Dual effects of N-acetyl-l-cysteine dependent on NQO1 activity: Suppressive or promotive of 9,10-phenanthrenequinone-induced toxicity

► NAC augmented the cytotoxicity of 9,10-PQ in skin cell lines. ► 9,10-PQ-induced DSBs accompanying γ-H2AX were also augmented by NAC. ► NAC suppressed the cyto- and genotoxicity of 9,10-PQ in adenocarcinoma cell lines. ► The dual effects of NAC on toxicity of 9,10-PQ were dependent on NQO1 activity.