Indolequinone antitumor agents:: Correlation between quinone structure, rate of metabolism by recombinant human NAD(P)H:quinone oxidoreductase, and in vitro cytotoxicity

A series of indolequinones bearing various functional groups has been synthesized, and the effects of substituents on the metabolism of the quinones by recombinant human NAD(P)H: quinone oxidoreductase (NQO1) were studied. Thus 5-methoxyindolequinones were prepared by the Nenitzescu reaction, followed by functional group interconversions. The methoxy group was subsequently displaced by amine nucleophiles to give a series of amine-substituted quinones. Metabolism of the quinones by NQO1 revealed that, in general, compounds with electron-withdrawing groups at the indole 3-position were among the best substrates, whereas those with amine groups at the 5-position were poor substrates. Compounds with a leaving group at the 3-indolyl methyl position generally inactivated the enzyme. The toxicity toward non-small-cell lung cancer cells with either high NQO1 activity (H460) or no detectable activity (H596) was also studied in representative quinones. Compounds which were good substrates for NQO1 showed the highest selectivity between the two cell lines.