This report describes the effects of a new radiosensitizer, metronidazole derivative (CM) synthesized in our laboratory, on membrane permeability of 51Cr labelled L7712 cells.It was found that CM could be incorporated into the cancer cells easily, and resulted in increased membrane permeability.Under aerobic condition, the release rate of 51Cr was increased when the cells were irradiated with more than 40 Gy Y-rays.At a dose of 0-80 Gy, the sensitization effects of CM on membrane permeability of irradiated cells were not found.

The sensitizing effects of radiosensitizer CMCa on S180 bearing mice in two f rac- tionated radiotherapy schedules were compared. The restlts showed that CMCa had the sensitizing effects in both fractionated schedules. The SER value of 2F/7D schedule was higher than that of 5F/7D. The TCD50(90) dose of 2F/7D was also decreased obviously. There was a significant difference of regression coefficients of dose-response curves between the experimental group and control one. The total radiation dose which was required for disapperance of tumor in all drug treated animals was reduced. The results indicate.that radiosensitizing effect of CMCa with 2F/7D schedule is better than that with 5F/7D.