Bioreductive prodrug; activated by hypoxia to yield the topoisomerase II inhibitor AQ4. Displays little to no cytotoxic activity against 60 tumor cell lines tested under oxic conditions (IC50 >100 μM). Exhibits anti-tumor efficacy in vivo when combined with oxic cell cytotoxins; enhances the anti-tumor effect of cyclophosphamide (Cat. No. 4091) in a mouse tumor model.