Thermal radiosensitization in Chinese hamster (V79) and mouse C3H 10T 1/2 cells. The thermotolerance effect

Abstract

The sensitivity of V79 cells and normal or morphologically transformed C3H-10T 1/2 cells to X-rays, heat or heat plus X-rays was examined. The normal and transformed C3H-10T 1/2 cell lines were equally sensitive to heat at 42.0°C and radiation. The V79 cells were more heat sensitive. Thermal radiosensitization occurred for all 3 cell lines for the combined heat and radiation treatments and was greatest for simultaneous treatment. Recovery occurred when the treatments were separated by an incubation interval at 37°C. For the V79 cells, recovery was much greater for X-rays preceding heat compared to X-rays following heat. This difference was not as great in the C3H-10T 1/2 cell lines. The transformed C3H-10T 1/2 cells were more sensitive compared to the normal for the simultaneous treatment or for heating followed by irradiation. For prolonged heating at 42.0°C, after which thermotolerance occurred in all 3 cell lines, the radiosensitivity still increased as a function of heating time even though no additional cell killing occurred from the heat treatment alone. For heating V79 cells at 41.0°C no further increase in radiosensitivity occurred, as cells became thermotolerant during prolonged heating. Also for the development of thermotolerance during incubation at 37°C between two heat treatments, thermal radiosensitization decreased demonstrating that thermotolerance can affect radiosensitization by hyperthermia. © 1983 The Macmillan Press Ltd.