Inhibition of HSV-1 replication and reactivation by the mutation-insensitive transcription inhibitor tetra-O-glycyl-nordihydroguaiaretic acid.

Methylated derivatives of nordihydroguaiaretic acid (NDGA)were previously shown to be potent mutation-resistant inhibitors of herpes simplex virus type 1 (HSV-1) which target Sp1 protein binding to critical viral promoters. The hydrophobic nature of these agents, however, renders them relatively water-insoluble and, therefore, limits their applicability. We report here on the anti-HSV-1 properties of a related but water-soluble glycylated derivative of NDGA, tetra-O-glycyl-NDGA (G(4)N). In yield reduction assays, G(4)N inhibited replication of laboratory and clinical strains of wild type HSV-1 and ACV-resistant (HSV-1(R)) strains of HSV-1 in a dose-dependent manner, with average IC(50) values of 4.7 and 3.2 microM against wild-type and HSV-1(R) strains, respectively. An MTT-based cytotoxicity assay revealed a TC(50) value of 73.2 microM for G(4)N on Vero cells, with no reduction in viability detected at concentrations below 30 microM. Similar to its methylated counterparts, G(4)N was found to inhibit transcription of the HSV-1 ICP4 gene, a major immediate early viral regulator, and gel mobility shift assays showed it can block Sp1 protein binding to cognate sites on the ICP4 promoter. In anticipation of its potential use as a systemic anti-HSV-1 agent, we tested G(4)N in a murine trigeminal ganglia (TG) explant model system, and found G(4)N was able to prevent HSV-1 reactivation from explanted and cultured latently infected TG.