Enhanced glutathione peroxidase expression protects cells from hydroperoxides but not from radiation or doxorubicin

Both radiation and anthracycline antibiotics may produce reactive oxygen species to cause cytotoxicity, and it has been suggested that some cellular antioxidant enzymes may be important for resistance to these agents. The human breast adenocarcinoma cell line MCF-7WT has a low level of glutathione peroxidase (GPX) activity. We have transfected MCF-7WT cells with a plasmid that contains the cDNA for human GPX under the transcriptional control of the human metallothionein IIA promoter. One transfected clone, MCF-GPX-6, contained multiple copies of GPX cDNA/cell and, after exposure to heavy metals, expressed a level of GPX enzyme activity that was 40-fold higher than that present in MCF-7WT cells and comparable to the GPX activity contained in the doxorubicin-resistant MCF-7DOX cell line. No differences in levels of glutathione, catalase, superoxide dismutase, glutathione S-transferase, or glutathione reductase were noted in MCF-GPX-6 cells compared to MCF-7WT cells. MCF-GPX-6 cells were relatively resistant to hydrogen peroxide and tert-butylhydroperoxide compared to MCF-7WT cells, e.g., exposure of both cell lines to 750 microM H2O2 for 1 h resulted in a relative surviving fraction of 0.07 for MCF-7WT and 0.35 for MCF-GPX-6 cells. However, no difference in sensitivity to either radiation or doxorubicin was noted between MCF-7WT and MCF-GPX-6 cells. These results suggest that GPX is not important for the development of cellular resistance to either radiation or doxorubicin.