Hypoxia inducible factor-1α inactivation unveils a link between tumor cell metabolism and hypoxia-induced cell death

Hypoxia and the acquisition of a glycolytic phenotype are intrinsic features of the tumor microenvironment. The hypoxia inducible factor-1 alpha (HIF-1 alpha) pathway is activated under hypoxic conditions and orchestrates a complex transcriptional program that enhances cell survival. Although the consequences of HIF-1 alpha inactivation in cancer cells have been widely investigated, only a few studies have addressed the role of HIF-1 alpha in the survival of cancer cells endowed with different glycolytic capacities. In this study, we investigated this aspect in ovarian cancer cells. Hypoxia-induced toxicity was increased in highly glycolytic cells compared with poorly glycolytic cells; it was also associated with a sharp decrease in intracellular ATP levels and was prevented by glucose supplementation. Stable HIF-1 alpha silencing enhanced hypoxia-induced cell death in vitro due to a lack of cell cycle arrest. Tumors bearing attenuated HIF-1 alpha levels had similar growth rates and vascularization as did controls, but tumors showed higher proliferation levels and increased necrosis. Moreover, tumors, formed by HIF-1 alpha deficient cells had higher levels of lactate and lower ATP concentrations than controls as shown by metabolic imaging. The findings that such metabolic properties can affect the survival of cancer cells under hypoxic conditions and that these properties contribute to the determination of the consequences of HIF-1 alpha inactivation could have important implications on the understanding of the effects of anti-angiogenic and HIF-1 alpha-targeting drugs in cancer.