Mitochondrial O₂^.- and H₂O₂ mediate glucose deprivation-induced cytotoxicity and oxidative stress in human cancer cells

The hypothesis that glucose deprivation-induced cytotoxicity in transformed human cells is mediated by mitochondrial O₂^.- and H ₂O₂ was first tested by exposing glucose-deprived SV40-transformed human fibroblasts (GM00637G) to electron transport chain blockers (ETCBs) known to increase mitochondrial O₂^.- and H₂O₂ production (antimycin A (AntA), myxothiazol (Myx), or rotenone (Rot)). Glucose deprivation (2-8 h) in the presence of ETCBs enhanced parameters indicative of oxidative stress (i.e. GSSG and steady-state levels of oxygen-centered radicals) as well as cytotoxicity. Glucose deprivation in the presence of AntA also significantly enhanced cytotoxicity and parameters indicative of oxidative stress in several different human cancer cell lines (PC-3, DU145, MDA-MB231, and HT-29). In addition, human osteosarcoma cells lacking functional mitochondrial electron transport chains (rho(0)) were resistant to glucose deprivation-induced cytotoxicity and oxidative stress in the presence of AntA. In the absence of ETCBs, aminotriazole-mediated inactivation of catalase in PC-3 cells demonstrated increases in intracellular steady-state levels of H₂O₂ during glucose deprivation. Finally, in the absence of ETCBs, overexpression of manganese containing superoxide dismutase and/or mitochondrial targeted catalase using adenoviral vectors significantly protected PC-3 cells from toxicity and oxidative stress induced by glucose deprivation with expression of both enzymes providing greater protection than was seen with either alone. Overall, these findings strongly support the hypothesis that mitochondrial O₂^.- and H ₂O₂ significantly contribute to glucose deprivation-induced cytotoxicity and metabolic oxidative stress in human cancer cells.