Reduction of nitroxides and radioprotective ability in glioblastoma cells

Electron spin resonance (ESR) analyses were performed to clarify whether glioblastoma cells scavenge hydroxyl radicals (*OH) generated by x-ray irradiation. The rate of bioreduction of nitroxides by three human glioblastoma cells was also evaluated by the same technique and compared with their x-ray sensitivity. Aerated culture media containing 200mM of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) with or without U87MG cells were irradiated with x-rays at a dose of 20Gy. ESR was measured immediately after each irradiation. Continuous changes of the ESR spectra of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol) were analyzed in cell suspensions of TK1, U87MG, and A172 at a concentration of 1.0 x 10(7) cells/ml containing 5 microM Tempol. As a result, the signal of DMPO-OH in the U87MG cell suspension decayed faster than that in the control culture media without cells, and the rate of bioreduction of Tempol in each glioblastoma cell suspension was correlated with the x-ray sensitivity defined from the colony-forming assay in those cell lines. It was indicated that the resistance of glioblastoma cells to ionizing radiation could be closely related to their ability to scavenge radical species generated by ionizing radiation.