Characterization of a thiourea derivative that targets viral transactivators of cytomegalovirus and herpes simplex virus type 1.

Although currently available antivirals against certain herpesviruses are effective, the development of resistance during long-term use has necessitated the search for seed compounds that work against novel target molecules. In this report, we identified a thiourea derivative compound, 147B3, that inhibits the infection of human cytomegalovirus (HCMV) in fibroblasts and herpes simplex virus type 1 (HSV-1) in Vero cells at a 50% effective concentration of 0.5 μM and 1.9 μM, respectively. Characterization of the compound provided the following clues regarding its mode of action. 1) Time-of-addition and block-release assays showed that 147B3 behaved similarly to ganciclovir. 2) 147B3 reduced the expression of early and late but not immediate-early gene products and the accumulation of viral genomic DNA in both HCMV-infected and HSV-1-infected cells. 3) 147B3 inhibited the HCMV IE2-dependent activation of viral early gene promoters. 4) Four HSV-1 clones resistant to 147B3 were isolated and next-generation sequencing analysis of their genome DNA revealed that all of them had a mutation(s) in the infected cell protein 4 (ICP4) gene, which encodes a viral transcriptional factor. 5) Although 147B3 did not reduce the amount of ICP4 in an immunoblotting analysis, it changed the localization of the ICP4 from the speckles in the nuclei to diffused dots in the cytoplasm. 6) 147B3 did not affect the localization of promyelocytic leukemia (PML) bodies. Our findings suggest that 147B3 targets viral transactivators, potentially through their interaction with factors required for the viral gene expression system.