Metabolic status modulates tumour cell sensitivity to apoptotic stimuli

Chronic lymphocytic leukaemia and mantle cell lymphoma (MCL) are resistant to TNF Related Apoptosis Inducing Ligand (TRAIL), which induces apoptosis via DISC-mediated activation of caspase-8, cleavage of Bid and activation of the mitochondrial cell death pathway. Cancer cells preferentially utilise aerobic glycolysis (‘Warburg effect’) for proliferative growth, and this is a potential therapeutic target. Using MCL-derived cell lines (UPN1 and Z138) the interplay between cancer cell metabolism and cell death was investigated. From this study it was found that active glycolysis appears to be critically required for the full execution of programmed necroptosis. Furthermore, it was observed that 2-deoxyglucose (2DG), a non-metabolisable glucose analogue and hexokinase inhibitor rapidly (0-1h) enhances the sensitivity and potentiates the effects of TRAIL and ABT-737 by inhibiting glycolysis. Extra-cellular flux analysis shows that 2DG rapidly inhibits glycolysis, inducing metabolic reprogramming to transiently increase oxidative-phosphorylation. Despite this increase in oxidative phosphorylation, ATP levels are reduced to 50%, an effect which is maintained for up to 20 h. We now show that the effects of 2DG are not restricted, solely to inhibition of glycolysis, and involve a rapid activation of signalling cascades. Early activation of the AMPK pathway produces a rapid inhibition of protein translation and decrease in the levels of the anti-apoptotic protein Mcl-1, an effect which appears be independent of canonical AMPK kinases LKB1 and CaMKK-β. Additionally, it was observed that cells maintained in galactose media are extremely sensitive to drugs that induce mitochondrial liabilities, however less sensitive to canonical inducers of apoptosis. As such, mass spectrometry analysis of immunopurified mitochondria were analysed to assess changes in the mitochondrial proteome following metabolic reprogramming. This showed that expression of the proteins which make up the mitochondrial oxidative phosphorylation system was up-regulated. Bioinformatics pathway mapping demonstrated that galactose grown cells switched towards a pro-survival phenotype.