title: Metformin inhibition of mTORC1 activation, DNA synthesis and proliferation in pancreatic cancer cells: dependence on glucose concentration and role of AMPK.
abstract: Metformin, a widely used anti-diabetic drug, is emerging as a potential anticancer agent but the mechanisms involved remain incompletely understood. Here, we demonstrate that the potency of metformin induced AMPK activation, as shown by the phosphorylation of its substrates acetyl-CoA carboxylase (ACC) at Ser(79) and Raptor at Ser(792), was dramatically enhanced in human pancreatic ductal adenocarcinoma (PDAC) cells PANC-1 and MiaPaCa-2 cultured in medium containing physiological concentrations of glucose (5 mM), as compared with parallel cultures in medium with glucose at 25 mM. In physiological glucose, metformin inhibited mTORC1 activation, DNA synthesis and proliferation of PDAC cells stimulated by crosstalk between G protein-coupled receptors and insulin/IGF signaling systems, at concentrations (0.05-0.1 mM) that were 10-100-fold lower than those used in most previous reports. Using siRNA-mediated knockdown of the α(1) and α(2) catalytic subunits of AMPK, we demonstrated that metformin, at low concentrations, inhibited DNA synthesis through an AMPK-dependent mechanism. Our results emphasize the importance of using medium containing physiological concentrations of glucose to elucidate the anticancer mechanism of action of metformin in pancreatic cancer cells and other cancer cell types.
authors.affiliation: Division of Digestive Diseases, Department of Medicine, CURE: Digestive Diseases Research Center, David Geffen School of Medicine and Molecular Biology Institute, University of California at Los Angeles, CA, USA.
authors.forename: James
authors.initials: J
authors.lastname: Sinnett-Smith
authors.forename: Krisztina
authors.initials: K
authors.lastname: Kisfalvi
authors.forename: Robert
authors.initials: R
authors.lastname: Kui
authors.forename: Enrique
authors.initials: E
authors.lastname: Rozengurt
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000096:biosynthesis* / Q000235:genetics; D000970:Antineoplastic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004261:DNA Replication / Q000187:drug effects*; D004789:Enzyme Activation; D055785:Gene Knockdown Techniques; D005947:Glucose / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D000076222:Mechanistic Target of Rapamycin Complex 1; D008687:Metformin / Q000494:pharmacology*; D046912:Multiprotein Complexes; D010190:Pancreatic Neoplasms / Q000378:metabolism*; D011506:Proteins / Q000037:antagonists & inhibitors*; D058570:TOR Serine-Threonine Kinases
chemical_list: D000970:Antineoplastic Agents; D007004:Hypoglycemic Agents; D046912:Multiprotein Complexes; D011506:Proteins; D008687:Metformin; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; C526180:PRKAA1 protein, human; D005947:Glucose