Effect of inhibition of DNA synthesis on recovery of X-irradiated L5178Y-S cells, II. 9-beta-D-arabinofuranosyladenine.

The effects of 9-beta-D-arabinofuranosyladenine (araA) on radiosensitivity, postirradiation changes in the cell cycle distribution and DNA synthesis in mouse L5178Y-S lymphoma cells are described. Increase in the araA concentration (from 25 to 200 mumol/l) was is correlated with reduction in clonogenic survival except in the low concentration range. where resistance was observed. AraA treatment (200 mumol/l for 2 h) temporarily inhibited progression through the G1/S boundary. AraA (200 mumol/l applied immediately after X-irradiation (1 Gy) for 2 h gave a radiosensitizing effect with only slight changes in postirradiation cell cycle distribution; at higher doses (4 and 6 Gy) the effect was less pronounced. AraA slowed down progression through the cell cycle after irradiation and enhances the lethal effect of radiation. The phenomenon was dependent on the time between irradiation and araA treatment. The differences in dose-related radiosensitization created araA + X-ray survival curves with extrapolation numbers lower than 1. This may reflect the existence of relatively radioresistant and radiosensitive subpopulations in the araA-treated population.