Determination of Nrf2 activity upon vorinostat treatment, alone or in combination with N-acetyl-L-cysteine (NAC), via luciferase reporter assay. (A) Treatment of a panel of cell lines with 3 µM vorinostat (gray bars) or vehicle (DMSO) (black bars) for 48 h led to vorinostat-induced increase of luciferase activity, indicating Nrf2 activation in most cell lines. Data represent the mean of luciferase measurements performed in duplicate. Additional experiments were performed in (B) MKN-45 and (C) MKN-74 cells treated with 5 µM vorinostat for 48 h or vehicle DMSO (“D”), showing opposite vorinostat effects on luciferase activity. Furthermore, the effect of NAC on vorinostat-mediated increase in luciferase activity was tested in (D) MKN-45 and (E) Hs746T cells. Graphs in (B–E) show mean values of at least three independent experiments + SEM. **, p < 0.01 and ***, p < 0.001.