The effect of caffeine on X-ray-induced mitotic delay in normal human and ataxia-telangiectasia fibroblasts.

We previously showed that radiation-sensitive fibroblasts from ataxia-telangiectasia (A-T) patients sustain less G2 delay after X-irradiation than normal fibroblasts (Scott and Zampetti-Bosseler, 1982). Caffeine is known to reduce the amount of X-ray-induced delay in various mammalian cell types. Painter and Young (1980) proposed that A-T cells have an altered chromatin structure, similar to that of caffeine-treated normal cells and that this results in a failure of A-T cells to delay their progression through the cell cycle to allow time for DNA repair. We now show that caffeine treatment after X-irradiation reduces G2 delay in both A-T and normal cells. We confirm the results previously obtained on lymphocytes that caffeine potentiates the chromosome-damaging effects of X-rays in both A-T and normal fibroblasts. These and other data suggest that the radiation responses of A-T cells and of caffeine-treated normal cells are caused by different mechanisms.