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Antimicrobial Agents and Chemotherapy, June 2008, p. 1901-1911, Vol. 52, No. 6
0066-4804/08/$08.00+0     doi:10.1128/AAC.01496-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Effects of Mutagenic and Chain-Terminating Nucleotide Analogs on Enzymes Isolated from Hepatitis C Virus Strains of Various Genotypes{triangledown}

Julie A. Heck, Angela M. I. Lam,{dagger} Nirupama Narayanan, and David N. Frick*

Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, New York 10595

Received 17 November 2007/ Returned for modification 16 January 2008/ Accepted 25 March 2008

The development of effective therapies for hepatitis C virus (HCV) must take into account genetic variation among HCV strains. Response rates to interferon-based treatments, including the current preferred treatment of pegylated alpha interferon administered with ribavirin, are genotype specific. Of the numerous HCV inhibitors currently in development as antiviral drugs, nucleoside analogs that target the conserved NS5B active site seem to be quite effective against diverse HCV strains. To test this hypothesis, we examined the effects of a panel of nucleotide analogs, including ribavirin triphosphate (RTP) and several chain-terminating nucleoside triphosphates, on the activities of purified HCV NS5B polymerases derived from genotype 1a, 1b, and 2a strains. Unlike the genotype-specific effects on NS5B activity reported previously for nonnucleoside inhibitors (F. Pauwels, W. Mostmans, L. M. Quirynen, L. van der Helm, C. W. Boutton, A. S. Rueff, E. Cleiren, P. Raboisson, D. Surleraux, O. Nyanguile, and K. A. Simmen, J. Virol. 81:6909-6919, 2007), only minor differences in inhibition were observed among the various genotypes; thus, nucleoside analogs that are current drug candidates may be more promising for treatment of a broader variety of HCV strains. We also examined the effects of RTP on the HCV NS3 helicase/ATPase. As with the polymerase, only minor differences were observed among 1a-, 1b-, and 2a-derived enzymes. RTP did not inhibit the rate of NS3 helicase-catalyzed DNA unwinding but served instead as a substrate to fuel unwinding. NS3 added to RNA synthesis reactions relieved inhibition of the polymerase by RTP, presumably due to RTP hydrolysis. These results suggest that NS3 can limit the incorporation of ribavirin into viral RNA, thus reducing its inhibitory or mutagenic effects.

* Corresponding author. Mailing address: Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, NY 10595. Phone: (914) 594-4190. Fax: (914) 594-4058. E-mail: David_Frick{at}NYMC.edu

{triangledown} Published ahead of print on 7 April 2008.

{dagger} Present address: XTL Biopharmaceutical Inc., 711 Executive Blvd., Suite Q, Valley Cottage, NY 10989.

Antimicrobial Agents and Chemotherapy, June 2008, p. 1901-1911, Vol. 52, No. 6
0066-4804/08/$08.00+0     doi:10.1128/AAC.01496-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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