Combined Effect of Radiation and YM-881 (Smancs) on Murine Tumors and Bone Marrow

Abstract

The combined effect of radiation and YM-881 (SMANCS) was studied in vitro and in vivo. When 0.25 μg/ml of YM-881 was simultaneously combined with radiation, during and after irradiation for 30 min in total, D_q decreased from 3.3 Gy to 1.4 Gy without changing D_o in the dose-survival curve of exponentially growing SCC VII tumor cells. Five or ten times administrations of 0.1 mg/kg YM-881 at an interval of 24 h did not inhibit tumor growth. However, administration of 0.1 mg/kg YM-881 just before every irradiation which was repeated five times at an interval of 24 h yielded dose modifying factors (DMFs) of 1.8–1.2 when the tumor response to treatment was evaluated by the time for the tumors to regrow to three times the original volume. Administration of YM-881 ten times just before every irradiation yielded DMFs of 1.3–1.2. Adverse effects of the combination on bone marrow were examined by spleen colony assay. After five injections of 0.1 mg/kg YM-881, the mean number of CFU-S per femur decreased to 77% of the pretreatment level, but this was not significant statistically (0.1 > p > 0.05). The slope of radiation response curve for CFU-S per femur was not affected by the combination.