Inhibition of hepatitis B virus expression and replication by RNA interference

Curcumin inhibits hepatitis B virus via down-regulation of the metabolic coactivator PGC-1alpha

Hepatitis B virus (HBV) infects the liver and uses its cell host for gene expression and propagation. Therefore, targeting host factors essential for HBV gene expression is a potential anti-viral strategy. Here we show that treating HBV expressing cells with the natural phenolic compound curcumin inhibits HBV gene expression and replication. This inhibition is mediated via down-regulation of PGC-1alpha, a starvation-induced protein that initiates the gluconeogenesis cascade and that has been shown to robustly coactivate HBV transcription. We suggest curcumin as a host targeted therapy for HBV infection that may complement current virus-specific therapies.

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.

Silencing Fas-associated phosphatase 1 expression enhances efficiency of chemotherapy for colon carcinoma with oxaliplatin

AIM: To investigate whether silencing Fas-associated phosphatase 1 (FAP-1) expression enhances the efficiency of chemotherapy for colon carcinoma with oxaliplatin.

METHODS: Expression of FAP-1 in mRNA and protein was detected by reverse transcription polymerase chain reaction (RT-PCR) and flow cytometry. Small interfering RNA (siRNA) was designed according to the FAP-1 mRNA sequence. Cell proliferation was evaluated by methyl thiazolyl tetrazolium (MTT) assay. Anenxin V- and propidine iodine (PI) were assayed by flow cytometry for the detection of apoptosis.

RESULTS: The expression of FAP-1 was increased in SW480 cells after chemotherapy with oxaliplatin. Transfection of FAP-1 siRNA into SW480 cells silenced the expression of FAP-1 and consequently abolished the inhibitory function of Fas/FasL-mediated apoptosis pathway, thus increasing the efficacy of chemotherapy for colon carcinoma with oxaliplatin.

CONCLUSION: RNA interference combined with conventional chemotherapy is more effective against colon cancer.

The "Trojan horse" model-delivery of anti-HBV small interfering RNAs by a recombinant HBV vector

Hepatitis B virus (HBV) is a small virus that infects the liver. The major obstacle in applying the RNA interference method as an anti-HBV weapon is the challenge to deliver the small interfering RNA molecules to the liver efficiently and specifically. Here we show that HBV-specific short hairpin RNAs (shRNAs) are efficiently expressed from a recombinant HBV into which an shRNA-expressing cassette was inserted, resulting in a significant knock-down of HBV gene expression. Notably, this recombinant HBV still expresses the HBV Core protein, which is targeted by the shRNAs produced by the same vector. Our results set the stage for further use of this recombinant HBV virus with the potential to function as a "Trojan horse"; one that specifically targets the liver and uses the resident virus as an helper for its own propagation, and at the same time eliminate itself and the resident HBV by knocking-down their gene expression.

Hepatitis B virus inhibition in mice by lentiviral vector mediated short hairpin RNA

BACKGROUND

Chronic hepatitis B virus (HBV) infection is an important cause of cirrhosis and hepatocellular carcinoma. The major challenges for current therapies are the low efficacy of current drugs and the occurrence of drug resistant HBV mutations. RNA interference (RNAi) of virus-specific genes offers the possibility of developing a new anti-HBV therapy. Recent reports have shown that lentiviral vectors based on HIV-1 are promising gene delivery vehicles due to their ability to integrate transgenes into non-dividing cells. Herein, a lentivirus-based RNAi system was developed to drive expression and delivery of HBV-specific short hairpin RNA (shRNA) in a mouse model for HBV replication.

METHODS

Hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) in the sera of the mice were analyzed by quantitative sandwich enzyme linked immunosorbent assay (ELISA) technique, hepatitis B core antigen (HBcAg) and HBsAg in the livers of the mice were detected by immunohistochemical assay, HBV DNA and HBV mRNA were measured by fluorogenic quantitative polymerase chain reaction (FQ-PCR) and quantitative real-time PCR respectively.

RESULTS

Co-injection of HBV plasmids together with the lentivirus targeting HBV shRNA induced an RNAi response. Secreted HBsAg was reduced by 89% in mouse serum, and HBeAg was also significantly inhibited, immunohistochemical detection of HBcAg or HBsAg in the liver tissues also revealed substantial reduction. Lentiviral mediated shRNA caused a significant suppression in the levels of viral mRNA and DNA synthesis compared to the control group.

CONCLUSION

Lentivirus-based RNAi can be used to suppress HBV replication in vivo, it might become a potential therapeutic strategy for treating HBV and other viral infections.

Involvement of mitochondrial permeability transition in hepatitis B virus replication

The HBx protein of human hepatitis B virus (HBV) activates a calcium-dependent kinase pathway which is essential for the viral replication. In this study, we found that HBx expression in the absence of other HBV proteins and in the context of HBV replication decreased the mitochondrial calcein-AM/CoCl(2) signals by 10% and 14% in HepG2 cells and by 15% and 10% in Huh7 cells, respectively. This indicates that HBx can induce mitochondrial permeability transition (MPT) and cause calcium effusion into the plasma. In addition, RNA interference of Cylophilin D decreased HBx-induced MPT and suppressed HBV DNA replication by 41% in HepG2 cells. Our results suggest that HBx expression can induce MPT and facilitate HBV DNA replication.

[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.

RNA interference targeted to the conserved dimerization initiation site (DIS) of HIV-1 restricts virus escape mutation

Short hairpin RNAs (shRNA) targeting viral or cellular genes can effectively inhibit human immunodeficiency virus type 1 (HIV-1) replication. This inhibition, however, may induce mutations in the targeted gene, leading to rapid escape from the shRNA-induced inhibition. We generated a lymphoid cell line that stably expressed a 19-bp shRNA targeting a well-conserved dimerization initiation site (DIS) of HIV-1, which strongly inhibited viral replication, thereby delaying virus escape. Furthermore, treatment of HIV-1 infection with DIS- and vif-shRNA combination therapy resulted in superior anti-viral responses compared to vif-shRNA monotherapy. Continuous challenge with HIV-1, however, generated virus mutants that could overcome the RNA interference restriction. Such anti-genes may be promising tools for HIV-1 gene therapy for HIV/acquired immunodeficiency syndrome.

Research progress of RNA interference in anti-infection of hepatitis B virus

RNA interference (RNAi) can specifically suppress the expression of genes, and it is the most effective gene-silencing technique. Both in vivo and in vitro researches have approved the effect of RNAi on hepatitis B virus (HBV) infection. In recent years, multiple researches have been launched on selection of target sequences of small interfering RNA (siRNA), application of chemical modification, and selection of transduction method, short hairpin RNA (shRNA) vector and combination strategies. In this paper, we briefly review the advances of RNAi in anti-HBV infection.

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

Hepatitis B virus (HBV) covalently closed circular (CCC) DNA is the source of HBV transcripts and persistence in chronically infected patients. The novel aspect of this study was to determine the effect of RNA interference (RNAi) on HBV CCC DNA when administered prior to establishment of HBV replication or during chronic HBV infection. HBV replication was initiated in HepG2 cells by transduction with HBV baculovirus. Subculture of HBV-expressing HepG2 cells at 10 days post-transduction generates a system in which HBV replication is ongoing and HBV is expressed largely from CCC DNA, thus simulating chronic HBV infection. HepG2 cells were transduced with short hairpin RNA (shRNA)-expressing baculovirus prior to initiation of HBV replication or during chronic HBV replication, and the levels of HBV RNA, HBV surface antigens (HBsAg) and replicative intermediates (RI), extracellular (EC) and CCC DNA species were measured. HBsAg, HBV RNA and DNA levels were markedly reduced until day 8 whether cells were transduced with shRNA prior to or during a chronic infection; however, the CCC DNA species were only affected when shRNA was administered prior to initiation of infection. We conclude that RNAi may have a therapeutic value for controlling HBV replication at the level of RI and EC DNA and for reducing establishment of CCC DNA during HBV infection. Our data support previous findings demonstrating the stability of HBV CCC DNA following antiviral therapy. This study also reports the development of a novel HBV baculovirus subculture system that can be used to evaluate antiviral effects on chronic HBV replication.

Comparative study of anti-hepatitis B virus RNA interference by double-stranded adeno-associated virus serotypes 7, 8, and 9

Using a hepatitis B virus (HBV) transgenic mouse model, we previously showed that a single dose of double-stranded adeno-associated virus (dsAAV) vector serotype 8 carrying a small hairpin RNA (shRNA) effectively reduces HBV replication and gene expression, but the effect gradually decreases with time. In this report, we compared the anti-HBV RNA interference (RNAi) effect of dsAAV8 with those of dsAAV7 and dsAAV9, two other hepatotropic AAV vectors, and examined whether the sequential use of these heterologous AAV vectors could prolong the anti-HBV effect. Our results showed that shRNA delivered by each of the three dsAAV vectors profoundly reduced the serum HBV titer and liver HBV mRNA and DNA levels in the transgenic mice for up to 22 weeks, with dsAAV8 having the greatest inhibitory effect, followed by dsAAV9 and dsAAV7. The potency of dsAAV8 correlated with the presence of higher levels of vector DNA and anti-HBV shRNA in the liver. An in vivo cross-administration experiment showed that preexisting anti-AAV8 antibody completely blocked the anti-HBV RNAi effect of dsAAV8, but had no effect on the potency of dsAAV7 and dsAAV9. Moreover, we demonstrated that a longer anti-HBV effect could be achieved by the sequential use of dsAAV8 and dsAAV9. These results indicate that effective and persistent HBV suppression might be achieved by a combination of the power of RNAi silencing effect and multiple treatments with different AAV serotypes.Molecular Therapy (2009) 17 2, 352-359 doi:10.1038/mt.2008.245.

Advance in the mouse model of hepatitis B virus infection

Hepatitis B virus (HBV) infection is a major worldwide healthy problem and now the virus and the virus-caused diseases have been known deeply. However, due to lack of a practical and convenient animal model, the study of HBV biology and the therapeutic development of HBV infection are still at a low level. As a common species used in laboratory, mice are studied most and the genetic and immune system are clearly understood. In this paper, we briefly describes the mouse models currently available in HBV.

Inhibition of woodchuck hepatitis virus gene expression in primary hepatocytes by siRNA enhances the cellular gene expression

Small interfering RNA (siRNA) has been shown to be active to inhibit the hepatitis B virus gene expression and replication in transient and stable transfection systems. Here in primary hepatocytes prepared from naturally woodchuck hepatitis virus (WHV)-infected woodchucks, four siRNAs targeting the WHV preS1, S, C, and X region led to a depletion of WHV transcripts and replicative intermediates with different kinetics and a decreased production of viral particles. Two siRNAs targeting WHV S and X region had the highest efficacy to deplete 70% of WHV transcripts and replicative intermediates. In addition, siRNA-mediated suppression of WHV enhanced the expression of cellular genes like MxA and MHC I. Specific siRNAs are able to inhibit the hepadnaviral replication and enhance the expression of cellular genes relevant for antiviral actions. Thus, siRNAs might be useful as novel antiviral agents for the treatment of chronic HBV infection.

Hypoxia-inducible enhancer/alpha-fetoprotein promoter-driven RNA interference targeting STK15 suppresses proliferation and induces apoptosis in human hepatocellular carcinoma cells

STK15 (Aurora A/BTAK) is an oncogenic serine/threonine kinase that plays a role in centrosome separation and in the formation of the mitotic bipolar spindle. It is highly expressed and constitutively activated in various human tumors including hepatocellular carcinoma (HCC). To investigate its possibility as a molecular target for future therapies directed against hepatocellular carcinoma, we constructed a tissue-specific RNA interference (RNAi) system mediated by hypoxia-inducible (HI) enhancer/alpha-fetoprotein (AFP) promoter and employed it to downregulate exogenous reporters (LUC and EGFP) and endogenous STK15 gene expression and analyzed the phenotypical changes in HCC cells. Results showed that the expression of exogenous reporters (LUC and EGFP) was specifically downregulated in hepatoma cells but not in non-hepatoma cells. Moreover, the specific downregulation of STK15 expression in hepatocellular carcinoma cells (HepG2) significantly inhibited in vitro cellular proliferation and in vivo tumorigenicity. Furthermore, we also found that the downregulation of STK15 expression led to cell arrest in the G(2)/M phase and finally apoptosis induction of HepG2 cells. Thus, the HI enhancer/AFP promoter-mediated RNAi targeting STK15 may be a potential therapeutic strategy for the treatment of hepatocellular carcinoma with tumor specificity and high efficacy.

Inhibition of the replication of feline immunodeficiency virus by lentiviral vector-mediated RNA interference in feline cell lines

RNA interference (RNAi) is a sequence-specific RNA degradation process. To inhibit feline immunodeficiency virus (FIV) replication by RNAi, we generated a lentiviral vector expressing a short hairpin RNA (shRNA) that targeted the gag gene of FIV (shGag). shGag transfer significantly inhibited viral replication in cell lines that were chronically infected with FIV, i.e., the 3201/UK8 low, 3201/UK8 high, FL4, and CRFK/FIV cell lines. Moreover, 3201 cells were transduced with the lentiviral vectors and then inoculated with FIV. Although the amount of FIV proviral DNA in shGag-transduced cells was similar to that in the cells transduced with unrelated shRNA or mock-transduced cells, the amount of reverse transcriptase (RT) activity was significantly reduced in the culture supernatant of shGag-expressing cells from 15 to 27 days after inoculation. Thirty days after inoculation, no significant difference was observed in the RT activities but virus with a mutation in the target region of shGag was detected in approximately 21% of the replicated viruses. Therefore, abolishment of the silencing effect of shGag may be due to reasons other than the emergence of escape mutants. These results are useful for developing an RNAi-based gene therapy strategy for controlling FIV infection.

Inhibition of hepatitis C virus infection and expression in vitro and in vivo by recombinant adenovirus expressing short hairpin RNA

BACKGROUND AND AIM

We have reported previously that synthetic small interfering RNA (siRNA) and DNA-based siRNA expression vectors efficiently and specifically suppress hepatitis C virus (HCV) replication in vitro. In this study, we investigated the effects of the siRNA targeting HCV-RNA in vivo.

METHODS

We constructed recombinant retrovirus and adenovirus expressing short hairpin RNA (shRNA), and transfected into replicon-expressing cells in vitro and transgenic mice in vivo.

RESULTS

Retroviral transduction of Huh7 cells to express shRNA and subsequent transfection of an HCV replicon into the cells showed that the cells had acquired resistance to HCV replication. Infection of cells expressing the HCV replicon with an adenovirus expressing shRNA resulted in efficient vector delivery and expression of shRNA, leading to suppression of the replicon in the cells by approximately 10(-3). Intravenous delivery of the adenovirus expressing shRNA into transgenic mice that can be induced to express HCV structural proteins by the Cre/loxP switching system resulted in specific suppression of virus protein synthesis in the liver.

CONCLUSION

Taken together, our results support the feasibility of utilizing gene targeting therapy based on siRNA and/or shRNA expression to counteract HCV replication, which might prove valuable in the treatment of hepatitis C.

Inhibition of hepatitis B virus gene expression and replication by artificial microRNA

AIM: To investigate the inhibitory effects of hepatitis B virus (HBV) replication and expression by transfecting artificial microRNA (amiRNA) into HepG2.2.15 cells.

METHODS: Three amiRNA-HBV plasmids were constructed and transfected into HepG2.2.15 cells. HBV antigen secretion was detected in the cells with transient and stable transfection by time-resolved fluoroimmunoassays (TRFIA). HBV DNA replication was examined by fluorescence quantitative PCR, and the level of HBV S mRNA was measured by semi-quantitative RT-PCR.

RESULTS: The efficiency of transient transfection of the vectors into 2.2.15 cells was 55%-60%. All the vectors had significant inhibition effects on HBsAg and HBeAg at 72 h and 96 h after transfection (P < 0.01 for all). The secretion of HBsAg and HBeAg into the supernatant was inhibited by 49.8% ± 4.7% and 39.9% ± 6.7%, respectively, at 72 h in amiRNA-HBV-S608 plasmid transfection group. The copy of HBV DNA within culture supernatant was also significantly decreased at 72 h and 96 h after transfection (P < 0.01 for all). In the cells with stable transfection, the secretion of HBsAg and HBeAg into the supernatant was significantly inhibited in all three transfection groups (P < 0.01 for all, vs negative control). The copies of HBV DNA were inhibited by 33.4% ± 3.0%, 60.8% ± 2.3% and 70.1% ± 3.3%, respectively.

CONCLUSION: In HepG2.2.15 cells, HBV replication and expression could be inhibited by artificial microRNA targeting the HBV S coding region. Vector-based artificial microRNA could be a promising therapeutic approach for chronic HBV infection.

Inhibition of hepatitis B virus replication by small interference RNA induces expression of MICA in HepG2.2.15 cells

Hepatitis B virus (HBV) replicates in most tumor tissues of patients with HBV-associated hepatocellular carcinoma (HCC). In the present study, we have shown that the expression of HBV in the HCC cell lines, HepG2 and Huh7, down-regulated the expression of MHC class I-related molecule A (MICA), a ligand of the NKG2D receptor. Inhibition of HBV expression by small interference RNAs (siRNAs) in HepG2.2.15, a cell line that constitutively expresses HBV, induced up-regulation of MICA. The up-regulation of MICA increased the lysis of HepG2.2.15 cells by NK cells. Our results suggest that HBV compromises the innate immune system in HCC patients and that inhibition of HBV replication by siRNAs may enhance the antitumor immune response.

Inhibition of foot-and-mouth disease virus replication in vitro and in vivo by small interfering RNA

By using bioinformatics computer programs, all foot-and-mouth disease virus (FMDV) genome sequences in public-domain databases were analyzed. Based on the results of homology analysis, 2 specific small interfering RNA (siRNA) targeting homogenous 3D and 2B1 regions of 7 serotypes of FMDV were prepared and 2 siRNA-expression vectors, pSi-FMD2 and pSi-FMD3, were constructed. The siRNA-expressing vectors were used to test the ability of siRNAs to inhibit virus replication in baby hamster kidney (BHK-21) cells and suckling mice, a commonly used small animal model. The results demonstrated that transfection of BHK-21 cells with siRNA-expressing plasmids significantly weakened the cytopathic effect (CPE). Moreover, BHK-21 cells transiently transfected with short hairpin RNA (shRNA)-expressing plasmids were specifically resistant to the infection of the FMDV serotypes A, O, and Asia I and this the antiviral effects persisted for almost 48 hours. We measured the viral titers, the 50% tissue culture infective dose (TCID₅₀) in cells transfected with anti-FMDV siRNAs was found to be lower than that of the control cells. Furthermore, subcutaneous injection of siRNA-expressing plasmids in the neck of the suckling mice made them less susceptible to infection with O, and Asia I serotypes of FMDV.

Combination of small interfering RNAs mediates greater suppression on hepatitis B virus cccDNA in HepG2.2.15 cells

AIM: To observe the inhibition of hepatitis B virus (HBV) replication and expression in HepG2.2.15 cells by combination of small interfering RNAs (siRNAs).

METHODS: Recombinant plasmid psil-HBV was constructed and transfected into HepG2.2.15 cells. At 48 h, 72 h and 96 h after transfection, culture media were collected and cells were harvested for HBV replication assay. HBsAg and HBeAg in the cell culture medium were detected by enzyme-linked immunoadsorbent assay (ELISA). Intracellular viral DNA and covalently closed circular DNA (cccDNA) were quantified by real-time polymerase chain reaction (PCR). HBV viral mRNA was reverse transcribed and quantified by reverse-transcript PCR (RT-PCR).

RESULTS: siRNAs showed marked anti-HBV effects. siRNAs could specifically inhibit the expression of HBsAg and the replication of HBV DNA in a dose-dependent manner. Furthermore, combination of siRNAs, compared with individual use of each siRNA, exerted a stronger inhibition on antigen expression and viral replication. More importantly, combination of siRNAs significantly suppressed HBV cccDNA amplification.

CONCLUSION: Combination of siRNAs mediates a stronger inhibition on viral replication and antigen expression in HepG2.2.15 cells, especially on cccDNA amplification.

Application of adenoviral vector in biotherapy for hepatitis B virus infection

Hepatitis B virus (HBV) infection is a worldwide public health problem. Especially in China about 120 million are estimated to be HBV chronic carriers. For those infected with HBV, there has been no curable treatment. However, biotherapy provides a new clue for future treatment. An appropriate vector is the essential factor in determining efficiency of biotherapy. Owe to its own properties, Adenoviral vector has gained increasing interest in the biotherapy of HBV infection resently. This review focused on the progress in the biotherapy of HBV infection using adenoviral vector.

siRNA pool targeting different sites of human hepatitis B surface antigen efficiently inhibits HBV infection

The main objective was to determine whether a pool of small interfering RNAs (siRNAs) targeting different regions of hepatitis B virus surface antigen (HBsAg) efficiently inhibits hepatitis B virus (HBV) infection. siRNAs targeting different regions of HBsAg were transfected into HBV-producing HepG2.2.15 cells and at 72 h post-transfection, the culture medium was collected for ELISA to determine HBsAg, while total RNA was isolated from the cells for real-time PCR. Three siRNA sequences that efficiently inhibited HBV infection were converted into small hairpin RNAs (shRNAs) and then cloned into a single plasmid psiSTRIKE driven by a single U6 promoter. These shRNA expressing plasmids were tested for HBsAg gene silencing in HepG2.2.15 cells. A pool of siRNAs targeting HBsAg efficiently inhibited HBV replication and antigen expression when transfected into HepG2.2.15 cells, compared with the use of single siRNA. Similarly, the plasmid encoding three different shRNAs driven by a single U6 promoter was more effective in silencing HBsAg at DNA, mRNA and protein levels compared with the plasmid encoding single shRNA. No apoptotic change was observed in the cells when the plasmid was transfected at a dose of 0.5-2 microg/1 x 10(6) cells after complex formation with Lipofectamine LTX. Furthermore, transfection with siRNA or shRNA did not increase interferon-gamma (IFNs-gamma) release, suggesting no induction of IFN response. In conclusion, a pool of chemically synthesised siRNAs as well as the shRNA expression plasmid encoding multiple shRNAs targeting different regions of HBsAg showed high gene silencing in HepG2.2.15 cells.

Long-term suppression of hepatitis B virus replication by short hairpin RNA expression using the scaffold/matrix attachment region-based replicating vector system pEPI-1

Since the emergence of viral resistance of hepatitis B virus (HBV) during treatment is becoming an important issue even with newer drugs, there is a need for alternative treatment options such as, for example, RNA interference (RNAi) technology. While short-term suppression of HBV replication is easily achieved with small interfering RNA oligonucleotides, this is not the case for long-term suppression due to the lack of an optimal vector system. Based on the nonviral scaffold/matrix attachment region (S/MAR)-based vector system pEPI-1, which is free of common side effects and is stably retained as an episome even in the absence of selection, we designed a short hairpin RNA (shRNA) expression vector called pEPI-RNAi for HBV suppression. HBV-replicating HepG2.2.15 cells were transfected with pEPI-RNAi, and the intracellular status of the plasmid was followed by PCR and Southern analysis. HBV replication was measured on the DNA, RNA, and protein level. HBV RNA expression was reduced by almost 85% 3 months posttransfection with pEPI-RNAi. At 8 months posttransfection in the absence of antibiotic selection pressure, the suppression level was still 70% and the vector was retained as an episome. The reduction of total intracellular HBV DNA at this point was 77%, showing a marked suppression of HBV DNA replication. At a comparable level, secretion of viral antigens, as well as progeny HBV virions, was inhibited. The S/MAR-based vector system pEPI-1 allows long-term suppression of HBV replication by the expression of suitable shRNAs. Due to its unique properties compared to commonly used vectors, it provides an interesting option for the treatment of chronically HBV-infected individuals.

Vector design for liver-specific expression of multiple interfering RNAs that target hepatitis B virus transcripts

RNA interference (RNAi) is a process that can target intracellular RNAs for degradation in a highly sequence-specific manner, making it a powerful tool that is being pursued in both research and therapeutic applications. Hepatitis B virus (HBV) is a serious public health problem in need of better treatment options, and aspects of its life cycle make it an excellent target for RNAi-based therapeutics. We have designed a vector that expresses interfering RNAs that target HBV transcripts, including both viral RNA replicative intermediates and mRNAs encoding viral proteins. Our vector design incorporates many features of endogenous microRNA (miRNA) gene organization that are proving useful for the development of reagents for RNAi. In particular, our vector contains an RNA pol II driven gene cassette that leads to tissue-specific expression and efficient processing of multiple interfering RNAs from a single transcript, without the co-expression of any protein product. This vector shows potent silencing of HBV targets in cell culture models of HBV infection. The vector design will be applicable to silencing of additional cellular or disease-related genes.

Expressed anti-HBV primary microRNA shuttles inhibit viral replication efficiently in vitro and in vivo

The use of RNA interference (RNAi) to inhibit gene expression is potentially applicable in the treatment of viral infections such as hepatitis B virus (HBV) persistence. Although efficient HBV gene silencing by short hairpin RNA (shRNA) expressed from RNA polymerase (Pol) III promoters has been reported, constitutive high-level transcription may cause harmful side effects. Here, we report an approach that allows the use of a Pol II promoter to improve transcription regulation of expressed RNAi effecters. Pol II [cytomegalovirus (CMV)] or Pol III (U6) promoter cassettes that transcribe anti-HBV primary microRNA (pri-miR)-122 and pri-miR-31 shuttles were generated. In cultured cells both types of pri-miR-like sequences effected knockdown of markers of viral replication (>80%) and were processed to form intended 21-nucleotide guides. The concentration of CMV-expressed miRs was approximately 85-fold lower than the U6 shRNA-derived guide RNA. When cells were co-transfected with pri-miR expression cassettes, attenuation of independent RNAi-mediated gene silencing was not observed, which is in contrast to the action of U6 shRNA expression cassettes. The efficacy of the anti-HBV pri-miR shuttles in vivo was verified using the murine hydrodynamic injection model. Employing Pol II-expressed pri-miR mimics may be useful in the treatment of HBV infection, and potentially also for generic application in RNAi-based therapy.

Inhibition of hepatitis B virus gene expression and replication by endoribonuclease-prepared siRNA

Endoribonuclease-prepared siRNA (esiRNA) is an alternative tool to chemical synthetic siRNA for gene silencing. Since esiRNAs are directed against long target sequences, the genetic variations in the target sequences will have little influence on their effectiveness. The ability of esiRNAs to inhibit hepatitis B virus (HBV) gene expression and replication was tested. EsiRNAs targeting the coding region of HBV surface antigen (HBsAg) and the nucleocapsid (HBcAg) inhibited specifically the expression of HBsAg and HBcAg when cotransfected with the respective expression plasmids. Both esiRNAs reduced the HBV transcripts and replication intermediates in transient transfected cells and cells with HBV genomes integrated stably. Compared with synthetic siRNA, esiRNA targeting HBsAg was less effective than the selected synthetic siRNA in terms of the inhibition of HBV gene expression and replication. However, while the ability of synthetic siRNAs for specific gene silencing was impaired strongly by the nucleotide substitutions within the target sequences. The efficiency of gene silencing by esiRNAs was not influenced by sequence variation. The transfection of esiRNA did not induce interferon-stimulated genes (ISGs) like STAT1 and ISG15, indicating the absence of off-target effects. In general, esiRNAs strongly inhibited HBV gene expression and replication and may have an advantage against HBV strains which are variable genetically.

In vitro effects of a novel nucleoside analog beta-LPA against hepatitis B virus

AIM: To explore the in vitro effects of a novel nucleoside analog (β-LPA) against hepatitis B virus (HBV).

METHODS: HepG2.2.2.15 cells were cultured and treated with various concentrations of β-LPA. Serum HBsAg and HBeAg were determined by enzyme-linked immunosorbent assay (ELISA). Intracelluar DNA was extracted and subjected to Southern blotting, hybridized with ³²P-labeled HBV probe and autoradiographed. The intensity of the autoradiographic bands was quantified by densitometric scans of computer and ED₅₀ value was calculated. Cytotoxicity with different concentrations of drugs was examined by methyl thiazolyl tetrazolium (MTT) method and ID₅₀ value was calculated.

RESULTS: Autoradiographic bands showed that β-LPA inhibited the replication of HBV DNA in a dose-dependent manner. ED₅₀ value was 0.01 μmol/L. Cytotoxicity experiment showed that the ID₅₀ value of β-LPA was 50 μmol/L. The contents of HBsAg and HBeAg were decreased in a concentration-dependent manner. β-LPA at a low concentration had no marked effect on HBsAg and HBeAg in supernate.

CONCLUSION: β-LPA possesses potent inhibitory effect on the replication of HBV in vitro with little cytotoxicity.

Yap1 phosphorylation by c-Abl is a critical step in selective activation of proapoptotic genes in response to DNA damage

Cells undergo apoptosis upon exposure to severe DNA damage stress. Under this condition, p73 is phosphorylated and activated by c-Abl. The transcription coactivator Yap1 binds p73 to generate a complex that escapes p73 proteasomal degradation and recruits p300 to support transcription of proapoptotic genes. However, the mechanism of selective activation of proapoptotic genes by Yap1 remained unclear. In this study, we show that c-Abl directly phosphorylates Yap1 at position Y357 in response to DNA damage. Tyrosine-phosphorylated Yap1 is a more stable protein that displays higher affinity to p73 and selectively coactivates p73 proapoptotic target genes. Furthermore, we show that Yap1 switches between p73-mediated proapoptotic and growth arrest target genes based on its phosphorylation state. Thus, our data demonstrate that modification of a transcription coactivator, namely the DNA damage-induced phosphorylation of Yap1 by c-Abl, influences the specificity of target gene activation.

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.

Progressive changes in hepatoma cells stably transfected with hepatitis B virus X gene

OBJECTIVE

The aim of this study is to investigate the molecular mechanism of hepatocellular carcinoma (HCC) development induced by hepatitis B virus X protein (HBx).

METHODS

We previously established a H7402-X cell line that constitutively expresses HBx protein. In the present study, H7402-X gene expression profiles and proteins were examined using cDNA microarrays and Western blot analysis. Apoptosis was induced by adriamycin in H7402-X cells. The transcriptional activities of NF-kappaB and AP-1 were examined using a luciferase reporter gene.

RESULTS

The DNA expression profiles identified candidate genes showing aberrant expression in cells overexpressing HBx. Western blot analysis showed that cyclin D, cyclin E, survivin, Bcl-2, and PCNA were up-regulated, whereas p27 was down-regulated in H7402-X cells. Treatment with RNAi targeting HBx mRNA led to the down-regulation of these genes. H7402-X cells were resistant to adriamycin-induced apoptosis. Luciferase reporter gene analysis revealed that HBx induces the transcriptional activities of NF-kappaB and AP-1.

CONCLUSION

Our data provide additional insight into cellular targets of HBx, which allows a better understanding of HBx function and the progressive changes during HBx-mediated hepatocarcinogenesis.

Knockdown of damage-specific DNA binding protein 1 (DDB1) enhances the HBx-siRNA-mediated inhibition of HBV replication

Recent studies have demonstrated that the effect of inhibition of HBV replication can be achieved by RNA interference (RNAi) at both the cellular and organismal levels. However, HBV replication cannot be completely inhibited by this method. To completely inhibit HBV replication, new strategies for improving the inhibition efficacy of HBV-specific siRNAs are needed. In this study, we demonstrated that knockdown of damage-specific DNA binding protein 1(DDB1), a protein involved in nucleotide-excision repair and HBV replication, significantly enhanced the HBx-siRNA-mediated inhibition of HBV replication. Although knockdown of DDB1 may be toxic to normal liver cells, our results indeed suggest a new direction to enhance the efficacy of HBV-siRNA-mediated inhibition of HBV replication.

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.

RNA interference against viruses: strike and counterstrike

RNA interference (RNAi) is a conserved sequence-specific, gene-silencing mechanism that is induced by double-stranded RNA. RNAi holds great promise as a novel nucleic acid–based therapeutic against a wide variety of diseases, including cancer, infectious diseases and genetic disorders. Antiviral RNAi strategies have received much attention and several compounds are currently being tested in clinical trials. Although induced RNAi is able to trigger profound and specific inhibition of virus replication, it is becoming clear that RNAi therapeutics are not as straightforward as we had initially hoped. Difficulties concerning toxicity and delivery to the right cells that earlier hampered the development of antisense-based therapeutics may also apply to RNAi. In addition, there are indications that viruses have evolved ways to escape from RNAi. Proper consideration of all of these issues will be necessary in the design of RNAi-based therapeutics for successful clinical intervention of human pathogenic viruses.

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.

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.

Inhibition of white spot syndrome virus in Litopenaeus vannamei shrimp by sequence-specific siRNA

RNA interference (RNAi) is a sequence-specific, post-transcriptional process of mRNA degradation. Here, we described specific silencing of five white spot syndrome virus (WSSV) genes in Litopenaeus vannamei in vivo with sequence-specific siRNAs. These genes included DNA polymerase (dnapol), ribonucleotide reductase small subunit (rr2), thymidine kinase and thymidylate kinase (tk-tmk), vp24 and vp28. At 6 days post-challenged, the relative survival rates of shrimp injected with siDNApol, siRR2, siTK-TMK, siVP24 and siVP28 (siRNAs for dnapol, rr2, tk-tmk, vp24 and vp28 genes) reached 50%, 50%, 66%, 33% and 33%, respectively. Specific siRNAs of the five WSSV genes could result in suppression of the target genes and a significant reduction in the viral proliferation. In negative controls, sequence-independent siRNA (mutant siRNA) could not inhibit expression of these five genes or viral replication. Consequently, injection of sequence-dependent siRNA could induce anti-WSSV activity in shrimp. These results suggest that siRNA can suppress WSSV efficiently in shrimp, and it may provide a potential approach to the therapy of aquaculture viral disease.

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.

Targeted inhibition of HBV gene expression by single-chain antibody mediated small interfering RNA delivery

RNA interference is highly effective at inhibiting HBV gene expression and replication. However, before small interfering RNA (siRNA) can be used in the clinic, it is essential to develop a system to target their delivery. Antibody-mediated delivery is a novel approach for targeting siRNA to appropriate cells. In this report, we asked whether this siRNA delivery strategy would be effective against HBV. Of 5 candidates, a specific siRNA that effectively inhibited HBV gene expression and replication was determined. Two fusion proteins, s-tP and sCkappa-tP, were constructed to contain a single chain of the human variable fragment, scFv, against hepatitis B surface antigen (HBsAg), a truncated protamine (tP), and in the case of sCkappa-tP, a constant region of the kappa chain (Ckappa). S-tP and sCkappa-tP were developed to provide targeted delivery of the siRNA, siRNA expressing cassettes (SEC), and siRNA-producing plasmids. Fluorescein isothiocyanate-siRNA, fluorescein isothiocyanate-SEC, and plasmid DNA were specifically delivered into HBsAg-positive cells using the sCkappa-tP fusion protein, and effectively inhibited HBV gene expression and replication. HBV gene expression was also inhibited by siRNA or siRNA-producing plasmids in HBV transgenic mice.

CONCLUSION

Our results describe a potential method for the targeted delivery of siRNA or siRNA-producing plasmids against HBV, using anti-HBsAg fusion proteins.

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.

Effective anti-hepatitis B virus hammerhead ribozymes derived from multimeric precursors

Endonucleolytic hammerhead ribozymes have advantages of inhibiting gene expression by acting specifically, independently of cellular pathways, and within all cell compartments. However, there are concerns about inefficient silencing because of reduced intracellular cleavage of target RNA by ribozymes. To enable production of defined single-unit ribozymes and thereby increase effectiveness, we developed self-cleaving multimeric cassettes that generate several trans-acting ribozyme units from a single transcript. cis and trans ribozyme cleavage, as assessed in vitro against three different sites within the X sequence of hepatitis B virus (HBV), occurred efficiently and precisely according to predictions deduced from the ribozyme designs. Significant knockdown of markers of viral replication in transfected cultured liver-derived cells was achieved by multiribozyme Pol II expression cassettes. To assess silencing efficacy of RNA prepared in vitro, transcription and cis cleavage reactions were carried out to prepare defined single-unit ribozymes. Transfection of ribozyme RNA was capable of inhibiting HBV surface antigen secretion from liver-derived cells without associated elevation of interferon-alpha or interferon-beta secretion into the culture upernatants. The approach described here is potentially useful for several applications, such as generation of RNA interference (RNAi) effectors, which require rapid and inexpensive generation of defined RNA sequences.

RNA interference against hepatitis B virus with endoribonuclease-prepared siRNA despite of the target sequence variations

RNA interference (RNAi) has proven to be very powerful in inhibiting hepatitis B virus (HBV) replication by cell culture and mouse model studies. We have previously reported that endoribonuclease-prepared short interfering RNAs (esiRNAs) were able to inhibit HBV replication more efficiently than synthesized siRNAs. Here we tested the hypothesis that esiRNAs are able to inhibit gene expression with limited mutations within the target region. Target sequences with different similarities to esiHBVP (esiRNA targeting the DNA polymerase and S antigen of Hepatitis B virus) were amplified and cloned into the 3' untranslated region of HBsAg, respectively. When the obtained expression vectors were co-transfected with esiHBVP into CHO cells, HBsAg expression was suppressed with same efficiency regardless of the target sequence similarities. In HepG2 cells, esiHP9 based on one of the amplified sequence that sharing 87% similarity to the target region suppressed HBsAg expression effectively and dose dependently. In vivo experiment showed that a single dose of 5 microg esiHP9 was able to reduce HBsAg and HBeAg level in the mouse sera by 88 and 77% despite of its 87% similarity to the target sequence, which was as good as esiHBVP that is 100% similar to the target sequence. All the data suggest that esiRNA can tolerate limited target sequence variations without losing its inhibitory capacity. It would be very helpful to suppress virus replication by RNAi despite of their high mutation rate.

Inhibition of hepatitis B virus expression and replication by RNA interference

AIM: To study the RNA interference on hepatitis B virus (HBV) replication by a reverse transcription virus vector which can express short hairpin RNA inside cells.

METHODS: pSIREN vectors with inserted oligonucleotides targeting on reverse transcriptase (RT) regions of HBV genome were constructed. These plasmids were co-transfected with pHBV3.8 into Huh-7 cells. Viral antigens were measured by enzyme-linked immunosorbent assay (ELISA). HBV core particle DNA was measured and quantified by real-time fluorescence quantitative polymerase chain reaction (RFQ-PCR) and Southern blot. Viral RNA was analyzed by Northern blot.

RESULTS: Three RNA interfering targets were identified, and three corresponding retrovirus vectors, named 154i, 312i and 734i, were obtained. It was found that 312i markedly inhibited the expression of pHBV3.8, and the levels of HBsAg and HBeAg were 39% and 41% of those in the negative control group (P = 0.001, P = 0.000). RFQ-PCR showed that the level of HBV core particle DNA was significantly lower in 312i group than that in the negative control group (21.3% ± 1.1% vs 100.0% ± 10.6%, P = 0.0046). Southern and Northern blot demonstrated a lowest replication and transcription level of HBV in 312i group (10.5%, 12.0%).

CONCLUSION: A new RNAi system is identified in the RT regions of HBV genome, and the corresponding retrovirus vectors, which can remarkably inhibit the replication and expression of HBV, are also constructed.

Combination of small interfering RNA and lamivudine on inhibition of human B virus replication in HepG2.2.15 cells

AIM: To observe the inhibition of hepatitis B virus (HBV) replication and expression by combination of siRNA and lamivudine in HepG2.2.15 cells.

METHODS: Recombinant plasmid psil-HBV was constructed and transfected into HepG2.2.15 cells. The transfected cells were cultured in lamivudine-containing medium (0.05 μmol/L) and harvested at 48, 72 and 96 h. The concentration of HBeAg and HBsAg was determined using ELISA. HBV DNA replication was examined by real-time PCR and the level of HBV mRNA was measured by RT-PCR.

RESULTS: In HepG2.2.15 cells treated with combination of siRNA and lamivudine, the secretion of HBeAg and HBsAg into the supernatant was found to be inhibited by 91.80% and 82.40% (2.89 ± 0.48 vs 11.73 ± 0.38, P < 0.05; 4.59 ± 0.57 vs 16.25 ± 0.48, P < 0.05) at 96 h, respectively; the number of HBV DNA copies within culture medium was also significantly decreased at 96 h (1.04 ± 0.26 vs 8.35 ± 0.33, P < 0.05). Moreover, mRNA concentration in HepG2.2.15 cells treated with combination of siRNA and lamivudine was obviously lower compared to those treated either with siRNA or lamivudine (19.44 ± 0.17 vs 33.27 ± 0.21 or 79.9 ± 0.13, P < 0.05).

CONCLUSION: Combination of siRNA and lamivudine is more effective in inhibiting HBV replication as compared to the single use of siRNA or lamivudine in HepG2.2.15 cells.