The anti-proliferative effect of metformin in triple-negative MDA-MB-231 breast cancer cells is highly dependent on glucose concentration: Implications for cancer therapy and prevention

Background: Metformin has been shown to have a strong anti-proliferative effect in many breast cancer cell lines, mainly due to the activation of the energy sensing kinase, AMP-activated protein kinase (AMPK). MDA-MB-231 cells are aggressive and invasive breast cancer cells that are known to be resistant to several anti-cancer agents as well as to the anti-proliferative effect of metformin. As metformin is a glucose lowering drug, we hypothesized that normoglycemia will sensitize MDA-MB-231 cells to the anti-proliferative effect of metformin. Methods: MDA-MB-231 cells were treated with increasing metformin concentrations in hyperglycemic or normoglycemic conditions. The growth inhibitory effect of metformin was assessed by MTT assay. The expression of several proteins involved in cell proliferation was measured by Western blotting. Results: In agreement with previous studies, treatment with metformin did not inhibit the growth of MDA-MB-231 cells cultured in hyperglycemic conditions. However, metformin significantly inhibited MDA-MB-231 growth when the cells were cultured in normoglycemic conditions. In addition, we show that metformin treatment of MDA-MB-231 cells cultured in normoglycemic conditions and not in hyperglycemic conditions caused a striking activation of AMPK, and an AMPK-dependent inhibition of multiple molecular signaling pathways known to control protein synthesis and cell proliferation. Conclusion: Our data show that normoglycemia sensitizes the triple negative MDA-MB-231 breast cancer cells to the anti-proliferative effect of metformin through an AMPK-dependent mechanism. General significance: These findings suggest that tight normoglycemic control may enhance the anti-proliferative effect of metformin in diabetic cancer patients. (C) 2014 Elsevier B.V. All rights reserved.