Long‐term RNA interference and its application to hepatitis B virus

Abstract

RNA interference (RNAi) is an ancient defensive mechanism in eukaryotes to control gene expressing and defend their genomes from foreign invaders. It refers to the phenomenon that double‐stranded RNA results in the sequence‐specific silencing of target gene expression. Although it was documented in a relatively short time ago, intensive research has facilitated making its mechanism clear. Researchers have found that it was a powerful tool for analyzing the functions of genes and treating tumors, infectious diseases and genetic abnormalities that are associated with a dominant gene defect. However, delivery in vivo, low blood stability and poor intracellular uptake present significant challenges for the development of RNAi reagents in clinical use. Thus, long‐term inducible RNAi was designed. There are hundreds of millions of hepatitis B virus (HBV) carriers in the world at present, a portion of whom will lose their lives after several years due to chronic complications such as cirrhosis, hepatocellular carcinomas or both. Although a preventive vaccine is now available, the present therapeutic options for chronically infected patients are limited and of low efficiency. Admittedly, to date most RNAi experiments have been done in vitro, but it is hoped that they may be developed into a therapeutic strategy for HBV in the near future. In this article the principles and construction of long‐term RNA are discussed. Its therapeutic potentiality and attention to the potential hazards will also outlined. We conclude that this ancient defensive mechanism can be recruited as a powerful weapon in the fight against HBV.

RNA interference approaches for treatment of HIV-1 infection

“…RNAi approaches have also been investigated to treat persistent viral infections such as HIV-1, hepatitis B, and hepatitis C. These are targeted in a different manner to acute infections because the RNA therapy must be present for a longer period of time [ 75 , 76 ]. The pre-clinical efficacy is promising; nevertheless, a different set of problems are associated with using RNAi for long-term infections and these issues must be further explored before moving to the clinic [ 77 , 78 ]. The viral proteins and cellular machinery necessary for viral replication are obvious targets for preventing initial infection, but viral targets are susceptible to mutational escape resulting from the relatively low fidelity of the viral RNA polymerase enzymes.…”

Effects of HBV Genetic Variability on RNAi Strategies

“…For hepatitis B virus (HBV) several approaches have been taken using various design and delivery strategies with good initial success (reviewed in [4, 5, 8, 9]) and some limitations [10–12]. …”

“…The antisense strand of the siRNA base pairs with its target RNA, with exact complementarity, and then RISC mediates cleavage and subsequent degradation of the target RNA [21–23] (Figure 1). Perfect base pairing between the siRNA and HBV RNA is a hallmark of siRNA effects, and single base substitutions in the target, due to genome variability, would disrupt this mode of action [4, 8, 17, 24]. …”

“…Following processing, the pre-miRNA is exported to the cytoplasm by the Ran-GTP-dependent cargo transporter Exportin-5 [27]. In the cytoplasm pre-miRNA is processed by Dicer into the mature miRNA, which is incorporated into RISC [4, 8, 17, 24] which targets the viral RNA [28]. Typical cellular miRNAs are not perfectly matched to their mRNA targets, and studies have indicated that they mainly exert silencing through translational repression, rather than degradation [29, 30] (Figure 1).…”

“…Rationally designed RNAs, targeted in combinations [40, 62–64], delivered by “state-of-the-art” vectors could be an effective anti-HBV treatment [4, 5, 8, 9]. Such design strategies would need to take into account conservation in the HBV genome.…”