Metformin, a diabetes drug, eliminates tumor-initiating hepatocellular carcinoma cells

PLoS One. 2013 Jul 29;8(7):e70010. doi: 10.1371/journal.pone.0070010. Print 2013.

Abstract

Metformin has been widely used as an oral drug for diabetes mellitus for approximately 60 years. Interestingly, recent reports showed that metformin exhibited an anti-tumor action in a wide range of malignancies including hepatocellular carcinoma (HCC). In the present study, we investigated its impact on tumor-initiating HCC cells. Metformin suppressed cell growth and induced apoptosis in a dose-dependent manner. Flow cytometric analysis showed that metformin treatment markedly reduced the number of tumor-initiating epithelial cell adhesion molecule (EpCAM)(+) HCC cells. Non-adherent sphere formation assays of EpCAM(+) cells showed that metformin impaired not only their sphere-forming ability, but also their self-renewal capability. Consistent with this, immunostaining of spheres revealed that metformin significantly decreased the number of component cells positive for hepatic stem cell markers such as EpCAM and α-fetoprotein. In a xenograft transplantation model using non-obese diabetic/severe combined immunodeficient mice, metformin and/or sorafenib treatment suppressed the growth of tumors derived from transplanted HCC cells. Notably, the administration of metformin but not sorafenib decreased the number of EpCAM(+) cells and impaired their self-renewal capability. As reported, metformin activated AMP-activated protein kinase (AMPK) through phosphorylation; however its inhibitory effect on the mammalian target of rapamycin (mTOR) pathway did not necessarily correlate with its anti-tumor activity toward EpCAM(+) tumor-initiating HCC cells. These results indicate that metformin is a promising therapeutic agent for the elimination of tumor-initiating HCC cells and suggest as-yet-unknown functions other than its inhibitory effect on the AMPK/mTOR pathway.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / drug effects
  • Carcinoma, Hepatocellular / drug therapy*
  • Cell Cycle / drug effects
  • Cell Line
  • Cell Proliferation / drug effects
  • Flow Cytometry
  • Hepatocytes / drug effects
  • Humans
  • Hypoglycemic Agents / therapeutic use*
  • Liver Neoplasms / drug therapy*
  • Metformin / therapeutic use*
  • Mice
  • Xenograft Model Antitumor Assays

Substances

  • Hypoglycemic Agents
  • Metformin

Grant support

This work was supported in part by grants for the Global COE program (Global Center for Education and Research in Immune System Regulation and Treatment) from the Ministry of Education, Culture, Sports, Science and Technology, Japan (http://www.jsps.go.jp/j-globalcoe/); grants from Core Research for Evolutional Science and Technology (CREST) of Japan Science and Technology Corporation (JST)(http://www.jst.go.jp/kisoken/crest/); and the Foundation for the Promotion of Cancer Research (http://www.fpcr.or.jp/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.