Activity of Antioxidant Enzymes and Content of Reduced Glutathione in Cells of Drug-Resistant Murine Leukemia P388 Strains

: Activities of superoxide dismutase and catalase and content of reduced glutathione in cells of drug-resistant murine leukemia P388 strains were studied without or after administration of antitumor compounds. In the absence of chemotherapeutic agents, no significant differences in activities of the studied enzymes in cells of the initial strain and strains resistant to cyclophosphamide, cisplatin, and rubomycin were observed. Compounds to which resistance was developed did not significantly affect activity of enzymes in cells of drug-resistant strains, while the use of compounds that were not resistance inductors was accompanied by a significant decrease in enzyme activity in cells resistant to cisplatin and rubomycin. In cells of strains resistant to cisplatin and cyclophosphamide, the content of reduced glutathione significantly differed from that in the initial strain. In addition, the concentration of reduced glutathione in cells of cyclophosphamide-resistant strain considerably decreased upon addition of the drug producing a therapeutic effect. Our findings suggest that the mechanism of resistance of in vivo derived cyclophosphamide resistant cell strain is related to increased level of reduced glutathione and activity of its metabolism.