NAD(P)H: Quinone Oxidoreductase enhances proliferation inhibition by 4-hydroxytamoxifen

The nonquinone compound, 4-OHT, was identified as a NQOR substrate as measured by reduction in the MTT assay. 4-OHT was then evaluated for effects on proliferation inhibition in two independent cell model systems, the MCF7 (NQ01+), MCF7 + dicoumarol (NQO1-) and the CHO (NQO1-) CHO-812 (NQO1+). NQOR activity predicts inhibition of proliferation by 4-OHT in these two models. MCF-7s were more sensitive to 4-OH tamoxifen with a P150 of 2.65 nM than MCF-7 + dicoumarol with a P150 of 1.84 μM (p<0.05, by one way ANOVA). CHO812s were also more sensitive to proliferation inhibition by 4-OH tamoxifen with a P150 of 80.2 μM compared to the CHOs with a P150 of 93.1 μM (p<0.05, by one-way ANOVA). Suggesting: 1) 4-OH tamoxifen is reduced by NQOR and 2) the reduced product is more active than the parent compound.