Evaluation of thermoradiosensitization and transformation in C3H-10T1/2 cells induced into a thermotolerant state.

C3H-10T1/2 cells were induced to a thermotolerant state by heating at 41.0 degrees C, 42.0 degrees C, 45.0 degrees C or by treatment with ethanol. As thermotolerance developed, cellular heat sensitivity and thermoradiosensitization decreased. Transformation was measured by scoring transformed foci as previously described (Raaphorst et al. 1986 a). Hyperthermia alone in normal and thermotolerant cells did not increase the transformation frequency above background levels. The level of transformation induced by irradiation increased up to three-fold as cells became thermotolerant. This was observed for thermotolerance induced by long-term heating at 41.0 degrees C or short acute heat treatments at 42.0 degrees C or 45.0 degrees C followed by incubation at 37.0 degrees C. Treatment with ethanol also induced thermotolerance, and reduced radiosensitization and increased transformation in the thermotolerant state.