Studies on adaptation to adriamycin in cells pretreated with hydrogen peroxide

Various investigations have reported the occurrence in bacterial and mammalian cells of an adaptive response to the toxic effects of oxidants or agents that cause oxidation via redox reactions. In our previous study, it was shown that several cell lines pretreated with a low dose of hydrogen peroxide (H2O2) exhibited an adaptive response to subsequent high doses of adriamycin (ADR), whereas other cell lines did not. Based on the observation that the cell lines utilized differed in their sensitivity towards adriamycin, we undertook the present investigation with the goal of evaluating possible relationships between the levels of antioxidant enzymes and sensitivity towards adriamycin. Another aim was to determine relationships between the inducibility of these enzymes and the occurrence of adaptation. We utilized African Green monkey kidney (V3), human embryo (CLV98), human melanoma (ME18), and Chinese hamster ovary (CHO) cell lines and experimentally developed adriamycin-resistant human melanoma (ME18/RN) and Chinese hamster ovary (CHO/RN) cell sublines. Cytotoxicity was measured by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and trypan blue exclusion. The levels of catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) were determined in the same kind of experiment as that revealing the occurrence of adaptation. The rank order established for catalase activities was similar to that for sensitivity towards adriamycin. Aberrant increases in the tested enzymes were demonstrated in experimental groups of all kinds of cells. We conclude that in our cell systems catalase is a major determinant of adriamycin resistance. Whether the occurrence of the adaptive response under study is dependent on the contribution of catalase, itself dependent on the degree of resistance to the drug, is discussed.