Kinetic profile of a heterocyclic HCV replicon RNA synthesis inhibitor

Abstract

Recently, a benzo-1,2,4-thiadiazine was shown to be a potent, specific inhibitor of the hepatitis C virus (HCV) RNA polymerase [J. Biol. Chem. 277 (2002) 32327]. Herein, we present several lines of evidence to demonstrate that thiadiazine compound 4 (C21H21N3O4S) is highly synergistic with interferon-α (IFN-α) and disrupts HCV replicon RNA synthesis with a distinct kinetic profile. A time course analysis after a single treatment with 5μM compound 4 showed a loss of viral RNA consistent with replicon RNA half-life, suggesting inhibition of 90% of ongoing or newly initiated replicative intermediates. This finding is consistent with the mechanism of action recently reported for compound 4, an RNA synthesis initiation inhibitor [J. Biol. Chem. 278 (2003) 16602]. Further, unlike IFN-α, an immediate reduction of HCV replicon RNA synthesis was apparent upon addition of compound 4. Treatment with IFN-α showed a delay of approximately 4h prior to inhibition of viral RNA replication, consistent with its signaling kinetics.