DNA Synthesis and Cell Survival after X-irradiation of Mammalian Cells Treated with Caffeine or Adenine

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Abstract
The expression of the transient depression in the rate of DNA synthesis normally observed after exposure of randomly-dividing Chinese hamster V-79 [lung fibroblast] or Chinese hamster CHO [ovary] cells to ionizing radiation was postponed or diminished by a post-irradiation treatment with 1.0-2.0 mM adenine or 1.5 mM caffeine. Caffeine may exert its effect by creating additional sites for replication in irradiated cells. Cells treated with caffeine or adenine for 2 or 4 h after exposure to 3000 rad of 300 kVp [kilovolt peak] X-rays exhibit depressed synthesis only after the removal of caffeine or adenine. These alterations in the timing of the X-ray-induced depression of the rate of DNA synthesis had no effect on X-ray-induced cell killing. Although a 4 h post-irradiation treatment of randomly-dividing Chinese hamster V-79 cells with 1.0 or 2.0 mM caffeine potentiates X-ray-induced cell killing, this reduction in survival was due primarily to effects on cells not in S-phase.