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Antimicrobial Agents and Chemotherapy, May 2007, p. 1795-1803, Vol. 51, No. 5
0066-4804/07/$08.00+0     doi:10.1128/AAC.01447-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Selective Phosphorylation of Antiviral Drugs by Vaccinia Virus Thymidine Kinase

Mark N. Prichard,^1* Kathy A. Keith,¹ Mary P. Johnson,¹ Emma A. Harden,¹ Alexis McBrayer,¹ Ming Luo,² Shihong Qiu,² Debasish Chattopadhyay,² Xuesen Fan,³ Paul F. Torrence,³ and Earl R. Kern¹

Departments of Pediatrics,¹ Microbiology, University of Alabama School of Medicine, Birmingham, Alabama 35233,² Department of Chemistry and Biochemistry, Northern Arizona University, Flagstaff, Arizona 86011³

Received 17 November 2006/ Returned for modification 5 January 2007/ Accepted 19 February 2007

The antiviral activity of a new series of thymidine analogs was determined against vaccinia virus (VV), cowpox virus (CV), herpes simplex virus, and varicella-zoster virus. Several compounds were identified that had good activity against each of the viruses, including a set of novel 5-substituted deoxyuridine analogs. To investigate the possibility that these drugs might be phosphorylated preferentially by the viral thymidine kinase (TK) homologs, the antiviral activities of these compounds were also assessed using TK-deficient strains of some of these viruses. Some of these compounds were shown to be much less effective in the absence of a functional TK gene in CV, which was unexpected given the high degree of amino acid identity between this enzyme and its cellular homolog. This unanticipated result suggested that the CV TK was important in the mechanism of action of these compounds and also that it might phosphorylate a wider variety of substrates than other type II enzymes. To confirm these data, we expressed the VV TK and human TK1 in bacteria and isolated the purified enzymes. Enzymatic assays demonstrated that the viral TK could efficiently phosphorylate many of these compounds, whereas most of the compounds were very poor substrates for the cellular kinase, TK1. Thus, the specific phosphorylation of these compounds by the viral kinase may be sufficient to explain the TK dependence. This unexpected result suggests that selective phosphorylation by the viral kinase may be a promising new approach in the discovery of highly selective inhibitors of orthopoxvirus replication.

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* Corresponding author. Mailing address: 128 Children's Harbor Building, 1600 6th Ave. South, Birmingham, AL 35233. Phone: (205) 975-1995. Fax: (205) 975-1992. E-mail: mprichard{at}peds.uab.edu

Published ahead of print on 26 February 2007.

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Antimicrobial Agents and Chemotherapy, May 2007, p. 1795-1803, Vol. 51, No. 5
0066-4804/07/$08.00+0     doi:10.1128/AAC.01447-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

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