RADIATION-INDUCED CHANGES IN NUCLEOID HALO DIAMETERS OF AEROBIC AND HYPOXIC SF-126 HUMAN BRAIN-TUMOR CELLS

Nucleoid halo diameters were measured to assay changes in DNA supercoi ling in human brain tumor cell Line SF-126 after irradiation under aer obic or hypoxic conditions. In unirradiated aerobic cells, a typical p ropidium iodide titration curve showed that with increasing concentrat ions of propidium iodide, the halo diameter increased and then decreas ed with the unwinding and subsequent rewinding of DNA. supercoils. In irradiated cells, the rewinding of DNA supercoils was inhibited, resul ting in an increased halo diameter, in a radiation dose-dependent mann er. To produce equal increases in halo diameter required about a three fold higher radiation dose in hypoxic cells than in aerobic cells. Qua ntitatively similar differences in the radiation sensitivities of hypo xic and aerobic cells were demonstrated by a colony-forming efficiency assay. These findings suggest that the nucleoid halo assay may be use d as a rapid measure of the inherent radiation sensitivity of human tu mors. (C) 1995 Wiley-Liss, Inc.