1-beta-D-arabinofuranosyl-5-azacytosine (
ara-AC) and
5,6-dihydro-5-azacytidine (DHAC) are two new
antitumor agents under clinical investigations, which exhibit the chemical similarities found in the tumoricidal
drug cytosine arabinoside (
ara-C) and the
nitrogen substitution in the 5 position of the
pyrimidine ring found in
5-azacytidine (5-aza-C). The cellular anabolism of
ara-AC and DHAC and their effect on DNA methylation have been examined in two new human
leukemia cell lines, which are sensitive (PER-145) and resistant (PER-163) to
ara-C. The triphos-phate anabolite of
ara-AC, ara-
ACTP, was the major cellular anabolite in the cellular extracts of the PER-145 cells, reaching a cellular saturation concentration of 64.1 +/- 3.2 microM using 25 microM of the
drug. Only trace levels of ara-
ACTP were detected in the PER-163 cell line, which lacks
deoxycytidine kinase, after exposure to a similar concentration. Notably, after 1 mM, the ara-
ACTP concentration averaged 12 +/- 3 microM. DHAC was anabolized by both cell lines to a similar degree but required much higher
nucleoside concentrations (100 microM or higher) to achieve similar cellular concentrations of its
triphosphate, DHACTP. Although the deoxy-derivative, DHAdCTP, was detected in both cell lines, it was detected at 1-2 log10 lower concentrations than DHACTP. DNA methylation studies showed that DHAC had a profound effect in inducing
DNA hypomethylation in both cell lines, with nadir values of 27.3 and 29.2% of control.(ABSTRACT TRUNCATED AT 250 WORDS)