Mode of action of phosphonoformate as an anti-herpes simplex virus agent

Phosphonoformate inhibited the replication of Herpes simplex virus (HSV) type 1 and type 2 in culture. The concentration required to inhibit the replication of both types of virus by 2 logs at 28 h post-infection was approximately 150 microM. It was more potent than phosphonoacetate against the growth of both virus types. A virus mutant which is resistant to phosphonoacetate was cross-resistant to phosphonoformate. Arsonoacetate, at 300 microM, had no antivirus activity. Phosphonoformate also inhibited HeLa and KB cell growth; at a concentration of about 500 microM, cell growth was inhibited by 50%. The anti-cell growth effects of the drug were completely reversible. The antivirus effect of phosphonoformate was partially reversible, depending on the time and duration of exposure of infected cultures to the drug. To obtain the maximum antivirus effect, phosphonoformate had to be added within the first 3 h post-virus-infection and be continuously present for at least 18 h. Phosphonoformate, added at 0 h post-infection, suppressed the induction of virus-specific DNA polymerase and DNAase activities. dTMP incorporation into DNA was preferentially inhibited in nuclei isolated from infected cells compared to uninfected cells, and the degree of inhibition varied with the ionic strength of the assay. Phosphonoformate was a potent inhibitor of the purified HSV-1 and HSV-2 DNA polymerases, inhibiting DNA polymerase activity by 50% at a concentration of 3 microM and ionic strength of 0.2.