A Quinoline Derivative HZ-6d Induces Antiviral Activity Against Hepatitis C Virus Via Apoptosis-Mediated Cytotoxicity

We previously demonstrated that interferon-stimulated gene 15 protein (ISG15) plays a role in enhancing hepatitis B virus (HBV) and hepatitis C virus (HCV) infections through the ISGylation of the HBV X protein (HBx) and the HCV NS5A protein. ISGylation is a post-translational modification where ISG15 is covalently attached to target proteins. These findings suggest that targeting ISGylation could be a potential therapeutic strategy for HBV and HCV infections. In this study, we evaluated the antiviral activity of HZ-6d, a quinoline derivative that inhibits HERC5-mediated ISGylation. Our results showed that HZ-6d did not inhibit HBx ISGylation and only modestly suppressed HBV replication in HBV-infected HepG2-NTCP cells and in HBV-replicating cells. Interestingly, HZ-6d also did not affect NS5A-ISGylation, however, it significantly suppressed HCV replication. These observations suggest that HZ-6d exerts its antiviral effects in HCV-replicating cells through mechanisms independent of HERC5-mediated NS5A-ISGylation. Furthermore, HZ-6d strongly activated the p53-mediated apoptosis signaling pathway, as evidenced by increased levels of phosphorylated p53, cleaved caspase-8, and cleaved caspase-3. Notably, activation of caspase-3 has been implicated in the proteolysis of HCV NS5A, indicating that apoptosis-related mechanisms may contribute to HCV suppression. Collectively, our findings suggest that HZ-6d induces antiviral activity against HCV through the p53-mediated apoptosis pathway, rather than by interfering with HERC5-mediated NS5A ISGylation.