A PEPTIDOMIMETIC ANTAGONIST OF THE INTEGRIN ALPHA(V)BETA(3) INHIBITS LEYDIG-CELL TUMOR-GROWTH AND THE DEVELOPMENT OF HYPERCALCEMIA OF MALIGNANCY

The integrin alpha(v) beta(3) interacts with the arginine-glycine-aspa rtic acid (RGD) tripeptide recognition sequence of a variety of extrac ellular matrix proteins. Recent studies show that alpha(v) beta(3) pla ys an important role in tumor-induced angiogenesis and tumor growth an d that antagonists of alpha(v) beta(3) inhibit angiogenic processes th at include endothelial cell adhesion and migration, Consequently, we r easoned that an Rep-based peptidomimetic antagonist of alpha(v) beta(3 ) might inhibit tumor angiogenesis and tumor growth in vivo. An RGD-pe ptidomimetic library was screened to identify antagonists of vitronect in binding to alpha(v) beta(3), and the compounds chosen were modified to produce selective and potent inhibitors of alpha(v) beta(3) One of these compounds, carbonyl]amino]amino]-3,5-dichlorobenzenepropanoic a cid (SC-68448), inhibited vitronectin binding to both alpha(v) beta(3) and the closely related platelet receptor, alpha(IIb)beta(3) in a dos e-responsive manner. SC-68448 inhibited vitronectin binding to alpha(v ) beta(3) (IC50, 1 nM) and fibrinogen binding to the platelet receptor alpha(IIb)beta(3) (IC50, >100 nM), demonstrating that SC-68448 was 10 0-fold more potent as an inhibitor of alpha(v) beta(3) versus alpha(II b)beta(3) In cell-based studies, SC-68448 inhibited alpha(v) beta(3)-m ediated endothelial cell proliferation in a dose-dependent manner but did not inhibit tumor cell proliferation, suggesting that effects on e ndothelial cell proliferation were not due to SC-68448-induced cytotox icity. Ln accord with these results, SC-68448 inhibited angiogenesis i n Five in a basic fibroblast growth factor-induced rat corneal neovasc ularization model. A xenogeneic severe combined immune deficiency mous e/rat Leydig cell tumor model was developed for testing SC-68448 as an inhibitor of tumor growth in vivo. Rat Leydig cell tumors grew rapidl y in severe combined immune deficiency mice and produced humoral hyper calcemia of malignancy, SC-68448 inhibited the growth of the tumors in mice by up to 80% and completely blocked the development of hypercalc emia, Together, these results demonstrate the feasibility of antitumor therapies based upon the development of nontoxic small molecule pharm acological antagonists of integrin alpha(v) beta(3).