Abstract 5156: Hyperglycemia enhances IGF-I responses and alters the AMPK activation profile that protects against metformin-induced growth inhibition in pancreatic cancer cells

Abstract

Abstract Epidemiological studies have shown direct associations between type 2 diabetes (T2D) and obesity, both conditions associated with hyperglycemia and hyperinsulinemia, and the risk of pancreatic cancer. Up to 80% of pancreatic cancer patients are diagnosed with either impaired glucose tolerance or new-onset T2D one or two years prior to their cancer diagnosis. Recent population studies indicate that the incidence of pancreatic cancer is reduced among diabetics taking metformin, an insulin-sensitizing and glucose lowering drug. We investigated the effects of exposure of pancreatic cancer cells to high glucose levels on their growth and response to metformin. We found that metformin significantly reduced the proliferation of pancreatic cancer cells under normal glucose conditions, but that hyperglycemia protected against the metformin-induced growth inhibition. The antiproliferative actions of metformin were associated with an activation of AMP-activated protein kinase AMPK(T172) together with a dose-dependent suppression of the insulin/insulin-like growth factor (IGF) signaling mediators IRS-1 and phosphorylated AKT. Furthermore, exposure to metformin during normal glucose led to increased apoptosis as measured by poly(ADP-ribose) polymerase (PARP) cleavage. In contrast, exposure to high glucose promoted a more robust IGF-I response and AKT activation, that stimulated AMPK(S485) phosphorylation and suppressed AMPK(T172) phosphorylation resulting in reduced antiproliferative and apoptotic effects by metformin. In conclusion, our results indicate that metformin has direct antitumor activities in pancreatic cancer cells involving AMPK(T172) activation and modulation of the insulin/IGF signaling pathways. However, hyperglycemic conditions enhance the insulin/IGF-I responses resulting in an altered AMPK activation profile that prevent metformin from fully switching of the growth promoting signals in pancreatic cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5156. doi:1538-7445.AM2012-5156