Patent Application
20180221483
Materials and methods are presented to deliver liquids to the interior of the eye, in a timed release, to treat ocular diseases and conditions. Formulations for liposomes as vehicles for substances to coat contact lenses are described.
Ocular angiogenesis is a serious complication in the eye mainly observed in the retina and the choroid. Angiogenesis is characterized by the growth of new blood vessels into the retina damaging its surface in the process. The new blood vessels are fragile, “leaky” and pool blood into the retinal space, further damaging the retina. Laser treatments and drugs like Lucentis® and Avastin® are available for controlling the growth of new blood vessels. These drugs are anti-VEGF antibodies that inhibit the growth of new blood vessels. Avastin® (Bevacizumab) is designed to directly bind VEGF extracellularly and prevent interaction with VEGF receptors (VEGFRs) on the surface of endothelial cells, and thereby may inhibit VEGF's angiogenic activity. Lucentis® is a recombinant humanized monoclonal antibody fragment (lacking an Fc region), and is the first VEGF inhibitor specifically designed for use in the eye to bind and inhibit VEGF-A, thereby, preventing angiogenesis and hyperpermeability of the blood vessels.
Inadequate drug levels reaching the target sites necessitate frequent drug administration. Use of colloidal dosage forms like liposomes, nanoparticles, microemulsions, and nanoemulsions for drug delivery has been highly exploited due to the versatility of the formulations. There are reports of various disadvantages associated with drug delivery, especially the use of colloidal delivery systems for proteins. Liposomes are an excellent choice for sustained-release ocular drug delivery because of their amphiphilic, non-toxic nature, versatility and their ability to carry diverse chemical payloads. However, the conventionally prepared liposomal formulations have several disadvantages such as low stability and short shelf life. These can be attributed to the fact that the phospholipids which form these liposomes are highly prone to oxidation and hydrolysis. Also, liposomes tend to fuse together and increase in the particle size, further causes light scattering when injected into the eye.
Another major problem with liposomes is the encapsulation efficiency. This varies with the concentration of cholesterol used to stabilize the phospholipid bilayers. High concentration of cholesterol leads to very inflexible bilayers leading to very low encapsulation and very slow release. On the other hand, low concentration of cholesterol causes very high encapsulation but very fast release. So, to overcome these disadvantages, there is a need to engineer the liposomal formulations to have higher stability, very low drug leakage, high encapsulation and slow release of the drug.
Poly unsaturated fatty acid chains on the phospholipids are the most sensitive component of the liposome bilayer to oxidative damage during long-term storage. The presence of cholesterol in the liposomes provides protection to the lipid bilayers by decreasing the degree of hydration. The presence of a water soluble anti-oxidant helps to prevent the oxidative and hydrolytic degradation of the lipid bilayers. The effect of the presence of sugars on liposome stability prevent leakage of the drug from liposomes during freeze-drying. It was reported that the mass ratio of carbohydrate to the lipids as well the osmotic balance helps in preventing solute leakage. Calorimetric studies suggest that sugars prevent phase separation during drying and phase transitions during rehydration, hence help in stabilizing the lipid bilayer.
Currently, eye drops, applied externally, are used as a method to treat internal ocular disorders. However, this method suffers from the disadvantage that the liquid has to pass through many ocular barriers, many of which have opposite properties. For example; the epithelial layer of the cornea allows hydrophobic drugs to pass, whereas the stroma (the next layer) allows hydrophilic drugs to pass, not hydrophobic. In addition, lacrimation and impermeability through the corneal epithelium are responsible for poor ocular bioavailability.
Ocular diseases and conditions include age related macular degeneration (AMD), a common, chronic degenerative condition of the macula, which is a part of the retina. AMD is characterized by loss of central vision, whereas peripheral vision remains unaffected. Growth and leakage of new blood vessels beneath the retina cause permanent damage to the light-sensitive retinal cells which then die off and create blind spots in the central vision. Treatment options for AMD include intravitreal injection of steroids and macromolecules (direct injection of the drugs into the vitreous humor), a very unpleasant technique that requires multiple applications. Complications include: endophthalmitis (an inflammatory condition of the intraocular cavities), increased IOP (intraocular pressure), retinal detachment, and development of glaucoma and cataracts. Other ocular conditions that require treatment are cataracts and infections. Treatments would benefit from timed release systems.
Liposomes are a possible choice for sustained release ocular drug delivery because of their amphiphilic nature. But, the conventional liposomal formulations have several disadvantages. The first major problem is the stability and low shelf life. These can be attributed to the fact that the phospholipids which form these liposomes are highly prone to oxidation and hydrolysis. Also liposomes have a tendency to fuse together, increasing the particle size and further cause light scattering.
Another major problem with the liposomes is the encapsulation efficiency. This depends on the concentration of cholesterol used to stabilize the phospholipid bilayers. High concentration of cholesterol leads to very inflexible bilayers leading to very low encapsulation and very slow release. On the other hand, low concentration of cholesterol causes very high encapsulation but very fast release. So, in order to overcome these disadvantages, there is a need to engineer the liposomal formulations to have higher stability, very low drug leakage, high encapsulation and slow release of the drug. Currently, there are no groups that have been successful in obtaining a protein drug release over 40 days.
Diabetic Retinopathy (DR) and Age-related Macular Degeneration (AMD) are the most common ocular diseases and a leading cause of blindness in American adults. Laser treatments and drug intervention with Lucentis® and Avastin® are available for controlling angiogenesis by inhibiting the growth of new blood vessels. These antibody injections are given monthly into the eye which are inconvenient as well as very expensive. The present disclosure focuses on encapsulating the protein drugs within the liposomes to obtain drug release over a longer period, thereby decreasing the frequency and cost of the injections. Calorimetric, spectroscopic and light scattering methods were used to identify the variations in the liposomes in terms of particle size, encapsulation efficiency, time of release and thermal stabilities, in order to screen and downsize formulations to three with the PC:PE:PG:cholesterol compositions of 60:10:0:30, 65:5:5:25 and 60:5:5:30. Bevacizumab loaded liposomes are suitable for extended released drug delivery to treat ocular angiogenesis. In vitro biological activity, RPE cytotoxicity tests and animal experiments were conducted to determine the efficacy of the drug delivery system for potential human use.
The present results were to determine the concentration of sugars and anti-oxidants to be included in compositions to increase the stability while controlling the drug release parameters. Emphasis in making liposomes is not towards the formation of lipid bilayers, but towards getting the membranes to properly form vesicles of the right size and structure, and to entrap proteins with high efficiency without leaking from the liposomes randomly.
The present disclosure is a pioneering work for understanding the structure of the liposomes in order to improve their stability as well drug release properties. Currently, encapsulating drugs in the liposomes for ocular drug delivery is not reported. The literature available attributes failures to lack of stability in the liposomes as well as several other factors mentioned above. Results disclosed herein are from experiments designed to understand the variations in the liposomes with change in compositions, addition of adjuvants, method of preparation, freeze thaw cycles, surface modifications. The best formulations were determined based on the particle size, encapsulation efficiency and the time of drug release. A variety of advanced methods—structural, spectroscopic, biophysical and biochemical assays were used. The present results are innovative, especially in the field of ocular drug delivery.
Liposomal formulations which are very stable and have a long shelf life are disclosed. This was achieved by modifying the method of preparation and including additives to prevent damage of liposomes due to oxidation and hydrolysis. Different batches of formulations were designed and carefully screened on the basis of particle size and percentage drug encapsulation in order to obtain the best results. From the preliminary data, 3 good formulations resulted which had optimum particle size and very slow release of about 35-45 days instead of 3-4 days. But, in order to further prolong the time of release, the surface of liposomes was modified by using PEG. This increased time of release to approximately 180-200 days in vitro. These formulations (compositions) are useful to encapsulate small drugs as well as macromolecules like proteins.
Knowledge of stable liposomes was used to encapsulate model protein (to replicate the encapsulation of anti-VEGF drugs like Lucentis® and Avastin®). But disclosed formulations have shown a drug release of about 4.5-5 months which is around 3 times slower release than reported by others. Thus, with this technology, instead of monthly intravitreal injections @ 2500$/injection, the frequency of injections can be reduced to 3/year. The decrease in frequency of injections also decreases the chance of infections.
Further, coating the intraocular lenses with liposomes for treatment of endophthalmitis (bacterial and fungal infection) and inflammation after cataract surgery is disclosed. Liposomes which release drug over 180-200 days are disclosed. In order to coat the liposomes onto the intraocular lens, an FDA approved biodegradable polymer PLGA is used which acts as a glue as well as a drug depot, and further extends the time of release of antibiotics; prevents infection for around 6 months. During this time, the eye develops its natural immunity and hence wards off any further infections.
In summary, very stable liposomal formulations with a slower drug release were developed. The technology described has a wide range of applications in ocular drug delivery for treating diseases especially endophthalmitis, inflammation, diabetic retinopathy and wet age related macular degeneration. The formulations can be customized to treat ocular diseases as well. The advantage of this technology is effective treatment lower frequency as well as cost of doses.
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Conventional Liposomes; ◯=Background (Glass capillary).).
Materials and methods are described to directly deliver substances (drugs, medicines and medicaments) to the interior of the eye. The substances are designed to be slowly released over time (sustained, controlled, release) to treat diseases and conditions of the mammalian eye.
One of the major challenges for treating ocular angiogenesis is delivering the drug to the target site. The main advantages of using anti-VEGF antibodies as therapeutic agents are their target specificity, strong affinity, bio-reactivity and low toxicity making them an excellent choice for treating angiogenesis. A disadvantage is that after administration of high concentrations of proteins in the eye, they tend to precipitate and lead to adverse reactions. Other challenges faced by protein drugs in the eye are their susceptibility to enzymatic degradation, short vitreous half-life, ion permeability, immunogenicity, post-translational modifications, aggregation and denaturation. To overcome the disadvantages as well as increase the patient compliance, projects disclosed herein was focused on encapsulating the protein drug in nanostructures to prolong the time of drug release into the eye, thereby, decreasing the frequency as well as the cost factor for these treatments.
Table 1 shows the differential scanning calorimetry data for IgG, Bevacizumab, phospholipids, cholesterol, conventional liposomes without any modifications, stealth liposomes with modifications and compositions with varying ratios of cholesterol.
Table 2 shows the time of release, % encapsulation and particle size of selected formulations with varying concentrations of PC, PE, PG and cholesterol. Variations in the phospholipid and cholesterol concentrations were based on the melting temperatures of the compounds reported in Table 2. This study was used to determine a relationship between the thermal stability and rate of release of the drug from liposomes.
Table 3 shows the time of release, % encapsulation and particle size of selected formulations with varying concentrations of PC, PE-PEG2000, PG and cholesterol after modifications made to the formulations by incorporating hydrophobic anti-oxidants, PEGylated phospholipids and a cryoprotectant sugar trehalose.
Table 4 represents the data from accelerated stability studies of liposomal formulations with encapsulated Bevacizumab.
Preliminary formulation development was performed using fluorescent tagged IgG to determine various factors that affect the stability and drug release of the liposomes. From the particle size measurements, it appeared that the liposomes with less concentration of cholesterol tend to be larger, on average, than liposomes with high cholesterol content. But, at the same time, the higher concentration of cholesterol decreases the protein encapsulation efficiency of the liposomes. Therefore, an optimum concentration of cholesterol is required to have stable bilayers as well as optimum release. Based on the results shown in Tables 1-3, it is determined that the use of 25-30% molar ratio of cholesterol with 70-75% molar ratio of total phospholipid content gives very stable formulations along with a sustained release. Calorimetric studies support the data and have shown that excess unconjugated cholesterol above 30% in the composition appeared as a peak at around 157° C. indicative of crystalline cholesterol.
The effect of lipid composition on the size and stability of the liposomes have been examined by preparing liposomes with different molar ratios of phospholipids while maintaining the molar ratio of cholesterol constant. The liposomes with high concentrations of phosphatidylcholine gave an optimum size of 100-200 nm. On the other hand, the compositions with high concentration of phosphatidylglycerol (PG) were found to promote fusion and an overall increase in particle size. This can be attributed to the oxidation of unsaturated fatty acids on phosphatidylglycerol. From the data seen in Table 1, the inference is that the lower the concentration of phosphatidylglycerol, the lower the chance of oxidation of the liposomes, thereby, increasing the stability and shelf life. Calorimetric studies revealed that the compositions with low or no phosphatidylglycerol content have more thermal stability as seen in Table 1. To overcome the disadvantage of oxidation and hydrolysis, hydrophobic anti-oxidants were incorporated within the formulations to be embedded in the lipid bilayers. A 3-fold difference was observed in the particle size of liposomes at different phospholipid and cholesterol concentrations in the presence of anti-oxidants. Lyophilization of liposomes promotes fusion and a concomitant increase in capture volume due to freeze fracture at extremely low temperatures. To avoid this problem, cryoprotectant sugars with non-eutectic behavior were used. Many groups have reported that even at high concentrations of the cryoprotectants, they could still observe about 8% of leakage per day. However, restricting the leakage to less than 0.5% was achieved by increasing the overall hydrophobicity of the liposome lipid bilayers by incorporating a hydrophobic anti-oxidant as seen in Table 1. A variety of sugars have been shown to act as protectants during dehydration/rehydration of liposomes. This protective ability can extend to prevent vesicle fusion and help in improved encapsulation of the marker within the liposomes. From the present results, we have observed that 175 mM of trehalose gives the best results in maintaining the stability during lyophilization. By adding the adjuvants and incorporating 8-10 freeze thaw cycles, the lipid hydration and extrusion method was modified to get stable liposomes with optimum particle size, higher encapsulation efficiency and slower release.
Using the information from all the preliminary studies based on particle size, encapsulation efficiency and time of release, formulations were downsized to three with the PC:PE:PG:cholesterol compositions of 60:10:0:30, 65:5:5:25 and 60:5:5:30 for encapsulating Bevacizumab and the relevant data can be seen in
Differential scanning calorimetry (DSC) was used to investigate the thermal stability as well as interaction between liposomes and entrapped protein. Thermal studies have shown that pure phospholipids, cholesterol and IgG gave sharp endotherms in a narrow temperature range and a combination of phospholipids as seen in the liposomes gave broader endotherms. The thermal behavior of the lipid bilayer phase transition was affected by the presence of adjuvants. This was clearly seen in both conventional and stealth liposomes as seen in Table 1. Another interesting feature is that the stealth liposomes produced endotherms approximately 5° C. higher than the conventional liposomes with same compositions. The increase in temperature is consistent with the results obtained by Hashizaki et al, who explained that the increase might be due to lateral phase separation of PEG on the phospholipids caused by PEG chain entanglement and intra chain hydrogen bonds.
Bevacizumab is widely used as an anti-angiogenic agent, and is FDA approved for cancer treatment. It is currently being used by ophthalmologists as an off-label intravitreal agent in the treatment of proliferative (neovascular) eye diseases, particularly for choroidal neovascular membrane (CNV) in AMD. The intravitreal half-life of Avastin is about 4.32 days, maintaining a concentration of about 10 μg/ml in the vitreous over a period of 30 days. This clinically translates to receiving an intravitreal injection monthly to prevent the growth of abnormal blood vessels. Frequent invasive injections into the eye have also been reported to increase the incidence of infections. To circumvent these problems, the anti-VEGF drugs need to be delivered through a sustained release drug delivery system over an extended period, thereby minimizing the number of injections.
This disclosure deals with the aspects of increasing the stability of liposomes, while increasing the payload and preserving activity of encapsulated Bevacizumab in the process. Prototype formulations were developed in vitro using IgG as a marker, formulations which were able to prolong the time of release while preventing protein degradation until release. Using the same molar compositions, Bevacizumab was formulated within the liposomes and studied in vitro drug release profiles and stability of the antibody at regular intervals of time. Results from ELISA as seen in
To determine the stability of the formulation, accelerated stability studies were performed at various storage conditions. Samples were aliquoted at different sampling points to ensure the thermal stability of the antibodies while in formulations. Potency of the antibodies was tested based on anti-VEGF activity of Bevacizumab in the aliquots using ELISA (data not shown). Presence of adjuvants like trehalose and beta carotene seem to maintain the stability of the antibody in liposomal solution. Use of trehalose in biologics as a cryoprotectant has been a common practice in the biopharmaceutical industry and hence, would be an ideal excipient even for liposomal drug delivery systems when administered in vivo.
Reports are that 2.5 mg/ml of Bevacizumab exhibited cytotoxic effects on RPE cells. To assess effect of liposomes on the viability of both cell lines, MTT assay was performed. In case of cells treated with varying concentrations of Avastin, the cell viability decreased slightly when exposed to 2 mg of the antibody. However, in case of cells treated with liposomes, the cell viability remained the same with liposomes encapsulating varying concentrations of Avastin. No cytotoxic effect of the vehicle (blank liposomes) could be observed as seen in
Reports are that the half-maximum inhibitory concentration of bevacizumab (IC50) is 22 ng/ml. As seen in
Overall, the in vitro efficacy of the Bevacizumab loaded liposomes in terms of slow release and retained anti-VEGF activity of the antibody are shown. Although administering high concentrations of the antibody can cause cytotoxic effects in vitro and in vivo, delivering the antibody through a vehicle exhibiting sustained release is an ideal and promising platform to reach the clinical setting.
A timed release system to deliver substances or compositions to the interior of a mammalian eye is disclosed that includes:
Suitable encapsulating vehicles include vesicles. The vehicles may be liposomes.
The substances encapsulated within the vehicles may be in the form of liquids or gels, and include drugs, medicaments or other treatments for diseases or conditions of the mammalian eye.
The diseases or conditions treated by the system include AMD, cataracts, dry eye, inflammation and infection.
A method of treating diseases of the mammalian eye is also disclosed:
Sustained release (controlled, timed) delivery is achieved by manipulating the sizes of the encapsulating vehicles or the number of layers of the vehicles.
Compositions are also disclosed, embodiments of which include a liposome and an ocular drug or medicament encapsulated therein. These formulations are disclosed as examples.
Drugs are encapsulated in liposomes and then embedded in a coating material that is then applied onto an ocular device (e.g., intraocular lens or shunt). A coating applied to contact lenses, intraocular lens, or ocular stents includes substances to treat diseases or conditions of the eye. The substances include drugs, medicines, and medicaments, delivered by sustained release. The ocular device is then implanted in the eye to give controlled release of the drug over a specific period of time.
Suitable drugs include any small molecule (hydrophilic or hydrophobic) or peptides or proteins. For example, the liposome formulations provide the controlled release of e.g. Lucentis, or its equivalent, Avastin, drugs that are the only current treatment for “wet” AMD. These treatments are antibodies, that is proteins (large molecules). The antibodies are encapsulated in the liposomes and are directly injected as a solution into the posterior chamber of the eye. The drug is then controlled released. Note that the coating step may be omitted, and the encapsulated drugs directly injected into the eye rather than surgically implanting a device in the eye. Currently, ophthalmologists directly inject drugs as an ophthalmic solution, so injection has to be repeated e.g. every month. The disclosed materials and methods reduce the number of annual injections because of the controlled release.
In ophthalmology, there are several plastic devices that can be coated and act as vehicles to deliver various drugs. These include contact lenses and intraocular lenses (IOL), which are prosthetic lenses used after cataract surgery, as shown in
The types of drugs that are imbedded in the plastic devices for the eye are those useful to treat dry eye, glaucoma, infection, and the like. Various drugs are encapsulated prior to delivery. The methods disclosed herein delay the loss of drugs from the vitreous and increase the effectiveness of the drugs.
Novel systems disclosed herein use inverted micelles for controlled and extended (sustained) delivery of substances (drugs, medicines and medicaments, e.g. antibiotics) across the retina. In an inverted micelle, the polar groups of the surfactants are concentrated in the interior of the micelle, and lipophilic groups extend towards the non-polar solvent. The methods disclosed include three steps (1) encapsulating both hydrophilic and hydrophobic drugs into the inverted micelles and uni-lamellar liposomes; (2) incorporating these inverted micelles and liposomes into a hydrogel coating composite, or by covalently tethering the liposomes to the surface, to form a mixture; and (3) coating the mixture onto a contact lenses, IOL or ocular stint, for drug release. By manipulating the sizes of the encapsulating vehicles, controlled and extended release of therapeutic drugs is achieved. Because hydrogels are superabsorbent toward water, they maintain the integrity of the liposomes over long periods of time. Local application of encapsulated coated contact lenses or IOLs helps in the controlled time release of the drug to the target site.
Numerous different emulsions are suitable. These include liposomes and normal and reversed phase vesicles. These micro-heterogeneous systems can contain particles that are unilamellar (single-walled) or multilamellar (multi-layered) and the number of layers controls the release time of the encapsulated drug. Liposomes have the ability to encapsulate both hydrophilic and hydrophobic drugs, and deliver drugs to a specific site. Liposomes are bilayered, microscopic vesicles surrounded by aqueous compartments. The liposomes are made from naturally occurring phospholipids and fatty acids with stabilizers such as cholesterol. After drugs are encapsulated, the liposomes are then dispersed into a biocompatible polymer matrix such as cellulose that can then be coated onto a silicone surface. All of these materials are commercially available, e.g. Avanti Polar Lipids (Alabaster, Ala.) and biocompatible polymers (hydrogels) from Sigma-Aldrich (St. Louis, Mo.).
Phospholipids used for preparing liposomes like 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (ammonium salt) (DSPE-PEG2000) and 1,2-dipalmitoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (sodium salt) (DPPG) were purchased from Avanti Polar lipids, Inc. Milli-Q-water was produced via Millipore Milli-Q Plus Purepak 2 water purification system (EMD Millipore, Billerica, Mass.). Sodium phosphate, potassium phosphate, mannitol, trehalose, chloroform and high-performance liquid chromatography (HPLC) grade Methanol (MeOH) were purchased from Thermo Fisher Scientific (Pittsburgh, Pa., USA). Immunoglobulin G (IgG) from human serum, sodium chloride, cholesterol, beta-carotene, canthaxanthin, phosphatidylcholine and 5,6-carboxyfluorescein succinimidyl ester were from Sigma-Aldrich (St. Louis, Mo., USA).
a) Fluorescent Tagging of Protein:
For easy detection of the model protein marker encapsulated within the liposomes, the proteins were labelled with fluorescein. IgG (model protein for preliminary studies) and Bevacizumab (Avastin) were tagged using NHS fluorescein (5,6-carboxyfluorescein succinimidyl ester). The protein (1 mg/ml) was dissolved in 20 mM sodium phosphate buffer with 0.15 M NaCl at pH 8.5. 4.7 μL of 15 mmol NHS-fluorescein solution in DMSO was added to the protein solution and incubated at room temperature for 2 hr. Unreacted NHS-fluorescein was removed by dialysis using 20 mM tris-glycine buffer at pH 8 for optimal results and accurate determination of the fluorophore-to-protein ratio. The absorbance of the labeled protein at 280 nm and 488 nm was measured to calculate the protein concentration and degree of labeling. Anti-VEGF activity of the antibody after fluorescent tagging was confirmed using ELISA.
b) Preparation of Liposomes by a Modified Lipid Hydration and Extrusion Method:
Different phospholipids and cholesterol were mixed at various molar ratios in a round bottom flask. To this, 10 ml of 2:1 ratio of methanol-chloroform mixture containing 1 μM anti-oxidant was added to make a uniform organic phase. The solvent was removed by rotary evaporator to get a uniform film of lipid layer. This lipid layer was hydrated using the protein solution in a pre-determined concentration of cryoprotectant sugar to get a final phospholipid concentration of 10 mg/ml. The dispersion was sonicated for 5 min in a bath sonicator. The liposome solution was extruded around 8-10 times to obtain a uniform particle size of 100-200 nm. The solution was then frozen at −70° C. for 30 min and then thawed to 400° C. for 20 min. The process was repeated at least 9-10 times and the final sample was lyophilized after removal of excess protein using gel permeation chromatography.
c) Particle Size Measurement:
The particle size was measured by Dynamic light scattering (DLS) on a Brookhaven BI-200SM Research Goniometer and Laser Light Scattering System (5 mW He—Ne laser, λ=632 nm) using CONTIN software. To obtain the diffusion coefficient, the intensity correlation function must be analyzed. The hydrodynamic diameter and the particle size distribution were generated by the software. Accuracy of the data was determined based on polydispersity and baseline difference from the correlation curve. Particle size of the samples was measured at various stages and time intervals to determine the stability and shelf-life.
d) Encapsulation Efficiency:
The change in fluorescence signal can be used to assess the membrane permeability. The extent of the leakage from an encapsulated liposome due to contact with a certain solute was determined from the relative fluorescence (% F) of the leaked protein and is calculated by equation:
where, FT— Fluorescence of liposomes after incubation with solute
e) Transmission Electron Microscopy for Imaging
Briefly, a drop of a water-diluted suspension of the liposomes (about 0.05 mg/mL) was placed on a 200-mesh formvar copper grid (Electron Microscopy Sciences), allowed to adsorb and the surplus was removed by filter paper. A drop of 2% (w/v) aqueous solution of uranyl acetate was added and left in contact with the sample for 5 minutes. The surplus water was removed, and the sample was dried at room temperature before the vesicles were imaged with a TEM operating at an acceleration voltage of 200 KV.
f) Drug Release Studies:
In vitro drug release studies from Bevacizumab encapsulated liposomes were performed using USP 4 dissolution apparatus (SOTAX Corporation). The flow rate was maintained at 1 ml/min. Aliquots were removed at regular intervals and the concentration of the drug released was screened using UV-Vis spectrophotometry. The concentration of protein in the solution was measured based on the absorbance using the equation:
g) Accelerated Stability Studies:
Accelerated stability testing of the formulations was performed by subjecting the samples to temperatures at 4° C. and 37° C. for a period of 30 days. During this period, aliquots collected on days 1, 14 and 30 were tested for protein released into the solution. % leakage was calculated based amount of protein in solution to total amount of protein encapsulated. The aliquots were then subjected to differential scanning calorimetry to determine thermal stability of the protein.
h) Differential Scanning Calorimetry for Thermal Stability Analysis
Two mg of standard lipids, protein and liposome samples were loaded in aluminum pans along with the standard reference aluminum in the differential scanning calorimeter (Shimadzu DSC, et. al.). The thermal profiles were recorded between 10° C. and 180° C. at a scan rate of 15° C./min for three cycles.
i) ELISA for Determining Bevacizumab:
Sandwich ELISA was employed for determining free Bevacizumab in the aliquots using Eagle Biosciences Bevacizumab ELISA Assay Kit. 100 μL of assay buffer was added into each of the wells. 50 μL of each 1:1000 diluted standard, and 1:1000 diluted aliquots were added into the respective wells of the microtiter plate and then covered with adhesive seal. The plates were then incubated for 60 min at room temperature. The incubation solution is aspirated, and the plate was washed 3 times with 300 μL of diluted wash buffer per well. After removing excess solution, 100 μL of Enzyme Conjugate (HRP-anti human IgG mAb) was pipetted into each well, covered and incubated for 30 min at room temperature. Washing the plate is repeated 3 times with 300 μL of diluted wash buffer per well. Finally, 100 μL of Ready-to-Use TMB Substrate Solution was added into each well and incubated for 15 min at room temperature. The substrate reaction is stopped by adding 100 μL of stop solution into each well. The color changes from blue to yellow and optical density (OD) is measured with a photometer at 450 nm within 15 min after pipetting the stop solution.
j) In Vitro Toxicity Studies:
ARPE-19 cells purchased from American Type Culture Collection were used. Cells used for this study were from passages 10-35 and were maintained in Dulbecco's Modified Eagle Medium supplemented with 10% fetal bovine serum, 1.1% L-glutamine and 1.1% antibiotic/antimycotic. Cells were plated in 12-well plates with an initial seeding density of 5×104 cells per ml in each plate. Cells were grown to confluency for 4 days prior to experimentation; 12-well plates were used for MTT assays. 1.5 ml of 25 mg/ml Avastin solution was sterile filtered to create a stock solution that was transferred to a sterile centrifuge tube. Each well of the 12 well plate had its media aspirated out and was then rinsed with buffer which was also aspirated out. Each well was then treated such that triplicates of 0.5 mg, 1 mg, 2 mg of avastin and liposomes with encapsulated avastin were being tested in the wells against controls. Enough media was added to each well to create a total volume of 1 ml in each well. The treated cells were incubated for 69 hours before the MTT assay. 1.3 ml of 10% MTT 5 mg/ml in PBS and 11.7 ml of 90% media (with phenol red) was used. MTT in PBS was added to the media in a centrifuge tube and then sterile filtered. The filtered mixture was then plated on the 12 well plate (1 ml per well). The plate was then incubated for 90 minutes. After incubation, the MTT media was aspirated. 1 ml of DMSO per well was added. The MTT assay was read at 560 nm.
k) Animal Studies:
Dutch Belted rabbits were used in the study. Rabbits were sedated by general anesthesia using Ketamine 45 mg/kg subcutaneous, xylazine 5 mg/kg subcutaneous and acepromazine 1 mg/kg subcutaneous plus topical tetracaine or proparacaine. Group 1 received a dose of 1 mg avastin in the right eye. Group 2 received a dose comprising a total of 1 mg avastin which included about 10-15% free drug and 85-90% liposome encapsulated drug. Left eyes in the both groups of rabbits were used as controls. Imaging the eyes was commenced during week 1 after the injections and was performed on a weekly basis. For imaging, the animals were sedated using a lower dose of 25 mg/kg Ketamine and 2.5 mg/kg xylazine. The concentration of fluorescent tagged Bevacizumab released over the time period was measured non-invasively using the Fluorotron. The excitation source irradiates, through a band-pass filter, an aperture Re which is imaged by the optical system on the retina as a 1.9×0.1 mm slit in the eye. Light re-emitted (reflection and fluorescence) by the fluorescent tag on the protein is sampled from the 1.9×0.1 mm slit, aligned to the excitation and defined by an aperture Rd (which is confocal to Re). Lens B is used to scan Rd and Re along the optical axis. The excitation and detection pupils are defined by the apertures Pc, located very close to lens C. These pupils are imaged anterior to the subject's cornea by the optics. The configuration of these pupils is in the plane of the subject's pupil minimizes contributions from the fluorescence outside of the measurement point by separating the excitation and detection paths. Another band-pass filter rejects reflected excitation light, and the fluorescence collected by aperture Rd is detected using a red-extended end-on photomultiplier tube selected for low (<100 count/sec.) dark noise. As the focus lens is driven forward the emission signal is continuously monitored from retina to cornea at 0.1 mm intervals, giving an intensity output as auxiliary concentration in ng/ml.
Results of investigations to determine the role of formulation (composition) variation, presence of adjuvants and methods of preparation on the structural stability of liposomes and their effects on drug release are disclosed, the roles of phospholipids, cholesterol, and anti-oxidants are shown in
The effect of lipid composition on the size and hence stability of the liposomes have been examined by preparing liposomes with different molar ratios of phospholipids. The molar ratio of cholesterol was kept constant. The liposomes with high concentrations of phosphatidyl choline were giving the optimum size of 100-200 nm. The compositions with high concentration of phosphatidyl glycerol were found to promote fusion and the overall increase in particle size. This can be attributed to the oxidation of unsaturated fatty acids on phosphatidyl glycerol. From this result, the lesser the concentration of phosphatidyl glycerol, the lesser the chance of oxidation of the liposomes, thereby, increasing the stability and shelf life.
Dynamic light scattering (DLS) measurements of liposomes show that the ones with less cholesterol tend to be somewhat larger, on average, than liposomes with high cholesterol content. But in further studies, the higher concentration of cholesterol appeared to prevent the encapsulation of the encapsulated marker. So, an optimum concentration of cholesterol is required to have stable bilayers as well as optimum release. Use of 25-30 molar ratio of cholesterol gives very stable formulations.
Cantaxanthin and Beta carotene were used as anti-oxidants to prevent the fusion of liposomes due to oxidation. A dramatic difference in the particle size of liposomes at different phospholipid and cholesterol concentrations in the presence and absence of the anti-oxidants is seen in the graphs: (
Conventional liposome preparation techniques were used to prepare the liposomes. The efficiency of these methods was determined based on the resulting particle size, encapsulation efficiency and the time of release of encapsulated marker (Fluorescein).
Different combinations of phospholipids with or without cholesterol were mixed to total lipid concentration of 10 mM in chloroform-methanol mixture in ratio of 2:1. The mixture was rotovaped to get a thin film on the surface of the round bottom flask. The film was further flushed with argon for complete drying. Now, the lipid film was hydrated with the drug solution in phosphate buffer overnight. Finally the milky suspension was extruded using 0.4 and 0.2 μm polycarbonate filters.
Dispense 200 μl of 2.6 μM total phospholipids dissolved in choloroform in a glass test tube. Phosphatidyl choline and phosphatidyl serine are in the volume ratio of 4:1. The phospholipid mixture was dried under N2 or Argon. Then, it is further dried under vacuum for an additional hr. To this film, 2.6 ml of HEPES buffer saline containing drug was added at room temperature. The dispersion was left to hydrate for 1 hr and vortexed to resuspend the pellet to get a milky suspension. The liposome solution was sonicated to get a clear solution.
Different combinations of PC-cholesterol were dissolved in 2:1 chloroform-methanol mixture. The solvents were evaporated off using a rotovap under vacuum at 400° C. The lipid film was re-dissolved in ether to produce reverse phase vesicles. 20 mg of drug was dissolved in acetone and 6 ml of PBS (pH 7.4). The system was sonicated for 4 min in a bath sonicator. The organic phase was then evaporated using a rotovap. The liposomes were allowed to equilibrate at room temperature and then 10 ml PBS was added to liposome suspension, which was refrigerated overnight.
EPC, DPPE, DPPG and cholesterol were mixed at various molar ratios in a round bottom flask. To this, 2 ml of chloroform was added to make a uniform organic phase. The solvent was argon dried to get a uniform film of lipid layer. This lipid layer was hydrated using the protein solution in 0.32 M mannitol to get a final phospholipid concentration of 10 mg/ml. The dispersion was sonicated for 5 min in a bath sonicator. Now, the solution was frozen at −70° C. for 30 min and then thawed to 40° C. The process was repeated at least 6-7 times and the final sample was lyophilized after removal of excess protein.
Conclusion: The best 3 formulations were identified. Lipid hydration and extrusion method gave moderate encapsulation and optimum particle size. But, a problem was that the liposomes started to fuse. In case of mannitol freeze thaw method, the particle size was small and also the liposomes showed very good encapsulation. The problem with this method is that the liposomes leak the solute at a very fast rate due to osmotic imbalance inside and outside the liposomes. So, a modified method was used where both the lipid hydration and extrusion as well as the mannitol freeze thaw method were combined. Good particle size as well as very good encapsulation was achieved.
PEGylation is a process for surface modification of the liposomes in order to increase the circulation time of the liposomes after being introduced into the host. The PEGylation process does not change the structure of the liposomes, but helps in preventing the leakage of drug encapsulated as well protects the liposomes from enzymatic degradation.
EPC, DPPE or PE-PEG 2000, DPPG and cholesterol were mixed at various molar ratios in a round bottom flask. To this, 10 ml of 2:1 ratio of methanol-chloroform mixture was added to make a uniform organic phase. The solvent was removed by rotovap to get a uniform film of lipid layer. This lipid layer was hydrated using the drug solution in 0.32 M mannitol to get a final phospholipid concentration of 10 mg/ml. The dispersion was sonicated for 5 min in a bath sonicator. The liposome solution was extruded around 10 times to obtain a uniform particle size of around 200 nm. Now, the solution was frozen at −70° C. for 30 min and then thawed to 40° C. for 20 min. The process was repeated at least 9-10 times and the final sample was lyophilized after removal of excess drug.
EPC, DPPE or PE-PEG 2000, DPPG and cholesterol were mixed at various molar ratios in a round bottom flask. To this, 10 ml of 2:1 ratio of methanol-chloroform mixture containing anti-oxidants like beta carotene or cantaxanthin were added to make a uniform organic phase. The solvent was removed by rotovap to get a uniform film of lipid layer. This lipid layer was hydrated using the drug solution in 0.32 M mannitol to get a final phospholipid concentration of 10 mg/ml. The dispersion was sonicated for 5 min in a bath sonicator. The liposome solution was extruded around 10 times to obtain a uniform particle size of around 200 nm. Now, the solution was frozen at −70° C. for 30 min and then thawed to 400° C. for 20 min. The process was repeated at least 9-10 times and the final sample was lyophilized after removal of excess drug.
9.
One of the goals of this study was to increase the lifetime of the liposomes in order to avoid multiple drug administration. The second goal is to treat endophthalmitis and inflammation that results from invasive ocular surgeries especially cataract surgery. In order to do this, artificial lenses can be coated with liposomes containing the drug. Currently there are drug-eluting lenses available in the market, however these do not have a controlled drug release. The technology disclosed helps to control the dosage—the drug is incorporated in poly-lactic glycolic acid (PLGA) primary coating and also a secondary hydrophilic muco-adhesive coating matrix embedded with drug encapsulated liposomes. By using this method, the amount of drug that is administered is controlled and quantifiable.
A barrier that prevents the coating of the lenses is that they are composed of silicones that prevent hydrophilic solutions from adhering. In order to modify the hydrophobicity and allow for the liposome coating, oxygen plasma treatment was used. In this method, the surface of the lenses is temporarily modified by turning the silicon dioxide into silanol groups. The hydrophilic surface of the lens however is transient and lasts approximately 15-20 minutes. During this time, a primary coating of PLGA containing the drug is coated on to the lens using spin coating. PLGA is a hydrophilic polymer that is biodegradable and FDA approved. Different coatings containing PEG as a plasticizer and PLGA were used. The most efficient one was determined by using fluorescein in the PLGA and PEG coating solutions and visualizing the fluorescence using confocal laser scanning microscopy (CLSM). The most uniform coating was found to be the PLGA solution with 1% PEG. The imaging of all the coatings can be observed below.
The surface of the silicone lenses is temporarily modified by turning the silicon dioxide into silanol groups. The hydrophilic surface of the lens however is transient and lasts approximately 15-20 minutes. During this time, a primary coating of PLGA containing the drug is coated on to the lens using spin coating. PLGA is a hydrophilic polymer that is biodegradable and FDA approved. Different coatings containing PEG as a plasticizer and PLGA were used. The most efficient one was determined by using fluorescein in the PLGA and PEG coating solutions and visualizing the fluorescence using confocal laser scanning microscopy (CLSM). The most uniform coating was found to be the PLGA solution with 1% PEG.
On the top of the primary PLGA coating, a secondary coating was applied multiple times by spin coating. In order to find the most suitable coating three polymers were tested, which included methyl cellulose, hydroxyl propyl cellulose, and hyaluronic acid. To these solutions, rhodamine was added and the fluorescence intensity measurement using a dual scanning system was used to construct the topography on the lens based on the intensities. The imaging of the secondary coatings appear in (
Conventional liposomes used in this case released the encapsulated fluorescein over a period of 30 days. Uncoated fluorescein-PLGA films showed drug release with linear kinetics for 50 days, releasing fluorescein in the film, with no release thereafter. Coating of the fluorescein-PLGA film with HPMC (hydroxyl propyl methyl cellulose) entrapped liposomes resulted in significantly slower and longer release kinetics, providing about 4 months of release with zero-order kinetics. This might be due to the fact that HPMC doesn't form a hydrogel and is readily soluble in aqueous environment releasing the liposomes. On the other hand, fluorescein PLGA film coated with HA (hyaluronic acid) showed a further slower release over a period of 6 months. Hyaluronic acid is biodegradable, viscoelastic and has good water binding ability making it an ideal biopolymer for coating the silicone intraocular lenses. The drug release profiles from coated lenses can be seen in
In order to synthesize liposomes, different methods can be used. The method used herein for the encapsulation of fluorescein tagged human serum albumin was a combination of lipid hydration, extrusion and mannitol freeze thaw methods. The human serum albumin was used as a protein model that is close in molecular weight to Lucentis®.
When synthesizing liposomes using the modified method, the phospholipids are first dissolved using organic solvents such chloroform and methanol mixtures. In general the solutions are prepared by mixing 10-20 mg of phospholipids per milliliter of organic solvent. The phospholipids and organic solvents are then thoroughly mixed. Then, the solvents are evaporated using a rotary evaporator. The temperature of the solution was kept above the transitory temperature where the liposomes undergo a phase change. The evaporation of the solvents leaves behind a thin lipid film that is rehydrated by adding an aqueous medium that contains the drug that is to be encapsulated. During the rehydration time, the phospholipids are vigorously shaken and left overnight in order to improve the homogeneity of the size. The particle size of the liposomes was then reduced by extrusion. Extrusion is a method where pore size filters are used. The liposomes solution is force to go through the filter by increasing the pressure. The process results in liposomes with a uniform smaller particle size. Then, the liposomes are put through 10 freeze thaw cycles to improve the encapsulation efficiency. The solution is then lyophilized, which yields a fluffy substance. The advantage of using mannitol/trehalose in the procedure is that the encapsulation of the drug is increased. The efficiency of encapsulation can be increased by 20% as the number of freeze-thaw cycles increase. The modified method gave best results in terms of particle size as well as encapsulation. The size of the liposomes was then measured using dynamic light scattering as shown in the figure below. The TEM images of the formulations are displayed in
(a) Conventional Liposomes (
(b) Stealth Liposomes or PEGylated Liposomes (
Conventional liposomes are liposomes that do not contain any surface modifications. Although the liposomes protect the encapsulated molecule from degradation, when administered into the body they are easily captured by the mononuclear phagocyte system and are removed from the blood stream. The elimination of conventional liposomes is a great disadvantage since their degradation prevents the drug from reaching its target zone in the back of the eye. The removal of the liposomes from circulation first begins when opsonin serum proteins attach to the surface. These proteins mark the liposomes for degradation and allow the binding phagocytic cells to the liposomes.
In order to increase the circulation longevity of liposomes, surface modification by hydrophilic polymers can be employed. PEG is a hydrophilic polymer that is biocompatible and biodegradable. When a liposome surface is modified by PEG, the polymer provides a hydrophilic protective layer that is able to repel the adsorption of proteins, such as opsonin, through steric repulsion forces.
The size of the liposomes was then measured using dynamic light scattering as shown in the figure below. The encapsulation efficiency was determined based on the fluorescence of the tag on the protein. TEM images of the formulations are also displayed below. The drug release studies were performed using the SOTAX USP 4 dissolution apparatus. (
From the results that were obtained, it can be observed that PEGylation increased the time of drug release. The slower time release of drugs that are encapsulated using stealth liposomes validates that liposomes can be used as slow drug delivery systems. The slow release of the drug using liposomes thus can decrease the frequency of injections and the cost for the treatment of AMD and DR.
The purpose of this analysis was to optimize compositions of liposomal formulations to be used as drug delivery vehicles. Liposomes are versatile and can be used to encapsulate various ocular drugs ranging from small drugs to macromolecules like proteins. Some of the ocular drugs currently available in the market include Bevacizumab (Avastin), Ranibizumab (Lucentis), Gentamicin, Bacitracin, Polymyxin B, Gramicidin, Prednisolone, Dexamethasone, Neomycin, Flurbiprofen sodium, Chloramphenicol, Timolol, Ciloxan, Miconazole, Tobramycin and Triamcinolone.
The molecular level design of liposomes to carry protein drugs to treat ocular disease is useful to design liposomal formulations with varying degrees of lamellarity and size so as to obtain sustained release of the drugs. In addition, liposomes designed with PEG surface modification will minimize the toxicity of the drugs as well as increase the longevity of the liposomes.
In addition, looking at very small angle scattering, the interactions between different vesicles, should provide guidance to improve the stability of prepared suspensions. A number of parameters including the lipid composition, the liposome size, presence of adjuvants like anti-oxidants, cryo-protectants and the type of drug encapsulated are varied.
Selective labeling of lipids and drugs with heavy elements such as Bromine may increase the sensitivity of the x-rays to obtain more refined structural details. Consequently examination of a single lipid-drug system provide SAXS patterns between neat liposomes, liposomes with drug encapsulations and stealth liposomes (PEGylated liposomes). Brominated drugs may enhance feature contrast in the SAXS patterns, and the tolerance of the samples to X-ray damage.
SAXS experiments were conducted using different liposomal formulations—conventional liposomes, conventional liposomes with anti-oxidant Vitamin F and liposomes with a cryoprotectant. The particle size was measured using Dynamic Light Scattering as shown in Table 3.
The scattered intensity curve features two regimes corresponding to two different length scales. In the case of low polydispersity unilamellar vesicles (ULVs), high frequency oscillations are observed at length scales corresponding to q<0.03 A°. These oscillations originate from scattering taking place over the entire vesicle and are inversely proportional to the ULV's radius, R. However, this feature decays quickly with increasing q. Scattering information from q>0.03 A° is mostly attributed to the bilayer itself. For these experiments, the scattering intensities were measured between 0.002-0.02 A° and the scattering profiles in this region can be seen as follows. From the data obtained, scattering from cryoprotectant freeze dried liposomes appears to be due to interaction of mannitol with the lipid bilayers and also the diffusion of mannitol between the layers helping in creating an osmotic balance.
The scattering intensities between 0.002-0.02 A° were measured and the scattering profiles in this region can be seen as above. From the data obtained, it appears that the scattering from cryoprotectant freeze dried liposomes might be due to interaction of mannitol with the lipid bilayers and also the diffusion of mannitol between the layers helping in creating an osmotic balance.
Free unentrapped drug was separated from the liposomes by centrifugation at 17000 rpm for 1 hr at 4° C. The pellets formed were washed with distilled water twice and then re-suspended, centrifuged again for 1 hr.
The change in fluorescence signal can be used to assess the membrane permeability. Interactions of certain solutes such as some drugs or antimicrobial peptides could reduce the stability and/or change the permeability of the bilayer membrane. The extent of the leakage from an encapsulated liposome due to contact with a certain solute is determined from the relative fluorescence (% F) of the leaked marker and is calculated by equation—
Where,
Ft— Fluorescence of liposomes after incubation with solute
F0— Initial fluorescence due to dilution in an isomolar buffer
F∞— Maximal fluorescence after lysis by Triton X-100
The particle size was measured by Dynamic light scattering (DLS) on a Brookhaven BI-200SM Research Goniometer and Laser Light Scattering System (5 mW He—Ne laser, λ=632 nm) using CONTIN software. Cumulant analysis was used to obtain the particle size distribution from the correlograms generated by the software. The temperature was fixed at 25° C. This random motion is modeled by the Stokes-Einstein equation. Below the equation is given in the form most often used for particle size analysis.
Where,
Dh is the hydrodynamic diameter
Dt is the translational diffusion coefficient
kB is Boltzmann's constant
T is thermodynamic temperature
η is dynamic viscosity
Briefly, a drop of a water-diluted suspension of the liposomes (about 0.05 mg/mL) was placed on a 200-mesh formvar copper grid, allowed to adsorb and the surplus was removed by filter paper. A drop of 2% (w/v) aqueous solution of uranyl acetate was added and left in contact with the sample for 5 minutes. The surplus water was removed and the sample was dried at room conditions before the vesicles were imaged with a TEM operating at an acceleration voltage of 200 KV
Drug release studies were performed using USP 4 dissolution apparatus (SOTAX Corporation). The flow rate was maintained at 0.5 ml/min. Aliquots were removed at regular intervals and the concentration of the drug released was measured using fluorescence spectrophotometry.
The primary coating solution was prepared by mixing appropriate pre-evaluated amounts of PLGA in volatile solvent. The PLGA solution is spin coated at 4000 rpm on plasma treated intraocular lenses. The lyophilized liposomes were mixed into a hydrophilic coating material and coated on the top of PLGA smeared IOLs and vacuum dried for 24 hr. The final products are stored in a sealed container and stored appropriately till further use. Using the primary coated lenses, a secondary coating was applied again by spin coating. In order to find the most suitable coating three polymers were tested, which included methyl cellulose, hydroxyl propyl cellulose, and hyaluronic acid. To these solutions, rhodamine was added and the fluorescence intensity measurement using a dual scanning system was used to construct the topography on the lens based on the intensities.
CLSM analysis was performed with a Zeiss LSM 5 Pascal Confocal Laser Scanning Microscope equipped with Argon (458, 488, and 514 nm) and HeNe (543 nm) lasers. In order to characterize and select the ideal composition for the coatings, Rhodamine was mixed with the PLGA coating and fluorescein encapsulated liposomes in hydrophilic coating material were used for secondary coating.
Drug release studies were performed using USP 4 dissolution apparatus (SOTAX Corporation). The coated IOLs were placed in the flow cells such that the buffer would wash the coating as well as the liposomes from the surface of the lenses over a period of time. The flow rate was maintained at 0.5 ml/min. Aliquots were removed at regular intervals and the concentration of the drug released was measured using fluorescence spectrophotometry.
The lipid mixture was made using 100 mg of egg phosphatidyl choline (PC), 40 mg of cholesterol and 10 mg of phosphatidyl glycerol (PG), in 5 ml of chloroform/methanol solvent mixture (2:1 vol./vol). The lipid solution was introduced into a 250 ml round bottom flask with a ground glass neck. The flask was attached to a rotary evaporator. The liquid was evaporated from the solution, and a dry lipid film was deposited on the walls of the flask. Then, 5 ml of drug solution was added to the film and mixed vigorously for 30 min. The suspension, so formed, was left for 24 hours for the liposomes to swell. In order to get unilamellar liposomes, the solution was sonicated for 1 hour. The particle size was measured using Dynamic Light Scattering®.
A series of encapsulated drugs are described that are suitable to coat IOLs, contact lenses and ocular stents. The drugs are encapsulated in liposomes which are in turn embedded in a polymer coating that is then applied to a contact lens, intraocular lens or an ocular stent. The embedded drugs are useful to treat various maladies such as dry eye or infection after cataract surgery, including treatment with an antibiotic or with prednisolone to fight post-operative inflammation. Other embedded drugs include antibiotics such as gatifloxicin, anti-inflammatories such as dexamethasone, prednisolone and other steroids.
Anti-vascular endothelial growth factor (Anti-VEGF) drugs and antioxidants are also used to treat age-related macular degeneration (AMD) and related conditions. The value of these nanodrugs is that they result in a slow release of the drug, increasing its residence time. For example, antioxidants are a class of drugs that are the phosphorylated thiols. The thiol is released in a cell via the hydrolysis of the phosphate by alkaline phosphatase, which can then control oxidative destructive processes.
One aspect of the methods disclosed herein is the detection of drugs following the release of highly fluorescent materials, such as fluorescein, from the coated IOL, which is placed in a cuvette. The stability of each coating, the concentration of the released compound, and the time it takes to release the compound, are determined. All of these parameters are necessary to determine the feasibility of the use of each emulsion in the human eye. In order to extrapolate to human use, animal experiments are performed in conjunction with an ophthalmologist. First, fluorescence is detected throughout the eye. However, because most drugs are not fluorescent, other methods are also suitable.
1. Fluorescence
Fluorescein was used as an encapsulated compound (substance) in each of the emulsions tested because its release can be readily detected. A fluorotron detects fluorescein directly, for example, in a rabbit model. From these studies the release of drugs are timed and estimates are made of the final concentrations released.
The optical components of a Fluorotron are a platform for a prototype.
The steady state experiment is more sensitive than the pulsed method, is monitored continuously and readily scanned from the back of the eye to the front. But the intensity of the fluorescence is determined in part by the concentration of fluorophore. This can be circumvented by determining the concentration of the probe. The pulsed method takes more time, but the lifetime is invariant with concentration which is ascertained directly from the measurements. These methods are therefore complimentary.
2. Direct Detection
There are two types of strategies for ocular drug delivery. Relatively short term treatments as would be needed for infections after surgery, or long term treatments with drugs that slow the growth of new blood vessels. (This is a major complication of diseases such as age-related macular degeneration and diabetic and myopic retinopathy.) In each case, vehicles such as liposomes and emulsions that are either suspensions or embedded in coatings that are applied to prosthetic devices, are used and the drug(s) are slowly released over time. As examples, the solutions can be directly injected into the vitreous and the coatings can be used on intraocular lens (IOL) implants that are inserted during cataract surgery. In each case, it is essential to determine how long the drug will be released and what concentration it will attain. Fluorescein, a fluorescent dye, is encapsulated in the vehicles (vesicles e.g. liposomes) and while encapsulated, no fluorescence is observed. As the fluorescein is slowly released out into the solution, an increase in fluorescence intensity is observed. This serves to compare various nanoparticle formulations, but does not give insight into the treatment using real drugs such as coatings with antibiotics for prevention of post-operative endophthalmitis or with prednisone, dexamethasone or other steroid drugs for prevention of post-operative inflammation. Further, the fluorescence assay does not give any information on the changes in drug concentration as a function of time.
In order to determine real drug concentrations that are being released, an apparatus is needed such as the SOTAX® flow-through cell systems (
The concentration of drug is then assessed using any appropriate analytical technique such as UV-Visible spectroscopy, high pressure liquid chromatography (HPLC) or mass spectrometry.
Cataract. Cataracts are changes in clarity of the natural lens inside the eye by the accumulation of turbulent fluid, which gradually degrades visual quality. Cataract surgery can be a very successful treatment for the restoration of vision. During surgery, the clouded lens, i.e. turbulent fluid, is removed and replaced with a clear, intra ocular lens.
Intra Ocular Lens (IOL). An intraocular lens (IOL) is a lens implanted in the eye used to treat cataracts or myopia. Thick eye glasses or special contact lenses that were previously required to see after cataract surgery have been replaced by several types of IOL implants. The main function of an IOL is to focus light on to the retina. Light rays are then converted into electrical impulses that travel to the brain, where they are then converted into images.
IOLs are round, corrective central portions of the lens with two arms or haptics. IOLs allow investigations of the sustained release of therapeutic levels of drugs for a desired period of time, thus overcoming the Blood Retinal Barrier (BRB) associated with systemic drug delivery. Varieties of IOL styles available for implantation include: monofocal lens; toric lens; and multifocal lens.
Structure of IOL. (
Drugs Used. The drugs used include sulfate drops, antibiotics (antibacterials) and anti-inflammatory drugs. An example of an antibacterial drug is Vancomycin. An example of an anti-inflammatory drug is Alclofenac. The drugs to be used also include hydrophilic and hydrophobic drugs. Hence, reverse micelle and liposomes are used for encapsulation of the drug.
More particularly, ocular drugs include Bevacizumab (Avastin), RTH258 (brolucizumab), Ranibizumab (Lucentis), Pegaptanib (Macugen), Aflibercept (Eylea), Atropine, Flurbiprofen, Physostimine, Azopt, Gentamicin, Pilocarpine, Bacitracin, Goniosol, Polymyxin B, Betadine, Gramicidin, Prednisolone, Betaxolol, Humorsol, Proparacaine, Betoptic, Hylartin, Propine, Brinzolamide, Hypertonic NaCl, Puralube, BSS, Indocycanine Green, Rose Bengal, Carbachol, Itraconazole, Sodium Hyaluronate, Cefazolin, Latanoprost, Suprofen, Celluvisc, Mannitol, Terramycin, Chloramphenicol, Methazolamide, Timolol, Ciloxan, Miconazole, Tobramycin, Ciprofloxacin, Miostat, Triamcinolone, Cosopt, Muro 128, Trifluridine, Demecarium, Neomycin, Tropicamide, Dexamethasone, Neptazane, Trusopt, Dipivefrin, Ocuflo, Vidarabine, Dorzolamide, Ofloxacin, Vira-A, Epinephrine, Oxytetracycline, Viroptic, Fluorescein, Phenylephrine and X alatan.”
Problems with Ocular Therapy: Problems with ocular therapy include multi drug resistance and systemic toxicity due to high doses. The method outlined here would obviate the latter problem because the drugs will be released slowly.
Liposomes: Liposomes are water-in-oil-in-water (w/o/w) emulsions with closed bilayer membranes that contain an entrapped aqueous volume. Liposomes encapsulate both hydrophilic and hydrophobic molecules. Liposomes are of two types: multilamellar vesicles (MLVs) and large unilamellar vesicles (LUVs).
Encapsulation of Drugs: Hydrophilic drugs are encapsulated in water in oil emulsions. The water in oil emulsion is titrated against the aqueous phase and surfactant, which leads to the formation of liposomes (i.e. w/o/w emulsion).
Liposome Procedures: Unilamellar (1-3) and multilamellar liposomes are prepared by standard methods and from commercially available phospholipids such as phosphatidylcholine and phosphatidylethanolamine. The drug-encapsulating liposomes are used as a liquid suspension (for intraocular injection) or attached to the surface of an IOL, stent or contact lens. Attachment is achieved by covalent tethering (4) or by embedding in a biocompatible hydrogel. (Lin and Marra, 2012; Mawood et al. 2012).
Preparation of water in oil emulsion (Inverted Micelles): Oil was heated gently on a low flame. Surfactant was then added to the oil phase and low heating was maintained with continuous stirring. Aqueous drug solution was added dropwise to this phase, maintaining low heat and continuous stirring.
Sustained Release (SR) Technology. Slow release of a drug over a time period may or may not be controlled release. Drug concentration varies with time because the initial release of a drug is sufficient to provide a therapeutic dose soon after the administration, and then there is a gradual release over an extended period.
Fluorescence intensity studies using nanoparticles/microparticles on IOLs showed that there is an increase in the intensity with respect to time. Increase in fluorescence intensities supports the prolonged release of the drug at a predetermined rate by maintaining a constant drug level at a specified period of time.
Advantages of SR: The advantages of sustained release technology include uniform release of drug substance over time, reduction in frequency of intakes, reduced side effects, and better patient compliance.
IOL Coating. An important part of the sustained release forms are biodegradable, highly flexible polymeric coatings with sustained release effect.
Purpose of coating: The purpose of the IOL coating includes: obtaining functional coats, i.e. coats that are stable and slowly release the drugs, providing chemical stability, and enhancing patient acceptance.
Preparation of the coated formulation: A polymer was dissolved in a suitable carrier solvent. Freeze dried liposome powderwas added to prepare a coating solution. Coating formulations were then applied on the IOL implants. Coated IOL implants were then placed in a suitablecontainer.
Sustained drug delivery using IOLs for the treatment of AMD is contemplated. The technique is simple, non-invasive and should improve the ocular bioavailability, therapeutic efficacy and patient compliance of the treatment substance.
PC—Phosphatidyl choline
PE—Phosphatidyl ethanolamine
PG—Phosphatidyl glycerol
PE-PEG 2000-1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (ammonium salt)
TEM—transmission electron microscopy
SAXS—Small angle X-ray Scattering
Summary of Methods to Prepare Lipid Vesicles (Ranging from 30 NM to 50 μM)
Part I Diameter: 30 nm-50 nm (SUV-Small Unilamellar Vesicle)
The shelf-time of these small lipid vesicles is very short due to their high surface tension. They are usually used immediately after preparation.
Two methods can be used to produce them.
The same procedures as in Part II, but choose a PC membrane with smaller pore size (30 nm-50 nm).
Make stock solution: dissolve DMPC lipids in chloroform initially to make 8 mg/ml concentrated lipid solution (stock solution).
Sample solution: use ˜0.23 g of stock solution, which should give ˜1.2 mg of DMPC lipid, and dilute the concentrated stock solution in more chloroform.
Evaporation: Blow-dry the dilute lipid sample using nitrogen for 2 hours to evacuate the solvent of chloroform.
Hydration: add ˜1.2 ml PBS buffer to hydrate the dry lipid sample as soon as the chloroform is all evaporated.
Sonication: Insert the titanium-tip sonicator inside the lipid suspension and do sonication. Vesicle size and distribution depend on sonication power, frequency and time.
Part II Diameter: 80 nm-800 nm (LUV—Large Unilamellar Vesicle)
The typical method to make LUV is “extrusion.” The detailed procedures are summarized as follows. Note that vesicles produced by this method are usually more polydisperse at larger sizes.
1. Make stock solution: dissolve DMPC lipids in chloroform initially to make 8 mg/ml concentrated lipid solution (stock solution).
2. Sample solution: use ˜0.45 g of stock solution, which should give ˜2.4 mg of DMPC lipid, and dilute the concentrated stock solution in more chloroform.
3. Evaporation: Blow-dry the dilute lipid sample using nitrogen for 2 hours to evacuate the solvent of chloroform.
4. Hydration: add ˜2.4 ml PBS buffer to hydrate the dry lipid sample as soon as the chloroform is all evaporated.
5. Incubation: Place the sample container in a sand bath at ˜40 deg. C. for 2 hours. During the 2 hours of incubation, mix the sample once every 10 minutes using a vortexer.
6. Freeze/thaw: Immerse the sample in liquid nitrogen followed by boiling water for 5 cycles totally.
7. Extrusion: assemble the membrane inside the extruder:
(1) Wet the Teflon piece with buffer;
(2) Place 2 pieces of membrane support in the center of the Teflon piece;
(3) Add a drop of water before putting the PC membrane;
(4) Put the PC membrane with proper pore size on the taller piece of the holder;
(5) Add a drop of buffer on top of the membrane;
(6) Place 2 pieces of Teflon holder together;
(7) Turn up the heater underneath the extruder to above Tm, and place the syringe on the heater to warm up;
(8) Fill the lipid solution into the syringe, and extrude 11 times;
(9) Eject the extruded sample from the acceptor syringe. The solution should look clearer than that before extrusion.
8. Cleaning: The Teflon piece, o-ring and syringe should be rinsed with copious 2-propanol and DI water after use. Otherwise the residues will contaminate your next sample.
Bearing in mind that even though there are various methods to make GUVs, the key principle is similar, encouraging dried lipid films to swell and form giant vesicles. Here are five typical methods of making GUV.
As is well known, LUVs are not stable in suspension because of vesicle fusion with each other. This method is taking the advantage of inter-vesicle fusion to form giant vesicles. This method is very simple, but it is inefficient to produce vesicles larger than 10 μm.
1. Prepare LUV: See Part II for details.
2. Prepare GUV: Keep the LUV suspension at room temperature for 1-2 days. Giant vesicles with diameter less than 10 μm formed massively in the suspension.
This method is widely used to produce GUVs with various components and inclusions. Advantages: (a) vesicle size is well controlled by tuning the electric field; (b) detaching vesicles from the Pt wires is possible; (c) transfer of the GUVs to other medium from the open chamber; (d) all GUVs are unilamellar. Disadvantages: (a) Time-consuming—each sample preparation needs many hours to clean the chamber; (b) Inefficient—just a few GUVs can be produced each time due to the small amount of lipids used for each sample; (c) It is tricky to add lipid stock solution onto the Pt wires.
This method is a derivative of method 2; using ITO glass to replace Pt wire. Compared with method 2, it has the advantages of (a) being much faster—there is no need to clean the chamber or other devices before sample preparation; (b) producing many GUVs each time; (c) making GUV patterning on ITO-coated glass surface possible. Disadvantages: (a) Because the two ITO glasses are glued together, it is hard to collect GUVs and transfer them somewhere else.
Advantages: (a) This method is very simple; (b) It takes several minutes to form GUVs; (c) Most of the GUVs are unilamellar. Disadvantages: (a) GUV size is relatively small, ˜10 μm; (b) it is hard to remove vesicles from the substrate surface;
Advantages: (a) Efficient—each sample preparation produces many GUVs; (b) It is very easy to generate osmotic pressure to the GUVs by controlling internal and external solute concentration. Disadvantages: (a) It uses too much sucrose, 100-500 mM, which may affect other measurements; (b) GUVs are not always unilamellar.
(a) 500 ml of Triton X-100 (0.485 mg) was dissolved in 4 ml of ethyl acetate to form organic/oil phase.
(b) a hydrophobic drug, i.e. 23 uM or 0.0948 gm in 10 ml of fluorscein, was prepared and 1 ml of water phase was taken from that solution.
(c) water phase was titrated drop by drop into organic phase by constant stirring to form w/o emulsion.
(d) heat the above emulsion until left with 3 ml of emulsion.
(e) 500 mg of PVA was dissolved in 40 ml of water. The w/o emulsion from (d) was added drop by drop to form w/o/w emulsion.
(f) 500 ml of Triton X-100 was dissolved in 10 ml of ethyl acetate. The liposomes from 9(e) were added to final organic phase.
Observation: milky white emulsion was formed and the colour of fluorescein solution disappeared.
(a) 200 mg of chitosan was dissolved in 40 ml of 2% artic acid solution.
(b) 1 ml of PEG was added to this solution.
(c) the solution was heated at 90° C. to form a viscous fluid.
(d) the product was sonicated for 1 hour.
Addition of nonparticle solution into the above mixture gave a homogenous solution.
1) dissolve riboflavin in ethyl acetate and prepare an organic phase by adding cellulose derivatives and heating at 50° C.
2) dissolve carbomer (0.4 g) in 20 ml of water and heat at 50° C. to form the aqueous phase.
3) add organic phase to the aqueous phase in a drop-wise manner under high shear.
4) heat the solution above 78° C. to remove ethyl acetate;
5) final solution is clear.
1) DLS was used
2) particle size—400 nm.
Need to change surfactant.
Preparation of w/o/w Microemulsion
1) florescein and carbomer were dissolved in water and heater.
2) this aqueous phase was poured in a drop-wise fashion into the oil phase containing vit-F and cellulose.
3) finally the w/o emulsion was added in a drop-wise manner into an aqueous phase containing polyvinyl alcohol.
Observation: w/o emulsion was good; w/o/w emulsion was not stable→may be because of less surfaction.
(a) 1 gm of chitosan was dissolved in 25 ml of 2.8% acetic acid and then 25 ml of ethanol was added.
(b) Little pyridine was dropped into the mixing solution until the solution because clear.
(c) Excess acetic anhydride was added.
(d) The solution was stirred at 25° C. for 2 hours.
(e) Formation of a clear semisolid can be observed.
(f) The reaction mixture was precipitated with ethanol.
(g) The precipitate was filtered out and washed with acetone to remove excess reactant.
N-acetylated chitosan was dried at 50° C.
(a) equimolar cone of riboflavin and HP-βCD and 0.28 gm of riboflaving)
(b) mixture was agitated for 48 hours at room temperature and filtered through 0.45 μm membrane filter and the filtrate was lypophilized.
(a) equimolar proportion of riboflavin in ethanol was added dropwise to HPβCD aq. Soln. the solution was stirred for 2 hours using a magnetic stirrer.
(b) obtained soln. was evaporated under vacuum at 50° C. The residue was finally dried at 40° C. for 24 hours.
H1 and c13 NMR of Chitosan and HP-β-CD
(a) 50 mg of riboflavin was mixed with different concentrations of HP-β-CD (5, 10, 15, 20, 25, 30 mM)
(b) the mixture was stirred on rotary shaker for 72 hours at 37° C.
(c) after reaching equilibrium, samples were filtered through a 0.2 μm filter and suitably analyzed using UV-vis spectrophotometer.
10 ml Chitosan soln (2 mg/ml) in 2% acetic and 4 ml TPP soln. (2 mg/ml) in D.I. water.
The above solutions were mixed and turbidity observed. On subjecting this solution to Dynamic Light Scattering, particles in the rage of 3000 nm were observed.
60 mg of chitosan in 20 ml of 2% acetic and 1 ml of 1% TPP adjusted pH 3 using HCl.
The above solutions were mixed and turbidity was observed. Need to increase the volume of TPP soln.
(a) 50 mg of riboflavin was mixed with different concentrations of methyl-β-cyclodextrin (5, 10, 15, 20, 25, 30 mM).
(b) The mixture was stirred for 72 hrs. on a rotary shaker at 37° C.
(c) After reaching equilibrium, samples were filtered through 0.2 μm membrane filter & analyzed using a spectrophotometer.
(a) Equimolar concentration (0.05M) of riboflavin (0.188 gm) was mixed with methyl Betacylodextrin (0.66 gm) and stirred for 48 hrs. with agitation in 50 ml of water.
(b) The mixture was filtered through a 0.2 μm membrane filter and analyzed using UV-vis spectroscopy.
Technique: Dynamic Light Scattering
Temp: 25° C.
Solutions: Riboflavin nanoparticles (Cyclodextrin). Control cyclodextrin solution.
Results: Nanoparticles—129 nm. Cyclodextrin—13.9 nm
(a) 50 mg of riboflavin was mixed with 5, 10, 15, 20, 25, & 30 mM methyl cyclodextrin in 3 ml of water.
(b) The solutions were left to equilibrate for 3 days on a shaker.
(c) After filtration, the solutions were analyzed by UV-vis spectroscopy.
Different niosomal preparations were made using lipid hydration.
Result: 1:1 ratio gave a particle size of 212 nm. (from DLS data)
The methyl β-cyclodestrin & hydroxy propyl beta cyclodextrin solutions were filtered.
The UV-vis absorption spectrum was obtained for each solution.
The data was used to plot a phase solubility curve for both the cyclodextrine.
Result: Solubility for methyl β CD—31.07 mg/ml.
Prepare 0.069 1/1 w/v chitosan solution in 4.6 mM HCl at pH 5 by adding IM NaOH. 0.0138 gm of chitosan was dissolved in 20 ml of 4.6 mM HCl.
The final solution was stored in refrigerator to check the stability.
50 mg of ofloxacin was added to each sample and then shaken for 72 hrs to attain equilibrium.
Result: Solubility was found to be 35.04 mg/ml.
Result: Average particle size was found to be 413 nm.
The chitosan nanoparticles prepared on Oct. 9, 2012 were coated using HA.
(a) 0.5% w/v chitosan in 1% arctic and solution was prepared—Solution 1.
(b) Adjust the pH of soln. 1 to 4.1 using 10 N NaOH.
10 ml of 2.5 mg/ml TPP solution was prepared—Soln. 2.
Solution 2 was added in a drop wise manner to 30 ml of solution 1.
This mixture was stirred at 1000 rpm for 15 minutes.
This was used for hydrophobic drugs which are soluble in alcohol.
Excess vit-E was dissolved in 5 ml of alcohol & the drug was dissolved in this solution. The solution is coated on a surface & left to dry at 100° C. for 1 hr. to get a uniform coating.
Particle size was found to be 379 nm. (Size distribution profile in data folder.)
Observation—Silicone sticks to glass. Need to change base to prepare the lenses.
1:1:1 ration of fluorescein, span 20 & cholesterol, each 200 mg was dissolved in 6 ml of diethyl ether. It was mixed with 2 ml of methanol containing dye after rotovaping the ether. The solution was left to equilibrate for 24 hrs. Particle size was found to be 565 nm.
Result: 1:1.5:1 ratio of dye:span:cholesterol gave the least particle size & are pretty stable.
Cellulose derivative Plasticizer.
a) Methyl cellulose (MC) PEG
b) Hydroxyl propyl methyl cellulose (HPMC) PEG
c) MC ethylene glycol
d) HPMC ethylene glycol
10% w/v solutions of cellulose derivatives with 2.5% plasticizer were prepared and located on to the prototype lenses.
Results PEG works better.
Procedure:—
a) 3% acetic acid was prepared
b) Different concentrations of acidic chitosan solutions were prepared, 2 mg/ml, 1 mg/ml, 0.7 mg/ml, 0.5 mg/ml, 0.3 mg/ml, 0.1 mg/ml
c) Different concentrations of TPP solutions were prepared—0.2, 0.4, 0.6, 0.8 and 1.0 mg/ml
d) Combinations of both the solutions were prepared and sonicated at 20 min.
e) These solutions were centrifuged at 15000 rpm for 10 min.
a) Water soluble chitosan coating
b) Vitamin E barrier coating
c) Methyl cellulose coating (with PEG)
d) HPMC coating (with PEG)
e) Hyaluronic acid coating (with PEG and PVA)
The coating solutions prepared, were coated onto glass slides by spin coating. The samples were let to air dry/vacuum dry depending on the material used.
a) 3 mg/ml of riboflavin was added to the chitosan solution (20 ml).
b) 3.5% w/v of chitosan solution was prepared using 2% acetic acid solution
c) 15 ml of 0.4% STPP soln. was added in a dropwise manner to the chitosan solution
d) A suspension was formed
a) 100 mg of BSA was dissolved in the chitosan solution
b) 3.5% w/v of chitosan solution was prepared by dissolving chitosan in 2% acetic acid soln.
c) 15 ml of 0.4% STPP soln. was added drop-wise
d) A clear solution was formed.
e) It has to be further visualized using TEM for formation of nanoparticles
Chitosan—citric acid coating soln.
Different concentrations of citric acid ranging from 25% to 55% was added into 10 ml of acetone. 10-20% of PEG and 30-35% of chitosan were added. Citric acid, PEG and chitosan constitute up to 4% of the total ingredients added to acetone. Citric acid is added to create an acidic environment to dissolve small amounts of chitosan.
a) Prepare a solution of chitosan in 2% glacial acetic acid to produce 3-5% w/v solution and add 0.5 ml of PEG-200.
b) Homogenize the solution at 2000 rpm.
c) Degar by sonication at 25° C. for 20 min.
d) The chitosan soln. was cast on a polycarbonate petri dish and dried at 45° C. for 48 hours.
Dissolve 40 mg of chitosan in 10 ml of 1% acetic acid solution by constant stirring.
Take 5 ml. of the above solution and add 5 ml of acetone.
It produces a homogenous mixture.
Now add 0.5 ml of PEG to work as a plasticizer
Store in refrigerator.
93 ± 2.1
89 ± 3.2
This application is a Continuation-in-Part of co-pending U.S. patent application Ser. No. 14/907,745, filed Jan. 26, 2016, which is a U.S. nationalization under 35 U.S.C. § 371 of International Application No. PCT/US2014/051134, filed Aug. 14, 2014, which claims priority to U.S. Provisional Application No. 61/866,810, filed Aug. 16, 2013. The disclosures set forth in the referenced applications are incorporated herein by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| 61866810 | Aug 2013 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14907745 | Jan 2016 | US |
| Child | 15945338 | US |
