Small interfering RNA effectively inhibits protein expression and negative strand RNA synthesis from a full-length hepatitis C virus clone

Consensus small interfering RNA targeted to stem-loops II and III of IRES structure of 5' UTR effectively inhibits virus replication and translation of HCV sub-genotype 4a isolates from Saudi Arabia

Being the most conserved region of all hepatitis C virus (HCV) genotypes and sub-genotypes, the 5′ untranslated region (5′ UTR) of HCV genome signifies it’s importance as a potential target for anti-mRNA based treatment strategies like RNA interference. The advent and approval of first small interference RNA (siRNA) -based treatment of hereditary transthyretin-mediated amyloidosis for clinical use has raised the hopes to test this approach against highly susceptible viruses like HCV. We investigated the antiviral potential of consensus siRNAs targeted to stem-loops (SLs) II and III nucleotide motifs of internal ribosome entry site (IRES) structure within 5′ UTR of HCV sub-genotype 4a isolates from the Saudi population. siRNA inhibitory effects on viral replication and translation of full-length HCV genome were determined in a competent, persistent, and reproducible Huh-7 cell culture system maintained for one month. Maximal inhibition of RNA transcript levels of HCV-IRES clones and silencing of viral replication and translation of full-length virus genome was demonstrated by siRNAs targeted to SL-III nucleotide motifs of IRES in Huh-7 cells. siRNA Usi-169 decreased 5′ UTR RNA transcript levels of HCV-IRES clones up to 75% (P < 0.001) at 24 h post-transfection and 80% (P < 0.001) at 48 h treatment in Huh-7 cells. 5′ UTR-tagged GFP protein expression was significantly decreased from 70 to 80% in Huh-7 cells co-transfected with constructed vectors (i.e. pCR3.1/GFP/5′ UTR) and siRNA Usi-169 at 24 h and 48 h time-span. Viral replication was inhibited by more than 90% (P < 0.001) and HCV core (C) and hypervariable envelope glycoproteins (E1 and E2) expression was also significantly degraded by intracytoplasmic siRNA Usi-169 activity in persistent Huh-7 cell culture system. The findings unveil that siRNAs targeted to 5′ UTR-IRES of HCV sub-genotype 4a Saudi isolates show potent silencing of HCV replication and blocking of viral translation in a persistent in-vitro Huh-7 tissue culture system. Furthermore, we also elucidated that siRNA silencing of viral mRNA not only inhibits viral replication but also blocks viral translation. The results suggest that siRNA potent antiviral activity should be considered as an effective anti-mRNA based treatment strategies for further in-vivo investigations against less studied and harder-to-treat HCV sub-genotype 4a isolates in Saudi Arabia.

Inhibition of hepatitis C virus using siRNA targeted to the virus and Hsp90

Hepatitis C (HCV) is a viral disease affecting millions of people worldwide, and persistent HCV infection can lead to progressive liver disease with the development of liver cirrhosis and hepatocellular carcinoma. During treatment for hepatitis C, the occurrence of viral resistance is common. To reduce the occurrence of resistance, new viral treatments should target both viral and cellular factors. Many interactions occur between viral and host proteins during the HCV replication cycle and might be used for the development of new therapies against hepatitis C. Heat shock protein 90 (Hsp90) plays a role in the folding of cellular and viral proteins and also interacts with HCV proteins. In the present study, we knocked down the expression of the Hsp90 gene and inhibited viral replication using siRNA molecules. Reducing the expression of Hsp90 successfully decreased HCV replication. All siRNA molecules specific to the viral genome showed the efficient inhibition of viral replication, particularly siRNA targeted to the 5'UTR region. The combination of siRNAs targeting the viral genome and Hsp90 mRNA also successfully reduced HCV replication and reduced the occurrence of viral resistance. Moreover, these results suggest that an approach based on the combination of cellular and viral siRNAs can be used as an effective alternative for hepatitis C viral suppression.

Target delivery of small interfering RNAs with vitamin E-coupled nanoparticles for treating hepatitis C

RNA interference (RNAi) represents a promising strategy for the treatment of HCV infection. However, the development of an effective system for in vivo delivery of small interfering RNA (siRNA) to target organ remains a formidable challenge. Here, we develop a unique nanoparticle platform (VE-DC) composed of α-tocopherol (vitamin E) and cholesterol-based cationic liposomes (DOTAP-Chol) for systemic delivery of siRNAs to the liver. A HCV-replicable cell line, Huh7.5.1-HCV, and a transient HCV core expressing cell line, Huh7.5.1-Core, were constructed and used to assess the in vitro anti-HCV activity of VE-DC/siRNAs. A transient in vivo HCV model was also constructed by hydrodynamic injection of pCDNA3.1(+)-3FLAG-Core (pCore-3FLAG) plasmid expressing core protein or pGL3-5′UTR-luciferase (pGL3-5′UTR-luc) plasmid expressing luciferase driven by HCV 5′UTR. Nanoscale VE-DC/siRNA was intravenously injected to assess the liver-targeting property as well as antiviral activity. The nanoscale VE-DC effectively exerted an anti-HCV activity in the in vitro cell models. Post-administration of VE-DC/siRNAs also effectively delivered siRNAs to the liver, suppressing core protein production and firefly luciferase activity, without inducing an innate immunity response or off-target and toxicity effects. The VE-DC platform has high potential as a vehicle for delivery of siRNAs to the liver for gene therapy for targeting hepatitis C.

Evaluation of canonical siRNA and Dicer substrate RNA for inhibition of hepatitis C virus genome replication--a comparative study

Hepatitis C virus (HCV) frequently establishes persistent infections in the liver, leading to the development of chronic hepatitis and, potentially, to liver cirrhosis and hepatocellular carcinoma at later stages. The objective of this study was to test the ability of five Dicer substrate siRNAs (DsiRNA) to inhibit HCV replication and to compare these molecules to canonical 21 nt siRNA. DsiRNA molecules were designed to target five distinct regions of the HCV genome - the 5' UTR and the coding regions for NS3, NS4B, NS5A or NS5B. These molecules were transfected into Huh7.5 cells that stably harboured an HCV subgenomic replicon expressing a firefly luciferase/neoR reporter (SGR-Feo-JFH-1) and were also tested on HCVcc-infected cells. All of the DsiRNAs inhibited HCV replication in both the subgenomic system and HCVcc-infected cells. When DsiRNAs were transfected prior to infection with HCVcc, the inhibition levels reached 99.5%. When directly compared, canonical siRNA and DsiRNA exhibited similar potency of virus inhibition. Furthermore, both types of molecules exhibited similar dynamics of inhibition and frequencies of resistant mutants after 21 days of treatment. Thus, DsiRNA molecules are as potent as 21 nt siRNAs for the inhibition of HCV replication and may provide future approaches for HCV therapy if the emergence of resistant mutants can be addressed.

Lipid nanoparticles as carriers for RNAi against viral infections: current status and future perspectives

The efforts made to develop RNAi-based therapies have led to productive research in the field of infections in humans, such as hepatitis C virus (HCV), hepatitis B virus (HBV), human immunodeficiency virus (HIV), human cytomegalovirus (HCMV), herpetic keratitis, human papillomavirus, or influenza virus. Naked RNAi molecules are rapidly digested by nucleases in the serum, and due to their negative surface charge, entry into the cell cytoplasm is also hampered, which makes necessary the use of delivery systems to exploit the full potential of RNAi therapeutics. Lipid nanoparticles (LNP) represent one of the most widely used delivery systems for in vivo application of RNAi due to their relative safety and simplicity of production, joint with the enhanced payload and protection of encapsulated RNAs. Moreover, LNP may be functionalized to reach target cells, and they may be used to combine RNAi molecules with conventional drug substances to reduce resistance or improve efficiency. This review features the current application of LNP in RNAi mediated therapy against viral infections and aims to explore possible future lines of action in this field.

Therapeutic potential of RNA interference: a new molecular approach to antiviral treatment for hepatitis C

Hepatitis C virus (HCV) infection remains a major cause of chronic liver disease with an estimated 170 million carriers worldwide. Current treatments have significant side effects and have met with only partial success. Therefore, alternative antiviral drugs that efficiently block virus production are needed. During recent decades, RNA interference (RNAi) technology has not only become a powerful tool for functional genomics but also represents a new therapeutic approach for treating human diseases including viral infections. RNAi is a sequence-specific and post-transcriptional gene silencing process mediated by double-stranded RNA (dsRNA). As the HCV genome is a single-stranded RNA that functions as both a messenger RNA (mRNA) and replication template, it is an attractive target for the study of RNAi-based viral therapies. In this review, we will give a brief overview about the history and current status of RNAi and focus on its potential application as a therapeutic option for treatment for HCV infection.

Design of Synthetic shRNAs for Targeting Hepatitis C: A New Approach to Antiviral Therapeutics

Small hairpin RNAs (shRNAs) are widely used as gene silencing tools and typically consist of a duplex stem of 19–29 bp, a loop, and often a dinucleotide overhang at the 3′ end. Like siRNAs, shRNAs show promise as potential therapeutic agents due to their high level of specificity and potency, although effective delivery to target tissues remains a challenge. Algorithms used to predict siRNA performance are frequently used to design shRNAs as well. However, the differences between these two kinds of RNAi mediators indicate that the factors affecting target gene silencing will not be the same for siRNAs and shRNAs. Stem and loop lengths, structures of the termini, the identity of nucleotides adjacent to and near the loop, and the position of the guide (antisense) strand all affect the efficacy of shRNAs. In addition, shRNAs with 19-bp or shorter stem lengths are processed and function differently than those with longer stems. In this review, we describe studies of targeting the hepatitis C virus that have provided guidelines for an optimal design for short (19 bp) shRNAs (sshRNAs) that are highly potent, stable in biological fluids, and have minimal immunostimulatory properties.

In vitro characterization of the activity of PF-05095808, a novel biological agent for hepatitis C virus therapy

PF-05095808 is a novel biological agent for chronic hepatitis C virus (HCV) therapy. It comprises a recombinant adeno-associated virus (AAV) DNA vector packaged into an AAV serotype 8 capsid. The vector directs expression of three short hairpin RNAs (shRNAs) targeted to conserved regions of the HCV genome. These shRNAs are processed by the host cell into the small interfering RNAs which mediate sequence-specific cleavage of target regions. For small-molecule inhibitors the key screens needed to assess in vitro activity are well defined; we developed new assays to assess this RNA interference agent and so to understand its therapeutic potential. Following administration of PF-05095808 or corresponding synthetic shRNAs, sequence-specific antiviral activity was observed in HCV replicon and infectious virus systems. To quantify the numbers of shRNA molecules required for antiviral activity in vitro and potentially also in vivo, a universal quantitative PCR (qPCR) assay was developed. The number of shRNA molecules needed to drive antiviral activity proved to be independent of the vector delivery system used for PF-05095808 administration. The emergence of resistant variants at the target site of one shRNA was characterized. A novel RNA cleavage assay was developed to confirm the spectrum of activity of PF-05095808 against common HCV clinical isolates. In summary, our data both support antiviral activity consistent with an RNA interference mechanism and demonstrate the potential of PF-05095808 as a therapeutic agent for chronic HCV infection.

Effect of combined siRNA of HCV E2 gene and HCV receptors against HCV

Background/Aim

Hepatitis C virus (HCV) is a major threat as almost 3% of the world's population (350 million individual) and 10% of the Pakistani population is chronically infected with this virus. RNA interference (RNAi), a sequence-specific degradation process of RNA, has potential to be used as a powerful alternative molecular therapeutic approach in spite of the current therapy of interferon-α and ribavirin against HCV which has limited efficiency. HCV structural gene E2 is mainly involved in viral cell entry via attachment with the host cell surface receptors i.e., CD81 tetraspanin, low density lipoprotein receptor (LDLR), scavenger receptor class B type 1 (SR-B1), and Claudin1 (CLDN1). Considering the importance of HCV E2 gene and cellular receptors in virus infection and silencing effects of RNAi, the current study was designed to target the cellular and viral factors as new therapeutic options in limiting HCV infection.

Results

In this study the potential of siRNAs to inhibit HCV-3a replication in serum-infected Huh-7 cells was investigated by combined treatment of siRNAs against the HCV E2 gene and HCV cellular receptors (CD81 and LDLR), which resulted in a significant decrease in HCV viral copy number.

Conclusion

From the current study it is concluded that the combined RNAi-mediated silencing of HCV E2 and HCV receptors is important for the development of effective siRNA-based therapeutic option against HCV-3a.

Down-regulation of IRES containing 5'UTR of HCV genotype 3a using siRNAs

Background

Hepatitis C virus (HCV) is a major causative agent of liver associated diseases leading to the development of hepatocellular carcinoma (HCC) all over the world and genotype-3a responsible for most of the cases in Pakistan. Due to the limited efficiency of current chemotherapy of interferon-α (IFN-α) and ribavirin against HCV infection alternative options are desperately needed out of which the recently discovered RNAi represent a powerful silencing approach for molecular therapeutics through a sequence-specific RNA degradation process to silence virus infection or replication. HCV translation is mediated by a highly conserved internal ribosome entry site (IRES) within the 5'UTR region making it a relevant target for new drug development.

Materials and methods

The present study was proposed to assess and explore the possibility of HCV silencing using siRNA targeting 5'UTR. For this analysis full length HCV 5'UTR of HCV-3a (pCR3.1/5'UTR) was tagged with GFP protein for in vitro analysis in Huh-7 cells. siRNA targeting 5'UTR were designed, and tested against constructed vector in Huh-7 cell line both at RNA and Protein levels. Furthermore, the effect of these siRNAs was confirmed in HCV-3a serum infected Huh-7 cell line.

Results

The expression of 5'UTR-GFP was dramatically reduced both at mRNA and protein levels as compared with Mock transfected and control siRNAs treated cells using siRNAs against IRES of HCV-3a genotype. The potential of siRNAs specificity to inhibit HCV-3a replication in serum-infected Huh-7 cells was also investigated; upon treatment with siRNAs a significant decrease in HCV viral copy number and protein expression was observed.

Conclusions

Overall, the present work of siRNAs against HCV 5'UTR inhibits HCV-3a expression and represents effective future therapeutic opportunities against HCV-3a genotype.

Inhibition of full length hepatitis C virus particles of 1a genotype through small interference RNA

Background

Hepatitis C virus (HCV), a member of the Flaviviridae family of viruses, is a major cause of chronic hepatitis, liver cirrhosis and hepatocellular carcinoma. Currently, the only treatment available consists of a combination of Pegylated interferon alpha (INF-α) and ribavirin, but only half of the patients treated show a sufficient antiviral response. Thus there is a great need for the development of new treatments for HCV infections. RNA interference (RNAi) represents a new promising approach to develop effective antiviral drugs and has been extremely effective against HCV infection.

Results

This study was design to assess or explore the silencing effect of small interference RNAs (siRNAs) against full length HCV particles of genotype 1a. In the present study six 21-bp siRNAs were designed against different regions of HCV structural genes (Core, E1 and E2). Selected siRNAs were labeled as Csi 301, Csi 29, E1si 52, E1si 192, E2si 86 and E2si 493. Our results demonstrated that siRNAs directed against HCV core gene showed 70% reduction in viral titer in HCV infected liver cells. Moreover, siRNAs against E1 and E2 envelop genes showed a dramatic reduction in HCV viral RNA, E2si 86 exhibited 93% inhibition, while E1si 192, E2si 493 and E1si 52 showed 87%, 80%, and 66% inhibition respectively. No significant inhibition was detected in cells transfected with the negative control siRNA.

Conclusion

Our results suggested that siRNAs targeted against HCV structural genes efficiently silence full length HCV particles and provide an effective therapeutic option against HCV infection.

Induction of matrix metalloproteinase-1 by small interfering RNA targeting connective tissue growth factor in dermal fibroblasts from patients with systemic sclerosis

We aimed to evaluate the effect of small interfering RNA (siRNA) targeting CTGF on extracellular matrices (ECMs) metabolism in normal and SSc fibroblasts. Normal and SSc fibroblasts were transfected with CTGF-specific siRNAs to silence CTGF synthesis. After silencing CTGF, production of type I collagen and matrix metalloproteinase (MMP)-1 by fibroblasts stimulated with TGF-beta was examined. Then quantitative analyses of protein production or mRNA expression of type I collagen, MMP-1,-2,-9 and tissue inhibitor of metalloproteinase (TIMP)-1 with TGF-beta stimulation were carried out. Furthermore, after silencing CTGF, proliferations of normal and SSc fibroblasts were investigated. CTGF-specific siRNA significantly reduced CTGF production. The production of type I collagen was significantly reduced by CTGF silencing in normal fibroblasts. The CTGF silencing significantly increased the production of MMP-1 and decreased the production of TIMP-1 in SSc fibroblasts. The mRNA expression of MMP-1 was increased in CTGF-silenced SSc fibroblasts, but not in normal fibroblasts. There were no significant changes in the production or mRNA expression of other ECM-related genes in normal and SSc fibroblasts. Fibroblast proliferations were suppressed by CTGF silencing in normal and SSc fibroblasts. Our data showed that MMP-1 was increased by CTGF-specific siRNA transfection only in SSc fibroblasts. RNAi targeting CTGF could be a novel therapeutic strategy for SSc.

Inhibition of hepatitis C virus genotype 3a by siRNAs targeting envelope genes

Hepatitis C virus (HCV) genotype 3a is considered a significant risk factor for the development of liver diseases and hepatocellular carcinoma for most of the cases in Pakistan. Because of the limited efficiency of the current therapy, RNA interference (RNAi), which results in sequence-specific degradation of HCV RNA, has potential as a powerful alternative molecular therapeutic approach. The envelope genes (E1 and E2) of HCV come in immediate contact with cells during infection and therefore might be a relevant target for new drug development. In the present study, the expression of E1 and E2 genes of HCV genotype 3a was dramatically reduced at both the mRNA and protein level using gene-specific small interfering RNAs (siRNA) when compared to mock-transfected and cells treated with control siRNAs. The potential of siRNAs to inhibit HCV-3a replication in serum-infected Huh-7 cells was also demonstrated by combined treatment of siRNAs against the E1 and E2 genes, which resulted in a significant decrease in HCV viral copy number. This clearly demonstrates that the RNAi-mediated silencing of HCV E1 and E2 is among the first of its type for the development of an effective siRNA-based therapeutic option against HCV-3a.

Inhibition of core gene of HCV 3a genotype using synthetic and vector derived siRNAs

Background

Hepatitis C virus (HCV) is a major causative agent of liver associated diseases throughout the world, with genotype 3a responsible for most of the cases in Pakistan. Due to the limited efficiency of current therapy, RNA interference (RNAi) a novel regulatory and powerful silencing approach for molecular therapeutics through a sequence-specific RNA degradation process represents an alternative option.

Results

The current study was purposed to assess and explore the possibility of RNAi to silence the HCV-3a Core gene expression, which play complex role in regulation of cell growth and host genes expression essential for infectivity and disease progression. To identify the potent siRNA target sites, 5 small interfering RNAs (siRNAs) against Core gene were designed and in vitro transcribed after consensus sequence analysis of different HCV-3a isolates. Antiviral effects of siRNAs showed upto 80% inhibition of Core gene expression by different siRNAs into Huh-7 cells as compared with Mock transfected and control siRNAs treated cells. For long lasting effect of siRNAs, vector based short hairpin siRNAs (shRNAs) were designed and tested against HCV-3a Core which resulted in a similar pattern of inhibition on RNA and protein expression of HCV Core as synthetic siRNAs. Furthermore, the efficacy of cell culture tested siRNA and shRNA, were evaluated for inhibition of HCV replication in HCV infected serum inoculated Huh-7 cells and a significant decrease in HCV viral copy number was observed.

Conclusions

Our results support the possibility of using consensus siRNA and shRNA-based molecular therapy as a promising strategy in effective inhibition of HCV-3a genotype.

Intracytoplasmic stable expression of IgG1 antibody targeting NS3 helicase inhibits replication of highly efficient hepatitis C Virus 2a clone

Background

Hepatitis C virus (HCV) infection is a major public health problem with more than 170 million cases of chronic infections worldwide. There is no protective vaccine currently available for HCV, therefore the development of novel strategy to prevent chronic infection is important. We reported earlier that a recombinant human antibody clone blocks viral NS3 helicase activity and inhibits replication of HCV 1b virus. This study was performed further to explore the mechanism of action of this recombinant antibody and to determine whether or not this antibody inhibits replication and infectivity of a highly efficient JFH1 HCV 2a virus clone.

Results

The antiviral effect of intracellular expressed antibody against the HCV 2a virus strain was examined using a full-length green fluorescence protein (GFP) labeled infectious cell culture system. For this purpose, a Huh-7.5 cell line stably expressing the NS3 helicase gene specific IgG1 antibody was prepared. Replication of full-length HCV-GFP chimera RNA and negative-strand RNA was strongly inhibited in Huh-7.5 cells stably expressing NS3 antibody but not in the cells expressing an unrelated control antibody. Huh-7.5 cells stably expressing NS3 helicase antibody effectively suppressed infectious virus production after natural infection and the level of HCV in the cell free supernatant remained undetectable after first passage. In contrast, Huh-7.5 cells stably expressing an control antibody against influenza virus had no effect on virus production and high-levels of infectious HCV were detected in culture supernatants over four rounds of infectivity assay. A recombinant adenovirus based expression system was used to demonstrate that Huh-7.5 replicon cell line expressing the intracellular antibody strongly inhibited the replication of HCV-GFP RNA.

Conclusion

Recombinant human anti-HCV NS3 antibody clone inhibits replication of HCV 2a virus and infectious virus production. Intracellular expression of this recombinant antibody offers a potential antiviral strategy to inhibit intracellular HCV replication and production.

Comparison of U2OS and Huh-7 cells for identifying host factors that affect hepatitis C virus RNA replication

Host cell factors are critical to all stages of the hepatitis C virus (HCV) life cycle. While many cellular proteins that regulate HCV genome synthesis have been identified, the mechanisms engaged in this process are incompletely understood. To identify novel cellular proteins involved in HCV RNA replication, we screened a library of small interfering RNAs (siRNAs) targeting 299 cellular factors, which principally function in RNA interactions. For the screen, a robust system was established using two cell lines (derived from Huh-7 and U2OS cells) that replicated tricistronic subgenomic replicons (SGRs). We found that the U2OS cell line gave lower levels of intracellular HCV RNA replication compared with Huh-7 cells and was more readily transfected by siRNAs. Consequently, increased gene silencing and greater effects on HCV replication were observed in the U2OS cell line. Thus, U2OS cells provided a suitable and more sensitive alternative to Huh-7 cells for siRNA studies on HCV RNA replication. From the screen, several cellular proteins that enhanced and suppressed HCV RNA replication were identified. One of the genes found to downregulate viral RNA synthesis, ISG15, is expressed in response to alpha interferon and may therefore partly contribute to the clearance of virus from infected individuals. A second gene that inhibited HCV RNA levels was the 5'-3' exoRNase XRN1, which suggested a role for cellular RNA degradation pathways in modulating the abundance of viral genomes. Therefore, this study provides an important framework for future detailed analyses of these and other cellular proteins.

RNAi as a new therapeutic strategy against HCV

Hepatitis C virus is a major cause of liver associated diseases all over the world. Irrespective of the significant advances in the current therapy, drugs and vaccines are restricted with many factors such as toxicity, complexity, cost and resistance. New technologies particularly RNA interference (RNAi) mediated by small interfering RNA (siRNA) have become more and more interesting and effective therapeutic entities to silence pathogenic gene products associated with disease, including cancer, viral infections and autoimmune disorders. RNAi works at a posttranscriptional level by targeting mRNA as a mean for inhibiting the synthesis of the encoded protein. Several reports have indicated the efficiency and specificity of synthetic and vector based siRNAs inhibiting HCV replication. In the present review, we focused on the recent development in the potential use and issues regarding siRNA as a therapy for HCV.

Antisense inhibitors, ribozymes, and siRNAs

The current standard of care for the treatment of hepatitis C virus infection, pegylated interferon-alpha and ribavirin, is costly, associated with significant side effects, and effective in only 50% of patients. There is therefore a need for the development of novel antiviral therapies. One such approach involves the application of gene silencing technologies, including antisense oligonucleotides, ribozymes, RNA interference, and aptamers. However, despite great scientific advances over the past decade, and promising in vitro data, several significant challenges continue to limit the translation of this technology to the clinical setting. This review provides a concise update of the current literature.

Liver target delivery of small interfering RNA to the HCV gene by lactosylated cationic liposome

BACKGROUND/AIMS

RNA interference has considerable therapeutic potential, particularly for anti-viral therapy. We previously reported that hepatitis C virus (HCV)-directed small interfering RNA (siRNA; siE) efficiently inhibits HCV replication, using HCV replicon cells. To employ the siRNA as a therapeutic strategy, we attempted in vivo silencing of intrahepatic HCV gene expression by siE using a novel cationic liposome.

METHODS

The liposomes consisted of conjugated lactose residues, based on the speculation that lactose residues would effectively deliver siRNA to the liver via a liver specific receptor. The lactosylated cationic liposome 5 (CL-LA5) that contained the most lactose residues introduced the most siRNA into a human hepatoma cell line, which then inhibited replication of HCV replicons.

RESULTS

In mice, the siRNA/CL-LA5 complexes accumulated primarily in the liver and were widespread throughout the hepatic parenchymal cells. Moreover, siE/CL-LA5 specifically and dose-dependently suppressed intrahepatic HCV expression in transgenic mice without an interferon response.

CONCLUSIONS

The present results indicate that the CL-LA5 we developed is a good vehicle to lead siRNA to the liver. Hence, CL-LA5 will be helpful for siRNA therapy targeting liver diseases, especially hepatitis C.

Potential role of RNAi in the treatment of HCV infection

Chronic HCV infection is a leading cause of chronic hepatitis and its sequelae, liver cirrhosis and hepatocellular carcinoma. Current therapeutic options are limited, associated with significant adverse effects and costly. Accordingly, there is strong impetus to develop novel therapeutic strategies that act through alternate mechanisms. RNAi has been widely used for the analysis of gene function and represents a potentially promising approach for the treatment of HCV infection. siRNAs are short RNA duplexes approximately 21 nts long. When introduced into mammalian cells, siRNA can silence specific gene expression. Although efficient suppression of HCV replicon RNA in cell culture has been demonstrated with siRNAs, there is much work to be done to improve delivery, limit off-target effects and minimize development of virus resistance. Here, we review the use of RNAi as a tool to inhibit HCV gene expression and discuss the potential advantages and obstacles for this new potential therapeutic approach against HCV infection.

Therapeutic application of RNA interference for hepatitis C virus

RNA interference (RNAi) is a sequence-specific post-transcriptional gene silencing by double-stranded RNA. Because the phenomenon is conserved and ubiquitous in mammalian cells, RNAi has considerable therapeutic potential for human pathogenic gene products. Recent studies have demonstrated the clinical potential of logically designed small interfering RNA (siRNA). However, there are still obstacles in using RNAi as an antiviral therapy, particularly for hepatitis C virus (HCV) that displays a high rate of mutation. Furthermore, delivery is also an important obstacle for siRNA based gene therapy. This paper presents the potential applications and the hurdles facing anti-HCV siRNA drugs. The present review provides insight into the feasible therapeutic strategies of siRNA technology, and its potential for silencing genes associated with HCV disease.

Knock down of gfp and no tail expression in zebrafish embryo by in vivo-transcribed short hairpin RNA with T7 plasmid system

A short-hairpin RNA (shRNA) expression system, based on T7 RNA polymerase (T7RP) directed transcription machinery, has been developed and used to generate a knock down effect in zebrafish embryos by targeting green fluorescent protein (gfp) and no tail (ntl) mRNA. The vector pCMVT7R harboring T7RP driven by CMV promoter was introduced into zebrafish embryos and the germline transmitted transgenic individuals were screened out for subsequent RNAi application. The shRNA transcription vectors pT7shRNA were constructed and validated by in vivo transcription assay. When pT7shGFP vector was injected into the transgenic embryos stably expressing T7RP, gfp relative expression level showed a decrease of 68% by analysis of fluorescence real time RT-PCR. As a control, injection of chemical synthesized siRNA resulted in expression level of 40% lower than the control when the injection dose was as high as 2 microg/microl. More importantly, injection of pT7shNTL vector in zebrafish embryos expressing T7RP led to partial absence of endogenous ntl transcripts in 30% of the injected embryos when detected by whole mount in situ hybridization. Herein, the T7 transcription system could be used to drive the expression of shRNA in zebrafish embryos and result in gene knock down effect, suggesting a potential role for its application in RNAi studies in zebrafish embryos.

Positional effects and strand preference of RNA interference against hepatitis C virus target sequences

The hepatitis C virus (HCV) 3'-untranslated region (UTR) and negative-strand RNA sequences contribute cis-acting functions essential to viral RNA replication. Although efficient suppression of HCV replicon RNA in cell culture has been demonstrated with small interfering RNAs (siRNAs) directed against various sequences in the 5' UTR and coding regions, data regarding siRNA targeting of the 3' UTR have been lacking. Furthermore, it has not been definitively shown whether the active constructs, identified to date, exert their effect exclusively via suppression of the replicon positive strand, negative strand or some combination of both strands. In the present study, we assayed inhibitory activity of various siRNAs targeting the 3' UTR by transient transfection in a subgenomic replicon cell culture model. A survey of 13 candidate target sites in the 3'-UTR X sequence indicated a uniformly low activity of siRNA constructs against the steady-state level of replicon. In contrast, the majority of these same siRNAs exhibited high activity against HCV X sequences of either polarity when these targets were presented in the context of a mammalian polymerase II mRNA transcript. Transfection of siRNAs directed against other regions of the replicon revealed differences in the magnitude of inhibitory effects against positive-strand and negative-strand target sites. Strand preference of siRNA activity was further demonstrated through the introduction of base-pair-destabilizing mutations that promote strand-specific targeting. The results suggest that the HCV positive-strand 5' UTR and coding region are efficiently and directly targeted by siRNA, whereas the 3' UTR and the entire negative strand are relatively resistant to RNA interference.

Small interfering RNA targeted to stem-loop II of the 5' untranslated region effectively inhibits expression of six HCV genotypes

Background

The antiviral action of interferon alpha targets the 5' untranslated region (UTR) used by hepatitis C virus (HCV) to translate protein by an internal ribosome entry site (IRES) mechanism. Although this sequence is highly conserved among different clinical strains, approximately half of chronically infected hepatitis C patients do not respond to interferon therapy. Therefore, development of small interfering RNA (siRNA) targeted to the 5'UTR to inhibit IRES mediated translation may represent an alternative approach that could circumvent the problem of interferon resistance.

Results

Four different plasmid constructs were prepared for intracellular delivery of siRNAs targeting the stem loop II-III of HCV 5' UTR. The effect of siRNA production on IRES mediated translation was investigated using chimeric clones between the gene for green fluorescence protein (GFP) and IRES sequences of six different HCV genotypes. The siRNA targeted to stem loop II effectively mediated degradation of HCV IRES mRNA and inhibited GFP expression in the case of six different HCV genotypes, where as siRNAs targeted to stem loop III did not. Furthermore, intracytoplasmic expression of siRNA into transfected Huh-7 cells efficiently degraded HCV genomic RNA and inhibited core protein expression from infectious full-length infectious clones HCV 1a and HCV 1b strains.

Conclusion

These in vitro studies suggest that siRNA targeted to stem-loop II is highly effective inhibiting IRES mediated translation of the major genotypes of HCV. Stem-loop II siRNA may be a good target for developing an intracellular immunization strategy based antiviral therapy to inhibit hepatitis C virus strains that are not inhibited by interferon.

The potential of oligonucleotides for therapeutic applications

Viral-derived particles have been widely used and described in gene therapy clinical trials. Although substantial results have been achieved, major safety issues have also arisen. For more than a decade, oligonucleotides have been seen as an alternative to gene complementation by viral vectors or DNA plasmids, either to correct the genetic defect or to silence gene expression. The development of RNA interference has strengthened the potential of this approach. Recent clinical trials have also tested the ability of aptamer molecules and decoy oligonucleotides to sequestrate pathogenic proteins. Here, we review the potential of oligonucleotides in gene therapy, outline what has already been accomplished, and consider what remains to be done.

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.

Therapeutic short hairpin RNA expression in the liver: viral targets and vectors

Over 500 million people worldwide are infected with one or more different and unrelated types of human hepatitis virus. Such individuals are at a high risk of developing acute or chronic hepatic disease, and ultimately dying from sequelae. Although a vaccine is available for hepatitis A and B virus, treatment options for chronically infected patients are limited, and particularly ineffective in case of hepatitis C virus (HCV) infection. A promising new avenue currently being explored is to harness the power of RNA interference for development of an antiviral therapy. The timing to pursue this particular approach is excellent, with the first in vivo animal models for HCV infection becoming available, and the technology for liver-specific expression of short hairpin RNAs advancing at a rapid pace. Here, we critically review these important current developments, and discuss the next steps to bring this novel approach into the clinics.

Oligonucleotide-Based Therapeutic Options against Hepatitis C Virus Infection

The hepatitis C virus (HCV) is the cause of a silent pandemic that, due to the chronic nature of the disease and the absence of curative therapy, continues to claim an ever-increasing number of lives. Current antiviral regimens have proven largely unsatisfactory for patients with HCV drug-resistant genotypes. It is therefore important to explore alternative therapeutic stratagems whose mode of action allows them to bypass viral resistance. Antisense oligonucleotides, ribozymes, small interfering RNAs, aptamers and deoxyribozymes constitute classes of oligonucleotide-based compounds designed to target highly conserved or functionally crucial regions contained within the HCV genome. The therapeutic expectation for such compounds is the elimination of HCV from infected individuals. Progress in oligonucleotide-based HCV antivirals towards clinical application depends on development of nucleotide designs that bolster efficacy while minimizing toxicity, improvement in liver-targeting delivery systems, and refinement of small-animal models for preclinical testing.