Abstract 2647: Anti-cancer effect of Phenformin and synergistic action of Phenformin-Oxamate combination

Abstract

Abstract Introduction. Metformin, a biguanide is a well established anti-diabetic agent and recently has drawn interest as a possible anti-cancer drug. Phenformin is 5-10 times more potent biguanide but lactic acidosis which is a major side effect of Phenformin has prevented its wide use. Metformin's anti-cancer effect is related to inhibition of complex 1 in the mitochondrial respiratory chain. However, Phenformin's effect on cancer cells has not been extensively studied. In this study, we evaluated the cytoxic effects of Phenformin in cancer cells and its possible mechanisms action. In addition, we added Oxamate, a lactate dehydrogenase inhibitor to phenformin to reduce lactic acidosis. The combination of these two drugs were evaluated in terms of prevention of lactic acidosis and cytotoxic effects in various cancer cell lines Eperimental procedure. Potency between Metformin and Phenformin was compared by dose-effect curve and EC50 in cancer cell death. Various dose combinations of Phenformin (0-2mM)/Oxamate (0-8mM) were tested in MCF7 (breast cancer), E6E7Ras (tonsil epithelial cancer), B16 (melanoma), and CT26 (colon cancer) cell lines. Among these cell lines, CT26 was further analyzed for cancer cell death pathways induced by Phenformin alone or in combination with oxamate. Apoptosis and PARP-dependant cell death were measured by the amount of cleaved PARP and release of apoptosis inducible factor (AIF), respectively. The degree of complex 1 inhibition, ROS production, ATP production, and DNA damage were measured. Finally, knock down of LDH was compared to Oxamate treatment. Conclusion. Phenformin was 7 times more potent than Metformin in promoting cancer cell death. In all cell lines, Phenformin showed cytotoxic effects and this was greatly increased by addition of Oxamate. Oxamate also reduced lactate production. Cancer cells died by both apoptosis and PARP-dependant pathways. However, apoptosis was dominant with Phenformin alone and PARP-dependant cell death was dominant with Phenformin/Oxamate. Cytotoxic effects with Phenformin were related to complex 1 inhibition and subsequent over production of ROS. Addition of Oxamate virtually shut down ATP production and accelerated ROS production by Phenformin. Elevated ROS levels led to mitochondrial DNA damage, as measured by detection of 8-OH-dG. The non-transformed cell line MCF10A was not affected by Phenformin or Phenformin/Oxamate. Phenformin/LDH Knock down was less effective than Phenformin/Oxamate, indicating that Oxamate might have effects than LDH inhibition alone. In conclusion, Phenformin has more potent cytotoxic effects on cancer cells than Metformin. Addition of Oxamate not only reduces lactic acidosis but also enhances the cytotoxicity of Phenformin. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2647. doi:10.1158/1538-7445.AM2011-2647