The effect of hypoxic radiosensitizer after mild hyperthermia in C3H mammary carcinoma.

The radiosensitizing effect of misonidazole after hyperthermia was investigated in C3H mammary carcinoma. The tumors transplanted into the flanks of the mice were heated in a 42.3 degrees C water bath for 30 min. When misonidazole was administrated before heating, the subsequent radiation effect was prominently enhanced, whereas post-heating administration of misonidazole did not enhance the radiation effect significantly. The effect of varying the time between heating and radiation with or without misonidazole was as follows. Without misonidazole, the radiation effect was decreased at 6 hours after heating but increased at 12 hours, then it returned to the initial level at 24 hours and remained until 96 hours after heating. With misonidazole administered 30 min before irradiation, the radiosensitizing effect was observed at 24, 48 and 96 hours after heating. However, the total effects of this procedure were almost the same as the results in the combination without heating. Changes in the hypoxic fraction after hyperthermia are also discussed.