A new screening system for NAD(P)H : quinone oxidoreductase (NQO1)-directed antitumor quinones: Identification of a new aziridinylbenzoquinone, RH1, as a NQO1-directed antitumor agent

NAD(P)H:quinone oxidoreductase (NQO1; DT-diaphorase) is elevated in certain tumors, such as non-small cell lung cancer (NSCLC). Compounds such as mito mycin C and streptonigrin are efficiently bioactivated by NQO1 and have bee n used in an enzyme-directed approach to chemotherapy. Previously, 2,5-diaz iridinyl-3,6-dimethyl-1,4-benzoquinone (MeDZQ) was identified as a potentia l antitumor agent based on its high rate of bioactivation by human NQO1 and its selective cytotoxicity to cells containing elevated NQO1, RH1, a water -soluble analogue of MeDZQ synthesized in this work, was a better substrate for recombinant human NQO1 than the parent compound. RH1 was, correspondin gly, more cytotoxic to human tumor cells expressing elevated NQO1 activity (H460 NSCLC and HT29 human colon carcinoma), as measured by 3-(4,5-dimethyl -thiazol-2,5-diphenyl)tetrazolium assay, than it was to cells deficient in NQO1 activity (H596 NSCLC and BE human colon carcinoma). RH1 exhibited a gr eater selective toxicity (ratio of IC(50)s in H596:H460 and BE:HT29) to cel ls with elevated NQO1 activity relative to MeDZQ, Additionally, we report t he establishment of a stable line of BE human colon carcinoma cells transfe cted with wild-type human NQO1 (BE-NQ7). BE cells are devoid of NQO1 activi ty due to a homozygous point mutation in the NQO1 gene. In comparison to th e parental cell line, RH1, MeDZQ, and mitomycin C mere significantly more c ytotoxic to BE-NQ7 cells (17-, 7-, and 3-fold, respectively), confirming th at the presence of NQO1 is sufficient to increase cytotoxicity of these ant itumor quinones, These data suggest that RH1 may be an effective NQO1-direc ted antitumor agent for the therapy of tumors with elevated NQO1 activity, such as NSCLC.