A small interfering RNA targeting coxsackievirus B3 protects permissive HeLa cells from viral challenge

GalNAc-siRNA conjugates: Prospective tools on the frontier of anti-viral therapeutics

The growing use of short-interfering RNA (siRNA)-based therapeutics for viral diseases reflects the most recent innovations in anti-viral vaccines and drugs. These drugs play crucial roles in the fight against many hitherto incurable diseases, the causes, pathophysiologies, and molecular processes of which remain unknown. Targeted liver drug delivery systems are in clinical trials. The receptor-mediated endocytosis approach involving the abundant asialoglycoprotein receptors (ASGPRs) on the surfaces of liver cells show great promise. We here review N-acetylgalactosamine (GalNAc)-siRNA conjugates that treat viral diseases such as hepatitis B infection, but we also mention that novel, native conjugate-based, targeted siRNA anti-viral drugs may also cure several life-threatening diseases such as hemorrhagic cystitis, multifocal leukoencephalopathy, and severe acute respiratory syndrome caused by coronaviruses and human herpes virus.

A food-responsive switch modulates TFEB and autophagy, and determines susceptibility to coxsackievirus infection and pancreatitis

Almost a billion people worldwide are chronically undernourished. Herein, using a mouse model of coxsackievirus B3 (CVB3) infection, we report that a single day of food restriction (FR) markedly increases susceptibility to attenuated enterovirus infection, replication, and disease. These "pro-viral" effects, which are rapidly-reversed by the restoration of food, are mediated by several genes whose expression is altered by FR, and which support CVB3 replication. Central to this is TFEB, a protein whose expression and activation status are rapidly increased by FR. TFEB, which regulates the transcription of >100 genes involved in macroautophagy/autophagy and lysosomal biogenesis, responds similarly to both FR and CVB3 infection and plays a pivotal role in determining host susceptibility to CVB3. We propose that, by upregulating TFEB, FR generates an intracellular environment that is more hospitable to the incoming virus, facilitating its replication. This interplay between nutritional status and enterovirus replication has implications for human health and, perhaps, for the evolution of these viruses.Abbreviations: Atg/ATG: autophagy-related; CAR: Coxsackievirus and adenovirus receptor; Cas9: CRISPR associated protein 9; Cre: recombinase that causes recombination; CRISPR: clustered regularly interspaced short palindromic repeats; Ctsb/CTSB: cathepsin B; CVB3: coxsackievirus B3; DsRedCVB3: a recombinant CVB3 that encodes the Discosoma red fluorescent protein; EL: elastase; FR: food restriction; GFP: green fluorescent protein; gRNA: guide RNA; HBSS: Hanks Buffered Salt Solution; LYNUS: lysosomal nutrient sensing machinery; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MFI: mean fluorescence intensity; MOI: multiplicity of infection; MTOR: mechanistic target of rapamycin kinase; Nluc: nanoluciferase; NlucCVB3: a recombinant CVB3 encoding nanoluciferase; pfu: plaque-forming unit(s); p.i.: post infection; rCVB: recombinant coxsackievirus B3; RPS6KB/p70S6K: ribosomal protein S6 kinase; RT: room temperature; siRNA: small interfering RNA; TFEB: transcription factor EB; tg: transgenic; TUBB: β-tubulin; UNINF: uninfected; wrt: with respect to; WT: wild type.

Natural Products as a Paradigm for the Treatment of Coxsackievirus - induced Myocarditis

Coxsackievirus B3 (CVB3), a member of the Picornaviridae family, is considered to be one of the most important infectious agents to cause virus-induced myocarditis. Despite improvements in studying viral pathology, structure and molecular biology, as well as diagnosis of this disease, there is still no virus-specific drug in clinical use. Structural and nonstructural proteins produced during the coxsackievirus life cycle have been identified as potential targets for blocking viral replication at the step of attachment, entry, uncoating, RNA and protein synthesis by synthetic or natural compounds. Moreover, WIN (for Winthrop) compounds and application of nucleic-acid based strategies were shown to target viral capsid, entry and viral proteases, but have not reached to the clinical trials as a successful antiviral agent. There is an urgent need for diverse molecular libraries for phenotype-selective and high-throughput screening.

A review on current status of antiviral siRNA

Viral diseases like influenza, AIDS, hepatitis, and Ebola cause severe epidemics worldwide. Along with their resistant strains, new pathogenic viruses continue to be discovered so creating an ongoing need for new antiviral treatments. RNA interference is a cellular gene‐silencing phenomenon in which sequence‐specific degradation of target mRNA is achieved by means of complementary short interfering RNA (siRNA) molecules. Short interfering RNA technology affords a potential tractable strategy to combat viral pathogenesis because siRNAs are specific, easy to design, and can be directed against multiple strains of a virus by targeting their conserved gene regions. In this review, we briefly summarize the current status of siRNA therapy for representative examples from different virus families. In addition, other aspects like their design, delivery, medical significance, bioinformatics resources, and limitations are also discussed.

Inhibition of coxsackievirus infection in cardiomyocytes by small dsRNA targeting its cognate coxsackievirus adenovirus receptor

Background & objectives:

Coxsackievirus B (CVB), a member of human Enterovirus group, is the most common cause of viral myocarditis. Coxsackievirus adenovirus receptor (CAR) is identified as a key determinant for the entry of CVB in the target cells. Thus, blockade of receptor by RNA interference (RNAi) may inhibit the entry and pathogenesis of CVB in cardiac cells. The present study was aimed to determine the effect of CAR small dsRNA (siRNA) on coxsackieviral load and CAR expression in coxsackievirus-infected cardiomyocytes.

Methods:

Transfection efficiency in rat cardiomyocytes (H9c2) was determined by the fluorescent microscopy and flow cytometry. CAR siRNA dose was optimized based on cell viability and relative CAR messenger RNA (mRNA) expression. Cardiomyocytes were transfected with CAR siRNA followed by infection with 100 multiplicity of infection of CVB, which were harvested after 24, 48 and 72 h post-infection (p.i.). RNA was extracted for relative CAR mRNA expression. Cells were freeze-thawed thrice for estimating coxsackieviral load.

Results:

The efficiency of transfection was optimized to be >80 per cent and CAR siRNA dose of 60 pmol was standardized. The knockdown of CAR by siRNA decreased its expression twice the expression in normal cardiomyocytes after 24 h p.i. of CVB. The treatment with CAR siRNA resulted in significant two log reduction of CVB load in cardiomyocytes infected with CVB at 24 h p.i. and retained till 72 h p.i.

Interpretation & conclusions:

The inhibition of CAR by siRNA was found to be effective against CVB in cardiomyocytes. However, this treatment strategy has to be evaluated in vivo to develop a new treatment strategy for patients suffering with viral myocarditis.

Small interfering (Si) RNA mediated baculovirus replication reduction without affecting target gene expression

The baculovirus expression vector system (BEVS) is widely used to produce large quantities of recombinant protein with posttranslational modification. Recombinant baculoviruses (such as Autographa californica multiple nuclear polyhedrosis virus) are especially useful in producing recombinant proteins and virus-like particles (VLPs) as biodrugs or candidate vaccines for the prevention of serious infectious diseases. However, during the bioprocessing of recombinant proteins in insect cells, baculovirus replication and viral budding are coincident. In some cases, residual baculovirus contaminants remain in the recombinant protein products, even though various purification processes are applied such as ion-exchange chromatography, ultracentrifugation, or gel filtration. To reduce unexpected contamination caused by replication and budding-out of the baculovirus, we designed short interfering (si) RNAs targeting glycoprotein 64 (GP64) or single-stranded DNA-binding protein (DBP) to inhibit baculovirus replication during overexpression of recombinant foreign genes. GP64 is known to be critical both for the entry of virions into cells and for the assembly of the budded virion at the cell surface. DBP is also essential for virus assembly by regulation of the capsid protein P39 and the polyhedrin protein. This study showed that GP64 expression was suppressed by GP64 siRNAs in Western blot experiments, while the expression of recombinant proteins was unaffected. In addition, transfection of GP64 siRNAs and DBP siRNAs reduced the level of baculovirus replication, compared with the treatment with scrambled siRNAs. However, DBP siRNA also suppressed the expression of recombinant proteins. In conclusion, our GP64 siRNAs showed that an interfering RNA system, such as siRNAs and short hairpin (sh) RNAs, can be applicable to reduce baculovirus contaminants during the bioprocessing of recombinant proteins in insect cells. Further investigation should be carried out to establish transformed insect cell lines with stable expression of corresponding interfering RNAs.

Antiviral activity of Bifidobacterium adolescentis SPM1605 against Coxsackievirus B3

Bifidobacteria are considered one of the most beneficial probiotics and have been widely studied for their effects against specific pathogens. The present study investigated the antiviral activity of probiotics isolated from Koreans against Coxsackievirus B3 (CVB3). The effect of probiotic isolates against CVB3 was measured by the plaque assay and cellular toxicity of bifidobacteria in HeLa cells was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Among 13 probiotic isolates, 3 Bifidobacterium adolescentis, 2 Bifidobacterium longum and 1 Bifidobacterium pseudocatenulatum had an antiviral effect against CVB3, while the others did not show such effect. B. adolescentis SPM1605 showed the greatest inhibitory properties against CVB3. When the threshold cycle (CT) values for the treated B. adolescentis SPM1605 samples were compared to the results for the non-treated samples, it was shown that the amplified viral sequences from the CVB3 had their copy number lowered by B. adolescentis SPM1605. Moreover, the gene expression in infected HeLa cells was also inhibited by 50%. The results suggest that B. adolescentis SPM1605 suppresses CVB3 and could be used as an alternative therapy against infectious diseases caused by coxsackieviruses.

Highlights in antiviral drug research: antivirals at the horizon

This review highlights ten "hot topics" in current antiviral research: (i) new nucleoside derivatives (i.e., PSI-352938) showing high potential as a direct antiviral against hepatitis C virus (HCV); (ii) cyclopropavir, which should be further pursued for treatment of human cytomegalovirus (HCMV) infections; (iii) North-methanocarbathymidine (N-MCT), with a N-locked conformation, showing promising activity against both α- and γ-herpesviruses; (iv) CMX001, an orally bioavailable prodrug of cidofovir with broad-spectrum activity against DNA viruses, including polyoma, adeno, herpes, and pox; (v) favipiravir, which is primarily pursued for the treatment of influenza virus infections, but also inhibits the replication of other RNA viruses, particularly (-)RNA viruses such as arena, bunya, and hanta; (vi) newly emerging antiarenaviral compounds which should be more effective (and less toxic) than the ubiquitously used ribavirin; (vii) antipicornavirus agents in clinical development (pleconaril, BTA-798, and V-073); (viii) natural products receiving increased attention as potential antiviral drugs; (ix) antivirals such as U0126 targeted at specific cellular kinase pathways [i.e., mitogen extracellular kinase (MEK)], showing activity against influenza and other viruses; and (x) two structurally unrelated compounds (i.e., LJ-001 and dUY11) with broad-spectrum activity against virtually all enveloped RNA and DNA viruses.

Multispecies-compatible antitumor effects of a cross-species small-interfering RNA against mammalian target of rapamycin

Successful development of sequence-specific siRNA (small interfering RNA)-based drugs requires an siRNA design that functions consistently in different organisms. Utilizing the CAPSID program previously developed by our group, we here designed siRNAs against mammalian target of rapamycin (mTOR) that are entirely complementary among various species and investigated their multispecies-compatible gene-silencing properties. The mTOR siRNAs markedly reduced mTOR expression at both the mRNA and protein levels in human, mouse, and monkey cell lines. The reduction in mTOR expression resulted in inactivation of both mTOR complex I and II signaling pathways, as confirmed by reduced phosphorylation of p70S6K (70-kDa ribosomal protein S6 kinase), 4EBP1 (eIF4E-binding protein 1), and AKT, and nuclear accumulation of FOXO1 (forkhead box O1), with consequent cell-cycle arrest, proliferation inhibition, and autophagy activation. Moreover, interfering with mTOR activity in vivo using mTOR small-hairpin RNA-expressing recombinant adeno-associated virus led to significant antitumor effects in xenograft and allograft models. Thus, the present study demonstrates that cross-species siRNA successfully silences its target and readily produces multispecies-compatible phenotypic alterations-antitumor effects in the case of mTOR siRNA. Application of cross-species siRNA should greatly facilitate the development of siRNA-based therapeutic agents.

Short hairpin RNA targeting 2B gene of coxsackievirus B3 exhibits potential antiviral effects both in vitro and in vivo

Background

Coxsackievirus B3 is an important infectious agent of viral myocarditis, pancreatitis and aseptic meningitis, but there are no specific antiviral therapeutic reagents in clinical use. RNA interference-based technology has been developed to prevent the viral infection.

Methods

To evaluate the impact of RNA interference on viral replication, cytopathogenicity and animal survival, short hairpin RNAs targeting the viral 2B region (shRNA-2B) expressed by a recombinant vector (pGCL-2B) or a recombinant lentivirus (Lenti-2B) were tansfected in HeLa cells or transduced in mice infected with CVB3.

Results

ShRNA-2B exhibited a significant effect on inhibition of viral production in HeLa cells. Furthermore, shRNA-2B improved mouse survival rate, reduced the viral tissues titers and attenuated tissue damage compared with those of the shRNA-NC treated control group. Lenti-2B displayed more effective role in inhibition of viral replication than pGCL-2B in vivo.

Conclusions

Coxsackievirus B3 2B is an effective target of gene silencing against coxsackievirus B3 infection, suggesting that shRNA-2B is a potential agent for further development into a treatment for enterviral diseases.

Antiviral effects of small interfering RNA simultaneously inducing RNA interference and type 1 interferon in coxsackievirus myocarditis

Antiviral therapeutics are currently unavailable for treatment of coxsackievirus B3, which can cause life-threatening myocarditis. A modified small interfering RNA (siRNA) containing 5'-triphosphate, 3p-siRNA, was shown to induce RNA interference and interferon activation. We aimed to develop a potent antiviral treatment using CVB3-specific 3p-siRNA and to understand its underlying mechanisms. Virus-specific 3p-siRNA was superior to both conventional virus-specific siRNA with an empty hydroxyl group at the 5' end (OH-siRNA) and nonspecific 3p-siRNA in decreasing viral replication and subsequent cytotoxicity. A single administration of 3p-siRNA dramatically attenuated virus-associated pathological symptoms in mice with no signs of toxicity, and their body weights eventually reached the normal range. Myocardial inflammation and fibrosis were rare, and virus production was greatly reduced. A nonspecific 3p-siRNA showed relatively less protective effect under identical conditions, and a virus-specific OH-siRNA showed no protective effects. We confirmed that virus-specific 3p-siRNA simultaneously activated target-specific gene silencing and type I interferon signaling. We provide a clear proof of concept that coxsackievirus B3-specific 3p-siRNA has 2 distinct modes of action, which significantly enhance antiviral activities with minimal organ damage. This is the first direct demonstration of improved antiviral effects with an immunostimulatory virus-specific siRNA in coxsackievirus myocarditis, and this method could be applied to many virus-related diseases.

Pharmacological and biological antiviral therapeutics for cardiac coxsackievirus infections

Subtype B coxsackieviruses (CVB) represent the most commonly identified infectious agents associated with acute and chronic myocarditis, with CVB3 being the most common variant. Damage to the heart is induced both directly by virally mediated cell destruction and indirectly due to the immune and autoimmune processes reacting to virus infection. This review addresses antiviral therapeutics for cardiac coxsackievirus infections discovered over the last 25 years. One group represents pharmacologically active low molecular weight substances that inhibit virus uptake by binding to the virus capsid (e.g., pleconaril) or inactivate viral proteins (e.g., NO-metoprolol and ribavirin) or inhibit cellular proteins which are essential for viral replication (e.g., ubiquitination inhibitors). A second important group of substances are interferons. They have antiviral but also immunomodulating activities. The third and most recently discovered group includes biological and cellular therapeutics. Soluble receptor analogues (e.g., sCAR-Fc) bind to the virus capsid and block virus uptake. Small interfering RNAs, short hairpin RNAs and antisense oligonucleotides bind to and led to degradation of the viral RNA genome or cellular RNAs, thereby preventing their translation and viral replication. Most recently mesenchymal stem cell transplantation has been shown to possess antiviral activity in CVB3 infections. Taken together, a number of antiviral therapeutics has been developed for the treatment of myocardial CVB infection in recent years. In addition to low molecular weight inhibitors, biological therapeutics have become promising anti-viral agents.

Targeted delivery of mutant tolerant anti-coxsackievirus artificial microRNAs using folate conjugated bacteriophage Phi29 pRNA

BACKGROUND

Myocarditis is the major heart disease in infants and young adults. It is very commonly caused by coxsackievirus B3 (CVB3) infection; however, no specific treatment or vaccine is available at present. RNA interference (RNAi)-based anti-viral therapy has shown potential to inhibit viral replication, but this strategy faces two major challenges; viral mutational escape from drug suppression and targeted delivery of the reagents to specific cell populations.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we designed artificial microRNAs (AmiRs) targeting the 3'untranslated region (3'UTR) of CVB3 genome with mismatches to the central region of their targeting sites. Antiviral evaluation showed that AmiR-1 and AmiR-2 reduced CVB3 (Kandolf and CG strains) replication approximately 100-fold in both HeLa cells and HL-1 cardiomyocytes. To achieve specific delivery, we linked AmiRs to the folate-conjugated bacterial phage packaging RNA (pRNA) and delivered the complexes into HeLa cells, a folate receptor positive cancer cells widely used as an in vitro model for CVB3 infection, via folate-mediated specific internalization. We found that our designed pRNA-AmiRs conjugates were tolerable to target mutations and have great potential to suppress viral mutational escape with little effect on triggering interferon induction.

CONCLUSION/SIGNIFICANCE

This study provides important clues for designing AmiRs targeting the 3'UTR of viral genome. It also proves the feasibility of specific deliver of AmiRs using conjugated pRNA vehicles. These small AmiRs combined with pRNA-folate conjugates could form a promising system for antiviral drug development.

Rapid construction of adeno-associated virus vectors expressing multiple short hairpin RNAs with high antiviral activity against echovirus 30

RNA interference has proven to be a powerful tool to inhibit viruses. For the prevention of viral escape, multiple short hairpin RNAs (shRNAs) will have to be employed. This article describes a rapid procedure for the generation of shRNA expression cassettes by parallel cloning as well as a simple strategy for the combination of selected units. After delivery of the shRNA expression cassettes with adeno-associated virus vectors, inhibition of echovirus 30 as well as silencing of an important cellular cofactor of virus replication were achieved. The procedure has the potential to be generally applicable for silencing of multiple endogenous targets or viruses.

Inhibition of adenovirus infections by siRNA-mediated silencing of early and late adenoviral gene functions

Adenoviruses are pathological agents inducing mild respiratory and gastrointestinal infections. Under certain circumstances, for example in immunosuppressed patients, they induce severe infections of the liver, heart and lung, sometimes leading to death. Currently, adenoviral infections are treated by palliative care with no curative antiviral therapy yet available. Gene silencing by RNA interference (RNAi) has been shown to be a potent new therapeutic option for antiviral therapy. In the present study, we examined the potential of RNAi-mediated inhibition of adenovirus 5 infection by the use of small interfering (si)RNAs targeting both early (E1A) and late (hexon, IVa2) adenoviral genes. Several of the initially analyzed siRNAs directed against E1A, hexon and IVa2 showed a distinct antiviral activity. Among them, one siRNA for each gene was selected and used for the further comparative investigations of their efficiency to silence adenoviruses. Silencing of the late genes was more efficient in inhibiting adenoviral replication than comparable silencing of the E1A early gene. A combination strategy involving down-regulation of any two or all three of the targeted genes did not result in an enhanced inhibition of viral replication as compared to the single siRNA approaches targeting the late genes. However, protection against adenovirus-mediated cytotoxicity was substantially improved by combining siRNAs against either of the two late genes with the siRNA against the E1A early gene. Thus, an enhanced anti-adenoviral efficiency of RNAi-based inhibition strategies can be achieved by co-silencing of early and late adenoviral genes, with down regulation of the E1A as a crucial factor.

Inhibition of coxsackievirus B3 and related enteroviruses by antiviral short interfering RNA pools produced using phi6 RNA-dependent RNA polymerase

Coxsackievirus B3 (CBV3) is a member of the human enterovirus B species and a common human pathogen. Even though much is known about the enteroviral life cycle, no specific drugs are available to treat enterovirus infections. RNA interference (RNAi) has evolved to be an important tool for antiviral experimental therapies and gene function studies. We describe here a novel approach for RNAi against CBVs by using a short interfering (siRNA) pool covering 3.5 kb of CBV3 genomic sequence. The RNA-dependent RNA polymerase (RdRP) of bacteriophage phi6 was used to synthesize long double-stranded RNA (dsRNA) from a cloned region (nt 3837-7399) of the CBV3 genome. The dsRNA was cleaved using Dicer, purified and introduced to cells by transfection. The siRNA pool synthesized using the phi6 RdRP (phi6-siRNAs) was considerably more effective than single-site siRNAs. The phi6-siRNA pool also inhibited replication of other enterovirus B species, such as coxsackievirus B4 and coxsackievirus A9.

A novel program to design siRNAs simultaneously effective to highly variable virus genomes

A major concern of antiviral therapy using small interfering RNAs (siRNAs) targeting RNA viral genome is high sequence diversity and mutation rate due to genetic instability. To overcome this problem, it is indispensable to design siRNAs targeting highly conserved regions. We thus designed CAPSID (Convenient Application Program for siRNA Design), a novel bioinformatics program to identify siRNAs targeting highly conserved regions within RNA viral genomes. From a set of input RNAs of diverse sequences, CAPSID rapidly searches conserved patterns and suggests highly potent siRNA candidates in a hierarchical manner. To validate the usefulness of this novel program, we investigated the antiviral potency of universal siRNA for various Human enterovirus B (HEB) serotypes. Assessment of antiviral efficacy using Hela cells, clearly demonstrates that HEB-specific siRNAs exhibit protective effects against all HEBs examined. These findings strongly indicate that CAPSID can be applied to select universal antiviral siRNAs against highly divergent viral genomes.

Antiviral activity of highly potent siRNAs against echovirus 30 and its receptor

RNA interference (RNAi) has been shown to be suitable to inhibit viruses in experimental setups and is considered a promising antiviral strategy that is currently being tested in various clinical trials. The present study provides an approach to design siRNAs with high potency against a virus-specific target gene. In recent years, several outbreaks of aseptic meningitis caused by an echovirus 30 (EV-30) infection have been described. Based on an initial set of 30 in silico designed siRNAs, six siRNAs targeting the 3D RNA-dependent RNA-Polymerase (3D(Pol)) of EV-30 were selected. All but one of them showed high efficiency in both, reporter and virus assays. A second aim of the study was to re-investigate the relevance of the decay-accelerating factor (DAF, also known as CD55) as cellular entry receptor of EV-30 by means of RNAi, a question which had been under debate in previous studies. Knockdown of DAF inhibited drastically infection by EV-30 indicating that DAF plays an important role either as an attachment factor or as a receptor.

Antiviral potency of a siRNA targeting a conserved region of coxsackievirus A24

Coxsackievirus A24 (CVA24) is responsible for acute hemorrhagic conjunctivitis, a highly contagious eye disease for which no prevention or treatment is currently available. We thus assessed the antiviral potential of a small interfering RNA (siRNA) targeting CVA24. HeLa cells with or without four different siRNAs complementary to 2C or 3D genome region, were challenged with various CVA24s. Among several siRNAs, a siRNA targeting the highly conserved genome region called the cis-acting replication element (CVA24-CRE), was the only siRNA that decreased virus replication and subsequent cytotoxicity by both CVA24 variant and clinical isolates. Furthermore, CVA24-CRE had effective antiviral activity against CVA24 in primary human conjunctival cells. In addition, CVA24-CRE was highly resistant to the emergence of genetically altered escape mutants. Collectively, the present study provides evidence that CVA24-CRE targeting a conserved viral genome region had universal, prolonged anti-CVA24 activity. This siRNA may thus hold a potential to act clinically as a novel anti-CVA24 agent.

Design of LNA-modified siRNAs against the highly structured 5' UTR of coxsackievirus B3

This study describes a strategy to develop LNA-modified small interfering RNA (siRNAs) against the highly structured 5' UTR of coxsackievirus B3 (CVB-3), which is an attractive target site due to its high degree of conservation. Accessible sites were identified based on structural models and RNase H assays with DNA oligonucleotides. Subsequently, LNA gapmers, siRNAs, siLNAs and small internally segmented interfering RNA (sisiLNAs) were designed against sites, which were found to be accessible in the in vitro assays, and tested in reporter assays and experiments with the infectious virus. The best siLNA improved viability of infected cells by 92% and exerted good antiviral activity in plaque reduction assays.

Primary neurons become less susceptible to coxsackievirus B5 following maturation: the correlation with the decreased level of CAR expression on cell surface

Coxsackievirus B (CVB) is one of the major pathogens of aseptic meningitis and meningioencephalitis, particularly in newborn infants. To analyze the influence of neural maturation on susceptibility to CVB infection, we prepared immature and mature neurons from 16-day-old BALB/c embryonic cortex. In contrast to immature neurons, mature neurons were less susceptible to CVB5 infection, as indicated by the decrease of cytopathic features. In mature neurons, progeny virus production was significantly hindered, and virus capsid protein VP1 synthesis and virus genome amplification were concomitantly reduced. In addition, the expression of coxsackievirus and adenovirus receptor (CAR), the major receptor of CVB5, was down-regulated in mature neurons. The antibody treatment specific to CAR significantly attenuated CVB5 susceptibility of immature neurons. These findings demonstrate that mature neurons become less susceptible to CVB by the decrease of CAR level. Thus, the data strongly support the idea that the level of virus receptor in neurons is one of the crucial determinants in the age-dependency of CVB virulence in central nervous system.

A morpholino oligomer targeting highly conserved internal ribosome entry site sequence is able to inhibit multiple species of picornavirus

Members of the genera Enterovirus and Rhinovirus (family Picornaviridae) cause a wide range of human diseases. An established vaccine is available only for poliovirus, and no effective therapy is available for the treatment of infections caused by any pathogenic picornavirus. Peptide-conjugated phosphorodiamidate morpholino oligomers (PPMO) are single-stranded DNA-like antisense agents that readily enter cells. A panel of PPMO was tested for their antiviral activities against various picornaviruses. PPMO targeting conserved internal ribosome entry site (IRES) sequence were highly active against human rhinovirus type 14, coxsackievirus type B2, and poliovirus type 1 (PV1), reducing PV1 titers by up to 6 log(10) in cell cultures. Comparative sequence analysis led us to design a PPMO (EnteroX) targeting 22 nucleotides of IRES sequence that are perfectly conserved across greater than 99% of all human enteroviruses and rhinoviruses. EnteroX reduced PV1 replication in cell culture to an extent similar to that of other IRES-specific PPMO. Resistant PV1 arose in cell cultures after 12 passages in the presence of EnteroX and were found to have two mutations within the EnteroX target sequence. Nevertheless, cPVR transgenic mice treated once daily by intraperitoneal (i.p.) injection with EnteroX before and/or after i.p. infection with 3 x 10(8) PFU (three times the 50% lethal dose) of PV1 had an approximately 80% higher rate of survival than the controls. The viral titer in tissues taken at day 5 postinfection showed that animals in the EnteroX-treated group averaged over 3, 4, and 5 log(10) less virus in the small intestine, spinal cord, and brain, respectively, than the amount in the control animals. These results suggest that EnteroX may have broad therapeutic potential against entero- and rhinoviruses.

Recombinant lentivirus-delivered short hairpin RNAs targeted to conserved coxsackievirus sequences protect against viral myocarditis and improve survival rate in an animal model

Coxsackieviruses are important human pathogens that induce myocarditis and pancreatitis. However, there are no vaccines or therapeutic reagents for their clinical treatment. Although RNA interference (RNAi)-based approaches to the prevention of viral production have been developed recently, limitations to the in vivo delivery systems and variations in the viral target sequences still hamper the strategy. In this study, to overcome these limitations, we have constructed recombinant lentivirus-delivered short hairpin RNAs (shRNAs) against sequences in highly conserved cis-acting replication element (CRE) within the 2C protein of coxsackievirus B3 (CVB3), designated MET-2C. A recombinant lentivirus, designated Met-2C lenti, was constructed that contains the MET-2C sequence, which acts as a shRNA. Met-2C lenti clearly reduced viral production in CVB3-infected cells in vitro. Moreover, the mice injected intraperitoneally with Met-2C lenti had significant reductions in viral titers, viral myocarditis, and proinflammatory cytokines after challenge with CVB3, compared with those in GFP lenti infected control mice. Moreover, Met-2C lenti improved survival rate compared with that of the GFP lenti infected control group. Therefore, Met-2C lenti is potentially a clinical therapeutic agent for the treatment of viral myocarditis.

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.

Current status of gene therapy in Asia

Asian countries, in particular China, Japan, and Korea, have been aggressively researching and developing gene medicines over the last 15 years or so. In China, an adenovirus expressing p53 was approved for commercial use in the year 2003, and has been on the actual market since then, becoming the world's first commercial gene-based drug. In Japan and Korea, many interesting scientific discoveries have been made, and industrially valuable technologies have been developed. It is particularly noteworthy to see that in these countries, gene therapy has been very keenly nurtured in relation with industrial and financial sectors. Despite remarkable progresses made in Asia, however, their activities have not been visibly noticed by many scientists in the US and European countries. This article briefly reviews key features of the past achievements and recent progresses made in three Asian countries.

Universal and mutation-resistant anti-enteroviral activity: potency of small interfering RNA complementary to the conserved cis-acting replication element within the enterovirus coding region

The promising potential of RNA interference-based antiviral therapies has been well established. However, the antiviral efficacy is largely limited by genomic diversity and genetic instability of various viruses, including human enterovirus B (HEB). In this work, the first evidence supporting the anti-HEB activity of the small interfering RNA (siRNA) targeting the highly conserved cis-acting replication element (CRE) within virus coding region 2C is presented. HeLa cells pre-treated with siRNA complementary to the conserved sequence of the loop region of CRE(2C) were effectively rescued from the cytopathic effects of HEBs. Downregulation of virus replication and attenuation of cytotoxicity were consistently observed in various reference strains and clinical isolates. Cells treated with this siRNA were resistant to the emergence of viable escape mutants and showed sustained antiviral ability. Collectively, the data suggest that the siRNA based on the disordered structure within the highly conserved cis-acting coding region has potential as a universal, persistent anti-HEB agent. The same strategy can be successfully applied to the development of siRNA with consistent antiviral effects in other virus groups possessing similar RNA elements.

Silencing of hepatitis A virus infection by small interfering RNAs

Infection by hepatitis A virus (HAV) can cause acute hepatitis and, rarely, fulminant liver failure, in particular in patients chronically infected with hepatitis C virus. Based on our previous observation that small interfering RNAs (siRNAs) can silence translation and replication of the firefly luciferase-encoding HAV replicon, we now exploited this technology to demonstrate the effect of siRNAs on viral infection in Huh-7 cells. Freshly and persistently infected cells were transfected with siRNAs targeting various sites in the HAV nonstructural genes. Compared to a single application, consecutive siRNA transfections targeting multiple sequences in the viral genome resulted in a more efficient and sustained silencing effect than a single transfection. In most instances, multiple applications of a single siRNA led to the emergence of viral escape mutants with mutated target sites that rendered these genomes resistant to RNA interference (RNAi). Efficient and sustained suppression of the viral infectivity was achieved after consecutive applications of an siRNA targeting a computer-predicted hairpin structure. This siRNA holds promise as a therapeutic tool for severe courses of HAV infection. In addition, the results provide new insight into the structural bases for sequence-specific RNAi.

Anti-coxsackieviral efficacy of RNA interference is highly dependent on genomic target selection and emergence of escape mutants

Enteroviral diseases are widespread and impose significant importance in medicine. Although the outcome of diseases that are associated with enteroviruses such as myocarditis, pancreatitis, hepatitis, or encephalomyelitis might be fatal, no specific antiviral therapy is yet available. We and others have shown that RNA interference (RNAi) effectively limits picornaviral replication and cytopathogenicity and improves survival in susceptible mice. However, little is known about the dependence of short interfering RNA (siRNA) efficacy on target region selection and emergence of viral escape mutants that may limit the effect of RNAi. The results of our study indicate that antiviral siRNA should be targeted preferentially to nonstructural protein coding regions because siRNA efficacy was consistently found to be superior compared to noncoding or structural protein coding regions. Further more, emergence of viral escape mutants that harbor single point mutations in the central part of the siRNA binding motif are the major factor that limits early therapeutic siRNA efficacy. The appearance of viral escape mutants can be sufficiently suppressed by combined administration of at least three distinct siRNA molecules. Therefore, genomic target selection and viral escape mutants are the most critical factors that limit early RNAi directed against enteroviral genomes. Both obstacles can be circumvented by appropriate target selection and combined siRNA administration.

Expression of short hairpin RNAs against the coxsackievirus B3 exerts potential antiviral effects in Cos-7 cells and in mice

Chemically synthesized small interfering RNA (siRNA) has been used as an anti-coxsackievirus B3 (CVB3) agent. Herein, we investigated whether vector-derived short hairpin RNAs (shRNA) targeting CVB3 can exert antiviral activities, prior to their further application to viral vector system for efficient in vivo administration. Employing transient transfection assays to in vivo mouse models as well as to in vitro Cos-7 cell cultures, we directly demonstrated the potential antiviral activity of shRNAs following challenges with infectious CVB3. Of the six shRNAs that we designed, three prevented cell death from CVB3 infection by suppressing viral replication and viral production in Cos-7 cells. These were shRNA 2, which targeted the capsid protein VP1, and shRNAs 4 and 5, which targeted two different regions of the RNA-dependent RNA polymerase 3D. Furthermore, shRNAs 2 and 5 also exerted strong antiviral effects in viral replication in vivo, accompanied by attenuated pancreatic tissue damage. Through this direct evaluation system we addressed the development and application of vector-derived shRNAs as an anti-CVB3 agent, revealing new target sequences.

Strand-specific silencing of a picornavirus by RNA interference: evidence for the superiority of plus-strand specific siRNAs

RNA interference triggered by small interfering RNAs (siRNAs) can be used to effectively contain viral spread. Here, we report on the mechanism of action of siRNAs targeting the medically important coxsackievirus B3 (CVB-3) as a typical representative of viruses with a non-segmented RNA genome in positive-strand orientation. Antiviral siRNAs can be designed to target the genomic (+)-strand, the (-)-strand that occurs as a replication intermediate, or both. In the present study, two complementary and systematic approaches are presented providing direct evidence that silencing of the viral (+)-strand is the key to inhibit CVB-3: first, we used rational siRNA design to direct silencing activity specifically against either of the two viral strands. As a second approach, we employed siRNA containing modified nucleotides to render them specific for one of the virus RNAs. Experiments with infectious coxsackievirus revealed that the inhibitory efficiency correlates exclusively with the activity of the siRNAs directed against the viral (+)-strand. Our finding that only (+)-strand specific siRNAs exert significant antiviral potency may hold true for other RNA viruses with (+)-stranded genomes as well and may therefore be helpful in the development of efficient strategies to inhibit virus propagation.

RNA interference for antiviral therapy

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