JAC Advance Access originally published online on December 5, 2006
Journal of Antimicrobial Chemotherapy 2007 59(1):51-58; doi:10.1093/jac/dkl455
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In vitro antiviral activity of SCH446211 (SCH6), a novel inhibitor of the hepatitis C virus NS3 serine protease
1 Department of Virology, Schering-Plough Research Institute Kenilworth, NJ 07033, USA 2 Divisions of Gastroenterology and Hepatology, University Hospital Geneva, Switzerland 3 Clinical Pathology, University Hospital Geneva, Switzerland 4 Chemical Research, Schering-Plough Research Institute, Kenilworth NJ 07033, USA 5 Drug Metabolism, Schering-Plough Research Institute Kenilworth, NJ 07033, USA
Received 29 June 2006; returned 5 September 2006; revised 15 September 2006; accepted 4 October 2006
*Corresponding author. Tel: +1-908-740-3031; Fax: +1-908-740-3032; E-mail: Rong.Liu{at}spcorp.com
Background: Current hepatitis C virus (HCV) therapies may cure 
60% of infections. They are often contraindicated or poorly tolerated, underscoring the need for safer and more effective drugs. A novel, 
-ketoamide-derived, substrate-based inhibitor of the HCV serine protease (SCH446211) was developed. Compared with earlier reported inhibitors of similar chemical class, it has a P1'–P2' extension which provides extended interaction with the protease active site. The aim of this study was to evaluate the in vitro antiviral activity of SCH446211.
Methods: Binding constant of SCH446211 to HCV NS3 protease was measured with the chromogenic substrate in vitro cleavage assay. Cell-based activity of SCH446211 was evaluated in replicon cells, which are Huh-7 hepatoma cells stably transfected with a subgenomic HCV RNA as reported previously. After 72 h of incubation with SCH446211, viral transcription and protein expression were measured by real-time RT–PCR (TaqMan), quantitative in situ hybridization, immunoblot and indirect immunofluorescence.
Results: The binding constant of SCH446211 to HCV NS3 protease was 3.8 ± 0.4 nM. HCV replication and protein expression were inhibited by SCH446211 in replicon cells as consistently shown by four techniques. In particular, based on quantitative real-time RT–PCR measurements, the IC50 and IC90 of SCH446211 were estimated to be 40 ± 20 and 100 ± 20 nM (n = 17), respectively. Long-term culture of replicon cells with SCH446211 reduced replicon RNA to <0.1 copy per cell. SCH446211 did not show cellular toxicity at concentrations up to 50 µM.
Conclusions: SCH446211 is a potent inhibitor of HCV protease in vitro. Its extended interaction with the HCV NS3 protease active site is associated with potent in vitro antiviral activity. This observation is potentially a useful guide for development of future potent inhibitors against HCV NS3 protease.
Keywords: chronic hepatitis , antiviral therapy , HCV replicon , in situ hybridization