Respiratory syncytial virus infections: Recent prospects for control

Antiviral nucleoside analogs

The minireview surveys the modification of native nucleosides as a result of which huge libraries of nucleoside analogs of various structures were synthesized. Particular attention is paid to the synthesis of the so-called prodrug forms of nucleoside analogs which ensure their penetration into the cell and metabolism to active 5'-triphosphate derivatives. All the best known antiviral cyclic nucleoside analogs approved for the treatment of HIV infections, hepatitis B, C, and influenza since the 1960s, as well as those in various stages of clinical trials in recent years, are listed. Nucleoside analogs that have shown the ability to inhibit the replication of SARS-CoV and MERS-CoV are discussed, including remdesivir, approved by the FDA for emergency use in the fight against COVID-19.

[Liquid chromatography-mass spectrometry-based metabolomics study of the efficacy of Chinese medicine asthma-relieving decoction on respiratory syncytial virus infection]

Respiratory syncytial virus (RSV) can cause lower respiratory tract infections, such as bronchiolitis in infants. In China, traditional asthma-relieving medicine has numerous clinical applications in the treatment of RSV infections. However, due to the complexity of the traditional Chinese medicine system, its therapeutic mechanism and main pharmacological components remain unclear. Metabolomics can be used to analyze the efficacy of traditional Chinese medicine to provide modern scientific evidence for such treatments. In this study, an animal model experiment was performed with seven groups of three-week-old rats. The model group and five intervention groups were inoculated nasally with RSV for three consecutive days, and the normal group was treated with the same amount of saline for three consecutive days under the same conditions. In parallel, the five intervention groups were treated separately with the following via intragastric administration for seven consecutive days: asthma-relieving traditional Chinese medicine decoction, its three constituent agents (ascending (xuan) therapy, descending (jiang) therapy, pyretic clearing (qing) therapy), and ribavirin. Both normal group and RSV model group were administered with normal saline via intragastric administration as controls for seven consecutive days. The fundus plasma of rats in each group was collected on day 0, day 3, and day 7. Liquid chromatography-mass spectrometry-based untargeted metabolomics analysis was performed to investigate the changes in the metabolome after RSV infection, the effects of the asthma-relieving decoction on the regulation of metabolites related to RSV infection, and the primary source of efficacy. The detected metabolite ions were corrected using internal standards. Multivariate analysis of ions with an RSD value of less than 30% in quality control (QC) samples was used to construct principal component analysis models to monitor the overall metabolic changes of each group. The results showed that, during RSV infection and treatment, the asthma-relieving decoction and the positive control ribavirin had similar effects on the overall metabolic regulation of RSV-infected rats. Among the three asthma-relieving decoction constituent agents, the ascending (xuan) therapy agents which was composed of ephedra and ginkgo had a closer metabolic regulation effect with asthma-relieving decoction, and might be the main source of pharmacological efficacy. Based on the retention time, m/z value and tandem mass spectra in the database established by our laboratory, a total of 150 metabolites were identified. Paired t-tests were performed using data of the identified metabolites before and after RSV infection in each group, and it was found that 83 metabolite levels significantly changed after RSV infection, indicating that RSV infection could lead to disorders of multiple metabolic pathways in rats. The altered pathways included aminoacyl-tRNA biosynthesis, phenylalanine, tyrosine, and tryptophan biosynthesis, primary bile acid biosynthesis, phenylalanine metabolism and sphingomyelin metabolism. On the third day, the asthma-relieving decoction had regulatory effects on several metabolites such as bile acids, amino acids, organic acids, lipids, etc. Among the three asthma-relieving decoction constituent agents, the ascending (xuan) therapy agents had more similar effects on the regulation of metabolites with the asthma-relieving decoction. On the other hand, the descending (jiang) therapy agents and pyretic clearing (qing) therapy agents down-regulated the abnormal increase in acylcarnitine caused by the RSV infection. Additionally, both asthma-relieving decoction and its constituent agents could maintain the stability of the immune system and metabolism of the intestinal flora in rats. This study used metabolomics to evaluate the efficacy of an asthma-relieving decoction and demonstrate the metabolites and the corresponding changes after asthma-relieving decoction-based treatment. It provides theoretical support for research on the therapeutic mechanism and active ingredients of asthma-relieving decoction.

Insights into Interactions of Flavanones with Target Human Respiratory Syncytial Virus M2-1 Protein from STD-NMR, Fluorescence Spectroscopy, and Computational Simulations

The human Respiratory Syncytial Virus (hRSV) is the most frequent agent of respiratory infections in infants and children with no currently approved vaccine. The M_2-1 protein is an important transcriptional antitermination factor and a potential target for viral replication inhibitor development. Hesperetin (HST) and hesperidin (HSD) are flavonoids from the flavanone group, naturally found in citrus and have, as one of their properties, antiviral activity. The present study reports on the interactions between hRSV M_2-1 and these flavanones using experimental techniques in association with computational tools. STD-NMR results showed that HST and HSD bind to M_2-1 by positioning their aromatic rings into the target protein binding site. Fluorescence quenching measurements revealed that HST had an interaction affinity greater than HSD towards M_2-1. The thermodynamic analysis suggested that hydrogen bonds and van der Waals interactions are important for the molecular stabilization of the complexes. Computational simulations corroborated with the experimental results and indicated that the possible interaction region for the flavonoids is the AMP-binding site in M_2-1. Therefore, these results point that HST and HSD bind stably to a critical region in M_2-1, which is vital for its biological function, and thus might play a possible role antiviral against hRSV.

Clinical and Pathogenic Characteristics of Lower Respiratory Tract Infection Treated at the Vietnam National Children's Hospital

Lower respiratory tract infections are commonly caused by viruses and cause significant morbidity and mortality among children. Early identification of the pathological agent causing these infections is essential to avoid unnecessary antibiotic use and improve patient management. Multiplex PCR techniques were recently developed to detect multiple viral pathogens using a single PCR reaction. In this study, we identify viral pathogens in children with respiratory infections. We collected 194 nasopharyngeal aspirates from infants (2-24 months old) with lower respiratory tract infections treated at the Vietnam National Children's Hospital between November 2014 and June 2015 and assessed the presence of 16 virus types and subtypes by multiplex PCR using the xTAG Respiratory Viral Panel (RVP) assay. Overall, 73.7% of the samples were positive for at least one virus, and 24.2% corresponded to infections with multiple viruses. The most common viruses were respiratory syncytial virus and enterovirus/rhinovirus. These viruses were more frequent among younger patients (2-5 months old) and caused symptoms similar to those of bronchiolitis and pneumonia. The most common clinical manifestation caused by respiratory tract infection was bronchiolitis. Elevated neutrophils levels were associated with adenovirus infection. Our results showed that the xTAG Respiratory Viral Panel (RVP) can effectively detect multiple viruses causing respiratory infections in children and that the nasopharyngeal aspirates are a good sample choice to detect respiratory viruses in children. Applying this approach in the clinical setting would improve patient management and allow early diagnosis, thus avoiding the unnecessary use of antibiotics.

Host Components Contributing to Respiratory Syncytial Virus Pathogenesis

Respiratory syncytial virus (RSV) is the most prevalent viral etiological agent of acute respiratory tract infection. Although RSV affects people of all ages, the disease is more severe in infants and causes significant morbidity and hospitalization in young children and in the elderly. Host factors, including an immature immune system in infants, low lymphocyte levels in patients under 5 years old, and low levels of RSV-specific neutralizing antibodies in the blood of adults over 65 years of age, can explain the high susceptibility to RSV infection in these populations. Other host factors that correlate with severe RSV disease include high concentrations of proinflammatory cytokines such as interleukins (IL)-6, IL-8, tumor necrosis factor (TNF)-α, and thymic stromal lymphopoitein (TSLP), which are produced in the respiratory tract of RSV-infected individuals, accompanied by a strong neutrophil response. In addition, data from studies of RSV infections in humans and in animal models revealed that this virus suppresses adaptive immune responses that could eliminate it from the respiratory tract. Here, we examine host factors that contribute to RSV pathogenesis based on an exhaustive review of in vitro infection in humans and in animal models to provide insights into the design of vaccines and therapeutic tools that could prevent diseases caused by RSV.

Biophysical and flavonoid-binding studies of the G protein ectodomain of group A human respiratory syncytial virus

The human Respiratory Syncytial Virus (hRSV) is the major causative agent of lower respiratory tract diseases in infants, young children and elderly. The membrane protein G is embedded in the viral lipid envelope and plays an adhesion function of the virus to host cells. The present study reports the production of the group A hRSV recombinant G protein ectodomain (edG) and its characterization of secondary structure and thermal unfolding by circular dichroism (CD), as well as the binding investigation of flavonoids quercetin and morin to this protein by fluorescent quenching. CD data reveal that edG is composed mostly of β-structure and its melting temperature is of 325 K. Fluorescence quenching experiments of hRSV edG show that the dissociation constants for the flavonoids binding are micromolar and the binding affinity for the edG/quercetin complex is inversely dependent on rising temperature while is directly dependent for the edG/morin interaction. The thermodynamic parameters suggest that hydrophobic contacts are important for the edG/morin association while van der Waals forces and hydrogen bonds contribute to the stabilization of the edG/quercetin complex. Thus, data reported herein may contribute to the development of new treatment strategies that prevent the viral infection by hRSV.

Genetic variability human respiratory syncytial virus subgroups A and B in Turkey during six successive epidemic seasons, 2009-2015

Human respiratory syncytial virus (HRSV) is most important viral respiratory pathogen of acute lower respiratory tract infections in infants and young children worldwide. The circulating pattern and genetic characteristics in the HRSV attachment glycoprotein gene were investigated in Turkey during six consecutive seasons from 2009 to 2015. HRSVA was dominant in the all epidemic seasons except 2011‐2012 season. Partial sequences of the HVR2 region of the G gene of 479 HRSVA and 135 HRSVB were obtained. Most Turkish strains belonged to NA1, ON1, and BA9, which were the predominant genotypes circulating worldwide. Although three novel genotypes, TR‐A, TR‐BA1, and TR‐BA2, were identified, they were not predominant. Clinical data were available for 69 HRSV‐positive patients who were monitored due to acute lower respiratory tract illness. There were no significant differences in the clinical diagnosis, hospitalization rates, laboratory findings and treatment observed between the HRSVA and HRSVB groups, and co‐infections in this study. The major population afflicted by HRSV infections included infants and children between 13 and 24 months of age. We detected that the CB1, GB5, and THB strains clustered in the same branch with a bootstrap value of 100%. CB‐B and BA12 strains clustered in the same branch with a bootstrap value of 65%. The BA11 genotype was clustered in the BA9 genotype in our study. The present study may contribute on the molecular epidemiology of HRSV in Turkey and provide data for HRSV strains circulating in local communities and other regions worldwide.

Biophysical characterization of the interaction between M2-1 protein of hRSV and quercetin

hRSV is the major causative agent of acute respiratory infections. Among its eleven proteins, M2-1 is a transcription antiterminator, making it an interesting target for antivirals. Quercetin is a flavonol which inhibits some virus infectivity and replication. In the present work, the M2-1 gene was cloned, expressed and the protein was purified. Thermal stability and secondary structure were analyzed by circular dichroism and the interaction with Quercetin was evaluated by fluorescence spectroscopy. Molecular docking experiments were performed to understand this mechanism of interaction. The purified protein is mainly composed of α-helix, with a melting temperature of 328.6K (≈55°C). M2-1 titration with Quercetin showed it interacts with two sites, one with a strong constant association K1 (site 1≈1.5×10⁶M^-1) by electrostatic interactions, and another with a weak constant association K2 (site 2≈1.1×10⁵M^-1) by a hydrophobic interaction. Ligand's docking shows it interacts with the N-terminus face in a more polar pocket and, between the domains of oligomerization and RNA and P protein interaction, in a more hydrophobic pocket, as predicted by experimental data. Therefore, we postulated this ligand could be interacting with important domains of the protein, avoiding viral replication and budding.

Application of Traditional Chinese Medical Herbs in Prevention and Treatment of Respiratory Syncytial Virus

Respiratory syncytial virus (RSV) is a common viral pathogen of the lower respiratory tract, which, in the absence of effective management, causes millions of cases of severe illness per year. Many of these infections develop into fatal pneumonia. In a review of English and Chinese medical literature, recent traditional Chinese medical herb- (TCMH-) based progress in the area of prevention and treatment was identified, and the potential anti-RSV compounds, herbs, and formulas were explored. Traditional Chinese medical herbs have a positive effect on inhibiting viral attachment, inhibiting viral internalization, syncytial formation, alleviation of airway inflammation, and stimulation of interferon secretion and immune system; however, the anti-RSV mechanisms of TCMHs are complicated, which should be further investigated.

A novel p38 mitogen activated protein kinase (MAPK) specific inhibitor suppresses respiratory syncytial virus and influenza A virus replication by inhibiting virus-induced p38 MAPK activation

Respiratory syncytial virus (RSV) and influenza A virus are leading causes of acute lower respiratory infectious disease. Respiratory diseases caused by RSV and influenza A virus result in serious economic burden and life-threatening disease for immunocompromised people. With the revelation that p38 mitogen-activated protein kinase (MAPK) activity in host cells is crucial for infection and replication of RSV and influenza A virus, inhibition of p38 MAPK activity has been suggested as a potential antiviral therapeutic strategy. However, the low selectivity and high toxicity of the p38 MAPK inhibitors necessitate the development of better inhibitors. Herein, we report the synthesis of a novel p38 MAPK inhibitor, NJK14047, with high kinase selectivity. In this work, it was demonstrated that NJK14047 inhibits RSV- and influenza A-mediated p38 MAPK activation in epithelial cells. Subsequently, NJK14047 treatment resulted in decreased viral replication and viral mRNA synthesis. In addition, secretion of interleukin-6 from infected cells was greatly diminished by NJK14047, suggesting that it can ameliorate immunopathological responses to RSV and influenza A. Collectively, the results suggest that NJK14047 has therapeutic potential to treat respiratory viral infection through the suppression of p38 MAPK activation, which is suggested to be an essential step for respiratory virus infection.

Ficus religiosa L. bark extracts inhibit human rhinovirus and respiratory syncytial virus infection in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Ficus religiosa L. is one of the most relevant members of the family of Moraceae. It is the most sacred tree of South Asia, and it is used in traditional Ayurvedic and Unani medicine to cure respiratory disorders like cough, wheezing and asthma. Some studies were performed to investigate the anti-asthmatic potential of F. religiosa bark, leaves and fruit extracts but none of them tested their antiviral activity against viruses responsible for the exacerbation of wheezing and asthma.

AIM OF THE STUDY

The present study was undertaken to investigate the antiviral activity of F. religiosa L. extracts against respiratory viruses such as human respiratory syncytial virus (RSV) and human rhinovirus (HRV).

MATERIALS AND METHODS

The antiviral activity of F. religiosa L. was tested in vitro by plaque reduction and virus yield assays and the major mechanism of action was investigated by virus inactivation and time-of-addition assays.

RESULTS

F. religiosa L. methanol bark extract was the most active against HRV with an EC50 of 5.52 µg/mL. This extract likely inhibited late steps of replicative cycle. Water bark extract was the most active against RSV with an EC50 between 2.23 and 4.37 µg/mL. Partial virus inactivation and interference with virus attachment were both found to contribute to the anti-RSV activity. Replication of both viruses was inhibited in viral yield reduction assays.

CONCLUSIONS

The results of the present study demonstrate that F. religiosa L. is endowed with antiviral activity against RSV and HRV in vitro. Further work remains to be done to identify the active components and to assess the therapeutic potential in vivo.

Therapeutic effect of post-exposure treatment with antiserum on severe fever with thrombocytopenia syndrome (SFTS) in a mouse model of SFTS virus infection

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging viral disease that is endemic in China, Korea and Japan. No effective vaccine or specific treatment for SFTS is currently available. Here, we used a mouse model to examine the effects of ribavirin, site-1 protease inhibitor PF-429242, steroids, and combination of minocycline and ciprofloxacin (MC) on SFTS infection. The antiserum from a patient who recovered from SFTS was also examined for its effect on mice. Administration of antiserum completely protected mice against lethal infection with SFTSV. It could also protect mice from showing clinical signs of the disease due to non-lethal infection. MC-treatment resulted in prolonged survival times during lethal infection. Although other agents had no significant protective effects, they did not provide detrimental effects that could lead to progression of the disease in mice. Our results suggest that antiserum treatment may be clinically useful for post-exposure prophylaxis against SFTSV infection.

Antiviral effects of Jinxin oral liquid against respiratory syncytial virus infection in the BALB/c mice model

ETHNOPHARMACOLOGICAL RELEVANCE

Jinxin oral liquid (JOL) is used in traditional Chinese medicine (TCM) to treat influenza, cough, asthma, and viral pneumonia, on the basis of Ma Xing Shi Gan Tang (MXSGT) and the clinical experience of Professor Wang Shouchuan, one of the most prestigious pediatricians in China.

AIM OF STUDY

To investigate the anti-inflammatory and antiviral activities of JOL in mice infected with respiratory syncytial virus (RSV).

MATERIALS AND METHODS

Mice were orally administered JOL at doses of 27.6 g kg(-1) d(-1) and 55.2 g kg(-1) d(-1) for 1, 3, or 6d after RSV challenge. The viral loads in the lung tissue were measured by real-time RT-PCR. The levels of IFN-β in bronchoalveolar lavage fluid (BLAF) and lung tissue were detected by ELISA and real-time RT-PCR, respectively. The mRNA and protein expression of TLR3, IRF3, and SOCS1 were detected by real-time RT-PCR and western blot, respectively. The protein expression of phoshorylated-IRF3 (p-IRF3) was detected by western blot.

RESULTS

JOL significantly ameliorated lung inflammation in RSV-infected mice, and significantly reduced the viral load in the lung tissues. On days 2 and 4 after infection, the mRNA and protein expression of IFN-β, TLR3, IRF3 (p-IRF3), and SOCS1 were significantly downregulated in RSV-infected mice treated with JOL. However, 7d after infection, JOL significantly upregulated the RSV-induced decrease in IFN-β, TLR3, and IRF3 (p-IRF3), but reduced SOCS1 expression.

CONCLUSIONS

JOL ameliorated lung inflammation and inhibited virus replication significantly in RSV-infected mice. During early stage infection, the effect of JOL was improved through inhibition of the TLR3-IRF3-IFN-β signaling pathway and the expression of SOCS1, whereas during the later stage of infection, JOL upregulated the expression of key signaling molecules in the TLR3 signaling pathway and downregulated the expression of SOCS1.

New host factors important for respiratory syncytial virus (RSV) replication revealed by a novel microfluidics screen for interactors of matrix (M) protein

Although human respiratory syncytial virus (RSV) is the most common cause of bronchiolitis and pneumonia in infants and elderly worldwide, there is no licensed RSV vaccine or effective drug treatment available. The RSV Matrix protein plays key roles in virus life cycle, being found in the nucleus early in infection in a transcriptional inhibitory role, and later localizing in viral inclusion bodies before coordinating viral assembly and budding at the plasma membrane. In this study, we used a novel, high throughput microfluidics platform and custom human open reading frame library to identify novel host cell binding partners of RSV matrix. Novel interactors identified included proteins involved in host transcription regulation, the innate immunity response, cytoskeletal regulation, membrane remodeling, and cellular trafficking. A number of these interactions were confirmed by immunoprecipitation and cellular colocalization approaches. Importantly, the physiological significance of matrix interaction with the actin-binding protein cofilin 1, caveolae protein Caveolin 2, and the zinc finger protein ZNF502 was confirmed. siRNA knockdown of the host protein levels resulted in reduced RSV virus production in infected cells. These results have important implications for future antiviral strategies aimed at targets of RSV matrix in the host cell.

In silico approach towards designing virtual oligopeptides for HRSV

HRSV (human respiratory syncytial virus) is a serious cause of lower respiratory tract illness in infants and young children. Designing inhibitors from the proteins involved in virus replication and infection process provides target for new therapeutic treatments. In the present study, in silico docking was performed using motavizumab as a template to design motavizumab derived oligopeptides for developing novel anti-HRSV agents. Additional simulations were conducted to study the conformational propensities of the oligopeptides and confirmed the hypothesis that the designed oligopeptide is highly flexible and capable of assuming stable confirmation. Our study demonstrated the best specific interaction of GEKKLVEAPKS oligopeptide for glycoprotein strain A among various screened oligopeptides. Encouraged by the results, we expect that the proposed scheme will provide rational choices for antibody reengineering which is useful for systematically identifying the possible ways to improve efficacy of existing antibody drugs.

Highly sulfated K5 Escherichia coli polysaccharide derivatives inhibit respiratory syncytial virus infectivity in cell lines and human tracheal-bronchial histocultures

Respiratory syncytial virus (RSV) exploits cell surface heparan sulfate proteoglycans (HSPGs) as attachment receptors. The interaction between RSV and HSPGs thus presents an attractive target for the development of novel inhibitors of RSV infection. In this study, selective chemical modification of the Escherichia coli K5 capsular polysaccharide was used to generate a collection of sulfated K5 derivatives with a backbone structure that mimics the heparin/heparan sulfate biosynthetic precursor. The screening of a series of N-sulfated (K5-NS), O-sulfated (K5-OS), and N,O-sulfated (K5-N,OS) derivatives with different degrees of sulfation revealed the highly sulfated K5 derivatives K5-N,OS(H) and K5-OS(H) to be inhibitors of RSV. Their 50% inhibitory concentrations were between 1.07 nM and 3.81 nM in two different cell lines, and no evidence of cytotoxicity was observed. Inhibition of RSV infection was maintained in binding and attachment assays but not in preattachment assays. Moreover, antiviral activity was also evident when the K5 derivatives were added postinfection, both in cell-to-cell spread and viral yield reduction assays. Finally, both K5-N,OS(H) and K5-OS(H) prevented RSV infection in human-derived tracheal/bronchial epithelial cells cultured to form a pseudostratified, highly differentiated model of the epithelial tissue of the human respiratory tract. Together, these features put K5-N,OS(H) and K5-OS(H) forward as attractive candidates for further development as RSV inhibitors.

Oral ribavirin therapy for respiratory syncytial virus infections in moderately to severely immunocompromised patients

BACKGROUND

Respiratory syncytial virus (RSV) infections may be fatal in immunocompromised patients. Aerosolized ribavirin is used for treatment, but it is very costly, teratogenic, and inconvenient. We aimed to assess the outcome of oral ribavirin treatment, with or without intravenous immunoglobulin (IVIG), for RSV infections in moderately to severely immunocompromised patients.

METHODS

Medical records of RSV polymerase chain reaction (PCR)-positive patients during 2011-2013 were reviewed retrospectively. Eligible patients were moderately to severely immunocompromised and received oral ribavirin (600-800 mg twice daily) with or without IVIG (500 mg/kg q 48 h) as per protocol.

RESULTS

Of 96 adults with PCR-proven RSV infection, 34 were moderately to severely immunocompromised and received oral ribavirin treatment. The mean age was 56.2 years (range: 18-90); 21 were male. Underlying conditions were hematologic malignancy with or without hematopoietic stem cell transplant (n = 25), lung transplant (n = 3), or receipt of cytotoxic chemotherapy (n = 11). The presenting symptoms were cough (94%), fever (62%), and dyspnea (59%). The most common radiographic findings were patchy and nodular infiltrates and opacities. Of 34 patients, 31 were hospitalized, with 13 admitted to the intensive care unit and 6 required mechanical ventilation. The median absolute lymphocyte count on presentation was 480 cells/mm(3) . RSV pneumonia developed in 24 patients. The median initial duration of oral ribavirin treatment was 10 days (range: 4-11); 4 patients were re-treated. Of 34 patients, 19 received a mean of 2.7 doses of IVIG. Two patients had adverse reactions to ribavirin (hemolytic anemia and lactic acidosis in 1 patient, and altered mental status in another). No patient died from RSV infection. Three patients died from complications of their underlying illness; all others recovered clinically.

CONCLUSIONS

Oral ribavirin with or without IVIG is a well-tolerated treatment for RSV infection in moderately to severely immunocompromised hosts. Comparative prospective studies should ideally be performed to determine if oral ribavirin is the optimal therapy for RSV infection in this patient population.

STAT5-induced lunatic fringe during Th2 development alters delta-like 4-mediated Th2 cytokine production in respiratory syncytial virus-exacerbated airway allergic disease

Notch activation plays an important role in T cell development and mature T cell differentiation. In this study, we investigated the role of Notch activation in a mouse model of respiratory syncytial virus (RSV)-exacerbated allergic airway disease. During RSV exacerbation, in vivo neutralization of a specific Notch ligand, Delta-like ligand (Dll)-4, significantly decreased airway hyperreactivity, mucus production, and Th2 cytokines. Lunatic Fringe (Lfng), a glycosyltransferase that enhances Notch activation by Dll4, was increased during RSV exacerbation. Lfng loss of function in Th2-skewed cells inhibited Dll4-Notch activation and subsequent IL-4 production. Further knockdown of Lfng in T cells in CD4Cre(+)Lfng(fl/fl) mice showed reduced Th2 response and disease pathology during RSV exacerbation. Finally, we identified STAT5-binding cis-acting regulatory element activation as a critical driver of Lfng transcriptional activation. These data demonstrate that STAT5-dependent amplification of Notch-modifying Lfng augments Th2 response via Dll4 and is critical for amplifying viral exacerbation during allergic airway disease.

RAGE inhibits human respiratory syncytial virus syncytium formation by interfering with F-protein function

Human respiratory syncytial virus (RSV) is a major cause of severe lower respiratory tract infection. Infection is critically dependent on the RSV fusion (F) protein, which mediates fusion between the viral envelope and airway epithelial cells. The F protein is also expressed on infected cells and is responsible for fusion of infected cells with adjacent cells, resulting in the formation of multinucleate syncytia. The receptor for advanced glycation end products (RAGE) is a pattern-recognition receptor that is constitutively highly expressed by type I alveolar epithelial cells. Here, we report that RAGE protected HEK cells from RSV-induced cell death and reduced viral titres in vitro. RAGE appeared to interact directly with the F protein, but, rather than inhibiting RSV entry into host cells, virus replication and budding, membrane-expressed RAGE or soluble RAGE blocked F-protein-mediated syncytium formation and sloughing. These data indicate that RAGE may contribute to protecting the lower airways from RSV by inhibiting the formation of syncytia, viral spread, epithelial damage and airway obstruction.

(S)-N-(2,5-Dimethylphenyl)-1-(quinoline-8-ylsulfonyl)pyrrolidine-2-carboxamide as a small molecule inhibitor probe for the study of respiratory syncytial virus infection

A high-throughput, cell-based screen was used to identify chemotypes as inhibitors for human respiratory syncytial virus (hRSV). Optimization of a sulfonylpyrrolidine scaffold resulted in compound 5o that inhibited a virus-induced cytopathic effect in the entry stage of infection (EC₅₀ = 2.3 ± 0.8 μM) with marginal cytotoxicity (CC₅₀ = 30.9 ± 1.1 μM) and reduced viral titer by 100-fold. Compared to ribavirin, sulfonylpyrrolidine 5o demonstrated an improved in vitro potency and selectivity index.

Inhibition of respiratory syncytial virus in vitro and in vivo by the immunosuppressive agent leflunomide

BACKGROUND

Respiratory syncytial virus (RSV) is the primary cause of bronchiolitis and pneumonia in infants and young children worldwide and is often the cause of infections in bone marrow, solid organ transplant, cystic fibrosis and congenital heart disease patients, as well as respiratory tract disease in elderly adults. Treatment options are limited to ribavirin, which is only marginally effective, and passive immunoprophylaxis, which is very expensive. The immunosuppressive agent leflunomide has been shown to exert potent antiviral activity against several herpesviruses and polyomavirus BK. In the current study we have tested the hypothesis that leflunomide exerts antiviral activity against RSV.

METHODS

Human Hep-2 or small airway epithelial cells were inoculated with RSV and treated with A77 1726, the active metabolite of leflunomide. Syncytia formation was assessed by immunohistochemical staining, and virus yield was measured by plaque assay. Cotton rats were intranasally inoculated with RSV, treated with leflunomide by gavage, and pulmonary viral loads were measured by plaque assay of lung homogenates.

RESULTS

Phase contrast microscopy and immunohistochemical staining demonstrated profound attenuation of RSV-induced syncytia formation in infected cultures treated with A77 1726, the active metabolite of leflunomide. Plaque assays of virus yield in RSV-inoculated cell cultures demonstrated potent, dose-dependent A77-mediated antiviral activity. Likewise, pulmonary viral loads in RSV-inoculated cotton rats were reduced by >3 log by leflunomide compared with vehicle-treated controls, even when leflunomide treatment was delayed until day 3 post-inoculation.

CONCLUSIONS

These findings suggest promise for leflunomide as a convenient, orally administered addition to the growing arsenal of antiviral therapeutics. While specific antiviral mechanisms remain to be elucidated, leflunomide shows unique bifunctional potential to both reduce viral load and, by virtue of its well-documented anti-inflammatory activity, attenuate the destructive inflammation associated with RSV disease.

Sheng-Ma-Ge-Gen-Tang (Shoma-kakkon-to) inhibited cytopathic effect of human respiratory syncytial virus in cell lines of human respiratory tract

ETHNOPHARMACOLOGICAL RELEVANCE

Sheng-Ma-Ge-Gen-Tang (SMGGT; Shoma-kakkon-to) has been used against pediatric viral infection for thousands of year in ancient China. However, it is unknown whether SMGGT is effective against human respiratory syncytial virus (HRSV).

AIM OF THE STUDY

HRSV is a major pediatric viral pathogen of low respiratory tract infection without effective management. This study tested the hypothesis that SMGGT effectively inhibited cytopathy induced by HRSV.

MATERIALS AND METHODS

Effect of the crude extract of SMGGT on HRSV was tested by plaque reduction assay in both human upper (HEp-2) and low (A549) respiratory tract cell lines. Ability of SMGGT to stimulate anti-viral cytokines was evaluated by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Crude extract of SMGGT dose-dependently inhibited HRSV-induced plaque formation. The crude extract was more effective when given before viral infection (p<0.0001). It inhibited viral attachment dose-dependently (p<0.0001) and could increase heparin effect on viral attachment. Furthermore, it was synergistic with very low-dose heparin on viral attachment. In addition, the crude extract time-dependently and dose-dependently (p<0.0001) inhibited HRSV internalization into HEp-2 cells. Epithelial cells secrete IFN-β and TNF-α to counteract viral infection. The crude extract could stimulate epithelial cells to secrete these cytokines beforehand and become resistant to viral infection. It also stimulated IFN-β to defense HRSV after viral inoculation.

CONCLUSIONS

Sheng-Ma-Ge-Gen-Tang could be effective to manage HRSV infection in young children.

The next ten stories on antiviral drug discovery (part E): advents, advances, and adventures

This review article presents the fifth part (part E) in the series of stories on antiviral drug discovery. The ten stories belonging to this fifth part are dealing with (i) aurintricarboxylic acid; (ii) alkenyldiarylmethanes; (iii) human immunodeficiency virus (HIV) integrase inhibitors; (iv) lens epithelium‐derived growth factor as a potential target for HIV proviral DNA integration; (v) the status presens of neuraminidase inhibitors NAIs in the control of influenza virus infections; (vi) the status presens on respiratory syncytial virus inhibitors; (vii) tricyclic (1,N‐2‐ethenoguanine)‐based acyclovir and ganciclovir derivatives; (viii) glycopeptide antibiotics as antivirals targeted at viral entry; (ix) the potential (off‐label) use of cidofovir in the treatment of polyoma (JC and BK) virus infections; and (x) finally, thymidine phosphorylase as a target for both antiviral and anticancer agents. © 2009 Wiley Periodicals, Inc. Med Res Rev, 31, No. 1, 118–160, 2010

A classification study of respiratory Syncytial Virus (RSV) inhibitors by variable selection with random forest

Experimental pEC₅₀s for 216 selective respiratory syncytial virus (RSV) inhibitors are used to develop classification models as a potential screening tool for a large library of target compounds. Variable selection algorithm coupled with random forests (VS-RF) is used to extract the physicochemical features most relevant to the RSV inhibition. Based on the selected small set of descriptors, four other widely used approaches, i.e., support vector machine (SVM), Gaussian process (GP), linear discriminant analysis (LDA) and k nearest neighbors (kNN) routines are also employed and compared with the VS-RF method in terms of several of rigorous evaluation criteria. The obtained results indicate that the VS-RF model is a powerful tool for classification of RSV inhibitors, producing the highest overall accuracy of 94.34% for the external prediction set, which significantly outperforms the other four methods with the average accuracy of 80.66%. The proposed model with excellent prediction capacity from internal to external quality should be important for screening and optimization of potential RSV inhibitors prior to chemical synthesis in drug development.

A fluorescence polarization assay using an engineered human respiratory syncytial virus F protein as a direct screening platform

Human respiratory syncytial virus (hRSV) typically affects newborns and young children. Even though it can cause severe and, in some cases, lifelong respiratory infections, there are currently no Food and Drug Administration (FDA)-approved therapeutics that control this virus. The hRSV F protein facilitates viral fusion, a critical extracellular event that can be targeted for therapeutic intervention by disrupting the assembly of a postfusion 6-helix bundle (6HB) within the hRSV F protein. Here we report the development of a fluorescence polarization (FP) assay using an engineered hRSV F protein 5-helix bundle (5HB). We generated the 5HB and validated its ability to form a 6HB in an FP assay. To test the potential of 5HB as a screening tool, we then investigated a series of truncated peptides derived from the "missing" sixth helix. Using this FP-based 5HB system, we have successfully demonstrated that short peptides can prevent 6HB formation and serve as potential hRSV fusion inhibitors. We anticipate that this new 5HB system will provide an effective tool to identify and study potential antivirals to control hRSV infection.

Pattern recognition receptors and genetic risk for rsv infection: value for clinical decision-making?

Respiratory syncytial virus (RSV) causes respiratory tract infections, especially among young infants. Practically, all infants are infected during epidemics and the clinical presentation ranges from subclinical to fatal infection. Known risk factors for severe RSV infection include prematurity, age of <2 months, underlying chronic lung or heart diseases, serious neurological or metabolic disorders, immune deficiency (especially a disorder of cellular immunity), crowded living conditions, and indoor smoke pollution. Twin studies indicate that host genetic factors affect susceptibility to severe RSV infection. Pattern recognition receptors (PRRs) are the key mediators of the innate immune response to RSV. In the distal respiratory tract, RSV is recognized by the transmembrane Toll-like receptor 4 (TLR4) and adapter proteins, which lead to production of proinflammatory cytokines and subsequent activation of the adaptive immune response. Surfactant proteins A and D are able to bind both RSV and TLR4, modulating the inflammatory response. Genetic variations in TLR4, SP-A, and SP-D have been associated with the risk of severe RSV bronchiolitis, but the results have varied between studies. Both the homozygous hyporesponsive 299Gly genotype of TLR4 and the non-synonymous SP-A and SP-D polymorphism influence the presentation of RSV infection. The reported relative risks associated with these markers are not robust enough to justify clinical use. However, current evidence indicates that innate immune responses including pattern recognition receptors (PRRs) and other components in the distal airways and airspaces profoundly influence the innate immune responses, playing a key role in host resistance to RSV in young infants. This information is useful in guiding efforts to develop better means to identify the high-risk infants and to treat this potentially fatal infection effectively.

The infectious march: the complex interaction between microbes and the immune system in asthma

There has been significant progress in our knowledge about the relationship between infectious disease and the immune system in relation to asthma, but many unanswered questions still remain. Respiratory tract infections such as those caused by respiratory syncytial virus and rhinovirus during the first 2 years of life are still clearly associated with later wheezing and asthma, but the mechanism has not been completely worked out. Is there an "infectious march" triggered by infection in infancy that progresses to disease pathology or are infants who contract respiratory infections predisposed to developing asthma? This review focuses on the common themes in the interaction between microbes and the immune system, and presents a critical appraisal of the evidence to date. The various mechanisms whereby microbes alter the immune response and how this might influence asthma are discussed along with new and promising clinical practices for prevention and therapy. Recent advances in using sensitive polymerase chain reaction detection methods have allowed more rigorous testing of the causality hypothesis of virus infection leading to asthma, but the evidence is still equivocal. Various exceptions and inconsistencies in the clinical trials are discussed in light of new guidelines for subject inclusion/exclusion in hopes of providing some standardization. Despite past failures in vaccination and disappointing results of some clinical trials, the new strategies for prophylaxis including RNA interference and targeted delivery of microbicides offer a large dose of hope to a world suffering from an increasing incidence of asthma as well as a huge burden of health care cost and loss of quality of life.

Use of a highly sensitive strand-specific quantitative PCR to identify abortive replication in the mouse model of respiratory syncytial virus disease

Background

The BALB/c mouse is commonly used to study RSV infection and disease. However, despite the many advantages of this well-characterised model, the inoculum is large, viral replication is restricted and only a very small amount of virus can be recovered from infected animals. A key question in this model is the fate of the administered virus. Is replication really being measured or is the model measuring the survival of the virus over time? To answer these questions we developed a highly sensitive strand-specific quantitative PCR (QPCR) able to accurately quantify the amount of RSV replication in the BALB/c mouse lung, allowing characterisation of RSV negative and positive strand RNA dynamics.

Results

In the mouse lung, no increase in RSV genome was seen above the background of the original inoculum whilst only a limited transient increase (< 1 log) in positive strand, replicative intermediate (RI) RNA occurred. This RNA did however persist at detectable levels for 59 days post infection. As expected, ribavirin therapy reduced levels of infectious virus and RI RNA in the mouse lung. However, whilst Palivizumab therapy was also able to reduce levels of infectious virus, it failed to prevent production of intracellular RI RNA. A comparison of RSV RNA kinetics in human (A549) and mouse (KLN205) cell lines demonstrated that RSV replication was also severely delayed and impaired in vitro in the mouse cells.

Conclusions

This is the first time that such a sensitive strand-specific QPCR technique has been to the RSV mouse system. We have accurately quantified the restricted and abortive nature of RSV replication in the mouse. Further in vitro studies in human and mouse cells suggest this restricted replication is due at least in part to species-specific host cell-viral interactions.

Respiratory syncytial virus-neutralizing monoclonal antibodies motavizumab and palivizumab inhibit fusion

Respiratory syncytial virus (RSV) is a major cause of virus-induced respiratory disease and hospitalization in infants. Palivizumab, an RSV-neutralizing monoclonal antibody, is used clinically to prevent serious RSV-related respiratory disease in high-risk infants. Motavizumab, an affinity-optimized version of palivizumab, was developed to improve protection against RSV. These antibodies bind RSV F protein, which plays a role in virus attachment and mediates fusion. Determining how these antibodies neutralize RSV is important to help guide development of new antibody drugs against RSV and, potentially, other viruses. This study aims to uncover the mechanism(s) by which palivizumab and motavizumab neutralize RSV. Assays were developed to test the effects of these antibodies at distinct steps during RSV replication. Pretreatment of virus with palivizumab or motavizumab did not inhibit virus attachment or the ability of F protein to interact with the target cell membrane. However, pretreatment of virus with either of these antibodies resulted in the absence of detectable viral transcription. These results show that palivizumab and motavizumab act at a point after F protein initiates interaction with the cell membrane and before virus transcription. Palivizumab and motavizumab also inhibited F protein-mediated cell-to-cell fusion. Therefore, these results strongly suggest that these antibodies block both cell-to-cell and virus-to-cell fusion, since these processes are likely similar. Finally, palivizumab and motavizumab did not reduce viral budding. Based on models developed from numerous studies of viral fusion proteins, our results indicate that these antibodies may prevent conformational changes in F protein required for the fusion process.

Toll-like receptor 4 Asp299Gly polymorphism in respiratory syncytial virus epidemics

The respiratory syncytial virus (RSV) antigen serves as ligand for Toll-like receptor (TLR) 4 that is a transmembrane signaling receptor in macrophages and dendritic cells. According to current evidence single nucleotide polymorphism involving amino acid 299 influences the susceptibility to severe RSV infections. The Asp299Gly allele has been shown to influence the TLR4-mediated signaling causing conformational change in the extracellular domain that recognizes pathogen-associated molecular patterns. The aim was to study the association between the TLR4 Asp299Gly polymorphism and the susceptibility to severe RSV bronchiolitis in infants. Altogether 312 cases and 356 controls, selected on the basis place of residence, date of birth, gender, and gestation at birth, were studied. When adjusted for multiple dependent variables, no allele or genotype frequency difference was found between the cases and the controls. Post hoc analysis revealed that during the year 2000 epidemics, the Gly299Gly genotype associated with protection against severe RSV and during 2004 epidemics Gly299Gly genotype and 299Gly allele associated with severe RSV. To conclude, we could not confirm the association of the Gly299 allele with severe RSV. This is consistent with the evidence that the susceptibility to severe RSV infection is principally dependent on environmental and constitutional factors. We propose that the risk of severe RSV infection may additionally depend on the interaction between individual TLR4 genotype and the particular RSV group causing bronchiolitis.

Pharmacologic advances in the treatment and prevention of respiratory syncytial virus

Currently, only 2 drugs have been approved for the treatment of respiratory syncytial virus (RSV). Palivizumab is a monoclonal antibody for the prevention of RSV in high-risk children. Ribavirin is approved for treatment of severe RSV disease; however, its effectiveness in improving outcomes is questionable. During the past 40 years, many obstacles have delayed the development of safe and effective vaccines and treatment regimens. This article reviews these obstacles and presents the novel development strategies used to overcome many of them. Also discussed are promising new antiviral treatment candidates and their associated mechanism of action, the significant advances made in vaccine development, and exciting, new studies directed at improving outcomes through pharmacologic manipulation of the host response to RSV disease.

Novel therapies for an old virus: treatment of RSV infections in the 21st Century

Respiratory syncytial virus (RSV) is a pathogen whose existence has been known for decades, causing mild-to-severe upper and lower respiratory tract infections that bear the risk of subsequent asthma and can even lead to a fatal outcome. RSV infects all groups of patients and is a major cause of hospitalization in children and in the elderly. This review briefly summarizes the current status of RSV drug development and clinical trials for drugs available for the treatment of RSV infections.

Generation of stable monoclonal antibody-producing B cell receptor-positive human memory B cells by genetic programming

B cell lymphoma (BCL)6 and Bcl-xL are expressed in germinal center (GC) B cells and enable them to endure the proliferative and mutagenic environment of the GC. By introducing these genes into peripheral blood memory B cells and culturing these cells with factors produced by follicular helper T cells, CD40L and IL-21, we convert them to highly proliferating, cell surface BCR positive, Ig-secreting B cells with features of GC B cells including expression of activation-induced cytidine deaminase. We generated cloned lines of B cells specific for respiratory syncytial virus and used these cells as a source of antibodies that effectively neutralized this virus in vivo. This method provides a new tool to study GC B cell biology, signal transduction through antigen-specific B cell receptors, and for the rapid generation of high affinity human monoclonal antibodies.

Potential benefits of sequential inhibitor-mutagen treatments of RNA virus infections

Lethal mutagenesis is an antiviral strategy consisting of virus extinction associated with enhanced mutagenesis. The use of non-mutagenic antiviral inhibitors has faced the problem of selection of inhibitor-resistant virus mutants. Quasispecies dynamics predicts, and clinical results have confirmed, that combination therapy has an advantage over monotherapy to delay or prevent selection of inhibitor-escape mutants. Using ribavirin-mediated mutagenesis of foot-and-mouth disease virus (FMDV), here we show that, contrary to expectations, sequential administration of the antiviral inhibitor guanidine (GU) first, followed by ribavirin, is more effective than combination therapy with the two drugs, or than either drug used individually. Coelectroporation experiments suggest that limited inhibition of replication of interfering mutants by GU may contribute to the benefits of the sequential treatment. In lethal mutagenesis, a sequential inhibitor-mutagen treatment can be more effective than the corresponding combination treatment to drive a virus towards extinction. Such an advantage is also supported by a theoretical model for the evolution of a viral population under the action of increased mutagenesis in the presence of an inhibitor of viral replication. The model suggests that benefits of the sequential treatment are due to the involvement of a mutagenic agent, and to competition for susceptible cells exerted by the mutant spectrum. The results may impact lethal mutagenesis-based protocols, as well as current antiviral therapies involving ribavirin.

RNA viruses are associated with many important human and animal diseases such as AIDS, influenza, hemorrhagic fevers and several forms of hepatitis. RNA viruses mutate at very high rates and, therefore, can adapt easily to environmental changes. Viral mutants resistant to antiviral inhibitors are readily selected, resulting in treatment failure. The simultaneous administration of three or more inhibitors is a means to prevent or delay selection of resistant mutants. A new antiviral strategy termed lethal mutagenesis is presently under investigation. It consists of the administration of mutagenic agents to elevate the mutation rate of the virus above the maximum level compatible with virus infectivity, without mutagenizing the host cells. Since low amounts of virus are extinguished more easily, the combination of a mutagen and inhibitor was more efficient than a mutagen alone in driving virus to extinction. Here we show that foot-and-mouth disease virus replicating in cell culture can be extinguished more easily when the inhibitor guanidine is administered first, followed by the mutagenic agent ribavirin, than when both drugs are administered simultaneously. Interfering mutants that contribute to extinction were active in the presence of ribavirin but not in the presence of guanidine. This observation provides a mechanism for the advantage of the sequential versus the combination treatment. This unexpected effectiveness of a sequential treatment is supported by a theoretical model of virus evolution in the presence of the inhibitor and the mutagen. The results can have an application for future lethal mutagenesis protocols and for current antiviral treatments that involve the antiviral agent ribavirin when it acts as a mutagen.

4-Methoxycinnamaldehyde inhibited human respiratory syncytial virus in a human larynx carcinoma cell line

4-Methoxycinnamaldehyde, an active constituent of Agastache rugosa, was examined for its cytoprotective activity against RSV by XTT method in human larynx carcinoma cell line. 4-Methoxycinnamaldehyde could effectively inhibit cytopathic effect of RSV (p<0.0001) with an estimated IC(50) of 0.055microg/ml and a selectivity index (SI) of 898.2. 4-Methoxycinnamaldehyde (0.03microg/ml) could inhibit viral entrance by interfering viral attachment (IC(50) of 0.06microg/ml; p<0.0001) and internalization (IC(50) of 0.01microg/ml; p<0.0001). 4-Methoxycinnamaldehyde significantly increased the basal production of IFN (p=0.0015), but not the virus-induced IFN production. Therefore, its cytoprotective activity against RSV was not mediated by interferon. In conclusion, 4-methoxycinnamaldehyde might be helpful to manage the disease induced by RSV infection.

Respiratory syncytial virus fusion inhibitors. Part 7: structure-activity relationships associated with a series of isatin oximes that demonstrate antiviral activity in vivo

A series of bezimidazole-isatin oximes were prepared and profiled as inhibitors of respiratory syncytial virus (RSV) replication in cell culture. Structure-activity relationship studies were directed toward optimization of antiviral activity, cell permeability and metabolic stability in human liver micorosomes (HLM). Parallel combinatorial synthetic chemistry was employed to functionalize isatin oximes via O-alkylation which quickly identified a subset of small, lipophilic substituents that established good potency for the series. Further optimization of the isatin oxime derivatives focused on introduction of nitrogen atoms to the isatin phenyl ring to provide a series of aza-isatin oximes with significantly improved PK properties. Several aza-isatin oximes analogs displayed targeted metabolic stability in HLM and permeability across a confluent monolayer of CaCo-2 cells. These studies identified several compounds, including 18i, 18j and 18n that demonstrated antiviral activity in the BALB/c mouse model of RSV infection following oral dosing.

Emerging drugs for respiratory syncytial virus infection

Although respiratory syncytial virus (RSV) was discovered > 40 years ago, treatment remains largely supportive. There are no safe and effective vaccines or specific treatments other than prophylaxis with passive antibody therapy (palivizumab). However, there are good reasons to think that the scene may soon change. As the pace of development of anti-viral drugs accelerates and optimism over vaccines increases, novel therapies are set to make a major impact in the management of this very common infection. The use and effect of such interventions are not easy to anticipate, but could ultimately include the interruption of RSV's transmission resulting in profound changes to the impact of RSV on human health.

Potential use of antiviral agents in polio eradication

In 1988, the World Health Assembly launched the Global Polio Eradication Initiative, which aimed to use large-scale vaccination with the oral vaccine to eradicate polio worldwide by the year 2000. Although important progress has been made, polio remains endemic in several countries. Also, the current control measures will likely be inadequate to deal with problems that may arise in the postpolio era. A panel convoked by the National Research Council concluded that the use of antiviral drugs may be essential in the polio eradication strategy. We here report on a comparative study of the antipoliovirus activity of a selection of molecules that have previously been reported to be inhibitors of picornavirus replication and discuss their potential use, alone or in combination, for the treatment or prophylaxis of poliovirus infection.

Potential use of antiviral agents in polio eradication

In 1988, the World Health Assembly launched the Global Polio Eradication Initiative, which aimed to use large-scale vaccination with the oral vaccine to eradicate polio worldwide by the year 2000. Although important progress has been made, polio remains endemic in several countries. Also, the current control measures will likely be inadequate to deal with problems that may arise in the postpolio era. A panel convoked by the National Research Council concluded that the use of antiviral drugs may be essential in the polio eradication strategy. We here report on a comparative study of the antipoliovirus activity of a selection of molecules that have previously been reported to be inhibitors of picornavirus replication and discuss their potential use, alone or in combination, for the treatment or prophylaxis of poliovirus infection.

Respiratory syncytial virus fusion inhibitors. Part 6: an examination of the effect of structural variation of the benzimidazol-2-one heterocycle moiety

The effect of structural variation of the benzimidazol-2-one ring of RSV fusion inhibitors related to BMS-433771 (1) was examined in conjunction with side chain modifications and the introduction of an aminomethyl substituent at the 5-position of the core benzimidazole moiety. Replacement of the benzimidazol-2-one moiety with benzoxazole, oxindole, quinoline-2-one, quinazolin-2,4-dione and benzothiazine derivatives provided a series of potent RSV fusion inhibitors 4. However, the intrinsic potency of 6,6-fused ring systems was generally less than that of comparably substituted 5,6-fused heterocycles of the type found in BMS-433771 (1). The introduction of an aminomethyl substituent to the benzimidazole ring enhanced antiviral activity in the 6,6-fused ring systems.

Respiratory viral diseases: access to RNA interference therapy

This review summarizes recent experimental achievements in the area of the development of new RNA interference (RNAi) therapeutics for the treatment of viral respiratory diseases. Delivery of siRNA to their intended target tissue remains the biggest problem for most therapeutic applications of these compounds. Appropriate formulations and chemical modifications for improved stability will boost the probability of utilization of RNAi drugs in the clinical applications.

Status presens of antiviral drugs and strategies: Part II: RNA VIRUSES (EXCEPT RETROVIRUSES)

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

Respiratory syncytial virus fusion inhibitors. Part 4: optimization for oral bioavailability

A series of benzimidazole-based inhibitors of respiratory syncytial virus (RSV) fusion were optimized for antiviral potency, membrane permeability and metabolic stability in human liver microsomes. 1-Cyclopropyl-1,3-dihydro-3-[[1-(4-hydroxybutyl)-1H-benzimidazol-2-yl]methyl]-2H-imidazo[4,5-c]pyridin-2-one (6m, BMS-433771) was identified as a potent RSV inhibitor demonstrating good bioavailability in the mouse, rat, dog and cynomolgus monkey that demonstrated antiviral activity in the BALB/c and cotton rat models of infection following oral administration.