Hepatitis C virus RNA-dependent RNA polymerase (NS5B) as a mediator of theantiviral activity of ribavirin

Ribavirin is administered in combination with interferon-a for treatment of hepatitis C virus (HCV) infection. Recently, we demonstrated that the anti viral activity of ribavirin can result from the ability of a viral RNA poly merase to utilize ribavirin triphosphate and to incorporate this nucleotide with reduced specificity, thereby mutagenizing the genome and decreasing t he yield of infectious virus (Crotty, S., Maag, D., Arnold, J. J., Zhong, W ., Lau, J. Y., Hong, Z., Andino, R., and Cameron, C. E. (2000) Nat. Med. 6, 1375-1379). In this study, we performed a quantitative analysis of a novel HCV RNA polymerase derivative that is capable of utilizing stably annealed primer-template substrates and exploited this derivative to evaluate wheth er lethal mutagenesis of the HCV genome is a possible mechanism for the ant i-HCV activity of ribavirin. These studies demonstrate HCV RNA polymerase-c atalyzed incorporation of ribavirin opposite cytidine and uridine. In addit ion, we demonstrate that templates containing ribavirin support CMP and UMP incorporation with equivalent efficiency. Surprisingly, templates containi ng ribavirin can also cause a significant block to RNA elongation. Together , these data suggest that ribavirin can exert a direct effect on HCV replic ation, which is mediated by the HCV RNA polymerase. We discuss the implicat ions of this work on the development of nucleoside analogs for treatment of HCV infection.