Mechanisms of inhibition of herpes simplex virus type 2 growth by 28-mer phosphorothioate oligodeoxycytidine

The 28-mer phosphorothioate oligodeoxycytidine (S-(dC)₂₈) has been reported previously to be a strong inhibitor of herpes simplex virus type 2 (HSV-2) DNA polymerase and HSV-2 growth in cell culture. In this study, the mechanism of action of S-(dC)₂₈ was studied. S-(dC)₂₈ was found to interfere with the adsorption of HSV-1 and HSV-2 to HeLa cells. HSV-2 infection, but not HSV-1, was found to potentiate the uptake of S-(dC)₂₈ into HeLa cells. The enhanced uptake reached a plateau at 6-9 h postinfection and appeared to be dose-dependent and saturable at concentrations higher than 1μM. The amount of S-(dC)₂₈ accumulated in HSV-2 infected cells was found to be 50 pmol/10⁶ cells at 6 h postinfection, whereas no significant drug accumulation was found in uninfected cells. S-(dC)₂₈ binding studies suggested that there are several types of tight binding sites associated with HSV-2 virions, which could play a role in the enhancement of S-(dC)₂₈ uptake. Subcellular distribution studies showed that intracellular S-(dC)₂₈ was associated with both nuclei and cytoplasm and remained intact. Mechanism studies suggested three different mechanisms which could be responsible for the anti-HSV-2 action of S-(dC)₂₈; (i) S-(dC)₂₈ could interfere with the uptake of HSV. (ii) HSV-2 infection enhances the uptake of S-(dC)₂₈ into cells (iii) S-(dC)₂₈ inhibits HSV-2 DNA synthesis, possibly, by inhibiting the viral DNA polymerase. The unique mechanisms of anti-HSV action of S-(dC)₂₈ suggest it could be a potential new agent in anti-HSV-2 chemotherapy.