DOXORUBICIN-MEDIATED FREE-RADICAL GENERATION IN INTACT HUMAN TUMOR-CELLS ENHANCES NITROXIDE ELECTRON-PARAMAGNETIC-RESONANCE ABSORPTION INTENSITY DECAY

The decay of nitroxide spin label electron paramagnetic resonance (EPR ) absorption intensity was used to investigate the doxorubicin-mediate d intracellular generation of free radicals. The effects of 50-500 mug /ml doxorubicin on human tumor cells (MCF-7, breast cancer cells, and HL-60, promyelocytic leukemia, cells) were studied by measuring 2,2,6, 6-tetramethylpiperidine-1-oxyl (TEMPO) absorption intensity decay (TAI D) at a TEMPO concentration of 10 muM. Doxorubicin accelerated the TAI D in both cell lines with a detection limit of 50 mug/ml for MCF-7 cel ls and 500 mug/ml doxorubicin for HL-60 cells. Preincubation of cells with the iron chelating agent, deferoxamine (5 mM), partially prevente d the effects of doxorubicin on the TAID. Catalase and copper, zinc-su peroxide dismutase (Cu,Zn-SOD) had no influence on the effects of doxo rubicin on the TAID in intact cells. However, Cu,Zn-SOD completely abo lished the effects of doxorubicin on the TAID in a MCF-7 cell-free sys tem. Our findings suggest that doxorubicin mediates the intracellular generation of O-2-radical-anion and that iron is involved in this proc ess.