Pérez García, Victor M.. Martínez González, Alicia. Pesic, Milica. Pérez Romasanta, Luis. 

Objectives: To investigate how the modulation of the oxidative balance affects cytotoxic therapies in glioblastoma, in vitro. ?Material and Methods: Human glioblastoma U251 and T98 cells and normal astrocytes C8D1A were loaded with coenzyme Q10 (CoQ). Mitochondrial superoxide ion (O2.-) and H2O2 were measured by fluorescence microscopy. OXPHOS performance was assessed in U251 cells with an oxytherm Clark-type electrode. Radio- and chemotherapy cytotoxicity was assessed by immunostaining of ?H2AX (24h), annexin V and nuclei morphology, at short (72h) and long (15d) time. Hif-1?, SOD1, SOD2 and NQO1 were determined by immunolabelling. Catalase activity was measured by classic enzymatic assay. Glutathione levels and total antioxidant capacity were quantified by using commercial kits. ?Results: CoQ did not affect oxygen consumption but reduced the level of O2.- and H2O2 while shifted to a pro-oxidant cell status mainly due to a decrease in catalase activity and SOD2 level. Hif-1? was dampened, echoed by a decrease lactate and several key metabolites involved in glutathione synthesis. CoQ-treated cells were two-fold more sensitive than control to radiation-induced DNA damage and apoptosis in short and long-term clonogenic assays, potentiating TMZ-induced cytotoxicity, without affecting non-transformed astrocytes. ?Conclusions: CoQ acts as sensitizer for cytotoxic therapies, disarming GBM cells, but not normal astrocytes, against further pro-oxidant injuries, being potentially useful in clinical practice for this fatal pathology.