RT Journal Article SR Electronic T1 Inhibition of ribonucleotide reduction in CCRF-CEM cells by 2',2'-difluorodeoxycytidine. JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 567 OP 572 VO 38 IS 4 A1 V Heinemann A1 Y Z Xu A1 S Chubb A1 A Sen A1 L W Hertel A1 G B Grindey A1 W Plunkett YR 1990 UL http://molpharm.aspetjournals.org/content/38/4/567.abstract AB The new deoxycytidine analogue 2',2'-difluorodeoxycytidine (dFdC) is a specific inhibitor of DNA synthesis that has marked cytotoxicity and therapeutic activity. A 2-hr incubation with 0.1-10 microM dFdC decreased cellular viability 78-97%. This treatment reduced deoxynucleoside triphosphate pools, similar to the action of the ribonucleotide reductase inhibitor hydroxyurea. The most pronounced decrease occurred in the dCTP pool, quantitatively followed by the decrease of dATP, dGTP, and dTTP. In contrast, inhibition of DNA synthesis by arabinosylcytosine did not affect the dCTP level, whereas dATP, dGTP, and dTTP pools increased, but less than 2-fold. The incorporation of [5-3H]cytidine into the dCTP pool, a measure of ribonucleotide reductase activity in whole cells, was reduced to 3% of controls by 0.1 microM dFdC, but to only 40% by 0.1 microM ara-C. Each drug decreased incorporation of [5-3H]cytidine into DNA to a similar extent (greater than 94%), suggesting limitation by a reaction proximal to this step. The cellular concentration of dFdC 5'-diphosphate was 0.3 microM at 50% inhibition of the in situ activity of ribonucleotide reductase. Direct assays of partially purified ribonucleoside diphosphate reductase (EC 1.17.4.1) demonstrated 50% inhibition by 4 microM dFdC 5'-diphosphate; dFdC 5'-triphosphate was much less inhibitory. We conclude that dFdC 5'-diphosphate acts as an inhibitor of ribonucleoside diphosphate reductase.