Involvement of NADPH: cytochrome P450 reductase in the activation of indoloquinone EO9 to free radical and DNA damaging species

Evidence suggests that DT-diaphorase is involved in the activation and mech anism of cytotoxicity of the investigational indoloquinone anticancer drug EO9 under aerobic conditions. Data also implicate a role for other enzymes including NADPH: cytochrome P450 reductase, especially in low DT-diaphorase tumour cells and under hypoxic conditions. Here, we used purified rat NADP H: cytochrome P450 reductase to provide additional evidence in support of a role for this enzyme in activation of EO9 to generate free radical and DNA -damaging species. Electron spin resonance spectrometry studies showed that NADPH: cytochrome P450 reductase reduced EO9 to a fret: radical species, i ncluding a drug radical (most likely the semiquinone) and reactive oxygen s pecies. Plasmid DNA experiments showed that reduction of EO9 catalysed by N ADPH: cytochrome P450 reductase results in single-strand breaks in DNA. The information obtained may contribute to the understanding of the molecular mechanism of DNA damage and cytotoxicity exerted by EO9 and may be useful i n the design of future bioreductive drugs. (C) 2001 Elsevier Science Inc. A ll rights reserved.