Novel Azapeptide Inhibitors of Hepatitis C Virus Serine Protease

International audienc

Combined X-ray, NMR, and Kinetic Analyses Reveal Uncommon Binding Characteristics of the Hepatitis C Virus NS3-NS4A Protease Inhibitor BI 201335*

Hepatitis C virus infection, a major cause of liver disease worldwide, is curable, but currently approved therapies have suboptimal efficacy. Supplementing these therapies with direct-acting antiviral agents has the potential to considerably improve treatment prospects for hepatitis C virus-infected patients. The critical role played by the viral NS3 protease makes it an attractive target, and despite its shallow, solvent-exposed active site, several potent NS3 protease inhibitors are currently in the clinic. BI 201335, which is progressing through Phase IIb trials, contains a unique C-terminal carboxylic acid that binds noncovalently to the active site and a bromo-quinoline substitution on its proline residue that provides significant potency. In this work we have used stopped flow kinetics, x-ray crystallography, and NMR to characterize these distinctive features. Key findings include: slow association and dissociation rates within a single-step binding mechanism; the critical involvement of water molecules in acid binding; and protein side chain rearrangements, a bromine–oxygen halogen bond, and profound pKa changes within the catalytic triad associated with binding of the bromo-quinoline moiety