Biological and molecular properties of a new αvβ3/αvβ5 integrin antagonist

The aim of the present study was to identify specific alpha(v)beta(3)/alpha(v)beta(5) integrin antagonists active on tumor-induced angiogenesis. To this purpose, in vitro integrin-binding assays were used to screen a library of conformationally constrained bicyclic lactam Arg-Gly-Asp -containing pseuclopeptides. The results identified ST1646 as a high-affinity specific ligand for alpha(v)beta(3) and alpha(v)beta(5) integrins with negligible interacting with alpha(5)beta(1) integrin. In all the assays, ST1646 was equipotent to or more potent than the well -characterized integrin antagonists c(RGDfV) and cyclo(Arg-Gly-Asp-D-Phe-[NMe]Val) (EMD121974). In the choriciallantoic membrane assay, topical administration of ST1646 was able to prevent the angiogenic responses elicited by recombinant fibroblast growth factor-2 or vascular endothelial growth factor. In addition, systemic administration of ST1646 in mice exerted a significant antiangiogenic activity on neovascularization triggered by mammary carcinoma MDA-MB435 cells implanted s.c. in a dorsal air sac via a (Millipore Filter Corporation, Bedford, MA) chamber. Moreover, ST1646 delivery via an osmotic pump inhibited the growth and vascularization of tumor xenografts originating from the injection of alpha(v)beta(3)/alpha(v)beta(5)-expressing human ovarian carcinoma cells in nude mice. In agreement with the biochemical and pharmacologic studies, Monte Carlo/Stochastic Dynamics simulation showed that the bicyclic scaffold in ST1646 forced the compound to assume a preferred conformation superimposable to the X-ray conformation Of alpha(v)beta(3)-bound EMD121974. Accordingly, computer-docking studies indicated that the ST1646-003 integrin complex maintains the ligand-receptor distances and interactions observed in the crystalline EMD121974-alpha(v)beta(3) integrin complex. Taken together, these observations indicate that ST1646 represents a dual alpha(v)beta(3)/alpha(v)beta(5) integrin antagonist with interesting biochemical and biological features to be tested in cancer therapy.