ROS generation by the combined treatment of SAS and PTX in OCCC cell lines. TOV21G, RMG-1, HAC-2 and ES-2 cells were cultured for 24 h in the presence of 10 nM PTX and/or 400 μM SAS and the intracellular ROS levels were analyzed by means of flow cytometry after staining with DCFH-DA. The ROS levels were calculated from the ratio of the intensity of the DCF fluorescence of treated cells to that of untreated cells (set as 1) (n = 5). Data are presented as the mean ± SD. Different letters above the bars indicate a significant difference (p < 0.05, n = 5, in each group). ROS, reactive oxygen species; PTX, paclitaxel; SAS, sulfasalazine; DCFH-DA, 2′,7′-dichlorofluorescin diacetate.