Abstract 4477: Dual-targeting of AMPK and PI3K/mTOR in a panel of breast cancer cell lines

Abstract

Abstract Several PI3K/AKT/mTOR pathway inhibitors are presently in early clinical trials for the treatment of cancer. Due to their mechanism of action, many of these compounds markedly increase the blood glucose levels. Metformin is an AMPK activator widely used in clinical practice to contrast hyperglycemia and is also known to reduce cancer risk as well as to improve cancer prognosis. The aim of this study is to explore the in vitro anti-tumor effect of metformin alone and in combination with the PI3K/mTOR inhibitor NVP-BEZ235 in a panel of breast cancer cell lines. Breast cancer cells (BT474, SKBR3, MCF7, MDA-468, MDA-231) were exposed to escalating doses of BEZ235 as single agent and in combination with metformin. Levels of phosphorylated and total AMPK, MAPK, EGFR, HER2 and S6 ribosomal protein were evaluated by western blot. Metformin induced dose-dependent growth inhibition. The combined treatment of NVP-BEZ235 plus metformin resulted in an inhibitory effect on cell proliferation greater than with either treatment alone in EGFR and HER2 positive breast cancer cell lines. At the IC50 of 20 mM we found that metformin activates AMPK reducing mTORC1 activity and, in turn, decreasing the levels of p-S6 ribosomal protein. Metformin treatment was also associated with reduced receptor tyrosine kinases (RTKs) expression (EGFR and HER2) and decreased p-MAPK. The dual PI3K/mTOR inhibitor NVP-BEZ235 potently decreases p-AKT and p-S6. As described for other mTOR inhibitors, NVP-BEZ235 increases MAPK phosphorylation by transactivation of several RTKs of the HER family. Treatment with metformin downregulates these RTKs preventing NVP-BEZ235-dependent MAPK pathway transactivation, providing a possible explanation for the potent anti-proliferative activity of the combination in HER2 positive breast cancer cell lines. The combination of metformin and NVP-BEZ235 significantly inhibits the growth of several breast cancer cell lines. We propose that inhibiting the PI3K/Akt/mTOR pathway in combination with metformin treatment would result in superior antitumor activity. Further studies are warranted to determine the applicability of this approach in the clinic. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4477.