Adriamycin effects on hydroperoxide metabolism and growth of human breast tumor cells

Human breast tumor cells MCF-7 were grown during 5 days in the presence of Adriamycin and the IC50 was 50 nM with the highest sublethal concentration 0.1 microM. At this latter concentration Adriamycin produced a complete inhibition of cell division and a partial reversion to a normal breast epithelial appearance. Similar effects of Adriamycin were observed in cells cultured in the presence of 10% FBS and in a chemically defined medium, with Se-glutathione peroxidase activities of 3.8 and 1.3 U/mg of protein, respectively. Cell size and cell oxygen uptake were increased by 41% and by 50%, respectively, in Adriamycin-treated cells. The spontaneous chemiluminescence of monolayers of intact MCF-7 cells (81 +/- 9 cps/mg protein) was increased by 48% in the Adriamycin-treated cultures (120 +/- 11 cps/mg of protein) in agreement with a 91% higher concentration of malondialdehyde in the same cultures. Adriamycin treatment produced a 71% increase in the steady state concentration of H2O2, which was estimated assuming diffusion equilibrium with the external medium, from 1.38 microM in the control cells to 2.38 microM in the treated cells. Cyanide-insensitive respiration was also higher in the cells exposed to the drug than in the control cells. Adriamycin did not affect the activity of the antioxidant enzymes, Cu-Zn and Mn-superoxide dismutase, Se and non-Se-glutathione peroxidase, and catalase. These results contribute to the current hypothesis that oxygen free radicals produced by Adriamycin redox cycling are responsible for at least part of the cytotoxic effects due to this drug.