Cell delivery of Met docking site peptides inhibit angiogenesis and vascular tumor growth.

Angiogenesis is a very complex biological process that drives the formation of new blood vessels starting from pre-existing one. In adulthood, it occurs both in physiological and pathological processes. Pathological angiogenesis is involved in several diseases, including cancer. In the last decade, the concept of anti-angiogenic therapy has been developed as a strategy to treat cancer inducing the inhibition of new vessels that provide sustenance to the tumor. Recently, Met receptor and its ligand HGF (Hepatocyte Growth Factor) has been proposed as target for the anti-angiogenic therapy. HGF and its receptor Met are responsible for a wide variety of cellular responses, both physiologically during embryo development and tissue homeostasis, and pathologically, particularly during tumor growth and dissemination. In cancer, Met can act as an oncogene on tumor cells, as well as a pro-angiogenic factor activating endothelial cells and inducing new vessel formation. Molecules interfering with Met activity could be valuable agents for anti-cancer treatment simultaneously inhibiting oncogenesis and angiogenesis. The aim of this study has been the identification of peptides able to interfere with HGF-induced angiogenesis. We synthesized three different peptides containing the Met docking site fused to the internalization sequences of Antennapedia homeodomain or of Tat transactivation domain which were used to deliver peptides into living cells. In vitro we treated human endothelial cells with peptides and we quantified proliferation. We then evaluated the ability of peptides to interfere with HGF-induced migration, invasion and morphogenesis of endothelial cells. By western blotting analysis we investigated whether these peptides affect Met activation and downstream signalling. In vivo we performed matrigel sponge assay and Kaposi’s sarcoma xenograft to test the peptides efficacy on angiogenesis and tumor growth. We observed that in endothelial cells internalized peptides inhibited ligand-dependent cell proliferation, motility, invasiveness and morphogenesis in vitro, to an even greater extent and with much less toxicity than the Met inhibitor PHA-665752, which correlated with interference of HGF-dependent downstream signalling, as shown by reduction in ERK1/2 activation (Cantelmo et al.). In vivo, the peptides inhibited HGF-induced angiogenesis in the matrigel sponge assay and impaired xenograft tumor growth and vascularization in Kaposi’s sarcoma (Cantelmo et al.). These data show that interference with the Met receptor intracellular sequence impairs HGF-induced angiogenesis, suggesting the use of antidocking site compounds as a therapeutic strategy to counteract angiogenesis in cancer as well as in other diseases.