Recent studies have revealed that angiogenesis plays a pivotal role in carcinogenesis and tumor growth. We previously reported that the clinically used vitamin K2 (VK) and angiotensin-converting enzyme inhibitor (ACE-I) exerted potent anti-angiogenic activities. The aim of our current study was to examine the combination effect of VK and ACE-I on hepatocarcinogenesis induced by diethyl-nitrosamine, and orthotopic hepatocellular carcinoma (HCC) growth in rats. When used individually, both VK and ACE-I at clinically comparable low doses exerted significant inhibitory effects on tumor development in the liver. A combination treatment of VK and ACE-I showed a more potent suppressive effect against hepatocarcinogenesis. Neovascularization increased during hepatocarcinogenesis, and VK and ACE-I significantly attenuated angiogenesis in the tumor. In orthotopic HCC transplantation, VK and ACE-I also showed marked suppressive effects against HCC development similar to those against hepatocarcinogenesis. In both experiments, the suppressive effects of VK and ACE-I against angiogenesis were similar in magnitude to their inhibitory effects against hepatocarcinogenesis and orthotopic HCC development. In the orthotopic model, VK and ACE-I treatment resulted in a marked increase of apoptosis in the tumor, whereas tumor cell proliferation itself was not altered. Since both VK and ACE-I are widely used in clinical practice without serious side effects, this combination therapy may be an effective new therapeutic strategy against hepatocarcinogenesis and HCC growth in the future.

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