Does misonidazole enhance radiation injury to the central nervous system?

Effect of misonidazole on the tolerance of the rat spinal cord to daily and multiple fractions per day of X rays

The effect of misonidazole on the induction of early and late delayed radiation damage in the rat cervical spinal cord has been determined for single doses, daily, and multiple fractions per day of X rays. Paralysis occurred in two separate waves, which could be attributed to histologically different types of damage. Administration of misonidazole before irradiation did not modify the early and late delayed radiation response of the spinal cord. This suggested that the targets for misonidazole and radiation toxicity in the central nervous system are different. Comparison of different types of anaesthesia, Nembutal and Ethrane, with or without breathing oxygen, indicated that hypoxia was not induced in the spinal cord by the experimental conditions. Irradiation with two or three fractions a day showed a reduction in spinal cord tolerance, but this reduction became less with decreasing doses per fraction.

Skin sensitization by misonidazole: a demonstration of uniform mild hypoxia

Skin reactions on irradiated mouse feet were used to measure the radiosensitization of normal tissues by misonidazole (MISO). Fractionation schedules of 1, 2, 5 and 10 daily doses of X-rays were combined with either 100 mg/kg or 670 mg/kg MISO. When unanaesthetized mice were irradiated in air, significant sensitization was observed with both the high and low drug doses, in all fractionation schedules. There was no decrease in sensitization with fractionation, even using fractions as small as 5 Gy. This indicates that many of the cells in mouse skin may be marginally hypoxic, and that sensitization at low doses is possible. Irradiation in O2 without MISO rendered the skin more sensitive to X-rays than in air. MISO given 30 min before single doses of radiation further sensitized the skin, but for 10 fractions in O2 no MISO sensitization was detected. There was little evidence for cytotoxic killing in skin by MISO. Repair of radiation damage was slightly reduced when MISO was present, during or after irradiation.

Effect of misonidazole on radiation injury to mouse spinal cord

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