UNUSUALLY MARKED HYPOXIC SENSITIZATION TO INDOLOQUINONE EO9 AND MITOMYCIN-C IN A HUMAN COLON-TUMOR CELL-LINE THAT LACKS DT-DIAPHORASE ACTIVITY

Studies with purified DT-diaphorase have shown that the enzyme is capa ble of catalyzing a two-electron reduction of the novel indoloquinone EO9 to a DNA-damaging alkylating species. The aim of this study war to determine to what extent DT-diaphorase may be involved in the metabol ic activation of EO9 and mitomycin C in both aerobic and hypoxic condi tions. Two human colon-carcinoma cell lines were used; HT29 has high l evels of DT-diaphorase whilst BE lacks this activity because of a poin t mutation in the NQOI gene. In aerobic conditions the 2 cell lines sh ow similar sensitivities to a number of cytotoxic drugs including cisp latin, doxorubicin and etoposide. They are equally sensitive to the be nzotriazine di-N-oxide SR 4233 but HT29 is more sensitive than BE to m itomycin C and EO9. Sensitivity to SR 4233 is increased by about 100-f old for both cell lines in hypoxic conditions. DT-diaphorase-deficient BE cells show markedly increased sensitivity to mitomycin C and parti cularly EO9 in hypoxic conditions, whereas DT-diaphorase-rich HT29 cel ls show little hypoxic sensitization to these agents unless exposed in the presence of dicoumarol. These results suggest that DT-diaphorase can reduce EO9 and mitomycin C to potent cytotoxic species in aerobic conditions, and this activity predominates over the one-electron-reduc ing enzymes even in hypoxic conditions. In the absence of DT-diaphoras e activity, EO9 and mitomycin C are reduced in hypoxic conditions, pre sumably by one-electron-reducing enzymes, to a similar or greater exte nt than is achieved with DT-diaphorase. (C) 1994 Wiley-Liss, Inc.