ABSTRACT
PURPOSE: Vascular endothelial growth factor (VEGF) is a potent regulator of angiogenesis, which exerts direct effects on vascular endothelial cells, including endothelial cell proliferation and survival, tubulogenesis, and vascular permeability. In this study, we examined whether Neovastat, a naturally occurring multifunctional antiangiogenic drug, could inhibit the endothelial cell response to VEGF stimulation. RESULTS: We demonstrated that Neovastat was able to block the VEGF-dependent microvessel sprouting from Matrigel-embedded rat aortic rings, and it also blocked the VEGF-induced endothelial cell tubulogenesis in vitro. In vivo studies showed that Neovastat was able to specifically inhibit VEGF-induced plasma extravasation in numerous tissues, including pancreas and skin. The mechanism of action of Neovastat on VEGF-mediated effects was also evaluated at the molecular level. Neovastat was shown to compete against the binding of VEGF to its receptor in endothelial cells and significantly inhibited the VEGF-dependent tyrosine phosphorylation of VEGF receptor-2, whereas it had no significant effect on VEGF receptor-1 activity. Moreover, the inhibition of receptor phosphorylation was correlated with a marked decrease in the ability of VEGF to induce pERK activation. Neovastat does not compete against the binding of basic fibroblast growth factor, indicating a preferential inhibitory effect on the VEGF receptor. CONCLUSIONS: Because Neovastat was shown previously to inhibit metalloproteinase activities, these results suggest that Neovastat is able to target multiple steps in tumor neovascularization, further emphasizing its use as a pleiotropic, multifunctional antiangiogenic drug.
