ROLE OF DT-DIAPHORASE AS A DETERMINANT OF SENSITIVITY TO MITOMYCIN ANALOGS IN NONSMALL CELL LUNG-CANCER CELL-LINES

DT-diaphorase (DT-D) is regarded as a two-electron reductase that play s an important role in the biotransformation of mitomycin C (MMC) to a ntitumor metabolites, which is enhanced under hypoxic conditions. To e valuate the role of DT-D as a bioactivator of MMC and its analogue, KW -2149, in non-small cell lung cancer (NSCLC) cell lines under an aerob ic or hypoxic condition, we examined the inhibitory effect of dicumaro l which was regarded as an inhibitor of DT-D on the sensitivity to the se anticancer agents in vitro. In this study, we used an MMC-resistant NSCLC cell line (PC-9/MC4) which was established in our laboratory fr om a PC-9 cell line as a parent cell line by continuous exposure to MM C. The subline PC-9/MC4 was 6.7-fold more resistant to MMC than PC-9, the parent cell line, under aerobic conditions, and 5.2-fold more resi stant even under hypoxic conditions. PC-9/MC4 cell lines did not show collateral resistance to KW-2149, a newly developed MMC analogue. The IC50 value of PC-9 against MMC significantly decreased by co-incubatio n with dicumarol under aerobic, but not under hypoxic conditions. KW-2 149 was cytotoxic to PC-9/MC4 as well as PC-9 cells, and the sensitivi ty to KW-2149 was not altered by coincubation with dicumarol or exposu re to hypoxia. There were no significant differences in intracellular uptake of MMC and the activities of cytosolic detoxification enzymes, GST and GSH, between PC-9 and PC-9/MC4 cell lines under aerobic condit ions. These findings suggest a partial role of DT-D in bioactivation o f MMC, but not of KW-2149, under aerobic conditions. However, the deta iled mechanisms of drug resistance to MMC under hypoxic conditions are still not clear.