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 Ser79 and Raptor at Ser792, was dramatically enhanced in human pancreatic ductal adenocarcinoma (PDAC) cells PANC-1 and MiaPaCa-2 cultured in medium containing physiological concentrations of glucose (5mM), 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 to 100-fold lower than those used in most previous reports. Using siRNA-mediated knockdown of the α1 and α2 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.

Mechanism of Metformin-dependent Inhibition of Mammalian Target of Rapamycin (mTOR) and Ras Activity in Pancreatic Cancer

“…ple, metformin inhibited constitutive and induced activation of mTOR in several pancreatic cancer cell lines, and the inhibitory effects were higher in cells grown in normal 5 mM glucose as compared with cells cultured in 25 mM glucose (19,23,24). It has also been reported that metformin suppresses the IGF-1R and mTOR signaling in pancreatic cancer cells, and this contributes to the antineoplastic activity of this agent (19).…”

“…Recent studies report that diabetic cancer patients who take metformin exhibit improved outcomes as compared with patients taking other antidiabetic drugs (10), and this has spurred interest in possible clinical applications of metformin for cancer therapy. One of the hallmarks of metformin action is associated with inhibition of the mTOR signaling in both cancer and non-cancer tissues and cells (15)(16)(17)(18)(19)(20)(22)(23)(24)(25). For exam- A, RNA interference with siRNA against EGFR (siEGFR) decreased cell proliferation.…”

“…Metformin inhibits growth and induces apoptosis and other antineoplastic responses in multiple cancer cell lines, and this is accompanied by modulation of different pathways and genes. Several studies demonstrate that metformin activates AMP-activated protein kinase␣ (AMPK␣), which results in the inhibition of the mTOR 2 signaling pathway and downstream effects (15)(16)(17)(18)(19)(20)(22)(23)(24)(25), and this compliments one of the proposed mechanisms of action of metformin as an antidiabetic drug (29,30).…”

“…The potential clinical applications for metformin in cancer chemotherapy also stems from studies on the anticancer activities of this drug in cancer cells in culture and in in vivo models (1)(2)(3)(4)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). Metformin inhibits growth and induces apoptosis and other antineoplastic responses in multiple cancer cell lines, and this is accompanied by modulation of different pathways and genes.…”

Metformin suppresses the expression of Sonic hedgehog in gastric cancer cells

“…However, the mechanism underlying the anticancer effects of metformin remain to be fully elucidated Previous studies have shown that, despite the complexity of the molecular signaling mechanisms of metformin, several critical molecules and pathways have been confirmed to be involved in this regulation, including the activation of AMPK (8,18), inhibition of mammalian target of rapamycin complex-1 (19), interruption of the crosstalk between insulin and insulin-like growth factor-1 receptor (20) and reductions in the expression of vascular endothelial growth factor and plasminogen activator inhibitor-1 (21).…”