Progress in the use of RNA interference as a therapy for chronic hepatitis B virus infection

Abstract

Chronic infection with hepatitis B virus (HBV) occurs in approximately 6% of the world's population and carriers of the virus are at risk for hepatocellular carcinoma and cirrhosis. Current treatment regimens, which include interferon-alpha and nucleoside/nucleotide analogs, are only partially effective and new treatment methods remain an important objective. Harnessing the RNA interference (RNAi) pathway to achieve post-transcriptional silencing of rogue genetic elements is an exciting avenue for development of novel therapeutic strategies. The specific and potent suppression of HBV gene expression and replication is an attractive option as a novel and effective approach for the treatment of chronic HBV infection. However, despite significant and rapid progress, existing RNAi technologies require further refinement before clinical applications can be realized. Here, we review current efforts aimed at improving the efficiency of anti-HBV RNAi-based delivery systems, at limiting the toxicities associated with RNAi modalities and at preventing reactivation of viral replication. We discuss the progress towards clinical implementation of anti-HBV RNAi therapies.

Figure 1

A schematic of the hepatitis B virus genome structure, gene arrangement and expressed transcripts. (a) The partially double-stranded genome is shown associated with a viral capsid (gray hexagon). (b) The four viral open reading frames encoding the core (C), polymerase (P), surface (S) and hepatitis B virus X (HBx) proteins, colored to show how they partially or fully overlap each other. (c) Four major viral RNA species (outer arrows) are transcribed from the covalently closed circular DNA (cccDNA) template and terminate at a single polyadenylation signal. Targeting the X transcript of the viral genome (indicated by shaded gray region) ensures that a single RNAi modality inhibits all viral-produced RNAs, including the greater-than-genome-length pregenomic RNA.