The antiviral xanthate compound D609 inhibits herpes simplex virus type 1 replication and protein phosphorylation

The mechanism of antiviral action of tricyclodecan-9-yl-xanthogenate (D609) was investigated in vitro. D609 inhibited herpes simplex virus type 1 (HSV-1) replication without apparent cytotoxicity. It reduced phosphorylation of virus-infected cell polypeptides and inhibited the HSV-1 encoded protein kinase (US3 PK) and, to a lesser extent, cellular protein kinase C in vitro. Virus production was reduced by D609 at concentrations greater than 3.8 microM, with complete inhibition at 75.2 microM at an MOI of 1 PFU/cell or less. Addition of D609 could be delayed until 7 h post-infection and still inhibit virus replication. Phosphorylation of infected cell viral polypeptides of 34 (similar molecular weight to the substrate of the viral US3 protein kinase) and 69 kDa was inhibited at 18.4 microM. Treatment of infected or uninfected cells with 37.6 microM D609 reduced protein phosphorylation to background levels. A concentration of 1.9 microM D609 in vitro inhibited the viral US3-encoded PK, which had been purified from infected cell lysates by affinity chromatography and identified by specific antibody. Purified cellular protein kinase C was inhibited at 75.2 microM D609 whereas other cellular kinases including casein kinase 1 and cAMP dependent kinase were not inhibited at concentrations as high as 188 microM D609. Collectively these data indicate that the mechanism of antiviral action of D609 is by inhibition of protein kinases and protein phosphorylation affecting a late step in HSV replication.