Radiosensitizing effect of misonidazole in acute and fractionated irradiation of a human osteosarcoma xenograft

Abstract

The radiosensitizing effect of misonidazole (Ro-07-0582) in acute and fractionated irradiation of a human osteosarcoma grown in the athymic mutant nude mouse was studied. A 60Co therapy unit was used for local irradiation of the tumors in non-anesthesized mice. Misonidazole in doses of 500 mg/kg bodyweight was administered to the mice by intraperitoneal injection 45 minutes before each exposure to radiation. Tumor regrowth delay was used as a measure of response. The enhancement ratio of misonidazole was found to be 1.45 for an acute dose of 12.50 Gy and 1.25 for four fractions of 3.75 Gy, delivered over four consecutive days. It is concluded that the present osteosarcoma xenograft reoxygenated inadequately during the three day period which elapsed from the first to the fourth fraction of 3.75 Gy.