The conditioning effect of rk-28 in a combined treatment with irradiation against v-79 cells

The conditioning effect of RK-28, one of the nitroimidazole nucleoside analogues, in a combined treatment with irradiation against aerobic V-79 cells in an exponentially-growing phase was investigated. The growth rate of the V-79 cells in 5% DMEM was not different from that in the medium containing 0.2 mM RK-28. The growth of V-79 cells treated with 6 Gy-irradiation in the medium containing 0.2 mM RK-28 showed a statistically more significant inhibition than that with a single modality treatment of irradiation. The number (3.3x10(3) cells/dish at 24 h after irradiation) of cells incubated for 24 straight hours in the medium containing RK-28 was significantly lower than that (9.5x10(3) cells/dish at 24 h after irradiation) of the cells which were placed into a fresh medium immediately after irradiation. Moreover, the number of the cells, in which the medium was changed to a conditioned medium containing 0.2 mM RK-28 immediately after irradiation with the same dose of RK-28, was 2.1x10(3) cells/dish at 24 h after irradiation, and thereafter did not increase. These results indicated that RK-28 induced growth inhibition factors from exponentially-growing V-79 cells in an aerobic state, due to the combined treatment with irradiation.