Small interfering RNA effectively inhibits protein expression and negative strand RNA synthesis from a full-length hepatitis C virus clone.

Hepatitis C virus (HCV) infection is usually treated with the combination of interferon and ribavirin, but only a small fraction of patients develop a sustained remission. There is need for the development of specific molecular approaches for the treatment of chronic HCV infection. We propose that RNA interference is highly effective antiviral strategy that offers great potential for the treatment of HCV infection. Three plasmid constructs expressing small interfering RNAs (siRNAs) targeted to sequences encoding the structural gene (E2) and non-structural genes (NS3, NS5B) of HCV1a genome were prepared. Antiviral properties of siRNAs against the HCV1a strain were studied in a transient replication model that involved the use of a transcription plasmid containing the full-length HCV genome and an adenovirus expressing T7 RNA polymerase. We found that siRNAs targeted to the E2, NS3 and NS5B regions of the HCV genome efficiently inhibited expression of the HCV core and NS5A protein measured by Western blot analysis and immunocytochemical staining. Intracytoplasmic immunization of siRNAs in HCV-transfected cells efficiently degraded genomic positive strand HCV RNA, as shown by ribonuclease protection assay (RPA). All three siRNAs efficiently inhibited synthesis of replicative negative strand HCV RNA in the transfected cells. A control siRNA plasmid against a Epstein--Barr virus latency gene did not inhibit protein expression and negative strand HCV RNA. These results suggest that RNAi is an effective and alternative approach that can be used to inhibit HCV expression and replication.