title: The cyclophilin inhibitor SCY-635 disrupts hepatitis C virus NS5A-cyclophilin A complexes.
abstract: The nonimmunosuppressive cyclophilin (Cyp) inhibitor SCY-635 blocks hepatitis C virus (HCV) replication both in vitro and in vivo and represents a novel potent anti-HCV agent. However, its mechanism of action remains to be fully elucidated. A growing body of evidence suggests that cyclophilin A (CypA) is absolutely necessary for HCV replication and that the HCV nonstructural 5A (NS5A) protein serves as a main viral ligand for CypA. In this study, we examined the effect of SCY-635 on HCV replication. Specifically, we asked whether SCY-635 blocks HCV replication by targeting CypA-NS5A interactions. We also investigated the possibility that HCV can escape SCY-635 selection pressure and whether this resistance influences either CypA-NS5A interactions or the dependence of HCV on CypA. We found not only that SCY-635 efficiently inhibits HCV replication, but it is sufficient alone to clear HCV replicon-containing cells. We found that SCY-635 prevents CypA-NS5A interactions in a dose-dependent manner. SCY-635 prevents the contact between CypA and NS5A derived from genotypes 1 to 3. Together, these data suggest that NS5A-CypA interactions control HCV replication and that SCY-635 blocks viral replication by preventing the formation of these complexes. We also found that NS5A mutant proteins found in SCY-635-resistant HCV replicons behave similarly to wild-type NS5A in terms of both CypA binding and SCY-635-mediated dissociation and inhibition of CypA binding. However, the NS5A mutations found in SCY-635-resistant HCV replicons rescued viral replication in CypA-knockdown cells, suggesting that the NS5A mutations, which arose in vitro under SCY-635 selection, do not alter the binding affinity of CypA for NS5A. These specific mutations in NS5A eliminate the dependence of HCV RNA replication on the expression of host CypA.
authors.affiliation: Scynexis, Inc, Research Triangle Park, North Carolina, USA.
authors.forename: Sam
authors.initials: S
authors.lastname: Hopkins
authors.forename: Michael
authors.initials: M
authors.lastname: Bobardt
authors.forename: Udayan
authors.initials: U
authors.lastname: Chatterji
authors.forename: Jose A
authors.initials: JA
authors.lastname: Garcia-Rivera
authors.forename: Precious
authors.initials: P
authors.lastname: Lim
authors.forename: Philippe A
authors.initials: PA
authors.lastname: Gallay
mesh_terms: D000998:Antiviral Agents / Q000494:pharmacology*; D021984:Cyclophilin A / Q000494:pharmacology*; D003524:Cyclosporins / Q000494:pharmacology*; D004797:Enzyme-Linked Immunosorbent Assay; D016174:Hepacivirus / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D017361:Viral Nonstructural Proteins / Q000378:metabolism*; D014779:Virus Replication / Q000187:drug effects; D012324:RNA-Dependent RNA Polymerase
chemical_list: D000998:Antiviral Agents; D021984:Cyclophilin A; D003524:Cyclosporins; D017361:Viral Nonstructural Proteins; C087036:NS-5 protein, hepatitis C virus; D012324:RNA-Dependent RNA Polymerase; C544142:SCY-635