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Phosphonoacetate was an effective inhibitor of both the Marek's disease herpesvirus- and the herpesvirus of turkey-induced DNA polymerase. Using the herpesvirus of turkey-induced DNA polymerase, phosphonoacetate inhibition studies for the DNA polymerization reaction and for the deoxyribonucleoside triphosphate-pyrophosphate exchange reaction were carried out. The results demonstrated that phosphonoacetate inhibited the polymerase by interacting with it at the pyrophosphate binding site to create an alternate reaction pathway. A detailed mechanism and rate equation for the inhibition were developed. For comparison to phosphonoacetate, pyrophosphate inhibition patterns and apparent inhibition constants were determined. Twelve analogues of phosphonoacetate were tested as inhibitors of the herpesvirus of turkey-induced DNA polymerase. At the concentrations tested, only one, 2-phosphonopropionate, was an inhibitor. The apparent inhibition constant for it was about 50 times greater than the corresponding apparent inhibition constant for phosphonoacetate. DNA polymerase alpha of duck embryo fibroblasts, the host cell for the herpesviruses, was inhibited by phosphonoacetate. The apparent inhibition constants for the alpha polymerase were about 10-20 times greater than the corresponding inhibition constants for the herpesvirus-induced DNA polymerase. Duck DNA polymerase beta, Escherichia coli DNA polymerase I, and avian myeloblastosis virus reverse transcriptase were not inhibited by phosphonoacetate.

Phosphonoformate was found to be an inhibitor of the deoxyribonucleic acid polymerase induced by the herpesvirus of turkeys. The apparent inhibition constants were 1 to 3 ,uM. Phosphonoformate was also able to block the replication in cell culture of Marek's disease herpesvirus, the herpesvirus of turkeys, and herpes simplex virus. It was as effective as phosphonoacetate. Phosphonoformate was not an effective inhibitor of a phosphonoacetate-resistant mutant of the herpesvirus of turkeys nor of its induced deoxyribonucleic acid polymerase.Phosphonoacetate is an effective inhibitor of the replication of herpesviruses (11,13,23,25). The inhibition of herpesvirus replication is through an effect on the viral-induced deoxyribonucleic acid (DNA) polymerase (9,(14)(15)(16)18). In animal model studies, the efficacy of phosphonoacetate as an antiherpesvirus drug has been clearly demonstrated (7,8,12). Its clinical use, however, may be limited because it is somewhat toxic to test animals and because it is accumulated in bone (4).Other phosphonate compounds are of interest as inhibitors of herpesvirus replication because they might exhibit an improved therapeutic ratio over phosphonoacetate either by being more effective inhibitors of virus replication or by being less toxic to animals. These compounds are also of interest at the enzymological level for the information that they might provide about the binding site on the herpesvirus-induced DNA polymerase. Consequently, using as an assay procedure the ability to inhibit the herpesvirus-induced DNA polymerase or the ability to block herpesvirus replication in cell culture or in animals, many other phosphonates have been looked at (10,13,14,23

No abstract

Phosphonoformate (PF) at a concentration of 5 to 10 μg/ml inhibited the growth of type 1 strains of herpes simplex virus (HSV) in tissue culture, whereas 20 to 30 μg/ml was required for inhibition of type 2 strains and about 50 μg/ml was required for murine cytomegalovirus. In mice inoculated intraperitoneally or intracerebrally with HSV or intraperitoneally with murine cytomegalovirus, treatment with 250 to 400 mg of PF per kg twice daily for 5 days had only minimal effectiveness. When mice were inoculated intravaginally (i.vg.) with HSV type 2 and treated i.vg. with 10% PF beginning 3 h after viral inoculation, treatment was effective in completely inhibiting viral replication in the genital tract. If i.vg. therapy was initiated 24 h after infection, when the mice had a mean virus titer of 10 5 plaque-forming units in vaginal secretions, a significant reduction in the mean virus titer was observed on days 3, 5, and 7 after infection as compared with control animals. In guinea pigs treated i.vg. with 10% PF beginning 6 h after i.vg. inoculation with HSV type 2 there was also complete inhibition of viral replication in the genital tract, and no extenal lesions developed. When therapy was initiated 24 h after infection there was a 4 to 5-log decrease in viral titers on days 3, 5, and 7 of the infection and a slight delay in the development of external lesions.