A series of 7-amino- and 7-acetamidoquinoline-5,8-diones with aryl substituents at the 2-position were synthesized, characterized, and evaluated as potential NAD(P)H:quinone oxidoreductase (NQO1) -directed antitumor agents. The synthesis of lavendamycin analogues is illustrated. Metabolism studies demonstrated that 7-amino analogues were generally better substrates for NQO1 than 7-amido analogues, as were compounds with smaller heteroaromatic substituents at the C-2 position. Surprisingly, only two compounds, 7-acetamido-2-(8'-quinolinyl)quinoline-5,8-dione (11) and 7-amino-2-(2-pyridinyl)quinoline-5,8-dione (23), showed selective cytotoxicity toward the NQO1-expressing MDA468-NQ16 breast cancer cells versus the NQO1-null MDA468-WT cells. For all other compounds, NQO1 protected against quinoline-5,8-dione cytotoxicity. Compound 22 showed potent activity against human breast cancer cells expressing or not expressing NQO1, with respective IC50 values of 190 nM and 140 nM and a low NQO1-mediated reduction rate, which suggests that the mode of action of 22 differs from that of lavendamycin and involves an unidentified target(s).