The radiosensitizing effect of misonidazole on hypoxic cells in the animal tumor

The radiosensitizing effect of Misonidazole on hypoxic cells in the animal tumor was studied. Three examinations were planned to evaluate. (1) LD50 value of total mice body irradiation combined with Misonidazole, (2) Radiosensitizing effect of Misonidazole on normal tissues (weight and cell number of intestines of mice), and (3) Radiosensitizing effect of Misonidazole on 48 hour-Ehrlich ascites tumor transplanted on the thighs of mice. In all these examinations 8 weeks ICR/JCL mice were used. Irradiation was carried out using Toshiba KXC-18 type X-ray therapy machine. LD50 value on 5th. day was 1340 rad in the radiation with Misonidazole-group and 1140 rad in the simple radiation-group. LD50 value on 30th day was 530 rad in the radiation with Misonidazole-group and 560 rad in the simple radiation group. There was no significant difference between LD50 of the simple radiation-group and that of the radiation with Misonidazole-group on both 5th and 30th day. There was no significant difference of 3.5th. day's weight and cell number of mice between both group. In aerobic condition TCD 50 (50 % Tumor Control Dose) value of the radiation with Misonidazole-group was 790 rad and TCD 50 value of the simple radiation-group was 900 rad, so there was no significant difference. On the contrally, in hypoxic condition TCD 50 value of the radiation with Misonidazole-group was 1160 rad and TCD 50 value of the simple radiation-group was 2900 rad. Misonidazole showed significant radiosensitizing effect (enhancement ratio 2.5) in hypoxic condition. These results demonstrates that Misonidazole presents high radiosensitizing effect on hypoxic cells of the mice tumor, but no significant radiosensitizing effect on normal tissues. (author)