Hepatocyte growth factor (HGF) promotes cell growth and motility and also increases neovascularization. Multiple myeloma (MM) cells produce HGF, and the plasma concentration of HGF is significantly elevated in patients with clinically active MM, suggesting that HGF might play a role in the pathogenesis of MM. NK4, an antagonist of HGF, is structurally homologous to angiostatin, and our previous report showed that NK4 inhibited the proliferation of vascular endothelial cells induced by HGF stimulation. The purposes of this study were to elucidate the contribution of HGF to the growth of MM cells as well as to investigate the possibility of the therapeutic use of NK4. In vitro study showed that NK4 protein stabilized the growth of MM cell lines and regulated the activation of c-MET, ERK1/2, STAT3, and AKT-1. Recombinant adenovirus containing NK4 cDNA (AdCMV.NK4) was injected intramuscularly into lcr/scid mice bearing tumors derived from HGF-producing MM cells. AdCMV.NK4 significantly inhibited the growth of these tumors in vivo. Histologic examination revealed that AdCMV.NK4 induced apoptosis of MM cells, accompanied by a reduction in neovascularization in the tumors. Thus, NK4 inhibited the growth of MM cells via antiangiogenic as well as direct antitumor mechanisms. The molecular targeting of HGF by NK4 could be applied as a novel therapeutic approach to MM.
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