In Situ Modulation of Oxidative Stress: A Novel and Efficient Strategy to Kill Cancer Cells

J.      Verrax; R.   Curi   Pedrosa; R.      Beck; N.      Dejeans; H.      Taper; P.   Buc   Calderon

Abstract

Cancer cells show an up-regulation of glycolysis, they readily take up vitamin C, and they appear more susceptible to an oxidative stress than the surrounding normal cells. Here we compare, analyse and discuss these particular hallmarks by performing experiments in murine hepatomas (TLT cells) and freshly isolated mouse hepatocytes. The results show that rates of lactate formation are higher in TLT cells as compared to mouse hepatocytes, but their ATP content represents less than 25% of that in normal cells. The uptake of vitamin C is more important in hepatoma cells as compared to normal hepatocytes. This uptake mainly occurs through GLUT1 transporters. Hepatoma cells have less than 10% of antioxidant enzyme activities as compared to normal hepatocytes. This decrease includes not only the major antioxidant enzymes, namely catalase, superoxide dismutase and glutathione peroxidase, but also the GSH content. Moreover, catalase is almost not expressed in hepatoma cells as shown by western blot analysis. We explored therefore a selective exposure of cancer cells to an oxidative stress induced by pro-oxidant mixtures containing pharmacological doses of vitamin C and a redox active compound such as menadione (vitamin K3). Indeed, the combination of vitamin C (which accumulates in hepatoma cells) and a quinone undergoing a redox cycling (vitamin K3) leads to an oxidative stress that kills cancer cells in a selective manner. This differential sensitivity between cancer cells and normal cells may have important clinical applications, as it has been observed with other pro-oxidants like Arsenic trioxide, isothiocyanates, Adaphostin.

Keywords: Antioxidant enzymes, ascorbate, glycolysis, hepatoma, menadione redox cycling, vitamin C uptake