Resistance Mutations Define Specific Antiviral Effects for Inhibitors of the Hepatitis C Virus p7 Ion Channel

Section of Oncology and Clinical Research, Leeds Institute of Molecular Medicine, St. James's University Hospital, Leeds, United Kingdom.
Hepatology (Impact Factor: 11.06). 07/2011; 54(1):79-90. DOI: 10.1002/hep.24371
Source: PubMed


The hepatitis C virus (HCV) p7 ion channel plays a critical role during infectious virus production and represents an important new therapeutic target. Its activity is blocked by structurally distinct classes of small molecules, with sensitivity varying between isolate p7 sequences. Although this is indicative of specific protein-drug interactions, a lack of high-resolution structural information has precluded the identification of inhibitor binding sites, and their modes of action remain undefined. Furthermore, a lack of clinical efficacy for existing p7 inhibitors has cast doubt over their specific antiviral effects. We identified specific resistance mutations that define the mode of action for two classes of p7 inhibitor: adamantanes and alkylated imino sugars (IS). Adamantane resistance was mediated by an L20F mutation, which has been documented in clinical trials. Molecular modeling revealed that L20 resided within a membrane-exposed binding pocket, where drug binding prevented low pH-mediated channel opening. The peripheral binding pocket was further validated by a panel of adamantane derivatives as well as a bespoke molecule designed to bind the region with high affinity. By contrast, an F25A polymorphism found in genotype 3a HCV conferred IS resistance and confirmed that these compounds intercalate between p7 protomers, preventing channel oligomerization. Neither resistance mutation significantly reduced viral fitness in culture, consistent with a low genetic barrier to resistance occurring in vivo. Furthermore, no cross-resistance was observed for the mutant phenotypes, and the two inhibitor classes showed additive effects against wild-type HCV. CONCLUSION: These observations support the notion that p7 inhibitor combinations could be a useful addition to future HCV-specific therapies.

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Available from: Stephen d. c. Griffin, Apr 17, 2015
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    • "Bundle models of p7 of GT 1a were generated using the abovementioned protocols [32] [33]. The hexameric bundle of GT 1b was generated using a monomeric NMR structure [40] and positioning six copies around a pseudo sixfold symmetry axis. The bundle of GT 5a derives from NMR spectroscopic data with the protein in an oligomerized (hexamer) form [29]. "
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    • "These drugs are developed to target soluble proteins. Promising small molecule drugs are on its way targeting a membrane protein encoded by HCV, namely p7, a channel forming protein (Pavlovi c et al., 2003; Luscombe et al., 2010; Foster et al., 2011). Viral channel forming proteins (VCPs) are found in a series of viruses (Fischer and Sansom, 2002; Gonzales and Carrasco, 2003; Wang et al., 2010; Nieva et al., 2012; Fischer et al., 2012; OuYang and Chou, 2014). "
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    • "These proteins are known to modulate membrane permeability to support virus entry, assembly or release (viroporins reviewed in (Nieva et al., 2012)). Depending on the genotype, p7 activity can be hindered by multiple ion-channel blockers, such as amantadine, rimantadine and iminosugar derivatives (Griffin et al., 2003, 2008; Pavlovic et al., 2003; Steinmann et al., 2007; Foster et al., 2011). In addition, p7 is dispensable for viral RNA replication, but is important for in vivo infectivity in the chimpanzee model, and for production of infectious HCVcc (Jones et al., 2007; Steinmann et al., 2007; Sakai et al., 2003; Brohm et al., 2009; Atoom et al., 2013). "
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