Background & Aims: Expression of the nonstructural protein (NS)3/4A protease in cells infected with hepatitis C virus (HCV) results in cleavage of the mitochondrial antiviral-signaling protein (MAVS) and disruption of signaling pathways that lead to viral activation of interferon regulatory factor 3 (IRF-3) and synthesis of type 1 interferons (IFN-α/β). High concentrations of inhibitors of NS3/4A reverse this signaling defect, but quantitative analyses of this potential therapeutic effect are lacking. This study quantitatively assessed the rescue of IRF-3 signaling by NS3/4A inhibitors, compared with in vitro antiviral activity. Methods: Antiviral activities of 2 NS3/4A protease inhibitors (TMC435350 and an analog, TMC380765) and a nonnucleoside polymerase inhibitor (Tib-3) were determined in HCV replicon cells and in cells infected with genotype 1a and 2a viruses. The capacity to rescue IRF-3 activation in these cells was assessed by monitoring IFN-β promoter activity following challenge with Sendai virus. Inhibitor-induced changes in NS3 and MAVS expression were assessed in immunoblots. Results: Both protease inhibitors were capable of rescuing IFN-β promoter activation but only at concentrations ∼100-fold the antiviral 50% effective concentration (EC50) for genotype 1 virus. No rescue was observed with the polymerase inhibitor, even at a concentration 600-fold greater than the EC50. IRF-3 activation did not correlate with reductions in NS3/4A levels or detection of full-length MAVS. Overexpression of the product of NS3/4A cleavage of MAVS did not result in a dominant-negative effect on signaling. Conclusions: NS3/4A protease inhibitors can restore IRF-3 signaling in HCV-infected cells but only at concentrations far in excess of the antiviral EC50.
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