Selectively Impairs p53-Deficient Tumor Cell Growth Systemic Treatment with the Antidiabetic Drug Metformin

The effect of the antidiabetic drug metformin on tumor growth was investigated using the paired isogenic colon cancer cell lines HCT116 p53 and HCT116 p53 / . Treatment with metformin selectively suppressed the tumor growth of HCT116 p53 / xenografts. Following treatment with metformin, we detected increased apoptosis in p53 / tumor sections and an enhanced susceptibility of p53 / cells to undergo apoptosis in vitro when subject to nutrient deprivation. Metformin is proposed to function in diabetes treatment as an indirect activator of AMP-activated protein kinase (AMPK). Treatment with AICAR, another AMPK activator, also showed a selective ability to inhibit p53 / tumor growth in vivo . In the presence of either of the two drugs, HCT116 p53 cells, but not HCT116 p53 / cells, activated autophagy. A similar p53-dependent induction of autophagy was observed when nontransformed mouse embryo fibroblasts were treated. Treatment with either metformin or AICAR also led to enhanced fatty acid B-oxidation in p53 MEFs, but not in p53 / MEFs. However, the magnitude of induction was significantly lower in metformin-treated cells, as metformin treatment also suppressed mitochondrial electron transport. Metformin-treated cells compensated for this suppression of oxidative phosphorylation by increasing their rate of glycolysis in a p53-dependent manner. Together, these data suggest that metformin treatment forces a metabolic conversion that p53 / cells are unable to execute. Thus, metformin is selectively toxic to p53-deficient cells and provides a potential mechanism for the reduced incidence of tumors observed in patients being treated with metformin. [Cancer Res 2007;67(14):6745–52]