Inhibitors of bovine herpes mammillitis virus infections in cultured cells and in vaginally infected guinea pigs

Abstract

Bovine herpes mammillitis virus or bovine herpesvirus type 2 (BHV-2) causes ulcerative lesions on the teats and udders of infected cows. The authors investigated several nucleoside and nucleotide analogues as potential BHV-2 inhibitors. These included acyclovir, ganciclovir, 5-iodo-2′-deoxyuridine (IUdR), 1-(2-deoxy-2′-fluoro-β-D-arabinofuranosyl) derivatives of 5-iodocytosine (FIAC), 5-iodouracil (FIAU), and 5-methyluracil (FMAU), and various 3-hydroxyphospho-nylmethoxypropyl (HPMP) and 2-phosphonylme-thoxyethyl (PME) derivatives of adenine (A), guanine (G), 2,6-diaminopurine (DAP), and/or cytosine (C). Of these, FIAU and FMAU were the most potent in cell culture, inhibiting 50% of BHV-2 plaques at >0.05 μm. HPMPA and HPMPG were active at 0.3 μm; FIAC, IUdR, and HPMPC at 1.3-2.3 μm; PMEDAP and ganciclovir at 20-25 μm; acyclovir and PMEA at >100 μm. The two most potent agents, FIAU and FMAU, inhibited uninfected embryonic bovine tracheal cell growth by 50% at > 100 μm and 53 μm, respectively, resulting in selectivity indices (ratio of the 50% inhibitory concentration for cell growth to the 50% inhibitory concentration for plaque formation) of >2200 and 1100. Greater degrees of antiviral activity and selectivity were obtained in infected guinea pig embryo cells treated with FIAU, FMAU, and HPMPC. Infected cell extracts containing BHV-2-induced thymidine kinase activity phosphorylated FIAU, FMAU, and lUdR at nearly the same rate as thymidine, whereas FIAC, acyclovir, and ganciclovir were phosphorylated at ≤5% the rate of thymidine. Phosphorylation by this enzyme is required to generate the antivirally active nucleoside triphosphate in infected cells. In guinea pigs infected intravaginally with BHV-2, FMAU treatments of 1, 3.2, and 10 mg kg−1 per day for 5 days starting 1 day after virus challenge reduced vaginal lesion scores and virus titres in a dose-dependent manner. FIAU (10 μm) was as effective as 1 μm FMAU by the same regimen. A single treatment with 10 μm HPMPC was as active as daily treatments with 3.2 mg FMAU kg−1. These results indicate the potential of using antiviral agents to treat bovine herpes mammillitis virus infections in cattle, and the application of guinea pigs to study BHV-2 disease.