Selective inhibition of hepatitis B virus replication by RNA interference

CRISPR-Cas13b-mediated suppression of hepatitis B virus replication and protein expression

BACKGROUND & AIMS

New antiviral approaches are urgently required that target multiple aspects of the hepatitis B virus (HBV) replication cycle to improve rates of functional cure. HBV RNA represents a novel therapeutic target. Here, we programmed Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas13b endonuclease, to specifically target the HBV pregenomic RNA (pgRNA) and viral mRNAs in a novel approach to reduce HBV replication and protein expression.

METHODS

Cas13b CRISPR RNAs (crRNAs) were designed to target multiple regions of HBV pgRNA. Mammalian cells with replication competent wildtype HBV DNA of different genotypes, a HBV stable cell line, a HBV infection model and a hepatitis B surface antigen (HBsAg)-expressing stable cell line were transfected with PspCas13b-blue fluorescent protein (BFP) and crRNAs plasmids and the impact on HBV replication and protein expression was measured. WT HBV DNA, PspCas13b-BFP and crRNA plasmids were simultaneously hydrodynamically injected into mice, and sera HBsAg was measured. PspCas13b mRNA and crRNA were also delivered by lipid nanoparticles (LNP) in a HBsAg-expressing stable cell line and the impact on secreted HBsAg determined.

RESULTS

Our HBV targeting crRNAs strongly suppressed HBV replication and protein expression in mammalian cells by up to 96% (p<0.0001). HBV protein expression was also reduced in an HBV stable cell line and in the HBV infection model. CRISPR-Cas13b crRNAs reduced HBsAg expression by 50% (p<0.0001) in vivo. LNP-encapsulated PspCas13b mRNA reduced secreted HBsAg by 87% (p=0.0168) in a HBsAg-expressing stable cell line.

CONCLUSIONS

Together, these results show that CRISPR-Cas13b can be programmed to specifically target and degrade HBV RNAs to reduce HBV replication and protein expression, demonstrating its potential as a novel therapeutic option for chronic HBV infection.

IMPACT AND IMPLICATIONS

There is an urgent need for new treatments that target multiple aspects of the HBV replication cycle. Here, we present CRISPR-Cas13b as a novel strategy to target HBV replication and protein expression paving the way for its development as a potential new treatment option for patients living with chronic hepatitis B.

Screening and identification of dominant monoclonal HepG2 cell strain with 1.3-fold HBV genome

BACKGROUND

Hepatitis B virus (HBV) infection model in vitro is the basis for studying HBV life cycle and pathogenesis and for drug screening. With the clinical anti-HBV therapy entering the new trend of "functional cure" and "complete cure", there is an urgent need for cell models that can stably simulate the transcription mechanism of covalently closed circular DNA (cccDNA) and the role of hepatitis B virus X protein (HBx). The 1.3-fold HBV genome contains all the biological information of HBV. It can start the transcription process by its own promoter, support the formation of cccDNA, and complete viral replication, which is closest to the life cycle of HBV in vivo. Lentivirus transfection is a technology that takes lentivirus as vector and introduces foreign molecules such as DNA and RNA into eukaryotic cells, which can form stable transfection.

AIM

To construct a HepG2 cell model with 1.3-fold HBV genome by lentivirus transfection technology, and to screen and identify the dominant monoclonal strain that can stably and efficiently express HBV biomarkers.

METHODS

A lentiviral plasmid containing 1.3-fold HBV genome information was constructed, and the recombinant lentivirus culture was used to infect HepG2 cells at the optimal multiplicity of infection (MOI). Blasticidin (BSD) was used to select HepG2 cell strains (1.3-fold HBV-HepG2) stably integrating the 1.3-fold HBV genome, and then the HBV in the cell model was identified by PCR. HepG2 cells stably carrying the 1.3-fold HBV genome were cultured and nine candidate positive monoclones were selected. The flanking sequences of each monoclonal cell were sequenced to determine the insertion position of the corresponding HBV genome in the genome of HepG2 cells. The most dominant monoclones were selected according to the expression levels of HBsAg and HBeAg. The expression levels and stability of HBsAg, HBeAg, HBx, cccDNA, and HBV DNA in HepG2 cells stably carrying the 1.3-fold HBV genome were compared.

RESULTS

The lentiviral plasmid plenti-bsd-1.3-fold HBV was used to infect HepG2 cells at an MOI of 30. After 72 h, BSD (final concentration 1 μg/mL) was added for screening. After 15-20 d of continuous culture, stable 1.3-fold HBV-HepG2 cell line was obtained. HBV DNA sequence was then identified by PCR. Among the nine selected candidate positive monoclones, A14, in which the 1.3-fold HBV genome was inserted into the HepG2 genome at 1:166461695-166461715 (named HepGA14), had the highest expression levels of HBsAg and HBeAg at 24.28 IU/mL and 39.62 NCU/mL, respectively. HepGA14 can stably and highly express HBV biomarkers. Compared with HepG2.2.15 cell line, the expression levels of HBx and cccDNA in Hepga14 dominant monoclonal line in 1-20 passages were significantly higher (P < 0.05).

CONCLUSION

We have successfully constructed and screened HepGA14, a dominant monoclonal HepG cell strain with HBV 1.3-fold genome, which lays a good foundation for further research of HBV-host relationship and pathogenesis as well as for drug screening.

Strategies to Inhibit Hepatitis B Virus at the Transcript Level

Approximately 240 million people are chronically infected with hepatitis B virus (HBV), despite four decades of effective HBV vaccination. During chronic infection, HBV forms two distinct templates responsible for viral transcription: (1) episomal covalently closed circular (ccc)DNA and (2) host genome-integrated viral templates. Multiple ubiquitous and liver-specific transcription factors are recruited onto these templates and modulate viral gene transcription. This review details the latest developments in antivirals that inhibit HBV gene transcription or destabilize viral transcripts. Notably, nuclear receptor agonists exhibit potent inhibition of viral gene transcription from cccDNA. Small molecule inhibitors repress HBV X protein-mediated transcription from cccDNA, while small interfering RNAs and single-stranded oligonucleotides result in transcript degradation from both cccDNA and integrated templates. These antivirals mediate their effects by reducing viral transcripts abundance, some leading to a loss of surface antigen expression, and they can potentially be added to the arsenal of drugs with demonstrable anti-HBV activity. Thus, these candidates deserve special attention for future repurposing or further development as anti-HBV therapeutics.

Transbody against virus core protein potently inhibits hepadnavirus replication in vivo: evidence from a duck model of hepatitis B virus

BACKGROUND AND PURPOSE

The therapeutic management of hepatitis B virus (HBV) infections remains challenging, and novel antiviral strategies are urgently required. The HBV transbody, a monoclonal antibody (MAb) against human HBcAg coupled with the trans-activator of transcription protein transduction domain (TAT PTD), was previously shown to possess cell-penetrating ability and potent antiviral activity in vitro. The purpose of the present study was to evaluate the antiviral activity of the HBcMAb-TAT PTD conjugate in vivo in a duck model of HBV.

EXPERIMENTAL APPROACH

Female Peking ducks were injected i.p. with 0.03-0.3 mg·kg^-1 ·day^-1 of the DHBV transbody (DHBcMAb-TAT PTD conjugate) for 30 days. Serum DHBV DNA levels and liver DHBV DNA and covalently closed circular DNA (cccDNA) loads were determined at scheduled time points. Immunohistological examination of DHBcAg in the duck liver was also performed.

KEY RESULTS

The DHBV transbody significantly reduced the serum and liver DHBV DNA levels at doses of 0.1 and 0.3 mg·kg^-1 ·day^-1 and liver cccDNA levels at a dose of 0.3 mg·kg^-1 ·day^-1 after 30 days of treatment. The suppressive effects of the DHBV transbody at 0.3 mg·kg^-1 ·day^-1 on the serum and liver DHBV DNA and liver cccDNA levels remained significant, even at 15 days after treatment cessation. Similarly, immunohistochemistry of liver sections revealed decreased DHBcAg levels within hepatocytes 15 days after treatment termination.

CONCLUSIONS AND IMPLICATIONS

The DHBV transbody inhibits DHBV replication and possesses potent anti-DHBV activities in vivo. The cell-permeable antibody against the virus core antigen may be developed as a novel treatment for patients with hepadnavirus infections.

In vitro antiviral activity of three enantiomeric sesquiterpene lactones from Senecio species against hepatitis B virus

Three enantiomeric sesquiterpene lactones were isolated under the bioguidance of the suppression of hepatitis B virus (HBV) surface antigen (HBsAg) from Senecio species, a widely distributed Chinese medicinal herb traditionally used for the treatment of hepatitis B, dermatosis and inflammation. The anti-HBV activity of the purified compounds was measured; all of them showed suppressive activity on the expression of HBsAg and HBV e antigen (HBeAg) in the HepG2.2.15 cell line. Realtime quantitative PCR analysis showed that the studied compounds decreased the number of infectious virions released, but did not inhibit the intracellular HBV DNA. The results suggest that enantiomeric sesquiterpene lactones may possess the potential to work synergistically with other antiviral compounds for the treatment of HBV infection.

Controllable inhibition of hepatitis B virus replication by a DR1-targeting short hairpin RNA (shRNA) expressed from a DOX-inducible lentiviral vector

As a highly efficient delivery system, lentiviral vectors (LVs) have become a powerful tool to assess the antiviral efficacy of RNA drugs such as short hairpin RNA (shRNA) and decoys. Furthermore, recent advanced systems allow controlled expression of the effector RNA via coexpression of a tetracycline/doxycycline (DOX) responsive repressor (tTR-KRAB). Herein, this system was utilized to assess the antiviral effects of LV-encoded shRNAs targeting three conserved regions on the pregenomic RNA of hepatitis B virus (HBV), namely the region coding for the reverse transcriptase (RT) domain of the viral polymerase (LV-HBV-shRNA1), the core promoter (CP; LV-HBV-shRNA2), and the direct repeat 1 (DR1; LV-HBV-shRNA3). Transduction of just the LV-HBV-shRNA vectors into the stably HBV expressing HepG2.2.15 cell line showed significant reductions in secreted HBsAg and HBeAg, intracellular HBcAg as well as HBV RNA and DNA replicative intermediates for all vectors, however, most pronouncedly for the DR1-targeting shRNA3. The corresponding vector was therefore applied in the DOX-controlled system. Notably, strong interference with HBV replication was found in the presence of the inducer DOX whereas the antiviral effect was essentially ablated in its absence; hence, the silencing effect of the shRNA and consequently HBV replication could be strictly regulated by DOX. This newly established system may therefore provide a valuable platform to study the antiviral efficacy of RNA drugs against HBV in a regulated manner, and even be applicable in vivo.

Inhibition of dengue virus entry into target cells using synthetic antiviral peptides

Despite the importance of DENV as a human pathogen, there is no specific treatment or protective vaccine. Successful entry into the host cells is necessary for establishing the infection. Recently, the virus entry step has become an attractive therapeutic strategy because it represents a barrier to suppress the onset of the infection. Four putative antiviral peptides were designed to target domain III of DENV-2 E protein using BioMoDroid algorithm. Two peptides showed significant inhibition of DENV when simultaneously incubated as shown by plaque formation assay, RT-qPCR, and Western blot analysis. Both DET4 and DET2 showed significant inhibition of virus entry (84.6% and 40.6% respectively) using micromolar concentrations. Furthermore, the TEM images showed that the inhibitory peptides caused structural abnormalities and alteration of the arrangement of the viral E protein, which interferes with virus binding and entry. Inhibition of DENV entry during the initial stages of infection can potentially reduce the viremia in infected humans resulting in prevention of the progression of dengue fever to the severe life-threatening infection, reduce the infected vector numbers, and thus break the transmission cycle. Moreover these peptides though designed against the conserved region in DENV-2 would have the potential to be active against all the serotypes of dengue and might be considered as Hits to begin designing and developing of more potent analogous peptides that could constitute as promising therapeutic agents for attenuating dengue infection.

Hepatitis B virus induces expression of antioxidant response element-regulated genes by activation of Nrf2

The expression of a variety of cytoprotective genes is regulated by short cis-acting elements in their promoters, called antioxidant response elements (AREs). A central regulator of ARE-mediated gene expression is the NF-E2-related factor 2 (Nrf2). Human hepatitis B virus (HBV) induces a strong activation of Nrf2/ARE-regulated genes in vitro and in vivo. This is triggered by the HBV-regulatory proteins (HBx and LHBs) via c-Raf and MEK. The Nrf2/ARE-mediated induction of cytoprotective genes by HBV results in a better protection of HBV-positive cells against oxidative damage as compared with control cells. Furthermore, there is a significantly increased expression of the Nrf2/ARE-regulated proteasomal subunit PSMB5 in HBV-positive cells that is associated with a decreased level of the immunoproteasome subunit PSMB5i. In accordance with this finding, HBV-positive cells display a higher constitutive proteasome activity and a decreased activity of the immunoproteasome as compared with control cells even after interferon α/γ treatment. The HBV-dependent induction of Nrf2/ARE-regulated genes might ensure survival of the infected cell, shape the immune response to HBV, and thereby promote establishment of the infection.

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.

Antiviral treatment of chronic hepatitis B virus (HBV) infections

While 25 compounds have been formally licensed for the treatment of HIV infection (AIDS), only seven licensed products are currently available for the treatment of chronic hepatitis B virus (HBV) infection: interferon-α, pegylated interferon-α, lamivudine, adefovir (dipivoxil), entecavir, telbivudine and tenofovir (disoproxil fumarate). In contrast to the treatment of HIV infections where the individual drugs are routinely used in combination, for the treatment of chronic HBV infection the individual drugs are generally used in monotherapy. In principle, combination drug therapy should allow reducing the likelihood of drug-resistant development.

Production, characterization and in vitro testing of HBcAg-specific VHH intrabodies

Hepatitis B virus (HBV) infections represent a global health problem, since these account for 350 million chronic infections worldwide that result in 500,000-700,000 deaths each year. Control of viral replication and HBV-related disease and mortality are of utmost importance. Because the currently available antiviral therapies all have major limitations, new strategies to treat chronic HBV infection are eagerly awaited. Six single-domain antibodies (VHHs) targeting the core antigen of HBV (HBcAg) have been generated and three of these bound strongly to HBcAg of both subtype ayw and adw. These three VHHs were studied as intrabodies directed towards the nucleus or the cytoplasm of a hepatoma cell line that was co-transfected with HBV. A speckled staining of HBcAg was observed in the cytoplasm of cells transfected with nucleotropic VHH intrabodies. Moreover, an increased intracellular accumulation of hepatitis B e antigen (HBeAg) and a complete disappearance of intracellular HBcAg signal were observed with nuclear targeted HBcAg-specific VHHs. These results suggest that HBcAg-specific VHHs targeted to the nucleus affect HBcAg and HBeAg expression and trafficking in HBV-transfected hepatocytes.

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

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.

[Inhibition of in vitro hepatitis B virus replication by lentivirus-mediated short-hairpin RNA against HBx]

BACKGROUNDS/AIMS

Hepatitis B virus (HBV) replicates via RNA intermediates, which could serve as targets for RNA interference (RNAi). Vector-mediated short-hairpin RNA (shRNA) can induce sustained RNAi in comparison to small interfering RNA. Lentiviral vector is known to induce prolonged RNAi with high transduction efficiency. In this study, we sought to test the in vitro efficacy of shRNA delivered by a lentiviral vector in suppressing the replication of HBV.

METHODS

Two shRNA sequences against the hepatitis B viral protein HBx (sh1580 and sh1685) were cloned downstream of the U6 promoter in an HIV-based plasmid to generate third-generation lentiviral vectors. HepAD38 cells were transduced with anti-HBx lentiviral vectors, and HBV replication was induced for 5 days. HBV DNA was isolated and quantified using real-time PCR.

RESULTS

Lentiviral vectors encoding the shRNA against HBV transduced HepAD38 cells with high efficacy. The total intracellular HBV DNA content was significantly reduced by both sh1580 and sh1685 (2.9% and 12.0%, respectively; P<0.05). HBV covalently closed circular DNA (cccDNA) was also suppressed significantly (19.7% and 25.5%, respectively; P<0.05).

CONCLUSIONS

Lentivirus-mediated delivery of shRNA against HBx can effectively suppress the replication of HBV and reduce HBV cccDNA in cell culture systems.

Nucleic acids-based therapeutics in the battle against pathogenic viruses

For almost three decades, researchers have studied the possibility to use nucleic acids as antiviral therapeutics. In theory, compounds such as antisense oligonucleotides, ribozymes, DNAzymes, and aptamers can be designed to trigger the sequence-specific inhibition of particular mRNA transcripts, including viral genomes. However, difficulties with their efficiency, off-target effects, toxicity, delivery, and stability halted the development of nucleic acid-based therapeutics that can be used in the clinic. So far, only a single antisense drug, Vitravene for the treatment of CMV-induced retinitis in AIDS patients, has made it to the clinic. Since the discovery of RNA interference (RNAi), there is a renewed interest in the development of nucleic acid-based therapeutics. Antiviral RNAi approaches are highly effective in vitro and in animal models and are currently being tested in clinical trials. Here we give an overview of antiviral nucleic acid-based therapeutics. We focus on antisense and RNAi-based compounds that have been shown to be effective in animal model systems.

Development of a novel mouse model to evaluate drug candidates against hepatitis B virus

Woodchuck hepatitis virus (WHV)-infected woodchucks have been used for preclinical development of drugs against hepatitis B virus (HBV). However, there is no simple in vivo model to evaluate small amounts of compounds against HBV. To develop such a model, HepAD38 cells, in which HBV replication is regulated by tetracycline (tet), were grown as subcutaneous tumours in nude mice. Mice developing viraemia were then left untreated or given tet in the drinking water. In some of the mice given tet, it was removed and the mice were injected intraperitoneally with phosphate buffer saline (PBS), lamivudine (3TC), clevudine (CLV) or tenofovir dipivoxil fumarate (TDF). Virus DNA titres were measured by real-time PCR during and after drug treatment. In water-fed and PBS-injected mice, virus titres reached approximately 10(9) copies/ml serum within 35 days of HepAD38 injection, whereas in tet-treated mice, virus titres remained at 10(4)-10(5) copies/ml. HBV DNA levels were suppressed by 3TC, TDF and CLV, with the latter two drugs showing more sustained virus suppression compared with 3TC. Combination therapy with CLV plus TDF was much more effective than either drug alone in suppressing virus titre for at least 3 weeks after the end of treatment. There was no demonstrable toxicity to HepAD38 cells in drug-treated mice. Hence, a robust tet-controlled system for HBV replication in vivo was demonstrated, validated with monotherapies against HBV and shown to be useful in assessing combination therapy. This system will be useful for preclinical assessment of small amounts of single or multiple compounds against HBV in vivo.

miR-122, a paradigm for the role of microRNAs in the liver

Recent studies have uncovered profound and unexpected roles for a family of tiny regulatory RNAs, known as microRNAs (miRNAs), in the control of diverse aspects of hepatic function and dysfunction, including hepatocyte growth, stress response, metabolism, viral infection and proliferation, gene expression, and maintenance of hepatic phenotype. In liver cancer, misexpression of specific miRNAs suggests diagnostic and prognostic significance. Here, we review the biology of the most abundant miRNA in human liver, miR-122, and consider the diversity of its roles in the liver. We provide a compilation of all miRNAs expressed in the liver, and consider some possible therapeutic opportunities for exploiting miRNAs in the different settings of liver diseases.

Harnessing the RNA interference pathway to advance treatment and prevention of hepatocellular carcinoma

Primary liver cancer is the fifth most common malignancy in the world and is a leading cause of cancer-related mortality. Available treatment for hepatocellular carcinoma (HCC), the commonest primary liver cancer, is rarely curative and there is a need to develop therapy that is more effective. Specific and powerful gene silencing that can be achieved by activating RNA interference (RNAi) has generated enthusiasm for exploiting this pathway for HCC therapy. Many studies have been carried out with the aim of silencing HCC-related cellular oncogenes or the hepatocarcinogenic hepatitis B virus (HBV) and hepatitis C virus (HCV). Proof of principle studies have demonstrated promising results, and an early clinical trial assessing RNAi-based HBV therapy is currently in progress. Although the data augur well, there are several significant hurdles that need to be overcome before the goal of RNAi-based therapy for HCC is realized. Particularly important are the efficient and safe delivery of RNAi effecters to target malignant tissue and the limitation of unintended harmful non-specific effects.

Antiviral treatment of chronic hepatitis B virus infections: the past, the present and the future

A decade ago, standard therapy against chronic hepatitis B virus infections only consisted of lamivudine or IFN-alpha. Treatment with lamivudine and IFN has been compounded by, respectively, the emergence of drug-resistant virus strains and the appearance of serious side effects. In the last 10 years, hepatitis B treatment has made much progress. Several treatments are now licensed for the treatment of patients with chronic hepatitis B and others are under development. Here, we provide an overview of the potential and mode of action of anti-HBV agents that are currently available, and/or may become available in the near future. Foremost among these newer compounds are adefovir dipivoxil, entecavir and telbivudine.

Molecular therapy and prevention of liver diseases

Molecular analyses have become an integral part of biomedical research as well as clinical medicine. The definition of the molecular and genetic basis of many human diseases has led to a better understanding of their pathogenesis and has in addition offered new perspectives for their diagnosis, therapy and prevention. Genetically, liver diseases can be classified as hereditary monogenic, acquired monogenic, complex genetic and diseases. Based on this classification, gene therapy is based on six concepts: gene repair, gene substitution, cell therapy, block of gene expression or function, DNA vaccination as well as gene augmentation. While recent developments are promising, various delivery, targeting and safety issues need to be addressed before gene therapy will enter clinical practice. In the future, molecular diagnosis and therapy liver diseases will be part of our patient management and complement existing diagnostic, therapeutic and preventive strategies.

Targeting Viral Heart Disease by RNA Interference

Viral heart disease (VHD) is an important clinical disease entity both in pediatric as well as adult cardiology. Coxsackieviruses (CVBs) are considered an important cause for VHD in both populations. VHD may lead to dilated cardiomyopathy and heart failure which can ultimately require heart transplantation. However, no specific treatment modality is so far available. We and others have shown that coxsackieviral replication and cytotoxicity can be successfully targeted by RNA interference, thus leading to increased cell viability and even prolongation of survival in vivo. However, considerable limitations have to be solved before this novel therapeutic approach may enter the clinical trials arena.

RNAi for treating hepatitis B viral infection

Chronic hepatitis B virus (HBV) infection is one of the leading causes of liver cirrhosis and hepatocellular carcinoma (HCC). Current treatment strategies of HBV infection including the use of interferon (IFN)-α and nucleotide analogues such as lamivudine and adefovir have met with only partial success. Therefore, it is necessary to develop more effective antiviral therapies that can clear HBV infection with fewer side effects. RNA interference (RNAi), by which a small interfering RNA (siRNA) induces the gene silence at a post-transcriptional level, has the potential of treating HBV infection. The successful use of chemically synthesized siRNA, endogenous expression of small hairpin RNA (shRNA) or microRNA (miRNA) to silence the target gene make this technology towards a potentially rational therapeutics for HBV infection. However, several challenges including poor siRNA stability, inefficient cellular uptake, widespread biodistribution and non-specific effects need to be overcome. In this review, we discuss several strategies for improving the anti-HBV therapeutic efficacy of siRNAs, while avoiding their off-target effects and immunostimulation. There is an in-depth discussion on the (1) mechanisms of RNAi, (2) methods for siRNA/shRNA production, (3) barriers to RNAi-based therapies, and (4) delivery strategies of siRNA for treating HBV infection.

Downregulation of HBx mRNA in HepG2.2.15 cells by small interfering RNA

OBJECTIVE

Hepatitis B virus (HBV) infection is one of the most prevalent viral infectious diseases in humans. And it is still a challenge for the development of an effective therapy for HBV infection. Recently, the progress in RNA interference (RNAi) has shed some light on the inhibition of HBV expression and replication by RNAi specific for the various genes of the HBV genome. Some prior researches suggests that the HBV x protein (HBx) plays an important role in viral transcription, cell growth, and apoptotic cell death.

METHODS

In the present study, we designed three siRNAs based on the X-protein of HBV sequences and tested their effects on the expression of HBx gene following sorting of siRNA-positive cells. The interference effect was tested in 24, 48, and 72 h. HBsAg in cultured media was assayed using western blot at various days post-transfection. The amount of HBx mRNA was quantitated by Real-time reverse-transcript PCR (RT-PCR).

RESULTS

There was a decrease in the levels of HBV mRNA and HBsAg from the the transfected cells. Among these three siRNAs, siRNA-2 was found to be the most effective at suppressing HBV gene expression.

[RNA interference and its clinical applications]

RNA interference is a type of posttranscriptional gene silencing, when short RNA molecules suppress the function of RNAs and block gene expression. Double-stranded RNAs or short interfering RNAs injected into cells activate the RNA-induced silencing complex which degrades the target messenger RNA. The short RNAs produced inside the cell are called micro RNAs. These form a hairpin and then have the same function as double-stranded RNAs. RNA interference is an evolutionary important mechanism having a role in the protection against transposon and viral infection and regulate gene expression. While a number of studies demonstrate the in vivo applicability of RNAi, the first potential clinical trials are arising. So far it has been used to treat viral infections, inhibit macula degeneration, decrease the level of cholesterol in blood, treat cancer and neurodegenerative diseases. However, its application is hampered by ineffective bioinformatics algorithms unable to design effective short interfering RNAs, by low delivery efficiency and by the limited use to temporary antagonist gene silencing. The most important advantage of its application is the exceptional specificity resulting minimal side-effects. For this reason therapies based on RNA interference can be expected to spread in the near future.

RNA interference and antiviral therapy

RNA interference (RNAi) is an evolutionally conserved gene silencing mechanism present in a variety of eukaryotic species. RNAi uses short double-stranded RNA (dsRNA) to trigger degradation or translation repression of homologous RNA targets in a sequence-specific manner. This system can be induced effectively in vitro and in vivo by direct application of small interfering RNAs (siRNAs), or by expression of short hairpin RNA (shRNA) with non-viral and viral vectors. To date, RNAi has been extensively used as a novel and effective tool for functional genomic studies, and has displayed great potential in treating human diseases, including human genetic and acquired disorders such as cancer and viral infections. In the present review, we focus on the recent development in the use of RNAi in the prevention and treatment of viral infections. The mechanisms, strategies, hurdles and prospects of employing RNAi in the pharmaceutical industry are also discussed.

Opportunities for treating chronic hepatitis B and C virus infection using RNA interference

Activating the RNA interference (RNAi) pathway to achieve silencing of specific genes is one of the most exciting new developments of molecular biology. A particularly interesting use of this technology is inhibition of defined viral gene expression. In this review, we discuss the potential application of RNAi to treatment of chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infection. Globally, these hepatotropic viruses are the most important causes of cirrhosis and liver cancer. Available treatments have their limitations, which makes development of novel effective RNAi-based therapies for HBV and HCV especially significant. Several investigations carried out in vitro and in vivo are summarized, which demonstrate proof of principle that HBV and HCV can be inhibited by RNAi activators. Challenges facing further development of this technology to a stage of clinical application are discussed.

Two approaches to construct mammalian expression vector of shRNA to reduce expression and replication of HBV in vitro

Two approaches have been developed to construct plasmids that mediate RNA interference to inhibit the replication and expression of HBV in 2.2.15 cell. The overlapping PCR extension and restriction enzyme-digestion were used to generate DNA fragments encoding designed shRNA based on sequences of ORF C of HBV genome. The pU6 derived vectors were constructed to develop plasmid based shRNA delivery systems termed pU6/HBVi. There were significant reductions in the expression of HBsAg and HBeAg between cells transfected with pU6/HBVi and control groups (as to HBsAg: P < 0. 01; and HBeAg: P < 0. 01). Consistently, the HBV DNA copies were reduced from 2.71 x 10(7) to <5 x 10(2) copies with or without pU6/HBVi. These results suggested that shRNA delivery by recombinant plasmids harboring shRNA encoding DNA fragment of interest generated either by overlapping PCR extension or restriction enzyme-digestion, could inhibit expressions of viral proteins and reduce viral replications. The pU6 derived plasmids might be a useful shRNA delivery system in mammalian cells. In addition, we found siRNA based on stealth 2311 was a potent RNAi target of HBV genome.

Inhibition of hepatitis B virus replication by shRNAs in stably HBV expressed HEPG2 2.2.15 cell lines

In this study, the effect of RNAi on HBV replication was observed in a cell culture model, HepG2 2.2.15 cell line, which supports human HBV ayw replication and expression. Aim of the study was to investigate effects of shRNAs (small hairpin RNAs) targeting hepatitis B virus mRNAs on the viral replication in HepG2 2.2.15 cells. We selected three target HBV mRNA regions with different putative secondary structures to test whether the secondary structure of RNA may affect the inhibition efficacy on the target HBV RNA. Three HBV-specific siRNAs (small interfering RNA) were designed targeting X (1689-1708), Core (2229-2248) and S (765-784 nt) transcripts. HepG2 2.2.15 cells were transfected with shRNA expressing plasmids, P765, P2229 and P1689 targeting S, core and X region, respectively or a mock plasmid targeting lacZ gene. The culture media was collected throughout six days after transfection and analyzed by real-time PCR. Viral DNA production was suppressed for 7 days. The HBV DNA levels were decreased by 73, 72 and 79% with P765, P2229 and P1689 vectors, respectively. In conclusion, the shRNAs designed for X, core and S regions, specifically and significantly suppressed HBV DNA. siRNAs potentially may be used in treatment of hepatitis B.

Status Presens of Antiviral Drugs And Strategies: Part I: DNA Viruses and Retroviruses

More than 40 compounds have been formally licensed for clinical use as antiviral drugs, and half of these are used for the treatment of HIV infections. The others have been approved for the therapy of herpesvirus (HSV, VZV, CMV), hepadnavirus (HBV), hepacivirus (HCV) and myxovirus (influenza, RSV) infections. New compounds are in clinical development or under preclinical evaluation, and, again, half of these are targeting HIV infections. Yet, quite a number of important viral pathogens (i.e. HPV, HCV, hemorrhagic fever viruses) remain in need of effective and/or improved antiviral therapies.

Stable inhibition of hepatitis B virus expression and replication in HepG2.2.15 cells by RNA interference based on retrovirus delivery

RNA interference (RNAi) of virus-specific genes has emerged as a potential antiviral strategy. In order to suppress hepatitis B virus (HBV) expression and replication, a retrovirus-based RNAi system was developed, which utilized the U6-RNA polymerase III (Pol III) promoter to drive efficient expression and deliver the HBV-specific short hairpin RNAs (shRNAs) in HepG2.2.15 (2215) cells. In this system, the retrovirus vector with a puromycin selection marker was integrated into the host cell genome and allowed stable expression of shRNAs. In Puro-resistant 2215 cells, the levels of both HBV protein and mRNA were dramatically reduced by over 88% and HBV replication was suppressed. The results demonstrated that retrovirus-based RNAi technology will have foreseeable applications both in experimental biology and molecular medicine.

RNA interference for antiviral therapy

Silencing gene expression through a process known as RNA interference (RNAi) has been known in the plant world for many years. In recent years, knowledge of the prevalence of RNAi and the mechanism of gene silencing through RNAi has started to unfold. It is now believed that RNAi serves in part as an innate response against invading viral pathogens and, indeed, counter silencing mechanisms aimed at neutralizing RNAi have been found in various viral pathogens. During the past few years, it has been demonstrated that RNAi, induced by specifically designed double‐stranded RNA (dsRNA) molecules, can silence gene expression of human viral pathogens both in acute and chronic viral infections. Furthermore, it is now apparent that in in vitro and in some in vivo models, the prospects for this technology in developing therapeutic applications are robust. However, many key questions and obstacles in the translation of RNAi into a potential therapeutic platform still remain, including the specificity and longevity of the silencing effect, and, most importantly, the delivery of the dsRNA that induces the system. It is expected that for the specific examples in which the delivery issue could be circumvented or resolved, RNAi may hold promise for the development of gene‐specific therapeutics. Copyright © 2006 John Wiley & Sons, Ltd.

RNA interference with measles virus N, P, and L mRNAs efficiently prevents and with matrix protein mRNA enhances viral transcription

In contrast to studies with genetically modified viruses, RNA interference allows the analysis of virus infections with identical viruses and posttranscriptional ablation of individual gene functions. Using RNase III-generated multiple short interfering RNAs (siRNAs) against the six measles virus genes, we found efficient downregulation of viral gene expression in general with siRNAs against the nucleocapsid (N), phosphoprotein (P), and polymerase (L) mRNAs, the translation products of which form the ribonucleoprotein (RNP) complex. Silencing of the RNP mRNAs was highly efficient in reducing viral messenger and genomic RNAs. siRNAs against the mRNAs for the hemagglutinin (H) and fusion (F) proteins reduced the extent of cell-cell fusion. Interestingly, siRNA-mediated knockdown of the matrix (M) protein not only enhanced cell-cell fusion but also increased the levels of both mRNAs and genomic RNA by a factor of 2 to 2.5 so that the genome-to-mRNA ratio was constant. These findings indicate that M acts as a negative regulator of viral polymerase activity, affecting mRNA transcription and genome replication to the same extent.

RNA interference-mediated prevention and therapy for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fourth leading cause of cancer-related death and is on the increase worldwide. Hepatocellular carcinoma results from chronic liver disease and cirrhosis most commonly associated with chronic hepatitis B (HBV) or hepatitis C (HCV) infection. The highest incidences of HCC are found in China and Africa, where chronic HBV infection is the major risk component. In the United States, Europe and Japan, the significant increase in HCC and HCC-related deaths within the last three decades is mainly attributed to the rise in the number of HCV-infected individuals; smaller increases of HCC are associated with HBV. Given that HCV and HBV infection account for the majority of HCCs, therapeutic and prophylactic approaches to control or eliminate virus infection may prove effective in reducing the occurrence of HCC. Although anti-viral therapies exist for both HBV and HCV infections, they are ineffective for a significant number of patients. In addition, some treatments such as interferon therapy are dose limiting owing to toxic side effects. Clearly, new approaches are needed. RNA interference (RNAi)-based approaches may meet this need and have already shown promising preclinical results in cell culture and animal models. Although this paper focuses on the potential of RNAi as a prophylactic for HCC development, the potential use of RNAi-mediated approaches for HCC therapy will also be discussed.

RNAi-Based Knockdown of HBx mRNA in HBx-Transformed and HBV-Producing Human Liver Cells

RNA interference (RNAi) is the process of sequence-specific gene silencing induced by 21-23-nt RNA of small interfering RNA (siRNA). The HBx of hepatitis B virus (HBV) causing human liver diseases has been known as a multifunctional protein which affects transcription, cell growth, and apoptotic cell death. Here, we demonstrate that the HBx-specific siRNA (siRNAx) and short hairpin RNA (shRNAx) effectively induce the degradation of HBx mRNA in HBx-transformed and HBV-producing human liver cells by up to 80-90%. Also, the HBx expression in HBx-transformed cells was continuously silenced by retransformation with the shRNAx expression vector. These results imply that HBx-driven RNAi, either delivery of siRNAx or expression of shRNAx, provides a promising anti-HBV approach to suppress the HBx expression in human hepatoma cells.

New targets and inhibitors of HBV replication to combat drug resistance

All the approved chemotherapeutic drugs for the treatment of HBV hepatitis are nucleoside analogs targeting on HBV DNA polymerase. Drugs targeting on other viral unique targets are needed. A new class of chemicals with novel action against HBV replication was discovered. A brief description of their mode of action is given.

RNA interference: its use as antiviral therapy

RNA interference (RNAi) is a sequence-specific gene-silencing mechanism that has been proposed to function as a defence mechanism of eukaryotic cells against viruses and transposons. RNAi was first observed in plants in the form of a mysterious immune response to viral pathogens. But RNAi is more than just a response to exogenous genetic material. Small RNAs termed microRNA (miRNA) regulate cellular gene expression programs to control diverse steps in cell development and physiology. The discovery that exogenously delivered short interfering RNA (siRNA) can trigger RNAi in mammalian cells has made it into a powerful technique for generating genetic knock-outs. It also raises the possibility to use RNAi technology as a therapeutic tool against pathogenic viruses. Indeed, inhibition of virus replication has been reported for several human pathogens including human immunodeficiency virus, the hepatitis B and C viruses and influenza virus. We reviewed the field of antiviral RNAi research in 2003 (Haasnoot et al. 2003), but many new studies have recently been published. In this review, we present a complete listing of all antiviral strategies published up to and including December 2004. The latest developments in the RNAi field and their antiviral application are described.

Inhibition of multiple gene expression and virus replication of HBV by stable RNA interference in 2.2.15 cells

BACKGROUND/AIMS

Hepatitis B virus (HBV) infection is a world-wide health problem. Recent studies have demonstrated the efficacy of RNA interference (RNAi) against HBV replication at cell culture and animal levels using transient transfection. The present study was to determine whether the stable transfection of short hairpin RNA (shRNA)-producing vector could achieve potent and sustained inhibition of the HBV replication in 2.2.15 cells.

METHODS

shRNA-producing vector against HBV and the empty vector were stably transfected into the 2.2.15 cells respectively. A series of experiments were performed in the producing stable lines to determine the changes of viral protein expression and replication.

RESULTS

The HBV protein expression and viral replication were suppressed dramatically and stably by the integrated shRNA-producing vectors. Most importantly, this suppression effect persists after 30 passages.

CONCLUSIONS

Our data provided the possibility of continuous and stable inhibition of HBV protein expression and replication in patients using RNAi, suggesting a potential clinical application of this novel approach. Furthermore, the established stable transfected cell lines provided a good platform for understanding the mechanism of anti-HBV by RNAi.

Genomic analysis of anti-hepatitis B virus (HBV) activity by small interfering RNA and lamivudine in stable HBV-producing cells

Hepatitis B virus (HBV) causes acute and chronic hepatitis and hepatocellular carcinoma. Small interfering RNA (siRNA) and lamivudine have been shown to have anti-HBV effects through different mechanisms. However, assessment of the genome-wide effects of siRNA and lamivudine on HBV-producing cell lines has not been reported, which may provide a clue to interrogate the HBV-cell interaction and to evaluate the siRNA's side effect as a potential drug. In the present study, we designed seven siRNAs based on the conserved HBV sequences and tested their effects on the expression of HBV genes following sorting of siRNA-positive cells. Among these seven siRNAs, siRNA-1 and siRNA-7 were found to effectively suppress HBV gene expression. We further addressed the global gene expression changes in stable HBV-producing cells induced by siRNA-1 and siRNA-7 by use of human genome-wide oligonucleotide microarrays. Data from the gene expression profiling indicated that siRNA-1 and siRNA-7 altered the expression of 54 and 499 genes, respectively, in HepG2.2.15 cells, which revealed that different siRNAs had various patterns of gene expression profiles and suggested a complicated influence of siRNAs on host cells. We further observed that 18 of these genes were suppressed by both siRNA-1 and siRNA-7. Interestingly, seven of these genes were originally activated by HBV, which suggested that these seven genes might be involved in the HBV-host cell interaction. Finally, we have compared the effects of siRNA and lamivudine on HBV and host cells, which revealed that siRNA is more effective at inhibiting HBV expression at the mRNA and protein level in vitro, and the gene expression profile of HepG2.2.15 cells treated by lamivudine is totally different from that seen with siRNA.

Inhibition of hepatitis B virus replication by various RNAi constructs and their pharmacodynamic properties

The strategy of RNA interference (RNAi)-based gene silencing has been suggested to have great potential in treating viral diseases. It provides new hope of being able to complement the limited therapeutic options currently available for chronic hepatitis B virus (HBV) infection. To advance such a strategy towards clinical use, the effects of various parameters on the anti-HBV efficiency of RNAi need to be well-defined. In this study, the efficacy and pharmacodynamic properties of different RNAi target sequences and constructs were examined. Several sequences were found to be effective in cell and animal models, achieving inhibition rates of approximately 80-90 %. Methyl-modified small interfering RNA (siRNA) molecules were found to be more stable inside cells than natural siRNA molecules and offered longer-lasting inhibitory effects. Both were effective at rather low doses (an equimolar ratio with HBV preS2-S protein expression vector). Plasmid DNA vectors were less dose-responsive, but their effectiveness in vivo lasted longer, for approximately 1 month. By analysing these different parameters and their possible mechanisms, some important issues in RNAi therapeutics that should assist the future development of clinical applications have been addressed.

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Inhibition of hepatitis viral replication by siRNA

Small interfering RNA (siRNA)-mediated sequence-specific gene silencing is a powerful tool to inhibit endogenous and exogenous gene expression, and it holds great potential to prevent and eradicate viral infection, for which existing therapy is inadequate, such as HIV, hepatitis B virus (HBV) and hepatitis C virus (HCV). A number of studies have documented the effectiveness of siRNA against HBV or HCV at various regions of the viral genome in infected human hepatoma cell lines. Selected siRNA may reduce the production of viral replicons, as well as structural or non-structural proteins by > 90%. Only a few in vivo studies that demonstrated the efficacy of siRNA in the suppression of HBV replication in mice are available. Thus, reliable models of HBV and HCV infection in small animals or non-human primates are needed to evaluate the delivery and efficacy of siRNA as a therapeutic modality for viral hepatitis.

Effective inhibition of HBV replication in vivo by anti-HBx short hairpin RNAs

Exploiting the RNA interference pathway has shown promise for developing novel and effective treatment of hepatitis B virus (HBV) infection. To advance this approach, we analyzed the antiviral efficacy of a panel of 10 Pol III U6 promoter-encoded short hairpin RNAs (shRNAs) that target conserved sequences of the oncogenic HBx open reading frame. To facilitate intracellular processing, the shRNAs included mismatches in the 25-bp stem region and a terminal loop of miRNA-23. Two shRNAs (shRNA 5 and shRNA 6) showed knockdown of HBV markers by 80-100% in transfected hepatocytes and also in a murine hydrodynamic injection model of HBV replication. Intracellular processing of hairpin RNA with the intended strand bias correlated with antiviral efficacy. Moreover, markers of HBV replication were inhibited without inducing genes associated with the nonspecific interferon response. To assess the antiviral efficacy of the shRNAs in a context that is similar to natural HBV infection, shRNA-encoding cassettes were tested against the virus in a HBV transgenic murine model. When delivered using recombinant adenovirus vectors, U6 shRNA 5 and U6 shRNA 6 mediated significant HBV knockdown. Collectively, these observations indicate that U6 shRNA 5 and U6 shRNA 6 are promising candidates for therapy of chronic HBV infection.

Stable inhibition of hepatitis B virus expression and replication by expressed siRNA

RNA interference might be an efficient antiviral therapy for some obstinate illness. Here, we studied the effects of hepatitis B virus (HBV)-specific 21-nt small interfering RNAs (siRNA) on HBV gene expression and replication in 2.2.15 cells. Seven vectors expressing specific hairpin siRNA driven by the RNA polymerase II-promoter were constructed and transfected into 2.2.15 cells. In the cell strain that can stably express functional siRNA, the HBV surface antigen (HBsAg) and the HBV e antigen (HBeAg) secretion into culture media was inhibited by 86% and 91%, respectively, as shown by an enzyme-linked immunosorbent assay. Immunofluorescence and Western blot indicated similar results. HBV DNA was markedly restrained by 3.28-fold, as assessed by the fluorescent quantitation PCR. Moreover, the HBV mRNA was significantly reduced by 80% based on semiquantitative RT-PCR. In conclusion, the specific siRNA can knock down the HBV gene expression and replication in vitro, and the silence effects have no relationship with interferon response.

Stable inhibition of hepatitis B virus proteins by small interfering RNA expressed from viral vectors

BACKGROUND

There has been much research into the use of RNA interference (RNAi) for the treatment of human diseases. Many viruses, including hepatitis B virus (HBV), are susceptible to inhibition by this mechanism. However, for RNAi to be effective therapeutically, a suitable delivery system is required.

METHODS

Here we identify an RNAi sequence active against the HBV surface antigen (HBsAg), and demonstrate its expression from a polymerase III expression cassette. The expression cassette was inserted into two different vector systems, based on either prototype foamy virus (PFV) or adeno-associated virus (AAV), both of which are non-pathogenic and capable of integration into cellular DNA. The vectors containing the HBV-targeted RNAi molecule were introduced into 293T.HBs cells, a cell line stably expressing HBsAg. The vectors were also assessed in HepG2.2.15 cells, which secrete infectious HBV virions.

RESULTS

Seven days post-transduction, a knockdown of HBsAg by approximately 90%, compared with controls, was detected in 293T.HBs cells transduced by shRNA encoding PFV and AAV vectors. This reduction has been observed up to 5 months post-transduction in single cell clones. Both vectors successfully inhibited HBsAg expression from HepG2.2.15 cells even in the presence of HBV replication. RT-PCR of RNA extracted from these cells showed a reduction in the level of HBV pre-genomic RNA, an essential replication intermediate and messenger RNA for HBV core and polymerase proteins, as well as the HBsAg messenger RNA.

CONCLUSIONS

This work is the first to demonstrate that delivery of RNAi by viral vectors has therapeutic potential for chronic HBV infection and establishes the ground work for the use of such vectors in vivo.

The therapeutic potential of RNA interference

In recent years, we have witnessed the discovery of a new mechanism of gene regulation called RNA interference (RNAi), which has revitalized interest in the development of nucleic acid‐based technologies for therapeutic gene suppression. This review focuses on the potential therapeutic use of RNAi, discussing the theoretical advantages of RNAi‐based therapeutics over previous technologies as well as the challenges involved in developing RNAi for clinical use. Also reviewed, are the in vivo proof‐of principle experiments that provide the preclinical justification for the continued development of RNAi‐based therapeutics.

Inhibition of coxsackievirus B3 replication by small interfering RNAs requires perfect sequence match in the central region of the viral positive strand

Coxsackievirus B3 (CVB3) is the most common causal agent of viral myocarditis, but existing drug therapies are of limited value. Application of small interfering RNA (siRNA) in knockdown of gene expression is an emerging technology in antiviral gene therapy. To investigate whether RNA interference (RNAi) can protect against CVB3 infection, we evaluated the effects of RNAi on viral replication in HeLa cells and murine cardiomyocytes by using five CVB3-specific siRNAs targeting distinct regions of the viral genome. The most effective one is siRNA-4, targeting the viral protease 2A, achieving a 92% inhibition of CVB3 replication. The specific RNAi effects could last at least 48 h, and cell viability assay revealed that 90% of siRNA-4-pretreated cells were still alive and lacked detectable viral protein expression 48 h postinfection. Moreover, administration of siRNAs after viral infection could also effectively inhibit viral replication, indicating its therapeutic potential. Further evaluation by combination found that no enhanced inhibitory effects were observed when siRNA-4 was cotransfected with each of the other four candidates. In mutational analysis of the mechanisms of siRNA action, we found that siRNA functions by targeting the positive strand of virus and requires a perfect sequence match in the central region of the target, but mismatches were more tolerated near the 3' end than the 5' end of the antisense strand. These findings reveal an effective target for CVB3 silencing and provide a new possibility for antiviral intervention.

Combination of small interfering RNAs mediates greater inhibition of human hepatitis B virus replication and antigen expression

OBJECTIVES

To evaluate the inhibitory effect mediated by combination of small interfering RNAs (siRNAs) targeting different sites of hepatitis B virus (HBV) transcripts on the viral replication and antigen expression in vitro.

METHODS

(1) Seven siRNAs targeting surface (S), polymerase (P) or precore (PreC) region of HBV genome were designed and chemically synthesized. (2) HBV-producing HepG2.2.15 cells were treated with or without siRNAs for 72 h. (3) HBsAg and HBeAg in the cell culture medium were detected by enzyme-linked immunoadsorbent assay. (4) Intracellular viral DNA was quantified by real-time PCR (Polymerase Chain Reaction). (5) HBV viral mRNA was reverse transcribed and quantified by real-time PCR. (6) The change of cell cycle and apoptosis was determined by flow cytometry.

RESULTS

Our data demonstrated that synthetic small interfering RNAs (siRNAs) targeting S and PreC gene could efficiently and specifically inhibit HBV replication and antigen expression. The expression of HBsAg and HBeAg and the replication of HBV could be specifically inhibited in a dose-dependent manner by siRNAs. Furthermore, our results showed that the combination of siRNAs targeting various regions could inhibit HBV replication and antigen expression in a more efficient way than the use of single siRNA at the same final concentration. No apoptotic change was observed in the cell after siRNA treatment.

CONCLUSION

Our results demonstrated that siRNAs exerted robust and specific inhibition on HBV replication and antigen expression in a cell culture system and combination of siRNAs targeting different regions exhibited more potency.

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