Doxorubicin‐induced lipid peroxidation and glutathione peroxidase activity in tumor cell lines selected for resistance to doxorubicin

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Abstract
Doxorubicin‐induced lipid peroxidation was evaluated in four human or murine cell strains in culture and in their doxorubicin‐resistant variants, by the quantification of malondialdehyde produced after a 2‐h incubation of cells with the drug. Significantly increased malondialdehyde levels were obtained 24 h after doxorubicin treatment in three of the wild‐type cell lines with doses as low as 0.05–0.1 μg/ml, which is within an order of magnitude of the concentration of the drug which inhibits cell growth by 50%. This production of malondialdehyde was abolished in two doxorubicinresistant strains, even with high doses of drug (100–300 μg/ml), but was maintained in the third resistant line. No malondialdehyde production was observed in the fourth cell line, sensitive or resistant. It is remarkable that an enhancement of selenium‐dependent and non‐selenium‐dependent glutathione peroxidase activities was exhibited during the acquisition of resistance to doxorubicin in the two first lines, but not in the third, whereas a constitutively high non‐selenium‐dependent glutathione peroxidase activity existed in the doxorubicin‐sensitive and doxorubicin‐resistant variants of the fourth cell line. Gene expression of selenium‐dependent glutathione peroxidase and of glutathione S‐transferase π, which is known partially to bear a non‐selenium‐dependent glutathione peroxidase activity, were correlated with the corresponding enzyme activities. It appears, therefore, that the already known enhancement of glutathione peroxidase activity and expression in doxorubicin‐resistant cell lines has a quantifiable consequence upon doxorubicin‐induced lipid peroxidation and may have consequences in the mechanism of resistance to this drug.