Changes in intracellular reactive oxygen species (ROS) content upon treatment with CAP (3 min, COST jet), TMZ (40 µM for U251, and 72 µM for U87-MG and T98G) alone and their combination (CAP + TMZ), in the presence or absence of NAC, in (a) U251 (TMZ-sensitive), (b) U87-MG and (c) T98G (TMZ-resistant) spheroids. A fluorescent Cell®Rox green probe was used to measure the percentage of ROS in treated versus untreated controls. Statistical analysis was performed using one-way analysis of variance (ANOVA), with Tukey’s comparison analysis. Data are representative of three independent experiments; mean ± SD. Statistically significant differences were found between the untreated control and corresponding treated samples. * = p ≤ 0.05; ** = p ≤ 0.01; *** = p ≤ 0.001, ns = not significant.