The radiosensitizing effect of metronidazole and misonidazole (Ro-07-0582) on a human malignant melanoma grown in the athymic mutant nude mouse.

The radiosensitizing effect of two electron-affinic nitroimidazoles, metronidazole and misonidazole (Ro-07-0582), has been tested on a human malignant melanoma grown subcutaneously in the athymic mutant nude mouse. A 60Co therapy unit was used for local irradiation of the mice. Metronidazole in doses of 750 mg/kg and misonidazole in doses of 500 mg/kg were administered intraperitoneally to the animals 45 min before exposure to 1250 rad. The time necessary for the tumours to regrow to their original sizes was compared with that of tumours treated with 1250, 1875 and 2500 rad without drug. The enhancement ratios were found to be 1.2-1.3 and 1.4-1.5 for metronidazole and misonidazole respectively. It is concluded that misonidazole is a more efficient hypoxic cell radiosensitizer for this human malignant melanoma than metronidazole. The former may prove to be of value in human radiotherapy.