Inhibitor of angiogenesis

Abstract: A purified inhibitor of capillary endothelial cell growth and of angiogenesis is obtainable from the bovine cornea.

Description: This invention relates to newly discovered angiogenesis inhibitors, more particularly to an essentially purified inhibitor of capillary endothelial cell growth and angiogenesis obtained from corneas, preferably from mammalian corneas. In its most preferred aspects, the invention relates to such an inhibitor obtainable by water extraction at 4°C from corneal tissue, e.g. the outer layer, including the corneal epithelium and Bowman's basement membrane, of bovine corneas. Although the inhibitor is specifically obtainable from the outer cornea, it appears to be dispersed throughout the whole cornea, and can be obtained from whole cornea extracts. The inventicn also relates to a method of purifying such inhibitors to angiogenesis. Finally, the invention relates to methods of preserving corneal tissue. Inhibitors of angiogenesis are useful inter alia in the treatment of pathologic conditions involving or dependent upon the occurrence of neovascularization, such as chronic inflammation, certain immune responses, and neoplasia (including most solid tumors). Other inhibitors of angiogenesis have previously been described, such as combinations of heparin or certain heparin fragments with certain steroids as taught by Crum et.al., Science, Vol. 230, 1375-1378 (1976). Other known angiogenesis inhibitors include protamine and platelet factor 4. See generally, M.J. Folkman, "Tumor Angiogenesis" Adv. Canc . Res. 43 : 175 and Ciba Symp . However, such prior inhibitors in some cases have exhibited undesired biological side effects or have lacked specificity and high efficacy. The inhibitor of the present invention, because it can be isolated from biological sources such as mammalian corneas, is relatively free from undesirable side effects and may be particularly effective in treatment of mammals displaying ocular angiogenesis such as corneal neovascularization, as well as in treatment of tumor angiogenesis or the angiogenesis associated with arthritis and psoriasis. It may be combined with a suitable non-toxic physiologically acceptable vehicle or carrier for administration topically, as in eyedrops, or systemically as in intramuscular, intravascular, or intraperitoneal injection. It may also be administered with previously described inhibitors of angiogenesis, enabling the latter to be used at lower, less toxic doses. Finally, the inhibitor may be included in an aqueous saline solution used to store corneal tissue. The effective dosage varies over a considerable range depending upon the condition being treated, the weight of the patient, and the mode of administration, but those skilled in the art can readily determine the dosage in any particular case by simple experiment. In many cases, the dosage would generally be in the range from 0.1 to 50 mg/Kg body weight. The inhibitor of the present invention preferably has at least one or more of the following characteristics: (a) it is somewhat heat stabile, e.g., it retains significant inhibitory activity after heating for five minutes at 100°C; (b) it can be extracted in large volumes of chloroform (e.g., over 50 ml chloroform per lyophilized inhibitor from 100 corneas); (c) it is of relatively low molecular weight, e.g., it passes through a molecular sieve which prevents passage of molecules larger than 2000 daltons; (d) it is eluted from chloroform-equilibrated silica gel HPLC column with chloroform-methanol at about 10-15% v/v methanol; (e) it is eluted from a reverse phase water-equilibrated n-octadecyl-modified silica gel column with methanol-water at approximately 80% methanol by volume. The angiogenesis inhibitors of the present invention are preferably obtained by extraction of corneas, preferably mammalian corneas, such as bovine, porcine, rabbit or human corneas, and preferably from the outer corneal layer, including the corneal epithelium and Bowman's basement layer. The solvent used for the extraction is preferably water, although the inhibitors also have some solubility in methanol, chloroform and acetonitrile. Preferably the extraction is carried out at low temperatures, e.g., around 1°C to 10°C, and most preferably at about 1°C. The extracted inhibitor is then purified, preferably by HPLC and/or reverse phase HPLC techniques, such as those mentioned above. Preferably the inhibitor is purified to at least 90% by weight, more preferably to at least 95%. A convenient assay or test for the presence of the angiogenesis inhibitor of the present invention has also been discovered, in that the effect of the inhibitor on endothelial cells, namely rounding of the cells (without detachment) and inhibition of their growth, is easily observed. The following specific example is intended to illustrate more clearly the nature of the invention and not to act as a limitation upon its scope. Unless otherwise indicated herein, all percentages are on a weight basis, and temperatures are in degrees centigrade, uncorrected. Examples The outer layer of bovine corneas, approximately 20% of the total corneal thickness and including the corneal epithelium and Bowman's basement membrane as determined histologically, was dissected away from the corneas on ice. The dissected layers from 30 corneas were suspended in about 15 ml distilled water enclosed in a cellophane dialysis bag serving as a molecular sieve which prevents passage of molecules larger than 3500 daltons. The bag was placed in a 50 ml sterile plastic tube and the tube was filled with distilled water and capped. The tube was incubated at 4°C for at least 3 hours, preferably 18-24 hr. with gentle rotation. The solution outside of the dialysis bag was then collected, transferred to a glass flask and lyophilized. The dry powder, which could be stored at -20°C, was then extracted twice with 5 ml chloroform, the undissolved residue was removed by centrifugation, and the extract was concentrated about 3.5-fold by evaporation at reduced pressure (Savant Speed-Vac apparatus). This procedure was repeated several times with successive specimens of corneal layers. Forty-six ml of the above extract (made from a total of 129 corneas) was concentrated to about 13 ml and filtered through a 0.45 micron Nylon 66 syringe filter. It was applied to a semi-preparative HPLC silica column (Supelco Supelcosil, 5 micron particles; 25 cm length; 10 mm diameter equilibrated in chloroform) at a flow rate of 2 ml/min, and the column was washed until the absorbance at 280 nm returned to the baseline. The column was then eluted with 180 ml solvent having a linear gradient from 100% chloroform to 50% methanol/50% chloroform by volume and collected in 3 ml fractions. The solvent was evaporated from the fractions at room temperature and each residue dissolved in 200 µl distilled water. A 20 µl aliquot of each redissolved fraction was subjected to a preliminary in vitro test for inhibitory activity by the following procedure. Approximately 5000 capillary endothelial cells were plated in a 96-well tissue culture plate with Eagle's medium and 10% serum. The plates could be used for the assay within 24 hours and remained useful for 7-8 days. The 20 µl specimen of each fraction was air dried, redissolved in 60-100 µl of the tissue culture medium, and transferred to a well of the plate. Presence of inhibitor was demonstrated by the rounding (but not detachment) of the endothelial cells as well as inhibition of their growth and was readily detected by visual observation; in the case of fractions containing no inhibitor no rounding occurred, the cells remaining flat and their growth uninhibited. By the foregoing test the inhibitor was found to be present in the two fractions eluting at about 15% methanol. The two fractions, which contained the active inhibitor after being dissolved in water were pooled and a 50 µl sample assayed for activity as an inhibitor by the generally accepted CAM procedure as described in Crum et al., loc. cit ., the sample first being divided into two equal aliquots, air dried, and each dissolved in 10 µl of 0.45% solution of methyl cellulose in distilled water at 4°C which was then air dried on a 2 mm. diameter Teflon mold. The resulting discs were each implanted on 6-day old chorioallantoic membranes and after 48 hours each exhibited an avascular zone greater than 4 mm. in diameter, demonstrating inhibitory effect of the sample on angiogenesis in vivo . A further specimen of pooled eluted active fractions dissolved in water, obtained from 195 bovine corneas as described above, was subjected to reverse phase high performance liquid chromatography by injecting it onto an analytical C₁₈ HPLC column (silica gel modified by reaction with n-octadecyl trichlorosilane, Supelco, Supelcosil LC-18, 5 micron particles, 15 cm x 4.6 mm) and equilibrating with water; the column was washed with water, then eluted with 30 ml solvent having a linear gradient of 100% water to 100% methanol at a flow rate of 1 ml/min., and fractions of one ml each were collected. The solvent was removed from each fraction by evaporation at reduced pressure and the residue dissolved in 50µl water. The inhibitor was found, by the endothelial cell rounding test described above, to be in the fraction eluting at approximately 80% methanol/20% water by volume. A specimen of the original water extract from the bovine corneas before lyophilization was boiled for five minutes and was then assayed by the in vitro cell-rounding test and found to retain its inhibitory activity. In a subsequent experiment, corneas were suspended in distilled water and dialyzed, generally as described above, and the solution was lyophilized. The resulting dry powder was extracted in a large excess of chloroform. For example the lyophylized extract from 154 corneas was extracted with 100 ml. chloroform. The inhibitor activity, purified by this additional chloroform extraction and silica chromatography, retained substantial activity after boiling. A specimen of the original water extract (before chloroform extraction) was incubated with an inscluble pronase preparation (Streptomyces griseus; Sigma) at 0.1 mg (0.0115 units)-/ml in PBS (pH 7.0) for 10 hr. at 37°C. The protease was removed by centrifugation at 14,000 x g. The pronase-treated extract induced endothelial cell rounding with similar potency to that of untreated extract. Other methods for extracting and purifying the newly discovered corneal angiogenesis inhibitors will be readily apparent to the skilled in the art from the above disclosure. While the above example is directed to extraction of the inhibitor from bovine corneas, the same or similar techniques can be used to obtain angiogenesis inhibitor from other corneas, preferably mammalian corneas, such as human, rabbit, porcine, equine, canine, feline, or other corneas. Other tests for antiangiogenesis activity, such as those referred to in the references cited above, can also be used. The above-described endothelial cell assay can also be used to advantage for assaying for antiangiogenesis activity of other angiogenesis inhibitors. In subsequent experiments conducted generally as described above using a molecular seive that will prevent passage of molecules larger than 2000 daltons, the inhibitor passes through this seive. Finally, the inhibiitor serves to preserve corneal tissue which is being transported or stored for transplantation. Specifically, undesirable vasculation has been associated with increased risk of tissue rejection. The usual aqueous storage medium for such tissue depletes inhibitor in the tissue. By including inhibitor in the storage medium, such depletion, and therefore the risk of tissue rejection by the host, can be diminished. Specifically, those skilled in the art are aware of standard aqueous saline cornea storage media, to which effective concentrations of inhibitor are added to reduce depletion of the inhibitor from corneal tissue. Significantly, the practice of preserving corneal tissue in ice also depletes the inhibitor, as compared to preserving the tissue in dry ice.

Claims: An essentially purified inhibitor of capillary endothelial cell growth obtainable from corneal tissue by extraction by the following method: a) providing said corneal tissue; b) extracting said tissue with water to produce an aqueous extract; c) removing from said extract molecules of a molecular weight greater than a molecular mass on the order of 2000-3500 daltons; d) removing the water from said extract to produce a residue; e) extracting said residue with chloroform to produce a chloroform solution; f) applying said chloroform solution to a chloroform equilibrated silica gel HPLC column; and g) eluting said column with a chloroform-methanol mixture. An inhibitor according to claim 1 wherein said corneal tissue includes corneal epithelium and Bowman's basement membrane. An inhibitor according to claim 1 or 2, wherein the inhibitor retains at least a portion of its inhibitory activity after heating for five minutes at 100°C. An inhibitor according to claim 3, wherein the inhibitor retains at least a portion of its inhibitory activity after incubation for 10 hours at 37°C and pH 7.0 in phosphate buffered saline containing 0.1 mg/ml of protease. An inhibitor obtained by the method according to claim 1, wherein said method comprises passing a solution comprising said inhibitor through a molecular sieve which prevents passage of molecules larger than 2000 daltons, and said inhibitor being contained in filtrate which passes through said sieve. An inhibitor according to any of the preceding claims wherein said chloroform methanol solution is 10-15% (by volume) methanol. An inhibitor according to any of the preceding claims, wherein said method comprises passing a solution comprising said inhibitor over a reverse phase water-equilibrated n-octodecyl- modified silica gel column and eluting said inhibior from said column with a methanol-water mixture. An inhibitor according to any of the preceding claims, wherein said method comprises extracting said tissue with water at about 1°C to 10°C. A method of producing an inhibitor of capillary endothelial cell growth from corneal tissue by: a) providing said corneal tissue; b) extracting said tissue with water to produce an aqueous extract; c) removing from said extract molecules of a molecular weight greater than a molecular mass on the order of 2000-3500 daltons; d) removing the water from said extract to produce a residue; e) extracting said residue with chloroform to produce a chloroform solution; f) applying said chloroform solution to a chloroform equilibrated silica gel HPLC column; and g) eluting said column with a chloroform-methanol mixture. A method according to claim 9 wherein said corneal tissue includes corneal epithelium and Bowman's basement membrane. A method according to claim 9 or 10 wherein said method comprises passing a solution comprising said inhibitor through a molecular sieve which prevents passage of molecules larger than 2000 daltons, and said inhibitor being contained in filtrate which passes through said sieve. A method according to any one of claims 9 to 11 wherein said chloroform methanol solution is 10-15% (by volume) methanol. A method according to any one of claims 9 to 12 wherein said method comprises passing a solution comprising said inhibitor over a reverse phase water-equilibrated n-octodecyl- modified silica gel column and eluting said inhibitor from said column with a methanol-water mixture. A method according to any one of claims 9 to 13 wherein said method comprises extracting said tissue with water at about 1°C to 10°C. A pharmaceutical composition, comprising the angiogenesis inhibitor of claim 1, and a pharmaceutically acceptable carrier. A method of assaying for the presence of an angiogenesis inhibitor according to claim 1 comprising exposing endothelial cells to a material to be tested and determining whether the endothelial cells become rounded.

Inventors: DOCTROW SUSAN R, FOLKMAN MOSES JUDAH, DOCTROW, SUSAN R., FOLKMAN, MOSES JUDAH
Applicants: CHILDRENS MEDICAL CENTER, THE CHILDREN'S MEDICAL CENTER CORPORATION
Application year: 1988
Main classification: C07G17
IPC codes: A61K35, A61P9, A01N1