Viruses utilize host factors for their efficient proliferation. By evaluating the inhibitory effects of compounds in our library, we identified inhibitors of cyclophilin A (CypA), a known immunosuppressor with peptidyl-prolyl cis-trans isomerase activity, can significantly attenuate EV71 proliferation. We demonstrated that CypA played an essential role in EV71 entry and that the RNA interference-mediated reduction of endogenous CypA expression led to decreased EV71 multiplication. We further revealed that CypA directly interacted with and modified the conformation of H-I loop of the VP1 protein in EV71 capsid, and thus regulated the uncoating process of EV71 entry step in a pH-dependent manner. Our results aid in the understanding of how host factors influence EV71 life cycle and provide new potential targets for developing antiviral agents against EV71 infection.

f Enterovirus 71 (EV71) (Picornaviridae family) and hepatitis C virus (HCV) (Flaviviridae family) are the causative agents of human hand, foot, and mouth disease (HFMD) and hepatitis C, resulting in a severe pandemic involving millions of infections in the Asia-Pacific region and worldwide. The great impact of EV71 and HCV on public health highlights the need to further our understanding of the biology of these two viruses and develop effective therapeutic antivirals. Here, we evaluated a total of 32 lycorine derivatives and demonstrated that 1-acetyllycorine suppressed the proliferation of multiple strains of EV71 in various cells. The results of the drug resistance analysis revealed that 1-acetyllycorine targeted a phenylalanine (F76) in EV71 2A protease (2A pro ) to stabilize the conformation of a unique zinc finger. Most interestingly, the zinc binding site in EV71 2A pro is the exclusive homolog of HCV NS3 among all viruses. Further analysis revealed that 1-acetyllycorine also inhibits HCV with high efficacy, and the mutation on R118 in HCV NS3, which corresponds to F76 in EV71 2A pro , confers the resistance of HCV to 1-acetyllycorine. These results revealed a conserved mechanism of 1-acetyllycorine against EV71 and HCV through targeting viral proteases. We also documented the significant synergistic anti-EV71 and anti-HCV effects of 1-acetyllycorine with reported inhibitors, supporting potential combination therapy for the treatment of EV71 and HCV infections. E nterovirus 71 (EV71) is one of the major etiological agents of human hand, foot, and mouth disease (HFMD) in the AsiaPacific region. Particularly, young children and immunodeficient populations are more susceptible to EV71 infection. EV71 infection results in severe aseptic meningitis, encephalitis, myocarditis, acute flaccid paralysis, and pulmonary edema, which lead to high fatality rates (1, 2). Chronic infection with hepatitis C virus (HCV) affects 180 million people worldwide, and 350,000 people die each year due to HCV-related complications (3). Hepatitis C not only affects the liver function but also induces liver fibrosis and cirrhosis, eventually leading to liver cancer (4).Both EV71 and HCV are positive-sense single-stranded RNA (ϩssRNA) viruses. EV71 is a member of the Enterovirus genus within the Picornaviridae family (5-7). The genome of EV71 encodes a polyprotein that is cleaved through viral proteases to generate four structural proteins (VP1 to VP4) required for viral capsid formation and seven nonstructural proteins (2A pro , 2B, 2C, 3A, 3B, 3C pro , and 3D pol ) for viral replication (8-10). HCV is a member of the Hepacivirus genus in the Flaviviridae family. The translated polyprotein of HCV is further processed into the structural proteins, including core protein and envelope glycoproteins E1 and E2; the nonstructural proteins are processed into NS2, NS3, NS4A, NS4B, NS5A, and NS5B (11).The successful replication of most viruses depends on the correct proteolytic processing of polyproteins. EV71 employs two viral proteases: 2A ...

The NS5B polymerase is one of the most attractive targets for developing new drugs to block Hepatitis C virus (HCV) infection. We describe the discovery of novel potent HCV NS5B polymerase inhibitors by employing a virtual screening (VS) approach, which is based on random forest (RB-VS), e-pharmacophore (PB-VS), and docking (DB-VS) methods. In the RB-VS stage, after feature selection, a model with 16 descriptors was used. In the PB-VS stage, six energy-based pharmacophore (e-pharmacophore) models from different crystal structures of the NS5B polymerase with ligands binding at the palm I, thumb I and thumb II regions were used. In the DB-VS stage, the Glide SP and XP docking protocols with default parameters were employed. In the virtual screening approach, the RB-VS, PB-VS and DB-VS methods were applied in increasing order of complexity to screen the InterBioScreen database. From the final hits, we selected 5 compounds for further anti-HCV activity and cellular cytotoxicity assay. All 5 compounds were found to inhibit NS5B polymerase with IC50 values of 2.01–23.84 μM and displayed anti-HCV activities with EC50 values ranging from 1.61 to 21.88 μM, and all compounds displayed no cellular cytotoxicity (CC50 > 100 μM) except compound N2, which displayed weak cytotoxicity with a CC50 value of 51.3 μM. The hit compound N2 had the best antiviral activity against HCV, with a selective index of 32.1. The 5 hit compounds with new scaffolds could potentially serve as NS5B polymerase inhibitors through further optimization and development.