Effects of Cytidine 5’0Triphosphate

ABSTRACT. Deoxycytidine kinase (dCK) and deoxycytidine deaminase (dCDA) are two key enzymes in the activation and inactivation, respectively, of deoxycytidine and its antiviral and anticancer analogues. One purpose of this study was to determine whether or not the deoxycytidine-converting activity of both enzymes would correlate with growth inhibition by 2’,2’-difluorodeoxycytidine (dFdC), a deoxycytidine analogue with established antitumour activity in solid tumours. Another aim of this work was to determine the effects of normal nucleotides on dCK. dCK and dCDA activities were measured with both deoxycytidine and dFdC as substrates in 5 solid tumour cell lines, but no correlation with cellular sensitivity to dFdC was found with either substrate. The normal dCK activities with deoxycytidine as substrate varied between 0.8 and 13 nmol/hr/lOh cells. The activities determined with dFdC as substrate were remarkably similar in all 5 cell lines (1.1-1.6 nmol/hr/106 cells). dCDA activities varied considerably with both substrates (20-30-fold). Because dFdC markedly affected intracellular concentrations of cytidine 5’-triphosphate (CTP) and uridine 5’-triphosphate (UTP), we studied their effects on deoxycytidine- and dFdC-phosphorylating activities in 3 cell lines (i.e., A2780, WiDr and C26-10) with a similar dCK activity but major differences in dFdC sensitivity. 1 mM CTP inhibited deoxy-cytidine phosphorylation (at 230 p,M) by 20-30 % in A2780 and C26-10 cells, but increased that of WiDr cells by approximately 70%. CTP did not affect dFdC phosphorylation (at 230 p,M) in A2780 cells, but did increas