Anti-Herpetic Activity of (±)-(1α,2β,3α)-9-[2-Hydroxy-3-(Hydroxymethyl)Cyclobutyl]Guanine and Inhibition of HSV-1 DNA Polymerase

Abstract

A novel nucleoside analogue, (±)-(1α, 2β, 3α)-9-[2-hydroxy -3-(hydroxymethyl)cyclobutyl]guanine [(±)-HHCG] was synthesized and has antiviral activity against herpes simplex virus (HSV) types 1 and 2, human cytomegalovirus (HCMV) and varicella-zoster virus (VZV) in plaque reduction assays. The antiviral activity of (±)-HHCG against HSV-2 shows a 10-40-fold dependence on the presence of a virally encoded thymidine kinase. (±)-HHCG is a substrate for HSV-1 thymidine kinase with a phosphorylation rate of 28 μm h⁻¹ compared to 15 μm h⁻¹ for acyclovir under identical conditions. Enzymatically prepared HHCG-triphosphate is a competitive inhibitor of dGTP incorporation into DNA by HSV-1 DNA polymerase with an inhibition constant corresponding to 0.0077 μm. Hybridization studies using an HSV-1-specific DNA probe indicated that DNA synthesis is reduced in HSV-1-infected WI-38 cells treated with (±)-HHCG, with an ED₅₀ comparable to that of acyclovir. These results suggest that the antiviral activity of (±)-HHCG is due to preferential inhibition of viral DNA synthesis.