Hepatitis B virus (HBV)-specific short hairpin RNA is capable of reducing the formation of HBV covalently closed circular (CCC) DNA but has no effect on established CCC DNA in vitro

Analysis of the pharmacokinetics and efficacy of RBD1016 - A GalNAc-siRNA targeting Hepatitis B Virus X gene using semi-mechanistic PK/PD model

Small interference RNA (siRNA) is a class of short double-stranded RNA molecules that cause mRNA degradation through an RNA interference mechanism and is a promising therapeutic modality. RBD1016 is a siRNA drug in clinical development for the treatment of chronic Hepatitis B Virus (HBV) infection, which contains a conjugated with N-acetylglucosamine moiety that can facilitate its hepatic delivery. We aimed to construct a semi-mechanistic model of RBD1016 in pre-clinical animals, to elucidate the pharmacokinetic/pharmacodynamic (PK/PD) profiles in mice and PK profiles in monkeys, which can lay the foundation for potential future translation of RBD1016 PK and PD from the pre-clinical stage to the clinic stage. The proposed semi-mechanistic PK/PD model fitted PK and PD data in HBV transgenic mice well and described plasma and liver concentrations in the monkeys well. The simulation results showed that our model has a reasonable predictive ability for Hepatitis B surface antigen (HBsAg) levels after multiple dosing in mice. Further PK and PD data for RBD1016, including clinical data, will assist in refining the model presented here. Our current effort focused on model building for RBD1016, we anticipate that the model could apply to other GalNAc-siRNA drugs.

Oligonucleotide-Based Therapies for Chronic HBV Infection: A Primer on Biochemistry, Mechanisms and Antiviral Effects

Three types of oligonucleotide-based medicines are under clinical development for the treatment of chronic HBV infection. Antisense oligonucleotides (ASOs) and synthetic interfering RNA (siRNA) are designed to degrade HBV mRNA, and nucleic acid polymers (NAPs) stop the assembly and secretion of HBV subviral particles. Extensive clinical development of ASOs and siRNA for a variety of liver diseases has established a solid understanding of their pharmacodynamics, accumulation in different tissue types in the liver, pharmacological effects, off-target effects and how chemical modifications and delivery approaches affect these parameters. These effects are highly conserved for all ASO and siRNA used in human studies to date. The clinical assessment of several ASO and siRNA compounds in chronic HBV infection in recent years is complicated by the different delivery approaches used. Moreover, these assessments have not considered the large clinical database of ASO/siRNA function in other liver diseases and known off target effects in other viral infections. The goal of this review is to summarize the current understanding of ASO/siRNA/NAP pharmacology and integrate these concepts into current clinical results for these compounds in the treatment of chronic HBV infection.

Advanced Therapeutics, Vaccinations, and Precision Medicine in the Treatment and Management of Chronic Hepatitis B Viral Infections; Where Are We and Where Are We Going?

The management of chronic hepatitis B virus (CHB) infection is an area of massive unmet clinical need worldwide. In spite of the development of powerful nucleoside/nucleotide analogue (NUC) drugs, and the widespread use of immune stimulators such as interferon-alpha (IFNα) or PEGylated interferon-alpha (PEG-IFNα), substantial improvements in CHB standards of care are still required. We believe that the future for CHB treatment now rests with advanced therapeutics, vaccination, and precision medicine, if all are to bring under control this most resilient of virus infections. In spite of a plethora of active drug treatments, anti-viral vaccinations and diagnostic techniques, the management of CHB infection remains unresolved. The reason for this is the very complexity of the virus replication cycle itself, giving rise to multiple potential targets for therapeutic intervention some of which remain very intractable indeed. Our review is focused on discussing the potential impact that advanced therapeutics, vaccinations and precision medicine could have on the future management of CHB infection. We demonstrate that advanced therapeutic approaches for the treatment of CHB, in the form of gene and immune therapies, together with modern vaccination strategies, are now emerging rapidly to tackle the limitations of current therapeutic approaches to CHB treatment in clinic. In addition, precision medicine approaches are now gathering pace too, starting with personalized medicine. On the basis of this, we argue that the time has now come to accelerate the design and creation of precision therapeutic approaches (PTAs) for CHB treatment that are based on advanced diagnostic tools and nanomedicine, and which could maximize CHB disease detection, treatment, and monitoring in ways that could genuinely eliminate CHB infection altogether.

Advances with using CRISPR/Cas-mediated gene editing to treat infections with hepatitis B virus and hepatitis C virus

Chronic infections with hepatitis B and hepatitis C viruses (HBV and HCV) account for the majority of cases of cirrhosis and hepatocellular carcinoma. Current therapies for the infections have limitations and improved efficacy is necessary to prevent complications in carriers of the viruses. In the case of HBV persistence, the replication intermediate comprising covalently closed circular DNA (cccDNA) is particularly problematic. Licensed therapies have little effect on cccDNA and HBV replication relapses following treatment withdrawal. Disabling cccDNA is thus key to curing HBV infections and application of gene editing technology, such as harnessing the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated 9 (Cas9) system, has curative potential. Several studies have reported good efficacy when employing CRISPR/Cas technologies to disable HBV replication in cultured cells and in hydrodynamically injected mice. Recent advances with HCV drug development have revolutionized treatment of the infection. Nevertheless, individuals may be refractory to treatment. Targeting RNA from HCV with CRISPR/Cas isolated from Francisella novicida may have therapeutic utility. Although preclinical work shows that CRISPR/Cas technology has potential to overcome infection with HBV and HCV, significant challenges need to be met. Ensuring specificity for viral targets and efficient delivery of the gene editing sequences to virus-infected cells are particularly important. The field is at an interesting stage and the future of curative antiviral drug regimens, particularly for treatment of chronic HBV infection, may well entail use of combinations that include derivatives of CRISPR/Cas.

Recent advances in use of gene therapy to treat hepatitis B virus infection

Chronic infection with hepatitis B virus (HBV) occurs in approximately 5 % of the world's human population and persistence of the virus is associated with serious complications of cirrhosis and liver cancer. Currently available treatments are modestly effective and advancing novel therapeutic strategies is a medical priority. Stability of the viral cccDNA replication intermediate is a major factor that has impeded the development of therapies that are capable of eliminating chronic infection. Recent advances that employ gene therapy strategies offer useful advantages over current therapeutics. Silencing of HBV gene expression by harnessing the RNA interference pathway has been shown to be highly effective in cell culture and in vivo. However, a potential limitation of this approach is that the post-transcriptional mechanism of gene silencing does not disable cccDNA. Early results using designer transcription activator-like effector nucleases (TALENs) and repressor TALEs (rTALEs) have shown potential as a mode of inactivating cccDNA. In this article, we review the recent advances that have been made in HBV gene therapy, with a particular emphasis on the potential anti-HBV therapeutic utility of designed sequence-specific DNA binding proteins and their derivatives.

Baculovirus-mediated gene delivery and RNAi applications

Baculoviruses are widely encountered in nature and a great deal of data is available about their safety and biology. Recently, these versatile, insect-specific viruses have demonstrated their usefulness in various biotechnological applications including protein production and gene transfer. Multiple in vitro and in vivo studies exist and support their use as gene delivery vehicles in vertebrate cells. Recently, baculoviruses have also demonstrated high potential in RNAi applications in which several advantages of the virus make it a promising tool for RNA gene transfer with high safety and wide tropism.

Gene therapeutic approaches to inhibit hepatitis B virus replication

Acute and chronic hepatitis B virus (HBV) infections remain to present a major global health problem. The infection can be associated with acute symptomatic or asymptomatic hepatitis which can cause chronic inflammation of the liver and over years this can lead to cirrhosis and the development of hepatocellular carcinomas. Currently available therapeutics for chronically infected individuals aim at reducing viral replication and to slow down or stop the progression of the disease. Therefore, novel treatment options are needed to efficiently combat and eradicate this disease. Here we provide a state of the art overview of gene therapeutic approaches to inhibit HBV replication. We discuss non-viral and viral approaches which were explored to deliver therapeutic nucleic acids aiming at reducing HBV replication. Types of delivered therapeutic nucleic acids which were studied since many years include antisense oligodeoxynucleotides and antisense RNA, ribozymes and DNAzymes, RNA interference, and external guide sequences. More recently designer nucleases gained increased attention and were exploited to destroy the HBV genome. In addition we mention other strategies to reduce HBV replication based on delivery of DNA encoding dominant negative mutants and DNA vaccination. In combination with available cell culture and animal models for HBV infection, in vitro and in vivo studies can be performed to test efficacy of gene therapeutic approaches. Recent progress but also challenges will be specified and future perspectives will be discussed. This is an exciting time to explore such approaches because recent successes of gene therapeutic strategies in the clinic to treat genetic diseases raise hope to find alternative treatment options for patients chronically infected with HBV.

Inhibition of hepatitis B virus replication in vivo using lipoplexes containing altritol-modified antiviral siRNAs

Chronic infection with the hepatitis B virus (HBV) occurs in approximately 6% of the world's population and carriers of the virus are at risk for complicating hepatocellular carcinoma. Current treatment options have limited efficacy and chronic HBV infection is likely to remain a significant global medical problem for many years to come. Silencing HBV gene expression by harnessing RNA interference (RNAi) presents an attractive option for development of novel and effective anti HBV agents. However, despite significant and rapid progress, further refinement of existing technologies is necessary before clinical application of RNAi-based HBV therapies is realized. Limiting off target effects, improvement of delivery efficiency, dose regulation and preventing reactivation of viral replication are some of the hurdles that need to be overcome. To address this, we assessed the usefulness of the recently described class of altritol-containing synthetic siRNAs (ANA siRNAs), which were administered as lipoplexes and tested in vivo in a stringent HBV transgenic mouse model. Our observations show that ANA siRNAs are capable of silencing of HBV replication in vivo. Importantly, non specific immunostimulation was observed with unmodified siRNAs and this undesirable effect was significantly attenuated by ANA modification. Inhibition of HBV replication of approximately 50% was achieved without evidence for induction of toxicity. These results augur well for future application of ANA siRNA therapeutic lipoplexes.

A rational study for identification of highly effective siRNAs against hepatitis B virus

RNA interference (RNAi) is a powerful gene knockdown technique used for study gene function. It also potentially provides effective agents for inhibiting infectious and genetic diseases. Most of RNAi studies employ a single siRNA designing program and then require large-scale screening experiments to identify functional siRNAs. In this study, we demonstrate that an assembly of results generated from different siRNA designing programs could provide clusters of predicting sites that aided selection of potent siRNAs. Based on the clusters, three siRNA target sites were selected on a conserved RNA region of hepatitis B virus (HBV), known as HBV post-transcriptional regulatory element (HBV PRE) at nucleotide positions 1317-1337, 1357-1377 and 1644-1664. All three chosen siRNAs driven by H1 promoter were highly effective and could drastically decrease expression of HBV transcripts (core, surface and X) and surface protein without induction of interferon response and cell cytotoxicity in liver cancer cell line (HepG2). Based on prediction of secondary structures, the silencing effects of siRNAs were less effective against a loop sequence of the mRNA target with hairpin structure. In summary, we demonstrate an effectual approach for identification of functional siRNAs. Moreover, highly potent siRNAs identified here may serve as novel agents for development of nucleic acid-based HBV therapy.

Effect of recombinant adenovirus-associated virus-mediated RNA interference on HBV replication and expression

AIM: To observe the effect of recombinant adenovirus-associated virus (rAAV)-mediated RNA interference on HBV replication and expression in HepG2.2.15 cells.

METHODS: The expression box of hu6-shRNA was placed between two ITRs of AAV and then ligated to the basic core promoter (BCP) of HBV and BCP-driven Rep gene of AAV, which resulted in rAAV. The rAAV was transfected into HepG2.2.15 cells (HCC cells in which the HBV gene was inserted). The expression of HBsAg and HBeAg and replication of HBV-DNA in cultured supernatant were determined on days 1, 2, 3 and 10 after transfection, and the AAVS1 region was sequenced on day 3 after transfection.

RESULTS: The target sequence-containing vectors PLRBR322-324, PLRBR522-324, PLRBR322-2424 and PLRBR522-2424 were successfully constructed. All the four vectors had inhibitory effects on the expression of HBsAg and HBeAg and on HBV-DNA replication, with the former two (PLRBR322-324 and PLRBR522-324) having more significant inhibitory effect on HBsAg expression, the latter two on HBeAg expression and the third on HBV-DNA replication. The inhibitory effects on HBsAg and HBeAg expression and HBV-DNA replication were most obvious on day 3 after transfection, and the inhibition rate remained high on day 10. Site-directed integration of the target sequence was located in the AAVS1 region.

CONCLUSION: The rAAV constructed by several elements of AAV and HBV, together with the help of site-directed integration mediated by Rep protein, is a good exploration to solve the problem of short-term effect of RNAi against HBV.

Changes in innate and permissive immune responses after hbv transgenic mouse vaccination and long-term-siRNA treatment [corrected]

Background

Currently, no licensed therapy can thoroughly eradicate hepatitis B virus (HBV) from the body, including interferon α and inhibitors of HBV reverse-transcription. Small interfering RNA (siRNA) seem to be a promising tool for treating HBV, but had no effect on the pre-existing HBV covalently closed circular DNA. Because it is very difficult to thoroughly eradicate HBV with unique siRNAs, upgrading the immune response is the best method for fighting HBV infection. Here, we aim to explore the immune response of transgenic mice to HBV vaccination after long-term treatment with siRNAs and develop a therapeutic approach that combines siRNAs with immunopotentiators.

Methodology/Principal Findings

To explore the response of transgenic mice to hepatitis B vaccine, innate and acquired immunity were detected after long-term treatment with siRNAs and vaccination. Antiviral cytokines and level of anti-hepatitis B surface antigen antibody (HBsAg-Ab) were measured after three injections of hepatitis B vaccine.

Results

Functional analyses indicated that toll-like receptor-mediated innate immune responses were reinforced, and antiviral cytokines were significantly increased, especially in the pSilencer4.1/HBV groups. Analysis of CD80+/CD86+ dendritic cells in the mouse liver indicated that dendritic cell antigen presentation was strengthened. Furthermore, the siRNA-treated transgenic mice could produce detectable HBsAg-Ab after vaccination, especially in the CpG oligonucleotide vaccine group.

Conclusions/Significance

For the first time, our studies demonstrate that siRNAs with CpG HBV vaccine could strengthen the immune response and break the immune tolerance status of transgenic mice to HBV. Thus, siRNAs and HBV vaccine could provide a sharp double-edged sword against chronic HBV infection.

Baculovirus as a gene delivery vector: recent understandings of molecular alterations in transduced cells and latest applications

Baculovirus infects insects in nature and is non-pathogenic to humans, but can transduce a broad range of mammalian and avian cells. Thanks to the biosafety, large cloning capacity, low cytotoxicity and non-replication nature in the transduced cells as well as the ease of manipulation and production, baculovirus has gained explosive popularity as a gene delivery vector for a wide variety of applications. This article extensively reviews the recent understandings of the molecular mechanisms pertinent to baculovirus entry and cellular responses, and covers the latest advances in the vector improvements and applications, with special emphasis on antiviral therapy, cancer therapy, regenerative medicine and vaccine.

Potential of adenovirus and baculovirus vectors for the delivery of shRNA against morbilliviruses

Morbilliviruses are important pathogens of humans, ruminants, carnivores and marine mammals. Although good vaccines inducing long-term immunity are available, recurrent outbreaks of measles, canine distemper and peste des petits ruminants (PPR) are observed. In control strategies, antivirals thus could be useful to confine virus spread and application of interfering RNAs is a promising approach, provided they can be delivered efficiently into the host cells. We have constructed recombinant adenovirus and baculovirus vectors expressing short hairpin RNAs (shRNAs) against the PPR virus (PPRV) and compared them in vitro. It was found that both recombinant viruses inhibited PPRV replication with the baculovirus vector, which inhibited generation of infectious progeny by more than 2 log10 and the nucleoprotein expression of PPRV by 73%, being the more efficient. The results show that baculoviral shRNA-expressing vectors have the potential for therapeutic use against morbillivirus infections.

Identification of an effective siRNA target site and functional regulatory elements, within the hepatitis B virus posttranscriptional regulatory element

Background

Infection with hepatitis B virus (HBV) is major public health concern. The limitations of available antiviral drugs require development of novel approaches to inhibit HBV replication. This study was conducted to identify functional elements and new siRNA target sites within the highly conserved regions of the 533 base post-transcriptional regulatory element (PRE) of HBV RNAs.

Results

Computational analysis of the PRE sequence revealed several conserved regulatory elements that are predicted to form local secondary structures some of these within known regulatory regions. A deletion analysis showed that sub-elements of the PRE have different effects on the reporter activity suggesting that the PRE contains multiple regulatory elements. Conserved siRNA targets at nucleotide position 1317-1337 and 1329-1349 were predicted. Although the siRNA at the position 1329-1349 had no effect on the expression of reporter gene, the siRNA target site at the position 1317-1337 was observed to significantly decrease expression of the reporter protein. This siRNA also specifically reduced the level of cccDNA in transiently HBV infected cells.

Conclusion

The HBV PRE is likely to contain multiple regulatory elements. A conserved target within this region at 1317-1337 is an effective siRNA target.

Quantitative assessment of the antiviral potencies of 21 shRNA vectors targeting conserved, including structured, hepatitis B virus sites

BACKGROUND & AIMS

RNA interference (RNAi) may offer new treatment options for chronic hepatitis B. Replicating via an RNA intermediate, hepatitis B virus (HBV) is known to be principally vulnerable to RNAi. However, beyond delivery, the relevant issues of potential off-target effects, target site conservation in circulating HBV strains, and efficacy of RNAi itself have not systematically been addressed, nor can the different existing data be quantitatively compared. The aim of this study was to provide such information.

METHODS

To focus on the intracellular RNAi process itself and minimise other variables affecting overall RNAi efficacy, we used a robust co-transfection system to quantitatively assess the relative potencies of 21 small-hairpin (sh) RNA vectors, targeting conserved sites throughout the HBV genome, against viral RNAs, proteins, nucleocapsids, and secreted virions under standardised conditions.

RESULTS

The approach enabled a distinct efficacy ranking, with the six most potent shRNAs achieving 95% reductions in virion formation, sequence-specifically and without detectable interferon induction, yet by differentially affecting different steps. Efficacy correlated poorly with predictions and was not principally abolished by target structure. Sequence comparisons suggest that truly conserved, RNAi-targetable sequences comprise less than 500 nucleotides of the circulating HBV genomes.

CONCLUSIONS

The HBV genome can harbour only a finite number of optimal target sites, but current predictions are poorly suited to constrain the number of possible candidates. However, the small size of the highly conserved sequence space suggests experimental identification as a viable option.

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

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-α 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.

trans-Complementation of HBV rtM204I mutant replication by HBV wild-type polymerase

The function of the hepatitis B virus (HBV) wild-type (WT) polymerase (pol) expressed alone or in the context of the intact genome when interacting with HBV rtM204I in HepG2 cells was compared. We show that WT pol expression from a packaging-defective RNA can complement defective rtM204I pol activity resulting in increased levels of HBV replicative intermediates (RI). Analysis of the genetically marked genomes showed that this restoration resulted from trans-complementation, rather than recombination. In contrast, we demonstrate that enhanced levels of total HBV RI observed when cells were cotransduced with both WT and rtM204I baculoviruses were predominantly WT RI. In this case, WT pol was produced from a full-length pregenomic RNA (pgRNA). We conclude that the WT pol has the capacity to trans-complement the replication defect of rtM204I; however, when expressed from an authentic pgRNA, as in a mixed infection, pol may not trans-complement efficiently.