The efficacy of targeting pH disruption to induce cell death in the acidic and hypoxic tumor microenvironment continues to be assessed. Here we analyzed the impact of varying levels of
hypoxia in acidic conditions on fibroblast and
tumor cell survival. Across all cell lines tested,
hypoxia (1% O(2)) provided protection against
acidosis induced cell death compared to normoxia. Meanwhile severe
hypoxia (0.1% O(2)) removed this protection and in some cases exacerbated
acidosis-induced cell death. Differential survival between cell types during external
acidosis correlated with their respective intracellular pH regulating capabilities. Cellular
ATP measurements were conducted to determine their contribution to cell survival under these combined stresses. In general,
hypoxia (1% O(2)) maintained elevated
ATP levels in acidic conditions while severe
hypoxia did not. To further explore this interaction we combined
acidosis with
ATP depletion using
2-deoxyglucose and observed an enhanced rate of cell mortality. Striking results were also observed with
hypoxia providing protection against cell death in spite of a severe metabolic stress induced by a combination of
acidosis and
oligomycin. Finally, we demonstrated that both HIF1α and HIF2α expression were drastically reduced in hypoxic and acidic conditions indicating a sensitivity of this
protein to cellular pH conditions. This knockdown of HIF expression by
acidosis has implications for the development of
therapies targeting the disruption of cellular pH regulation. Our results reinforce the proof of concept that
acidosis and metabolic disruption affecting
ATP levels could be exploited as a
tumor cell killing strategy.