Gene targeting of DT-diaphorase in mouse embryonic stem cells: establishment of null mutant and its mitomycin C-resistance.

It is generally accepted that DT-diaphorase is primarily involved in the detoxification of quinone compounds and is capable of metabolically activating some cancer chemotherapeutic quinones including mitomycin C. However, these conclusions have mainly been drawn from the experiments using the DT-diaphorase inhibitor, dicoumarol. To understand directly the roles of this enzyme in quinone metabolism, we have established heterozygously and homozygously DT-diaphorase-targeted mutant embryonic stem (ES) cells by homologous recombination. Cytotoxicity experiments using these cells clearly demonstrated that DT-diaphorase acts as an activator of mitomycin C in ES cells. These mutant cell lines seem to be very useful for investigating the functions of DT-diaphorase including the bioactivation and detoxification of quinone species. The generation of a DT-diaphorase-targeted mouse is under investigation.