Unusually marked hypoxic sensitization to indoloquinone EO9 and mitomycin C in a human colon-tumour cell line that lacks DT-diaphorase activity.
Studies with purified DT-diaphorase have shown that the enzyme is capable of catalyzing a two-electron reduction of the novel indoloquinone EO9 to a DNA-damaging alkylating species. The aim of this study was to determine to what extent DT-diaphorase may be involved in the metabolic activation of EO9 and mitomycin C in both aerobic and hypoxic conditions. Two human colon-carcinoma cell lines were used; HT29 has high levels of DT-diaphorase whilst BE lacks this activity because of a point mutation in the NQOI gene. In aerobic conditions the 2 cell lines show similar sensitivities to a number of cytotoxic drugs including cisplatin, doxorubicin and etoposide. They are equally sensitive to the benzotriazine di-N-oxide SR 4233 but HT29 is more sensitive than BE to mitomycin C and EO9. Sensitivity to SR 4233 is increased by about 100-fold for both cell lines in hypoxic conditions. DT-diaphorase-deficient BE cells show markedly increased sensitivity to mitomycin C and particularly EO9 in hypoxic conditions, whereas DT-diaphorase-rich HT29 cells 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-reducing enzymes even in hypoxic conditions. In the absence of DT-diaphorase activity, EO9 and mitomycin C are reduced in hypoxic conditions, presumably by one-electron-reducing enzymes, to a similar or greater extent than is achieved with DT-diaphorase.
Plumb
J A
JA
CRC Department of Medical Oncology, University of Glasgow, Bearsden, UK.
Workman
P
P
D000332:Aerobiosis / Q000187:drug effects; D000970:Antineoplastic Agents / Q000627:therapeutic use* / Q000633:toxicity; D001388:Aziridines / Q000627:therapeutic use* / Q000633:toxicity; D015687:Cell Hypoxia / Q000187:drug effects; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000201:enzymology*; D004305:Dose-Response Relationship, Drug; D004354:Drug Screening Assays, Antitumor; D006801:Humans; D045563:Indolequinones; D007211:Indoles / Q000627:therapeutic use* / Q000633:toxicity; D016685:Mitomycin / Q000627:therapeutic use* / Q000633:toxicity; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000172:deficiency* / Q000187:drug effects; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000201:enzymology
D000970:Antineoplastic Agents; D001388:Aziridines; D045563:Indolequinones; D007211:Indoles; D016685:Mitomycin; D016660:NAD(P)H Dehydrogenase (Quinone); C060817:apaziquone