The human cytomegalovirus alkaline nuclease UL98 as a novel antiviral target

Abstract

Human cytomegalovirus (HCMV, human herpesvirus 5) is an opportunistic pathogen with a worldwide seroprevalence ranging from 35% to >95%. It is a leading cause of congenital sequelae in neonates and severe life-threatening disease in immunocompromised patients. To date, a vaccine against HCMV is not available and the majority of the marketed anti-HCMV drugs target viral DNA amplification and packaging. However, the dose-limiting side effects of licensed antivirals and the emergence of drug resistance indicate a need for novel anti-HCMV therapeutic targets with new modes of action. One such target is the viral alkaline nuclease (AN), a DNase highly conserved among the Herpesviridae. Alpha- and gammaherpesvirus ANs are reported to have multiple functions and are important for viral replication. However, less is known about the betaherpesviral AN. In this study, I could show that similarly to its homologs, the DNase activity of HCMV AN UL98 and the complete UL98 protein is needed for efficient viral replication. The extremely limited viral replication and spreading of UL98 deletion HCMV mutant validated pUL98 as a new antiviral target. This study could also show that when treated with a pUL98 specific inhibitor, 7- bromo-5-oxo-1-sulfanylidene-n-[3 (trifluoromethyl)phenyl]-1h,4h,5h-[1,3]thiazolo[3,4- a]quinazoline-3-carboxamide (AD-51), the DNase activity of pUL98 is blocked (IC50=0.24 µM) and HCMV replication and spread are inhibited. The anti-HCMV efficacy of AD-51 is neither MOI-dependent nor strain-specific. AD-51 shows very similar inhibition efficacies on the replication of GCV, FOS, and LMV-resistant HCMVs compared to WT HCMV, suggesting AD-51 has a different mode of action. Moreover, AD-51 is also active against herpes simplex virus, Kaposi’s sarcoma-associated herpesvirus, and murine CMV, a mouse virus serving as a model for HCMV diseases, confirming that the thioxothiazolo[3,4-a]quinazoline derivative is a novel herpesvirus inhibitor targeting the viral AN.