Thermotolerance effects on thermoradiosensitization in human glioma cells

Human glioma cells were tested to evaluate thermotolerance (TT) development and its effect on radiosensitization. The data show that long duration mild hyperthermia (LDMH) at 40, 41 and 42 degrees C when given before acute irradiation resulted in increased radiosensitization with heating time. Furthermore, radiosensitization was not reduced by TT. When LDMH was given before 45 degrees C hyperthermia there was evidence of TT development which reduced radiosensitization compared to heating at 45 degrees C alone. For 40 and 41 degrees C heating the effect was maximum for the 8 h heating time while for 42 degrees C it was generally maximum for the 4 h heating time. At longer heating times of 24 to 48 h the effect of TT declined. Thus while LDMH itself does not display TT for radiosensitization it can in fact produce a TT effect on radiosensitization when used in a stepup-heating protocol with 45 degrees C.