Patent Grant
7399743
The present invention relates to the fields of blood coagulation, thrombosis, tumor angiogenesis, and cancer therapy. The present invention provides various compositions and methods to treat solid tumors by inducing site-selective thrombosis in tumor blood vessels.
Although many advances in cancer therapy have been made during the last thirty years, many prevalent forms of human cancer currently resist chemotherapeutic intervention. For example, prostate cancer is the second leading cause of cancer death in men. The incidence of prostate cancer has increased 141.8% between 1973 and 1994. In 1998, new prostate cancer cases totaled 184,500, representing about one new case every three minutes, and 29% of all new cancer cases in American men. In 1998, an estimated 39,200 men died of prostate cancer. A life is lost to prostate cancer in this country every 13 minutes. According to the National Cancer Institute, the annual cost of prostate cancer to the country, including medical care, lost wages and lost productivity, may be as high as $15 billion.
Certain types of tumors are more amenable to therapy than others because they are more accessible to therapeutic agents. For example, soft tissue tumors such as lymphomas, and tumors of the blood and blood-forming organs such as leukemia, have generally been more responsive to chemotherapeutic therapy than have solid tumors such as carcinomas. One reason for the susceptibility of soft and blood-based tumors to chemotherapy is that they are physically more accessible to chemotherapeutic intervention. It is simply more difficult for most chemotherapeutic agents to reach all of the cells of a solid tumor mass than it is for such agents to reach the cells of soft tumors and blood-based tumors. While it is possible to increase dosages, chemotherapeutic agents are toxic at higher doses. Hence, conventional anti-tumor agents generally have a limited range of effectiveness against solid tumors and a need exists for the development of novel strategies for the treatment of solid tumors.
One strategy for treating solid tumors is to use anti-tumor cell antibodies to deliver a toxin to the tumor cells. However, this method suffers from certain drawbacks. For example, antigen-negative or antigen-deficient cells can survive to repopulate the tumor or lead to further metastasis. Also, a solid tumor is generally impermeable to large molecules like antibodies, especially when linked to a toxin molecule.
Recently, there is increasing interest in developing methods to induce site-selective thrombosis within blood vessels of a selected tissue and thereby infarct and destroy that tissue. This approach derived from the notion that in order for a tumor to grow beyond a critical size, it must recruit and activate endothelial cells to form its own new microvasculature (Denekamp 1990; Folkman 1992). Some investigators have therefore targeted tumor blood vessels for destruction in order to destroy the supply of oxygen and nutrients needed for local tumor cells to proliferate and survive (Huang, Molema et al. 1997).
WO 96/01653 discloses antibodies against tumor vasculature markers to deliver thrombogens to the vasculature of solid tumors. Vascular targeting strategies are also described in Burrows et al. (1992), in Burrows and Thorpe (1993) and in WO 93/17715. U.S. Pat. No. 6,156,321 discloses that a truncated form of Tissue Factor can bind to A20 lymphoma cells when co-administered with a bispecific non-neutralizing antibody that binds to Tissue Factor and to an antigen on the A20 lymphoma cells.
The invention provides Selective Tissue Vascular Thrombogens (STVTs) that can induce targeted thrombosis, infarction and destruction of selected tissues, for example, tumors. Targeting the blood vessels of tumors has certain advantages in that it is not likely to lead to the development of resistant tumor cells or populations thereof. Delivery of Selective Tissue Vascular Thrombogens to blood vessels avoids the accessibility problems associated with targeting cells that are deep within a solid tumor. Moreover, destruction of the blood vessels may have an amplified anti-tumor effect because many tumor cells rely on a single vessel for their oxygen and nutrient supply.
The Selective Tissue Vascular Thrombogens (STVTs) of the invention are novel proteins having at least two functional domains. The first functional domain is a Tissue Factor polypeptide that can induce thrombogenesis, for example, the extracellular domain of Tissue Factor. The second functional domain is a Selective Binding Domain that can selectively bind to a cell-specific or tissue-specific molecule. Preferably, the Selective Binding Domain can bind to a molecule within a tumor, for example, a molecule on the luminal surface of a tumor blood channel. Upon binding, the Tissue Factor polypeptide can induce thrombosis.
Additional domains may be incorporated into the Selective Tissue Vascular Thrombogens of the invention. For example, Selective Tissue Vascular Thrombogens can include membrane associating domains or transmembrane domains of any protein known to one of skill in the art. Other domains that can be incorporated into the Selective Tissue Vascular Thrombogens of the invention include spacer domains to optimize spacing and/or interaction or non-interaction between elements of the domains.
Selective Binding Domains selectively localize the Selective Tissue Vascular Thrombogens, for example, a thrombogenic Tissue Factor domain, to a particular cell type, a particular tissue or a particular tumor type. However, to efficiently induce thrombosis, the Selective Binding Domain is selected to bind to a component within a blood channel. More than one Selective Binding Domain can be incorporated into the Selective Tissue Vascular Thrombogens of the invention, for example, to enhance thrombogenic function, and to increase the selectivity of localization or the selectivity of action.
According to the invention, certain tumor cells can form channels that mimic the function of blood vessels. The channels formed by such tumor cells are deep within the solid tumor and join with the normal circulatory system of the animal at the periphery of the tumor. Hence, Selective Binding Domains are preferably tumor cell membrane proteins that allow the Selective Tissue Vascular Thrombogens of the invention to bind with specificity to a selected tumor cell type.
Accordingly, the invention provides a Selective Tissue Vascular Thrombogen comprising a Selective Binding Domain associated with a Tissue Factor polypeptide. The Selective Binding Domain can bind to a channel for blood within a tissue and the human tissue factor can initiate thrombosis within the channel. The Selective Tissue Vascular Thrombogen can be made by covalent or non-covalent association of the Tissue Factor polypeptide with the Selective Binding Domain.
Such Selective Tissue Vascular Thrombogens can bind to channels within any tissue, for example, within a solid tumor. Such tissues can be lung, breast, ovary, stomach, pancreas, larynx, esophagus, testes, liver, parotid, biliary tract, colon, rectum, cervix, uterus, endometrium, kidney, bladder, prostate, thyroid, benign prostate hyperplasia, squamous cell carcinoma, adenocarcinoma, small cell carcinoma, melanoma, glioma, or neuroblastoma tissues or tumors. In one embodiment, the tissue is a prostate tumor. The Tissue Factor polypeptide is preferably a human Tissue Factor polypeptide, for example, a polypeptide comprising SEQ ID NO:3, SEQ ID NO:4, SEQ ID NO:5 or SEQ ID NO:6.
The Selective Binding Domain can be any molecule, peptide or polypeptide that can selectively bind or associate with a selected cell or tissue type. For example, the Selective Binding Domain can be a ligand for a cellular receptor, a receptor for a cellular ligand, or an inhibitor for a membrane-associated protein. The selective binding domain can, for example, bind selectively to endoglin, integrin, VEGF receptor, a glycosaminoglycan or Prostate Specific Membrane Antigen. In one embodiment, the selective binding domain is an integrin binding site from fibronectin. In another embodiment, the selective binding domain is an inhibitor of prostate specific membrane antigen, for example, Asp-β-Glu, N-succinyl-glutamic acid or quisqalic acid.
In certain embodiments, the Selective Tissue Vascular Thrombogen has SEQ ID NO:9 or SEQ ID NO:10.
The invention also provides therapeutic compositions comprising a therapeutically effective amount of at least one Selective Tissue Vascular Thrombogen of the invention and a pharmaceutically acceptable carrier, wherein the Selective Tissue Vascular Thrombogen comprises a Selective Binding Domain associated, fused or attached to a Tissue Factor polypeptide, wherein the Selective Binding Domain can bind to a channel for blood within a tissue and the Tissue Factor polypeptide can initiate a coagulation protease cascade within the channel. The Selective Tissue Vascular Thrombogen composition can also include a chemotherapeutic agent, a Factor VII polypeptide or a Factor VIIa polypeptide. Liposomes are one example of pharmaceutically acceptable carrier for the present compositions. In general, the therapeutic compositions are administered intravenously.
The invention further provides a method of treating a solid tumor in an animal that comprises administering a therapeutically effective amount of a Selective Tissue Vascular Thrombogen comprising a Selective Binding Domain fused or attached to a Tissue Factor polypeptide, wherein the Selective Binding Domain can bind to a channel for blood within a tumor and the human tissue factor can induce coagulation within the channel. The compositions of the invention can also be used in such therapeutic methods.
Together,
The present invention provides new compositions and methods for targeted thrombosis at selected vascular sites within an animal, for example, within tumors. Such targeted thrombosis is achieved by administering novel Tissue-Selective Vascular Thrombogens and compositions thereof. Such Tissue-Selective Vascular Thrombogens contain at least two domains. The first domain comprises a coagulation-activating Tissue Factor polypeptide. The second domain is a Selective Binding Domain. The Selective Binding Domain can recognize and bind to a selected cell type, for example, a specific tumor cell type. More than one Tissue Factor polypeptide and/or more than one Selective Binding Domain can be included in the Tissue-Selective Vascular Thrombogens of the invention.
Other domains can be incorporated into the Tissue-Selective Vascular Thrombogens of the invention. Such additional domains can be used, for example, to help spatially orient one or more of the other domains, to add additional Selective Binding Domains, to facilitate insertion of the Tissue-Selective Vascular Thrombogen into a cell membrane, to orient the Tissue-Selective Vascular Thrombogen with the cell surface or to enhance, or prevent neutralization of, the activity of the Tissue-Selective Vascular Thrombogen.
These compositions and methods can be used to activate the thrombogenic cascade in the tumor blood vessels, thereby blocking blood flow to the tumor and killing tumor cells within the tumor. The present invention provides that such compositions may be administered alone, in combination with conventional chemotherapeutics, in combination with Factor VIIa or other factors involved in the cascade of events leading to localized thrombogenesis.
Target Diseases
Angiogenesis in undesired locations is involved in wide range of diseases. The concepts, compositions and methods provided by this invention are broadly applicable to the treatment of any disease that has a vascular component, including benign or malignant tumors. Such vasculature-associated diseases include benign prostate hyperplasia (BPH), diabetic retinopathy, vascular restenosis, arteriovenous malformations (AVM), meningioma, hemangioma, neovascular glaucoma and psoriasis; and also angiofibroma, arthritis, atherosclerotic plaques, corneal graft neovascularization, hemophilic joints, hypertrophic scars, osler-weber syndrome, pyogenic granuloma retrolental fibroplasia, scleroderma, trachoma, vascular adhesions, synovitis, dermatitis and even endometriosis.
An important application of the present compositions and methods is to treat solid tumors. Typical vascularized tumors are the solid tumors, particularly carcinomas, which require a vascular component for the provision of oxygen and nutrients via the blood. Exemplary solid tumors that may be treated using the invention include, but are not limited to, carcinomas of the lung, breast, ovary, stomach, pancreas, larynx, esophagus, testes, liver, parotid, biliary tract, colon, rectum, cervix, uterus, endometrium, kidney, bladder, prostate, thyroid, squamous cell carcinomas, adenocarcinomas, small cell carcinomas, melanomas, gliomas, neuroblastomas, and the like.
Table 1 is provided for the purpose of exemplifying human tumor cell lines that are publicly available. The information presented in Table 1 is provides by means of an example, and not intended to be limiting either by year or by scope. One of skill in the art may consult the ATCC Catalogue of any subsequent year to identify other appropriate cell lines. Also, if a particular cell type is desired, the means for obtaining such cells, and/or their instantly available source, will be known to those of skill in the particular art. An analysis of the scientific literature can thus readily reveal an appropriate choice of cell for any tumor cell type to be targeted.
Tissue Factor
According to the invention, any Tissue Factor polypeptide that can initiate thrombosis and that includes the extracellular domain of Tissue factor can be used as the Tissue Factor domain of the present Selective Tissue Vascular Thrombogens. The Tissue Factor polypeptide can be mutant or wild type. The Tissue Factor polypeptide can include all of the extracellular domain or part of it. Preferably, the Tissue Factor polypeptide is not the full-length native Tissue Factor. For example, the Tissue Factor polypeptide generally lacks the cytoplasmic domain, and may have none or only a part of the transmembrane domain.
Tissue Factor is the major receptor for initiating thrombogenic (blood coagulation) cascades (Davie, et al. 1991). Human Tissue Factor has been cloned and is available to those of skill in the art (Morrissey et al., 1987; Edgington et al., 1991; U.S. Pat. No. 5,110,730). In certain early studies, the same protein currently identified as human Tissue Factor may be referred to as human Tissue Factor heavy chain protein or the heavy chain of Tissue Factor. The gene encodes a polypeptide precursor of 295 amino acids in length, which includes a peptide leader with alternative cleavage sites, which is lead to the formation of a protein of 263 amino acids in length. Mature Tissue Factor is a single chain, 263 amino acid membrane glycoprotein (SEQ ID NO:2), and its primary sequence has structural similarity with the cytokine receptor family (Edgington et al., 1991). The recombinant expression of human Tissue Factor in CHO cells has been reported to lead to the production of Tissue Factor at a level that is described as being one of the highest expression levels reported for a recombinant transmembrane receptor following production in mammalian cells (Rehemtulla et al., 1991).
The amino acid sequence of the precursor form of human Tissue Factor (SEQ ID NO:1) is provided below:
The amino acid sequence of the mature form of human Tissue Factor (SEQ ID NO:2) is provided below:
The amino acid sequence of the extracellular domain of human Tissue Factor (SEQ ID NO:3), which is sometimes called TF1-219, is provided below:
The amino acid sequence of a slightly shorter extracellular domain of human Tissue Factor (SEQ ID NO:4), which is sometimes called TF1-218, is provided below:
A slightly truncated extracellular domain of human Tissue Factor that is sometimes called TF3-219 (SEQ ID NO:5), because it does not have the first two amino acids of SEQ ID NO:3, can also be used as a Tissue Factor polypeptide in the Tissue-Selective Vascular Thrombogens of the invention. This TF3-219 polypeptide has SEQ ID NO:5, provided below:
A similar amino acid sequence of a slightly truncated extracellular domain of human Tissue Factor that is sometimes called TF3-218 (SEQ ID NO:6), because it does not have the first two amino acids of SEQ ID NO:3, can also be used as a Tissue Factor polypeptide in the Tissue-Selective Vascular Thrombogens of the invention. This TF3-218 polypeptide has SEQ ID NO:6, provided below:
Moreover, the C-terminal end of the Tissue Factor polypeptide can be manipulated as desired by one of skill in the art. For example, the transmembrane domain of Tissue Factor starts at about amino acid 220 and ends at about amino position 241. This domain and the cytoplasmic sequences that lie C-terminal to this domain can be removed and replaced with other polypeptide sequences, for example, other tranmembrane domains. In addition, a peptide comprising approximate amino acid position 211 to approximate amino acid position 219 can be removed and replaced with any convenient peptide sequence that can link a transmembrane domain to the active portion of Tissue Factor. Any such manipulations can be performed to modify or enhance the activity or membrane association propertied of the STVT, so long as the Tissue Factor domain retains activity and is capable of initiated a thrombogenic response.
A number of domains can be used to facilitate association of Tissue Factor with a selected cellular membrane. For example, a membrane association domain can be provided by the Selective Binding Domain or by any membrane protein or member of the Superfamily of Hematopoietic-Cytokine Receptors selected by one of skill in the art. In one embodiment, the Selective Tissue Vascular Thrombogens of the invention includes the entire transmembrane domain of human Tissue Factor, or a portion thereof. The amino acid sequence of the transmembrane domain of human Tissue Factor (SEQ ID NO:7) is provided below:
Tissue Factor is a transmembrane cell surface receptor. Tissue Factor functions as the receptor and requisite cofactor for Factors VII and VIIa. Tissue Factor binds Factor VIIa to form a proteolytically active binary complex on the cell surface (Ruf and Edgington, 1991 b, 1994; Ruf et al., 1991, 1992a, 1992b). This complex rapidly activates the serine protease zymogens Factors IX and X by limited proteolysis, leading to the formation of thrombin and, then to the conversion of plasma fibrinogen to fibrin resulting in gelation of plasma and blood.
A limited number of cells constitutively express Tissue Factor. Lung and central nervous system tissues contain high levels of Tissue Factor activity, with Tissue Factor being found in bronchial mucosa and alveolar epithelial cells in the lung and in glial cells and astrocytes in the nervous system. Expression of Tissue Factor has also been reported in cardiac myocytes, renal glomeruli, and in certain epithelial or mucosal tissues of the intestine, bladder and respiratory tract. Over expression of Tissue Factor has been linked to thrombotic diseases and sepsis (Drake, Morrissey et al. 1989; Levi, ten Cate et al. 1994). Tissue Factor expression on endothelial cells and monocytes is induced by exposure to inflammatory cytokines and bacterial lipopolysaccaride (Drake and Pang 1989; Oeth, Pany et al. 1994). There can also be very small amounts of Tissue Factor associated with membrane vesicles shed by cells into the blood. Tissue Factor is generally constitutively expressed at tissue barriers between body tissues and the external environment (Drake et al., 1989; Ruf and Edgington, 1994). The expression of Tissue Factor in this manner acts as an envelope that allows Tissue Factor to arrest bleeding.
The disruption of the Tissue Factor gene in mice revealed an unexpected role for Tissue Factor in supporting vascular development (Carmeliet, Mackman et al. 1996). Beside the roles it has in hemostasis and thrombosis, Tissue Factor is also implicated in signal transduction (Zioncheck, Roy et al. 1992), cellular adhesion (Ott, Fischer et al. 1998), and the tumor metastasis and angiogenesis (Mueller and Ruf 1998).
Tissue Factor is typically not expressed to any significant degree on blood cells or on the surface of endothelial cells that form the vasculature, but such expression can be induced in endothelial cells and monocytes within the vasculature by infectious agents and certain inflammatory processes. Monocytes, for example, are induced to express Tissue Factor by cytokines and T cells. Expression of Tissue Factor in the vasculature can result in disseminated intravascular coagulation or localized initiation of blood clots or thrombogenesis. In this context, it is important to note that Tissue Factor must be available at all sites of the body where hemostasis would be necessary following tissue damage, infection or other insults.
Tissue Factor is the major initiator of the blood coagulation protease cascades and is generally not in direct contact with the blood under physiologically normal conditions (Osterud et al., 1986; Nemerson, 1988; Broze, 1992; Ruf and Edgington, 1994). After vascular damage or activation by certain cytokines or endotoxin, however, Tissue Factor is exposed to the blood by the exposure of (sub)endothelial tissue and cells (Weiss et al., 1989), by induction within the endothelium, or by certain blood cells (Warr et al., 1990). Tissue Factor then complexes with Factor VII and VIIa, which under normal conditions circulate at low concentrations in the blood (Wildgoose et al., 1992). The Tissue Factor:Factor VII complex is converted to a Tissue Factor:Factor VIIa complex. The Tissue Factor/Factor VIIa complex starts the coagulation cascade through the activation of Factor X to Factor Xa. Ultimately, the cascade results in formation of thrombin that produces fibrin.
For this sequence of events to occur, the Tissue Factor:Factor VIIa complex must be associated with a supportive phospholipid membrane surface in order for efficient assembly of the coagulation-initiation complexes with Factors IX or X (Ruf and Edgington, 1991a; Ruf et al., 1992c; Paborsky et al., 1991; Bach et al., 1986; Krishnaswamy et al., 1992; ten Cate et al., 1993). The association of Tissue Factor with an anionic phospholipid membrane increases the coagulative activity of this complex by promoting the proper orientation of Factor VIIa relative to Tissue Factor through the interaction of Gla domain of Factor VIIa with phospholipid. This enhances the binding of Factor VIIa to Tissue Factor, facilitates the catalytic conversion of Factor VII to Factor VIIa, and enhances the activity of Tissue Factor:Factor VIIa toward its substrates, Factor X and Factor IX. It also provides a cellular membrane binding for Factor X and Factor IX.
A recombinant form of Tissue Factor has been constructed that contains only the cell surface or extracellular domain (Ruf et al., 1991b; Stone, et al., 1995) and that lacks the transmembrane and cytoplasmic regions of Tissue Factor. This truncated Tissue Factor is 219 amino acids in length and is a soluble protein with approximately 105 times less factor X-activating activity than native Tissue Factor in an appropriate phospholipid membrane environment (Ruf, et al., 1991b). This difference in activity is related to the association of Tissue Factor and the lack of membrane-association by truncated Tissue Factor. The Tissue Factor:VIIa complex binds and activates Factors IX and X far more efficiently when associated with a negatively charged phospholipid surface (Ruf, et al., 1991b; Paborsky, et al., 1991). Consequently, the native transmembrane Tissue Factor is 100,000 fold more active than the soluble Tissue Factor extracellular domain. In order to achieve site-selective induction of thrombosis to occlude undesired vessels under pathologic conditions using Tissue Factor, a soluble Tissue Factor molecule that retains coagulative function upon proper positioning onto a cell surface structure is desirable.
However, according to the present invention, the extracellular domain of Tissue Factor, without the natural transmembrane and cytoplasmic regions of Tissue Factor, can promote blood coagulation when properly associated with a cellular membrane by any “Selective Binding Domain.”
Selective Binding Domains
A Selective Binding Domain is a peptide, peptidyl analogue or polypeptide that can associate with a cellular membrane, through direct interaction with the membrane or through interaction with a protein present on the membrane, or both. Association with the cellular membrane by the Selective Binding Domain need only be transient, however, it must be selective so that the Selective Tissue Vascular Thrombogen can provide targeted, localized thrombosis.
One or more Selective Binding Domains are associated or integrated with one or more Tissue Factor polypeptides to form a Selective Tissue Vascular Thrombogen. Association between the Tissue Factor polypeptide(s) and the Selective Binding Domain(s) can be via a covalent bond, or via any other stable interaction, such as by hydrogen bonding.
A Selective Binding domain can be a ligand for a cellular receptor, a membrane-associated domain for any cell membrane protein known to one of skill in the art, an inhibitor for a membrane-associated protein, a component of tumor vasculature, a component that binds to, or is generally associated with, tumor cells, a component that binds to, or is generally associated with, tumor vasculature, a component of the tumor extracellular matrix or stroma, a cell found within the tumor vasculature or any peptide or polypeptide that preferentially interacts with a cellular membrane. In general the Selective Binding domain is preferably not an antibody.
Selective Binding domains can be made to bind to any relatively specific marker on the tumor cell, for example, endoglin, integrin, VEGF receptor, PSMA and the like. Many so-called “tumor antigens” have been described, any one which could be employed as a target to which the Selective Binding domain may bind. A large number of exemplary solid tumor-associated antigens are listed herein in Table 2.
abbreviations: Abs, antibodies; Ags, antigens; EGF, epidermal growth factor; GI, gastrointestinal; GICA, gastrointestinal-associated antigen; GP, glycoprotein; GY, gynecological; HMFG, human milk fat globule; Kd, kilodaltons; Mabs, monoclonal antibodies; Mr, molecular weight; NS, not specified; PLAP, placental alkaline phosphatase; TAG, tumor-associated glycoprotein; CEA, carcinoembryonic antigen. Note: the CA 199 Ag (GICA) is sialosylfucosyllactotetraosylceramide, also termed sialylated Lewis pentaglycosyl ceramide or sialyated lacto N-fucopentaose II; p97 Ags are believed to be chondroitin sulphate proteoglycan; antigens reactive with Mab 9.2.27 are believed to be sialylated glycoproteins associated with chondroitin sulphate proteoglycan; unless specified, GY can include cancers of the cervix, endocervix, endometrium, fallopian tube, ovary, vagina or mixed Mullerian tumor; unless specified GI can include cancers of the liver, small intestine, spleen, pancreas, stomach and oesophagus.
In one embodiment, the Selective Binding Domain is an inhibitor of prostate specific membrane antigen (PSMA) or folate glutamate hydrolase. Prostate specific membrane antigen (PSMA) is a signal marker for prostate that is over-expressed in prostate carcinoma, especially in advanced tumors. The PSMA protein is a glutamyl preferring carboxypeptidase that can release glutamate with either gamma or alpha linkages. New data indicates that PSMA is selectively expressed and apparently present on the endothelial surface of tumor microvasculature.
According to the invention, endothelial-like tumor cells that express PSMA can undergo a novel differentiation process termed “vasculogenic mimicry.” Such vasculogenic mimicry occurs when such endothelial-like tumor cells form vessels within solid prostate tumors. These tumor vessels connect with the normal circulatory system and may provide blood nutrients and oxygen to the interior of solid tumors. Therefore, according to the invention, proteins that are expressed on endothelial-like solid tumor cells can serve as recognition sites or targets for the Selective Tissue Vascular Thrombogens of the invention.
PSMA is one such target for the Selective Tissue Vascular Thrombogens of the invention. According to the invention, any molecule that can bind to PSMA can be used as a Selective Binding Domain for a Selective Tissue Vascular Thrombogen that can be used to treat prostate tumors. Selective Binding Domains that can be used to target PSMA include PSMA inhibitors and modified substrates, for example, the dipeptide Asp-β, linked-Glu (DβE), and N-succinyl-glutamic acid. The Asp-β linked-Glu dipeptide is a suicidal inhibitor of the PSMA protease. According to the invention, a Asp-β linked-Glu-biotin:avidin-Tissue Factor:VIIa thrombogen complex induces tumor infarction in PSMA expressing prostate tumors without harming the animal.
In another embodiment, inhibitors of N-Acetylated α-Linked Acidic Dipeptidase (NAALADase) are used as the Selective Binding Domain to deliver the thrombogen to the selected target. Examples of such NAALADase inhibitors include phosphonate moieties, such as 2-(phosphonomethyl)pentanedioic acid. Further examples include the following:
2-Methylhydroxyphosphinyl oxypentanedioic acid;
2-Ethylhydroxyphosphinyl oxypentanedioic acid;
2-Propylhydroxyphosphinyl oxypentanedioic acid;
2-Butylhydroxyphosphinyl oxypentanedioic acid;
2-Phenylhydroxyphosphinyl oxypentanedioic acid;
2-(Phenylmethyl)hydroxyphosphinyl oxypentanedioic acid;
(2-Phenylethyl)methyl)hydroxyphosphinyl oxypentanedioic acid.
Another group of NAALADase enzyme inhibitors that can be used to deliver the present thrombogen contain phosphoramidates and related groups, for example:
Methylhydroxyphosphinyl glutamic acid;
Ethylhydroxyphosphinyl glutamic acid;
Propylhydroxyphosphinyl glutamic acid;
Butylhydroxyphosphinyl glutamic acid;
Phenylhydroxyphosphinyl glutamic acid;
(Phenylmethyl)hydroxyphosphinyl glutamic acid;
((2-Phenylethyl)methyl)hydroxyphosphinyl glutamic acid; and
Methyl-N->Phenylhydroxyphosphinyl glutamic acid.
Another group of NAALADase enzyme inhibitors that can be used to deliver thrombogens have a phosphinic acid group. Such inhibitors contain any one of the following moieties:
2-methylhydroxyphosphinyl methylpentanedioic acid;
2-ethylhydroxyphosphinyl methylpentanedioic acid;
2-propylhydroxyphosphinyl methylpentanedioic acid;
2-butylhydroxyphosphinyl methylpentanedioic acid;
2-cylobexylhydroxyphosphinyl methylpentanedioic acid;
2-phenylhydroxyphosphinyl methylpentanedioic acid;
2-(phenylmethyl) hydroxyphosphinyl methylpentanedioic acid;
2-((2-phenylethyl)methyl)hydroxyphosphinyl methylpentanedioic acid;
2-((3-phenylpropyl)methyl)hydroxyphosphinyl methylpentanedioic acid;
2-((3-phenylbutyl)methyl)hydroxyphosphinyl methylpentanedioic acid;
2-((2-phenylbutyl)methyl)hydroxyphosphinyl methylpentanedioic acid;
2-(4-phenylbutyl) hydroxyphosphinyl methylpentanedioic acid;
2-(aminomethyl) hydroxyphosphinyl methylpentanedioic acid.
Certain sulfoxide and sulfone derivatives also act as inhibitors of NAALADase enzymes and can be used to deliver the thrombogen of the invention. Such inhibitors contain any one of the following moieties:
2-(sulfinyl)methylpentanedioic acid;
2-(methylsulfinyl)methylpentanedioic acid;
2-(ethylsulfinyl)methylpentanedioic acid;
2-(propylsulfinyl)methylpentanedioic acid;
2-(butylsulfinyl)methylpentanedioic acid;
2-(phenylsulfinyl methylpentanedioic acid;
2-(2-phenylethyl)sulfinyl methylpentanedioic acid;
2-(3-phenylpropyl)sulfinyl methylpentanedioic acid;
2-(4-pyridyl)sulfinyl methylpentanedioic acid; and
2-(benzylsulfinyl)methylpentanedioic acid.
2-(sulfonyl)methylpentanedioic acid;
2-(methylsulfonyl)methylpentanedioic acid;
2-(ethylsulfonyl)methylpentanedioic acid;
2-(propylsulfonyl)methylpentanedioic acid;
2-(butylsulfonyl)methylpentanedioic acid;
2-(phenylsulfonyl)methylpentanedioic acid;
2-(2-phenylethyl)sulfonyl methylpentanedioic acid;
2-(3-phenylpropyl)sulfonyl methylpentanedioic acid;
2-(4-pyridyl)sulfonylmethylpentanedioic acid; and
2-(N-hydroxy)carbamoyl methylpentanedioic acid;
Yet another group of NAALADase inhibitors contain hydroxamic acid moieties. Examples of such moieties include the following.
2-(N-hydroxy-N-methyl)carbamoyl methylpentanedioic acid;
2-(N-butyl-N-hydroxy)carbamoyl methylpentanedioic acid;
2-(N-benzyl-N-hydroxy)carbamoyl methylpentanedioic acid;
2-(N-hydroxy-N-phenyl)carbamoyl methylpentanedioic acid;
2-(N-hydroxy-N-2-phenylethyl) carbamoylmethylpentanedioic acid;
2-(N-ethyl-N-hydroxy)carbamoyl methylpentanedioic acid;
2-(N-hydroxy-N-propyl)carbamoylmethylpentanedioic acid;
2-(N-hydroxy-N-3-phenylpropyl)carbamoyl methylpentanedioic acid; and
2-(N-hydroxy-N-4-pyridyl)carbamoyl methylpentanedioic acid
2-(benzylsulfonyl)methylpentanedioic acid.
One of skill in the art can readily prepare and integrate these types of moieties and inhibitor molecules into the Selective Tissue Vascular Thrombogens of the invention with one or more Tissue Factor polypeptides using available procedures. See, e.g., U.S. Pat. Nos. 5,795,877; 5,863,536; 5,902,817; 5,968,915; and 5,880,112.
Another Selective Binding domain contemplated by the invention is a peptide or polypeptide containing an Arg-Gly-Asp (RGD) tripeptide sequence. Any RGD-containing Selective Binding Domain that can bind to an integrin is contemplated by the invention. A number of integrins exist and, according to the invention, such integrin subtypes will all support the coagulative activity of a Tissue Factor:RGD Selective Binding Domain construct. For example, VLA is the major integrin expressed on the CHO cell surface, and the Alpha V beta III integrins are reported to be expressed on angiogenic tumor vessels. Inhibition of alpha V beta III integrin with LM609 antibody was shown to inhibit angiogenesis and tumor growth (Brooks, Montgomery et al. 1994). According to the invention, RGD Selective Binding Domain:Tissue Factor constructs can be used to occlude blood vessels within integrin-expressing tumors.
One type of RGD bearing Selective Binding Domain useful in the invention can be derived from the extra-cellular matrix glycoprotein fibronectin. Fibronectin contains a number of domains that mediate its association with integrin molecules. One region of fibronectin that mediates its interaction with integrin is the Central Cell Binding Domain (CCBD). This region contains a number of homologous repeating polypeptide modules termed Fibronectin Type III Repeats, each being about 90 amino acids residues long. An RGD sequence, located in the tenth Fibronectin type III repeat, is a key recognition site for several different integrins, including the Alpha5beta 1 integrin family.
According to the invention, synthetic peptides having the RGD sequence and the Fibronectin type III repeat domains 8-11 are a useful Selective Binding Domains that can successfully confer coagulative properties to the surface of the cells that are otherwise inactive. Alternatively, one may use only the fibronectin 10th type III repeat domain.
In one embodiment, the Selective Binding Domain is selected from human fibronectin, having, for example, SEQ ID NO:8.
The selected Selective Binding Domain can be fused, attached or associated with a Tissue Factor polypeptide to generate The Selective Tissue Vascular Thrombogen by any available procedure. For example, the Tissue Factor extracellular domain (e.g., SEQ ID NO:3, 4, 5 or 6) can be made by known procedures. Such a Tissue Factor polypeptide can be modified to contain a convenient attachment site or moiety at any location that does not substantially interfere with initiation of thrombosis. One convenient attachment site is the N-terminus of the Tissue Factor polypeptide.
In one embodiment, the Selective Binding Domain is fused to the Tissue Factor polypeptide by use of recombinant technology. One of skill in the art can readily employ known cloning procedures to fuse a nucleic acid encoding the desired Selective Binding Domain to a nucleic acid encoding a Tissue Factor polypeptide. See, e.g., Sambrook et al., Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Laboratory, N.Y., 1989; Sambrook et al., Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Laboratory, N.Y., 2001.
The selected Selective Binding Domain can also be attached or associated to a Tissue Factor polypeptide by formation of covalent or non-covalent bonds. Such attachment or association can be done directly or indirectly to the N-terminus, or other convenient site, on the Tissue Factor polypeptide. For example, an indirect attachment or association can be achieved via a convenient reactive moiety or through a flexible linker to facilitate formation of the Selective Tissue Vascular Thrombogen and/or to promote proper association between the Tissue Factor polypeptide and the cellular membrane to which it will associate. Use of such a linker to achieve optimal integration and functioning of the domains within the Selective Tissue Vascular Thrombogen is at the discretion of one of skill in the art, who can readily ascertain whether membrane association by the Tissue Factor-Selective Binding Domain protein is improved by use of a linker.
By way of example, attachment of a Selective Binding Domain can be at the N-terminus of a Tissue Factor polypeptide that has been modified to contain a reactive moiety, for example a cysteine, at the N-terminus. A cysteine can be attached to the N-terminus of Tissue Factor, for example, by attaching a peptide containing poly His tag and a processing protease (FXa) cleavage site followed by a cysteine (MXXX-HHHHHH-XXXX-IEGR-C, SEQ ID NO:18) to the N-terminus of Tissue Factor (SEQ ID NO:6). Factor Xa digestion cleaves off the majority of this peptide but leaves a cysteine at the N-terminus of the Tissue Factor polypeptide. This Cys-Tissue Factor polypeptide can then be attached to a desired Selective Binding Domain by available protein ligation reactions (see, e.g., Erlanson, Chytil et al. 1996).
A Selective Binding Domain comprising a compound, peptide or polypeptide can therefore be linked to the N-terminus of the Tissue Factor extracellular domain (SEQ ID NO:3, 4, 5 or 6) through a disulfide bond. Alternatively, such a Selective Binding Domain can be linked to a lysine containing linker and then attached to a Cys-Tissue Factor polypeptide by a thiazolidine ring formed by reaction the cysteine and the lysine (see, e.g., Zhang, Torgerson et al. 1998). One such lysine containing linker is KSGGG (SEQ ID NO:19). In one embodiment, the D-β-E dipeptide is attached to the C-terminal glycine of SEQ ID NO:19 and this seven-amino acid peptide is linked to an N-terminal cysteine of a Tissue Factor polypeptide via a thiazolidine ring formed by reaction the cysteine and the lysine.
In another embodiment, a biotin and streptavidin can be used to associate a Selective Binding Domain with a Tissue Factor polypeptide. Because the binding of biotin to streptavidin is so stable, there is no need for covalent linkage. Instead, biotin can be linked to a Selective Binding Domain and Streptavidin can be linked to a selected Tissue Factor polypeptide. The two preparations can be incubated together to form a Selective Binding Domain-biotin:streptavidin-Tissue Factor complex that is a functional Selective Tissue Vascular Thrombogen. Of course, one of skill in the art can, alternatively, link streptavidin to a Selective Binding Domain and biotin to a Tissue Factor polypeptide to achieve a similar complex.
One such biotin:streptavidin Selective Tissue Vascular Thrombogen was made and tested for thrombogenic activity. This complex had a biotinylated PSMA inhibitor, Asp-β-linked-L-Glutamate (DβE ), as a Selective Binding Domain. A streptavidin moiety was N-terminally attached to the extracellular domain of Tissue Factor (SEQ ID NO:5). After incubation of the two domains a DβE-biotin:streptavidin-Tissue Factor complex was formed. Injection of this complex into animals leads to extensive thrombosis and necrosis of tumors within the animals.
Before use as a therapeutic agent, the Selective Tissue Vascular Thrombogens can be mixed with Factor VIIa under conditions permitting formation of the functional Selective Tissue Vascular Thrombogen:Factor VIIa thrombogenic complex.
Specific Selective Tissue Vascular Thrombogens
In one embodiment, the Selective Tissue Vascular Thrombogen has a Selective Binding Domain that is an integrin binding site comprising the Fibronectin type III repeat domains 8-11 from human fibronectin. One example of this type of Selective Tissue Vascular Thrombogen has SEQ ID NO:9:
In another embodiment, the Selective Tissue Vascular Thrombogen has a Selective Binding Domain that is an integrin binding site from the Fibronectin 10th type III repeat domain of human fibronectin fused to an extracellular domain of Tissue Factor. An example of this type of Selective Tissue Vascular Thrombogen has SEQ ID NO:10:
Methods of Use
The invention provides a method of treating a solid tumor in an animal that includes administering a therapeutically effective amount of a Selective Tissue Vascular Thrombogen of the invention to the animal. Such a Selective Tissue Vascular Thrombogen has at least one Selective Binding Domain associated with one or more thrombogenically active Tissue Factor polypeptides. Additional domains can be added to achieve optimized localization and/or thrombogenic activity. As described above, the Selective Binding Domain can selectively bind to a blood channel within a tumor and the Tissue Factor Domain can induce localized thrombin production and thrombosis within the blood channel. According to the invention, such thrombosis results in tumor infarction and necrosis. In a preferred embodiment, the Selective Tissue Vascular Thrombogen, and compositions of the invention are administered intravenously in solution or, alternatively, in liposomes.
In another embodiment, the invention provides methods of inhibiting tumor vascularization by administering PSMA inhibitors. According to the invention, PSMA can influence vascularization of prostate tumors. Moreover, inhibitors of PSMA activity can exert a cytotoxic effect on prostate tumor cells that express PSMA. PSMA inhibitors can also have a synergistically beneficial effect when administered with other chemotherapeutic agents and with the Selective Tissue Vascular Thrombogens of the invention.
The balance between gamma-glutamate hydrolase and synthase activity is known to effect cancer cell susceptibility to anti-folate chemotherapy. Over-expression of gamma glutamyl hydroxylase activity, which is an activity of PSMA, can promote to cancer cell resistance to anti-folate drugs (Rhee, Wang et al. 1993). Methotrexate is the most widely used anti-folate for clinical cancer chemotherapy; its own retention in cell is also dependent on polyglutamation. PSMA can remove glutamate from folic acid and other cellular components. Prostate cancers are notoriously resistant to chemotherapy, possibly because PSMA is over-expressed in prostate tumor cells.
However, according to the invention, PSMA inhibitors have a synergistic effect on reducing cancer cell growth when combined with anti-folate chemotherapeutic agents and PSMA inhibition can enhance the sensitivity of prostate cancer to anti-folate drugs. Accordingly, PSMA inhibitors can be administered with other chemotherapeutic agent such as an anti-folate drug used to treat prostate cancer. Such anti-folate drugs include those listed herein (Table 3). PSMA inhibitors include any inhibitor available to one of skill in the art that inhibits the activity of PSMA, for example, any inhibitor of the gamma glutamyl hydrolase activity of PSMA. PSMA inhibitors contemplated by the invention include listed herein, especially, the Asp-β linked-Glu dipeptide, N-succinyl-glutamic acid, quisqalic acid (Sigma), 2-(phosphonomethyl)pentanedioic acid and related compounds. Quisqalic acid is a non-competitive inhibitor of NAALADase activity with Ki=1.9 uM, and D-β-E is a competitive inhibitor with Ki=0.7 uM. PSMA enzymatic activity can substantially reduced with such inhibitors.
Any solid tumor can be treated by the present methods. For example, the solid tumor can be any of the tumors or carcinomas listed herein. Examples of tumors and carcinomas contemplated include lung, breast, ovary, stomach, pancreas, larynx, esophagus, testes, liver, parotid, biliary tract, colon, rectum, cervix, uterus, endometrial, kidney, bladder, prostate, thyroid, squamous cell carcinoma, adenocarcinoma, small cell carcinoma, melanoma, glioma, or neuroblastoma tumor. In one embodiment the tumor is a prostate tumor.
Any chemotherapeutic agent known to one of skill in the art can also be administered in conjunction with the PSMA inhibitors and Selective Tissue Vascular Thrombogens of the invention. According to the invention, combinations of therapeutic agents that include the present Selective Tissue Vascular Thrombogens can act synergistically to provide enhanced tumor necrosis. Chemotherapeutic agents that can be co-administered with these Thrombogens and inhibitors of the invention include, for example, methotrexate, doxorubicin, paclitaxil, carboplatin and the like. Further examples of chemotherapeutic agent that can be administered with the Selective Tissue Vascular Thrombogens of the invention are provided in Table 3.
The activity and pharmacological effects of the Selective Tissue Vascular Thrombogens and inhibitors of the invention can be characterized using any method available to one of skill in the art. In one embodiment, these Selective Tissue Vascular Thrombogens and inhibitors can be tested in vivo using prostate cancer model animals, for example, in Lucap58, Mat Lu and LnCaP tumors. Therapeutic regimens and dosages can also be optimized by observing the degree of in vivo infarction of Lucap58, Mat Lu and LnCaP tumors after administration of compositions contained the present Selective Tissue Vascular Thrombogens and/or inhibitors. Inhibition of tumor growth can also be used to determine ED50 (median effective dose) of the Selective Tissue Vascular Thrombogens and PSMA inhibitors. The activity and pharmacological effects of the Selective Tissue Vascular Thrombogens and inhibitors of the invention can also be characterized in vitro using tumors and tumor cells in culture.
For example, compositions containing inhibitors and/or Selective Tissue Vascular Thrombogens can be analyzed for efficiency of induction of apoptosis, for example, by measuring apoptosis in prostate cancer cells and endothelial cells using a TUNEL assay (Boehringer Mannheim). The efficacy of the inhibitors can be determined using a calorimetric cell proliferation assay (Boehringer Mannheim), which is based on the cleavage of tetrazolium salt WST-1 by mitochondrial dehydrogenases in viable LnCap cells and other PSMA positive cells. PSMA inhibitors can further be characterized in vitro by enzymatic assay of PSMA gamma glutamyl hydrolase activity in the presence and absence of selected PSMA inhibitors. For example, the ability of an inhibitor to inhibit PSMA activity can be assessed using a γ-glutamyl hydrolase assay with 4-NH2-10CH3 PteGlu5 as a substrate (O'Connor, Rotundo et al. 1991; Wang, Rotundo et al. 1993). The Ki for inhibitors tested in this assay can be determined to serve as a reference point in determining the proper in vitro and in vivo dosages for that inhibitor.
Compositions
The Selective Tissue Vascular Thrombogens and inhibitors of the invention can be formulated as pharmaceutical compositions and administered to a mammalian host, such as a human patient in a variety of forms adapted to the chosen route of administration. Preferred routes for administration include, for example, intravenous and intraarterial routes.
Solutions of the active constructs and inhibitors or their salts can be prepared in water or saline, and optionally mixed with a nontoxic surfactant. Formulations for intravenous or intraarterial administration may include sterile aqueous solutions that may also contain buffers, liposomes, diluents and other suitable additives.
The pharmaceutical dosage forms suitable for injection or infusion can include sterile aqueous solutions or dispersions comprising the active ingredient that are adapted for administration by encapsulation in liposomes. In all cases, the ultimate dosage form must be sterile, fluid and stable under the conditions of manufacture and storage.
Sterile injectable solutions are prepared by incorporating the active constructs and inhibitors in the required amount in the appropriate solvent with various of the other ingredients enumerated above, as required, followed by filter sterilization.
Useful dosages of the constructs and inhibitors can be determined by comparing their in vitro activity, and in vivo activity in animal models. Methods for the extrapolation of effective dosages in mice, and other animals, to humans are known to the art; for example, see U.S. Pat. No. 4,938,949.
In general, a suitable dose will be in the range of from about 1 to about 2000 μg/kg, for example, from about 2.0 to about 1500 μg/kg of body weight per treatment. Preferred doses are in the range of about 3 to about 500 μg per kilogram body weight of the recipient per treatment, more preferably in the range of about 10 to about 300 μg/kg/treatment, most preferably in the range of about 20 to about 200 μg/kg/treatment.
The compound is conveniently administered in unit dosage form; for example, containing 5 to 1000 μg, conveniently 10 to 750 μg, most conveniently, 50 to 500 μg of active ingredient per unit dosage form.
Ideally, the active ingredient should be administered to achieve peak plasma concentrations of the active compound of from about 0.1 to about 10 nM, preferably, about 0.2 to 10 nM, most preferably, about 0.5 to about 5 nM. This may be achieved, for example, by the intravenous injection of a 0.05 to 25% solution of the active ingredient, optionally in saline. Desirable blood levels may be maintained by continuous infusion to provide about 0.01-10.0 μg/kg/hr or by intermittent infusions containing about 0.4-50 μg/kg of the active ingredient(s).
The desired dose may conveniently be presented in a single dose or as divided doses administered at appropriate intervals, for example, as two, three, four or more sub-doses per day. The sub-dose itself may be further divided, for example, into a number of discrete loosely spaced administrations; such as multiple intravenous doses. For example, it is desirable to administer the present compositions intravenously over an extended period, either by continuous infusion or in separate doses.
The ability of the constructs and inhibitors of the invention to act as thrombosis-inducing agents and tumor inhibitors may be determined using pharmacological models known to the art, or using tests described herein.
The invention will be further described by reference to the following detailed examples, which are given for illustration of the invention, and are not intended to be limiting thereof.
In this example, a recombinant protein that contains the N-terminal, extracellular domain of Tissue Factor was fused to the integrin-binding domain of fibronectin type III repeat domains 8-11 (SEQ ID NO:9). As illustrated below, this Selective Tissue Vascular Thrombogen conferred coagulation activity to integrin-expressing cells that otherwise did not activate the coagulation cascade. These data showed that the coagulation cascade is efficiently activated by creation of a four domain protein incorporating the extracellular domain of Tissue Factor and the fibronectin type III repeat domains 8-11. This Selective Tissue Vascular Thrombogen became associated with the cellular membrane carrying an integrin polypeptide. According to the invention, this paradigm can be used to engineer Tissue Factor-based thrombogens that are capable of occluding the blood vessels in a tissue-selective and/or cell-selective manner.
Construction of a Fibronectin-Tissue Factor Fusion Protein
Fibronectin nucleic acids were obtained by PCR amplification from marathon-ready cDNA library of human placental origin (Clontech, Inc.) using vent DNA polymerase (New England Biolabs) and the following primers:
After 35 cycles of 1 min 94° C., 1 min 60° C., and 1 min 75° C., a 1445 bp fragment was purified. The 1445 fragment was used as template for another PCR amplification using the following primers:
5′ ACCATCACGGATCCGGGGTCGTCGACACCTCC TCCCACTGACCTGCGA 3′ (SEQ ID NO:13, the “FN5a primer”) and
5′ GGTACC GGAGGAGCTCGTTACCTGCAGTCTGAACCAGAGG 3′ (SEQ ID NO:14). An 1131 bp fragment was obtained.
Tissue Factor nucleic acids were obtained by amplification from plasmid pTrcHisC-tTF (Stone et. al. 1995) using the following primers:
5′ ACGAGCTCCTCCGGTACCACAAATACTGTGGGCAGC 3′ (SEQ ID NO:15 and 5′ TCTGCGTTCTGATTTAATCT 3′ (SEQ ID NO:16, the “ptrc-seg” primer) to produce a 714 bp fragment.
The 1131 bp fragment and 714 bp fragment were combined and amplified as a fusion by PCR with the FN5a (SEQ ID NO:13) and ptrc-seq (SEQ ID NO: 16) primers to yield a 1827 bp fragment. This 1827 fragment was digested with HindIII, partially digested with BamHI, and the resulting 1753 bp fragment was ligated into the BamHI and HindIII sites of the vectorpTrcHisC (Invitrogen).
The resulting plasmid (FNTF2) encodes a protein fusion having SEQ ID NO:9 with a short His 6 Tag at the N-terminus, followed by fibronectin residues 1237 to 1603, a five-residue linker peptide, and Tissue Factor residues 3-218 at the C-terminus. Plasmid FNTF2 was transformed into the E. coli host BL21 (Stratagene) for protein production.
Proteins
The soluble extracellular domain of Tissue Factor (SEQ ID NO:5, termed TF3-218) was expressed in E. coli, then purified and refolded as previously described (Stone, Ruf et al. 1995). Factor X was purified from plasma (Fair, Plow et al. 1979), followed by immunoaffinity chromatography with immobilized monoclonal antibody F21-4.2 to reduce VII contamination (Dickinson, Kelly et al. 1996). Factor VII was affinity purified with a calcium dependent antibody to the Gla domain and followed by a Mono-Q ion-exchange chromatography that is associated with spontaneous activation of VII to VIIa.
The fibronectin-Tissue Factor (Fn-TF) fusion protein was expressed in E. coli. and refolded as follows. Briefly, BL21 bacteria were pelleted from cultures obtained 5 hours after IPTG induction. Bacteria were lysed using lysozyme digestion. Inclusion bodies were isolated using repeated sonication and centrifugation, then resuspended in Ni-NTA affinity purification buffer containing 6M guanidium chloride by sonication. The suspension was affinity purified using Ni-NTA column. Purified fractions were combined and DTT was added to final concentration of 50 mM at room temperature overnight to reduce disulfide bonds. Refolding of the protein was at 4° C. for 4 days in buffer containing 50 mM Tris, 2M urea and a combination of oxidized glutathione (0.5 mM) and reduced glutathione (2.5 mM). The refolded soluble fraction was collected and cleaned with a round of size-exclusion chromatography. The purified fusion protein appears as a homogenous band of approximately 96 kD on a silver staining gel (
The LD50 (median lethal dose) of wild type soluble TF (SEQ ID NO:4) in 20 gm Balb/C mice is greater than 500 ug, while the LD50 of the Fn-TF construct was about 8 ug.
Western Blot Analysis
The immunoreactivity of Tissue Factor was quantified by Western blot with an anti-human Tissue Factor (anti-huTF) antibody. Varying amounts of protein were electrophoretically separated and transferred to nitrocellulose membrane. Membranes were blocked with 5% non-fat milk in TBS. Primary antibody, at a concentration of 1 ug/ml, was incubated with the membranes for 1 hour at 37° C. An appropriate enzyme-linked secondary antibody was used to permit visualization of Tissue Factor bands using an enhanced chemiluminescence system (Amershan-Pharmacia). The intensity of the bands are quantified with scanning laser densitometry and compared to that of Tissue Factor standards of known concentration.
Amidolytic Assay of Bound Factor VIIa to Fn-TF or TF 1-218.
The catalytic activity of Factor VIIa bound to Fn-TF for a peptidyl substrate was analyzed by hydrolysis of chromozym t-Pa (Boehringer Mannheim) and compared with that of the soluble TF 1-218. Varying concentrations TF 1-218 or Fn-TF were incubated with Factor VIIa at a final concentration of 5nM in the presence of 5 mM Ca++ at ambient temperature for 15 minutes. Chromozym t-PA was added to a concentration of 1 mM. The initial rate of hydrolysis was measured at 406 nm with a kinetic micro-titer plate reader for 1 minute.
Proteolytic Activity of Tissue Factor Constructs Toward Factor X
The proteolytic activities of both Fn-TF:Factor VIIa and TF 1-218:Factor VIIa complexes toward Factor X were determined by a functional assay (Schullek, Ruf et al. 1994) using Spectrozyme Factor Xa to assess Factor Xa generation. Briefly, varying concentrations of Fn-TF and TF1-218 were pre-incubated with Factor VIIa (75 nM) for 5 minutes at 37° C. in the presence of 5 mM CaCl2. The reaction was initiated by addition of substrate Factor X (1.5 uM). After incubation for 10 minutes at 37° C., the reaction was terminated by adding EDTA to a concentration of 0.1M. The amount of Factor Xa generated was determined by measuring Factor Xa amidolytic activity using 50 mM of the chromogenic substrate Spectrozyme Fxa (American Diagnostica, Greenwich, Conn.). The rate of absorbance increase at 405 nM was measured in a kinetic micro-titer plate reader.
Coagulation Assay
Coagulation assays were performed using an established procedure with some modifications to include a step for binding Tissue Factor constructs to cells. Platelet depleted, citrated human plasma pooled from multiple donors was used for these experiments. Cells are dislodged with trypsin free cell dissociation buffer (Gibco), and washed twice with TBS. Cells were then counted with cytometer. Only cells with viability greater than 90% were used for the assay. Varying concentrations of thrombogen were incubated with 105 cells in 100 ul TBS containing Ca++ 10 mM and Mg++ 5 mM for 15 minutes at 37° C. The assays were initiated by addition of 100 ul of pooled citrated plasma pre-warmed to 37° C. Clotting times were recorded as the interval between assay initiation and clot appearance.
Model Ternary Structure of Tissue Factor Constructs with Factor VIIa:Factor X
The model of ternary structure is based on the crystal structure of TF and Factor VIIA (Banner, D'Arcy et al. 1996). A Gla deleted Factor X structure (Padmanabhan et al. 1993) is the primary source for the Factor X model docked onto the Tissue Factor:VIIa complex using the InsightII program docking module.
Production of a Fibronectin-Tissue Factor Fusion Protein
Two fibronectin-TF fusion proteins were created by recombinant methods described above to test the feasibility of localizing the thrombogenic activity of Tissue Factor selectively to the cell surface of integrin-expressing cells. The human fibronectin sequence that encodes typeII repeats 8 through 11 was amplified by PCR and fused to sequences encoding the extracellular segment of TF residues 3-218 to generate a protein with SEQ ID NO:9. Another fusion protein having SEQ ID NO:10 contained the fibronectin type III repeat domain 10 with the TF3-218 polypeptide. These proteins had similar properties and are referred to herein as Fn-TF or Tn-TF proteins. Like TF 1-218, when expressed in E. coli, the Fn-TF proteins accumulated in inclusion bodies. The Fn-TF proteins also behaved similarly to TF1-218 through refolding and purification. A silver staining gel of purified TF 1-218 and Fn-TF (SEQ ID NO:9) is shown in
Amidolytic Activity of Factor VIIa Bound to Fn-TF
The activity of Fn-TF as cofactor for enhancement of Factor VIIa amidolytic activity is shown in
Very little difference in amidolytic activity is discernable for Tissue Factor and Fn-TF except at high concentrations. This suggests the that affinity of Tissue Factor for Factor VIIa is not affected by the addition of fibronectin domains in the FN-TF fusion protein. Furthermore, the addition of fibronectin moiety to the N-terminus of Tissue Factor does not affect the subtle protein-protein interactions in the protease domain of Factor VIIa that are responsible for the allosteric enhancement of Factor VIIa amidolytic activity.
Proteolytic Activity of Fn-TF:Factor VIIa Toward Factor X
The effect of the fused docking structure on the proteolytic activity of TF:VIIa was studied by a linked functional assay (Schullek, Ruf et al. 1994). Varying concentrations of Fn-TF or TF1-218 were allowed to bind to 10 pM Factor VIIa for 5 minutes. To measure the proteolytic activity of the resulting TF:Factor VIIa or FN-TF:Factor VIIa complexes, Factor X was added to a concentration of 100 nM and the mixture was incubated for 10 minutes at 37 ° C. The reaction was stopped by addition of 50 mM EDTA and the amount of Factor Xa generated was determined by measuring the Factor Xa amidolytic activity in the assay mixture using spetrozyme FXa as described above.
Binding of Fn-TF to Integrin-Expressing CHO Cells
The beta-1 family (VLA) of integrins is widely distributed on the CHO cells. No endogenous Tissue Factor expression in CHO K1 cells was detected by Western Blot analysis or by the coagulation assay (data not shown). Hence, CHO K1 cells are an ideal system to study the docking of Fn-TF to integrin.
The binding of the Fn-TF protein to the integrin on CHO cells was monitored through direct incubation of varying concentrations of recombinant Fn-TF with 105 CHO K1 cells in TBS, 10 mM CaCl2, 5 mM MgSO4. The bound and unbound proteins were separated by centrifugation, and the bound Tissue Factor immunoreactivity was detected by Western blot. The amount of Tissue Factor bound was quantified by comparing the intensity of resulting bands on the membrane to that of a standard curve of Tissue Factor protein of known concentration using a densitometer.
Induction of Localized Coagulation by Docked Fn-TF
Activation of the coagulation cascade was measured using a coagulation assay. Varying concentrations of Fn-TF or Tissue Factor were incubated with CHO K1 cells for 15 minutes. Coagulation assays were initiated with addition of 100 ul of pooled normal human plasma. The coagulation time was recorded as the interim between the initiation of assay and the appearance of the first fibrin strands.
Inhibition of Fn-TF Coagulation Activity by the RGD Peptide
The coagulation activity of the Fn-TF fusion protein can be fully blocked by addition of the RGDS (SEQ ID NO:17) (
Coagulation Activity of Fn-TF Versus Full Length Tissue Factor
The coagulation activity of the Fn-TF fusion protein with CHO K1 cells was compared with the coagulation activity of a CHO K1 cell line that stably expressed full-length recombinant Tissue Factor. Approximately, 5×105 Fn-TF molecules are bound per cell when 75 nM Fn-TF fusion protein is incubated with 105 CHO K1 cells in 100 ul. A similar number of CHO K1 cells that are expressing approximately 5×105 native Tissue Factor molecules have approximately the same level of coagulation activity as the 105 CHO K1 cells exposed to 75 nM Fn-TF (
Hence, the thrombogenic activity of Tissue Factor is largely dependent upon binding to a cellular membrane and upon physical alignment with the cell surface in a manner that is similar to that of native Tissue Factor structure. Whereas the lack of a membrane assembly domain eliminates the major mechanism for proper docking of the Tissue Factor:Factor VIIa:Factor X complex on the cell surface, as well as the associated protease activities, the data provided in this example indicate that the N-terminus of Tissue Factor tolerates introduction of heterologous selective binding domains and that those binding domains can facilitate proper cell membrane association and orientation to restore the protease activity of Tissue Factor.
Hence, fusion of tissue-selective binding domain to the extracellular domain of Tissue Factor can target coagulation within that selected tissue type.
In this example, intravascular thrombosis was induced within mouse tumors by administration of an Asp-β linked-Glu (DβE)-biotin:streptavidin-Tissue Factor complex. The Asp-β linked-Glu dipeptide is a binding inhibitor of PSMA and, in this example, acts as a Selective Binding Domain. Use of a small peptide inhibitor such as D-β-E has benefits over the use of an anti-PSMA antibody because it is easier to produce, and it is small so that the thrombogenic potential is maximized, for example, with small tumor vessels. The Asp-β linked-Glu Selective Binding Domain directs an associated Tissue Factor polypeptide to PSMA-expressing cells that line the blood channels of prostate tumors. After association with PSMA-expressing cells, the Tissue Factor domain initiates localized thrombosis and infarctive necrosis of the prostate tumor. This results in tumor regression without harming the animal host.
Reagents
Purified human plasma factor VIIa was from Hematologic Technologies (Essex Junction, Vt.). Liposome incorporated doxorubicin (Doxil™) was from ALZA corporation (Mountain View, Calif.). Streptomyces avidinii was from the ATCC and grown for isolation of DNA using the QIAmp kit method (QIAGEN, Valencia, Calif.).
Antibodies
Anti-PSMA antibodies (7E11C5) were used to characterize the Mat Lu rat and LuCap mouse prostate tumor models. Monoclonal antibodies against mouse CD31 (MEC 13.3) and rat CD31 (TLD-3A 12) were from PharMingen (La Jolla, Calif.). Biotinylated rat anti-mouse CD31 antibody and a FITC labeled mouse anti-human CD31 antibody were also purchased from Pharmingen, La Jolla, Calif. Murine monoclonal antibody J591 specific for the extracellular domain of PSMA was provided by Dr. N. Bander (School of Medicine, Cornell University). Biotinylated 7E11C-5 antibody was from Dr. J. Murphy, Pacific Northwest Cancer Foundation, Seattle, Wash. The 7E11C-5 antibody epitope was mapped to the N-terminal intracellular portion of human PSMA that is not present in the mouse PSMA homologue. The anti-CD31 antibodies react with endothelial cells.
Streptavidin-Tissue Factor Fusion Protein
To determine whether a PSMA inhibitor could serve as a Selective Binding Domain to target Tissue Factor to prostate tumors and then induce tumor necrosis, an Asp-β-linked-L-Glutamate (DβE) biotinylated dipeptide was synthesized. This peptide was made to interact with and bind to a streptavidin moiety that was N-terminally attached to the extracellular domain of Tissue Factor (SEQ ID NO:5), termed streptavidin-TF. The streptavidin-TF fusion protein was produced in E. coli and folded to generate a tetramer capable of binding to four biotin molecules. The details involved in generating this protein are described below.
Tissue Factor cDNA containing amino acids 3 to 311 was obtained by PCR of a human cDNA library (Clontech, Palo Alto, Calif.) with the following primers:
The resulting 639 bp fragment was isolated by gel electrophoresis and subjected to a second PCR with primer BM33 (SEQ ID NO:21) and the following primer:
The resulting 670 bp fragment was digested with BamHI and HindIII and ligated into the BamHI and HindIII sites of the vector pTrcHisC (Invitrogen, Carlsbad, Calif.). The BM51 oligo also encodes a thrombin cleavage site (Val-Pro-Arg-Gly-Ser, SEQ ID NO:23) for selective proteolytic deletion of the His tag from the expressed protein. This plasmid (NuV120) was further modified to contain a linker sequence with three repeats of Gly4Ser (SEQ ID NO:24) between the thrombin cleavage sequences and those of Tissue Factor. The following overlapping oligos were annealed and inserted into the BamHI and Aval sites of NuV120:
The resulting plasmid (NuV127) encodes a His-tag, a thrombin cleavage site, three repeats of the spacer Gly4Ser (SEQ ID NO:37), and Tissue Factor residues 3 to 211. This vector can be used to create expression vectors for various Selective Tissue Vascular Thrombogens by inserting a cDNA sequence encoding the derived amino acids into unique BamHI and KpnI sites. The streptavidin gene was amplified by PCR with Pfu polymerase (Stratagene) using the following oligonucleotides:
Such PCR amplification results in a 514 bp fragment. The 514 bp fragment was purified and used as template for a second PCR amplification, this time with the following oligonucleotides:
BamHI and KpnI sites, respectively, are underlined in the above oligonucleotide sequences and extra nucleotides in italics were added for efficient enzyme digestion. The resulting DNA fragment of 486 bp was purified, digested with BamHI and KpnI and cloned into the BamHI and KpnI sites of NuV127. The resulting plasmid, NuV159, expresses a Streptavidin-Tissue Factor.
BL21 cells transformed with the NuV159 plasmid were grown in Super Medium (25 g tryptone, 15 g yeast extract and 5 g NaCl per liter) supplemented with biotin. Cells were induced with 1 mM IPTG when the OD600 reached 0.6 and were cultured for 24 hours at 37° C. The protein (Strep-TF) accumulated in inclusion bodies, which were isolated as described in Donate et al., Dimerization of tissue factor supports solution-phase autoactivation of factor VII without influencing proteolytic activation of factor X. Biochemistry, 39: 11467-11476, 2000. The inclusion bodies were solubilized in 6 M guanidinium hydrochloride (GuHCl), pH 8.0, and the protein construct was partially purified in a Ni-NTA (QIAGEN) column equilibrated and washed with 6 M GuHCl pH 8.0 and eluted with 250 mM imidazole, 6 M GuHCl, pH 8.0. Protein folding was performed by dilution of GuHCl solubilized Strep-TF in 20 mM Tris, 300 mM NaCl, 0.8 M GuHCl pH 8.0 and glutathione redox buffer. After 16 hours at 4° C., the sample was concentrated with a Pellicon XL concentrator (MWCO, 10,000). The His tag is removed by thrombin digestion and the protein construct purified in two steps with a Source 15Q 16/10 column followed by a Sephacryl S-200 gel filtration.
A DβE-biotin:streptavidin-TF complex was prepared by mixing excess DβE-biotin (>10 to 1 molar concentration ratio) with streptavidin-TF protein in saline. The binding of the DβE-biotin peptide to the streptavidin-TF protein was allowed to proceed for 30 min. The resulting DβE-biotin:streptavidin-TF complex was dialyzed against two changes of saline.
Before injection into animals, the DβE-biotin:streptavidin-TF complex was mixed with an equal molar ratio of Factor VIIa for 10 min. This permitted formation of the functional DβE-TF:Factor-TF:Factor VIIa thrombogenic complex.
Cell Culture
Cell lines LnCap and the Mat Lu cell were from ATCC. The LnCap cells were cultivated in RPMI-1640 medium supplemented with 10% fetal calf serum, glutamine (2 mM), HEPES (10 mM), sodium pyruvate (1 mM) and glucose (4.5 g/L). Mat Lu cells were cultured in RPMI-1640 with 10% fetal calf serum, glutamine (2 mM), and 250 nM dexamethasone.
Factor Xa Generation Assay
Factor Xa generation assays were performed as described in Ruf, et al. (J. Biol. Chem., 266, pg. 2158-66, 1991) with modifications to provide for association of the STVT constructs to PSMA expressing LnCap cells. LnCap cells were plated at 8×104 per well in 96 well plates and allowed to attach for 4 hours in the medium described above. Medium was replaced with HBSA buffer (150 mM NaCl, 5 mM CaCl2, 0.5% BSA, 20 mM Hepes, pH 7.4) and serial concentrations of DβE:Strep-TF:VIIa or Strep-TF:VIIa complex were added to the wells. After incubation for 5 minutes, factor X was then added to a final concentration of 1 μM. After 5 minutes at 37° C. the limited proteolytic conversion of factor X to factor Xa was arrested with 100 mM EDTA. Factor Xa amidolytic chromogenic substrate Spectrozyme Xa (American Diagnostica, Greenwich, Conn.) was added to a final concentration of 200 μM and substrate hydrolysis was determined kinetically at OD 405 in a spectrophotometric plate reader (Molecular Devices, Sunnyvale, Calif.).
Animal Models
Cell lines LnCap and the Mat Lu cell were from ATCC. The PSMA positive human prostate carcinoma (CaP) xenograft, LuCap 58, was carried as a xenograft in WEHI nude mice (The Scripps Research Institute Breeding Facility). See Bladou et al., In vitro and in vivo models developed from human prostatic cancer. Prog. Urol., 7: 384-396, 1997. The tumors were passaged by implantation of ˜2 mm3 fragments in the subcutaneous tissue of the back of the mice. The rat Mat Lu prostate carcinoma was carried in male Copenhagen rats aged 4 to 6 weeks (Harlan Sprague-Dawley, Germantown, N.Y.) innoculated with 5×105 Mat Lu cells per subcutaneous site on the back.
Treatment of tumors was initiated once tumors reached 200 mm3 through bolus intravenous injection of the Selective Tissue Vascular Thrombogen or a control protein (0.1 mg/Kg based on strep-TF protein) and repeated twice at two-day intervals. For combination therapies, liposomal doxorubicin (Doxil™) at 2 mg/kg was separately injected intravenously. Tumor growth and other physical signs were monitored daily including gross evidence of tumor necrosis, local tumor ulceration as well as evidence of toxicity including mobility, response to stimulus, eating, and weight of each animal. The studies have been reviewed and approved by the Institutional Animal Care and Use Committee of The Scripps Research Institute. The work was conducted in the TSRI facilities which are accredited by the Association for the Assessment and Accreditation of Laboratory Animal Care. The Scripps Research Institute maintains an assurance with the Public Health Service, is registered with the United States Department of Agriculture and is in compliance with all regulations relating to animal care and welfare.
Immunohistochemistry
Immunohistochemical analysis was performed on formalin fixed as well as fresh frozen 5 μm tissue sections mounted on poly-lysine coated slides. For endothelial identification, biotinylated murine anti-rat CD-31 monoclonal antibody (TLD-3A12) or biotinylated rat anti-mouse CD-31 monoclonal antibody (MEC 13.3) were used at 1 μg/ml as first antibody then the reaction was developed with fluorescein conjugated strepavidin. For identification of PSMA in frozen sections, reaction with mouse monoclonal antibody J591 was followed by biotinylated rabbit anti-mouse IgG and the reaction was visualized with Texas-red conjugated strepavidin. Staining of PSMA in formalin fixed tissue was performed with biotinylated 7E11C-5 antibody. The tissue sections were analyzed with the aid of laser scanning confocal microscopy (Bio-Rad, Hercules, Calif.).
Coagulation Assay
The coagulation activity of the DβE-biotin:streptavidin-TF:Factor VIIa thrombogenic complex was assayed using a cell mediated coagulation assay employing CHO K1 cells that stably express PSMA. Different concentrations of DβE-biotin:streptavidin-TF:Factor VIIa thrombogenic complex (in 50 ul) were incubated with 105 PSMA expressingCHO K1 cells (also in 50 ul) at room temperature for 15 min to allow the DβE-biotin:streptavidin-TF:Factor VIIa thrombogenic complex to associate with PSMA on the cell surface. At the end of this incubation, 100 ul citrated pooled human plasma was added and the assay was initiated by adding 100 ul 20 mM CaCl2 that had been pre-warmed to at 37° C. Assays using CHO K1 cells without PSMA were used as controls. The clotting time was recorded as the interim between the initiation of the reaction and the occurrence of the first strands of fibrin gel. This assay was used to guide the construction of fusion proteins and to quantify the activity of the DβE-biotin:streptavidin-TF:Factor VIIa thrombogenic complex in different preparations.
Combined Treatment with the DβE-biotin:streptavidin-TF:Factor VIIa Thrombogenic Complex and Doxorubicin
Treatment of tumor-bearing rodents was initiated when tumors reached 200 mm3 by bolus i.v. injection. Some test animals were injected with DβE-biotin:streptavidin-TF:Factor VIIa thrombogenic complex (0.1 mg/Kg based on streptavidin-TF total protein) plus doxorubicin (2 mg/kg, 3.5umol/kg). Other test animals were injected with DβE-biotin:streptavidin-TF:Factor VIIa thrombogenic complex (0.1 mg/Kg based on streptavidin-TF total protein) alone. Control animals were injected with doxorubicin (2 mg/kg, 3.5umol/kg). Mock-treated animals received no doxorubicin and no thrombogenic complex. The treatment is repeated daily. The doxorubicin dosage is determined according to the MTD (maximum tolerated dose) published for daily injection for five days, which between 2.8 umol/kg to 3.6 umol/kg. Tumor growth was monitored daily through 4 weeks and until death. Tumor size was measured daily from the day of initial treatment.
Statistical analysis
Statistical significance was determined by the two-tailed Student=s t test, except for statistical significance of survival curves which utilized the Logrank test using GraphPad Prism version 3.00 (GraphPad Software, San Diego Calif. USA).
Immunohistological Analysis
PSMA was detected on the vessels of a xenograft model of human prostate tumors (LuCap 58) using the 7E11 antibody, and also using a biotinylated peptidyl inhibitor (Asp-β-Glu) of PSMA enzymatic activity. Strong PSMA expression was detected on the luminal surfaces of the vessels of the PSMA positive human LuCap 58 xenograft grown in nude mice (
Immunohistochemical analysis of the human LuCap tumors clearly identified PSMA positive cells that line and thereby delineate the microscopic channels with structural characteristics not unlike microvascular channels (
A second piece of evidence indicates that the PSMA-positive cells lining the vessels of the tumors are not endothelial cells. Frozen sections of LuCap 58 tumors were immunohistochemically stained with biotinylated rat anti-mouse CD31 antibody and with an FITC-labeled mouse anti-human CD31 antibody. While the FITC-labeled anti-mouse CD31 reacted positively with the tumor vessels lining cells in these sections (
To investigate that whether the PSMA-positive cells that lined the channels in these tumors were part of the tumor vasculature, bacteriophage M13 was injected into the blood stream of the animal as a marker. Tumors were harvested minutes after the injection and frozen sections were prepared from these samples. Extensive experience with in vivo phage panning has proven that phage will remain in the tumor vasculature and can be easily recognized with anti-phage antibody staining. Double staining with PSMA antibody and anti-phage antibody revealed that PSMA lined the channel structures stained by phage and through which blood flows (
The STVT Functionally Associates with PSMA Positive Cells.
A factor Xa generation assay was used to test whether the DβE-biotin:streptavidin-TF:Factor VIIa complex could align properly on an anionic cell membrane surface and properly associate with factor X substrate that has localized to the same locus. As illustrated in
The factor Xa generation assay requires the functional assembly of the assembled DβE:Strep-TF:VIIa complex on PSMA expressing LnCap cells. Unlike most tumor cells, LnCap cells do not express Tissue Factor as indicated by coagulation assays and western blot examination (data not shown). LnCap cells also do not directly form factor Xa from factor X and therefore cannot drive the thrombogenic cascade (see streptavidin-Tissue Factor control in
Tumor Necrosis
Mat Lu tumors were generated by subcutaneous inoculation of 0.5×106 tumor cells per site in the subcutaneous tissue of the back of the Copenhagen rats. After 7 days the tumors grew to an average diameter of 1 cm. Treatment is initiated at this time by bolus intravenous injection of the DβE-biotin:streptavidin-TF:Factor VIIa complex at a dose of 0.1 mg streptavidin-TF per Kg body weight. Treatment was repeated daily for 7 days. Tumor growth was measured daily and graphed. Key physical signs were monitored, including:
The control streptavidin-TF protein was not toxic in rats over a wide range of concentrations, thereby permitting evaluation of the potential for selective tumor thrombosis and infarctive necrosis in tumor bearing rats.
Intravenous injection of the DβE-biotin:streptavidin-TF: Factor VIIa complex was associated with a rapid wave of localized microthrombosis of blood channels within Mat Lu tumors, leading to infarctive necrosis of Mat Lu prostate tumors. As shown in
Pathological studies were performed to confirm that intravenous administration of an DβE-biotin:streptavidin-TF:Factor VIIa complex induced selective thrombosis of tumor vasculature in rats bearing Mat Lu prostate cancers. Signs of tumor vasculature thrombosis were observed in tumors immediately following treatment. The center of the treated tumors showed gross signs of ischemic changes. In Hematoxylin and Eosin stained sections, the number of vessels that were occluded increased dramatically. After one hour, blood vessel thrombosis was extensive. Occlusive platelet aggregates were frequently observed in thrombi as well as red blood cells and fibrin. By 72 hours and after three treatments, the tumors showed advanced necrosis. In some tumors, the entire central region was completely liquified.
Combined Therapy with Doxorubicin.
To address the potential to enhance selective tumor microvascular thrombosis and infarction of tumors, infusions of both the DβE-biotin:streptavidin-TF: Factor VIIa construct and low doses of liposomal doxorubicin (2 mg/Kg) were conducted. Three infusions of each were administered at two-day intervals as described above. There was virtually a complete arrest of tumor growth and gross eradication of tumors in some rats that received doxorubicin with the DβE-biotin:streptavidin-TF: Factor VIIa construct (
Therapy with PSMA Inhibitors
These experiments illustrated the therapeutic potential of reduction of a tumor cell viability, combined with selective tumor vascular thrombosis in prostate cancer by targeting cells that express PSMA. The data indicate that PSMA-expressing tumor cells create vascular channels that are lined by tumor cells. Some tumor tissue on the periphery of the tumor often escaped thrombosis, indicating that these tumor cells may survive because they are not in direct contact with tumor blood vessels. However, these peripheral tumor cells are more accessible to cytotoxic drugs delivered by the circulatory system. A combination of therapeutic agents that includes the present Selective Tissue Vascular Thrombogens and an anti-tumor drug may effectively eradicate solid tumors.
Hence, the compositions and methods of the invention are peculiarly suited to treat here-to-fore inaccessible tumor cells within the heart of solid tumors.
The foregoing specification, including the specific embodiments and examples, is intended to be illustrative of the present invention and is not to be taken as limiting. Numerous other variations and modifications can be effected without departing from the true spirit and scope of the present invention.
The following references, to the extent that they provide exemplary procedural or other details supplementary to those set forth herein, are specifically incorporated herein by reference.
This application is a non-provisional application which claims priority to provisional application entitled “Targeted Thrombosis” filed Sep. 20, 2002, U.S. Serial No. 60/412,194 and provisional application entitled “Targeted Thrombosis” filed Oct. 26, 2001, U.S. Ser. No. 60/336,331, the specifications of which are incorporated herein by reference.
This invention was made with Government support under Grant No. PO1 HL16411 awarded by the National Institutes of Health. The Government has certain rights in this invention.
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