In vitro activity of pleconaril and AG7088 against selected serotypes and clinical isolates of human rhinoviruses

7-Amino-3-phenyl-2-methyl-pyrazolopyrimidine derivatives inhibit human rhinovirus replication

Small molecules that exhibit broad-spectrum enteroviral inhibitory activity by targeting viral replication proteins are highly desired in antiviral drug discovery studies. To discover new human rhinovirus (hRV) inhibitors, we performed a high-throughput screening of 100,000 compounds from the Korea Chemical Bank library. This search led to identification of two phosphatidylinositol-4-kinase IIIβ (PI4KIIIβ) inhibitors having the pyrazolo-pyrimidine core structure, which display moderate anti-rhinoviral activity along with mild cytotoxicity. The results of a study aimed at optimizing the activity of the hit compounds showed that the pyrazolo-pyrimidine derivative 6f exhibits the highest activity (EC50 = 0.044, 0.066, and 0.083 μM for hRV-B14, hRV-A16, and hRV-A21, respectively) and moderate toxicity (CC50 = 31.38 μM). Furthermore, 6f has broad-spectrum activities against various hRVs, coxsackieviruses and other enteroviruses, such as EV-A71, EV-D68. An assessment of kinase inhibition potencies demonstrated that 6f possesses a high and selective kinase inhibition activity against PI4KIIIβ (IC50 value of 0.057 μM) and not against PI4KIIIα (>10 μM). Moreover, 6f exhibits modest hepatic stability (46.9 and 55.3 % remaining after 30 min in mouse and human liver microsomes, respectively). Finally, an in vivo study demonstrated that 6f possesses a desirable pharmacokinetic profile reflected in low systemic clearance (0.48 L∙h-1 kg-1) and modest oral bioavailability (52.4 %). Hence, 6f (KR-26549) appears to be an ideal lead for the development of new antiviral drugs.

Small Molecules Targeting 3C Protease Inhibit FMDV Replication and Exhibit Virucidal Effect in Cell-Based Assays

Foot-and-mouth disease (FMD) is a highly contagious disease in cloven-hoofed animals, caused by the foot-and-mouth disease virus (FMDV). It is endemic in Asia and Africa but spreads sporadically throughout the world, resulting in significant losses in the livestock industry. Effective anti-FMDV therapeutics could be a supportive control strategy. Herein, we utilized computer-aided, structure-based virtual screening to filter lead compounds from the National Cancer Institute (NCI) diversity and mechanical libraries using FMDV 3C protease (3Cpro) as the target. Seven hit compounds were further examined via cell-based antiviral and intracellular protease assays, in which two compounds (NSC116640 and NSC332670) strongly inhibited FMDV, with EC50 values at the micromolar level of 2.88 µM (SI = 73.15) and 5.92 µM (SI = 11.11), respectively. These compounds could inactivate extracellular virus directly in a virucidal assay by reducing 1.00 to 2.27 log TCID50 of the viral titers in 0-60 min. In addition, the time-of-addition assay revealed that NSC116640 inhibited FMDV at the early stage of infection (0-8 h), while NSC332670 diminished virus titers when added simultaneously at infection (0 h). Both compounds showed good FMDV 3Cpro inhibition with IC50 values of 10.85 µM (NSC116640) and 4.21 µM (NSC332670). The molecular docking of the compounds on FMDV 3Cpro showed their specific interactions with amino acids in the catalytic triad of FMDV 3Cpro. Both preferentially reacted with enzymes and proteases in physicochemical and ADME analysis studies. The results revealed two novel small molecules with antiviral activities against FMDV and probably related picornaviruses.

Vemurafenib Inhibits Acute and Chronic Enterovirus Infection by Affecting Cellular Kinase Phosphatidylinositol 4-Kinase Type IIIβ

Enteroviruses are one of the most abundant viruses causing mild to serious acute infections in humans and also contributing to chronic diseases like type 1 diabetes. Presently, there are no approved antiviral drugs against enteroviruses. Here, we studied the potency of vemurafenib, an FDA-approved RAF kinase inhibitor for treating BRAFV600E mutant-related melanoma, as an antiviral against enteroviruses. We showed that vemurafenib prevented enterovirus translation and replication at low micromolar dosage in an RAF/MEK/ERK-independent manner. Vemurafenib was effective against group A, B, and C enteroviruses, as well as rhinovirus, but not parechovirus or more remote viruses such as Semliki Forest virus, adenovirus, and respiratory syncytial virus. The inhibitory effect was related to a cellular phosphatidylinositol 4-kinase type IIIβ (PI4KB), which has been shown to be important in the formation of enteroviral replication organelles. Vemurafenib prevented infection efficiently in acute cell models, eradicated infection in a chronic cell model, and lowered virus amounts in pancreas and heart in an acute mouse model. Altogether, instead of acting through the RAF/MEK/ERK pathway, vemurafenib affects the cellular PI4KB and, hence, enterovirus replication, opening new possibilities to evaluate further the potential of vemurafenib as a repurposed drug in clinical care. IMPORTANCE Despite the prevalence and medical threat of enteroviruses, presently, there are no antivirals against them. Here, we show that vemurafenib, an FDA-approved RAF kinase inhibitor for treating BRAFV600E mutant-related melanoma, prevents enterovirus translation and replication. Vemurafenib shows efficacy against group A, B, and C enteroviruses, as well as rhinovirus, but not parechovirus or more remote viruses such as Semliki Forest virus, adenovirus, and respiratory syncytial virus. The inhibitory effect acts through cellular phosphatidylinositol 4-kinase type IIIβ (PI4KB), which has been shown to be important in the formation of enteroviral replication organelles. Vemurafenib prevents infection efficiently in acute cell models, eradicates infection in a chronic cell model, and lowers virus amounts in pancreas and heart in an acute mouse model. Our findings open new possibilities to develop drugs against enteroviruses and give hope for repurposing vemurafenib as an antiviral drug against enteroviruses.

27-Hydroxycholesterol inhibits rhinovirus replication in vitro and on human nasal and bronchial histocultures without selecting viral resistant variants

The genetic plasiticity of viruses is one of the main obstacles to the development of antivirals. The aim of this study has been to assess the ability of two physiologic oxysterols and host-targeting antivirals - namely 25- and 27-hydroxycholesterol (25OHC and 27OHC) - to select resistant strains, using human rhinovirus (HRV) as a challenging model of a viral quasispecies. Moreover, we selected 27OHC for further studies aimed at exploring its potential for the development of antiviral drugs. The results obtained with clonal or serial passage approaches show that 25OHC and 27OHC do not select HRV oxysterol-resistant variants. Moreover, we demonstrate the ability of 27OHC to inhibit the yield of HRV in 3D in vitro fully reconstituted human nasal and bronchial epithelia from cystic fibrosis patients and prevent virus-induced cilia damage. The promising antiviral activity of 27OHC and its competitive advantages over direct-acting antivirals, make this molecule a suitable candidate for further studies to explore its clinical potential.

Experimental Antiviral Therapeutic Studies for Human Rhinovirus Infections

Rhinovirus infection is common and usually causes mild, self-limiting upper respiratory tract symptoms. Rhinoviruses can cause exacerbation of chronic respiratory diseases, such as asthma or chronic obstructive pulmonary disease, leading to a significant burden of morbidity and mortality. There has been a great deal of progress in efforts to understand the immunological basis of rhinovirus infection. However, despite a number of in vitro and in vivo attempts, there have been no effective treatments developed. This review article summarises the up to date virological and immunological understanding of these infections. We discuss the challenges researchers face, and key solutions, in their work to investigate potential therapies including in vivo rhinovirus challenge studies. Finally, we explore past and present experimental therapeutic strategies employed in the treatment of rhinovirus infections and highlight promising areas of future work.

Rhinovirus and asthma: Challenges and opportunities

Human rhinoviruses (RVs) are the primary aetiological agent of the common cold. Generally, the associated infection is mild and self‐limiting, but may also be associated with bronchiolitis in infants, pneumonia in the immunocompromised and exacerbation in patients with pulmonary conditions such as asthma or chronic obstructive pulmonary disease. Viral infection accounts for as many as two thirds of asthma exacerbations in children and more than half in adults. Allergy and asthma are major risk factors for more frequent and severe RV‐related illnesses. The prevalence of RV‐induced wheezing will likely continue to increase given that asthma affects a significant proportion of the population, with allergic asthma accounting for the majority. Several new respiratory viruses and their subgroups have been discovered, with various degrees of relevance. This review will focus on RV infection in the context of the epidemiologic evidence, genetic variability, pathobiology, clinical studies in the context of asthma, differences with other viruses including COVID‐19 and current treatment interventions.

Rupintrivir reduces RV-induced TH-2 cytokine IL-4 in precision-cut lung slices (PCLS) of HDM-sensitized mice ex vivo

Background

Antiviral drugs such as rupintrivir may have an immune-modulatory effect in experimentally induced allergic asthma with subsequent RV infection. We infected lung slices of house-dust mite (HDM)-sensitized asthmatic mice ex vivo with human rhinovirus (RV) and investigated the effect of the antiviral drug rupintrivir on RV-induced cytokine response in lung tissue of HDM-sensitized mice ex vivo.

Methods

Mice were sensitized with HDM. Precision-cut lung slices (PCLS) were prepared from HDM-sensitized or non-sensitized mice. Lung slices were infected ex vivo with RV or RV together with rupintrivir. Modulation of immune responses was evaluated by cytokine secretion 48 h post infection.

Results

In vivo HDM sensitization resulted in a T_H-2/T_H-17-dominated cytokine response that persisted in PCLS ex vivo. RV infection of PCLS from non-sensitized mice resulted in the induction of an antiviral and pro-inflammatory immune response, as indicated by the secretion of IFN-α, IFN-β, IFN-γ, TNF-α, MCP-1, IP-10, IL-10, and IL-17A. In contrast, PCLS from HDM-sensitized mice showed an attenuated antiviral response, but exaggerated IL-4, IL-6, and IL-10 secretion upon infection. Rupintrivir inhibited exaggerated pro-inflammatory cytokine IL-6 and T_H-2 cytokine IL-4 in HDM-sensitized mice.

Conclusions

In summary, this study demonstrates that treatment with rupintrivir influences virus-induced IL-4 and IL-6 cytokine release under experimental conditions ex vivo.

Electronic supplementary material

The online version of this article (10.1186/s12931-019-1175-y) contains supplementary material, which is available to authorized users.

Cryo-EM structure of pleconaril-resistant rhinovirus-B5 complexed to the antiviral OBR-5-340 reveals unexpected binding site

Viral inhibitors, such as pleconaril and vapendavir, target conserved regions in the capsids of rhinoviruses (RVs) and enteroviruses (EVs) by binding to a hydrophobic pocket in viral capsid protein 1 (VP1). In resistant RVs and EVs, bulky residues in this pocket prevent their binding. However, recently developed pyrazolopyrimidines inhibit pleconaril-resistant RVs and EVs, and computational modeling has suggested that they also bind to the hydrophobic pocket in VP1. We studied the mechanism of inhibition of pleconaril-resistant RVs using RV-B5 (1 of the 7 naturally pleconaril-resistant rhinoviruses) and OBR-5-340, a bioavailable pyrazolopyrimidine with proven in vivo activity, and determined the 3D-structure of the protein-ligand complex to 3.6 Å with cryoelectron microscopy. Our data indicate that, similar to other capsid binders, OBR-5-340 induces thermostability and inhibits viral adsorption and uncoating. However, we found that OBR-5-340 attaches closer to the entrance of the pocket than most other capsid binders, whose viral complexes have been studied so far, showing only marginal overlaps of the attachment sites. Comparing the experimentally determined 3D structure with the control, RV-B5 incubated with solvent only and determined to 3.2 Å, revealed no gross conformational changes upon OBR-5-340 binding. The pocket of the naturally OBR-5-340-resistant RV-A89 likewise incubated with OBR-5-340 and solved to 2.9 Å was empty. Pyrazolopyrimidines have a rigid molecular scaffold and may thus be less affected by a loss of entropy upon binding. They interact with less-conserved regions than known capsid binders. Overall, pyrazolopyrimidines could be more suitable for the development of new, broadly active inhibitors.

Antiviral therapeutic approaches for human rhinovirus infections

Human rhinoviruses are the primary etiological agent of the common cold. This infection can be mild and self-limiting in immunocompetent hosts, but can be associated with bronchiolitis in infants, pneumonia in the immunosuppressed and exacerbations of pre-existing pulmonary conditions such as asthma or chronic obstructive pulmonary disease. Many of these conditions can place significant economic costs upon healthcare infrastructure. There is currently no licensed vaccine for rhinovirus, as the large variety of rhinovirus serotypes has posed significant challenges for research. In this review, we discuss current knowledge around antiviral drugs and small molecule inhibitors of rhinovirus infection, as well as antiviral host defense peptides as exciting prospects to approach the development of novel therapeutics which target human rhinovirus.

Direct-acting antivirals and host-targeting strategies to combat enterovirus infections

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Enteroviruses cause many human diseases, yet no antiviral drugs are available.

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Capsids and viral enzymes are promising targets for direct-acting antiviral therapy.

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Fundamental research has unveiled host factors for broad-spectrum drug development.

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Drug repurposing screens have yielded new promising enterovirus inhibitors.

Enteroviruses (e.g., poliovirus, enterovirus-A71, coxsackievirus, enterovirus-D68, rhinovirus) include many human pathogens causative of various mild and more severe diseases, especially in young children. Unfortunately, antiviral drugs to treat enterovirus infections have not been approved yet. Over the past decades, several direct-acting inhibitors have been developed, including capsid binders, which block virus entry, and inhibitors of viral enzymes required for genome replication. Capsid binders and protease inhibitors have been clinically evaluated, but failed due to limited efficacy or toxicity issues. As an alternative approach, host-targeting inhibitors with potential broad-spectrum activity have been identified. Furthermore, drug repurposing screens have recently uncovered promising new inhibitors with disparate viral and host targets. Together, these findings raise hope for the development of (broad-range) anti-enteroviral drugs.

Unexpectedly Higher Morbidity and Mortality of Hospitalized Elderly Patients Associated with Rhinovirus Compared with Influenza Virus Respiratory Tract Infection

Rhinovirus is a common cause of upper and lower respiratory tract infections in adults, especially among the elderly and immunocompromised. Nevertheless, its clinical characteristics and mortality risks have not been well described. A retrospective analysis on a prospective cohort was conducted in a single teaching hospital center over a one-year period. We compared adult patients hospitalized for pneumonia caused by rhinovirus infection with those hospitalized for influenza infection during the same period. All recruited patients were followed up for at least 3 months up to 15 months. Independent risk factors associated with mortality for rhinovirus infection were identified. Between 1 March 2014 and 28 February 2015, a total of 1946 patients were consecutively included for analysis. Of these, 728 patients were hospitalized for rhinovirus infection and 1218 patients were hospitalized for influenza infection. Significantly more rhinovirus patients were elderly home residents and had chronic lung diseases (p < 0.001), whereas more influenza patients had previous stroke (p = 0.02); otherwise, there were no differences in the Charlson comorbidity indexes between the two groups. More patients in the rhinovirus group developed pneumonia complications (p = 0.03), required oxygen therapy, and had a longer hospitalization period (p < 0.001), whereas more patients in the influenza virus group presented with fever (p < 0.001) and upper respiratory tract symptoms of cough and sore throat (p < 0.001), and developed cardiovascular complications (p < 0.001). The 30-day (p < 0.05), 90-day (p < 0.01), and 1-year (p < 0.01) mortality rate was significantly higher in the rhinovirus group than the influenza virus group. Intensive care unit admission (odds ratio (OR): 9.56; 95% confidence interval (C.I.) 2.17–42.18), elderly home residents (OR: 2.60; 95% C.I. 1.56–4.33), requirement of oxygen therapy during hospitalization (OR: 2.62; 95% C.I. 1.62–4.24), and hemoglobin level <13.3 g/dL upon admission (OR: 2.43; 95% C.I. 1.16–5.12) were independent risk factors associated with 1-year mortality in patients hospitalized for rhinovirus infection. Rhinovirus infection in the adults was associated with significantly higher mortality and longer hospitalization when compared with influenza virus infection. Institutionalized older adults were particularly at risk. More stringent infection control among health care workers in elderly homes could lower the infection rate before an effective vaccine and antiviral become available.

Susceptibilities of enterovirus D68, enterovirus 71, and rhinovirus 87 strains to various antiviral compounds

Compounds were evaluated for antiviral activity in rhabdomyosarcoma (RD) cells against a recent 2014 clinical isolate of enterovirus D68 (EV-D68), a 1962 strain of EV-68D, rhinovirus 87 (RV-87, serologically the same as EV-D68), and enterovirus 71 (EV-71). Test substances included known-active antipicornavirus agents (enviroxime, guanidine HCl, pirodavir, pleconaril, and rupintrivir), nucleobase/nucleoside analogs (3-deazaguanine and ribavirin), and three novel epidithiodiketopiperazines (KCN-2,2'-epi-19, KCN-19, and KCN-21). Of these, rupintrivir was the most potent, with 50% inhibition of viral cytopathic effect (EC50) and 90% inhibition (EC90) of virus yield at 0.0022-0.0053 μM against EV-D68. Enviroxime, pleconaril and the KCN compounds showed efficacy at 0.01-0.3 μM; 3-deazaguanine and pirodavir inhibited EV-D68 at 7-13 μM, and guanidine HCl and ribavirin were inhibitory at 80-135 μM. Pirodavir was active against EV-71 (EC50 of 0.78 μM) but not against RV-87 or EV-D68, and all other compounds were less effective against EV-71 than against RV-87 and EV-D68. The most promising compound inhibiting both virus infections at low concentrations was rupintrivir. Antiviral activity was confirmed for the ten compounds in virus yield reduction (VYR) assays in RD cells, and for enviroxime, guanidine HCl, and pirodavir by cytopathic effect (CPE) assays in A549, HeLa-Ohio-1, and RD cells. These studies may serve as a basis for further pre-clinical discovery of anti-enterovirus inhibitors. Furthermore, the antiviral profiles and growth characteristics observed herein support the assertion that EV-D68 should be classified together with RV-87.

Chinese herbal medicines as a source of molecules with anti-enterovirus 71 activity

Enterovirus 71 (EV71) is one of the causative agents of hand, foot, and mouth disease (HFMD), which sometimes leads to severe neurological disease and death in the Asia-Pacific region. In Chinese medicine, HFMD is caused mainly by an accumulation of damp-heat and toxicity in the body. No effective drugs are currently available for the treatment and prevention of EV71 infection. This review summarizes the potential Chinese herbal extracts and isolated compounds with antiviral activity against EV71 and their clinical applications, especially those categorized as heat-clearing and detoxifying.

Replication and Inhibitors of Enteroviruses and Parechoviruses

The Enterovirus (EV) and Parechovirus genera of the picornavirus family include many important human pathogens, including poliovirus, rhinovirus, EV-A71, EV-D68, and human parechoviruses (HPeV). They cause a wide variety of diseases, ranging from a simple common cold to life-threatening diseases such as encephalitis and myocarditis. At the moment, no antiviral therapy is available against these viruses and it is not feasible to develop vaccines against all EVs and HPeVs due to the great number of serotypes. Therefore, a lot of effort is being invested in the development of antiviral drugs. Both viral proteins and host proteins essential for virus replication can be used as targets for virus inhibitors. As such, a good understanding of the complex process of virus replication is pivotal in the design of antiviral strategies goes hand in hand with a good understanding of the complex process of virus replication. In this review, we will give an overview of the current state of knowledge of EV and HPeV replication and how this can be inhibited by small-molecule inhibitors.

Inhaled anti-infective chemotherapy for respiratory tract infections: successes, challenges and the road ahead

One of the most common causes of illnesses in humans is from respiratory tract infections caused by bacterial, viral or fungal pathogens. Inhaled anti-infective drugs are crucial for the prophylaxis and treatment of respiratory tract infections. The benefit of anti-infective drug delivery via inhalation is that it affords delivery of sufficient therapeutic dosages directly to the primary site of infection, while minimizing the risks of systemic toxicity or avoiding potential suboptimal pharmacokinetics/pharmacodynamics associated with systemic drug exposure. This review provides an up-to-date treatise of approved and novel developmental inhaled anti-infective agents, with particular attention to effective strategies for their use, pulmonary pharmacokinetic properties and safety.

Synthesis of N-benzyl-N-phenylthiophene-2-carboxamide analogues as a novel class of enterovirus 71 inhibitors

A series ofN-benzyl-N-phenylthiophene-2-carboxamide analogues were identified as novel human enterovirus 71 inhibitors with EC₅₀values up to 1.42 μM.

The capsid binder Vapendavir and the novel protease inhibitor SG85 inhibit enterovirus 71 replication

Antivirals against enterovirus 71 (EV71) are urgently needed. We demonstrate that the novel enteroviral protease inhibitor (PI) SG85 and capsid binder (CB) vapendavir efficiently inhibit the in vitro replication of 21 EV71 strains/isolates that are representative of the different genogroups A, B, and C. The PI rupintrivir, the CB pirodavir, and the host-targeting compound enviroxime, which were included as reference compounds, also inhibited the replication of all isolates. Remarkably, the CB compound pleconaril was devoid of any anti-EV71 activity. An in silico docking study revealed that pleconaril-unlike vapendavir and pirodavir-lacks essential binding interactions with the viral capsid. Vapendavir and SG85 (or analogues) should be further explored for the treatment of EV71 infections. The data presented here may serve as a reference when developing yet-novel inhibitors.

Multiple classes of antiviral agents exhibit in vitro activity against human rhinovirus type C

Human rhinovirus type C (HRV-C) is a newly discovered enterovirus species frequently associated with exacerbation of asthma and other acute respiratory conditions. Until recently, HRV-C could not be propagated in vitro, hampering in-depth characterization of the virus replication cycle and preventing efficient testing of antiviral agents. Herein we describe several subgenomic RNA replicon systems and a cell culture infectious model for HRV-C that can be used for antiviral screening. The replicon constructs consist of genome sequences from HRVc15, HRVc11, HRVc24, and HRVc25 strains, with the P1 capsid region replaced by a Renilla luciferase coding sequence. Following transfection of the replicon RNA into HeLa cells, the constructs produced time-dependent increases in luciferase signal that can be inhibited in a dose-dependent manner by known inhibitors of HRV replication, including the 3C protease inhibitor rupintrivir, the nucleoside analog inhibitor MK-0608, and the phosphatidylinositol 4-kinase IIIβ (PI4K-IIIβ) kinase inhibitor PIK93. Furthermore, with the exception of pleconaril and pirodavir, the other tested classes of HRV inhibitors blocked the replication of full-length HRVc15 and HRVc11 in human airway epithelial cells (HAEs) that were differentiated in the air-liquid interface, exhibiting antiviral activities similar to those observed with HRV-16. In summary, this study is the first comprehensive profiling of multiple classes of antivirals against HRV-C, and the set of newly developed quantitative HRV-C antiviral assays represent indispensable tools for the identification and evaluation of novel panserotype HRV inhibitors.

Antiviral activity of Isatis indigotica root-derived clemastanin B against human and avian influenza A and B viruses in vitro

Clemastanin B, 7S,8R,8'R-(-)-lariciresinol-4,4'-bis-O-β-D-glucopyranoside, is one of the major lignans extracted from Isatis indigotica root (IIR). In this study, the anti-influenza activities of clemastanin B were evaluated in vitro. Clemastanin B was found to inhibit different subtypes of human (H1N1, including swine-origin H1N1; H3N2 and influenza B) and avian influenza viruses (H6N2, H7N3, H9N2) at different magnitudes of activity (IC50 0.087-0.72 mg/ml) while this compound was inactive against respiratory syncytial virus (RSV), adenovirus 3 (ADV3), parainfluenza virus 3 (PIV3), enterovirus 71 (EV71) and human rhinovirus (HRV). An apparent virus titer reduction was detected when MDCK cells were treated with clemastanin B after viral infection, particularly at the early stage, and the ribonucleoprotein (RNP) of the influenza virus was retained in the nucleus after treatment with clemastanin B. These results demonstrated that clemastanin B targets viral endocytosis, uncoating or RNP export from the nucleus. Furthermore, treatment with clemastanin B did not easily result in the emergence of viral drug resistance. The effects of clemastanin B demonstrated in this study may promote the antiviral study of IIR, but additional studies are required to define the anti-influenza mechanism(s).

Niclosamide is a proton carrier and targets acidic endosomes with broad antiviral effects

Viruses use a limited set of host pathways for infection. These pathways represent bona fide antiviral targets with low likelihood of viral resistance. We identified the salicylanilide niclosamide as a broad range antiviral agent targeting acidified endosomes. Niclosamide is approved for human use against helminthic infections, and has anti-neoplastic and antiviral effects. Its mode of action is unknown. Here, we show that niclosamide, which is a weak lipophilic acid inhibited infection with pH-dependent human rhinoviruses (HRV) and influenza virus. Structure-activity studies showed that antiviral efficacy and endolysosomal pH neutralization co-tracked, and acidification of the extracellular medium bypassed the virus entry block. Niclosamide did not affect the vacuolar H(+)-ATPase, but neutralized coated vesicles or synthetic liposomes, indicating a proton carrier mode-of-action independent of any protein target. This report demonstrates that physico-chemical interference with host pathways has broad range antiviral effects, and provides a proof of concept for the development of host-directed antivirals.

Pleconaril revisited: clinical course of chronic enteroviral meningoencephalitis after treatment correlates with in vitro susceptibility

BACKGROUND

Human enteroviruses (HEVs) can cause severe infections, especially in patients with a deficient humoral immune response, such as X-linked agammaglobulinemia. In this patient group, chronic enteroviral meningitis (CEMA) is feared because of extensive morbidity and high fatality rate. Treatment options consist of intravenous immunoglobulin (IVIG), with various outcomes. Pleconaril is an antiviral agent with in vitro activity against HEVs that has been used in the treatment of HEV infections.

METHODS

The efficacy of pleconaril and IVIG against HEV isolated from the patients was assessed in vitro in two patients with CEMA.

RESULTS

Echovirus 11 was found in the cerebrospinal fluid (CSF) of case 1. Treatment with high-dose IVIG and pleconaril did not provide any clinical improvement and HEV PCR in CSF remained positive. Case 2 (echovirus 13 positive in CSF) was also treated with IVIG and pleconaril. The patient recovered completely and HEV PCR in CSF became negative. Recent IVIG batches contained low titres of neutralizing antibodies against the patient strains. Echovirus 11 (case 1) was resistant to pleconaril in vitro, whereas echovirus 13 (case 2) was susceptible, in accordance with virological response after treatment and subsequent clinical results.

CONCLUSIONS

This is the first report that evaluates efficacy of antiviral treatment in CEMA patients in relation to in vitro susceptibility of clinical virus isolates. Since pleconaril is no longer available for compassionate use we strongly propagate that new drugs should be developed against these potential life threatening HEV infections.

Structural basis for antiviral inhibition of the main protease, 3C, from human enterovirus 93

Members of the Enterovirus genus of the Picornaviridae family are abundant, with common human pathogens that belong to the rhinovirus (HRV) and enterovirus (EV) species, including diverse echo-, coxsackie- and polioviruses. They cause a wide spectrum of clinical manifestations ranging from asymptomatic to severe diseases with neurological and/or cardiac manifestations. Pandemic outbreaks of EVs may be accompanied by meningitis and/or paralysis and can be fatal. However, no effective prophylaxis or antiviral treatment against most EVs is available. The EV RNA genome directs the synthesis of a single polyprotein that is autocatalytically processed into mature proteins at Gln↓Gly cleavage sites by the 3C protease (3C(pro)), which has narrow, conserved substrate specificity. These cleavages are essential for virus replication, making 3C(pro) an excellent target for antivirus drug development. In this study, we report the first determination of the crystal structure of 3C(pro) from an enterovirus B, EV-93, a recently identified pathogen, alone and in complex with the anti-HRV molecules compound 1 (AG7404) and rupintrivir (AG7088) at resolutions of 1.9, 1.3, and 1.5 Å, respectively. The EV-93 3C(pro) adopts a chymotrypsin-like fold with a canonically configured oxyanion hole and a substrate binding pocket similar to that of rhino-, coxsackie- and poliovirus 3C proteases. We show that compound 1 and rupintrivir are both active against EV-93 in infected cells and inhibit the proteolytic activity of EV-93 3C(pro) in vitro. These results provide a framework for further structure-guided optimization of the tested compounds to produce antiviral drugs against a broad range of EV species.

Complete coding sequence characterization and comparative analysis of the putative novel human rhinovirus (HRV) species C and B

Background

Human Rhinoviruses (HRVs) are well recognized viral pathogens associated with acute respiratory tract illnesses (RTIs) abundant worldwide. Although recent studies have phylogenetically identified the new HRV species (HRV-C), data on molecular epidemiology, genetic diversity, and clinical manifestation have been limited.

Result

To gain new insight into HRV genetic diversity, we determined the complete coding sequences of putative new members of HRV species C (HRV-CU072 with 1% prevalence) and HRV-B (HRV-CU211) identified from clinical specimens collected from pediatric patients diagnosed with a symptom of acute lower RTI. Complete coding sequence and phylogenetic analysis revealed that the HRV-CU072 strain shared a recent common ancestor with most closely related Chinese strain (N4). Comparative analysis at the protein level showed that HRV-CU072 might accumulate substitutional mutations in structural proteins, as well as nonstructural proteins 3C and 3 D. Comparative analysis of all available HRVs and HEVs indicated that HRV-C contains a relatively high G+C content and is more closely related to HEV-D. This might be correlated to their replication and capability to adapt to the high temperature environment of the human lower respiratory tract. We herein report an infrequently occurring intra-species recombination event in HRV-B species (HRV-CU211) with a crossing over having taken place at the boundary of VP2 and VP3 genes. Moreover, we observed phylogenetic compatibility in all HRV species and suggest that dynamic mechanisms for HRV evolution seem to be related to recombination events. These findings indicated that the elementary units shaping the genetic diversity of HRV-C could be found in the nonstructural 2A and 3D genes.

Conclusion

This study provides information for understanding HRV genetic diversity and insight into the role of selection pressure and recombination mechanisms influencing HRV evolution.

The human rhinovirus: human-pathological impact, mechanisms of antirhinoviral agents, and strategies for their discovery

As the major etiological agent of the common cold, human rhinoviruses (HRV) cause millions of lost working and school days annually. Moreover, clinical studies proved an association between harmless upper respiratory tract infections and more severe diseases e.g. sinusitis, asthma, and chronic obstructive pulmonary disease. Both the medicinal and socio-economic impact of HRV infections and the lack of antiviral drugs substantiate the need for intensive antiviral research. A common structural feature of the approximately 100 HRV serotypes is the icosahedrally shaped capsid formed by 60 identical copies of viral capsid proteins VP1-4. The capsid protects the single-stranded, positive sense RNA genome of about 7,400 bases in length. Both structural as well as nonstructural proteins produced during the viral 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, interferon and phytoceuticals were shown to protect host cells. Most of the known inhibitors of HRV replication were discovered as a result of empirical or semi-empirical screening in cell culture. Structure-activity relationship studies are used for hit optimization and lead structure discovery. The increasing structural insight and molecular understanding of viral proteins on the one hand and the advent of innovative computer-assisted technologies on the other hand have facilitated a rationalized access for the discovery of small chemical entities with antirhinoviral (anti-HRV) activity. This review will (i) summarize existing structural knowledge about HRV, (ii) focus on mechanisms of anti-HRV agents from synthetic and natural origin, and (iii) demonstrate strategies for efficient lead structure discovery.

Per aspera ad astra: application of Simplex QSAR approach in antiviral research

This review explores the application of the Simplex representation of molecular structure (SiRMS) QSAR approach in antiviral research. We provide an introduction to and description of SiRMS, its application in antiviral research and future directions of development of the Simplex approach and the whole QSAR field. In the Simplex approach every molecule is represented as a system of different simplexes (tetratomic fragments with fixed composition, structure, chirality and symmetry). The main advantages of SiRMS are consideration of the different physical–chemical properties of atoms, high adequacy and good interpretability of models obtained and clear procedures for molecular design. The reliability of developed QSAR models as predictive virtual screening tools and their ability to serve as the basis of directed drug design was validated by subsequent synthetic and biological experiments. The SiRMS approach is realized as the complex of the computer program ‘HiT QSAR’, which is available on request.

Picornaviral 3C protease inhibitors and the dual 3C protease/coronaviral 3C-like protease inhibitors

IMPORTANCE OF THE FIELD

Picornaviruses are small non-enveloped RNA viruses with genomic RNA of 7500 - 8000 nucleotides, whereas coronaviruses (CoV) are RNA viruses with larger genome of 27 - 32 kb. Both types of viruses translate their genetic information into polyprotein precursors that are processed by virally encoded 3C proteases (3C(pro)) and 3C-like proteases (3CL(pro)), respectively, to generate functional viral proteins. The most studied human rhinoviruses (HRV) belonging to picornaviridae family are the main etiologic agents of the common cold. Due to lack of effective drugs, 3C(pro) has served as an excellent target for anti-viral intervention and considerable efforts have been made in the development of inhibitors. Interestingly, the inhibitors of 3C(pro) cannot inhibit 3CL(pro) potently without modification due to subtle differences in their active-site structures, but a group of common inhibitors against 3C(pro) and 3CL(pro) were found recently.

AREAS COVERED IN THIS REVIEW

The inhibitors against 3C(pro) reported in the literatures and patents, with a focus on those inhibiting HRV and the dual picornaviral 3C(pro)/coronaviral 3CL(pro) inhibitors, are summarized in this review.

WHAT THE READERS WILL GAIN

Readers will rapidly gain an overview of the individual and dual 3C(pro) inhibitors and the structural basis for discriminating them.

TAKE HOME MESSAGE

In the future, more selective potent inhibitors against each protease and dual inhibitors against both proteases can be further developed to treat the diseases caused by picornaviruses and CoV.

Virtual Screening and Molecular Design Based on Hierarchical Qsar Technology

This chapter is devoted to the hierarchical QSAR technology (HiT QSAR) based on simplex representation of molecular structure (SiRMS) and its application to different QSAR/QSPR tasks. The essence of this technology is a sequential solution (with the use of the information obtained on the previous steps) of the QSAR paradigm by a series of enhanced models based on molecular structure description (in a specific order from 1D to 4D). Actually, it’s a system of permanently improved solutions. Different approaches for domain applicability estimation are implemented in HiT QSAR. In the SiRMS approach every molecule is represented as a system of different simplexes (tetratomic fragments with fixed composition, structure, chirality, and symmetry). The level of simplex descriptors detailed increases consecutively from the 1D to 4D representation of the molecular structure. The advantages of the approach presented are an ability to solve QSAR/QSPR tasks for mixtures of compounds, the absence of the “molecular alignment” problem, consideration of different physical–chemical properties of atoms (e.g., charge, lipophilicity), and the high adequacy and good interpretability of obtained models and clear ways for molecular design. The efficiency of HiT QSAR was demonstrated by its comparison with the most popular modern QSAR approaches on two representative examination sets. The examples of successful application of the HiT QSAR for various QSAR/QSPR investigations on the different levels (1D–4D) of the molecular structure description are also highlighted. The reliability of developed QSAR models as the predictive virtual screening tools and their ability to serve as the basis of directed drug design was validated by subsequent synthetic, biological, etc. experiments. The HiT QSAR is realized as the suite of computer programs termed the “HiT QSAR” software that so includes powerful statistical capabilities and a number of useful utilities.

Real-time monitoring of human enterovirus (HEV)-infected cells and anti-HEV 3C protease potency by fluorescence resonance energy transfer

A real-time assay system that allows monitoring of intracellular human enterovirus (HEV) protease activity was established using the principle of fluorescence resonance energy transfer (FRET). It was accomplished by engineering cells to constitutively express a genetically encoded FRET probe. The FRET-based probe was designed to contain an enterovirus 71 3C protease (3C(pro)) cleavage motif flanked by the FRET pair composed of green fluorescent protein 2 and red fluorescent protein 2 (DsRed2). Efficient FRET from the stable line was detected in a real-time manner by fluorescence microscopy, and the disruption of FRET was readily monitored upon HEV infection. The level of the repressed FRET was proportional to the input virus titer and the infection duration as measured by the fluorometric method. The FRET biosensor cell line was also responsive to other related HEV serotypes, but not to the phylogenetically distant herpes simplex virus, which was confirmed by Western blot analysis. The FRET biosensor was then utilized to develop a format for the determination of antiviral susceptibility, as the reduced FRET appeared to reflect viral replication. Evaluations of the FRET biosensor system with representative HEV serotypes demonstrated that their susceptibilities to a 3C(pro) inhibitor, rupintrivir, were all accurately determined. In summary, this novel FRET-based system is a means for rapid detection, quantification, and drug susceptibility testing for HEVs, with potential for the development of a high-throughput screening assay.

Selective inhibitors of picornavirus replication

Picornaviruses cover a large family of pathogens that have a major impact on human but also on veterinary health. Although most infections in man subside mildly or asymptomatically, picornaviruses can also be responsible for severe, potentially life-threatening disease. To date, no therapy has been approved for the treatment of picornavirus infections. However, efforts to develop an antiviral that is effective in treating picornavirus-associated diseases are ongoing. In 2007, Schering-Plough, under license of ViroPharma, completed a phase II clinical trial with Pleconaril, a drug that was originally rejected by the FDA after a New Drug Application in 2001. Rupintrivir, a rhinovirus protease inhibitor developed at Pfizer, reached clinical trials but was recently halted from further development. Finally, Biota's HRV drug BTA-798 is scheduled for phase II trials in 2008. Several key steps in the picornaviral replication cycle, involving structural as well as non-structural proteins, have been identified as valuable targets for inhibition. The current review aims to highlight the most important developments during the past decades in the search for antivirals against picornaviruses.

New pleconaril and [(biphenyloxy)propyl]isoxazole derivatives with substitutions in the central ring exhibit antiviral activity against pleconaril-resistant coxsackievirus B3

Amino acid 1092 (AA1092) in capsid protein 1 of coxsackievirus B3 (CVB3) is located in close vicinity to the central phenoxy group of capsid binders (i.e. pleconaril). Whereas isoleucine is associated with drug susceptibility, leucine and methionine confer resistance to pleconaril. In the present study, novel analogues with different substitutions in the central phenoxy group were synthesized to study their influence on anti-CVB3 activity with the aim to overcome pleconaril resistance. Two [(biphenyloxy)propyl]isoxazoles and pleconaril were synthesized without methyl groups in the central phenoxy ring using Suzuki coupling reaction and tested for antiviral activity against the pleconaril-resistant CVB3 Nancy. Furthermore, pleconaril with 3-methyl, 3-methoxy, 3-bromine, 2,3-dimethyl in the central ring as well as the external rings in meta position were synthesized for structure-activity relationship analysis with CVB3 variants containing leucine, methionine or isoleucine at position 1092, other coxsackieviruses B (CVB) as well as several rhinoviruses. The results demonstrate a high impact of substituents in the central ring of capsid inhibitors for anti-enteroviral activity. Pleconaril resistance of CVB3 based on Leu1092 or Met1092 was overcome by unsubstituted analogues or by monosubstitution with 3-methyl as well as 3-bromine in the central phenyl. The 3-bromine derivative inhibited a broad spectrum of CVB and rhinoviruses.

In vitro resistance study of rupintrivir, a novel inhibitor of human rhinovirus 3C protease

Rupintrivir (formerly AG7088) is an irreversible inhibitor of the human rhinovirus (HRV) 3C protease that has been demonstrated to have in vitro activity against all HRVs tested, consistent with its interaction with a strictly conserved subset of amino acids in the 3C protease. The potential for resistance was studied following in vitro serial passage of HRV serotypes 14, 2, 39, and Hanks in the presence of increasing rupintrivir concentrations. HRV variants with reduced susceptibilities to rupintrivir (sevenfold for HRV 14) or with no significant reductions in susceptibility but genotypic changes (HRV 2, 39, and Hanks) were initially isolated following 14 to 40 cumulative days in culture (three to six passages). Sequence analysis of the 3C protease identified one to three substitutions in diverse patterns but with common features (T129T/A, T131T/A, and T143P/S in HRV 14; N165T in HRV 2; N130N/K and L136L/F in HRV 39; T130A in HRV Hanks). Notably, three of the four HRV variants contained a substitution at residue 130 (residue 129 in HRV 14). Continued selection in the presence of escalating concentrations of rupintrivir (40 to 72 days) resulted in the accumulation of additional mutations (A121A/V and Y139Y/H in HRV 14, E3E/G and A103A/V in HRV 2, S105T in HRV 39), with only minimal further reductions in susceptibility (up to fivefold). The ability of specific substitutions to confer resistance was examined by susceptibility testing of HRV 14 variants constructed to contain 3C protease mutations. In summary, the slow accumulation of multiple amino acid substitutions with only minimal to moderate reductions in susceptibility highlight the advantages of 3C protease as an antiviral target.

Quantitative structure-activity relationship studies of [(biphenyloxy)propyl]isoxazole derivatives. Inhibitors of human rhinovirus 2 replication

The 50% cytotoxic concentration (CC50) in HeLa cells, the 50% inhibitory concentration (IC50) against human rhinovirus 2 (HRV-2), and the selectivity index (SI = CC50/IC50) of [(biphenyloxy)propyl]isoxazole derivatives were used to develop quantitative structure-activity relationships (QSAR) based on simplex representation of molecular structure. Statistic characteristics for partial least-squares models are quite satisfactory (R2 = 0.838 - 0.918; Q2 = 0.695 - 0.87) for prediction of CC50, IC50, and SI values and permit the virtual screening and molecular design of new compounds with strong anti-HRV-2 activity. The quality of prognosis for designed compounds was additionally estimated by analysis of domain applicability for each QSAR model. A hypothesis to the effect that terminal benzene substituents must have negative electrostatic potential and definite length (approximately 5.5-5.6 A) to possess strong antiviral activity has been suggested. The quality of developed analysis, i.e., high level of antiviral action of three new designed compounds, has been confirmed experimentally.

VII International Symposium on Respiratory Viral Infections

The VII International Symposium on Respiratory Viral Infections was a multidisciplinary forum for the presentation of recent advances in respiratory virus research with special emphasis on antiviral therapies and vaccine strategies. Topics covered in invited lectures included detection of novel respiratory viral pathogens and viral evolution, characterization of the 1918 pandemic virus, human metapneumovirus infections, human respiratory epithelial cultures for studying viral pathogenesis, the role of respiratory viruses in the pathogenesis of asthma, influenza-bacterial interactions, advances in generating vaccine candidates against global respiratory threats like avian influenza and SARS, antiviral resistance surveillance in influenza viruses, and a mini-symposium on advances in viral diagnostics. Other talks covered the live, attenuated intranasal influenza vaccine, monoclonals for respiratory syncytial virus (RSV), mechanisms of antiviral resistance in influenza B, and novel inhibitors for influenza, RSV and rhinovirus infections.

Chronic Rhinoviral Infection in Lung Transplant Recipients

RATIONALE

Lung transplant recipients are particularly at risk of complications from rhinovirus, the most frequent respiratory virus circulating in the community.

OBJECTIVES

To determine whether lung transplant recipients can be chronically infected by rhinovirus and the potential clinical impact.

METHODS

We first identified an index case, in which rhinovirus was isolated repeatedly, and conducted detailed molecular analysis to determine whether this was related to a unique strain or to re-infection episodes. Transbronchial biopsies were used to assess the presence of rhinovirus in the lung parenchyma. The incidence of chronic rhinoviral infections and potential clinical impact was assessed prospectively in a cohort of 68 lung transplant recipients during 19 mo by screening of bronchoalveolar lavages.

MEASUREMENTS AND MAIN RESULTS

We describe 3 lung transplant recipients with graft dysfunctions in whom rhinovirus was identified by reverse transcriptase-polymerase chain reaction in upper and lower respiratory specimens over a 12-mo period. In two cases, rhinovirus was repeatedly isolated in culture. The persistence of a unique strain in each case was confirmed by sequence analysis of the 5'NCR and VP1 gene. In the index case, rhinovirus was detected in the lower respiratory parenchyma. In the cohort of lung transplant recipients, rhinoviral infections were documented in bronchoalveolar lavage specimens of 10 recipients, and 2 presented with a persistent infection.

CONCLUSIONS

Rhinoviral infection can be persistent in lung transplant recipients with graft dysfunction, and the virus can be detected in the lung parenchyma. Given the potential clinical impact, chronic rhinoviral infection needs to be considered in lung transplant recipients.

Protease inhibitors and their peptidomimetic derivatives as potential drugs

Precise spatial and temporal regulation of proteolytic activity is essential to human physiology. Modulation of protease activity with synthetic peptidomimetic inhibitors has proven to be clinically useful for treating human immunodeficiency virus (HIV) and hypertension and shows potential for medicinal application in cancer, obesity, cardiovascular, inflammatory, neurodegenerative diseases, and various infectious and parasitic diseases. Exploration of natural inhibitors and synthesis of peptidomimetic molecules has provided many promising compounds performing successfully in animal studies. Several protease inhibitors are undergoing further evaluation in human clinical trials. New research strategies are now focusing on the need for improved comprehension of protease-regulated cascades, along with precise selection of targets and improved inhibitor specificity. It remains to be seen which second generation agents will evolve into approved drugs or complementary therapies.

Modeling the Ligand−Receptor Interaction for a Series of Inhibitors of the Capsid Protein of Enterovirus 71 Using Several Three-Dimensional Quantitative Structure−Activity Relationship Techniques

The structure of enterovirus 71 (EV71) capsid protein VP1 has been constructed by using homology modeling and molecular dynamics simulation techniques. The ligand structures were a series of EV71 VP1 inhibitors synthesized by Shia et al. in 2002 and Chern et al. in 2004. The training set was selected by the VOLSURF4.1/PCA program and the IC50 values varied from 0.06 to 10.83 microm. Then, the training set was analyzed by the following three-dimensional quantitative structure-activity relationship techniques: CoMFA, CoMSIA, CATALYST4.9, and VOLSURF4.1/PCA. The model generated by a two-stage flexible docking procedure and without any structural alignment has far more significant statistics. Highly accurate activities for the test sets were then predicted by the top hypothesis of the CATALYST program and were compared with those predicted by CoMFA, CoMSIA, and VOLSURF. These studies identified some important clues for searching or making more potent inhibitors against the EV71 infection.

The effect of oral pleconaril on hepatic cytochrome P450 3A activity in healthy adults using intravenous midazolam as a probe

Pleconaril is a viral capsid inhibitor under evaluation for treatment of infections caused by rhinoviruses and enteroviruses. This study evaluated the effect of pleconaril on hepatic cytochrome P450 (CYP) 3A activity as assessed by intravenous (IV) midazolam. Healthy adults received oral pleconaril 400 mg 3 times daily for 16 doses. Single-dose, IV midazolam 0.025 mg/kg was administered before and during pleconaril administration. Midazolam and pleconaril plasma concentrations were assayed by LC/MS/MS. Bioequivalence was assessed by least squares geometric mean ratios (LS-GMR) with 90% confidence intervals (90% CIs) for the measured midazolam pharmacokinetic parameters. Sixteen subjects were enrolled, and 14 subjects completed the study. Pleconaril decreased midazolam AUC(0-infinity) 28% and increased systemic clearance 39%. LS-GMR (90% CI) were 0.718 (0.674-0.765) and 1.392 (1.307-1.483), respectively. Plasma pleconaril concentrations steadily increased over time. Observed changes in midazolam AUC(0-infinity) and systemic clearance suggest that oral pleconaril increased hepatic CYP3A activity in healthy adults.

Treatment of respiratory virus infections

Respiratory viral infections (RVIs) can be associated with a wide range of clinical manifestations ranging from self-limited upper respiratory tract infections to more devastating conditions, such as pneumonia. RVIs constitute the most frequent reason for medical consultations in the world and they have a considerable impact on quality of life and productivity. Therefore, the prevention and control of RVIs remain major clinical goals. Currently, there are approximately 200 known respiratory viruses that can be grouped into one family of DNA viruses (Adenoviridae) and four families of RNA viruses (Orthomyxoviridae, Paramyxoviridae, Picornaviridae and Coronaviridae). In this paper, we review the major respiratory viruses that cause disesases in humans, with an emphasis on current treatment options.

Rhinovirus chemotherapy

Human rhinoviruses (HRV), members of the Picornaviridae family, are comprised of over 100 different virus serotypes. HRV represent the single most important etiological agents of the common cold [Arruda, E., Pitkaranta, A., Witek Jr., T.J., Doyle, C.A., Hayden, F.G., 1997. Frequency and natural history of rhinovirus infections in adults during autumn. J. Clin. Microbiol. 35, 2864–2868; Couch, R.B., 1990. Rhinoviruses. In: Fields, B.N., Knipe, D.M. (Eds.), Virology. Raven Press, New York, pp. 607–629; Turner, R.B., 2001. The treatment of rhinovirus infections: progress and potential. Antivir. Res. 49 (1), 1–14]. Although HRV-induced upper respiratory illness is often mild and self-limiting, the socioeconomic impact caused by missed school or work is enormous and the degree of inappropriate antibiotic use is significant. It has been estimated that upper respiratory disease accounts for at least 25 million absences from work and 23 million absences of school annually in the United States [Anzueto, A., Niederman, M.S., 2003. Diagnosis and treatment of rhinovirus respiratory infections. Chest 123 (5), 1664–1672; Rotbart, H.A., 2002. Treatment of picornavirus infections. Antivir. Res. 53, 83–98]. Increasing evidences also describe the link between HRV infection and more serious medical complications. HRV-induced colds are the important predisposing factors to acute otitis media, sinusitis, and are the major factors in the induction of exacerbations of asthma in adults and children. HRV infections are also associated with lower respiratory tract syndromes in individuals with cystic fibrosis, bronchitis, and other underlying respiratory disorders [Anzueto, A., Niederman, M.S., 2003. Diagnosis and treatment of rhinovirus respiratory infections. Chest 123 (5), 1664–1672; Gern, J.E., Busse, W.W., 1999. Association of rhinovirus infections with asthma. Clin. Microbiol. Rev. 12 (1), 9–18; Pitkaranta, A., Arruda, E., Malmberg, H., Hayden, F.G., 1997. Detection of rhinovirus in sinus brushings of patients with acute community-acquired sinusitis by reverse transcription-PCR. J. Clin. Microbiol. 35, 1791–1793; Pitkaranta, A., Virolainen, A., Jero, J., Arruda, E., Hayden, F.G., 1998. Detection of rhinovirus, respiratory syncytial virus, and coronavirus infections in acute otitis media by reverse transcriptase polymerase chain reaction. Pediatrics 102, 291–295; Rotbart, H.A., 2002. Treatment of picornavirus infections. Antivir. Res. 53, 83–98]. To date, no effective antiviral therapies have been approved for either the prevention or treatment of diseases caused by HRV infection. Thus, there still exists a significant unmet medical need to find agents that can shorten the duration of HRV-induced illness, lessen the severity of symptoms, minimize secondary bacterial infections and exacerbations of underlying disease and reduce virus transmission. Although effective over-the-counter products have been described that alleviate symptoms associated with the common cold [Anzueto, A., Niederman, M.S., 2003. Diagnosis and treatment of rhinovirus respiratory infections. Chest 123 (5), 1664–1672; Gwaltney, J.M., 2002a. Viral respiratory infection therapy: historical perspectives and current trials. Am. J. Med. 22 (112 Suppl. 6A), 33S–41S; Turner, R.B., 2001. The treatment of rhinovirus infections: progress and potential. Antivir. Res. 49 (1), 1–14; Sperber, S.J., Hayden, F.G., 1988. Chemotherapy of rhinovirus colds. Antimicrob. Agents Chemother. 32, 409–419], this review will primarily focus on the discovery and development of those agents that directly or indirectly impact virus replication specifically highlighting new advances and/or specific challenges with their development.

Relationship of pleconaril susceptibility and clinical outcomes in treatment of common colds caused by rhinoviruses

Pleconaril, a specific inhibitor of human picornaviruses, showed therapeutic efficacy against community-acquired colds caused by rhinoviruses in two placebo-controlled trials. Virological assessments were conducted during these trails, including virus culture and drug susceptibility testing. Nasal mucus samples collected from the enrolled patients were tested for the presence of picornavirus by reverse transcriptase PCR and culture. In total, 827 baseline nasal mucus samples were positive by virus culture (420 in the placebo group and 407 in the pleconaril group). Pleconaril treatment was associated with a more rapid loss of culturable virus. By study day 3, the number of samples positive by culture fell to 282 for the placebo-treated subjects and 202 for the pleconaril-treated subjects (P < 0.0001); and by day 6, the number of samples in the two groups positive by culture fell to 196 and 165, respectively (P = 0.07). The clinical benefit correlated strongly with the pleconaril susceptibility of the baseline virus isolate. Pleconaril-treated subjects infected with the more highly susceptible viruses (50% effective concentration < or = 0.38 microg/ml) experienced a median 1.9- to 3.9-day reduction in symptom duration compared with that for the placebo-treated subjects. By contrast, subjects whose baseline virus isolate susceptibility was >0.38 microg/ml did not benefit from pleconaril treatment. These results indicate that the magnitude of symptomatic improvement in pleconaril-treated subjects with community-acquired colds is related to the drug susceptibility of the infecting virus, clearly linking the antiviral effects of the drug to clinical efficacy. Post-baseline virus isolates with reduced susceptibility or full resistance to pleconaril were recovered from 10.7% and 2.7% of drug-treated subjects, respectively. These patients shed low levels of virus and had no unusual clinical outcomes. Nevertheless, studies on the biologic properties and transmissibility of these variant viruses are warranted.

Structure of the virus capsid protein VP1 of enterovirus 71 predicted by some homology modeling and molecular docking studies

The homology modeling technique has been used to construct the structure of enterovirus 71 (EV 71) capsid protein VP1. The protein is consisted of 297 amino acid residues and treated as the target. The amino acid sequence identity between the target protein and sequences of template proteins 1EAH, 1PIV, and 1D4M searched from NCBI protein BLAST and WorkBench protein tools were 38, 37, and 36%, respectively. Based on these template structures, the protein model was constructed by using the InsightII/Homology program. The protein model was briefly refined by energy minimization and molecular dynamics (MD) simulation steps. The protein model was validated using some web available servers such as ERRAT, PROCHECK, PROVE, and PROSA2003. However, an inconsistency between the docking scores and the measured activity was observed for a series of EV 71 VP1 inhibitors synthesized by Shia et al. (J Med Chem 2002, 45, 1644) and docked into the binding pocket of the protein model using the DOCK 4.0.2 program. The protein model with an EV 71 VP1 inhibitor docked and engulfed was then refined further by some MD simulation steps in the presence of water molecules. The docking scores obtained for these inhibitors after such a MD refinement were well correlated with the activities. The structure-activity relationships for the ligand-protein model system was also analyzed using the GRID-VOLSURF programs and the corresponding noncrossvalidated and crossvalidated (by leave-one-out) r2 and q2 were 0.99 and 0.61, respectively. The hydrophobic nature of the binding pocket of the protein model was also examined using the GRID21 program. The possibility of improving the potency of the current series of EV 71 VP1 inhibitors was discussed based on all the studies presented.

New treatment regimes for virus-induced exacerbations of asthma

This review will focus on the role of viruses as causes of asthma exacerbations. The article will briefly review the current literature supporting this view, with a special focus on human rhinovirus (RV), the main virus associated with exacerbations of asthma. The review will then refer to possible strategies for treatment, and will include discussion on treatment with specific anti-viral therapy and type I interferon as a treatment for RV. The review will also include a discussion on current therapies for asthma, such as glucocorticosteroid and beta(2) agonist therapy alone and in combination and why this may be relevant to virus-induced exacerbations of asthma. Finally, the potential for future anti-inflammatory/immunomodulatory therapies with a focus on NF-kappaB inhibition will be discussed.

Synthesis and antipicornavirus activity of (R)- and (S)-1-[5-(4′-chlorobiphenyl-4-yloxy)-3-methylpentyl]-3-pyridin-4-yl-imidazolidin-2-one

The new pyridyl imidazolidinone derivative, 1-[5-(4'-chlorobiphenyl-4-yloxy)-3-methylpentyl]-3-pyridin-4-yl-imidazolidin-2-one (+/-)-1a, was synthesized and found to have an excellent antiviral activity against EV71 (IC50 = 0.009 microM). Therefore, both the enantiomers, (S)-(+)-1a and (R)-(-)-1a, have been prepared starting from readily available monomethyl (R)-3-methylglutarate (7) as a useful chiral building block and their antiviral activity was evaluated in a plaque reduction assay. Interestingly, we observed that the enantiomer (S)-(+)-1a was 10-fold more active against enterovirus71 (EV71) (IC50 = 0.003 microM) than the corresponding enantiomer (R)-(-)-1a (IC50 = 0.033 microM). Similar results were found against all five strains (1743, 2086, 2231, 4643, and BrCr) of EV71 tested. This demonstrated that the absolute configuration of the chiral carbon atom at the 3-position of the alkyl linker considerably influenced the anti-EV71 activity of these pyridyl imidazolidinones.

Pharmacophore Modeling, Docking, and Principal Component Analysis Based Clustering: Combined Computer-Assisted Approaches To Identify New Inhibitors of the Human Rhinovirus Coat Protein

The development and application of a sophisticated virtual screening and selection protocol to identify potential, novel inhibitors of the human rhinovirus coat protein employing various computer-assisted strategies are described. A large commercially available database of compounds was screened using a highly selective, structure-based pharmacophore model generated with the program Catalyst. A docking study and a principal component analysis were carried out within the software package Cerius and served to validate and further refine the obtained results. These combined efforts led to the selection of six candidate structures, for which in vitro anti-rhinoviral activity could be shown in a biological assay.