Enzymology and pathogenicity in mice of a herpes simplex virus type 1 mutant resistant to 2'-fluoro-2'-deoxy-1-beta-D-arabinofuranosyl-5-iodocytosine

The deoxypyrimidine nucleoside analog 2'-fluoro-2'-deoxy-1-beta-D-arabinofuranosyl-5-iodocytosine (FIAC) is a potent and selective inhibitor of herpes simplex virus type 1 in vitro (C. Lopez, K. A. Watanabe, and J. J. Fox, Antimicrob. Agents Chemother. 17:803-806, 1980). Isopycnographic analysis demonstrated that 1 microM FIAC inhibited herpes simplex virus DNA replication by more than 95% but inhibited cellular DNA replication by only 32%. Mutant herpes simplex virus type 1 selected resistant to FIAC displayed linked resistance to other nucleoside analogs, including arabinosylthymine and acyclovir. Lysates derived from Vero cells infected with FIAC-resistant virus showed markedly lower levels of thymidine kinase activity and were unable to phosphorylate selectively arabinosylthymine or FIAC, in contrast to lysates from cells infected with wild-type herpes simplex virus type 1. Finally, drug-resistant virus displayed a 6,000-fold decrease in pathogenicity when inoculated intraperitoneally into genetically susceptible A/J mice. These results indicate that resistance to deoxypyrimidine nucleoside analogs is due, at least in part, to alterations in viral thymidine kinase and is accompanied by decreased pathogenicity in vivo.