Title: Therapeutic inhibitor of vascular smooth muscle cells
United States Patent: 6,599,928
Issued: July 29, 2003
Inventors: Kunz; Lawrence L. (Redmond, WA); Klein; Richard A. (Lynnwood, WA)
Assignee: NeoRx Corporation (Seattle, WA)
Appl. No.: 910387
Filed: July 20, 2001
Methods are provided for inhibiting stenosis following vascular trauma or disease in a mammalian host, comprising administering to the host a therapeutically effective dosage of a therapeutic conjugate containing a vascular smooth muscle binding protein that associates in a specific manner with a cell surface of the vascular smooth muscle cell, coupled to a therapeutic agent dosage form that inhibits a cellular activity of the muscle cell. Methods are also provided for the direct and/or targeted delivery of therapeutic agents to vascular smooth muscle cells that cause a dilation and fixation of the vascular lumen by inhibiting smooth muscle cell contraction, thereby constituting a biological stent.
DETAILED DESCRIPTION OF THE INVENTION
As used herein the following terms have the meanings as set forth below:
"Therapeutic conjugate" means a vascular smooth muscle or an interstitial matrix binding protein coupled (e.g., optionally through a linker) to a therapeutic agent.
"Target" and "marker" are used interchangeably in describing the conjugate aspects of the present invention to mean a molecule recognized in a specific manner by the matrix or vascular smooth muscle binding protein, e.g., an antigen, polypeptide antigen or cell surface carbohydrate (e.g., a glycolipid, glycoprotein, or proteoglycan) that is expressed on the cell surface membranes of a vascular smooth muscle cell or a matrix structure.
"Epitope" is used to refer to a specific site within the "target" molecule that is bound by the matrix or smooth muscle binding protein, e.g., a sequence of three or more amino acids or saccharides.
"Coupled" is used to mean covalent or non-covalent chemical association (i.e., hydrophobic as through van der Waals forces or charge-charge interactions) of the matrix or vascular smooth muscle binding protein with the therapeutic agent. Due to the nature of the therapeutic agents employed, the binding proteins will normally be associated with the therapeutic agents by means of covalent bonding.
"Linker" means an agent that couples the matrix or smooth muscle binding protein to a therapeutic agent, e.g., an organic chemical coupler.
"Migration" of smooth muscle cells means movement of these cells in vivo from the medial layers of a vessel into the intima, such as may also be studied in vitro by following the motion of a cell from one location to another (e.g., using time-lapse cinematography or a video recorder and manual counting of smooth muscle cell migration out of a defined area in the tissue culture over time).
"Proliferation," i.e., of smooth muscle cells or cancer cells, means increase in cell number, i.e., by mitosis of the cells.
"Expressed" means mRNA transcription and translation with resultant synthesis, glycosylation, and/or secretion of a polypeptide by a cell, e.g., CSPG synthesized by a vascular smooth muscle cell or pericyte.
"Macrocyclic trichothecene" is intended to mean any one of the group of structurally related sesquiterpenoid macrocyclic mycotoxins produced by several species of fungi and characterized by the 12,13-epoxytrichothec-9-ene basic structure, e.g., verrucarins and roridins that are the products of secondary metabolism in the soil fungi Myrothecium verrucaria and Myrothecium roridium.
"Sustained release" means a dosage form designed to release a therapeutic agent therefrom for a time period ranging from about 3 to about 21 days. Release over a longer time period is also contemplated as a "sustained release" dosage form of the present invention.
"Dosage form" means a free (non-targeted or non-binding partner associated) therapeutic agent formulation, as well as sustained release therapeutic formulations, such as those incorporating microparticulate or nanoparticulate, biodegradable or non-biodegradable polymeric material capable of binding to one or more binding proteins or peptides to deliver a therapeutic moiety dispersed therein to a target cell population.
"Staurosporin" includes staurosporin, a protein kinase C inhibitor, as well as diindoloalkaloids. More specifically, the term "staurosporin" includes K-252 (see, for example, Japanese Patent Application No. 62,164,626), BMY-41950 (U.S. Pat. No. 5,015,578), UCN-01 (U.S. Pat. No. 4,935,415), TAN-999 (Japanese Patent Application No. 01,149,791), TAN-1030A (Japanese Patent Application No. 01,246,288), RK-286C (Japanese Patent Application No. 02,258,724) and functional equivalents and derivatives thereof. Derivatives of staurosporin include those discussed in Japanese Patent Application Nos. 03,72,485; 01,143,877; 02,09,819 and 03,220,194, as well as in PCT International Application Nos. WO 89 07,105 and WO 91 09,034 and European Patent Application Nos. EP 410,389 and EP 296,110. Derivatives of K-252, a natural product, are known. See, for example, Japanese Patent Application Nos. 63,295,988; 62,240,689; 61,268,687; 62,155,284; 62,155,285; 62,120,388 and 63,295,589, as well as PCT International Application No. WO 88 07,045 and European Patent Application No. EP 323,171.
"Cytochalasin" includes fungal metabolites exhibiting an inhibitory effect on target cellular metabolism, including prevention of contraction or migration of vascular smooth muscle cells. Preferably, cytochalasins inhibit the polymerization of monomeric actin (G-actin) to polymeric form (F-actin), thereby inhibiting cell functions requiring cytoplasmic microfilaments. Cytochalasins typically are derived from phenylalanine (cytochalasins), tryptophan (chaetoglobosins), or leucine (aspochalasins), resulting in a benzyl, indol-3-yl methyl or isobutyl group, respectively, at position C-3 of a substituted perhydroisoindole-1-one moiety (Formula V or VI).
The perhydroisoindole moiety in turn contains an 11-, 13- or 14-atom carbocyclic- or oxygen-containing ring linked to positions C-8 and C-9. All naturally occurring cytochalasins contain a methyl group at C-5; a methyl or methylene group at C-12; and a methyl group at C-14 or C-16. Exemplary molecules include cytochalasin A, cytochalasin B, cytochalasin C, cytochalasin D, cytochalasin E, cytochalasin F, cytochalasin G, cytochalasin H, cytochalasin J, cytochalasin K, cytochalasin L, cytochalasin M, cytochalasin N, cytochalasin O, cytochalasin P, cytochalasin Q, cytochalasin R, cytochalasin S, chaetoglobosin A, chaetoglobosin B, chaetoglobosin C, chaetoglobosin D, chactoglobosin E, chaetoglobosin F, chaetoglobosin G, chaetoglobosin J, chaetoglobosin K, deoxaphomin, proxiphomin, protophomin, zygosporin D, zygosporin E, zygosporin F, zygosporin G, aspochalasin B, aspochalasin C, aspochalasin D and the like, as well as functional equivalents and derivatives thereof. Certain cytochalasin derivatives are set forth in Japanese Patent Nos. 72 01,925; 72 14,219; 72 08,533; 72 23,394; 72 01924; and 72 04,164. Cytochalasin B is used in this description as a prototypical cytochalasin.
As referred to herein, smooth muscle cells and pericytes include those cells derived from the medial layers of vessels and adventitia vessels which proliferate in intimal hyperplastic vascular sites following injury, such as that caused during PTCA.
Characteristics of smooth muscle cells include a histological morphology (under light microscopic examination) of a spindle shape with an oblong nucleus located centrally in the cell with nucleoli present and myofibrils in the sarcoplasm. Under electron microscopic examination, smooth muscle cells have long slender mitochondria in the juxtanuclear sarcoplasm, a few tubular elements of granular endoplasmic reticulum, and numerous clusters of free ribosomes. A small Golgi complex may also be located near one pole of the nucleus. The majority of the sarcoplasm is occupied by thin, parallel myofilaments that may be, for the most part, oriented to the long axis of the muscle cell. These actin containing myofibrils may be arranged in bundles with mitochondria interspersed among them. Scattered through the contractile substance of the cell may also be oval dense areas, with similar dense areas distributed at intervals along the inner aspects of the plasmalemma.
Characteristics of pericytes include a histological morphology (under light microscopic examination) characterized by an irregular cell shape. Pericytes are found within the basement membrane that surrounds vascular endothelial cells and their identity may be confirmed by positive immuno-staining with antibodies specific for alpha smooth muscle actin (e.g., anti-alpha-sm1, Biomakor, Rehovot, Israel), HMW-MAA, and pericyte ganglioside antigens such as MAb 3G5 (11); and, negative immuno-staining with antibodies to cytokeratins (i.e., epithelial and fibroblast markers) and von Willdebrand factor (i.e., an endothelial marker). Both vascular smooth muscle cells and pericytes are positive by immunostaining with the NR-AN-01 monoclonal antibody.
The therapeutic conjugates and dosage forms of the invention are useful for inhibiting the activity of vascular smooth muscle cells, e.g., for reducing, delaying, or eliminating stenosis following angioplasty. As used herein the term "reducing" means decreasing the intimal thickening that results from stimulation of smooth muscle cell proliferation following angioplasty, either in an animal model or in man. "Delaying" means delaying the time until onset of visible intimal hyperplasia (e.g., observed histologically or by angiographic examination) following angioplasty and may also be accompanied by "reduced" restenosis. "Eliminating" restenosis following angioplasty means completely "reducing" and/or completely "delaying" intimal hyperplasia in a patient to an extent which makes it no longer necessary to surgically intervene, i.e., to re-establish a suitable blood flow through the vessel by repeat angioplasty, atheroectomy, or coronary artery bypass surgery. The effects of reducing, delaying, or eliminating stenosis may be determined by methods routine to those skilled in the art including, but not limited to, angiography, ultrasonic evaluation, fluoroscopic imaging, fiber optic endoscopic examination or biopsy and histology. The therapeutic conjugates of the invention achieve these advantageous effects by specifically binding to the cellular membranes of smooth muscle cells and pericytes.
Therapeutic conjugates of the invention are obtained by coupling a vascular smooth muscle binding protein to a therapeutic agent. In the therapeutic conjugate, the vascular smooth muscle binding protein performs the function of targeting the therapeutic conjugate to vascular smooth muscle cells or pericytes, and the therapeutic agent performs the function of inhibiting the cellular activity of the smooth muscle cell or pericyte.
Therapeutic dosage forms (sustained release-type) of the present invention exhibit the capability to deliver therapeutic agent to target cells over a sustained period of time. Therapeutic dosage forms of this aspect of the present invention may be of any configuration suitable for this purpose. Preferred sustained release therapeutic dosage forms exhibit one or more of the following characteristics:
microparticulate (e.g., from about 0.5 micrometers to about 100 micrometers in diameter, with from about 0.5 to about 2 micrometers more preferred) or nanoparticulate (e.g., from about 1.0 nanometer to about 1000 nanometers in diameter, with from about 50 to about 250 nanometers more preferred), free flowing powder structure;
biodegradable structure designed to biodegrade over a period of time between from about 3 to about 180 days, with from about 10 to about 21 days more preferred, or non-biodegradable structure to allow therapeutic agent diffusion to occur over a time period of between from about 3 to about 180 days, with from about 10 about 10 to about 21 days preferred;
biocompatible with target tissue and the local physiological environment into which the dosage form is being administered, including biocompatible biodegradation products;
facilitate a stable and reproducible dispersion of therapeutic agent therein, preferably to form a therapeutic agent-polymer matrix, with active therapeutic agent release occurring through one or both of the following routes: (1) diffusion of the therapeutic agent through the dosage form (when the therapeutic agent is soluble in the polymer or polymer mixture forming the dosage form); or (2) release of the therapeutic agent as the dosage form biodegrades; and
capability to bind with one or more cellular and/or interstitial matrix epitopes, with from about 1 to about 10,000 binding protein/peptide-dosage form bonds preferred and with a maximum of about 1 binding peptide-dosage form per 150 square angstroms of particle surface area more preferred. The total number bound depends upon the particle size used. The binding proteins or peptides are capable of coupling to the particulate therapeutic dosage form through covalent ligand sandwich or non-covalent modalities as set forth herein.
Nanoparticulate sustained release therapeutic dosage forms of preferred embodiments of the present invention are biodegradable and bind to the vascular smooth muscle cells and enter such cells primarily by endocytosis. The biodegradation of such nanoparticulates occurs over time (e.g., 10 to 21 days) in prelysosomic vesicles and lysosomes. The preferred larger microparticulate therapeutic dosage forms of the present invention bind to the target cell surface or interstitial matrix, depending on the binding protein or peptide selected, and release the therapeutic agents for subsequent target cell uptake with only a few of the smaller microparticles entering the cell by phagocytosis. A practitioner in the art will appreciate that the precise mechanism by which a target cell assimilates and metabolizes a dosage form of the present invention depends on the morphology, physiology and metabolic processes of those cells.
The size of the targeted sustained release therapeutic particulate dosage forms is also important with respect to the mode of cellular assimilation. For example, the smaller nanoparticles can flow with the interstitial fluid between cells and penetrate the infused tissue until it binds to the normal or neoplastic tissue that the binding protein/peptide is selected to target. This feature is important, for example, because the nanoparticles follow lymphatic drainage channels from infused primary neoplastic foci, targeting metastatic foci along. the lymphatic tract. The larger microparticles tend to be more easily trapped interstitially in the infused primary tissue.
Preferable sustained release dosage forms of the present invention are biodegradable microparticulates or nanoparticulates. More preferably, biodegradable microparticles or nanoparticles are formed of a polymer containing matrix that biodegrades by random, nonenzymatic, hydrolytic scissioning to release therapeutic agent, thereby forming pores within the particulate structure.
Polymers derived from the condensation of alpha hydroxycarboxylic acids and related lactones are preferred for use in the present invention. A particularly preferred moiety is formed of a mixture of thermoplastic polyesters (e.g., polylactide or polyglycolide) or a copolymer of lactide and glycolide components, such as poly(lactide-co-glycolide). An exemplary structure, a random poly(DL-lactide-co-glycolide), is shown below, with the values of x and y being manipulable by a practitioner in the art to achieve desirable microparticulate or nanoparticulate properties.
Other agents suitable for forming particulate dosage forms of the present invention include polyorthoesters and polyacetals (Polymer Letters, 18:293, 1980) and polyorthocarbonates (U.S. Pat. No. 4,093,709) and the like.
Preferred lactic acid/glycolic acid polymer containing matrix particulates of the present invention are prepared by emulsion-based processes, that constitute modified solvent extraction processes such as those described by Cowsar et al., "Poly(Lactide-Co-Glycolide) Microcapsules for Controlled Release of Steroids," Methods Enzymology, 112:101-116, 1985 (steroid entrapment in microparticulates); Eldridge et al., "Biodegradable and Biocompatible Poly(DL-Lactide-Co-Glycolide) Microspheres as an Adjuvant for Staphylococcal Enterotoxin B Toxoid Which Enhances the Level of Toxin-Neutralizing Antibodies," Infection and Immunity, 59:2978-2986, 1991 (toxoid entrapment); Cohen et al., "Controlled Delivery Systems for Proteins Based on Poly(Lactic/Glycolic Acid) Mcrospheres," Pharmaceutical Research, 8(6):713-720, 1991 (enzyme entrapment); and Sanders et al., "Controlled Release of a Luteinizing Hormone-Releasing Hormone Analogue from Poly(D,L-Lactide-Co-Glycolide) Microspheres," J. Pharmaceutical Science, 73(9):1294-1297, 1984 (peptide entrapment).
In general, the procedure for forming particulate dosage forms of the present invention involves dissolving the polymer in a halogenated hydrocarbon solvent, dispersing a therapeutic agent solution (preferably aqueous) therein, and adding an additional agent that acts as a solvent for the halogenated hydrocarbon solvent but not for the polymer. The polymer precipitates out from the polymer-halogenated hydrocarbon solution onto droplets of the therapeutic agent containing solution and entraps the therapeutic agent. Preferably the therapeutic agent is substantially uniformly dispersed within the sustained release dosage form of the present invention. Following particulate formation, they are washed and hardened with an organic solvent. Water washing and aqueous non-ionic surfactant washing steps follow, prior to drying at room temperature under vacuum.
For biocompatibility purposes, particulate dosage forms, characterized by a therapeutic agent dispersed therein in matrix form, are sterilized prior to packaging, storage or administration. Sterilization may be conducted in any convenient manner therefor. For example, the particulates can be irradiated with gamma radiation, provided that exposure to such radiation does not adversely impact the structure or function of the therapeutic agent dispersed in the therapeutic agent-polymer matrix or the binding protein/peptide attached thereto. If the therapeutic agent or binding protein/peptide is so adversely impacted, the particulate dosage forms can be produced under sterile conditions.
Release of the therapeutic agent from the particulate dosage forms of the present invention can occur as a result of both diffusion and particulate matrix erosion. Biodegradation rate directly impacts therapeutic agent release kinetics. The biodegradation rate is regulable by alteration of the composition or structure of the sustained release dosage form. For example, alteration of the lactide/glycolide ratio in preferred dosage forms of the present invention can be conducted, as described by Tice et al., "Biodegradable Controlled-Release Parenteral Systems," Pharmaceutical Technology, pp. 26-35, 1984; by inclusion of polymer hydrolysis modifying agents, such as citric acid and sodium carbonate, as described by Kent et al., "Microencapsulation of Water Soluble Active Polypeptides," U.S. Pat. No. 4,675,189; by altering the loading of therapeutic agent in the lactide/glycolide polymer, the degradation rate being inversely proportional to the amount of therapeutic agent contained therein, and by judicious selection of an appropriate analog of a common family of therapeutic agents that exhibit different potencies so as to alter said core loadings; and by variation of particulate size, as described by Beck et al., "Poly(DL-Lactide-Co-Glycolide)/Norethisterone Microcapsules: An Injectable Biodegradable Contraceptive," Biol. Reprod., 28:186-195, 1983, or the like. All of the aforementioned methods of regulating biodegradation rate influence the intrinsic viscosity of the polymer containing matrix, thereby altering the hydration rate thereof.
The preferred lactide/glycolide structure is biocompatible with the mammalian physiological environment. Also, these preferred sustained release dosage forms have the advantage that biodegradation thereof forms lactic acid and glycolic acid, both normal metabolic products of mammals.
Functional groups required for binding protein/peptide-particulate dosage form bonding to the particles, are optionally included in the particulate structure, along with the non-degradable or biodegradable polymeric units. Functional groups that are exploitable for this purpose include those that are reactive with peptides, such as carboxyl groups, amine groups, sulfhydryl groups and the like. Preferred binding enhancement moieties include the terminal carboxyl groups of the preferred (lactide-glycolide) polymer containing matrix or the like.
Useful vascular smooth muscle binding protein is a polypeptide, peptidic, or mimetic compound (as described below) that is capable of binding to a target or marker on a surface component of an intact or disrupted vascular smooth muscle cell in such a manner that allows for either release of therapeutic agent extracellularly in the immediate interstitial matrix with subsequent diffusion of therapeutic agent into the remaining intact smooth muscle cells and/or internalization by the cell into an intracellular compartment of the entire targeted biodegradable moiety, permitting delivery of the therapeutic agent. Representative examples of useful vascular smooth muscle binding proteins include antibodies (e.g., monoclonal and polyclonal affinity-purified antibodies, F(ab')2, Fab', Fab, and Fv fragments and/or complementarity determining regions (CDR) of antibodies or functional equivalents thereof, (e.g., binding peptides and the like)); growth factors, cytokines, and polypeptide hormones and the like; and macromolecules recognizing extracellular matrix receptors (e.g., integrin and fibronectin receptors and the like).
Other preferred binding peptides useful in targeting the dosage form embodiment of the present invention include those that localize to intercellular stroma and matrix located between and among vascular smooth muscle cells. Such binding peptides deliver the therapeutic agent to the interstitial space between the target cells. The therapeutic agent is released into such interstitial spaces for subsequent uptake by the vascular smooth muscle cells. Preferred binding peptides of this type are associated with epitopes on collagen, extracellular glycoproteins such as tenascin, reticulum and elastic fibers and other intercellular matrix material.
Preferred tumor cell binding peptides are associated with epitopes of myc, ras, bcr/Abl, erbB and like gene products, as well as mucins, cytokine receptors such as IL-6, EGF, TGF and the like, which binding peptides localize to certain lymphomas (myc), carcinomas such as colon cancer (ras), carcinoma (erbB), adenocarcinomas (mucins), breast cancer and hepatoma (IL-6 receptor), and breast cancer (EGF and TGF), respectively. Preferred immune system effector cell-binding peptides are anti-TAC, IL-2 and the like, which localize to activated T cells and macrophages, respectively. Other preferred binding proteins/peptides useful in the practice of the present invention include moieties capable of localizing to pathologically proliferating normal tissues, such as pericytes of the intraocular vasculature implicated in degenerative eye disease.
Therapeutic agents of the invention are selected to inhibit a cellular activity of a vascular smooth muscle cell, e.g., proliferation, migration, increase in cell volume, increase in extracellular matrix synthesis (e.g., collagens, proteoglycans, and the like), or secretion of extracellular matrix materials by the cell. Preferably, the therapeutic agent acts either: a) as a "cytostatic agent" to prevent or delay cell division in proliferating cells by inhibiting replication of DNA (e.g., a drug such as adriamycin, staurosporin or the like), or by inhibiting spindle fiber formation (e.g., a drug such as colchicine) and the like; or b) as an inhibitor of migration of vascular smooth muscle cells from the medial wall into the intima, e.g., an "anti-migratory agent" such as a cytochalasin; or c) as an inhibitor of the intracellular increase in cell volume (i.e., the tissue volume occupied by a cell; a "cytoskeletal inhibitor" or "metabolic inhibitor"); or d) as an inhibitor that blocks cellular protein synthesis and/or secretion or organization of extracellular matrix (i.e., an "anti-matrix agent").
Representative examples of "cytostatic agents" include, e.g., modified toxins, methotrexate, adriamycin, radionuclides (e.g., such as disclosed in Fritzberg et al., U.S. Pat. No. 4,897,255), protein kinase inhibitors (e.g., staurosporin), inhibitors of specific enzymes (such as the nuclear enzyme DNA topoisomerase II and DNA polymerase, RNA polymerase, adenyl guanyl cyclase), superoxide dismutase inhibitors, terminal deoxynucleotidyl- transferase, reverse transcriptase, antisense oligonucleotides that suppress smooth muscle cell proliferation and the like, which when delivered into a cellular compartment at an appropriate dosage will act to impair proliferation of a smooth muscle cell or pericyte without killing the cell. Other examples of "cytostatic agents" include peptidic or mimetic inhibitors (i.e., antagonists, agonists, or competitive or non-competitive inhibitors) of cellular factors that may (e.g., in the presence of extracellular matrix) trigger proliferation of smooth muscle cells or pericytes: e.g., cytokines (e.g., interleukins such as IL-1), growth factors, (e.g., PDGF, TGF-alpha or -beta, tumor necrosis factor, smooth muscle- and endothelial-derived growth factors, i.e., endothelin, FGF), homing receptors (e.g., for platelets or leukocytes), and extracellular matrix receptors (e.g., integrins). Representative examples of useful therapeutic agents in this category of cytostatic agents for smooth muscle proliferation include: subfragments of heparin, triazolopyrimidine (Trapidil; a PDGF antagonist), lovastatin, and prostaglandins E1 or I2.
Representative examples of "anti-migratory agents" include inhibitors (i.e., agonists and antagonists, and competitive or non-competitive inhibitors) of chemotactic factors and their receptors (e.g., complement chemotaxins such as C5a, C5a desarg or C4a; extracellular matrix factors. e.g., collagen degradation fragments), or of intracellular cytoskeletal proteins involved in locomotion (e.g., actin, cytoskeletal elements, and phosphatases and kinases involved in locomotion). Representative examples of useful therapeutic agents in this category of anti-migratory agents include: caffeic acid derivatives and nilvadipine (a calcium antagonist), and steroid hormones. Preferred anti-migratory therapeutic agents are the cytochalasins.
Representative examples of "cytoskeletal inhibitors" include colchicine, vinblastin, cytochalasins, taxol and the like that act on microtubule and microfilament networks within a cell.
Representative examples of "metabolic inhibitors" include staurosporin, trichothecenes, and modified diphtheria and ricin toxins, Pseudomonas exotoxin and the like. In a preferred embodiment, the therapeutic conjugate is constructed with a therapeutic agent that is a simple trichothecene or a macrocyclic trichothecene, e.g., a verrucarin or roridin. Trichothecenes are drugs produced by soil fungi of the class Fungi imperfecti or isolated from Baccharus megapotamica (Bamburg, J. R. Proc. Molec. Subcell. Biol. 8:41-110, 1983; Jarvis & Mazzola, Acc. Chem. Res. 15:338-395, 1982). They appear to be the most toxic molecules that contain only carbon, hydrogen and oxygen (Tamm, C. Fortschr. Chem. Org. Naturst. 31:61-117, 1974). They are all reported to act at the level of the ribosome as inhibitors of protein synthesis at the initiation, elongation, or termination phases.
There are two broad classes of trichothecenes: those that have only a central sesquiterpenoid structure and those that have an additional macrocyclic ring (simple and macrocyclic trichothecenes, respectively). The simple trichothecenes may be subdivided into three groups (i.e., Group A, B, and C) as described in U.S. Pat. Nos. 4,744,981 and 4,906,452 (incorporated herein by reference). Representative examples of Group A simple trichothecenes include: Scirpene, Roridin C, dihydrotrichothecene, Scirpen-4, 8-diol, Verrucarol, Scirpentriol, T-2 tetraol, pentahydroxyscirpene, 4-deacetylneosolaniol, trichodermin, deacetylcalonectrin, calonectrin, diacetylverrucarol, 4-monoacetoxyscirpenol, 4,15-diacetoxyscirpenol, 7-hydroxydiacetoxyscirpenol, 8-hydroxydiacetoxy-scirpenol (Neosolaniol), 7,8-dihydroxydiacetoxyscirpenol, 7-hydroxy-8-acetyldiacetoxyscirpenol, 8-acetylneosolaniol, NT-1, NT-2, HT-2, T-2, and acetyl T-2 toxin.
Representative examples of Group B simple trichothecenes include: Trichothecolone, Trichothecin, deoxynivalenol, 3-acetyldeoxynivalenol, 5-acetyldeoxynivalenol, 3,15-diacetyldeoxynivalenol, Nivalenol, 4-acetylnivalenol (Fusarenon-X), 4,15-idacetylnivalenol, 4,7,15-triacetylnivalenol, and tetra-acetylnivalenol. Representative examples of Group C simple trichothecenes include: Crotocol and Crotocin. Representative macrocyclic trichothecenes include Verrucarin A, Verrucarin B, Verrucarin J (Satratoxin C), Roridin A, Roridin D, Roridin E (Satratoxin D), Roridin H, Satratoxin F, Satratoxin G, Satratoxin H, Vertisporin, Mytoxin A, Mytoxin C, Mytoxin B, Myrotoxin A, Myrotoxin B, Myrotoxin C, Myrotoxin D, Roritoxin A, Roritoxin B, and Roritoxin D. In addition, the general "trichothecene" sesquiterpenoid ring structure is also present in compounds termed "baccharins" isolated from the higher plant Baccharis megapotamica, and these are described in the literature, for instance as disclosed by Jarvis et al. (Chemistry of Alleopathy, ACS Symposium Series No. 268: ed. A. C. Thompson, 1984, pp. 149-159).
Representative examples of "anti-matrix agents" include inhibitors (i.e., agonists and antagonists and competitive and non-competitive inhibitors) of matrix synthesis, secretion and assembly, organizational cross-linking (e.g., transglutaminases cross-linking collagen), and matrix remodeling (e.g., following wound healing). A representative example of a useful therapeutic agent in this category of anti-matrix agents is colchicine, an inhibitor of secretion of extracellular matrix.
For the sustained release dosage form embodiments of the present invention, therapeutic agents preferably are those that inhibit vascular smooth muscle cell activity without killing the cells (i.e., cytostatic therapeutic agents). Preferred therapeutic agents for this purpose exhibit one or more of the following capabilities: to inhibit DNA synthesis prior to protein synthesis inhibition or to inhibit migration of vascular smooth muscle cells into the intima. These therapeutic agents do not significantly inhibit protein synthesis (i.e., do not kill the target cells) and, therefore, facilitate cellular repair and matrix production to stabilize the vascular wall lesion caused by angioplasty, by reducing smooth muscle cell proliferation.
Exemplary of such preferred therapeutic agents are protein kinase inhibitors, such as staurosporin (staurosporine is available from Sigma Chemical Co., St. Louis, Mo.) cytochalasins, such as cytochalasin B (Sigma Chemical Co.), and suramin (FBA Pharmaceuticals, West Haven, Conn.), as well as nitroglycerin (DuPont Pharmaceuticals, Inc., Manuti, Puerto Rico) or analogs or functional equivalents thereof. These compounds are cytostatic and have been shown to exert minimal protein synthesis inhibition and cytotoxicity at concentrations where significant DNA synthesis inhibition occurs (see Example 8 and FIGS. 10A-10D). A useful protocol for identifying therapeutic agents useful in sustained release dosage form embodiments of the present invention is set forth in Example 8, for example. A practitioner in the art is capable of designing substantially equivalent experimental protocols for making such an identification for different target cell populations, such as adherent monolayer target cell types.
Other embodiments of the present invention involve agents that are cytotoxic to cancer cells. Preferred agents for these embodiments are Roridin A, Pseudomonas exotoxin and the like or analogs or functional equivalents thereof. A plethora of such therapeutic agents, including radioisotopes and the like, have been identified and are known in the art. In addition, protocols for the identification of cytotoxic moieties are known and employed routinely in the art.
Modulation of immune system-mediated disease effector cells can also be accomplished using the sustained release dosage forms of the present invention. Such modulation is preferably conducted with respect to diseases having an effector cell population that is accessible through local sustained release dosage form administration. Therapeutic moieties having the requisite modulating activity, e.g., cytocidal, cytostatic, metabolism modulation or like activity upon lymphorecticular cells in the treatment of arthritis (intra-articular administration), sprue (oral administration), uveitis and endophthalmitis (intra-ocular administration) and keratitis (sub-conjunctival administration), are identifiable using techniques that are known in the art. These agents can also be used to reduce hyperactivity of epithelial glands and endocrine organs that results in multiple disorders. Preferred agents for these embodiments include Roridin A, Pseudomonas exotoxin, suramin, protein kinase inhibitors (e.g., staurosporin) and the like, or analogs or functional equivalents thereof.
Other preferred therapeutic agents useful in the practice of the present invention include moieties capable of reducing or eliminating pathological proliferation, migration or hyperactivity of normal tissues. Exemplary of such therapeutic agents are those capable of reducing or eliminating hyperactivity of corneal epithelium and stroma, pathological proliferation or prolonged contraction of smooth muscle cells or pericytes of the intraocular vasculature implicated in degenerative eye disease resulting from hyperplasia or decreased vascular lumen area. Preferred agents for this purpose are staurosporin and cytochalasin B.
Vascular smooth muscle binding proteins of the invention bind to targets on the surface of vascular smooth muscle cells. It will be recognized that specific targets, e.g., polypeptides or carbohydrates, proteoglycans and the like, that are associated with the cell membranes of vascular smooth muscle cells are useful for selecting (e.g., by cloning) or constructing (e.g., by genetic engineering or chemical synthesis) appropriately specific vascular smooth muscle binding proteins. Particularly useful "targets" are internalized by smooth muscle cells, e.g., as membrane constituent antigen turnover occurs in renewal. Internalization by cells may also be by mechanisms involving phagolysosomes, clathrin-coated pits, receptor-mediated redistribution or endocytosis and the like. In a preferred embodiment, such a "target" is exemplified by chondroitin sulfate proteoglycans (CSPGs) synthesized by vascular smooth muscle cells and pericytes, and a discrete portion (termed an epitope herein) of the CSPG molecule having an apparent molecular weight of about 250 kD is especially preferred. The 250 kD target is an N-linked glycoprotein that is a component of a larger 400 kD proteoglycan complex (14). In one presently preferred embodiment of the invention, a vascular smooth muscle binding protein is provided by NR-AN-01 monoclonal antibody (a subculture of NR-ML-05) that binds to an epitope in a vascular smooth muscle CSPG target molecule. The monoclonal antibody designated NR-ML-05 reportedly binds a 250 kD CSPG synthesized by melanoma cells (Morgan et al., U.S. Pat. No. 4,897,255). Smooth muscle cells and pericytes also reportedly synthesize a 250 kD CSPG as well as other CSPGs (11). NR-ML-05 binding to smooth muscle cells has been disclosed (Fritzberg et al., U.S. Pat. No. 4,879,225). Monoclonal antibody NR-ML-05 and subculture NR-ML-05 No. 85-41-4I-A2, freeze # A2106, have both been deposited with the American Type Culture Collection, Rockville, Md. and granted Accession Nos. HB-5350 and HB-9350, respectively. NR-ML-05 is the parent of, and structurally and functionally equivalent to, subclone NR-AN-01, disclosed herein. It will be recognized that NR-AN-01 is just one example of a vascular smooth muscle binding protein that specifically associates with the 400 kD CSPG target, and that other binding proteins associating with this target and other epitopes in this target (14) are also useful in the therapeutic conjugates and methods of the invention. In the present case, six other murine monoclonal antibodies and two human chimeric monoclonal antibodies have also been selected, as described herein, that specifically target to the 250 kD CSPG of vascular smooth muscle cells. The antibodies also appear to be internalized by the smooth muscle cells following binding to the cell membrane. Immunoreactivity studies have also shown the binding of the murine MAbs to the 250 kD antigen in 45 human normal tissues and 30 different neoplasms and some of these results have been disclosed previously (U.S. Pat. No. 4,879,225). In this disclosure and other human clinical studies, MAbs directed to the CSPG 250 kD antigen localized to vascular smooth muscle cells in vivo. Further, it will be recognized that the amino acid residues involved in the multi-point kinetic association of the NR-AN-01 monoclonal antibody with a CSPG marker antigenic epitope (i.e., the amino acids constituting the complementarity determining regions) are determined by computer-assisted molecular modeling and by the use of mutants having altered antibody binding affinity. The binding-site amino acids and three dimensional model of the NR-AN-01 antigen binding site serve as a molecular model for constructing functional equivalents, e.g., short polypeptides ("minimal polypeptides"), that have binding affinity for a CSPG synthesized by vascular smooth muscle cells and pericytes.
In a presently preferred embodiment for treating stenosis following vascular surgical procedures, e.g., PTCA, selected binding proteins, e.g., antibodies or fragments, for use in the practice of the invention have a binding affinity of >104 liter/mole for the vascular smooth muscle 250 kD CSPG, and also the ability to be bound to and internalized by smooth muscle cells or pericytes.
Three-dimensional modeling is also useful to construct other functional equivalents that mimic the binding of NR-AN-01 to its antigenic epitope, e.g., "mimetic" chemical compounds that mimic the three-dimensional aspects of NR-AN-01 binding to its epitope in a CSPG target antigen. As used herein, "minimal polypeptide" refers to an amino acid sequence of at least six amino acids in length. As used herein, the term "mimetic" refers to an organic chemical polymer constructed to achieve the proper spacing for binding to the amino acids of, for example, an NR-AN-01 CSPG target synthesized by vascular smooth muscle cells or pericytes.
It will be recognized that the inventors also contemplate the utility of human monoclonal antibodies or "humanized" murine antibody as a vascular smooth muscle binding protein in the therapeutic conjugates of their invention. For example, murine monoclonal antibody may be "chimerized" by genetically recombining the nucleotide sequence encoding the murine Fv region (i.e., containing the antigen binding sites) with the nucleotide sequence encoding a human constant domain region and an Fc region, e.g., in a manner similar to that disclosed in European Patent Application No. 0,411,893 A2. Humanized vascular smooth muscle binding partners will be recognized to have the advantage of decreasing the immunoreactivity of the antibody or polypeptide in the host recipient, which may thereby be useful for increasing the in vivo half-life and reducing the possibility of adverse immune reactions.
Also contemplated as useful binding peptides for restenosis treatment sustained release dosage forms of the present invention are those that localize to intercellular stroma and matrix located between and among vascular smooth muscle cells. Such binding peptides deliver the therapeutic agent to the interstitial space between the target cells. The therapeutic agent is released into such interstitial spaces for subsequent uptake by the vascular smooth muscle cells. Preferred binding peptides of this type are associated with epitopes on collagen, extracellular glycoproteins such as tenascin, reticulum and elastic fibers, cytokeratin and other intercellular matrix components. Minimal peptides, mimetic organic chemical compounds, human or humanized monoclonal antibodies and the like that localize to intracellular stroma and matrix are also useful as binding peptides in this embodiment of the present invention. Such binding peptides may be identified and constructed or isolated in accordance with known techniques. In preferred embodiments of the present invention, the interstitial matrix binding protein binds to a target epitope with an association constant of at least about 10-4 M.
Useful binding peptides for cancer treatment embodiments of the present invention include those associated with cell membrane and cytoplasmic epitopes of cancer cells and the like. These binding peptides localize to the surface membrane of intact cells and internal epitopes of disrupted cells, respectively, and deliver the therapeutic agent for assimilation into the target cells. Minimal peptides, mimetic organic compounds and human or humanized antibodies that localize to the requisite tumor cell types are also useful as binding peptides of the present invention. Such binding peptides may be identified and constructed or isolated in accordance with known techniques. Preferred binding peptides of these embodiments of the present invention bind to a target epitope with an association constant of at least about 10-6 M.
Binding peptides to membrane and cytoplasmic epitopes and the like that localize to immune system-mediated disease effector cells, e.g., cells of the lymphoreticular system, are also useful to deliver sustained release dosage forms of the present invention. The therapeutic agent is delivered to target cells for internalization therein by such sustained release dosage forms. Minimal peptides, mimetic organic compounds and human or humanized antibodies that localize to the requisite effector cell types are also useful as binding peptides of the present invention. Such binding peptides may be identified and constructed or isolated in accordance with known techniques. Preferred binding peptides of these embodiments of the present invention bind to a target epitope with an association constant of at least about 10-6 M.
Other preferred binding proteins or peptides useful in the practice of the present invention include moieties capable of localizing to pathologically proliferating normal tissues, such as pericytes of the intraocular vasculature implicated in degenerative eye disease. The therapeutic agent is delivered to target cells for internalization therein by such sustained release dosage forms. Minimal peptides, mimetic organic compounds and human or humanized antibodies that localize to the requisite pathologically proliferating normal cell types are also useful as binding peptides of the present invention. Such binding peptides may be identified and constructed or isolated in accordance with known techniques. Preferred binding peptides of these embodiments of the present invention bind to a target epitope with an association constant of at least about 10-6 M.
Representative "coupling" methods for linking the therapeutic agent through covalent or non-covalent bonds to the vascular smooth muscle binding protein include chemical cross-linkers and heterobifunctional cross-linking compounds (i.e., "linkers") that react to form a bond between reactive groups (such as hydroxyl, amino, amido, or sulfhydryl groups) in a therapeutic agent and other reactive groups (of a similar nature) in the vascular smooth muscle binding protein. This bond may be, for example, a peptide bond, disulfide bond, thioester bond, amide bond, thioether bond, and the like. In one illustrative example, conjugates of monoclonal antibodies with drugs have been summarized by Morgan and Foon (Monoclonal Antibody Therapy to Cancer: Preclinical Models and Investigations, Basic and Clinical Tumor Immunology, Vol. 2, Kluwer Academic Publishers, Hingham, Mass.) and by Uhr J. of Immunol. 133:i-vii, 1984). In another illustrative example where the conjugate contains a radionuclide cytostatic agent, U.S. Pat. No. 4,897,255, Fritzberg et al., incorporated herein by reference, is instructive of coupling methods that may be useful. In one presently preferred embodiment, the therapeutic conjugate contains a vascular smooth muscle binding protein coupled covalently to a trichothecene drug. In this case, the covalent bond of the linkage may be formed between one or more amino, sulfhydryl, or carboxyl groups of the vascular smooth muscle binding protein and a) the trichothecene itself; b) a trichothecene hemisuccinate carboxylic acid; c) a trichothecene hemisuccinate (HS) N-hydroxy succinimidate ester; or d) trichothecene complexes with poly-L-lysine or any polymeric carrier. Representative examples of coupling methods for preparing therapeutic conjugates containing a trichothecene therapeutic agent are described in U.S. Pat. Nos. 4,906,452 and 4,744,981, incorporated herein by reference. Other examples using a hydrazide for forming a Schiff base linkage between binding proteins and trichothecenes are disclosed in pending U.S. patent application Ser. No. 07/415,154, incorporated herein by reference.
The choice of coupling method will be influenced by the choice of vascular smooth muscle binding protein or peptide, interstitial matrix binding protein or peptide and therapeutic agent, and also by such physical properties as, e.g., shelf life stability, and/or by such biological properties as, e.g., half-life in cells and blood, intracellular compartmentalization route, and the like. For example, in one presently preferred therapeutic conjugate, hemisuccinate conjugates of the Roridin A therapeutic agent have a longer serum half-life than those of Verrucarin A, and this increased stability results in a significantly increased biological activity.
The sustained release embodiment of the present invention includes a therapeutic agent dispersed within a non-biodegradable or biodegradable polymeric structure. Such dispersion is conducted in accordance with the procedure described Cowsar et al., "Poly(Lactide-Co-Glycolide) Microcapsules for Controlled Release of Steroids," Methods Enzymology, 112:101-116, 1985; Eldridge et al., "Biodegradable and Biocompatible Poly(DL-Lactide-Co-Glycolide) Microspheres as an Adjuvant for Staphylococcal Enterotoxin B Toxoid Which Enhances the Level of Toxin-Neutralizing Antibodies," Infection and Immunity, 59:2978-2986, 1991; Cohen et al., "Controlled Delivery Systems for Proteins Based on Poly(Lactic/Glycolic Acid) Microspheres," Pharmaceutical Research, 8(6):713-720, 1991; and Sanders et al., "Controlled Release of a Luteinizing Hormone-Releasing Hormone Analogue from Poly(D,L-Lactide-Co-Glycolide) Microspheres," J. Pharmaceutical Science, 73(9):1294-1297, 1984.
The physical and chemical character of the sustained release dosage form of the present invention is amenable to several alternative modes of attachment to binding proteins or peptides. Dosage forms (sustained release-type) of the present invention are capable of binding to binding proteins/peptides through, for example, covalent linkages, intermediate ligand sandwich attachment, or non-covalent adsorption or partial entrapment. When the preferred poly-lactic/glycolic acid particulates are formed with the therapeutic agent dispersed therein, the uncharged polymer backbone is oriented both inward (with the quasi lipophilic therapeutic agent contained therein) and outward along with a majority of the terminal carboxy groups. These surface carboxy groups may serve as covalent attachment sites when activated by, for example, a carbodiimide) for nucleophilic groups of the binding protein/peptide. Such nucleophilic groups include lysine epsilon amino groups (amide linkage), serine hydroxyl groups (ester linkage) or cysteine mercaptan groups (thioester linkage). Reactions with particular groups depend upon pH and the reduction state of the reaction conditions.
For example, poly-lactic/glycolic acid particulates having terminal carboxylic acid groups are reacted with N-hydroxybenztriazole in the presence of a water soluble carbodiimide of the formula R--N=C=N--R' (wherein R is a 3-dimethylaminopropyl group or the like and R' is an ethyl group or the like). The benztriazole-derivatized particulates (i.e., activated imidate-bearing moieties) are then reacted with a protein/peptide nucleophilic moiety such as an available epsilon amino moiety. Alternatively, p-nitrophenol, tetrafluorophenol, N-hydroxysuccinimide or like molecules are useful to form an active ester with the terminal carboxy groups of poly-lactic/glycolic acid particulates in the presence of carbodiimide. Other binding protein/peptide nucleophilic moieties include hydroxyl groups of serine, endogenous free thiols of cysteine, thiol groups resulting from reduction of binding protein/peptide disulfide bridges using reducing agents commonly employed for that purpose (e.g., cysteine, dithiothreitol, mercaptoethanol and the like) and the like. Additionally, the terminal carboxy groups of the poly lactic/glycolic acid particulates are activatable by reaction with thionyl chloride to form an acyl chloride derivatized moiety. The derivatized particulates are then reacted with binding peptide/protein nucleophilic groups to form targeted dosage forms of the present invention.
Direct sustained release dosage form-binding protein or peptide conjugation may disrupt binding protein/peptide target cell recognition. Ligand sandwich attachment techniques are useful alternatives to achieve sustained release dosage form-binding protein/peptide attachment. Such techniques involve the formation of a primary peptide or protein shell using a protein that does not bind to the target cell population. Binding protein/peptide is then bound to the primary peptide or protein shell to provide the resultant particulate with functional binding protein/peptide. An exemplary ligand sandwich approach involves covalent attachment of avidin or streptavidin to the particulates through functional groups as described above with respect to the "direct" binding approach. The binding protein or peptide is derivatized, preferably minimally, with functionalized biotin (e.g., through active ester, hydrazide, iodoacetal, maleimidyl or like functional groups). Ligand (i.e., binding peptide or protein/ functionalized biotin) attachment to the available biotin binding sites of the avidin/streptavidin primary protein shell occurs through the use of a saturating amount of biotinylated protein/peptide.
For example, poly-lactic/glycolic acid particulates having terminal carboxylic acid groups are activated with carbodiimide and subsequently reacted with avidin or streptavidin. The binding protein or peptide is reacted with biotinamidocaproate N-hydroxysuccinimide ester at a 1-3 molar offering of biotin-containing compound to the binding protein/peptide to form a biotinylated binding protein/peptide. A molar excess of the biotinylated binding protein/peptide is incubated with the avidin-derivatized particulates to form a targeted dosage form of the present invention.
Alternatively, the particulate carboxy groups are biotinylated (e.g., through carbodiimide activation of the carboxy group and subsequent reaction with amino alkyl biotinamide). The biotinylated particulates are then incubated with a saturating concentration (i.e., a molar excess) of avidin or streptavidin to form protein coated particulates having free biotin binding sites. Such coated particulates are then capable of reaction with a molar excess of biotinylated binding protein formed as described above. Another option involves avidin or streptavidin bound binding peptide or protein attachment to biotinylated particulates.
In addition, binding protein/peptide-particulate attachment can be achieved by adsorption of the binding peptide to the particulate, resulting from the nonionic character of the partially exposed polymer backbone of the particulate. Under high ionic strength conditions (e.g., 1.0 molar NaCl), hydrogen and hydrophobic particulate-binding protein/peptide binding are favored.
Moreover, binding protein/peptide may be partially entrapped in the particulate polymeric matrix upon formation thereof. Under these circumstances, such entrapped binding protein/peptide provides residual selective binding character to the particulate. Mild particulate formation conditions, such as those employed by Cohen et al., Pharmaceutical Research, 8: 713-720 (1991), are preferred for this embodiment of the present invention. Such entrapped binding protein is also useful in target cell reattachment of a partially degraded particulate that has undergone exocytosis. Other polymeric particulate dosage forms (e.g., non-biodegradable dosage forms) having different exposed functional groups can be bound to binding proteins or peptides in accordance with the principles discussed above.
Exemplary non-biodegradable polymers useful in the practice of the present invention are polystyrenes, polypropylenes, styrene acrylic copolymers and the like. Such non-biodegradable polymers incorporate or can be derivatized to incorporate functional groups for attachment of binding protein/peptide, including carboxylic acid groups, aliphatic primary amino groups, aromatic amino groups and hydroxyl groups.
Carboxylic acid functional groups are coupled to binding protein or peptide using, for example, the reaction mechanisms set forth above for poly-lactic/glycolic acid biodegradable polymeric particulate dosage forms. Primary amino functional groups are coupled by, for example, reaction thereof with succinic anhydride to form a terminal carboxy moiety that can be bound to binding peptide/protein as described above. Additionally, primary amino groups can be activated with cyanogen bromide and form guanidine linkages with binding protein/peptide primary amino groups. Aromatic amino functional groups are, for example, diazotized with nitrous acid to form diazonium moieties which react with binding protein/peptide tyrosines, thereby producing a diazo bond between the non-biodegradable particulate and the binding protein/peptide. Hydroxyl functional groups are coupled to binding protein/peptide primary amino groups by, for example, converting the hydroxyl moiety to a terminal carboxylic acid functional group. Such a conversion can be accomplished through reaction with chloroacetic acid followed by reaction with carbodiimide. Sandwich, adsorption and entrapment techniques, discussed above with respect to biodegradable particulates, are analogously applicable to non-biodegradable particulate-binding protein/peptide affixation.
In a preferred embodiment, targeting is specific for potentially proliferating cells that result in increased smooth muscle in the intimal region of a traumatized vascular site, e.g., following angioplasty, e.g., pericytes and vascular smooth muscle cells. Aspects of the invention relate to therapeutic modalities in which the therapeutic conjugate of the invention is used to delay, reduce, or eliminate smooth muscle proliferation after angioplasty, e.g., PTCA, atheroectomy and percutaneous transluminal coronary rotational atheroblation.
In another preferred embodiment, targeting is specific for primary or metastatic tumor foci accessible to local administration, e.g., tumors exposed for infiltration by laparotomy or visible for fluoroscopic or computerized tomography guiding and infusion needle administration to internal tumor foci or tumors confined to a small area or cavity within the mammal, e.g., ovarian cancer located in the abdomen, focal or multifocal liver tumors or the like. Aspects of this embodiment of the invention involve therapeutical modalities wherein the therapeutic agent is cytotoxic to the target cells or metabolically modulates the cells, increasing their sensitivity to chemotherapy and/or radiation therapy.
In another embodiment, targeting is specific for a local administration accessible effector cell population implicated in immune system-mediated diseases, e.g., arthritis, intra-ocular immune system-mediated disease or sprue. Aspects of this embodiment of the present invention involve therapeutic modalities wherein the therapeutic agent is cytotoxic or modifies the biological response of the target cells to effect a therapeutic objective.
In another embodiment, targeting is specific for a local administration accessible pathologically proliferating or hyperactive normal cell population implicated in, e.g., degenerative eye disease, corneal pannus, hyperactive endocrine glands or the like. Aspects of this embodiment of the present invention involve therapeutic modalities wherein the therapeutic agent reduces or eliminates proliferation or hyperactivity of the target cell population.
For treatment of a traumatized or diseased vascular site, the therapeutic conjugates or dosage forms of the invention may be administered to the host using an infusion catheter, such as produced by C. R. Bard Inc., Billerica, Mass., or that disclosed by Wolinsky (7; U.S. Pat. No. 4,824,436) or Spears (U.S. Pat. No. 4,512,762). In this case, a therapeutically effective dosage of the therapeutic conjugate will be typically reached when the concentration of conjugate in the fluid space between the balloons of the catheter is in the range of about 10-3 to 10-12 M. It will be recognized from the Examples provided herewith that therapeutic conjugates of the invention may only need to be delivered in an anti-proliferative therapeutic dosage sufficient to expose the proximal (6 to 9) cell layers of the intimal or tunica media cells lining the lumen to the therapeutic anti-proliferative conjugate, whereas the anti-contractile therapeutic dosage needs to expose the entire tunica media, and further that this dosage can be determined empirically, e.g., by a) infusing vessels from suitable animal model systems and using immunohistochemical methods to detect the conjugate and its effects (e.g., such as exemplified in the EXAMPLES below); and b) conducting suitable in vitro studies such as exemplified in EXAMPLES 3, 4, and 5, below).
In a representative example, this therapeutically effective dosage is achieved by preparing 10 ml of a 200 .mu.g/ml therapeutic conjugate solution, wherein the vascular smooth muscle protein binding protein is NR-AN-01 and the therapeutic agent is Roridin A, a trichothecene drug. For treating vascular trauma, e.g., resulting from surgery or disease (e.g., see below), when the therapeutic conjugate is administered with an infusion catheter, 10 ml will commonly be sufficient volume to fill the catheter and infuse 1 to 1.5 ml into one to three traumatic lesion sites in the vessel wall. It will be recognized by those skilled in the art that desired therapeutically effective dosages of a therapeutic conjugate according to the invention will be dependent on several factors, including, e.g.: a) the binding affinity of the vascular smooth muscle binding protein in the therapeutic conjugate; b) the atmospheric pressure applied during infusion; c) the time over which the therapeutic conjugate administered resides at the vascular site; d) the nature of the therapeutic agent employed; and/or e) the nature of the vascular trauma and therapy desired. Those skilled practitioners trained to deliver drugs at therapeutically effective dosages (e.g., by monitoring drug levels and observing clinical effects in patients) will determine the optimal dosage for an individual patient based on experience and professional judgment. In a preferred embodiment, about 0.3 atm (i.e., 300 mm of Hg) to about 3 atm of pressure applied for 15 seconds to 3 minutes directly to the vascular wall is adequate to achieve infiltration of a therapeutic conjugate containing the NR-AN-01 binding protein into the smooth muscle layers of a mammalian artery wall. Those skilled in the art will recognize that infiltration of the therapeutic conjugate into intimal layers of a diseased human vessel wall will probably be variable and will need to be determined on an individual basis.
Sustained release dosage forms of an embodiment of the invention may only need to be delivered in an anti-proliferative therapeutic dosage sufficient to expose the proximal (6 to 9) cell layers of the tunica media smooth muscle cells lining the lumen to the dosage form. This dosage is determinable empirically, e.g., by a) infusing vessels from suitable animal model systems and using immunohistochemical, fluorescent or electron microscopy methods to detect the dosage form and its effects; and b) conducting suitable in vitro studies.
In a representative example, this therapeutically effective dosage is achieved by determining in smooth muscle cell tissue culture the pericellular agent dosage, which at a continuous exposure results in a therapeutic effect between the toxic and minimal effective doses. This therapeutic level is obtained in vivo by determining the size, number and therapeutic agent concentration and release rate required for particulates infused between the smooth muscle cells of the artery wall to maintain this pericellular therapeutic dosage. The dosage form should release the therapeutic agent at a rate that approximates the pericellular dose of the following exemplary therapeutic agents: from about 0.01 to about 100 micrograms/ml nitroglycerin, from about 1.0 to about 1000 micrograms/ml of suramin, from about 0.001 to about 100 micrograms/ml for cytochalasin, and from about 0.01 to about 105 nanograms/ml of staurosporin.
It will be recognized by those skilled in the art that desired therapeutically effective dosages of the sustained release dosage form of the invention will be dependent on several factors, including, e.g.: a) the binding affinity of the binding protein associated with the dosage form; b) the atmospheric pressure and duration of the infusion; c) the time over which the dosage form administered resides at the target site; d) the rate of therapeutic agent release from the particulate dosage form; e) the nature of the therapeutic agent employed; f) the nature of the trauma and/or therapy desired; and/or g) the intercellular and/or intracellular localization of the particulate dosage form. Those skilled practitioners trained to deliver drugs at therapeutically effective dosages, (e.g., by monitoring therapeutic agent levels and observing clinical effects in patients) are capable of determining the optimal dosage for an individual patient based on experience and professional judgment. In a preferred embodiment, about 0.3 atm (i.e., 300 mm of Hg) to about 3 atm of pressure applied for 15 seconds to 3 minutes to the arterial wall is adequate to achieve infiltration of a sustained release dosage form bound to the NR-AN-01 binding protein into the smooth muscle layers of a mammalian artery wall. Wolinsky et al., "Direct Intraarterial Wall Injection of Microparticles Via a Catheter: A Potential Drug Delivery Strategy Following Angioplasty," Am. Heart Jour., 122(4):1136-1140, 1991. Those skilled in the art will recognize that infiltration of a sustained release dosage form into a target cell population will probably be variable and will need to be determined on an individual basis.
It will also be recognized that the selection of a therapeutic agent that exerts its effects intracellularly, e.g., on ribosomes or DNA metabolism, will influence the dosage and time required to achieve a therapeutically effective dosage, and that this process can be modeled in vitro and in animal studies, such as those described in the Examples provided below, to find the range of concentrations over which the therapeutic conjugate or dosage form should be administered to achieve its effects of delaying, reducing or preventing restenosis following angioplasty. For example, therapeutic conjugates radiolabeled with alpha-, beta- or gamma-emitters of known specific activities (e.g., millicuries per millimole or milligram of protein) are useful for determining the therapeutically effective dosage by using them in animal studies and human trials with quantitative imaging or autoradiography of histological tissue sections to determine the concentration of therapeutic conjugate that is required by the therapeutic protocol. A therapeutically effective dosage of the therapeutic conjugate or dosage form will be reached when at least three conditions are met: namely, (1) the therapeutic conjugate or dosage form is distributed in the intimal layers of the traumatically injured vessel; (2) the therapeutic conjugate or dosage form is distributed within the desired intracellular compartment of the smooth muscle cells, i.e., that compartment necessary for the action of the therapeutic agent, or the therapeutic agent released from the dosage form extracellularly is distributed within the relevant intracellular compartment; and (3) the therapeutic agent inhibits the desired cellular activity of the vascular smooth muscle cell, e.g., proliferation, migration, increased cellular volume, matrix synthesis, cell contraction and the like described above.
It will be recognized that where the therapeutic conjugate or dosage form is to be delivered with an infusion catheter, the therapeutic dosage required to achieve the desired inhibitory activity for a therapeutic conjugate or dosage form can also be anticipated through the use of in vitro studies. In a preferred aspect, the infusion catheter may be conveniently a double balloon or quadruple balloon catheter with a permeable membrane. In one representative embodiment, a therapeutically effective dosage of a therapeutic conjugate or dosage form is useful in treating vascular trauma resulting from disease (e.g., atherosclerosis, aneurysm, or the like) or vascular surgical procedures such as angioplasty, atheroectomy, placement of a stent (e.g., in a vessel), thrombectomy, and grafting. Atheroectomy may be performed, for example, by surgical excision, ultrasound or laser treatment, or by high pressure fluid flow. Grafting may be, for example, vascular grafting using natural or synthetic materials or surgical anastomosis of vessels such as, e.g., during organ grafting. Those skilled in the art will recognize that the appropriate therapeutic dosage for a given vascular surgical procedure (above) is determined in in vitro and in vivo animal model studies, and in human preclinical trials. In the EXAMPLES provided below, a therapeutic conjugate containing Roridin A and NR-AN-01 achieved a therapeutically effective dosage in vivo at a concentration which inhibited cellular protein synthesis in test cells in vitro by at least 5 to 50%, as judged by incorporation of radiolabeled amino acids.
In the case of therapeutic agents of conjugates or dosage forms containing anti-migratory or anti-matrix therapeutic agents, cell migration and cell adherence in in vitro assays, respectively, may be used for determining the concentration at which a therapeutically effective dosage will be reached in the fluid space created by the infusion catheter in the vessel wall.
While one representative embodiment of the invention relates to therapeutic methods employing an infusion catheter, it will be recognized that other methods for drug delivery or routes of administration may also be useful, e.g., injection by the intravenous, intralymphatic, intrathecal, intraarterial, local delivery by implanted osmotic pumps or other intracavity routes. For intravenous administration, nanoparticulate dosage forms of the present invention are preferred. Intravenous administration of nanoparticulates is useful, for example, where vascular permeability is increased in tumors for leakage, especially in necrotic areas of tumors having damaged vessels which allow the leakage of particles into the interstitial fluid, and where artery walls have been denuded and traumatized allowing the particles to enter the interstitial area of the tunica media.
Advantageously, non-coupled vascular smooth muscle cell binding protein (e.g., free NR-AN-01 antibody) is administered prior to administration of the therapeutic agent conjugate or dosage form to provide a blocker of non-specific binding to cross-reactive sites. Blocking of such sites is important because vascular smooth muscle cell binding proteins will generally have some low level of cross-reactivity with cells in tissues other than the desired smooth muscle cells. Such blocking can improve localization of the therapeutic conjugate or dosage form at the specific vascular site, e.g., by making more of the therapeutic conjugate available to the cells. As an example, non-coupled vascular smooth muscle binding protein is administered from about 5 minutes to about 48 hours, most preferably from about 5 minutes to about 30 minutes, prior to administration of the therapeutic conjugate or dosage form. In one preferred embodiment of the invention, the unlabeled specific "blocker" is a monovalent or bivalent form of an antibody (e.g., a whole antibody or an F(ab)'2, Fab, Fab', or Fv fragment of an antibody). The monovalent form of the antibody has the advantage of minimizing displacement of the therapeutic conjugate or dosage form while maximizing blocking of the non-specific cross-reactive sites. The non-coupled vascular smooth muscle cell binding protein is administered in an amount effective to blocking binding of a least a portion of the non-specific cross-reactive sites in a patient. The amount may vary according to such factors as the weight of the patient and the nature of the binding protein. In general, about 0.06 mg to 0.20 mg per kg body weight or more of the unlabeled specific blocker is administered to a human.
In addition, a second irrelevant vascular smooth muscle cell binding protein may optionally be administered to a patient prior to administration of the therapeutic conjugate or dosage form to reduce non-specific binding of the therapeutic conjugate or dosage form to tissues. In a preferred embodiment, the irrelevant binding protein may be an antibody which does not bind to sites in the patient through antigen-specific binding, but instead binds in a non-specific manner, e.g., through Fc receptor binding reticuloendothelial cells, asialo-receptor binding, and by binding to ubiquitin-expressing cells. The irrelevant "blocker" decreases non-specific binding of the therapeutic conjugate or dosage form and thus reduces side-effects, e.g., tissue toxicity, associated with the use of the therapeutic conjugate or dosage form. The irrelevant "blocker" is advantageously administered from 5 minutes to 48 hours, most preferably from 15 minutes to one hour, prior to administration of the therapeutic conjugate or dosage form, although the length of time may vary depending upon the therapeutic conjugate and route or method of injection. Representative examples of irrelevant "blockers" include antibodies that are nonreactive with human tissues and receptors or cellular and serum proteins prepared from animal sources that when tested are found not to bind in a specific manner (e.g., with a Ka<103 M-1) to human cell membrane targets.
It will be recognized that the conjugates and dosage forms of the invention are not restricted in use for therapy following angioplasty; rather, the usefulness of the therapeutic conjugates and dosage forms will be proscribed by their ability to inhibit cellular activities of smooth muscle cells and pericytes in the vascular wall. Thus, other aspects of the invention include therapeutic conjugates and dosage forms and protocols useful in early therapeutic intervention for reducing, delaying, or eliminating (and even reversing) atherosclerotic plaques and areas of vascular wall hypertrophy and/or hyperplasia. Therapeutic conjugates and dosage forms of the invention also find utility for early intervention in pre-atherosclerotic conditions, e.g., they are useful in patients at a high risk of developing atherosclerosis or with signs of hypertension resulting from atherosclerotic changes in vessels or vessel stenosis due to hypertrophy of the vessel wall.
For example, in another embodiment of the invention, the therapeutic conjugates and dosage forms may be used in situations in which angioplasty is not sufficient to open a blocked artery, such as those situations which require the insertion of an intravascular stent. In this embodiment of the invention, a metallic, plastic or biodegradable intravascular stent is coated with a biodegradable coating or with a porous non-biodegradable coating, having dispersed therein the sustained-release dosage form. In an alternative embodiment, a biodegradable stent may also have the therapeutic agent impregnated therein, i.e., in the stent matrix. Utilization of a biodegradable stent with the therapeutic agent impregnated therein which is further coated with a biodegradable coating or with a porous non-biodegradable coating having the sustained release-dosage form dispersed therein is also contemplated. This embodiment of the invention would provide a differential release rate of the therapeutic agent, i.e., there would be a faster release of the therapeutic agent from the coating followed by delayed release of the therapeutic agent that was impregnated in the stent matrix upon degradation of the stent matrix. Preferably, in this embodiment of the invention, the therapeutic agent is a cytochalasin, and most preferably is cytochalasin B, or a functionally equivalent analogue thereof. The intravascular stent thus provides a mechanical means of providing an increase in luminal area of a vessel, in addition to that provided via the biological stenting action of the cytochalasin B releasably embedded therein.
Furthermore, this embodiment of the invention also provides an increase in the efficacy of intravascular stents by reducing or preventing intimal proliferation. Additionally, cytochalasin B inhibits the proliferation and migration of pericytes, which can transform into smooth muscle cells and contribute to intimal thickening. This inhibition of intimal smooth muscle cells, stroma produced by the smooth muscle and pericytes allows for more rapid and complete re-endothelization following the intraventional placement of the vascular stent. The increased rate of re-endothelization and stabilization of the vessel wall following stent placement would reduce the loss of luminal area and decreased blood flow which is the primary cause of vascular stent failures.
Preferably, in the practice of this embodiment of the invention, the biodegradable microparticles containing the therapeutic agent are from about 1 to 50 microns. It is further preferred that the microparticles would biodegrade over a period of 30 to 120 days, releasing into the tunica media and intima a sustained cellular concentration of approximately from about 0.05 .mu.g/ml to about 0.25 .mu.g/ml of cytochalasin B into the cytosol, thus providing the diffusion of therapeutic levels of cytochalasin B without toxicity to cells adjacent to the stent/vessel wall interface.
The therapeutic conjugates and dosage forms of the invention may also be used in therapeutic modalities for enhancing the regrowth of endothelial cells in injured vascular tissues and in many kinds of wound sites including epithelial wounds. In these therapeutic modalities, the therapeutic conjugates and dosage forms of the invention find utility in inhibiting the migration and/or proliferation of smooth muscle cells or pericytes. Smooth muscle cells and pericytes have been implicated in the production of factors in vitro that inhibit endothelial cell proliferation, and their proliferation can also result in a physical barrier to establishing a continuous endothelium. Thus, the therapeutic conjugates and dosage forms of the invention find utility in promoting neo-angiogenesis and increased re-endothelialization, e.g., during wound healing, vessel grafts and following vascular surgery. The dosage forms may also release therapeutic modalities that stimulate or speed up re-endothelialization of the damaged vessel wall. An exemplary therapeutic agent for this purpose is vascular permeability factor.
Still other aspects of the invention relate to therapeutic modalities for enhancing wound healing in a vascular site and improving the structural and elastic properties of healed vascular tissues. In these therapeutic modalities using the therapeutic conjugate or dosage form of the invention, i.e., to inhibit the migration and proliferation of smooth muscle cells or pericytes in a vessel wall, the strength and quality of healing of the vessel wall are improved. Smooth muscle cells in the vascular wound site contribute to the normal process of contraction of the wound site which promotes wound healing. It is presently believed that migration and proliferation of smooth muscle cells and matrix secretion by transformed smooth muscle cells may detract from this normal process and impair the long-term structural and elastic qualities of the healed vessel. Thus, other aspects of the invention provide for therapeutic conjugates and dosage forms that inhibit smooth muscle and pericyte proliferation and migration as well as morphological transformation, and improve the quality of the healed vasculature.
For example, one embodiment of the present invention comprises the in vivo or ex vivo infusion of a solution of a therapeutic agent such as cytochalasin B into the walls of isolated vessels (arteries or veins) to be used for vascular grafts. In this embodiment of the invention, the vessel that is to serve as the graft is excised or isolated and subsequently distended by an infusion of a solution of a therapeutic agent. Preferably the infusion is accomplished by a pressure infusion at a pressure of about 0.2 to 1 atmosphere for a time period of from about 2 to about 4 minutes. This infusion regime will result in the penetration of an efficacious dose of the therapeutic agent to the smooth muscle cells of the vessel wall. Preferably, the therapeutic agent will be at a concentration of from about 0.1 .mu.g/ml to about 0.8 .mu.g/ml of infusate. Preferably, the therapeutic agent will be a cytochalasin, and most preferably, the therapeutic agent employed will be cytochalasin B, or a functionally equivalent analogue thereof.
It is known to those of ordinary skill in the art that peripheral vessels that are used for vascular grafts in other peripheral sites or in coronary artery bypass grafts, frequently fail due to post surgical stenosis. Since cytochalasin B infusion maintains the vascular luminal area in surgically traumatized vessels by virtue of its biological stenting activity, its administration in this process will retard the ability of the vessel to contract, resulting in a larger lumenal area. Furthermore, it is an advantage of this embodiment of the present invention that the administration of cytochalasin B in this manner will prevent the constriction or spasm that frequently occurs after vascular grafts are anastomosed to both their proximal and distal locations, that can lead to impaired function, if not total failure, of vascular grafts. Thus, the vessel stenting produced by cytochalasin b should decrease the incidence of spasms, which can occur from a few days to several months following the graft procedure.
The present invention also provides a combination therapeutic method involving a cytocidal therapeutic conjugate and a cytostatic therapeutic agent. The cytocidal conjugate includes a binding partner (such as a protein or peptide) capable of specifically localizing to vascular smooth muscle cells and an active agent capable of killing such cells. The cytocidal conjugate is administered, preferably intravenously or through any other convenient route therefor, localizes to the target smooth muscle cells, and destroys proliferating cells involved in stenotic or restenotic events. This cellular destruction causes the release of mitogens and other metabolic events, which events generally lead, in turn, to vascular smooth muscle cell proliferation. The sustained release anti-proliferative or anti-contractile dosage forms of the present invention are next administered, preferably through an infusion catheter or any convenient dosage form therefor. The sustained release dosage form retards the vascular smooth muscle cell proliferation and/or migration and contraction, thereby maintaining luminal diameter. This treatment methodology constitutes a biological arteromyectomy useful in stenotic vessels resulting from vascular smooth muscle cell hyperplasia and the like.
The present invention also provides methods for the treatment of cancer and immune system-mediated diseases through local administration of a targeted particulate dosage form. The particulate dosage form is, for example, administered locally into primary and/or metastatic foci of cancerous target cells. Local administration is preferably conducted using an infusion needle or intraluminal administration route, infusing the particulate dosage form in the intercellular region of the tumor tissue or in luminal fluid surrounding the tumor cells.
Primary foci introduction is preferably conducted with respect to target cells that are generally situated in confined areas within a mammal, e.g., ovarian carcinomas located in the abdominal cavity. The dosage form of the present invention binds to the target cell population and, optionally, is internalized therein for release of the therapeutic agent over time. Local administration of dosage forms of the present invention to such primary foci results in a localized effect on such target cells, with limited exposure of other sensitive organs, e.g., the bone marrow and kidneys, to the therapeutic agent.
When metastatic foci constitute the target cell population, the administered microparticles and larger nanoparticles are primarily bound to the target cells situated near the infusion site and are, optionally, internalized for release of the therapeutic agent, thereby generating a marked and localized effect on the target cells immediately surrounding the infusion site. In addition, smaller nanoparticles follow interstitial fluid flow or lymphatic drainage channels and bind to target cells that are distal to the infusion site and undergoing lymphatic metastasis.
The targeted dosage forms of this embodiment of the present invention can be used in combination with more commonly employed immunoconjugate therapy. In this manner, the immunoconjugate achieves a systemic effect within the limits of systemic toxicity, while the dosage form of the present invention delivers a concentrated and sustained dose of therapeutic agent to the primary and metastatic foci, which often receive an inadequate therapeutic dose from such "systemic" immunoconjugate administration alone, and avoids or minimizes systemic toxic effects.
Where the target cell population can be accessed by local administration, the dosage forms of the present invention are utilized to control immune system-mediated diseases. Exemplary of such diseases are arthritis, sprue, uveitis, endophthalmitis, keratitis and the like. The target cell populations implicated in these embodiments of the present invention are confined to a body cavity or space, such as joint capsules, pleural and abdominal cavity, eye and sub-conjunctival space, respectively. Local administration is preferably conducted using an infusion needle for a intrapleural, intraperitoneal, intraocular or sub-conjunctival administration route.
This embodiment of the present invention provides a more intense, localized modulation of immune system cells with minimal effect on the systemic immune system cells. Optionally, the systemic cells of the immune system are simultaneously treatable with a chemotherapeutic agent conjugated to a binding protein or peptide. Such a conjugate preferably penetrates from the vascular lumen into target immune system cells.
The local particulate dosage form administration may also localize to normal tissues that have been stimulated to proliferate, thereby reducing or eliminating such pathological (i.e., hyperactive) conditions. An example of this embodiment of the present invention involves intraocular administration of a particulate dosage form coated with a binding protein or peptide that localizes to pericytes and smooth muscle cells of neovascularizing tissue. Proliferation of these pericytes causes degenerative eye disease. Preferred dosage forms of the present invention release compounds capable of suppressing the pathological proliferation of the target cell population. The preferred dosage forms can also release compounds that increase vessel lumen area and blood flow, reducing the pathological alterations produced by this reduced blood supply.
Still another aspect of the present invention relates to therapeutic modalities for maintaining an expanded luminal volume following angioplasty or other vessel trauma. One embodiment of this aspect of the present invention involves administration of a therapeutic agent capable of inhibiting the ability of vascular smooth muscle cells to contract. Exemplary agents useful in the practice of this aspect of the present invention are those capable of causing a traumatized artery to lose vascular tone, such that normal vascular hydrostatic pressure (i.e., blood pressure) expands the flaccid vessel to or near to its maximal physiological diameter. Loss of vascular tone may be caused by agents that interfere with the formation or function of contractile proteins (e.g., actin, myosin, tropomyosin, caldesmon, calponin or the like). This interference can occur directly or indirectly through, for example, inhibition of calcium modulation, phosphorylation or other metabolic pathways implicated in contraction of vascular smooth muscle cells.
Inhibition of cellular contraction (i.e., loss of vascular tone) may operate through two mechanisms to reduce the degree of vascular stenosis. First, inhibition of cellular contraction for a prolonged period of time limits the number of smooth muscle cells that migrate from the tunica media into the intima, the thickening of which results in vascular luminal stenosis. Second, inhibition of cellular contraction causes the smooth muscle wall to relax and dilate under normal vascular hydrostatic pressure (i.e., blood pressure). Therapeutic agents, such as the cytochalasins, inhibit smooth muscle cell contraction without abolishing the protein synthesis necessary for traumatized, post-angioplasty or other surgically- or disease-damaged, smooth muscle cells to repair themselves. Protein synthesis is also necessary for the smooth muscle cells to secrete matrix, which fixes or retains the lumen in a state near its maximum systolic diameter as the vascular lesion stabilizes (i.e., a biologically-induced stenting effect).
This biological stenting effect not only results in an expanded vessel luminal area and increased blood flow rate through the vessel, but also significantly reduces elastic recoil following angioplasty. Elastic recoil is an acute closure of the vessel associated with vasospasm or early relaxation of the muscular wall, due to trauma shock resulting from vessel over-stretching by a balloon catheter during angioplasty. This spasm of the tunica media which leads to decreases in the luminal area may occur within hours, days or weeks after the balloon dilation, as restoration of vascular muscle wall tone occurs. Recent observations during microscopic examination of atheroectomy specimens suggest that elastic recoil may occur in up to 25% of angioplasty procedures classified as successful, based on the initial post-procedure angiogram. Because the biological stenting procedure relaxes the artery wall following balloon angioplasty, the clinician can eliminate over-inflation and its resultant trauma shock as a means to diminish or delay the vessel spasm or elastic recoil. Reduction or elimination of over-inflation decreases trauma to the muscular wall of the vessel, thereby reducing the determinants of smooth muscle cell proliferation in the intima and, therefore, reducing the incidence or severity of restenosis.
Biological stenting also decreases the incidence of thrombus formation. In pig femoral arteries treated with cytochalasin B, for example, the incidence of mural microthrombi was decreased as compared to the balloon traumatized arteries that were not treated with the therapeutic agent. This phenomenon appears to be a secondary benefit that may result from the increased blood flow through the traumatized vessel, said benefit being obtained through the practice of the present invention.
Cytochalasins are exemplary therapeutic agents capable of generating a biological stenting effect on vascular smooth muscle cells. Cytochalasins are thought to inhibit both migration and contraction of vascular smooth muscle cells by interacting with actin. The cytochalasins interact with the ends of filamentous actin to inhibit the elongation of the actin filaments. Low doses of cytochalasins (e.g., cytochalasin B) also disrupt microfilament networks of actin. In vitro data indicate that after vascular smooth muscle cells clear cytochalasin B, the cells regenerate enough polymerized actin to resume migration within about 24 hours. In vivo assessments reveal that vascular smooth muscle cells regain vascular tone within 2 to 4 days. It is during this recuperative period that the lumen diameter fixation and biological stenting effect occurs.
The therapeutic agent may be targeted, but is preferably administered directly to the traumatized vessel following the angioplasty or other traumatic event. The biological stenting effect of cytochalasin B, for example, is achievable using a single infusion of the therapeutic agent into the traumatized region of the vessel wall at a dose concentration ranging from about 0.1 microgram/ml to about 1.0 micrograms/ml.
Inhibition of vascular smooth muscle cell migration (from the tunica media to the intima) has been demonstrated in the same dose range (Example 11); however, a sustained exposure of the vessel to the therapeutic agent is preferable in order to maximize these anti-migratory effects. If the vascular smooth muscle cells cannot migrate into the intima, they cannot proliferate there. Should vascular smooth muscle cells migrate to the intima, a subsequently administered anti-proliferative sustained release dosage form inhibits the intimal proliferation. As a result, the sustained release dosage form of the present invention, incorporating a cytochalasin or other anti-proliferative therapeutic agent, can be administered in combination with a free cytochalasin therapeutic agent. In this manner, the biological stenting effect, as well as an anti-proliferative or anti-migratory effect, can be achieved in a single administration protocol.
Agents useful in the protocols of the present invention are identifiable, for example, in accordance with the following procedures. A potential agent for free agent (i.e., non-targeted) administration exhibits one or more of the following characteristics:
(i) retains an expanded luminal volume following angioplasty (e.g., PTCA, percutaneous transluminal angioplasty (PTA) or the like) or other trauma, including atheroectomy (e.g., rotoblater, laser and the like), coronary artery bypass procedures or the like; or resulting from vascular disease (e.g., atherosclerosis, eye diseases secondary to vascular stenosis or atrophy, cerebral vascular stenotic diseases or the like);
(ii) the initial increase in luminal area facilitated by the agent does not result in or accentuate chronic stenosis of the lumen;
(iii) inhibits target cell contraction or migration; and
(iv) is cytostatic.
Preferably, a therapeutic agent employed herein will have all four properties; however, the first and third are more important than the second and fourth for practice of the present invention. Cytochalasin B, for example, was evaluated to determine suitability for use in free therapeutic agent protocols. The biological stenting effect of cytochalasin B is achievable using a single infusion of the therapeutic agent into the traumatized region of the vessel wall at a dose concentration ranging from about 0.1 microgram/ml to about 1.0 micrograms/ml.
An agent useful in the sustained release embodiments of the present invention exhibits one or more of the following characteristics:
(i) retains an expanded luminal volume following angioplasty (e.g., PTCA, percutaneous transluminal angioplasty (PTA) or the like) or other trauma, including atheroectomy (e.g., rotoblater, laser and the like), coronary artery bypass procedures or the like; or resulting from vascular disease (e.g., atherosclerosis, eye diseases secondary to vascular stenosis or atrophy, cerebral vascular stenotic diseases or the like);
(ii) inhibits target cell proliferation (e.g., following 5 minute and 24 hour exposure to the agent, in vitro vascular smooth muscle tissue cultures demonstrate a level of inhibition of 3 H-thymidine uptake and, preferably, display relatively less inhibition of 3 H-leucine uptake);
(iii) at a dose sufficient to inhibit DNA synthesis, produces only mild to moderate (e.g., grade 2 or 3 in the assays described below) morphological cytotoxic effects;
(iv) inhibits target cell contraction; and
(v) is cytostatic.
Upon identification of a therapeutic agent exhibiting one or more of the preceding attributes, the agent is subjected to a second testing protocol that involves longer exposure of vascular smooth muscle cells to the therapeutic agent.
An agent useful in the sustained release embodiments of the present invention exhibits the following characteristics:
(i) upon long term (e.g., 5 days) exposure, the agent produces the same or similar in vitro effect on vascular smooth muscle tissue culture DNA synthesis and protein synthesis, as described above for the 5 minute and 24 hour exposures; and
(ii) at an effective dose in the long term in vitro assay for DNA synthesis inhibition, the agent exhibits mild to moderate morphological cytotoxic effects over a longer term (e.g., 10 days).
Further evaluation of potential anti-proliferative agents within the present invention is conducted in an in vivo balloon traumatized pig femoral artery model. Preferably, such agents demonstrate a 50% or greater inhibition of cell proliferation in the tunica media vascular smooth muscle cells, as indicated by a 1 hour "BRDU flash labeling" prior to tissue collection and histological evaluation. If an agent is effective for a period of time sufficient to inhibit intimal smooth muscle proliferation 50% or greater with a single exposure, it is an agent within the present invention that does not require administration in a sustained release dosage form. Agents having shorter duration activity are evaluated for sustained release if the systemic toxicity and potential therapeutic index appear to permit intravenous administration to achieve the 50% inhibition, or if the agent is amenable to local delivery to the vascular smooth muscle cells with sustained release at an effective anti-proliferative dose. Sustained release agents are evaluated in a sustained release dosage form for dose optimization and efficacy studies. Preferably, anti-proliferative agents useful in the practice of the present invention decrease vascular stenosis by 50% in balloon traumatized pig femoral arteries and, more preferably, to decrease vascular stenosis to a similar extent in pig coronary arteries. Such agents are then evaluable in human clinical trials.
Cell proliferation (i.e., DNA synthesis) inhibition is the primary characteristic for sustained release of agents. Staurosporin, for example, exhibits a differential between 3 H-leucine and 3 H-thymidine uptake such that it is cytostatic at administered doses. Longer duration cytotoxicity studies did not indicate that prolonged exposure to the therapeutic agent would adversely impact the target cells. In addition, BRDU pulsing indicated that staurosporin inhibits target cell proliferation. Any convenient method for evaluating the capability of inhibiting cell proliferation may alternatively be employed, however. Consequently, staurosporin is effective in retaining an expanded luminal volume.
Claim 1 of 43 Claims
What is claimed is:
1. A method for maintaining vessel luminal area, comprising inserting into a mammalian vessel an intravascular stent comprising a cytostatic agent that does not exhibit substantial cytotoxicity in an amount which allows for vascular repair and extracellular matrix production and reduces stenosis or restenosis upon placement of the stent.