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Metformin Disrupts Crosstalk between G Protein–Coupled Receptor and Insulin Receptor Signaling Systems and Inhibits Pancreatic Cancer Growth

Division of Digestive Diseases, Departments of ¹ Medicine and ² Surgery, CURE, Digestive Diseases Research Center, David Geffen School of Medicine and Molecular Biology Institute, University of California at Los Angeles, Los Angeles, California

Requests for reprints: Enrique Rozengurt, Department of Medicine, David Geffen School of Medicine, University of California at Los Angeles, Warren Hall Room 11-124, 900 Veteran Avenue, Los Angeles, CA 90095-1786. Phone: 310-794-6610; Fax: 310-267-2399; E-mail: erozengurt{at}mednet.ucla.edu.

Recently, we identified a novel crosstalk between insulin and G protein–coupled receptor (GPCR) signaling pathways in human pancreatic cancer cells. Insulin enhanced GPCR signaling through a rapamycin-sensitive mTOR-dependent pathway. Metformin, the most widely used drug in the treatment of type 2 diabetes, activates AMP kinase (AMPK), which negatively regulates mTOR. Here, we determined whether metformin disrupts the crosstalk between insulin receptor and GPCR signaling in pancreatic cancer cells. Treatment of human pancreatic cancer cells (PANC-1, MIAPaCa-2, and BxPC-3) with insulin (10 ng/mL) for 5 minutes markedly enhanced the increase in intracellular [Ca²⁺] induced by GPCR agonists (e.g., neurotensin, bradykinin, and angiotensin II). Metformin pretreatment completely abrogated insulin-induced potentiation of Ca²⁺ signaling but did not interfere with the effect of GPCR agonists alone. Insulin also enhanced GPCR agonist–induced growth, measured by DNA synthesis, and the number of cells cultured in adherent or nonadherent conditions. Low doses of metformin (0.1–0.5 mmol/L) blocked the stimulation of DNA synthesis, and the anchorage-dependent and anchorage-independent growth induced by insulin and GPCR agonists. Treatment with metformin induced striking and sustained increase in the phosphorylation of AMPK at Thr¹⁷² and a selective AMPK inhibitor (compound C, at 5 µmol/L) reversed the effects of metformin on [Ca²⁺]_i and DNA synthesis, indicating that metformin acts through AMPK activation. In view of these results, we tested whether metformin inhibits pancreatic cancer growth. Administration of metformin significantly decreased the growth of MIAPaCa-2 and PANC-1 cells xenografted on the flank of nude mice. These results raise the possibility that metformin could be a potential candidate in novel treatment strategies for human pancreatic cancer. [Cancer Res 2009;69(16):6539–45]