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Relevance of DT‐diaphorase activity to mitomycin C (MMC) efficacy on human cancer cells: Differences in in vitro and in vivo systems
Author(s) -
Nishiyama Masahiko,
Saeki Shuji,
Aogi Kenjiro,
Hirabayashi Naoki,
Toge Tetsuya
Publication year - 1993
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/ijc.2910530626
Subject(s) - mitomycin c , cytotoxicity , in vivo , cell culture , in vitro , dicoumarol , biology , microbiology and biotechnology , cancer research , nad+ kinase , biochemistry , enzyme , genetics
Using 4 human cancer cell lines, 4 tumors xenografted into nude mice, and 11 fresh tumor specimens removed at surgery, we investigated the relevance of NAD(P)H:quinone oxidoreductase (DT‐diaphorase, DTD) activity (nmoles/min/mg protein) to mitomycin C (MMC)‐induced cytotoxicity. In culture cell lines, KB cells had significantly higher levels of DTD activity (8260) than PH101 (1934), SH101 (1805) or K562 (1796), and the highest sensitivity to MMC. In contrast, the higher the DTD activity of xenografts, the greater their resistance to MMC, while the inhibition rate of relative tumor growth for MMC, as evaluated by the NCI protocol, was highest in SH‐6, high in CH‐5, lower in CH‐4 and lowest in EH‐6. The investigation using 11 fresh tumor specimens also showed an inverse relationship between IC 50 values after a 30‐min MMC treatment, as evaluated by ATP assay and DTD activities. Moreover, a non‐toxic DTD inhibitor, dicoumarol (DIC), or flavin adenine dinucleotide (FAD), suppressed the efficacy of MMC in culture cells, but enhanced it in xenografts. Thus, we suggest that DTD may play an important role in MMC‐induced cytotoxicity but MMC metabolism by DTD in solid tumors may differ from that in culture cells.