Characterization of inhibitory action of concanamycins against herpes simplex virus

Concanamycins A (Conmy A) and B (Conmy 13), well-known inhibitors of the vacuolar proton-ATPase, were isolated from the culture broth of Streptomyces sp. strain FK51 as antiherpetic agents. These compounds showed potent inhibition of herpes simplex virus type 1 (HSV-1) replication in an in vitro assay system, having antiviral activities with 50% inhibitory concentrations of 0.072 and 0.51 ng/ml for Conmy A and Conmy B, respectively. While the attachment of HSV-1 to Vero cells was not inhibited, both of the compounds blocked the penetration of virus into host cells. When added to the late stages of virus replication, the concanamycins also exerted marked inhibitory effects on the production of viruses. Release of progeny viruses was found to be suppressed by the agents. SDS-PAGE analysis of isotope-labelled HSV-specific proteins revealed that the synthesis of beta proteins was moderately inhibited and some of the glycoproteins were synthesized with reduced molecular weights. Western blot analysis using antibodies against two HSV-specific glycoproteins (gC and gD) showed differences in their syntheses between untreated and Conmy A-treated cells. Syncytium formation by HSV-1 strain HF was inhibited, and small plaques with rounded cells were formed in Conmy A-treated cell cultures. When wild-type HSV-1 was serially propagated under the selective pressure of Conmy A, and the resulting progeny viruses were grown in drug-free medium, their plaque morphology of syncytium and sensitivity to Conmy A were the same as those of parent virus. From these findings, antiherpetic activities of Conmy A and B might be mainly dependent on their activities as vacuolar proton-ATPase inhibitors with intracellular translocation of glycoproteins and the inhibition of the maturation of virus glycoproteins.