Suppression of nuclear ADP-ribosyltransferase activity in Ehrlich ascites tumor cells by 5-azacytidine and its analogs.

The exposure of freshly isolated, activity growing Ehrlich ascites tumor cells to the antileukemic agent 5-azacytidine and its analogs, 5-azacytosine (but not 6-azacytosine), 5-aza-2'-deoxycytidine and, in particular, 5-fluorocytidine in the serum-free medium caused a time- and dose-dependent suppression of the nuclear ADP-ribosyltransferase activity. The azacytidine suppression was apparently dependent on the cellular activity of DNA synthesis but not related to the nuclear activity of DNA methylation, indicating the 5-azacytidine incorporation into DNA, but not drug-induced hypomethylation of DNA, being responsible for the 5-azacytidine-suppression of chromatin-bound ADP-ribosyltransferase.