CHARACTERIZATION OF A SET OF CHINESE-HAMSTER OVARY VARIANT CELL-LINESDEMONSTRATING DIFFERING SENSITIVITY TO MITOMYCIN-C

Three related Chinese hamster ovary (CHO) cell lines derived from CHO- K1(R) cells (MMC3-A2, 21-1 and G1B) previously shown to differ in thei r sensitivity to mitomycin C (MMC), were investigated in more detail t o determine the factors controlling this sensitivity. A separately mai ntained wild type cell line (CHO-K1(TOR)) was included in this study f or comparison. Continuous (chronic) exposure of the five cell lines to MMC during the 10-day colony forming assay demonstrated a 15-fold ran ge in MMC sensitivity between the most sensitive cell line (MMC3-A2) a nd the most resistant cell line (G1B) with CHO-K1(R), 21-1 and CHO-K1( TOR) falling at intermediate levels. Acute aerobic exposure (0-5 h) to MMC resulted in a reduced five-fold range of sensitivities, which was further reduced to a three-fold range under hypoxic exposure conditio ns. These results were suggestive of differences in the aerobic enzyma tic activation of MMC as a possible mechanism contributing to the vary ing sensitivities. There was rio correlation between the one-electron reducing enzyme NADPH:cytochrome P-450 oxidoreductase (P450R) activity and cellular sensitivity to MMC. The five cell lines had similar leve ls of reduced glutathione (GSH), suggesting that oxygen homeostasis wa s not correlated with the cells. differing sensitivity to MMC. A corre lation did exist between NAD(P)H:quinone oxidoreductase (DT-diaphorase ) activity and cellular sensitivity to MMC under chronic exposure cond itions for the cell lines. High DT-diaphorase levels were also correla ted with a reduced ability of oxygen to modulate MMC toxicity. Levels of P450R and DT-diaphorase were not altered significantly during five- hour aerobic or hypoxic exposures of control cells. These results sugg est that DT-diaphorase levels are a major contributor to the sensitivi ty of these cells to MMC under aerobic but not hypoxic exposure condit ions.