition that can cause the walls of an artery to weaken may lead to an aneurysm. Factors that may influence the formation of an aneurysm include atherosclerosis, high blood pressure, smoking, injuries to the arteries, including infections, congenital abnormalities and inherited diseases such as Marfan syndrome.
There are various possible causes and potential contributing factors that influence the formation of aneurysms. It is believed that many aneurysms are caused by a breakdown in the proteins that provide the structural strength in arteries. These proteins, called collagen and elastin, can gradually deteriorate naturally with age, but it has been found that the factors described above may play a factor in the breakdown of collagen and elastin. In addition, there are also naturally occurring enzymes that cause the breakdown of elastin and/or collagen. An excess amount of these enzymes or other factors that activate these enzymes may also contribute to the formation or growth of an aneurysm.
Collagen is a major structural protein and comprises about twenty-five percent of the body's protein. Elastin is also a protein, but rather than. providing structural support like collagen, elastin provides elasticity. Collagen and elastin work in conjunction to provide various organs with the ability to stretch and relax. For example, collagen provides strength and rigidity to arteries while elastin, allows the arteries to stretch and then revert to their original positions. Accordingly, these two proteins play an important role in the potential formation of aneurysms.
As set forth above, rapamycin may act to reduce negative remodeling in several ways. By specifically blocking the proliferation of fibroblasts in the vascular wall in response to injury, rapamycin may reduce the formation of vascular scar tissue. Rapamycin may also affect the translation of key proteins involved in collagen formation or metabolism.
Accordingly, the local administration of rapamycin in conjunction with an aneurysmal repair device such as the stent-grafts described above may be utilized to treat aneurysmal diseases. Essentially, by controlling collagen and other matrix forming proteins, the progression of aneurysmal disease may be substantially slowed or even arrested. The rapamycin may be affixed to the stent-graft or locally or regionally delivered by any of the methods and devices described above.
In accordance with another exemplary embodiment, tetracycline compounds may be utilized in combination with a rapamycin for the treatment of aneurysms or aneurysmal disease.
The two basic types of blood vessels, arteries and veins, may be distinguished by their structural components. Arteries and veins both have a layered structure, in which several distinct layers are arranged coaxially. In arteries the layers include an inner coat or endothelial layer (tunica intima), an internal elastic lamina, a middle coat (tunica media), and an outer coat (tunica adventitia). Like arteries, veins include an inner coat (tunica intima), a middle coat (tunica media) and an outer coat (tunica adventitia), but the layers are not as thick as in arteries, and provide much less structural rigidity. For example, veins collapse when a vessel is cut and they are no longer supported by internal blood pressure.
Because of their greater structural strength, arteries are better adapted to withstand higher internal pressures. This feature corresponds directly to their role in carrying blood away from the heart, since the heart generates large transient pressures. Internal arterial pressures normally range between about 70 (diastolic pressure) and about 120 mm Hg (systolic pressure), but arterial structure is compliant enough to withstand higher baseline pressures for extended periods, and to accommodate higher systolic peaks as well. Venous pressures are typically in the range of about 10 mm Hg, but again somewhat higher pressures may be withstood. Because the veins transport blood back to the heart after it has been distributed to tissues, veins are exposed to fewer and less severe transient fluctuations in blood pressure.
Both arteries and veins are elastic, and are capable of limited deformation in response to pressure changes. Arteries, as mentioned above, have an extra internal elastic layer, which imparts greater elasticity to the arterial structure. The arteries within the thorax are extremely distensible due to a much higher proportion of rubbery (elastin) to stiff (collagen) fibers in their walls than is found in nonthoracic arteries. Their distensibility allows the arteries to act as a reservoir of blood during ejection of blood during the cardiac cycle. As a result, peak pressures may be lower in proximal arteries than in the distal arteries which are stiffer and not as accommodating to pulsatile blood pressure transients. However, the compliance of these vascular structures is not unlimited, and high blood pressure (hypertension) may overcome their ability to compensate, resulting in abnormal (excessive) dilatation and even causing the blood vessels to burst.
When a blood vessel is exposed to hypertension, it tends not to overdilate along its entire length, but instead dilates in a localized region. Typically these dilations are produced at the region in the wall which is weakest, whether inherently or as a result of disease or trauma as is explained herein. As the dilation progresses, a more pronounced widening or sac, typically referred to as an aneurysm, is produced. If blood pressure remains high or goes higher, the aneurysm may burst. In the brain, ruptured blood vessels manifest as stroke, but hemorrhage from compromised vasculature may occur also in other parts of the body, leading to a life-threatening situation. Aortic aneurysms are of especial concern since, as it is the main artery leading away from the heart to the rest of the body, the aorta carries a huge volume of blood, and a rupture typically causes rapid fatal hemorrhaging.
As briefly described herein, there are a number of possible causes of aneurysms. Among the causes of aneurysms are arteriosclerosis, syphilis, degenerative changes and cystic necrosis of the tunica media of vessels, trauma, bacterial infections, arteritis, and congenital deformities.
Arteriosclerotic and syphilitic aneurysms are the most common types and involve principally the thoracic and abdominal aorta. Thoracic aneurysms commonly compress and erode various structures as they expand. They may erode in to the lungs or the spinal column, through the anterior chest wall and present externally as a pulsating mass. Blood flow through aneurysms is relatively low, and as a result they become lined with clonted blood (thrombus), but this accumulation offers little structural support against the blood pressure.
Another specialized type of aneurysm is the dissecting aneurysm of the aorta, in which blood enters between, and separates, the layers of the aortic wall. Such aneurysms are typically caused by hypertension, and are accompanied by localized degenerative changes in the tissues of the vessel, potentially resulting in perforation and consequent lethal hemorrhage.
Berry aneurysms are congenital defects which occur in cerebral arteries, most commonly at the junctions of vessels in the circle of Willis. These aneurysms appear to be related to defects in the muscular coat of the vessels. Rupture is common, resulting in subarachnoid (intracranial) hemorrhage.
Of special clinical interest are aortic aneurysms, especially abdominal aortic aneurysms, which are characterized by transmural aortic wall degeneration leading to dilation, progressive growth, and eventual rupture. Other types of aneurysms include arteriovenous fistulae, cardiac aneurysms (typically resulting from myocardial infarction), and miliary aneurysms (aneurysms in a minute artery, e.g., retinal), and the like.
While aneurysms may not be readily detected if not explicitly being looked for, they may be detected in many cases by means of characteristic clinical signs. For example, arterial aneurysm may exhibit the formation of a pulsating tumor, and often a “bruit” heard over the swelling. Pressure on contiguous parts may also be observed.
Treatment of aneurysms typically involves surgical intervention as described herein. Excision of the aneurysm, and anastomosis of the vessel may be performed, often using a replacement vessel or an artificial prosthesis. Alternately, a supporting structure such as a stent or other intravascular device, as described herein, may be implanted into the vessel to relieve stress as described herein. However, surgical interventions are useful only after the aneurysm has arisen, typically not being capable of prophylactic use. Moreover, such methods are invasive, requiring surgical operation and hospitalization of the patient.
Prophylactic methods for preventing the formation of aneurysm tend to rely on reducing blood pressure, in an effort to reduce mechanical stress on the vasculature. These methods involve use of drugs which may have undesirable side effects, e.g., kidney or liver damage, especially over long term use. More important, these drugs are not indicated for improving the structure of the blood vessel or altering the cellular and molecular processes involved in abnormal dilatation. Moreover, no evidence has been found that these drugs can cause the regression of established aneurysms.
The most conspicuous histologic findings in many aneurysms, especially abdominal aortic aneurysms, are the destruction of the medial elastic lamellae, chronic inflammation within the outer aortic wall, and medial neovascularization. Increased local production of connective tissue proteinases including serine proteases, plasminogen activators, and matrix metalloproteinases (MMPs) has been documented in aneurysmal tissue. Any of these enzymes might contribute to the degradation of structurally important extracellular matrix proteins in aneurysms, but it has not been clear which if any specific mechanism might play a particularly important role in the progressive pathobiologic condition of abdominal aortic aneurysms.
The tetracyclines are a well known and successful class of antibiotics. Compounds such as tetracycline, sporocycline, etc., are broad spectrum antibiotics, having utility against a wide variety of bacteria.
Tetracycline, as well as the 5-OH (terramycin) and 7-Cl (aureomycin) derivatives, exist in nature, and are all well known antibiotics. However, natural tetracyclines may be modified without losing their antibiotic properties, although certain elements of the structure must be retained to do so. The modifications that may and may not be made to the basic tetracycline structure have been reviewed by Mitscher (Mitscher, L.A., The Chemistry of the Tetracycline Antibiotics, Ch. 6, Marcel Dekker, New York (1978)). According to Mitscher, the modification at positions 5-9 of the tetracycline ring system can be made without causing the complete loss of antibiotic properties. However, changes to the basic structure of the ring system, or replacement of substituents at positions 1-4 or 10-12,, generally lead to synthetic tetracyclines with substantially less, or essentially no, antibacterial activity. For example, 4-dedimethylaminotetracycline is commonly considered to be a non-antibacterial tetracycline.
The use of tetracycline antibiotics, while generally effective for treating infection, may lead to undesirable side effects. For example, the long-term administration of antibiotic tetracyclines may reduce or eliminate healthy flora, such as intestinal flora, and may lead to the production of antibiotic resistant organisms or the overgrowth of yeast and fungi.
Recently, a new class of compounds has been defined which are structurally related to the antibiotic tetracyclines, but which have had their antibiotic activity substantially or completely extinguished by chemical modification. These compounds, known as chemically-modified tetracyclines (CMTs), have been found to possess a number of interesting properties, such as the inhibition of excessive collagenolytic activity in vivo. Specifically, CMTs have been shown to inhibit collagen degradation by some MMPs, a family of zinc-dependent enzymes with a broad spectrum of connective tissue substrates. See, for example, Golub et al. (Golub, L. M. Ramamurthy, N. S., McNamara, T. F., Greenwald, R. A., and Rifkin, B. R., “Tetracyclines inhibit connective tissue breakdown: New therapeutic implications for an old family of drugs,” Crit. Rev. in Oral Biol. And Med. 2(2):297-322)(1991); Ryan (Ryan, M. E., Ramamurthy, N. S., and Golub, L. M., “Matrix metalloproteases and their inhibition in periodontal treatment,” Curr. Opin. Periodontal. 3:85-96 (1996).
In this exemplary embodiment, a tetracycline compound may be utilized in combination with anti-inflammatory compounds, such as dexamethasone and rapamycins for the treatment of vascular aneurysms. These agents may be delivered locally from an aneurysmal repair system 1000 as described herein, or from a separate delivery depot. As stated above, rapamycin may be utilized to inhibit or prevent the inception and growth of vascular aneurysms as well as to induce regression of established aneurysms by a number of mechanisms, including the reduction of fibroblasts in the vascular wall in response to injury, thereby reducing the formation of vascular scar tissue, reducing inflammation and affecting the translation of key proteins involved in collagen formation or metabolism. These mechanisms of action are different than the actions of tetracycline compounds as briefly described above and detailed below. Accordingly, the use of tetracycline compounds in combination with rapamycin may result in synergistic effects in the treatment of aneurysms. A rapamycin, as set forth herein, offers a number of advantages; however, any number of anti-inflammatories may be utilized.
An exemplary pharmaceutical composition for use in accordance with the present the method of the invention comprises a tetracycline compound in a suitable pharmaceutical carrier or excipient as understood by practitioners in the art. The compositions are formulated with carriers suitable for administration orally, topically, by injection, or by other means as discussed and described herein. Time-release or controlled-delivery administration can be employed according to known methods. The means of delivery of the tetracycline compound with the pharmaceutical carrier can be in the form of a capsule, compressed tablet, pill, solution, or suspension suitable for oral administration to the subject.
The chemical and physical characteristics of the agent can influence the efficiency of particular modes of administration. For example, a more lipophilic tetracycline compound could produce better blood levels by oral administration, but lower blood levels by subcutaneous injection, whereas another agent might have properties predisposing it to be more effectively delivered by vascular perfusion. The skilled artisan will understand how to effectively deal with such considerations as needed in the particular case.
The conditions treatable by means of the present invention occur in mammalian subjects. Human patients are by far the most important subjects treatable according to the method of the invention, but the method may be practiced for the benefit of other mammals, including, for example, pet animals such as dogs and cats, laboratory animals such as rats and mice, as well as farm animals such as horses and cows.
The method of the present invention may be implemented by directed delivery of the tetracycline compound or other inhibitory compound to the site of the incipient or existing vessel dilatation or aneurysm. In one exemplary embodiment, the present invention involves the use of medical apparatus, such as an intravascularly implantable device as described herein, which enables intravascular delivery of the active agent. Implantable devices suitable for use include devices such as stents, catheters, embolic coils, filters, cannulas, protheses, and other such devices known in the art. The active agent may be included by coating onto a surface of the device, or if the device is made of polymeric material, the agent may be incorporated into the material for release into the surrounding tissue when implanted. Alternately, the coating may include a polymeric material such as a water-soluble polymer, so that the active agent may be delivered in situ in a controlled release fashion. Polymers suitable for use in these methods are well known in the art, and include polymers such as cellulosic polymers, polyacrylates and polyacrylamides, polyvinyl alcohols, polyvinylpyrrolidone, and other hydrophilic polymers. Alternately, polymers have porosity suited to release of the active agent into the surrounding tissues of fluids can be employed. In addition, catheters can be used to directly infuse or perfuse the agent or agents in micro and/or nano particle formulations, into the blood vessel for controlled and localized or systemic delivery of the agent. It is important to note that any number of polymers may be utilized in accordance with the present invention. A preferred mode of delivery for the agent is to employ a stent, a stent-graft and/or an aneuyemal repair device with a coating of material for releasing the agents directly into the blood vessel wall at the site of implantation, while also providing direct structural support for the vessel at that site. Alternately, a dual balloon perfusion catheter is used to isolate the site of dilation or aneurysm, and the tetracycline compound or other protease inhibitor can be delivered to the isolated area without involvement of surrounding tissues.
Tetracycline compounds suitable for use according to the present invention are commercially available or can be prepared by methods known in the art. Some suitable methods include those described by Mitscher (1978).
The following example is provided to assist in a further understanding of the present invention. The particular materials and conditions employed are intended to be further illustrative of the invention and are not limiting upon the reasonable scope thereof Male Wistar rats (350-400 g) were subjected to perfusion of an isolated segment of the infrarenal abdominal aorta with 50 units of porcine pancreatic elastase, using the method described by Anidjar et al. (Anidjar, S. Salzmann, J L, Generic, D, Lagneau, P, Camilleri, J P, and Michel, J B, “Elastase induced experimental aneurysms in rats,” Circulation 82:973-981 (1990); Halpern et al. (Halpern, V J. Liao, Nackman, G B, Gandhi, R H, Irizarry, E, Scholes, J V, Ramey, W G, and Tilson, M D, “The elastase infusion model of experimental aortic aneurysms: Synchrony of induction of endogenous protinases with matrix destruction and inflammatory cell response, “J. Vasc. Surg. 20:51-60 (1994)); and Petrinec (Petrinec , D, Liao, S, Holmes, D R, Reilly, J M, Parks, W C, and Thompson, R W, “Doxycycline inhibition of aneuryssmal degeneration in an elastase-induced rat model of abdominal aortic aneuyssm: Preservation of aortic elastin associated with suppressed production of 92 kD gelatinase,” J. Vasc. Surg 23:336-346(1996)). This method is an accepted model for experimental induction of abdominal aortic aneurysms. The animals (n=6 rats in each group) were then treated with twice-daily subcutaneous injections of either saline vehicle (control), or various doses of doxycycline (Dox) or one of four different, non-antibiotic, chemically-modified tetracyclines (CMTs; CollaGenex, Inc., Newtown, Pa.). Aortic diameter (AD) was measured with microcalipers before and after elastase perfusion, and just prior to sacrifice on day 7. Abdominal aortic aneurysms were defined as an increase in final AD to at least twice that measured before perfusion (.gtoreq.100% increase). Aortic tissues from two animals in each group were perfusion-fixed with 10% neutral buffered formalin, embedded in paraffin, and stained with Verhoeff-van Geisen (VVG) for elastin. Tissues from the remaining animals were extracted, normalized to total protein, and analyzed by gelatin substrate zymography as described (Thompson et al. 1995; Halpern et al. 1994; Petrinec 1996).
For saline-treated control animals, mean AD increased by 125.+−.18%, and 5 of the 6 (83%) of the animals had abdominal aortic aneurysms as defined. Rats treated with 60 mg/kg/day Dox had significantly less aortic dilatation (mean 61.+−.7%) than the control animals, and no abdominal aortic aneurysms were observed (p<0.01). The effects of Dox were dose-dependent, with maximal inhibition at about 12.5 mg/kg/day.
Accordingly, tetracycline derivatives inhibit aortic dilation and elastin degradation in the elastase-perfused rat aorta. The tetracycline compounds also decrease elastolytic activity associated with the increased production of elastolytic gelatinase characteristic of dilatated and aneurysmal vascular tissue. This observed effect of the tetracycline compounds appears to be independent of the inflammatory response in affected tissues. Pharmacologic inhibition of such elastolytic activity may thereby be employed as a novel therapeutic strategy by which to suppress ongoing aortic wall matrix destruction and to limit the progressive growth of abdominal aortic aneurysms. Indeed, the regression of abdominal aortic aneurysms and aortic dilatation may be effected by inhibition of MMPs according to the present invention.
In accordance with the exemplary embodiment, the method of the present invention involves administration of an anti-aneurysmal amount of a tetracycline compound in combination with an anti-aneurysmal amount of a rapamycin or other anti-inflammatory to a subject in need of anti-aneurysmal therapy. An anti-aneurysmal amount of a tetracycline is an amount which prevents the formation of an aneurysm in a blood vessel, or which inhibits the progression or induces the regression of an established (pre-existing) aneurysm. Thus, a mammal in need of anti-aneurysmal therapy is a mammal which is vulnerable to the formation of an abnormal blood vessel-dilatation or aneurysm, or a mammal which exhibits an established blood vessel dilatation or aneurysm. The method of the present invention is effective in resisting the formation of such aneurysms, and is helpful in causing the regression of pre-existing aneurysms to return the involved blood vessel (aneurysmal tissue) to a safer state, preferably to a normal or near normal state.
The method of this exemplary embodiment employs any suitable tetracycline compound having an anti-aneurysmal effect. In using a tetracycline compound as the agent administered according to the invention, the observed anti-aneurysmal effect appears to be unrelated to, and independent of, any antimicrobial activity such a compound might have. Accordingly, the tetracycline may be an antimicrobial tetracycline compound, or it may be a tetracycline analogue having little or no significant antimicrobial activity. For the purposes herein a tetracycline analogue having little or no significant antimicrobial activity is referred to as a CMT.
Exemplary antimicrobial tetracycline compounds (anti-aneurysmal agents) include, for example, tetracycline per se, as well as derivatives thereof. Exemplary derivatives include, for example, aureomycin and chloromycin.
If a CMT is to be employed, it is preferred that the CMT lack the dimethylamino group at position 4 of the ring structure of tetracycline. Such chemically-modified tetracyclines include, for example, 4-dimethylaminotetracycline (CMT-1), 4-dedimethylamino-5-oxytetracycline, 4-dedimethylamino-7-chlorotetra-cycline (CMT-4), 4-hydroxy-4-dedimethyl-aminotetracycline (CMT-6), 5a,6-anhydro-4-hydroxy-4-dedimethylaminotetracycline, 6-demethyl-6-deoxy-4-dedimethylaminotetracycline (CMT-3), 4-dedimethylamino-12a-deoxytetracycline (CMT-7), and 6-.alpha.-deoxy-5-hydroxy-4-dedimethylaminotetracycline (CMT-8). Also, tetracyclines modified at the 2 carbon position to produce a nitrile, e.g., tetracyclinonitrile, are useful as non-antibacterial, anti-metalloproteinase agents.
Further examples of tetracyclines modified for reduced antimicrobial activity include 6-.alpha.-benzylthiomethylenetetracycline, the mono-N-alkylated amide of tetracycline, 6-fluoro-6-demethyltetracycline, and 11.alpha.-chlorotetracycline.
Among the advantages of the present invention is that a tetracycline compound may be administered in an amount which has substantially no antibacterial activity, but which is effective for reducing pathology, or for inhibiting the undesirable consequences, associated with aneurysms in blood vessels. Thus, antibacterial tetracyclines may be used in amounts which are effectively non-antimicrobial. Alternately, as noted above, the tetracycline compound may have been modified chemically to reduce or eliminate its antimicrobial properties. The use of such modified tetracyclines is preferred in the present invention since they may be used at higher levels than antimicrobial tetracyclines, while avoiding certain disadvantages, such as the indiscriminate killing of beneficial microbes which often accompanies the use of antimicrobial or antibacterial amounts of such compounds. This is particularly relevant for systemic delivery of the one or more agents.
Inter alia, the present invention provides a method for protecting elastic fibers in the medial lamellae of blood vessels from abnormal degradation which may otherwise lead to dilatation and/or aneurysm. Accordingly, the method involves selectively inhibiting elastolytic activity in the vascular tissue. Elastolytic activity includes protease-associated structural deterioration of arterial elastin and associated materials, such as extracellular matrix components. It appears that elastolytic activity can increase following insult or trauma to a blood vessel, and that this phenomenon is associated with dilatation of the vessel. Accordingly, in this exemplary embodiment, the invention encompasses the selective inhibition of such abnormal or elevated elastolytic activity in the vascular tissue.
In this exemplary embodiment, the method involves contacting vascular tissue with an inhibitor of elastolytic activity in an amount (an anti-elastolytic amount) sufficient to selectively inhibit elastolytic activity in the tissue. The method may be performed in vitro, as in experimental or diagnostic inhibition of elastolytic activity in isolated specimens of vascular tissue, or in vivo, wherein a living mammalian subject is treated to reduce elastolytic activity in a vascular tissue in which such activity might cause abnormal vessel dilatation or aneurysm.
The inhibition of elastolytic activity is preferably selectively directed against proteolytic activity associated with tissue matrix metalloproteases. Among other anti-metalloprotease effects, the present invention is effective to accomplish the selective inhibition of gelatinase, i.e., MMP-9 (92 kD gelatinase). Thus, in general, inhibitors of matrix metalloproteases (including collagenases, etc.), and more specifically inhibitors of gelatinase, are capable of use according to the method of the invention
Other inhibitors of MMP activity are also suitable for use in inhibiting abnormal vascular dilatations and aneurysms.
Suitable inhibitors include, for example, endogenous inhibitors, such as tissue inhibitors of MMPs (TIMPs) and .alpha.-macroglobulins, and synthetic inhibitors, such as chelating agents (e.g., EDTA and 1,10-phenanthroline), peptides, antibodies, and the like. Other suitable inhibitors are known, e.g., Ryan et al. (1996). Thus, the present invention further provides a method of inhibiting MMP-related activity in vascular tissue in which such activity is considered to be excessive. Effective anti-aneurysmal inhibition of proteolytic activity may be accomplished by inhibiting the synthesis or expression of involved MMPs, or may by accomplished by inhibiting the proteolytic activity of an expressed MMP.
The maximal dosage of the active agent for a mammal is the highest dosage that is effectively anti-aneurysmal, and that does not cause undesirable or intolerable side effects. For example, a tetracycline compound may be administered in an amount of from about 0.1 mg/kg/day to about 30 mg/kg/day, and preferably from about 1 mg/kg/day to about 18 mg/kg/day. For the purpose of the present invention, side effects include clinically significant antimicrobial or antibacterial activity, as well as toxic effects. For example, a dose in excess of about 50 mg/kg/day would likely produce side effects in most mammals, including humans. In any event, the practitioner is guided by skill and knowledge in the field, and the present invention includes without limitation dosages which are effective to achieve the described phenomena.
The agents useful according to the method of the present invention exhibit their beneficial effect in a dose-dependent manner. For example, within broad limits, administration of larger quantities of a tetracycline compound will induce a larger or stronger response than will administration of a smaller amount. Moreover, anti-aneurysmal efficacy has been observed at dosages below the level at which toxicity is seen.
A tetracycline compound may be administered to a subject by any available and effective route, including enteral and parenteral routes. Oral administration is one mode of administration. Injection of the agent, e.g., intravenous, intraarterial, intramuscular, subcutaneous, etc., may also be employed as determined by the skilled artisan. In accordance with the present invention, a combination of an anti-inflammatory such as a rapamycin and a tetracycline, in therapeutic doses may be administered to a patient for the treatment of an aneurysm. The agents may be delivered by any suitable means as described herein. For example, the agents may be directly or indirectly associated with an aneurysmal repair device or separate drug delivery depot. The agents may be incorporated in any number of biocompatible polymers. The rapamycin may be utilized to block the proliferation of fibroblasts in the vascular wall and reduce the formation of vascular scar tissue. A rapamycin may also affect the translation of key proteins involved in collagen formation or metabolism. A rapamycin may also reduce inflammation. A tetracycline may be utilized to inhibit the elastolytic activity of a matrix metalloproteinase (MMP) and gelatinase. Each of these compounds may be utilized on different aspects of aneurysmal disease thereby resulting in a synergistic effect.
Alternatively, tetracycline may be utilized in combination with agents that bind to a high infinity cytosolic protein, FKBP12. As described herein, rapamycin includes rapamycin and all analogs, derivatives, congeners and conjugates that bind to FKBP12, and other immunophillins and possesses the same pharmacological properties as rapamycin including the inhibition of mTOR. However, an effective combination may similarly include a combination of a tetracycline compound and agents that bind to FKBP12 that do not inhibit mTOR to reduce inflammation.
FKBP12 is the intracellular immunophylin protein to which rapamycin and other immunosuppressants bind. The complex of FKBP12 and the immunosuppressant rapamycin inhibit an intracellular kinase referred to as the mammalian target of rapamycin or mTOR as briefly described above. This action inhibits a number of protein kinases that are associated with mitogen-induced cell proliferation, specifically causing G1 arrest. This is true for a number of cell types, including smooth muscle cells, as described in detail herein, and T cells which are the major inflammatory cell targets. It is this action that provides for one of the beneficial aspects of the combination of a tetracycline compound and agents that bind to FKBP12.
FKBP12 also interacts with tacrolimus (FK-506). The FKBP12-tacrolimus complex blocks the function of calcineurin. Cyclosporin A, another immunosuppressant, forms a complex with a different protein called cyclophylin that also blocks the function of calcineurin. Blocking calcineurin prevents the activation of a protein called Nuclear Factor of Activated T Cells or NFAT and thereby inhibits T cell function. FKBP12 is typically present intracellulary at high concentrations.
As described above, other implantable medical devices that may. be coated with various drugs, agents and/or compounds include surgical staples and sutures. These medical devices may be coated with any of the above-described drugs, agents and/or compounds to treat various conditions and/or to minimize or substantially eliminate the organisms' reaction to the implantation of the device.
Although any number of drugs, agents and/or compounds may be used in conjunction with the surgical staple 3000 to treat a variety of conditions and/or to minimize or substantially eliminate the organisms' reaction to the implantation of the staple 3000, in a preferred embodiment, the surgical staple 3000 is coated with an anti-proliferative. The advantage of such a device is that the anti-proliferative coating would function as a prophylactic defense against neo-intimal hyperplasia. As described above, neo-intimal hyperplasia often happens at the site of what the body perceives to be injuries, for example, anastomatic sites, either tissue to tissue or tissue to implant, which are often sites of hyperplastic events. By utilizing a staple that comprises an anti-proliferative agent, the incidence of neo-intimal hyperplasia may be substantially reduced or eliminated.
Rapamycin is a known anti-proliferative that may be utilized on or in the surgical staple 3000 and may be incorporated into any of the above-described polymeric materials. An additional benefit of utilizing rapamycin is its action as an anti-inflammatory. The dual action not only functions to reduce neo-intimal hyperplasia but inflammation as well. As used herein, rapamycin includes rapamycin, sirolimus, everolimus and all analogs, derivatives and conjugates that bind FKBP12, and other immunophilins and possesses the same pharmacologic properties as rapamycin including inhibition of MTOR.
In yet another alternate exemplary embodiment, the surgical staple 3000 may be fabricated from a material, such as a polymeric material, which incorporates the one or more drugs, agents, and/or compounds. Regardless of the particular embodiment, the elution rate of the one or more drugs, agents and/or compounds may be controlled as described above.
Referring now to
In yet another alternate exemplary embodiment, the suture 4000 may be formed from a material, for example, a polymeric material that incorporates the one or more drugs, agents and/or compounds. For example, the one or more drugs, agents, and/or compounds may be mixed within the polymer matrix and then extruded and/or formed by a dip method to form the suture material.
The particular polymer(s) utilized depend on the particular material upon which it is affixed. In addition, the particular drug, agent, and/or compound may also affect the selection of polymers. Rapamycin may be utilized with poly(vinylidenefluoride)/hexafluoropropylene.
The introduction of medical devices into a living organism, and more particularly into the vasculature of a living organism, provokes a response by the living organism. Typically the benefit provided by the medical device far exceeds any complications associated with the living organism's response. Endothelialization is one preferable manner or means for making devices fabricated from synthetic materials more blood compatible. The endothelium is a single layer of endothelial cells that forms the lining of all blood vessels. The endothelium regulates exchanges between blood and surrounding tissues and is surrounded by a basal lamina, i.e. extracellular matrix that separates epithelia layers and other cell types, including fat and muscle cells from connective tissue.
Endothelial cells cover or line the inner surface of the entire vascular system, including the heart, arteries, veins, capillaries and everything in between. Endothelial cells control the passage of materials and the transit of white blood cells into and out of the blood stream. While the larger blood vessels comprise multiple layers of different tissues, the smallest blood vessels consist essentially of endothelial cells and a basal lamina. Endothelial cells have a high capacity to modify or adjust their numbers and arrangement to suit local requirements. Essentially, if it were not for endothelial cells multiplying and remodeling, the network of blood vessel/tissue growth and repair would be impossible.
Even in an adult living organism, endothelial cells throughout the vascular system retain a capacity for cell division and movement. For example, if one portion of a vein or artery is missing endothelial cells through damage or disease, neighboring endothelial cells proliferate and migrate to the affected area in order to cover the exposed surface. Endothelial cells not only repair areas of missing endothelial cells, they are capable of creating new blood vessels. In addition, and directly related to the present invention, newly formed endothelial cells will cover implantable medical devices, including stents and other similar devices.
As stated above, endothelialization is a means for making devices fabricated from synthetic materials more blood compatible and thus more acceptable to the living organism. For the introduction of certain medical devices anywhere in the vasculature, one goal is the reduction of the thrombogenicity of the medical device. This is device specific, for example, certain medical devices would require thrombus formation for healing and fixation. Therefore, the endothelialization of these specific medical devices is preferable. The source of autologous endothelial cells is crucial and thus an amplification step is preferable to obtain enough cells to cover the entire exposed surface of the medical device regardless of the complexity of design of the medical device. Accordingly, it would be preferable to coat the medical device or provide some localized means for the introduction of a chemical, agent, drug, compound and/or biological element for the promotion or proliferation of endothelial cells at the site of the implant.
In accordance with one exemplary embodiment, implantable intraluminal medical devices, such as stents, may be affixed with, in any of the above described manners, with vascular endothelial growth factor, VEGF, which acts selectively on endothelial cells. Vascular endothelial growth factor and its various related isoforms may be affixed directly to any of the medical devices illustrated and described herein by any of the means described herein. For example, VEGF may be incorporated into a polymeric matrix or affixed directly to the medical device.
Other factors that promote the stimulation of endothelial cells include members of the fibroblast growth factor family. Various agents that accelerate cellular migration may increase endothelialization, including agents that upregulate integrins. Nitric oxide may promote endothelialization. In addition, pro-angiogenic agents may stimulate endothelialization.
Alternately, the medical device may be fabricated from a material which by its physical material characteristics promotes the migration of endothelial towards the device. Essentially, since the living organism creates endothelial cells, any material or coating that attracts endothelial cells would be preferable.
It is generally known in the art that the application of a topcoat of a biocompatible material, for example, a polymer, may be utilized to control the elution of a therapeutic dosage of a pharmaceutical drug, agent and/or compound, or combinations thereof, from a medical device base coating, for example, a stent base coating. The basecoat generally comprises a matrix of one or more drugs, agents and/or compounds and a biocompatible material such as a polymer. The control over elution results from either a physical barrier, a chemical barrier, or a combination physical and chemical barrier supplied by the topcoat material. When the topcoat material acts as a physical barrier, the elution is controlled by varying the thickness of the topcoat, thereby changing the diffusion path length for the drugs, agents and/or compounds to diffuse out of the basecoat matrix. Essentially, the drugs, agents and/or compounds in the basecoat matrix diffuse through the interstitial spaces in the topcoat. Accordingly, the thicker the topcoat, the longer the diffusion path, and conversely, the thinner the topcoat, the shorter the diffusion path. It is important to note that both the basecoat and the topcoat thickness may be limited by the desired overall profile of the medical device. For action as a chemical barrier, the topcoat preferably comprises a material that is less compatible with the drugs, agents and/or compounds to substantially prevent or slow the diffusion, or is less compatible with the basecoat matrix to provide a chemical barrier the drugs, agents and/or compounds must cross prior to being released. It is important to note that the concentration of the drugs, agents and/or compounds may affect diffusion rate; however, the concentration of the drugs, agents and/or compounds is dictated to a certain extent by the required therapeutic dosage as described herein.
In one exemplary embodiment, a medical device such as a stent, may utilize a polymeric material that acts primarily as a chemical barrier for the control of elution of rapamycin from the stent. As used herein, rapamycin includes rapamycin, sirolimus, everolimus and all analogs, derivatives and conjugates that bind FKBP12, and other immunophilins and possesses the same pharmacologic properties as rapamycin including inhibition of mTOR. In this exemplary embodiment, the coating comprises a basecoat drug, agent and/or compound and polymer matrix with a topcoat that includes only a polymer. The topcoat polymer and the basecoat polymer are immiscible or incompatible, thereby creating the chemical barrier. Comparisons, however, are made with basecoat and topcoats comprising the exact same polymers or with polymers containing the same constituents in different ratios. Although the primary control mechanism is the chemical barrier, the topcoat also provides a limited physical barrier, as will be described subsequently.
In this exemplary embodiment, the basecoat may comprise any suitable fluoropolymer and the topcoat may comprise any suitable acrylate or methacrylate. In preferred embodiments, the basecoat drugs, agent and/or compound/polymer matrix comprises the copolymer polyvinylidenefluoride-co-hexafluoropropylene (PVDF/HFP) as described above in detail. The copolymers utilized in this exemplary basecoat embodiment comprises vinylidenefluoride copolymerized with hexafluoropropylene in the weight ratio of sixty weight percent vinyldenefluoride to forty weight percent hexafluoropropylene. The topcoat polymer may, as described above, comprise any suitable acrylate or methacrylate. In the preferred embodiment, the topcoat polymer comprises poly(n-butylmethacrylate) or BMA.
PVDF/HFP and BMA are immiscible or incompatible polymers that when mixed and precipitated from solution utilizing known techniques will undergo phase separation. It is this incompatibility that allows a topcoat of an acrylic polymer to act as both a chemical barrier (primary mechanism) and physical barrier (secondary mechanism) to the release of a drug, agent and/or compound, such as rapamycin, from the basecoat matrix.
The combination of a PVDF/HFP basecoat and a BMA topcoat offers a number advantages over other combinations, including increased durability, increased lubriciousness and increased elution rate control. PVDF/HFP is a flexible polymer. Flexible polymers result in more durable medical device coatings as they tend to move or give as the stent or other device undergoes deformations. Poly(n-butylmethacrylate) or BMA is a more thermoplastic polymer rather than a more elastomeric polymer, and therefore more rigid than PVDF/HFP. A more rigid polymer equates to a harder surface and a harder surface is a more lubricious surface. The lubriciousness of the polymer topcoat is important during device delivery and deployment as described in detail herein. A lubricious coating is particularly advantageous in the delivery of self-expanding stents which typically require the retraction of a delivery sheath. If the coating were not lubricious, the retraction of the delivery sheath may remove a position of the coating, including the drugs, agents and/or compounds contained therein. Lubricious coatings are also advantageous for balloon expandable stents where stent/balloon separation during deployment may also remove coating. Acrylic polymers utilized in conjunction with fluoropolymers are excellent chemical and physical barriers as described above and thus provide increase elution rate control.
Although the coatings in this exemplary embodiment may be utilized on any number of implantable medical devices as described herein, the exemplary coating embodiments described below are utilized in conjunction with nickel-titanium self-expanding stents.
Referring now to
The data presented in
The data represented in
The idea of utilizing incompatible polymer chemistries in conjunction with varying the thickness of the topcoat in accordance with the present invention takes advantage of what may normally be viewed as a negative aspect of chemical incompatibility to achieve a desired effect. As indicated in curve 4912, the peak elution release at three days is substantially less than fifty percent, whereas the peak elution release at three days for a PVDF/HFP basecoat and a PVDF/HFP topcoat is substantially greater than seventy-five percent as indicated in curve 4902.
Although demonstrated here with specific examples of a PVDF/HFP (sixty-forty weight ratio of VDF:HFP) copolymer and a BMA polymer, the concept would apply to any polymer in the family of fluoropolymers in combination with any polymer in the family of acrylics (poly(alkyl)acrylate and poly(alkyl)meth)acrylate).
Referring to
The results from the in vitro testing are similar to the results from the in vivo testing. Essentially, a review of 5002, 5004, 5006, 5008, 5010 and 5012 indicate that once again, the most substantial barrier to the elution of rapamycin is observed with a PVDF/HFP basecoat matrix and a BMA topcoat because of the chemical barrier that results from the incompatible polymer chemistries and the physical barrier provided by the thicker topcoat as shown by curve 5012.
It is also interesting to note that a stent coated with a PVDF/HFP (sixty/forty weight ratio of VDF:HFP) basecoat matrix and a BMA topcoat is more durable than a stent coated with a PVDF/HFP (sixty/forty weight ratio of VDF:HFP) basecoat matrix and a PVDF/HFP (sixty/forty weight ratio of VDF:HFP) topcoat.
The design of a coated implantable medical device that elutes a therapeutic drug, agent and/or compound requires the balancing of a number of design factors. For example, the addition of a coating to an implantable medical device alters the profile of the device which in turn may have an impact on device delivery. More specifically, the addition of a coating on a stent increases the diameter of the stent, which in turn may make delivery more difficult. Accordingly, it may be preferable to minimize the thickness of the coating while increasing the concentration of the therapeutic drug, agent and/or compound. Increasing the concentration of the therapeutic drug, agent and/or compound may increase its elution rate into the surrounding tissue or bloodstream. Increasing the elution rate may in turn deplete the drug, agent and/or compound prematurely. Therefore, the present invention provides a mechanism whereby drug, agent and/or compound concentrations may be increased while maintaining control over the elution rate and maintaining a lower profile. Essentially, the chemical and physical barrier provided by the topcoat in the two layer approach provides a means for increasing drug, agent and/or compound concentrations, if preferable, maintaining a lower profile, if preferable, and maintaining more precise control over elution rates.
In addition, it is important to emphasize the multiple layers; multiple polymer approach offers the advantages of durability, flexibility and lubriciousness that a single layer approach may not be able to provide.
Vascular diseases include diseases that affect areas containing blood vessels. For example, stenosis is a narrowing or constricting of arterial lumen in a living organism (e.g., a human) usually due to atherosclerosis/coronary heart disease (CHD). Restenosis is a recurrence of stenosis after a percutaneous intervention such as angioplasty and stenting. The underlying mechanisms of restenosis comprise a combination of effects from vessel recoil, negative vascular remodeling, thrombus formation and neointimal hyperplasia. It has been shown that restenosis after balloon angioplasty is mainly due to vessel remodeling and neointimal hyperplasia and after stenting is mainly due to neo-intimal hyperplasia.
Treatment for stenosis and restenosis varies. Stenosis caused by CHD often affects quality of life and can lead to stroke, heart attack, sudden death and loss of limbs or function of a limb stemming from the stenosis. The recanalization of blood vessels may also be needed to treat individuals suffering from stenosis and restenosis. Coronary bypass can be utilized to revascularize the heart and restore normal blood flow. In other cases, balloon angioplasty may be conducted to increase the lumen size of affected areas. Overall, these treatments address the problems associated with stenosis, but they can also create the problem of restenosis that can result in recurrence of cardiac symptoms and mortality. Moreover, these treatments are not curative in nature, and therefore generally are not utilized until significant disease progression has occurred.
One type of stenosis is atherosclerosis. Atherosclerosis affects medium and large arteries and is characterized by a patchy, intramural thickening that encroaches on the arterial lumen and, in most severe form, causes obstruction. The atherosclerotic plaque consists of an accumulation of intracellular and extracellular lipids, smooth muscle cells and connective tissue matrix. The earliest lesion of atherosclerosis is the fatty streak that evolves into a fibrous plaque coating the artery. Atherosclerotic vessels have reduced systolic expansion and abnormal wave propagation. Treatment of atherosclerosis is usually directed at its complications, for example, arrhythmia, heart failure, kidney failure, stroke, and peripheral arterial occlusion.
More particularly, atherosclerosis is a thickening and hardening of the arteries and is generally believed to be caused by the progressive buildup of fatty substances, for example, cholesterol, cellular debris, inflammatory cells, calcium and other substances in the inner lining or intima of the arteries. The buildup of these substances may in turn stimulate cells in the walls of the affected arteries to produce additional substances that result in the further recruitment of cells.
Atherosclerosis is a slow, complex disease process that typically starts in childhood and progresses as the individual ages. The rate of progression may be affected by a number of factors, including blood cholesterol levels, diabetes, obesity, physical inactivity, high blood pressure and tobacco use. This buildup in commonly referred to as plaque and may grow large enough to significantly reduce blood flow through the affected arteries.
Essentially, the deposits of the various substances set forth above, and the proliferation of additional cellular substances or constituents caused thereby, substantially enlarge the intima, which in turn reduces luminal cross-sectional area of the affected arteries, which in turn reduces the oxygen supply to one or more organs. The deposits or plaque may also rupture and form thrombi that can completely obstruct blood flow in the affected artery or break free and embolize in another part of the body. If either of these events occurs, the individual may suffer a myocardial infarction if the artery affected perfuses the heart or a stroke if the artery affected supplies blood to the brain. If the artery affected supplies blood to a limb or appendage, gangrene may result.
Conventional wisdom holds that myocardial infarction originates from severe blockages created by atherosclerosis. Increase deposition of lipids in the arteries and ensuing tissue reaction leads to a narrowing of the affected artery or arteries, which in turn, can result in angina and eventual coronary occlusion, sudden cardiac death or thrombotic stroke. More recent research, however, is leading to a shift in understanding atherosclerosis. Researchers now believe that at least some coronary artery disease is an inflammatory process, in which inflammation causes plaque buildup or progression and rupture. These plaques which are prone to rupture, commonly referred to as vulnerable plaques, do not obstruct flow in the affected artery or arteries per se, but rather, much like an abscess, they may be ingrained in the arterial wall so that they are difficult to detect. Essentially, these vulnerable plaques cannot be seen by conventional angiography and/or fluoroscopy, and they do not typically cause symptoms of ischemia. Techniques for determining the presence of vulnerable plaques are, however, improving as discussed subsequently.
For a variety of reasons, these so-called vulnerable plaques are more likely to erode or rupture, creating emboli and exposed tissue surfaces that are highly thrombogenic. Accordingly, it is now accepted that the majority of cases of acute myocardial infarction, sudden cardiac death and thrombotic stroke result from the disruption of vulnerable atherosclerotic plaques leading to thrombosis. Therefore, these vulnerable plaques are more life-threatening than other plaques and may be responsible for as much as sixty to eighty percent of all myocardial infarctions.
More specifically, unstable or vulnerable plaques are inflammatory vascular lesions that develop in atherosclerotic blood vessels. Vulnerable plaques are characterized by active inflammation, cellular hyperplasia and variable degrees of lumen obstruction. Morphologically, vulnerable plaques comprise a fibrous cap in contact with the lumen of the vessel overlying a core of lipid and cellular material. Vulnerable plaque lesions are not typically obstructive, in contrast to chronic stable plaques that produce ischemic symptoms. For that reason, they are not easily detected.
The hallmark of vulnerable plaques is active inflammation with significant inflammatory cell infiltration, predominantly T-lymphocytes and macrophage, causing the generation of proteolytic enzymes that essentially digest the wall of the fibrous cap thereby inducing plaque instability and eventually plaque rupture. Plaque rupture exposes highly thrombogenic material in the lipid core to flowing blood leading to the rapid development of occlusive thrombi. Ruptured vulnerable plaque, as stated above, is the primary cause of acute coronary and cerebral syndromes. These include unstable angina, myocardial infarction, both Q-wave and non-Q-wave myocardial infarction, cerebral stroke and transient cerebral ischemia. In other words, ruptured vulnerable plaque accounts for a significant percentage of cardiovascular morbidity and mortality.
Given the lack of currently available effective technologies for detecting vulnerable plaque, the treatment of vulnerable plaque is typically initiated only after the plaque has ruptured and clinical symptoms have developed. Detection technologies currently under investigation include refined magnetic resonance imaging, thermal sensors that measure the temperature of the arterial wall on the premise that the inflammatory process generates heat, elasticity sensors, intravascular ultrasound, optical coherence tomography, contrast agents, and near-infrared and infrared light. As better diagnostic methods evolve to identify vulnerable plaque lesions before they rupture, it becomes possible to treat discrete lesions before dangerous clinical symptoms occur. The treatment of vulnerable plaque, however, is preferably as described below.
There are two fundamental physiologic processes ongoing in active vulnerable plaque, inflammation and lipid accumulation and metabolism. Inflammation is an ongoing process which includes the inflammation of the fibrous cap and creating a cap vulnerable to rupture. Lipid metabolism is the formation of an active lipid pool or core comprising a pliable, cholesterolemic lipid material susceptible to rupture. The inflammation process is the acute phase and the lipid metabolism is the chronic phase of vulnerable plaque disease.
A stent or other scaffold structure designed to maintain vessel potency and comprising a multilaminate coating architecture that includes one or more therapeutic agents, drugs, and/or compounds for treating both the inflammation and lipid metabolism processes, may be utilized to effectively treat vulnerable plaques. In one exemplary embodiment, a stent comprising a coating having a two tier release profile may be utilized to treat both the acute and chronic phases of vulnerable plaque. For example, anti-inflammatory therapeutic agents, such as corticosteroids, non-steroidal anti-inflammatories, acetylsalicyclic acid, acetaminophen and ibuprofen may be incorporated into the coating architecture for “fast release” and shorter overall duration to address the acute phase of vulnerable plaque disease and lipid lowering or lipid modifying agents may be incorporated into the coating architecture for “slow release” and longer overall duration to address the chronic phase of vulnerable plaque disease. The stent/drug architecture may utilize a variety of non-resorbable or resorbable polymers to control, modulate and/or optimize the delivery profile for optimal physiologic effect. In other words, specific therapeutic drugs and/or compound delivery profiles may be utilized in conjunction with the stent to treat all aspects of vulnerable plaques, for example, fast release anti-inflammatory drugs, agents and/or compounds to address the inflammatory rupture of the fibrous cap and slow release lipid lowering or lipid modifying drugs, agents and/or compounds to affect the size and composition of the vulnerable plaque lipid pool.
The stent may comprise any suitable scaffold structure, including balloon expandable stents, constructed from stainless steel or other metal alloys, and/or self-expanding stents, constructed from nitinol or other shape memory metal alloys. Alternately, the stent may be made from non-metallic materials, such as ceramics and/or polymers, which may be biodegradable. The biodegradable stent would serve as a temporary scaffold and eventually dissolve over a period of time raging from days or weeks to months and years. The stent would be mounted on a delivery catheter and delivered percutaneously through the lumen of a blood vessel to the site of the vulnerable plaque lesion as described in detail above with respect to treating restenosis. The stent, as described above, is designed to maintain vessel patency and also provide structural support to the weakened or potentially weakened fibrous cap and prevent it from rupturing. The stent also provides a means for preventing further encroachment by the lesion.
Recent research has uncovered that different sex hormones may have different effects on vascular function. For example, gender differences in cardiovascular disease have largely been attributed to the protective effects of estrogen in women; premenopausal women have a lower incidence of Coronary Heart Disease. In particular, estrogen has well-known beneficial effects on lipid profile. More importantly, estrogen may directly affect vascular reactivity, which is an important component of atherosclerosis. Recent epidemiological studies suggest that hormone replacement therapy (HRT) may reduce the risk of coronary-artery disease in post-menopausal women. More particularly, many epidemiological studies suggest that estrogen replacement therapy (ERT) may be cardioprotective in postmenopausal women. The beneficial effects of these hormone therapies may also be applicable to males. Unfortunately the systemic use of estrogen has limitations due to the possible hyperplastic effects of estrogen on the uterus and breast in women, and the feminizing effects in males.
The mechanisms for these beneficial effects are-probably multifactorial. Estrogen is known to favorably alter the atherogenic lipid profile and may also have a direct action on blood vessel walls. Estrogen can have both rapid and long-term effects on the vasculature including the local production of coagulation and fibrinolytic factors, antioxidants and the production of other vasoactive molecules, such as nitric oxide and prostaglandins, all of which are known to influence the development of vascular disease.
Experimental work suggests that estrogen can also act on the endothelium and smooth muscle cells either directly or via estrogen receptors in both men and women. This appears to have an inhibitory effect on many steps in the atherosclerotic process. With respect to the interventional cardiology, estrogen appears to inhibit the response to balloon injury to the vascular wall. Estrogen can repair and accelerate endothelial cell growth in-vitro and in-vivo. Early restoration of endothelial cell integrity may contribute to the attenuation of the response to injury by increasing the availability of nitric oxide. This in turn can directly inhibit the proliferation of smooth muscle cells. In experimental studies, estrogen has been shown to inhibit the proliferation and migration of smooth muscle cells in response to balloon injury. Estrogen has also proved to inhibit adventitial fibroblast migration, which may in turn have an effect on negative remodeling.
Accordingly, in addition to the drugs described herein, the local or regional administration of an estrogen, a rapamycin and/or a combination thereof may be utilized in the treatment or stabilization of vulnerable plaque lesions. Estrogen as utilized herein shall include 17 beta-estradiol (chemically described as 1, 3, 5(10)-estradien-3, 17 beta-diol having the chemical notation C18H24O2), synthetic or natural analogs or derivatives of 17 beta-estradiol with estrogenic activity, or biologically active metabolites of 17 beta-estradiol, such as 2 methoxy estradiol. 17 beta-estradiol is a natural estrogen produced in the body itself. Accordingly, there should be no biocompatibility issues when 17 beta-estradiol is administered locally, regionally or systemically.
17 beta-estradiol is generally regarded as the most potent female hormone. It is generally known that premenopausal women have a lower incidence of coronary heart disease than other individuals and that these women produce higher levels of 17 beta-estradiol. 17 beta-estradiol has been referred to as a natural vasculoprotective agent providing a vasculoprotective effect mediated via a number of cellular mechanisms. It has been determined that 17 beta-estradiol may inhibit smooth muscle cell proliferation and migration, promote re-endothelialization, and restore normal endothelial function following vascular injury. In addition, 17 beta-estradiol is known to have pleomorphic properties, i.e. the ability to occur in various distinct forms, anti-atherogenic properties, anti-inflammatory properties and antioxidant properties.
Accordingly, 17 beta-estradiol may be combined with rapamycin to treat vulnerable plaque. The treatment of vulnerable plaque may be achieved through the combined effect of two therapeutic agents acting synergistically through different mechanisms to reduce smooth muscle proliferation, inflammation and atherosclerosis.
The one or more therapeutic drugs, agents and/or compounds utilized in combination with the stent would preferably prevent neointimal hyperplasia that is commonly encountered in stenting and which could lead to restenosis and device failure as described in detail above. In addition, the same or additional therapeutic drugs, agents and/or compounds would preferably stabilize or passivate the lesion by reducing local inflammation and preventing further erosion of the fibrous cap. The one or more therapeutic drugs, agents and/or compounds may be delivered in a polymer matrix coating applied to the stent struts or embedded into the material forming the stent itself and would release into the vessel wall over a predetermined period of time, preferably utilizing the dual profile release rate as briefly described above.
In treating both restenosis following vascular injury and treating vulnerable plaque, it may be advantageous to provide for the regional delivery of various drugs, agents and/or compounds in addition to the local delivery of various drugs, agents and/or compounds as described herein. The drugs, agents, and/or compounds delivered regionally may be the same as those delivered locally or they may be different. Regional delivery, as used herein, shall mean delivery to an area greater than the area covered by a local delivery device such as those disclosed herein, including stents and other implantable medical devices. For example, an infusion catheter may be utilized to administer a predetermined therapeutic dosage or range of dosages of one or more drugs, agents and/or compounds to a number of sites proximate to the disease site, for example, stenotic or vulnerable plaque lesions. Essentially, the drug or drugs may be administered proximal to the lesion, distal to the lesion, directly into the lesion or any combination thereof. The drug or drugs may be administered in any number of ways, including adventitial injection. The dosage and number of injection sites depends on a number of factors, including the type of drug, agent and/or compound, the diffusion characteristics of the drug, agent and/or compound and the area in the body that is to be treated. In practice, the drug, agent and/or compound is injected into the adventitial tissue proximal and/or distal to the lesion, as well as the adventitial tissue surrounding the lesion, and then distributes axially and longitudinally away from the site of injection.
As set forth herein, drug coated stents may be utilized in the treatment and/or prevention of restenosis and vulnerable plaque. The stents may be coated with any number of drugs or combinations of drugs as described herein. For example, rapamycin alone or in combination, may be locally delivered from a stent or other implantable medical devices. In this exemplary embodiment, the same or different drugs may also be regionally delivered via a catheter-based device. Essentially, the catheter-based device may be utilized to deliver additional quantities of the drug or drugs associated with the local delivery device or completely different drugs. The regional delivery of drugs may be beneficial for a number of reasons, including higher dose quantities and broader coverage areas. In addition, certain drugs may be more efficacious in injectable form rather than dissolved or suspended in a polymeric coating. Also, drug therapies may be tailored to the individual patient.
In addition to rapamycin, other drugs that may be regionally delivered for the treatment of vulnerable plaque include non-steroidal anti-inflammatories such as aspirin and celecoxib, steroidal agents such as estrogen, metabolic agents such as troglitazone and anti-coagulants such as enoxaparin, probucol, hirudin and apo-A1MILANO. Accordingly, these drugs may be utilized alone or in combination with rapamycin.
Any number of catheter-based devices may be utilized for regional drug delivery. In one exemplary embodiment, the drug delivery device comprises a microfabricated surgical device for interventional procedures or microneedle. The device is the EndoBionics MicroSyringe™ Infusing Catheter available from EndoBionics, Inc., San Leandros Calif. and may be generally characterized set forth below.
The microneedle is inserted substantially normal to the wall of a vessel (artery or vein) to eliminate as much trauma to the patient as possible. Until the microneedle is at the site of an injection, it is positioned out of the way so that it does not scrape against arterial or venous walls with its tip. Specifically, the microneedle remains enclosed in the walls of an actuator or sheath attached to a catheter so that it will not injure the patient during intervention or the physician during handling. When the injection site is reached, movement of the actuator along the vessel is terminated, and the actuator is controlled to cause the microneedle to be thrust outwardly, substantially perpendicular to the central axis of a vessel, for instance, in which the catheter has been inserted.
As shown in
The actuator may be capped at its proximal end 7212e and distal end 7212f by a lead end 7216 and a tip end 7218, respectively, of a therapeutic catheter 7220. The catheter tip end serves as a means of locating the actuator inside a blood vessel by use of a radio opaque coatings or markers. The catheter tip also forms a seal at the distal end 7212f of the actuator. The lead end of the catheter provides the necessary interconnects (fluidic, mechanical, electrical or optical) at the proximal end 7212e of the actuator.
Retaining rings 7222a and 7222b are located at the distal and proximal ends, respectively, of the actuator. The catheter tip is joined to the retaining ring 7222a, while the catheter lead is joined to retaining ring 7222b. The retaining rings are made of a thin, on the order of ten to one hundred microns, substantially rigid material, such as Parylene (types C, D or N), or a metal, for example, aluminum, stainless steel, gold, titanium or tungsten. The retaining rings form a rigid substantially C-shaped structure at each end of the actuator. The catheter may be joined to the retaining rings by, for example, a butt-weld, an ultra-sonic weld, integral polymer encapsulation or an adhesive such as an epoxy.
The actuator body further comprises a central, expandable section 7224 located between retaining rings 7222a and 7222b. The expandable section 7224 includes an interior open area 7226 for rapid expansion when an activating fluid is supplied to that area. The central section 7224 is made of a thin, semi-rigid or rigid, expandable material, such as a polymer, for instance, Parylene (types C, D or N), silicone, polyurethane or polyimide. The central section 7224, upon actuation, is expandable somewhat like a balloon-device.
The central section is capable of withstanding pressures of up to about one-hundred atmospheres upon application of the activating fluid to the open area 7226. The material from which the central section is made of is rigid or semi-rigid in that the central section returns substantially to its original configuration and orientation (the unactuated condition) when the activating fluid is removed from the open area 7226. Thus, in this sense, the central section is very much unlike a balloon which has no inherently stable structure.
The open area 7226 of the actuator is connected to a delivery conduit, tube or fluid pathway 7228 that extends from the catheter's lead end to the actuator's proximal end. The activating fluid is supplied to the open area via the delivery tube. The delivery tube may be constructed of Teflon® or other inert plastics. The activating fluid may be a saline solution or a radio-opaque dye.
The microneedle 7214 may be located approximately in the middle of the central section 7224. However, as discussed below, this is not necessary, especially when multiple microneedles are used. The microneedle is affixed to an exterior surface 7224a of the central section. The microneedle is affixed to the surface 7224a by an adhesive, such as cyanoacrylate. Alternatively, the microneedle may be joined to the surface 7224a by a metallic or polymer mesh-like structure 7230, which is itself affixed to the surface 7224a by an adhesive. The mesh-like structure may be made of, for instance, steel or nylon.
The 2 microneedle includes a sharp tip 7214a and a shaft 7214b. The microneedle tip can provide an insertion edge or point. The shaft 7214b can be hollow and the tip can have an outlet port 7214c, permitting the injection of a pharmaceutical or drug into a patient. The microneedle, however, does not need to be hollow, as it may be configured like a neural probe to accomplish other tasks. As shown, the microneedle extends approximately perpendicularly from surface 7224a. Thus, as described, the microneedle will move substantially perpendicularly to an axis of a vessel or artery into which it has been inserted, to allow direct puncture or breach of vascular walls.
The microneedle further includes a pharmaceutical or drug supply conduit, tube or fluid pathway 7214d which places the microneedle in fluid communication with the appropriate fluid interconnect at the catheter lead end. This supply tube may be formed integrally with the shaft 7214b, or it may be formed as a separate piece that is later joined to the shaft by, for example, an adhesive such as an epoxy.
The needle 7214 may be a 30-gauge, or smaller, steel needle. Alternatively, the microneedle may be microfabricated from polymers, other metals, metal alloys or semiconductor materials. The needle, for example, may be made of Parylene, silicon or glass.
The catheter 7220, in use, is inserted through an artery or vein and moved within a patient's vasculature, for instance, a vein 7232, until a specific, targeted region 7234 is reached, as illustrated in
During maneuvering of the catheter 7220, well-known methods of fluoroscopy or magnetic resonance imaging (MRI) can be used to image the catheter and assist in positioning the actuator 7212 and the microneedle 7214 at the target region. As the catheter is guided inside the patient's body, the microneedle remains unfurled or held inside the actuator body so that no trauma is caused to the vascular walls.
After being positioned at the target region 7234, movement of the catheter is terminated and the activating fluid is supplied to the open area 7226 of the actuator, causing the expandable section 7224 to rapidly unfurl, moving the microneedle 7214 in a substantially perpendicular direction, relative to the longitudinal central axis 7212b of the actuator body 7212a, to puncture a vascular wall 7232a. It may take only between approximately one-hundred milliseconds and two seconds for the microneedle to move from its furled state to its unfurled state.
The ends of the actuator at the retaining rings 7222a and 7222b remain rigidly fixed to the catheter 7220. Thus, they do not deform during actuation. Since the actuator begins as a furled structure, its so-called pregnant shape exists as an unstable buckling mode. This instability, upon actuation, produces a large scale motion of the microneedle approximately perpendicular to the central axis of the actuator body, causing a rapid puncture of the vascular wall without a large momentum transfer. As a result, a microscale opening is produced with very minimal damage to the surrounding tissue. Also, since the momentum transfer is relatively small, only a negligible bias force is required to hold the catheter and actuator in place during actuation and puncture.
The microneedle, in fact, travels so quickly and with such force that it can enter perivascular tissue 7232b as well as vascular tissue. Additionally, since the actuator is “parked” or stopped prior to actuation, more precise placement and control over penetration of the vascular wall are obtained.
After actuation of the microneedle and delivery of the pharmaceutical to the target region via the microneedle, the activating fluid is exhausted from the open area 7226 of the actuator, causing the expandable section 7224 to return to its original, furled state. This also causes the microneedle to be withdrawn from the vascular wall. The microneedle, being withdrawn, is once again sheathed by the actuator.
As set forth above, the microneedle or other catheter-based delivery systems may be utilized to deliver one or more drugs, agents and/or compounds, including rapamycin, to the site of atherosclerotic plaque. This type of regional delivery may be utilized alone or in combination with an implantable medical device with the same or different drugs affixed thereto. The one or more drugs, agents and/or compounds are preferably delivered to the adventitial space proximate the lesion.
As described herein, there are a number of advantages to the local or regional delivery of certain drugs, agents and/or compounds via means other than or in addition to delivery from an implantable medical device. However, the efficacy of the drugs, agents and/or compounds may, to a certain extent, depend on the formulation thereof.
It is typically very difficult to create solution dosage forms of water insoluble and lipohilic (having an affinity for and/or tending to combine with lipids) drugs such as rapamycin without resorting to substantial quantities of surfactants, co-solvents and the like. Often times, these excipients (inert substance that acts as a vehicle), such as Tween 20 and 80, Cremophor and polyethylene glycol (PEG) come with varying degrees of toxicity to the surrounding tissue. Accordingly, the use of organic co-solvents such as dimethol sulfoxide (DMSO), N-methylpyrrolidone (NMP) and ethanol need to be minimized to reduce the toxicity of the solvent. Essentially, the key for a liquid formulation of a water insoluble drug is to find a good combination of excipient and co-solvent, and an optimal range of the additives in the final dosage form to balance the improvement of drug solubility and necessary safety margins.
As the outstanding results from clinical trials of recent drug eluting stents such as the Cypher® and Taxus® drug eluting stents demonstrated, a prolonged local high concentration and tissue retention of a potent anti-inflammatory and anti-neoplastic agent released from a stent coating can substantially eliminate the neointimal growth following an angioplasty procedure. Rapamycin, released from the Cypher® stent has consistently demonstrated superior efficacy against restenosis after stent implantation as compared to a bare metal stent. However, there are clinical situations where a non-stent approach for the local delivery or regional delivery may be advantageous, including bifurcated junctions, small arteries and the restenosis of previously implanted stents. Accordingly, there may exist a need for potent therapeutics that only need to be deposited locally or regionally and the drug will exert its pharmacological functions mainly through its good lipophilic nature and long tissue retention property.
A locally or regionally delivered solution of a potent therapeutic agent, such as rapamycin, offers a number of advantages over a systemically delivered agent or an agent delivered via an implantable medical device. For example, a relatively high tissue concentration may be achieved by the direct deposition of the pharmaceutical agent in the arterial wall. Depending on the location of the deposition, a different drug concentration profile may be achieved than through that of a drug eluting stent. In addition, with a locally or regionally delivered solution, there is no need for a permanently implanted device such as a stent, thereby eliminating the potential side affects associated therewith, such as inflammatory reaction and long term tissue damage. It is, however, important to note that the locally or regionally delivered solution may be utilized in combination with drug eluting stents or other coated implantable medical devices. Another advantage of solution or liquid formulations lies in the fact that the adjustment of the excipients in the liquid formulation would readily change the drug distribution and retention profiles. In addition, the liquid formulation may be mixed immediately prior to the injection through a pre-packaged multi-chamber injection device to improve the storage and shelf life of the dosage forms.
In accordance with exemplary embodiments of the present invention, a series of liquid formulations were developed for the local or regional delivery of water insoluble compounds such as sirolimus and its analogs, including CCI-779, ABT-578 and everolimus, through weeping balloons and catheter injection needles. Sirolimus and its analogs are rapamycins, and rapamycin as used herein, includes rapamycin and all analogs, derivatives and congeners that bind FKBP12 and possess the same pharmacologic properties as rapamycin. These liquid formulations increase the apparent solubility of the pharmacologically active but water insoluble compounds by two to four orders. of magnitude as compared to the solubility limits of the compounds in water. These liquid formulations rely on the use of a very small amount of organic solvents such as Ethanol (typically less than two percent) and a larger amount of safe-amphiphilic (of or relating to a molecule having-a polar; water soluble group attached to a non-polar, water insoluble hydration chain) excipients such as polyethylene glycol (PEG 200, PEG 400) and vitamin E TPGS to enhance the solubility of the compounds. These liquid formulations of highly. water insoluble compounds are stable and readily flowable at room temperature. Certain excipients, such as Vitamin E TPGS and BHT may be utilized to enhance the storage stability of sirolimus compounds through their anti-oxidation properties.
Table 8, shown below, summarizes the concentrations of the excipient, the co-solvents and the drug for four different liquid formulations in accordance with exemplary embodiments of the present invention. The concentrations of each constituent were determined by liquid chromatography and are presented as weight by volume figures. As may be seen from Table 8, a 4 mg/ml concentration of sirolimus was achieved with an ethanol concentration of two percent, a water concentration of twenty-five percent and a PEG 200 concentration of seventy-five percent. The concentration of ethanol is preferably two or less percent so as to avoid ethanol becoming an active ingredient in the formulation.
As set forth above, a liquid formulation comprising 4 mg/ml of sirolimus may be achieved utilizing PEG 200 as the excipient and ethanol and water as the co-solvents. This concentration of sirolimus is about four hundred to about one thousand times higher than the solubility of sirolimus in water. The inclusion of an effective co-solvent, PEG 200, ensures that the high concentration of sirolimus does not start to precipitate out of solution until diluted five to ten fold with water. The high concentration of sirolimus is necessary to maintain an effective and high local concentration of sirolimus after delivery to the site. The liquid formulations are flowable at room temperature and are compatible with a number of delivery devices. Specifically, each of these formulations were successfully injected through an infusion catheter designated by the brand name CRESCENDO™ from Cordis Corporation, Miami, Fla., as described in more detail subsequently, and the EndoBionics Micro Syringe™ Infusion Catheter available from EndoBionics, Inc., San Leandros, Calif., as described in more detail above, in porcine studies.
In another exemplary embodiment, the liquid formulation of sirolimus comprises water and ethanol as co-solvents and Vitamin E TPGS as the excipient. The liquid formulation was created utilizing the following process. Two hundred milligrams of sirolimus and two grams of ethanol were added to a pre-weighed twenty milliliter scintillation vial. The vial was vortexed and sonicated until the sirolimus was completely dissolved. Approximately six hundred milligrams of Vitamin E TPGS was then added to the solution of ethanol and sirolimus. The vial was vortexed again until a clear yellowish solution was obtained. Nitrogen gas was then used to reduce the amount of ethanol in the vial to approximately two hundred twenty-nine milligrams. In a separate vial, three hundred milligrams of Vitamin E TPGS was dissolved in eleven milliliters of purified water while undergoing vortexing. The Vitamin E TPGS and water solution was then added to the first vial containing the sirolimus, Vitamin E TPGS and ethanol. The first vial was then vortexed vigorously and continuously for three minutes. The resulting. sirolimus solution was clear with a foam on top. The foam gradually disappeared after sitting at room temperature. An HPLC assay of sirolimus indicated that the sirolimus concentration in the final solution was 15 mg/ml. The final solution had an ethanol concentration of less than two percent, which as stated above is important so as to maintain ethanol as an inactive ingredient. Accordingly, utilizing Vitamin E TPGS as the excipient rather than PEG, resulted in a higher concentration of sirolimus in the final formulation.
Table 9, as shown below, summarizes the composition and visual observations for aqueous formulations of sirolimus utilizing ethanol, Vitamin E TPGS and water at different ratios. The solutions represented by the data contained in Table 9 were generated using essentially the same procedure as described above, except that the ratios between sirolimus and Vitamin E TPGS were varied.
All of the above preparations except for number five remained as stable solutions at both room temperature and under refrigerated condition. The results in Table 9 indicate that, Vitamin E TPGS may be utilized over a wide range of concentrations to increase the solubility of sirolimus in an aqueous solution.
In another exemplary embodiment, a liquid formulation of CCl-779, a sirolimus analog, is prepared utilizing ethanol, Vitamin E TPGS and water. This liquid formulation was made under similar conditions as to that described above. Because of its better solubility in ethanol, only 0.8 grams of ethanol was used to dissolve two hundred milligrams of CCl-779 as opposed to the two grams of sirolimus. After the amount of ethanol was reduced to approximately two hundred thirty milligrams, eleven milliliters of purified water containing three hundred milligrams of Vitamin E TPGS was added to the vial of ethanol and CCl-779. The combined solution was vortexed for three minutes and resulted in a clear solution. An HPLC assay of CCl-779 indicated that the concentration of CCl-779 in the final solution was 15 mg/ml. The concentration of ethanol in the final solution was less than two percent. Accordingly, the results are substantially identical to that achieved for the sirolimus.
As stated above, a number of catheter-based delivery systems may be utilized to deliver the above-described liquid formulations. One such catheter-based system is the CRESCENDO™ infusion catheter. The CRESCENDO™ infusion catheter is indicated for the delivery of solutions, such as heparinized saline and thrombolytic agents selectively to the coronary vasculature. The infusion catheter may also be utilized for the delivery of the liquid formulations, including the liquid solution of sirolimus, described herein. The infusion region includes an area comprised of two inflatable balloons with multiple holes at the catheter's distal tip. The infusion region is continuous with a lumen that extends through the catheter and terminates at a Luer port in the proximal hub. Infusion of solutions is accomplished by hand injection through an infusion port. The catheter also comprises a guidewire lumen and a radiopaque marker band positioned at the center of the infusion region to mark its relative position under fluoroscopy.
In accordance with another exemplary embodiment, thin films may be utilized in combination with stents for local drug delivery. It is important to note; however, that while stents are extensively set forth herein, thin films may be utilized with any number of implantable medical devices. As used herein, drug shall mean any agent, chemical, compound or combination thereof, including all of the drugs and drug combinations described in this specification. The use of thin films may increase the drug dosage amount available on a given stent, provide for increased uniformity of drug distribution along the length of the vessel and decrease the potential for emboli migration during stenting. The thin films may comprise any suitable biocompatible material including metals, metal alloys such as nickel-titanium alloys, ceramics and polymers. The thin films may be applied to the outer or abluminal surface of the stent, to the inner or luminal surface of the stent or to both the luminal and abluminal surfaces of the stent. It is important to note that the thin film may be applied to any type of stent, the exact configuration of which would vary depending on a number of factors, including vessel size, stent type, dosage and disease state. The drug may then be applied to the thin film or any portion thereof utilizing any of the methodologies and materials described herein.
The conventional process for manufacturing a drug eluting stent typically involves applying a primer to the bare. metal stent, if a metal stent is utilized, to facilitate the adhesion and leveling characteristics of the polymer/drug composition to the stent surface, then an additional polymer may be applied for controlling the elution rate of the drug. As described herein, various polymer combinations may be utilized to create both chemical and physical barriers for more precise control of elution rate. The coatings may be applied utilizing any suitable. process as disclosed herein and may include spray coating, dip coating and more advanced techniques such as ink-jet type printing, and powder coating transfer printing. Currently utilized coating techniques may require the additional step of polishing in order to achieve smooth surfaces. The polishing step may be done in any number of ways, including polishing through the use of solvents. The thin film enhanced stent of the present invention may be utilized to overcome some of the disadvantages with current devices and processes. For example, the thin film enhanced stent may provide more physical contact surface area and potential micro surface features for adhesion enhancement without the need for a primer coat. The thin film may also function as a reservoir for the drug through a micro feature opening or openings created in the thin film. In addition, the thin film may reduce the complexity of the coating design and process.
As stated above, the thin films may comprise any suitable biocompatible material. In one exemplary embodiment, the thin film may be fabricated from an alloy of nickel and titium (nitinol). A nitinol film has unique shape memory and/or superelastic characteristics and may be produced at very thin thicknesses, for example, in the range from submicron to about one-hundred (100) microns.
Nitinol, as described above, exhibits shape memory and/or superelastic characteristics. Shape memory characteristics may be simplistically described as follows. A metallic structure, for example, a nitinol tube that is in an Austenite phase may be cooled to a temperature such that it is in the Martensite phase. Once in the Martensite phase, the nitinol tube may be deformed into a particular configuration and/or shape by the application of stress. As long as the nitinol tube is maintained in the Martensite phase, the nitinol tube will remain in its deformed shape. If the nitinol tube is heated to a temperature sufficient to cause the nitinol tube to reach the Austenite phase, the nitinol tube will return to its original or programmed shape. The original shape is programmed. to be a particular shape by well known techniques. Superelastic characteristics may be simplistically described as follows. A metallic structure, for example, a nitinol tube that is in an Austenite phase may be deformed to a particular shape or configuration by the application of mechanical energy. The application of mechanical energy causes a stress induced Martensite phase transformation. In other words, the mechanical energy causes the nitinol tube to transform from the Austenite phase to the Martensite phase. By utilizing the appropriate measuring instruments, one can determine that the stress from the mechanical energy causes a temperature drop in the nitinol tube. Once the mechanical energy or stress is released, the nitinol tube undergoes another mechanical phase transformation back to the Austenite phase and thus its original or programmed shape. As described above, the original shape is programmed by well known techniques. The Martensite and Austenite phases are common phases in many metals.
Medical devices constructed from nitinol are typically utilized in both the Martensite phase and/or the Austenite phase. The Martensite phase is the low temperature phase. A material in the Martensite phase is typically very soft and malleable. These properties make it easier to shape or configure the nitinol tube into complicated or complex structures. The Austenite phase is the high temperature phase. A material in the Austenite phase is generally much stronger than the material in the Martensite phase. Typically, many medical devices are cooled to the Martensite phase for manipulation and loading into delivery systems, as described herein with respect to stents and then when the device is deployed at body temperature, they return to the Austenite phase.
The thin films may be utilized in any number of ways and on any number of devices. In addition, the thin films may be fabricated into stand alone devices as described subsequently. Essentially, in one exemplary embodiment the thin film may simply be utilized as a thin film deposited on a particular surface of another device. In another exemplary embodiment, the thin film may be fabricated into a mesh which then may be affixed to another particular device. In yet another exemplary embodiment, a thin film may be deposited on a particular surface of another device and then etched or otherwise modified into a surface having a particular pattern therein. In yet another exemplary embodiment, a thin film may be utilized as an intermediate layer sandwiched between other layers, for example, between layers of other metals, polymers and/or ceramics.
Referring to
The thin film mesh of this exemplary embodiment offers a number of advantages. The higher surface area of the thin film mesh as compared to the stent allows for more drug to be delivered. The surface areas of thin films may be up to ten to twenty times higher than a stent. The higher drug content is especially desirable for patients with certain other diseases such as diabetes who may require higher doses of a particular drug. In order to increase the drug content, the existing drug eluting stents may require a thicker coating using the same coating formulation as is currently utilized. However, the thicker coating may have a higher crossing profile and the coating strength may also be compromised such that the coating may flake off and become emboli. Additionally, the thicker coating on a stent may lead to high push forces in the catheter delivery system as described herein. In this exemplary embodiment, the higher drug content may be achieved by using a nitinol thin film on the stent. With the increased surface area of the thin film compared to the stent, a larger total dose may be applied to the combination stent and thin film mesh device, while keeping the drug and/or drug and polymer combination coating thin to avoid increasing the profile or making the drug and/or drug and polymer combination susceptible to flaking. In addition, with the larger surface area and concomitant increased drug loading capability of the thin film, abluminal coating of the combination stent and thin film mesh device delivery system becomes easier than with a stent alone. Abluminal coating has shown clinical value. in vessel wall response but the decreased drug loading on stents alone may result in a slight decrease in efficacy in a small percentage of patients.
A deployed stent in a large vessel has more uncovered vessel area than a deployed stent in a small vessel. The use of a drug coated thin film mesh addresses drug dosage variation by size of vessel, due to the thin film's capability to cover the empty spaces between struts. This advantage is apparent in large vessels such as a superficial femoral artery or SFA, a carotid artery and sophenous vein grafts or SVG.
In addition, emboli migration during stenting is also addressed by the coverage of the thin film mesh between the stent struts. Here the thin film mesh may pin the emboli against the vessel wall during stenting. This issue is especially relevant for Carotid and SVG stenting. Furthermore, some stent designs have been predicated on the need to have a sufficient number of struts opposing the vessel wall in order to impede emboli release into the bloodstream during stent deployment. A mesh of thin film over a stent may act to replace a number of struts by pinning emboli against the vessel wall upon stent deployment. This reduction in stent struts acts to reduce the profile of the device,. allowing for easier access to diseased regions.
Referring now to
The thin film may be patterned with micron-scale patterns, providing a very large surface area compared to a stent. Alternately, a microporous or microtextured surface may be created, formed, and/or modified on an existing stent or on a stent cover to improve cell reproduction, cell differentiation, cell migration and/or agent delivery. The patterns may be realized via fully etched fenestrations, partially etched regions to create wells, or a combination of both, though non-etched thin films may also be acceptable, depending on the disease state and area of the disease. Patterned thin films may work with existing drug eluting stent platforms without altering the mechanical performance of the stent, such as radial force. The uniform and large surface area of the thin film provides more design freedom for delivering drugs more uniformly than stents alone, adding more drug dosage, for thinner coatings, for preventing emboli migration and the formation of aneurysms. Nitinol itself is also a proven alloy for implantable devices as stents. The film also reduces the need for high anti-proliferative drug concentration in the bulk blood flow, restricting the delivery to a localized lumen surface. The combination of a suitable pattern and localized uniform delivery helps control acute inflammation response while encouraging longer-term healing response. There is evidence to suggest that faster healing response may reduce longer-term thrombosis rates seen with current drug eluting stent approaches.
The thin film may be patterned to create various surface features such as reservoirs, grooves, and holes and/or with the fine openings as micromesh with different porosity. The thin film may be used on all stent materials, including stainless steel, nitinol, cobalt-chromium alloys, durable polymers, biodegradable polymers and ceramics. The thin film may also be part of a multi-layer composite for various functional performance characteristics such as multiple drug delivery designs and bio-actives delivery. Thin films of polymeric composition could also be formed, deposited and etched.
The thin film may be set to a specific flat or three-dimensional shape, of cylindrical cross-section, of non-cylindrical cross-section, flat, or any other suitable or desirable shape. The shape-setting may occur during deposition of the thin film or after the thin film is released from the deposition substrate. Though shape setting is not a requirement for this application. The thin film, if formed from nitinol could remain in the superelastic state. The creation of the thin film may be achieved with a wide-variety of techniques such as Pulsed Laser Ablation (PLA), Physical Vapor Deposition (PVD) including magnetron sputtering, Chemical Vapor Deposition (CVD), Molecular Beam Epitaxy (MBE), thermal deposition (via electron-beam or resistive heating), electroplating, dip coating, spin coating or other methods of depositing a metal. Batch deposition of metals on two-dimensional substrates is presently done on a regular basis in many industries. Deposition onto three-dimensional substrates has also been demonstrated. The thin films could be etched via chemical, laser, or dry etch methods as is known in the art.
The thin film may be bonded, treated or modified by polymers or metallic materials to enhance the stent's radiopacity and/or interfacial properties such as fixation, lubricity and surface tension reduction. The film may also be used to treat tumors and cancer by either blocking the blood flow into cancer tissue or deliver anti-cancer agents.
Alternately, the film may be made into a low-profile [less than five hundred (500) micron cross-section thickness] donut-shaped pouch that allows blood flow through the center of the donut structure. The surface of the pouch may be patterned and/or coated with VEGF for rapid endothelialization for use in such devices as aneurismal repair devices described herein.
Alternately, the thin film may comprise other shapes, such as a spherical depot, a symmetric or asymmetric balloon, or a flat sheet.
Alternately, the thin film or drug and/or drug and polymer coated thin film may be made electrically, mechanically, chemically, and thermally active, for example, for ablation and cauterization of blood vessels and tumors, for resection, for sampling, or surgical removal, for example, in the GI tract or in the epileptic regions of the brain. Also, for example, chemically sensitive “gates” could be created that dissolve, preferentially, upon a certain concentration or lack of concentration of certain biomarkers. In the case of inflammatory response, markers such as TNF-alpha or other suitable agents might be of use.
Alternately, the film may be patterned to control the rate of blood flow through the film or across the film to achieve different biological response, such as tumor starving, and a better control of drug delivery rates. An example of the application is in advanced or age related macula degeneration where the undesirable angiogenesis may be countered by restricting the blood leakage out of the macula and by delivering anti-angiogenic drugs at a predetermined specific control rate.
Alternately, the thin film could have an additional bioresorbable layer that covers the outer or inner layer of the drug reservoirs and maintains and protects the release of the drug via enhanced diffusion.
Alternately, beyond endoluminal applications, this thin film nitinol technology could also be used for non-endoluminal applications such as for the spine and cardiology.
Additional metallic layers or markers could be added or embedded into the structure to improve radiopacity as described above.
Although shown and described is what is believed to be the most practical and preferred embodiments, it is apparent that departures from specific designs and methods described and shown will suggest themselves to those skilled in the art and may be used without departing from the spirit and scope of the invention. The present invention is not restricted to the particular constructions described and illustrated, but should be constructed to cohere with all modifications that may fall within the scope of the appended claims.
