PROTECTIVE EFFECT OF ADENINE ON DNA-SYNTHESIS IN IRRADIATED EHRLICH ASCITES TUMOR-CELLS

Ehrlich ascites tumor cells were cultured in the presence of adenine f or several hours before gamma irradiation. The inhibition of DNA synth esis that is normally observed when these cells are irradiated was pre vented. More detailed analysis using the velocity sedimentation techni que provided evidence that this protective effect occurred at the leve l of initiation of DNA replication. This conclusion is supported by th e fact that adenine failed to prevent the inhibition of DNA synthesis induced by hydroxyurea. The ability of adenine to suppress the gamma-r ay-induced inhibition of DNA synthesis was dependent on both its conce ntration and the exposure time. This suppression was already pronounce d by about 4 h after exposure of the cells to adenine, and the maximum effect was observed within 6-20 h. The optimum concentration of adeni ne was about 0.1 mM. Among other purines tested, a similar effect was caused only by guanine. (C) 1997 by Radiation Research Society.