Fig. 4. Antioxidant activity of Ir-TEMPO1 and Ir-TEMPO2 in A2780 ovarian cancer cells. (a) Comparison between the fluorescence of 2′,7′-dichlorofluorescein diacetate (DCFH-DA) on its own or in the presence of equipotent concentrations of Ir-TEMPO1 or Ir-TEMPO2. (b, c) The relative fluorescence normalised to the controls of A2780 cancer cells stained with DCFH-DA when ROS has been induced with hydrogen peroxide (575 μM, b) or tert-butyl hydroperoxide (TBHP) (250 μM, c). In all cases: the concentrations of the complexes used were equipotent with 1- or 2-fold of their IC₅₀ concentrations in this cancer cell line, drug exposure to the iridium complexes was 24 h prior to staining, followed by 4 h of ROS induction. Fluorescence measurements were carried out using excitation at 485 nm and emission at 530 nm for DCFH-DA. Each measurement was carried out in duplicates of triplicates and their statistical significance was determined using an independent two-sample t-tests with unequal variances, Welch's tests, (p < 0.01 for **, and p < 0.05 for *).