THERMAL RADIOSENSITIZATION BY PROTRACTED LOW-TEMPERATURE HYPERTHERMIAIN HUMAN GLIOMA-CELLS

Human glioma cells were studied to evaluate the effect long duration m ild hyperthermia (LDMH), (up to 48 h) had on radiosensitization follow ing heating and this was compared to LDMH given concurrently during lo w dose-rate irradiation. LDMH did not induce thermotolerance in glioma cells. Thermal radiosensitization was observed for acute irradiation following LDMH. The thermal enhancement ratios (TER) increased with he ating time and temperature over the temperature range studied (40-42 d egrees C). The TER ranged from 1.0 to 4.7. For equivalent heating duri ng LDR, the TER was larger than for heating before acute irradiation. Analysis of DNA polymerase inactivation showed the TER for LDMH was co rrelated to residual polymerase alpha levels for heat at 40 and 41 deg rees C. This was not observed for polymerase beta. For heating at 42 d egrees C there was correlation between TER and polymerase alpha! and b eta; however, the curve had a different slope than for the lower tempe ratures. In addition, it was shown that the TERs for heating at temper atures between 42 and 45 degrees C correlated well with polymerase bet a inactivation, and not as well with polymerase alpha inactivation. Th ese results show that LDMH (40,41 degrees C) can cause thermoradiosens itization and that its mechanism may be different than the radiosensit ization observed for heating at temperatures at or above 42 degrees C. Copyright (C) 1996 Elsevier Science Ltd.