Patent Publication Number: US-2006014727-A1

Title: Angiogenic compounds and uses thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is a continuation-in-part application of application serial no. PCT/CA2003/002024 filed Dec. 24, 2003 and designating the United States; which application claims priority pursuant to 35 U.S.C. § 119 (e) to the filing date of the U.S. Provisional Patent Application Ser. No. 60/435,864 filed Dec. 24, 2002; the disclosures of which applications are herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION  
      The invention is in the field of angiogenesis. More specifically, the invention is in the field of compounds that promote angiogenesis.  
     BACKGROUND OF THE INVENTION  
      New blood vessels develop from pre-existing vasculature in a complex physiological process known as angiogenesis. Angiogenesis involves a coordinated cascade of events initiated by the transmission of an angiogenic signal, which leads to the secretion of proteases by endothelial cells that line the inside of blood vessels, and subsequent infiltration and degradation of the basal lamina, followed by proliferation and differentiation of the endothelial cells into capillary tubes and the establishment of a new basement membrane (2). Angiogenesis is required during embryonic development for the formation of tissues and organs, and for the maintenance of organ function in the adult, for example, during endometrial cycling.  
      Stimulation or maintenance of appropriate angiogenesis has many therapeutic applications. For example, ischemic coronary artery disease is a major cause of morbidity and the leading cause of mortality in the west (1, 13). Current therapeutic options for patients with advanced ischemic heart disease include medical therapy or coronary revascularization by percutaneous coronary angioplasty or bypass surgery (1, 4). Many of these patients however exhibit residual symptoms of ischemia despite therapy (4). Furthermore, the incidence of restenosis or reocclusion in patients who have had invasive revascularization procedures remains high (4). The clinical situation is similar for patients with peripheral vascular disease (i.e. occlusion or stenosis of arteries other than coronary arteries) (5, 6).  
      Angiogenesis is also important for the prompt and appropriate healing of wounds and fractures (7), and promoting angiogenesis may hasten the healing of wounds in various situations. For instance, chronic skin ulcerations in diabetics may be treatable by improving the blood supply (8). In other situations (e.g. in burn injuries, or in chronic non-healing peptic ulcer disease) stimulating angiogenesis may promote healing (9, 10). Angiogenesis may also be important in fields that involve the growth of new tissues or organs (in vitro or in vivo), for example, for the vascularisation of synthetic skin grafts.  
      To date, therapeutic attempts at promoting angiogenesis have included use of Fibroblast growth factor-2 (FGF-2) and Vascular endothelial growth factor (VEGF) for treatment of myocardial and limb ischemia (11, 12). These attempts however have encountered a number of problems. First, both proteins are relatively large molecules that have to be synthesized as recombinant molecules or delivered to cells using gene therapy methods, and as such, the optimal method of delivery has not been determined, although intravenous, intra-arterial, intramuscular, and gene therapy delivery of recombinant protein have been tested (11, 12). In addition, the tissue half-life of both proteins is limited, and they can cause hypotension when delivered systemically (11, 12).  
      With respect to small molecules, estrogen and other sex steroids have been implicated in the promotion of angiogenesis (15; 23; U.S. Pat. No. 5,866,561, issued Feb. 2, 1999 to Ungs). Estrogen however has also been reported to inhibit angiogenesis (25), and thus its role in angiogenesis may be controversial. Furthermore, administration of estrogen as a therapeutic for promoting angiogenesis may be contraindicated due to adverse effects, such as feminization in men, and the increased risk of some cancers, for example, uterine cancer or breast cancer, and blood clots in the legs in women. The ginsenoside Rg1 has been reported as having estrogen-like activity, including angiogenesis (24, 28), and beta-sitosterol, a compound derived from Aloe vera, was reported as having angiogenic activity (39, 40).  
     SUMMARY OF THE INVENTION  
      The invention provides, in part, sterol sulphate compounds and compositions for promoting angiogenesis. In some embodiments, the invention provides novel compounds of Formula I and salts thereof, as promoters of angiogenesis, where compounds of Formula I include the structure:  
                 
 
 where 
          R is a linear or branched, saturated or unsaturated one to 15 carbon alkyl group; X, Y, and Z, at carbons 2, 3, and 6, respectively, are independently selected from H, OH, or OSO 3   − , and at least one of X, Y, or Z is OSO 3   − , provided that the compound does not have the precise structure of sokotrasterol sulphate or any of the structures listed in Tables I or II.        

      In some embodiments, R may be the side chain at the equivalent position of sokotrasterol sulphate. In some embodiments, R does not have the precise structure of the side chain of cholesterol. In some embodiments, X, Y, and Z are all sulphate. In alternative embodiments, X and Y are sulphate, Z is H or OH; X and Z are sulphate, Y is H or OH; Y and Z are sulphate, X is H or OH; X is sulphate, Y and Z are H or OH; Y is sulphate, X and Z are H or OH; or Z is sulphate, X and Y are H or OH. In some embodiments, the compound is substantially pure.  
      In some embodiments, the invention provides the use of compounds of Formula I, including sokotrasterol sulphate, and the structures listed in Tables I or II, for preparation of a medicament for promoting angiogenesis (for example, in the chorioallantoic membrane of chick embryo, or in a human), and/or for preparation of a medicament for promoting endothelial cell proliferation or sprouting, and/or for preparation of a medicament for treating or preventing a disorder associated with sub-optimal angiogenesis such as ischemia (e.g., ischemic stroke, cerebral ischemia, myocardial ischemia, intestinal ischemia, retinal or ocular ischemia, or spinal ischemia), circulatory disorders, vascular disorders, myocardial disease, pericardial disease, congenital heart disease, peripheral vascular pathologies, diabetes, coronary artery disease, atherosclerosis, infertility, insufficient endometrial vascularization, occluded blood vessels, conditions involving the pathology of endothelial cells, peptic ulcerations, endothelial ulcerations, restenosis, or wounds.  
      In some aspects, the invention provides a pharmaceutical composition including a pharmaceutically acceptable carrier and one or more compounds of Formula I or pharmaceutically acceptable salts thereof,  
                 
 
 where R is a linear or branched, saturated or unsaturated one to 15 carbon alkyl group; X, Y, and Z are independently selected from H, OH, or OSO 3   − ; and at least one of X, Y, or Z is OSO 3   − . In some embodiments, the one or more compounds of Formula I is not solely a compound listed in Table I. In some embodiments, the pharmaceutical composition includes sokotrasterol sulphate. In some embodiments, the pharmaceutical composition includes a novel compound as described herein, or includes a compound listed in Table II. In some embodiments, the pharmaceutical composition further includes vascular endothelial growth factor or fibroblast growth factor 2. In some embodiments, the pharmaceutical composition is capable of promoting angiogenesis (e.g., in the chorioallantoic membrane of chick embryo) and/or is capable of promoting endothelial cell proliferation or sprouting, and/or is capable of treating or preventing a disorder associated with sub-optimal angiogenesis, such as ischemia (e.g., ischemic stroke, cerebral ischemia, myocardial ischemia, intestinal ischemia, retinal or ocular ischemia, or spinal ischemia), circulatory disorders, vascular disorders, myocardial disease, pericardial disease, congenital heart disease, peripheral vascular pathologies, diabetes, coronary artery disease, atherosclerosis, infertility, insufficient endometrial vascularization, occluded blood vessels, conditions involving the pathology of endothelial cells, peptic ulcerations, endothelial ulcerations, restenosis, or wounds. In some embodiments, the invention provides a method of treatment or prophylaxis of a disorder associated with sub-optimal angiogenesis by administering to a subject in need thereof (e.g., a human) an effective amount of a pharmaceutical composition according to the invention. 
 
      In some aspects, the invention provides a method of promoting angiogenesis or promoting proliferation or sprouting of endothelial cells by administering an amount of one or more compounds of Formula I or pharmaceutically acceptable salts thereof,  
                 
 
 where R is a linear or branched, saturated or unsaturated one to 15 carbon alkyl group; X, Y, or Z are independently selected from H, OH, or OSO 3   − ; and at least one of X, Y, and Z is OSO 3   − ; and where the amount is sufficient to promote angiogenesis or to promote proliferation or sprouting of endothelial cells, for example, in the chorioallantoic membrane of chick embryo. The compound may be sokotrasterol sulphate, or may be a structure listed in Tables I or II, or may be a novel compound according to the invention. 
 
      In some aspects, the invention provides a method of treating or preventing a disorder associated with sub-optimal angiogenesis by administering an effective amount of one or more compounds of Formula I or pharmaceutically acceptable salts thereof,  
                 
 
 where R is a linear or branched, saturated or unsaturated one to 15 carbon alkyl group; X, Y, and Z are independently selected from H, OH, or OSO 3   − ; and at least one of X, Y, or Z is OSO 3   − ; and where the amount is sufficient to treat or prevent the disorder associated with sub-optimal angiogenesis. The compound may be sokotrasterol sulphate, or a compound according to the invention, such as the compounds listed in Tables I or II or a novel compound according to the invention. The disorder may be ischemia (e.g., ischemic stroke, cerebral ischemia, myocardial ischemia, intestinal ischemia, retinal or ocular ischemia, or spinal ischemia), circulatory disorders, vascular disorders, myocardial disease, pericardial disease, congenital heart disease, peripheral vascular pathologies, diabetes, coronary artery disease, atherosclerosis, infertility, insufficient endometrial vascularization, occluded blood vessels, conditions involving the pathology of endothelial cells, peptic ulcerations, endothelial ulcerations, restenosis, or wounds. The subject may be a human. The methods may be carried out in vivo or in vitro. 
 
      In some aspects, the invention provides a method of identifying a sterol sulphate compound that is capable of promoting angiogenesis, the method comprising screening the compound for activity in promoting angiogenesis. The method may include contacting the chorioallantoic membrane of a first group of chick embryos with the compound; contacting the chorioallantoic membrane of a second group of chick embryos with a composition lacking the compound; determining the angiogenic response of the first and second groups of chick embryos; and selecting a compound that increases the angiogenic response in the first group of chick embryos compared to the second group of chick embryos by at least 10%. Alternatively or additionally, the method may include contacting a first group of endothelial cells with the compound; contacting a second group of endothelial cells with a composition lacking the compound; determining the angiogenic response of the first and second groups of endothelial cells; and selecting a compound that increases the angiogenic response in the first group of endothelial cells as compared to the second group of endothelial cells by at least 10%. The endothelial cells may be human umbilical vein endothelial cells. The angiogenic response may be determined by determining the sprouting of the endothelial cells. The compound may have the chemical structure of Formula I or pharmaceutically acceptable salts thereof,  
                 
          where R is a linear or branched, saturated or unsaturated one to 15 carbon alkyl group; X, Y, and Z are independently selected from H, OH, or OSO 3 —; and at least one of X, Y, and Z is OSO 3 —.        

      In some embodiments, the methods and uses according to the invention specifically exclude previously known compounds, such as those listed in Tables I or II. In some embodiments, the methods and uses according to the invention specifically exclude compounds having the precise structure of the side chain of cholesterol.  
      By “promoting angiogenesis” is meant increasing or maintaining any step in the cascade of events leading to the formation of new blood vessels. These events may include, without limitation, the transmission of an angiogenic signal, migration, proliferation, differentiation, or sprouting of endothelial cells, or inhibition of apoptosis of endothelial cells. The increase or maintenance may be at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%, or may be over 100%, as compared to an appropriate control.  
      A “disorder associated with sub-optimal angiogenesis” is any disorder that may benefit from promoting angiogenesis, as described herein or known to those of skill in the art.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  Sokotrasterol sulphate promotes endothelial sprouting in vitro. Dose-response curve of sokotrasterol sulphate endothelial sprouting function.  
       FIG. 2  Dose-response curve of endothelial sprouting function of sulphated and unsulphated compounds, including sokotrasterol sulphate, IN96-89, sokotrasterol, and cholestanol.  
       FIG. 3  Sokotrasterol sulphate promotes angiogenesis in an in vivo chick chorioallantoic membrane model. Quantitation by image analysis of the number of vessels entering the gelatin sponge (per mm of circumference) with different concentrations of agent. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The invention provides in part sterol sulphate compounds, compositions, and methods for promoting angiogenesis, or for the preparation or identification of agents for promoting angiogenesis, in cells, tissues, cultures, organs, or organisms in vivo or in vitro. The sterol sulphate compounds and compositions of the invention are not estrogen or compounds closely related thereto. The compounds and compositions of the invention retain activity or exhibit enhanced activity upon sulphation. In some embodiments, the compounds and compositions of the invention are capable of creating new blood vessels, in contrast to the repair of an existing blood vessel (e.g., in the process of revascularization using balloons or stents). In some embodiments, the compounds and compositions of the invention include small molecules that can be synthesized, and/or are unlikely to provoke an immune response, and/or have known delivery mechanisms, and/or are locally deliverable to areas of interest, and/or are minimally invasive as compared to traditional therapies such as bypass surgery or angioplasty.  
      Angiogenic Compounds  
      Angiogenic compounds according to the invention, in general, include all stereoisomers and enantiomers of Formula I, including those at carbons 2, 3, or 6, as identified in the conventional steroidal numbering system. In some embodiments, the compounds include saturated or unsaturated carbons in any of the tetracyclic steroidal ring system. Some embodiments have the same relative configuration of chiral centers as does sokotrasterol sulphate or are enantiomers thereof. Some embodiments have the same absolute configuration of sokotrasterol sulphate at chiral centers. In some embodiments, compounds having a side chain (R) of the precise structure of the side chain of cholesterol are specifically excluded.  
      In some embodiments, angiogenic compounds according to the invention may include compounds that are in a complex with a compound of Formula I, a chemical or breakdown product of a compound of Formula I, a derivative of a compound of Formula I, or a naturally occurring precursor of Formula I. Novel compounds of Formula I of the invention do not include the precise structures of previously described compounds, for example, those described in Tables I or II. Table I describes sterol sulphate compounds which have been reported as having activities including antifoulant, antimicrobial, antiviral (e.g., as HIV inhibitors), antileukemia, cryoprotectant, antitoxicity, 1.3-glucanase activities, or guanosine diphosphate/G-protein RAS exchange assay inhibition. Table II describes sterol sulphate compounds that have not been reported as having a biological activity.  
                       TABLE I                       No.   Structure   Reference No.                  1                         31               2                         32               3                         33                                                                                                                                                                                                                                                                     4                         34                  
 
     
       
         
           
               
               
               
             
               
                 TABLE II 
               
               
                   
               
               
                   
               
               
                 No. 
                 Structure 
                 Reference No. 
               
               
                   
               
             
            
               
                 1 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 35 
               
               
                   
               
               
                 2 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 36 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
               
                 3 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 37 
               
               
                   
               
               
                 4 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 38 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
            
           
         
       
     
      Compounds and salts thereof of this invention and for use in this invention are generally provided in substantially purified form. A compound or salt (if naturally occurring) is “substantially pure” or “isolated” when it is separated from the components that naturally accompany it (e.g, cells of a source organism or tissue). A compound may be substantially pure or isolated when it is substantially free of cellular contaminants, i.e, that it is present ex vivo and in a concentration greater than that of the compound in a source organism, tissue, or other natural source. Typically, a compound is substantially pure or isolated when it is at least 10%, 20%, 30%, 40%, 50%, or 60%, more generally 70%, 75%, 80%, or 85%, or over 90%, 95%, or 99% by weight, of the total material in a sample. Thus, for example, a compound that is chemically synthesized will be generally be substantially free from its naturally associated components. A substantially pure compound can be obtained, for example, by extraction from a natural source or by chemical synthesis. Purity can be measured using any appropriate method such as column, gas, or liquid chromatography or mass spectrometry.  
      Sources and Synthesis of Compounds  
      Compounds according to the invention, or for use according to the invention, including pharmaceutically acceptable salts thereof, may be obtained by synthesis making use of common procedures as exemplified herein. Some compounds that may be used according to the invention can be obtained from natural sources. For example, compounds according to Formula I may be prepared in part or in whole from natural sources, e.g., by fractionating biological extracts (e.g., from marine organisms such as sponges or starfish, or from plants) or by derivatizing compounds available from such sources. In some embodiments, compounds according to Formula I may be prepared by total synthesis.  
      The synthesis schemes shown in Table III outline example syntheses for the sterol sulphate compounds of the invention and analogs thereof, where R is the correct steroid side chain, and P and P 1  are alcohol protecting groups (adapted from 26 and 27). For example, for compounds where R is the side chain of cholesterol, the starting material in Scheme 1 is cholesterol and in Scheme 2 is cholestanol. In some embodiments, R is a known steroid side chain. The example syntheses may be adapted to make any combination of the claimed sterol sulphates. In some embodiments, compounds may be made by partial de-sulphation of sulphated sterols as known in the art.  
               TABLE III                       Example Synthesis Schemes                  Scheme 1:                                                                                                                                                                                                                     P and P 1  are alcohol protecting groups                    Scheme 2:                                                                                                                                                  
 
 Angiosenesis Assays 
 
      The angiogenicity of the sterol sulphates of the invention may be assayed using a variety of techniques, including those described herein or known to those of ordinary skill in the art, for example, attachment assays, wounding migration assays, Boyden Chamber migration assays, proliferation assays, Transwell assays, apoptosis assays, or endothelial sprouting assays (14-22). Such assays may also be used to assess the angiogenicity of compounds prepared by total synthesis as described herein, or of compounds extracted from natural sources. The angiogenicity of a compound may be determined in a number of ways, for example, relative to a control sample lacking the compound, or relative to a known angiogenic factor such as VEGF, FGF-2, angiogenin, epidermal growth factor, etc.  
      Angiogenesis may be assayed using suitable cells such as endothelial cells, for example, human umbilical vein endothelial cells (HUVECs). Cells and cell lines may be obtained from commercial sources, for example, ATCC, Manassas, Va., USA. Angiogenesis may also be assayed in vivo using suitable animal models, such as chick chorioallantoic membrane (CAM) assays, ovariectomized mice, mouse models of hindlimb ischemia, etc. (15, 29, 30). Some animal models may be obtained from, for example, The Jackson Laboratory, Bar Harbor, Me., USA.  
      Disorders  
      The compounds, compositions, or methods of this invention may be used for the treatment or prevention of any disorders or conditions that may benefit from promotion or maintenance of angiogenesis by for example promoting new blood vessel growth, improving blood flow, or reducing tissue damage. Such disorders or conditions may include, for example, those conditions that exhibit insufficient or sub-optimal angiogenesis.  
      Thus, the compounds, compositions, or methods of this invention may be used for treatment or prevention of disorders and conditions such as ischemia, including without limitation ischemic stroke (for example, from stenosis), cerebral ischemia, myocardial ischemia (for example, coronary artery disease), intestinal ischemia, retinal or ocular ischemia, spinal ischemia; circulatory disorders; vascular disorders; myocardial disease; pericardial disease; congenital heart disease; peripheral vascular pathologies (associated for example with diabetes); infertility due to insufficient endometrial vascularization; occluded blood vessels for example due to atherosclerosis; conditions involving the pathology of endothelial cells, such as endothelial ulcerations in diabetics, peptic ulcerations, or wounds (e.g., due to surgery, burns, fracture, cuts, or infection).  
      The compounds, compositions, or methods of this invention may be used to promote angiogenesis in for example tissues such as fibrous, muscle, endothelial, epithelial, vesicular, cardiac, cerebrovascular, vascular tissues, or avascular tissues, including the transparent structures of the eye (e.g. cornea, lens, vitreous), discs, ligaments, cartilage, tendons, epidermis etc.; organs, for example, organs for transplantation or artificial organs (e.g., heart, liver, lung, kidney, skin, pancreas, eye), or organs in need of regeneration. For tissue or organ transplants, the compounds, compositions, or methods of this invention may be applied to the tissues or organs prior to transplantation (e.g., in vitro) or may be administered to the transplant recipient (e.g., in vivo). The compounds, compositions, or methods of this invention may be used to promote angiogenesis in when using artificial implants, for example, mammary implants, penile implants, or artificial urinary sphincters, or using prostheses, to facilitate better vascularization and tolerance of the implant or prosthesis, or to inhibit restenosis of stents.  
      Pharmaceutical Compositions, Administration and Dosages  
      Compounds according to the invention or for use in the invention, for example, sokotrasterol sulphate or compounds of Formula I, may be water soluble and may be formed as salts. In general, the sulphation provides greater solubility in polar solutions, such as water or physiological solutions. In such cases, pharmaceutical compositions in accordance with this invention may include a salt of such a compound, preferably a pharmaceutically acceptable salt such as the HCl salt. Other suitable salts are known in the art. The term “pharmaceutically acceptable salt” includes salts of compounds of Formula I derived from the combination of a compound of this invention and an organic or inorganic acid or base. The compounds of Formula I are useful in both non-ionized and salt form. In practice, the use of a salt form amounts to use of a base form; both forms are within the scope of the invention.  
      Compounds according to the invention can be provided alone or in combination with other compounds (for example, nucleic acid molecules, small molecules, amino acid molecules or analogs thereof), in the presence of a liposome, an adjuvant, or any pharmaceutically acceptable carrier, in a form suitable for administration to mammals, for example, humans, cattle, sheep, etc. If desired, treatment with a compound according to the invention may be combined with existing modes for promoting angiogenesis, such administration of VEGF or FGF-2, or with a compound that is effective in the treatment of an associated disorder.  
      Conventional pharmaceutical practice may be employed to provide suitable formulations or compositions, taking into account the advantages of sulphation of the compounds of the invention, to administer the compounds to subjects suffering from or presymptomatic for conditions which would benefit from the promotion of angiogenesis. Any appropriate route of administration may be employed, for example, parenteral, intravenous, subcutaneous, intramuscular, intracranial, intraorbital, ophthalmic, intraventricular, intracapsular, intraperitoneal, intranasal, aerosol, oral, topical, lavage, injection, or any other mode suitable for the selected treatment or prophylaxis. In some embodiments, the mode of administration is non-systemic, e.g., topical or local, e.g, by injection or some other means of targeted delivery to the desired organ, tissue, or cell. Compounds or pharmaceutical compositions in accordance with this invention, or for use in this invention, may be administered by means of a medical device or appliance such as an implant, graft, prosthesis, stent, etc. For example, a stent may be coated with such a composition for promotion of angiogenesis or the inhibition of restenosis. Also, implants may be devised that are intended to contain and release such compounds or compositions. An example would be an implant made of a polymeric material adapted to release the compound over a period of time.  
      Pharmaceutical compositions will typically include one or more pharmaceutically acceptable carriers or excipients suitable for the mode of administration of the preparation. As used herein “pharmaceutically acceptable carrier” or “excipient” includes any and all solvents, dispersion media, coatings, antibacterial and antifingal agents, isotonic and absorption delaying agents, and the like that are physiologically compatible. In one embodiment, the carrier is suitable for parenteral administration. Alternatively, the carrier can be suitable for intravenous, intraperitoneal, intramuscular, sublingual or oral administration. Pharmaceutically acceptable carriers include sterile aqueous solutions or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersion. The use of such media and agents for pharmaceutically active substances is well known in the art. Except insofar as any conventional media or agent is incompatible with the active compound, use thereof in the pharmaceutical compositions of the invention is contemplated. Supplementary active compounds can also be incorporated into the compositions. Suitable carriers are those known in the art for use in the selected modes of administration.  
      Methods well known in the art for making formulations are found in, for example, “Remington&#39;s Pharmaceutical Sciences” (19 th  edition), ed. A. Gennaro, 1995, Mack Publishing Company, Easton, Pa. Formulations for parenteral administration may, for example, contain excipients, sterile water, or saline, polyalkylene glycols such as polyethylene glycol, oils of vegetable origin, or hydrogenated napthalenes. Biocompatible, biodegradable lactide polymer, lactide/glycolide copolymer, or polyoxyethylene-polyoxypropylene copolymers may be used to control the release of the compounds. Other potentially useful parenteral delivery systems for angiogenic compounds include ethylene-vinyl acetate copolymer particles, osmotic pumps, implantable infusion systems, and liposomes. Formulations for inhalation may contain excipients, for example, lactose, or may be aqueous solutions containing, for example, polyoxyethylene-9-lauryl ether, glycocholate and deoxycholate, or may be oily solutions for administration in the form of nasal drops, or as a gel. Formulations may be in the form of liquid solutions or suspensions; for oral administration, formulations may be in the form of tablets or capsules.  
      For therapeutic or prophylactic compositions, the compounds are administered to an individual in an effective amount, i.e., an amount sufficient to promote angiogenesis, depending on the disorder. An “effective amount” of a compound according to the invention includes a therapeutically effective amount or a prophylactically effective amount. A “therapeutically effective amount” refers to an amount effective, at dosages and for periods of time necessary, to achieve the desired therapeutic result, such as promotion of angiogenesis. A therapeutically effective amount of a compound may vary according to factors such as the disease state, age, sex, and weight of the individual, and the ability of the compound to elicit a desired response in the individual. Dosage regimens may be adjusted to provide the optimum therapeutic response. A therapeutically effective amount is also one in which any toxic or detrimental effects of the compound are outweighed by the therapeutically beneficial effects. A “prophylactically effective amount” refers to an amount effective, at dosages and for periods of time necessary, to achieve the desired prophylactic result, such as promotion of angiogenesis. Typically, a prophylactic dose is used in subjects prior to or at an earlier stage of disease, so that a prophylactically effective amount may be less than a therapeutically effective amount. A preferred range for therapeutically or prophylactically effective amounts of a compound may be any integer from 0.1 nM-0.1 M, 0.1 nM-0.05M, 0.05 nM-15 μM or 0.01 nM-10 μM. Such dosages are readily determinable by persons of ordinary skill in the relevant art. An “angiogenesis promoting amount” of a compound is an amount that is sufficient to promote angiogenesis, as determined for example using an angiogenesis assay as described herein or known in the art.  
      It is to be noted that dosage values may vary with the severity of the condition to be alleviated. For any particular subject, specific dosage regimens may be adjusted over time according to the individual need and the professional judgement of the person administering or supervising the administration of the compositions. Dosage ranges set forth herein are exemplary only and do not limit the dosage ranges that may be selected by medical practitioners. The amount of active compound in the composition may vary according to factors such as the disease state, age, sex, and weight of the individual. Dosage regimens may be adjusted to provide the optimum therapeutic response. For example, a single bolus may be administered, several divided doses may be administered over time or the dose may be proportionally reduced or increased as indicated by the exigencies of the therapeutic situation. It may be advantageous to formulate parenteral compositions in dosage unit form for ease of administration and uniformity of dosage.  
      In general, compounds of the invention should be used without causing substantial toxicity. Toxicity of the compounds of the invention can be determined using standard techniques, for example, by testing in cell cultures or experimental animals and determining the therapeutic index, i.e., the ratio between the LD50 (the dose lethal to 50% of the population) and the LD100 (the dose lethal to 100% of the population). In some circumstances however, such as in severe disease conditions, it may be necessary to administer substantial excesses of the compositions. Ultimately, dosage and duration of treatment is determined by the practitioner in accordance with standard protocols and information concerning the activity and toxicity of the chosen compound.  
      Various alternative embodiments and examples of the invention are described herein. These embodiments and examples are illustrative and should not be construed as limiting the scope of the invention.  
     EXAMPLES  
      Identification of Angiogenic Compounds  
      A collection of crude natural extracts were screened to identify small molecules that would promote the sprouting of endothelial cells in vitro, as described below. Three extracts out of a total of sixty tested had the ability to induce endothelial sprouting. Purification of one of these extracts led to the identification of sokotrasterol sulphate, a sulphated steroid with an extensively methylated side chain, isolated from a marine sponge collected in the Dominica Republic, and having the following chemical structure (3):  
                 
 
      As used herein the term “sokotrasterol sulphate” refers to the trisulphated compound, and “sokotrasterol” refers to a compound that lacks sulphation, but possesses the same side chain as sokotrasterol sulphate.  
      Endothelial Sprouting Assay  
      Human umbilical vein endothelial cells (HUVEC) from normal umbilical cords were obtained by collagenase treatment. Cultures were propagated in MCDB medium supplemented with 15% FCS, heparin, and endothelial cell growth supplement. Endothelial sprouting was assessed by a modification of the method of Nehls and Drenckhahn  14 . Briefly, microcarrier beads coated with gelatin (Cytodex 3, Sigma) were seeded with HUVEC. When the cells reached confluence on the beads, equal numbers of HMEC-coated beads were embedded in fibrin gels in 96-well plates. For preparation of fibrin gels, bovine fibrinogen was dissolved in MCDB at a concentration of 2.5 mg/ml. Aprotinin was added at a concentration of 0.05 mg/ml and the solution filtered through a 0.22 micron filter. Fibrinogen solution was supplemented with FGF-2 or sokotrasterol sulphate. As a control, fibrinogen solution without angiogenic factor was used. Following transfer of the fibrinogen solution to 96-well plates, HUVEC-coated beads were added at a density of 50 beads/well, and clotting was induced by the addition of thrombin (1.2 U/ml). After clotting was complete, gels were equilibrated with MCDB+2% FCS at 37° C. Following 60 min of incubation, the overlying medium was changed for all wells. MCDB+2% FCS alone or containing FGF-2 (1 ng/ml) or sokotrasterol (from 0.625 μg/ml to 5 μg/ml) was added to the wells. After 3 days of incubation with daily medium changes, the number of capillary-like tubes formed was quantitated by counting the number of tube-like structures per microcarrier bead (sprouts/bead). Only sprouts greater than 150 μm in length and composed of at least 3 endothelial cells were counted. Analysis of sokotrasterol sulphate showed that it promoted endothelial sprouting in vitro in a concentration-dependent manner ( FIG. 1 ). Data in  FIG. 1  are averages from seven independent experiments. The endothelial sprouting assay was also performed using sokotrasterol (i.e., not sulphated), cholestanol (not sulphated), and a trisulphate of cholestane (IN 98-89, having the chemical structure shown below), in addition to sokotrasterol sulphate ( FIG. 2 ). Both sulphated compounds exhibited enhanced angiogenic activity when compared with their un-sulphated analogs.  
                 
 
 Chick Chorioallantoic Membrane (CAM) Assay 
 
      Fertilized White Leghorn chicken eggs ( Gallus gallus domesticus ) were incubated at 37° C. under conditions of constant humidity. All chick eggs were handled according to institutional animal care procedures. On embryonic day 6, the developing chick chorioallantoic membrane (CAM) was separated from the shell by opening a small circular window at the broad end of the egg above the air sac. The embryos were checked for normal development, the window sealed with Parafilm, and the eggs returned to the incubator for 2 more days. On day 8, CAMs were treated with FGF-2 (30 ng/ml), sokotrasterol sulphate (20, 40 and 60 μg/ml) or PBS by loading 20 μl onto 2-mm 3  gelatin sponges (Gelfoam; Pharmacia Upjohn), which were then placed on the surface of the developing CAM. Eggs were resealed and returned to the incubator. On day 10, images of the CAMs were captured digitally using an Olympus SZX9 stereomicroscope (Olympus America) equipped with a Spot RT digital imaging system (Diagnostic Instruments). Neovascularization was quantitated for each CAM by counting the number of vessels that entered the sponge area, and dividing by the perimeter of the sponge (vessels/mm). Northern Eclipse version 6.0 (Empix Imaging Inc.) was used for manual vessel counting and mesh perimeter measurements. Thus, there was a positive concentration-dependent effect of sokotrasterol sulphate in the promotion of new blood vessel growth in an in vivo model of angiogenesis on the chick chorioallantoic membrane ( FIG. 2 ).  
      No toxicity was noted at any of the test concentrations in either the endothelial sprouting or the CAM assay.  
     Other Embodiments  
      Although various embodiments of the invention are disclosed herein, many adaptations and modifications may be made within the scope of the invention in accordance with the common general knowledge of those skilled in this art. Such modifications include the substitution of known equivalents for any aspect of the invention in order to achieve the same result in substantially the same way. Numeric ranges are inclusive of the numbers defining the range. In the specification, the word “comprising” is used as an open-ended term, substantially equivalent to the phrase “including, but not limited to”, and the word “comprises” has a corresponding meaning. Citation of references herein shall not be construed as an admission that such references are prior art to the present invention. All publications are incorporated herein by reference as if each individual publication was specifically and individually indicated to be incorporated by reference herein and as though fully set forth herein. The invention includes all embodiments and variations substantially as hereinbefore described and with reference to the examples and drawings.  
     REFERENCES  
     
         
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