More than 70 years ago Warburg proposed that cancer was a disease of altered or dysregulated metabolism with a shift in energy production from oxidative phosphorylation to glycolysis. While this property of cancer cells allows for in vivo imaging by positron emission tomography (PET), this is also a vulnerability that could be exploited for sensitizing cancer cells to death stimuli. To that end, a number of reports have demonstrated that deprivation of glucose sensitizes cancer cells to apoptosis via recruitment of the apical caspase 8, however the precise mechanism(s) and signaling component(s) remain poorly understood. Our previous work has highlighted the regulatory role of intracellular reactive oxygen species in cellular response to apoptotic stimuli. Using a variety of models we showed that a slight increase in intracellular superoxide anion inhibited death signaling and/or promoted cell survival in tumor cells. Here we set out to investigate the effect of glucose deprivation on the sensitivity of Bcl-2 over-expressing leukemia cells (CEM and CEM-Bcl-2) to CD95-mediated apoptosis. Glucose deprivation significantly enhanced cancer cells’ sensitivity to antiCD95-induced apoptosis, irrespective of Bcl-2 over-expression. Interestingly, within 60 minutes of glucose deprivation there was a significant decrease in intracellular superoxide, which was followed by enhanced activities of caspases 8, 9, and 3, mitochondrial translocation of Bax, and egress of cytochrome C. To provide evidence that this was a function of a decrease in superoxide anion, the intracellular levels of superoxide were manipulated with PMA (62.5ng/ml) or paraquat (100uM), or by transient transfection with RacV12, and the effect on glucose deprivation-induced apoptosis was assessed. Indeed, increasing intracellular superoxide strongly inhibited death signaling by blocking upstream caspase 8 activation. The mechanism behind superoxide-induced inhibition of caspase 8 activation was the upregulation of cFLIP; decrease in superoxide downregulated cFLIP and restored caspase activation and apoptotic signaling. Overall, these finding suggest that the glycolytic pathway may be an attractive target for intervention to facilitate apoptosis in tumor cells, even in the presence of Bcl-2, by reducing intracellular superoxide and downregulating the death inhibitor, cFLIP.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA