INHIBITION OF VIRUS-ENCODED THYMIDINE KINASE SUPPRESSES HERPES-SIMPLEX VIRUS-REPLICATION IN-VITRO AND IN-VIVO

Both herpes simplex virus type 1 (HSV-1) and HSV-2 encode a thymidine kinase enzyme which differs from cellular thymidine kinase in substrat e specificity. Viral thymidine kinase enables the virus to replicate i n cells that lack cellular thymidine kinase, namely those of the senso ry neurons where the virus establishes, and periodically reactivates f rom, a latent state. Thymidine kinase-dependent HSV replication follow ing viral reactivation at the site of latency is thought to precede th e emergence of virus at mucosal surfaces. The ability to inhibit such an essential viral enzyme would potentially prevent HSV from replicati ng within neuronal tissue, and thus stop the recurrent disease cycle. Ro 32-2313 was designed as a selective and competitive inhibitor of HS V thymidine kinase and in vitro studies have confirmed this mechanism of action. In vivo evaluation of a soluble prodrug of Ro 32-2313, Ro 3 2-4397, was undertaken in murine models where pathogenesis was depende nt upon viral replication in neuronal tissue. It was shown that in viv o administration of Ro 32-4397 (i) significantly reduced the viral tit re detected in isolated dorsal root ganglia; (ii) prevented HSV-2-indu ced lethality in a systemic infection model; and (iii) reduced zosteri form lesion development in a model of dermal infection. Administration of Ro 32-4397 produced dose-related changes in viral pathogenicity to wards those of the phenotype of a thymidine kinase-deficient virus. Ov erall, the study confirmed that thymidine kinase inhibitors can suppre ss the replication of HSV in vivo, and suggest that such inhibitors ma y reduce reactivation of the virus from latency if used prophylactical ly in recurrent HSV infection.