FIGURE 4: ROS production is lower in GBM cells with acquired radioresistance. (A) Quantification of mitochondrial O₂^•− production in radiosensitive (U251, D456, and Jx39) and isogenic radioresistant (U251-RR, D456-RR, and Jx39-RR) cell lines, determined by MitoSOX assays. Data are presented as the mean ± SEM (n=4). (B) Quantification of mitochondrial O₂^•− production in the radiosensitive and radioresistant cells treated without or with AA (10 μM, 15 min) to inhibit complex III. Data are presented as the mean ± SEM (n=3). (C) Quantification of mitochondrial O₂^•− production in vector control- and SOD₂-transfected U251 cells treated without or with AA (10 μM, 15 min). Data are presented as the mean ± SEM (n=2). (D) Quantification of complex II/III activity in radiosensitive and radioresistant cells. Data are presented as the mean ± SEM (n=3). (E) Quantification of mitochondrial membrane potential (Δψm) and O₂^•− production (F) in radiosensitive and radioresistant cells treated without or with the uncoupler FCCP (10 μM, 15 min). Data are presented as the mean ± SEM (n=3). (G) Quantification of mitochondrial H₂O₂ production, determined by Amplex Red oxidation assays, in radiosensitive and radioresistant cells treated without or with the uncoupler FCCP (10 μM, 15 min). Data are presented as the mean ± SEM (n=2). p < 0.05 (*), p < 0.01 (**), p < 0.001 (***) and p < 0.0001 (****), respectively, calculated by Student t-test. a.u., arbitrary units; ns, not significant; CS, citrate synthase; Δψ_m, mitochondrial membrane potential; and FCCP, carbonyl cyanide p-trifluoromethoxyphenylhydrazone.