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

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Abstract
The radiosensitizing effect of 2 electron-affinic nitroimidazoles, metronidazole and misonidazole (Ro-07-0582), was tested on a human malignant melanoma grown s.c. 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 i.p. to the animals 45 min before exposure to 1250 rad. The time necessary for the tumors to regrow to their original sizes was compared with that of tumors treated with 1250, 1875 and 2500 rads without drug. The enhancement ratios were 1.2-1.3 and 1.4-1.5 for metronidazole and misonidazole, respectively. 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.