In vitro and in vivo antitumoral action of metformin on hepatocellular carcinoma

Aims: Metformin is a biguanide that has been widely used to treat type 2 diabetes. Several studies have shown that metformin is also effective in treating cancer, including hepatocellular carcinoma (HCC). The objective of this study was to evaluate the antitumor effects of metformin in HCC, and to investigate the potential molecular target(s) of metformin-mediated antitumor activity. Methods: The antiproliferative effects of metformin were assessed in human HCC cell lines and normal human liver cells at various concentrations. Orthotopic xenograft tumors were established in athymic nude mice, and tumor growth was monitored after metformin treatment. Western blot analysis and cell cycle regulation were performed to determine the involvement of various mediators of apoptosis. Results: Metformin specifically inhibited the growth of HCC cells without affecting the growth of normal liver cells both in vitro and in vivo. Metformin caused cell cycle arrest in HCC cells, which resulted in caspase-3 activation. Livin levels decreased in a dose-dependent manner upon metformin treatment. Metformin activated 5'-adenosine monophosphate-activated protein kinase, inhibited the mammalian target of rapamycin pathway and downregulated Livin protein expression. Conclusion: Our findings indicate that metformin is effective at initiating apoptosis and inhibiting key survival signaling pathways in HCC cells. These data provide a foundation for further studies to evaluate metformin in the clinic either as a single agent or in combination with other first-line agents as a treatment option for HCC.