Journal
ANTIVIRAL RESEARCH
Volume 85, Issue 3, Pages 470-481Publisher
ELSEVIER
DOI: 10.1016/j.antiviral.2009.10.020
Keywords
Antiviral drugs; siRNA; Nucleoside/nucleotide derivatives; Metabolism and activation; Uridine-cytidine kinase; Deoxycytidine kinase
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Nucleoside analogs are effective inhibitors of the hepatitis C virus (HCV) in the clinical setting. One such molecule, 2'-C-methyl-cytidine (2'-MeC), entered clinical development as NM283, a valine ester prodrug form of 2'-MeC possessing improved oral bioavailability. To be active against HCV, 2'-MeC must be converted to 2'-MeC triphosphate which inhibits NS5B, the HCV RNA-dependent RNA polymerase. Conversion of 2'-MeC to 2'-MeC monophosphate is the first step in 2'-MeC triphosphate production and is thought to be the rate-limiting step. Here we investigate which of three possible enzymes, deoxycytidine kinase (dCK), uridine-cytidine kinase 1 (UCK1), or uridine-cytidine kinase 2 (UCK2), mediate this first phosphorylation step. Purified recombinant enzymes UCK2 and dCK, but not UCK1, could phosphorylate 2'-MeC in vitro. However, siRNA knockdown experiments in three human cell lines (HeLa, Huh7 and HepG2) defined UCK2 and not dCK as the key kinase for the formation of 2'-MeC monophosphate in cultured human cells. These results underscore the importance of confirming enzymatic kinase data with appropriate cell-based assays. Finally, we present data suggesting that inefficient phosphorylation by UCK2 likely limits the antiviral activity of 2'-MeC against HCV. This paves the way for the use of a nucleotide prodrug approach to overcome this limitation. (C) 2009 Elsevier B.V. All rights reserved.
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