HGF/NK4, a four-kringle antagonist of hepatocyte growth factor, is an angiogenesis inhibitor that suppresses tumor growth and metastasis in mice

We reported that NK4, composed of the N-terminal hairpin and subsequent four kringle domains of hepatocyte growth factor (HGF), acts as the competitive antagonist for HGF. We now provide the first evidence that NK4 inhibits tumor growth and metastasis as an angiogenesis inhibitor as well as an HGF antagonist. Administration of NK4 suppressed primary tumor growth and lung metastasis of Lewis lung carcinoma and Jyg-MC(A) mammary carcinoma s.c. implanted into mice, although neither HGF nor NK4 affected proliferation and survival of these tumor cells in vitro. NK4 treatment resulted in a remarkable decrease in microvessel density and an increase of apoptotic tumor cells in primary tumors, which suggests that the inhibition of primary tumor growth by NK4 may be achieved by suppression of tumor angiogenesis. In vivo, NK4 inhibited angiogenesis in chick chorioallantoic membranes and in rabbit corneal neovascularization induced by basic fibroblast growth factor (bFGF). In vitro, NK4 inhibited growth and migration of human microvascular endothelial cells induced by bFGF and vascular endothelial growth factor (VEGF) as well as by HGF. HGF and VEGF activated the Met/HGF receptor and the KDR/VEGF receptor, respectively, whereas NK4 inhibited HGF-induced Met tyrosine phosphorylation but not VEGF-induced KDR phosphorylation. NK4 inhibited HGF-induced ERK1/2 (p44/42 mitogen-activated protein kinase) activation, but allowed for bFGF- and VEGF-induced ERK1/2 activation. These results indicate that NK4 is an angiogenesis inhibitor as well as an HGF antagonist, and that the antiangiogenic action of NK4 is independent of its activity as HGF antagonist. The bifunctional properties of NK4 to act as an angiogenesis inhibitor and as an HGF antagonist raises the possibility that NK4 may prove therapeutic for cancer patients.