Abstract 1897: Metformin treatment leads to the accumulation of lipid in breast cancer cell lines - a potential new biomarker of response and mechanism of action.

Abstract

Abstract There is growing interest in the anticancer effect of the diabetes drug, metformin, and several clinical studies are underway worldwide. Metformin's anticancer effects are thought to be mediated by its activation of AMPK and subsequent downstream catabolic effects on protein and lipid metabolism pathways that are commonly dysregulated in cancer cells. We have used mass spectrometry techniques and stable isotopes to investigate the effects of metformin on breast cancer cell lipid metabolism. There was great variability in lipid metabolism response to 2mM metformin treatment in a panel breast cancer cell lines (MCF7, BT474, ZR-75-1, T47D MDA-MB-157, MDA-MB-468 and MDA-MB-231). Levels of stearic acid (p=0.019), palmitoleic acid (p=0.01), oleic acid (p=0.002), cis-vaccenic acid (p=0.003) increased 3-4 fold with metformin treatment in MCF7 cells but there was no significant change for MDA-MB-231 cells. 2mM Metformin decreased fatty acid β-oxidation of oleate 4-fold (p=0.03). Accumulation of de novo lipogenesis derived (p=0.004) and exogenous fatty acid (p=0.02) occurred in MCF7 cells but siRNA knockdown of AMPK did not abrogate these effects. A 3-fold decrease in the diglyceride to triglyceride ratio (p=0.02) suggested reduced lipolysis and inhibited adipose triglyceride lipase activity. Reduced incorporation of exogenous fatty acid into phospholipid was evident (p=0.002). Heterogeneity of lipid metabolism response correlated with effects on proliferation, oxygen consumption and mitochondrial morphology. Our data shows that metformin has marked effects on accumulation of fatty acid in breast cancer cells most likely due to reduced lipolysis and β-oxidation and these effects cannot be explained as a result of AMPK activation. This work will contribute to developing biomarkers for metformin's metabolic anticancer effect and our understanding of how to combine it with other therapies to exploit synthetic lethality. We have initiated a multicenter, phase II, single arm clinical study, to further characterise metformin influenced, cancer relevant metabolic pathways. We will look to assess the correlation between metabolic biomarkers, including the use of mass spectrometry and gas chromatography analysis of tissue samples, and metabolic response using 18F-FDG PET-CT scans. Citation Format: Simon Lord, Jennifer Collins, Barbara Fielding, Neel Patel, Fergus Gleeson, Adrian Harris, Fredrik Karpe. Metformin treatment leads to the accumulation of lipid in breast cancer cell lines - a potential new biomarker of response and mechanism of action. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1897. doi:10.1158/1538-7445.AM2013-1897