Treatment of picornavirus infections

Effects of climatic factors on the prevalence of influenza virus infection in Cheonan, Korea

Big data can be used to correlate diseases and climatic factors. The prevalence of influenza (flu) virus, accounting for a large proportion of respiratory infections, suggests that the effect of climate variables according to seasonal dynamics of influenza virus infections should be investigated. Here, trends in flu virus detection were analyzed using data from 9,010 tests performed between January 2012 and December 2018 at Dankook University Hospital, Cheonan, Korea. We compared the detection of the flu virus in Cheonan area and its association with climate change. The flu virus detection rate was 9.9% (894/9,010), and the detection rate was higher for flu virus A (FLUAV; 6.9%) than for flu virus B (FLUBV; 3.0%). Both FLUAV and FLUBV infections are considered an epidemic each year. We identified 43.1% (n = 385) and 35.0% (n = 313) infections in children aged < 10 years and adults aged > 60 years, respectively. The combination of these age groups encompassed 78.1% (n = 698/894) of the total data. Flu virus infections correlated with air temperature, relative humidity, vapor pressure, atmospheric pressure, particulate matter, and wind chill temperature (P < 0.001). However, the daily temperature range did not significantly correlate with the flu detection results. This is the first study to identify the relationship between long-term flu virus infection with temperature in the temperate region of Cheonan.

Enteroviral replication inhibition by N-Alkyl triazolopyrimidinone derivatives through a non-capsid binding mode

Small-molecule inhibitors exhibiting broad-spectrum enteroviral inhibition by targeting viral replication proteins are highly desirable in antiviral drug discovery. We used the previously identified antiviral compound 1 as the starting material to develop a novel compound series with high efficacy against human rhinovirus (hRV). Further optimization of N-substituted triazolopyrimidinone derivatives revealed that the N-alkyl triazolopyrimidinone derivatives (2) had more potent antiviral activity against hRVs than compound 1. The new compounds showed improved selectivity index values, and compound 2c (KR-25210) displayed broad anti-hRV activity, with half-maximal effective concentration values ≤ 2 µM against all tested hRVs. In addition, 2c showed notable activity against other enteroviruses. Drug-likeness elucidation showed that 2c exhibited reasonable human and rat liver microsomal phase-I stability and safe CYP inhibition. Replication studies revealed that 2c is not a capsid inhibitor, and a time-of-addition assay indicated that 2c targets the virus replication stages.

Syntheses, Characterizations, and Inhibition Activities Against Coxsackievirus B3 of Iodobenzoic Hydrazide Functionalized Hexamolybdates

A class of iodobenzoyldiazenido-functionalized POMs (TBA)₃ [Mo₆O₁₈(=N=NCOAr)] (Ar = Ph-o-I (1); Ph-m-I (2); Ph-p-I (3); Ph-3,4-I₂(4); Ph-2,3,5-I₃(5) (TBA = tetrabutylammonium) were prepared via the refluxing reaction of α-octamolybdates, DCC, and corresponding hydrazides in dry acetonitrile. Their structures were determined by Fourier-transform infrared spectroscopy, ultraviolet–visible spectra, X-ray photoelectron spectroscopy, hydrogen-1 nuclear magnetic resonance, and high-resolution mass spectrometry. Research on the biological activity of title compounds shows that L3, L5, 3, and 5 demonstrate potent inhibitory activity against coxsackievirus B3 and low in vitro cytotoxic activity against Hep-2 cell lines. The covalent linkage between the iodobenzoyldiazenido components and POMs can enhance the molecular inhibitory efficiency of iodobenzohydrazides.

Association between climatic factors and respiratory syncytial virus detection rates in Cheonan, Korea

The use of big data may facilitate the recognition and interpretation of causal relationships between disease occurrence and climatic variables. This study examined the effects of various climatic variables on the seasonal epidemiology of respiratory syncytial virus (RSV) infections in the temperate climate of Korea. Trends in RSV detection were analyzed using 9010 samples tested between January 1, 2012, and December 31, 2018, at Dankook University Hospital in Cheonan, Korea. Seasonal patterns in RSV detection frequency were compared with local climatic variables during the same period. RSV detection rate of 12.8% (n = 1150/9010) was observed, which was higher for RSV-A (7.1%) than RSV-B (5.8%) and RSV-A and RSV-B alternated each year. Children < 1 year exhibited high infection rates with RSV-A (68.5%) and RSV-B (58.7%). RSV-A and RSV-B infection rates in children under 9 years old were 96.2% and 92.1%, respectively. RSV had a significant relationship with several climatic factors. Air temperature, wind chill temperature, and particulate matter concentration were lower on days with a higher frequency of RSV detection. In contrast, atmospheric pressure was higher on days with lower RSV detection. Although the detection rates for RSV-A and RSV-B increased on days with lower air temperatures, those for RSV-B also increased on days with lower wind chill temperatures. Our findings suggest that climatic variables affect the RSV detection rate among children under 10 years of age. The present data may help predict the time when prevention strategies may be the most effective.

Picornaviral 2C proteins: A unique ATPase family critical in virus replication

The 2C proteins of Picornaviridae are unique members of AAA+ protein family. Although picornavirus 2C shares many conserved motifs with Super Family 3 DNA helicases, duplex unwinding activity of many 2C proteins remains undetected, and high-resolution structures of 2C hexamers are unavailable. All characterized 2C proteins exhibit ATPase activity, but the purpose of ATP hydrolysis is not fully understood. 2C is highly conserved among picornaviruses and plays crucial roles in nearly all steps of the virus lifecycle. It is therefore considered as an effective target for broad-spectrum antiviral drug development. Crystallographic investigation of enterovirus 2C proteins provide structural details important for the elucidation of 2C function and development of antiviral drugs. This chapter summarizes not only the findings of enzymatic activities, biochemical and structural characterizations of the 2C proteins, but also their role in virus replication, immune evasion and morphogenesis. The linkage between structure and function of the 2C proteins is discussed in detail. Inhibitors targeting the 2C proteins are also summarized to provide an overview of drug development. Finally, we raise several key questions to be addressed in this field and provide future research perspective on this unique class of ATPases.

Characterization of the gut DNA and RNA Viromes in a Cohort of Chinese Residents and Visiting Pakistanis

Trillions of viruses inhabit the gastrointestinal tract. Some of them have been well-studied on their roles in infection and human health, but the majority remains unsurveyed. It has been established that the composition of the gut virome is highly variable based on the changes of diet, physical state, and environmental factors. However, the effect of host genetic factors, for example ethnic origin, on the gut virome is rarely investigated. Here, we characterized and compared the gut virome in a cohort of local Chinese residents and visiting Pakistani individuals, each group containing twenty-four healthy adults and six children. Using metagenomic shotgun sequencing and assembly of fecal samples, a huge number of viral operational taxonomic units (vOTUs) were identified for profiling the DNA and RNA viromes. National background contributed a primary variation to individuals' gut virome. Compared with the Chinese adults, the Pakistan adults showed higher macrodiversity and different compositional and functional structures in their DNA virome and lower diversity and altered composition in their RNA virome. The virome variations of Pakistan children were not only inherited from that of the adults but also tended to share similar characteristics with the Chinese cohort. We also analyzed and compared the bacterial microbiome between two cohorts and further revealed numerous connections between viruses and bacterial host. Statistically, the gut DNA and RNA viromes were covariant to some extent (P < 0.001), and they both correlated the holistic bacterial composition and vice versa. This study provides an overview of the gut viral community in Chinese and visiting Pakistanis and proposes a considerable role of ethnic origin in shaping the virome.

Anti-Human Rhinovirus 1B Activity of Dexamethasone viaGCR-Dependent Autophagy Activation

Objectives

Human rhinoviruses (HRVs) are the major cause of the common cold. Currently there is no registered, clinically effective, antiviral chemotherapeutic agent to treat diseases caused by HRVs. In this study, the antiviral activity of dexamethasone (DEX) against HRV1B was examined.

Methods

The anti–HRV1B activity of DEX was assessed by sulforhodamine B assay in HeLa cells, and by RT-PCR in the lungs of HRV1B-infected mice. Histological evaluation of HRV1B-infected lungs was performed and a histological score was given. Anti-HRV1B activity of DEX via the glucocorticoid receptor (GCR)-dependent autophagy activation was assessed by blocking with chloroquine diphosphate salt or bafilomycin A1 treatment.

Results

In HRV1B-infected HeLa cells, treatment with DEX in a dose-dependent manner, resulted in a cell viability of > 70% indicating that HRV1B viral replication was reduced by DEX treatment. HRV1B infected mice treated with DEX, had evidence of reduced inflammation and a moderate histological score. DEX treatment showed antiviral activity against HRV1B via GCR-dependent autophagy activation.

Conclusion

This study demonstrated that DEX treatment showed anti-HRV1B activity via GCR-dependent autophagy activation in HeLa cells and HRV1B infected mice. Further investigation assessing the development of topical formulations may enable the development of improved DEX effectiveness.

The Origin, Dynamic Morphology, and PI4P-Independent Formation of Encephalomyocarditis Virus Replication Organelles

Picornaviruses induce dramatic rearrangements of endomembranes in the cells that they infect to produce dedicated platforms for viral replication. These structures, termed replication organelles (ROs), have been well characterized for the Enterovirus genus of the Picornaviridae However, it is unknown whether the diverse RO morphologies associated with enterovirus infection are conserved among other picornaviruses. Here, we use serial electron tomography at different stages of infection to assess the three-dimensional architecture of ROs induced by encephalomyocarditis virus (EMCV), a member of the Cardiovirus genus of the family of picornaviruses that is distantly related. Ultrastructural analyses revealed connections between early single-membrane EMCV ROs and the endoplasmic reticulum (ER), establishing the ER as a likely donor organelle for their formation. These early single-membrane ROs appear to transform into double-membrane vesicles (DMVs) as infection progresses. Both single- and double-membrane structures were found to support viral RNA synthesis, and progeny viruses accumulated in close proximity, suggesting a spatial association between RNA synthesis and virus assembly. Further, we explored the role of phosphatidylinositol 4-phosphate (PI4P), a critical host factor for both enterovirus and cardiovirus replication that has been recently found to expedite enterovirus RO formation rather than being strictly required. By exploiting an EMCV escape mutant, we found that low-PI4P conditions could also be overcome for the formation of cardiovirus ROs. Collectively, our data show that despite differences in the membrane source, there are striking similarities in the biogenesis, morphology, and transformation of cardiovirus and enterovirus ROs, which may well extend to other picornaviruses.IMPORTANCE Like all positive-sense RNA viruses, picornaviruses induce the rearrangement of host cell membranes to form unique structures, or replication organelles (ROs), that support viral RNA synthesis. Here, we investigate the architecture and biogenesis of cardiovirus ROs and compare them with those induced by enteroviruses, members of the well-characterized picornavirus genus Enterovirus The origins and dynamic morphologies of cardiovirus ROs are revealed using electron tomography, which points to the endoplasmic reticulum as the donor organelle usurped to produce single-membrane tubules and vesicles that transform into double-membrane vesicles. We show that PI4P, a critical lipid for cardiovirus and enterovirus replication, is not strictly required for the formation of cardiovirus ROs, as functional ROs with typical morphologies are formed under phosphatidylinositol 4-kinase type III alpha (PI4KA) inhibition in cells infected with an escape mutant. Our data show that the transformation from single-membrane structures to double-membrane vesicles is a conserved feature of cardiovirus and enterovirus infections that likely extends to other picornavirus genera.

Enterovirus inhibitory activity of C-8-tert-butyl substituted 4-aryl-6,7,8,9-tetrahydrobenzo[4,5]thieno[3,2-e][1,2,4]triazolo[4,3-a]pyrimidin-5(4H)-ones

Members of a series of 4-aryl-6,7,8,9-tetrahydrobenzo[4,5]thieno[3,2-e][1,2,4]triazolo[4,3-a]pyrimidin-5(4H)-ones (1, Fig. 2) were prepared and tested against representative enteroviruses including Human Coxsackievirus B1 (Cox B1), Human Coxsackievirus B3 (Cox B3), human Poliovirus 3 (PV3), human Rhinovirus 14 (HRV14), human Rhinovirus 21 (HRV 21) and human Rhinovirus 71 (HRV 71). The C-8-tert-butyl group on the tetrahydrobenzene ring in these substances was found to be crucial for their enterovirus activity. One member of this group, 1e, showed single digit micromolar activities (1.6-8.85μM) against a spectrum of viruses screened, and the highest selectivity index (SI) values for Cox B1 (>11.2), for Cox B3 (>11.5), and for PV3 (>51.2), respectively. In contrast, 1p, was the most active analog against the selected HRVs (1.8-2.6μM), and showed the highest selectivity indices among the group of compounds tested. The SI values for 1p were 11.5 for HRV14, 8.4 for HRV21, and 12.1 for HRV71, respectively.

Virion Structure of Black Queen Cell Virus, a Common Honeybee Pathogen

Viral diseases are a major threat to honeybee (Apis mellifera) populations worldwide and therefore an important factor in reliable crop pollination and food security. Black queen cell virus (BQCV) is the etiological agent of a fatal disease of honeybee queen larvae and pupae. The virus belongs to the genus Triatovirus from the family Dicistroviridae, which is part of the order Picornavirales. Here we present a crystal structure of BQCV determined to a resolution of 3.4 Å. The virion is formed by 60 copies of each of the major capsid proteins VP1, VP2, and VP3; however, there is no density corresponding to a 75-residue-long minor capsid protein VP4 encoded by the BQCV genome. We show that the VP4 subunits are present in the crystallized virions that are infectious. This aspect of the BQCV virion is similar to that of the previously characterized triatoma virus and supports the recent establishment of the separate genus Triatovirus within the family Dicistroviridae. The C terminus of VP1 and CD loops of capsid proteins VP1 and VP3 of BQCV form 34-Å-tall finger-like protrusions at the virion surface. The protrusions are larger than those of related dicistroviruses.

IMPORTANCE The western honeybee is the most important pollinator of all, and it is required to sustain the agricultural production and biodiversity of wild flowering plants. However, honeybee populations worldwide are suffering from virus infections that cause colony losses. One of the most common, and least known, honeybee pathogens is black queen cell virus (BQCV), which at high titers causes queen larvae and pupae to turn black and die. Here we present the three-dimensional virion structure of BQCV, determined by X-ray crystallography. The structure of BQCV reveals large protrusions on the virion surface. Capsid protein VP1 of BQCV does not contain a hydrophobic pocket. Therefore, the BQCV virion structure provides evidence that capsid-binding antiviral compounds that can prevent the replication of vertebrate picornaviruses may be ineffective against honeybee virus infections.

Virion Structure of Israeli Acute Bee Paralysis Virus

The pollination services provided by the western honeybee (Apis mellifera) are critical for agricultural production and the diversity of wild flowering plants. However, honeybees suffer from environmental pollution, habitat loss, and pathogens, including viruses that can cause fatal diseases. Israeli acute bee paralysis virus (IAPV), from the family Dicistroviridae, has been shown to cause colony collapse disorder in the United States. Here, we present the IAPV virion structure determined to a resolution of 4.0 Å and the structure of a pentamer of capsid protein protomers at a resolution of 2.7 Å. IAPV has major capsid proteins VP1 and VP3 with noncanonical jellyroll β-barrel folds composed of only seven instead of eight β-strands, as is the rule for proteins of other viruses with the same fold. The maturation of dicistroviruses is connected to the cleavage of precursor capsid protein VP0 into subunits VP3 and VP4. We show that a putative catalytic site formed by the residues Asp-Asp-Phe of VP1 is optimally positioned to perform the cleavage. Furthermore, unlike many picornaviruses, IAPV does not contain a hydrophobic pocket in capsid protein VP1 that could be targeted by capsid-binding antiviral compounds.

IMPORTANCE Honeybee pollination is required for agricultural production and to sustain the biodiversity of wild flora. However, honeybee populations in Europe and North America are under pressure from pathogens, including viruses that cause colony losses. Viruses from the family Dicistroviridae can cause honeybee infections that are lethal, not only to individual honeybees, but to whole colonies. Here, we present the virion structure of an Aparavirus, Israeli acute bee paralysis virus (IAPV), a member of a complex of closely related viruses that are distributed worldwide. IAPV exhibits unique structural features not observed in other picorna-like viruses. Capsid protein VP1 of IAPV does not contain a hydrophobic pocket, implying that capsid-binding antiviral compounds that can prevent the replication of vertebrate picornaviruses may be ineffective against honeybee virus infections.

ATP Is an Allosteric Inhibitor of Coxsackievirus B3 Polymerase

The RNA-dependent RNA polymerases from positive-strand RNA viruses, such as picornaviruses and flaviviruses, close their active sites for catalysis via a unique NTP-induced conformational change in the palm domain. Combined with a fully prepositioned templating nucleotide, this mechanism is error-prone and results in a distribution of random mutations in the viral progeny often described as a quasi-species. Here we examine the extent to which noncognate NTPs competitively inhibit single-cycle elongation by coxsackievirus B3 3D(pol), a polymerase that generates three to four mutations per 10 kb of RNA synthesized during viral infection. Using an RNA with a templating guanosine combined with 2-aminopurine fluorescence as a reporter for elongation, we find that the cognate CTP has a Km of 24 μM and the three noncognate nucleotides competitively inhibit the reaction with Kic values of 500 μM for GTP, 1300 μM for ATP, and 3000 μM for UTP. Unexpectedly, ATP also acted as an uncompetitive inhibitor with a Kiu of 1800 μM, resulting in allosteric modulation of 3D(pol) that slowed the polymerase elongation rate ≈4-fold. ATP uncompetitive inhibition required the β- and γ-phosphates, and its extent was significantly diminished in two previously characterized low-fidelity polymerases. This led to further mutational analysis and the identification of a putative allosteric binding site below the NTP entry channel at the interface of conserved motifs A and D, although cocrystallization failed to reveal any density for bound ATP in this pocket. The potential role of an ATP allosteric effect during the virus life cycle is discussed.

SAR evolution and discovery of benzenesulfonyl matrinanes as a novel class of potential coxsakievirus inhibitors

Materials & methods: Fifty-one novel 12N-substituted matrinic acid derivatives were synthesized and evaluated for their anti-coxsackievirus B3 activities. Results: Structure–activity relationship studies revealed that the 11-side chain could be determinant for the selectivity index by adjusting overall lipophilicity, and 11-butane was the best one for both potency and druggability. The optimized 35d showed the broad-spectrum anti-coxsackieviruse effects, an excellent pharmacokinetics and a good safety profile. More importantly, it displayed a potential effect for the pleconaril-resistant coxsackievirus B3 as well. Its mode of action is targeting on the viral transcription and translation stage, a different mechanism from that of pleconaril. Conclusion: Thus, we considered that 35d is a promising anti-enteroviral candidate for the treatment of various diseases infected with coxsackieviruses.

Virus-inhibiting activity of dihydroquercetin, a flavonoid from Larix sibirica, against coxsackievirus B4 in a model of viral pancreatitis

Members of the family Picornaviridae, in particular, enteroviruses, represent a serious threat to human health. They are responsible for numerous pathologies ranging from mild disease to fatal outcome. Due to the limited number of safe and effective antivirals against enteroviruses, there is a need for search and development of novel drugs with various mechanisms of activity against enteroviruses-induced pathologies. We studied the effect of dihydroquercetin (DHQ), a flavonoid from larch wood, on the course of pancreatitis of white mice caused by coxsackievirus B4 (CVB4). DHQ was applied intraperitoneally at doses of 75 or 150 mg/kg/day once a day for 5 days postinfection (p.i.) starting on day 1 p.i., and its effect was compared to that of the reference compound ribavirin. The application of DHQ resulted in a dose-dependent decrease in the virus titer in pancreatic tissue, reaching, at the highest dose, 2.4 logs on day 5 p.i. Also, the application of DHQ led to restoration of antioxidant activity of pancreatic tissue that was impaired in the course of pancreatitis. Morphologically, pancreatic tissue of DHQ-treated animals demonstrated less infiltration with inflammatory cells and no signs of tissue destruction compared to placebo-treated mice. Both ribavirin- and DHQ-treated animals developed fewer foci of pancreatic inflammation per mouse, and these foci contained fewer infiltrating cells than those in placebo-treated mice. The effect of DHQ was comparable to or exceeded that of ribavirin. Taken together, our results suggest high antiviral activity of DHQ and its promising potential in complex treatment of viral pancreatitis.

Antiviral effect of emodin from Rheum palmatum against coxsakievirus B5 and human respiratory syncytial virus in vitro

Viral infections are the major causes of morbidity and mortality in elderly people and young children throughout the world. The most common pathogens include coxsackie virus (CV) and respiratory syncytial virus (RSV). However, no antiviral agents with low toxicity and drug resistance are currently available in clinic therapy. The present study aimed to examine the antiviral activities of emodin (an ingredient of Rheum palmatum) against CVB5 and RSV infections, in an attempt to discover new antiviral agents for virus infection. The monomer emodin was extracted and isolated from Rheum palmatum. The antiviral activities of emodin on HEp-2 cells were evaluated, including virus replication inhibition, virucidal and anti-absorption effects, by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tet-razolium bromide (MTT) assay and plaque reduction assay (PRA). The kinetics of virus inhibition by emodin in a period of 14 h was further determined by plaque assay and quantitative real time PCR (qPCR). Cytokine (IFN-γ, TNF-α) mRNA expressions after emodin treatment (7.5, 15, 30 μmol/L) were also assessed by qPCR post-infection. The results showed that emodin had potent inhibitory activities against CVB5 and RSV, with the 50% effective concentration (EC₅₀) ranging from 13.06 to 14.27 μmol/L and selectivity index (SI) being 5.38–6.41 μmol/L. However, emodin couldn’t directly inactivate the viruses or block their absorption to cells. It acted as a biological synthesis inhibitor against CVB₄ and RSV in a concentration- and time-dependent manner, especially during the first 0–4 h post-infection. Moreover, emodin could decrease the mRNA expression of IFN-α but enhance TNF-γ expression significantly compared to the viral controls in vitro. Our results provide a molecular basis for development of emodin as a novel and safe antiviral agent for human enterovirus and respiratory virus infection in the clinical therapy.

Complete sequence analysis and antiviral screening of medicinal plants for human coxsackievirus a16 isolated in Korea

Objectives

Coxsackievirus A group 16 strain (CVA16) is one of the predominant causative agents of hand, foot, and mouth disease (HFMD).

Methods

Using a specimen from a male patient with HFMD, we isolated and performed sequencing of the Korean CVA16 strain and compared it with a G10 reference strain. Also, we were investigated the effects of medicinal plant extract on the cytopathic effects (CPE) by CPE reduction assay against Korean CVA16.

Results

Phylogenetic analysis showed that the Korean CVA16 isolate belonged to cluster B-1 and was closely related to the strain PM-15765-00 isolated in Malaysia in 2000. The Korean CVA16 isolate showed 73.2% nucleotide identity to the G10 prototype strain and 98.7% nucleotide identity to PM-15765-00. Next, we assessed whether the Korean CVA16 isolate could be used for in vitro screening of antiviral agents to treat HFMD infection. Vero cells infected with the Korean CVA16 isolate showed a cytopathic effect 2 days after the infection, and the treatment of cells with Cornus officinalis, Acer triflorum, Pulsatilla koreana, and Clematis heracleifolia var. davidiana Hemsl extracts exhibited strong antiviral activity against CVA16.

Conclusion

Collectively, our work provides potential candidates for the development of vaccine and novel drugs to treat the CVA16 strain isolated from a Korean patient.

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.

Conformationally locked bicyclo[4.3.0]nonane carbanucleosides: synthesis and bio-evaluation

D-Ribose was converted into 3 novel carbobicyclic nucleosides bearing a bicyclo[4.3.0]nonane framework in 16-19 steps with 5-12% overall yields involving a Wittig olefination and an intramolecular Diels-Alder reaction as the key steps. The present synthesis also provides an efficient entry for chiral hydrindenones. The conformation studies of these carbanucleosides and their bio-evaluation as potential antiviral agents are reported.

Genetic and antigenic structural characterization for resistance of echovirus 11 to pleconaril in an immunocompromised patient

Pleconaril is a capsid inhibitor used previously to treat enterovirus infections. A pleconaril-resistant echovirus 11 (E11) strain was identified before pleconaril treatment was given in an immunocompromised patient. The patient was also treated with intravenous Ig (IVIg) for a long period but remained unresponsive. The pleconaril-resistant strains could not be neutralized in vitro, confirming IVIg treatment failure. To identify the basis of pleconaril resistance, genetic and structural analyses were conducted. Analysis of a modelled viral capsid indicated conformational changes in the hydrophobic pocket that could prevent pleconaril docking. Substitutions (V117I, V119M and I188L) in the pleconaril-resistant viruses were found in the pocket region of VP1. Modelling suggested that V119M could confer resistance, most probably due to the protruding sulfate side chain of methionine. Although pleconaril resistance induced in vitro in a susceptible E11 clinical isolate was characterized by a different substitution (I183M), resistance was suggested to also result from a similar mechanism, i.e. due to a protruding sulfate side chain of methionine. Our results showed that resistant strains that arise in vivo display different markers from those identified in vitro and suggest that multiple factors may play a role in pleconaril resistance in patient strains. Based on IVIg treatment failure, we predict that one of these factors could be immune related. Thus, both IVIg and capsid inhibitors target the viral capsid and can induce mutations that can be cross-reactive, enabling escape from both IVIg and the drug. This could limit treatment options and should be investigated further.

Semisynthesis of the antiviral abietane diterpenoid jiadifenoic acid C from callitrisic acid (4-epidehydroabietic acid) isolated from sandarac resin

The semisynthesis of the antiviral abietane diterpenoid (+)-jiadifenoic acid C starting from the available methyl ester of callitrisic acid (4-epidehydroabietic acid) isolated from sandarac resin is reported. A protocol for the isolation of methyl callitrisate (methyl 4-epidehydroabietate) in gram quantities from sandarac resin is also described. Allylic C-17 oxygenation was introduced by regioselective dehydrogenation of the isopropyl group of methyl callitrisate with DDQ followed by selenium-catalyzed allylic oxidation. Ester hydrolysis afforded (+)-jiadifenoic acid C in 22% overall yield from methyl callitrisate. This semisynthetic route provides a convenient source of this anti-Coxsackie virus B natural product for further biological studies.

Human induced pluripotent stem cell-derived cardiomyocytes as an in vitro model for coxsackievirus B3-induced myocarditis and antiviral drug screening platform

RATIONALE

Viral myocarditis is a life-threatening illness that may lead to heart failure or cardiac arrhythmias. A major causative agent for viral myocarditis is the B3 strain of coxsackievirus, a positive-sense RNA enterovirus. However, human cardiac tissues are difficult to procure in sufficient enough quantities for studying the mechanisms of cardiac-specific viral infection.

OBJECTIVE

This study examined whether human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) could be used to model the pathogenic processes of coxsackievirus-induced viral myocarditis and to screen antiviral therapeutics for efficacy.

METHODS AND RESULTS

hiPSC-CMs were infected with a luciferase-expressing coxsackievirus B3 strain (CVB3-Luc). Brightfield microscopy, immunofluorescence, and calcium imaging were used to characterize virally infected hiPSC-CMs for alterations in cellular morphology and calcium handling. Viral proliferation in hiPSC-CMs was quantified using bioluminescence imaging. Antiviral compounds including interferonβ1, ribavirin, pyrrolidine dithiocarbamate, and fluoxetine were tested for their capacity to abrogate CVB3-Luc proliferation in hiPSC-CMs in vitro. The ability of these compounds to reduce CVB3-Luc proliferation in hiPSC-CMs was consistent with reported drug effects in previous studies. Mechanistic analyses via gene expression profiling of hiPSC-CMs infected with CVB3-Luc revealed an activation of viral RNA and protein clearance pathways after interferonβ1 treatment.

CONCLUSIONS

This study demonstrates that hiPSC-CMs express the coxsackievirus and adenovirus receptor, are susceptible to coxsackievirus infection, and can be used to predict antiviral drug efficacy. Our results suggest that the hiPSC-CM/CVB3-Luc assay is a sensitive platform that can screen novel antiviral therapeutics for their effectiveness in a high-throughput fashion.

Antiviral activity and possible mode of action of ellagic acid identified in Lagerstroemia speciosa leaves toward human rhinoviruses

BACKGROUND

Human rhinoviruses (HRVs) are responsible for more than half of all cases of the common cold and cause billions of USD annually in medical visits and school and work absenteeism. An assessment was made of the cytotoxic and antiviral activities and possible mode of action of the tannin ellagic acid from the leaves of Lagerstroemia speciosa toward HeLa cells and three rhinoviruses, HRV-2, -3, and -4.

METHODS

The antiviral property and mechanism of action of ellagic acid were evaluated using a sulforhodamine B assay and real-time reverse transcription-PCR (RT-PCR) with SYBR Green dye. Results were compared with those of the currently used broad-spectrum antiviral agent, ribavirin.

RESULTS

As judged by 50% inhibitory concentration values, natural ellagic acid was 1.8, 2.3, and 2.2 times more toxic toward HRV-2 (38 μg/mL), HRV-3 (31 μg/mL), and HRV-4 (29 μg/mL) than ribavirin, respectively. The inhibition rate of preincubation with 50 μg/mL ellagic acid was 17%, whereas continuous presence of ellagic acid during infection led to a significant increase in the inhibition (70%). Treatment with 50 μg/mL ellagic acid considerably suppressed HRV-4 infection only when added just after the virus inoculation (0 h) (87% inhibition), but not before -1 h or after 1 h or later (<20% inhibition). These findings suggest that ellagic acid does not interact with the HRV-4 particles and may directly interact with the human cells in the early stage of HRV infections to protect the cells from the virus destruction. Furthermore, RT-PCR analysis revealed that 50 μg/mL ellagic acid strongly inhibited the RNA replication of HRV-4 in HeLa cells, suggesting that ellagic acid inhibits virus replication by targeting on cellular molecules, rather than virus molecules.

CONCLUSIONS

Global efforts to reduce the level of antibiotics justify further studies on L. speciosa leaf-derived materials containing ellagic acid as potential anti-HRV products or a lead molecule for the prevention or treatment of HRV infection.

More-powerful virus inhibitors from structure-based analysis of HEV71 capsid-binding molecules

Enterovirus 71 (HEV71) epidemics in children and infants result mainly in mild symptoms; however, especially in the Asia-Pacific region, infection can be fatal. At present, no therapies are available. We have used structural analysis of the complete virus to guide the design of HEV71 inhibitors. Analysis of complexes with four 3-(4-pyridyl)-2-imidazolidinone derivatives with varying anti-HEV71 activities pinpointed key structure-activity correlates. We then identified additional potentially beneficial substitutions, developed methods to reliably triage compounds by quantum mechanics-enhanced ligand docking and synthesized two candidates. Structural analysis and in vitro assays confirmed the predicted binding modes and their ability to block viral infection. One ligand (with IC50 of 25 pM) is an order of magnitude more potent than the best previously reported inhibitor and is also more soluble. Our approach may be useful in the design of effective drugs for enterovirus infections.

Current progress in antiviral strategies

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Antiviral agents function as either viral targets or host factors.

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Virus-targeting antivirals (VTAs) function through a direct (DVTAs) or an indirect (InDVTAs) method in the viral life cycle.

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Host-targeting antivirals (HTAs) include reagents that target the host proteins that are involved in the viral life cycle.

The prevalence of chronic viral infectious diseases, such as human immunodeficiency virus (HIV), hepatitis C virus (HCV), and influenza virus; the emergence and re-emergence of new viral infections, such as picornaviruses and coronaviruses; and, particularly, resistance to currently used antiviral drugs have led to increased demand for new antiviral strategies and reagents. Increased understanding of the molecular mechanisms of viral infection has provided great potential for the discovery of new antiviral agents that target viral proteins or host factors. Virus-targeting antivirals can function directly or indirectly to inhibit the biological functions of viral proteins, mostly enzymatic activities, or to block viral replication machinery. Host-targeting antivirals target the host proteins that are involved in the viral life cycle, regulating the function of the immune system or other cellular processes in host cells. Here we review key targets and considerations for the development of both antiviral strategies.

In vitro and in vivo studies of the inhibitory effects of emodin isolated from Polygonum cuspidatum on Coxsakievirus B₄

The lack of effective therapeutics for Coxsackievirus B₄ (CVB₄) infection underscores the importance of finding novel antiviral compounds. Emodin (1,3,8-trihydroxy-6-methylanthraquinone) is one of the natural anthraquinone derivatives obtained from the root and rhizome of Polygonum cuspidatum. In the present study, the possibility of using emodin as a potential antiviral to treat CVB₄ infection was explored in vitro and in mice. Emodin reduced CVB₄ entry and replication on Hep-2 cells in a concentration- and time-dependent manner, with a 50% effective concentration (EC₅₀) of 12.06 μM and selectivity index (SI) of 5.08, respectively. The inhibitory effect of emodin for CVB₄ entry and replication was further confirmed by a quantitative real time PCR (qPCR) assay. The results further showed that the mice orally treated with different dosages of emodin displayed a dose dependent increase of survival rate, body weight and prolonged mean time of death (MTD), accompanied by significantly decreased myocardial virus titers and pathologic scores/lesions. Moreover, emodin could inhibit CVB₄-induced apoptosis in vitro and in vivo. Our results indicated that emodin could be used as potential antiviral in the post-exposure prophylaxis for CVB₄ infection.

Anti-human rhinovirus 2 activity and mode of action of quercetin-7-glucoside from Lagerstroemia speciosa

Human rhinoviruses (HRVs) are a major cause of the common cold, but there is currently, no registered clinically effective antiviral chemotherapeutic agent for treatment of diseases caused by HRVs. In this study, we examined the antiviral activity of quercetin 7-glucoside (Q7G) from Lagerstroemia speciosa against human rhinovirus 2 (HRV2) using a cytopathic effect (CPE) reduction method. Furthermore, to elucidate the action of Q7G on HRV2 multiplication in more detail, we investigated the effect of Q7G on the infection cycle of HRV2 through time-of-addition study, reverse transcription-polymerase chain reaction analysis, and effects of Q7G on the infectivity of HRV2 particles. Q7G potently showed anti-HRV2 activity by reducing the formation of a visible CPE. Q7G also inhibited virus replication in the initial stage of virus infection by indirect interaction with virus particles, and ribavirin had a relative weaker efficacy compared to Q7G. Therefore, these data suggest that Q7G exerted its anti-HRV2 effect via the inhibition of virus replication in the early stage and these findings provide important information for the utilization of Q7G for HRV2 treatment.

Differential TLR7-mediated expression of proinflammatory and antiviral cytokines in response to laboratory and clinical enterovirus strains

Enteroviruses (EVs) are single stranded RNA viruses associated with many serious diseases. The exact mechanism by which an EV is able to evade innate immunity and cause tissue damage still remain unknown. Toll-like receptor 7 (TLR7) mediates the activation of type I interferon genes and the development of inflammatory cytokine response. The main aim of the study was to explore the antiviral activity and the pattern of cytokine expression in human embryonic kidney cells (HEK-293 cells) expressing TLR7 protein following challenging with laboratory and clinical EV strains. The TLR7 open reading frame was cloned into the pcDNA3.1/nV5-DEST™ expression vector, followed by transfection into HEK-293 cells. TLR7- and mock-transfected cells were infected with laboratory and clinical strains of CVB1 and CVB5. The levels of cytokines (IL-6, IL-8, TNF-α, IFN-α and IFN-β) were measured by ELISA. The EV RNA concentrations were measured by real-time RT-PCR, and normalized against GAPDH RNA concentrations. The clinical EV strains were more effective activators of cytokines production in TLR7-transfected cells than the laboratory EV strains. The inhibition of EV replication in TLR7-transfected cells was correlated to the production of type I IFNs. The cytopathic effects observed in TLR7-transfected cells were correlated to the levels of IL-6 and TNF-α. The results suggest a clear segregation between laboratory and clinical EV strains on the basis of their cytokine induction ability, and a possible role of TLR7-induced proinflammatory cytokines in the pathogenesis of EV infection.

Antiviral drug discovery for the treatment of enterovirus 71 infections

Enterovirus 71 (EV71) is a small, positive-sense, single-stranded RNA virus in the genus Enterovirus, family Picornavirus. It causes hand, foot and mouth disease in infants and children, which in a small percentage of cases progresses to central nervous system infection, ranging from aseptic meningitis to fatal encephalitis. Sporadic cases of EV71 infection occur throughout the world, but large epidemics have occurred recently in Southeast Asia and China. There are currently no approved vaccines or antiviral therapies for the prevention or treatment of EV71 infection. This paper reviews efforts to develop antiviral therapies against EV71.

Enterovirus infection in Korean children and anti-enteroviral potential candidate agents

Although most enterovirus infections are not serious enough to be life threatening, several enteroviruses such as enterovirus 71 are responsible for severe, potentially life-threatening disease. The epidemic patterns of enteroviruses occur regularly during the year, but they may change due to environmental shifts induced by climate change due to global warming. Therefore, enterovirus epidemiological studies should be performed continuously as a basis for anti-viral studies. A great number of synthesized antiviral compounds that work against enteroviruses have been developed but only a few have demonstrated effectiveness in vivo. No proven effective antiviral agents are available for enterovirus disease therapy. The development of a new antiviral drug is a difficult task due to poor selective toxicity and cost. To overcome these limitations, one approach is to accelerate the availability of other existing antiviral drugs approved for antiviral effect against enteroviruses, and the other way is to screen traditional medicinal plants.

Identification of site-specific adaptations conferring increased neural cell tropism during human enterovirus 71 infection

Enterovirus 71 (EV71) is one of the most virulent enteroviruses, but the specific molecular features that enhance its ability to disseminate in humans remain unknown. We analyzed the genomic features of EV71 in an immunocompromised host with disseminated disease according to the different sites of infection. Comparison of five full-length genomes sequenced directly from respiratory, gastrointestinal, nervous system, and blood specimens revealed three nucleotide changes that occurred within a five-day period: a non-conservative amino acid change in VP1 located within the BC loop (L97R), a region considered as an immunogenic site and possibly important in poliovirus host adaptation; a conservative amino acid substitution in protein 2B (A38V); and a silent mutation in protein 3D (L175). Infectious clones were constructed using both BrCr (lineage A) and the clinical strain (lineage C) backgrounds containing either one or both non-synonymous mutations. In vitro cell tropism and competition assays revealed that the VP1₉₇ Leu to Arg substitution within the BC loop conferred a replicative advantage in SH-SY5Y cells of neuroblastoma origin. Interestingly, this mutation was frequently associated in vitro with a second non-conservative mutation (E167G or E167A) in the VP1 EF loop in neuroblastoma cells. Comparative models of these EV71 VP1 variants were built to determine how the substitutions might affect VP1 structure and/or interactions with host cells and suggest that, while no significant structural changes were observed, the substitutions may alter interactions with host cell receptors. Taken together, our results show that the VP1 BC loop region of EV71 plays a critical role in cell tropism independent of EV71 lineage and, thus, may have contributed to dissemination and neurotropism in the immunocompromised patient.

Valosin-containing protein (VCP/p97) is required for poliovirus replication and is involved in cellular protein secretion pathway in poliovirus infection

Poliovirus (PV) modifies membrane-trafficking machinery in host cells for its viral RNA replication. To date, ARF1, ACBD3, BIG1/BIG2, GBF1, RTN3, and PI4KB have been identified as host factors of enterovirus (EV), including PV, involved in membrane traffic. In this study, we performed small interfering RNA (siRNA) screening targeting membrane-trafficking genes for host factors required for PV replication. We identified valosin-containing protein (VCP/p97) as a host factor of PV replication required after viral protein synthesis, and its ATPase activity was essential for PV replication. VCP colocalized with viral proteins 2BC/2C and 3AB/3B in PV-infected cells and showed an interaction with 2BC and 3AB but not with 2C and 3A. Knockdown of VCP did not suppress the replication of coxsackievirus B3 or Aichi virus. A VCP-knockdown-resistant PV mutant had an A4881G (a mutation of E253G in 2C) mutation, which is known as a determinant of a secretion inhibition-negative phenotype. However, knockdown of VCP did not affect the inhibition of cellular protein secretion caused by overexpression of each individual viral protein. These results suggested that VCP is a host factor required for viral RNA replication of PV among membrane-trafficking proteins and provides a novel link between cellular protein secretion and viral RNA replication.

Comparative proteome analyses of host protein expression in response to Enterovirus 71 and Coxsackievirus A16 infections

Enterovirus 71 (EV71) and Coxsackievirus A16 (CA16) are the main etiological agents of Hand, Foot and Mouth Disease (HFMD), a common disease among children and had caused several outbreaks in the Asia-Pacific region. Although being genetically close to each other, EV71 infection can cause serious and fatal neurological complications like encephalitis, myocarditis, acute flaccid paralysis (AFP) and aseptic meningitis, but not in CA16 infections. In this study, the cellular response of host cells infected with EV71 and CA16 was characterized and compared by 2-dimensional proteome analyses. A total of 16 proteins were identified to be differentially expressed in EV71 and CA16-infected host cells. Desmin and HSP27, both indirectly regulate the contraction of muscle cells, were significantly downregulated as a result of EV71 infection, suggesting a link to acute flaccid paralysis. The ability of EV71 to evade host immune system may be due to the downregulation of MHC-I synthesis proteins like protein disulfide isomerase A3 and calreticulin. Proteins such as nucleophosmin, nuclear ribonucleoprotein C, and eukaryotic translation initiation factor 2 were all downregulated significantly, suggesting the rapid shutting down of host translation machinery by EV71. These findings provide insight into the nature of high virulent EV71 infection as compared to CA16.

Detection of enteroviruses from clinical specimens

Enteroviruses are positive stranded RNA viruses belonging to the genus Enterovirus of the Picornaviridae family. Human enteroviruses are transmitted through the fecal-oral route and have been shown to cause mild to life-threatening diseases. Various diagnostic methods have been developed to detect enteroviruses from clinical specimens but many were impeded by requirements for special reagents, lengthy procedures, low sensitivity or cross-reactivity. This chapter describes rapid and highly sensitive methods of enteroviral detection directly from clinical specimens based on a conventional one-step Reverse Transcription polymerase chain reaction (RT-PCR) and a one-step real-time RT-PCR.

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.

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.

Design, synthesis, and biological evaluation of novel coxsackievirus B3 inhibitors

The synthesis and SAR study of a novel class of coxsackievirus B3 (CVB3) inhibitors are reported. These compounds could be considered as the 6-chloropurines substituted at position 9 with variously substituted bicyclic scaffolds (bicyclo[2.2.1]heptane/ene-norbornane or norbornene). The synthesis and biological evaluation of 31 target compounds are described. Several of the analogues inhibited CVB3 in the low micromolar range (0.66-2muM). Minimal or no cytotoxicity was observed.

Difference in susceptibility to MxA protein between a coxsackievirus B1 isolate and prototype, impact of serial cell culture passage

Human enteroviruses (EVs) cause a broad spectrum of acute and chronic diseases including meningitis and myocarditis. The type I interferon-induced MxA protein has been shown to inhibit the replication of an EV, coxsackievirus B4 (CVB4), but not cardioviruses such as encephalomyocarditis virus and mengo virus, members of the Picornaviridae family. EVs consist of more than 60 distinct serotypes against which the antiviral activity of MxA was not investigated yet. The main aim of this study was to explore the antiviral activity of MxA protein against a clinical CVB1 isolate and other EV prototypes. Vero cells expressing constituvely MxA protein were infected with EVs, and the percentage of inhibiton of expression of enteroviral RNA and capsid VP1 protein was determined. Following infection of MxA-transfected Vero cells with EVs, the expression of enteroviral RNA was inhibited by up to 99%, and that of VP1 protein by up to 85%. However, there was a difference in the percentage of MxA inhibition of EV replication between the different EV prototypes. This difference in MxA sensitivity was not due to a difference in the viral replication rates. The MxA protein was inactive against the clinical CVB1 isolate, and the replication rate of CVB1 isolate in MxA-transfected Vero cells was higher than that in mock-transfected Vero cells. A serial passage of the clinical CVB1 isolate and other EV prototypes resulted in an increase in their susceptibility to MxA protein. These results suggest the presence of MxA-resistant EV variants that may escape innate immunity and cause disease. J. Med. Virol. 82:424-432, 2010. (c) 2010 Wiley-Liss, Inc.

Enterovirus 71: epidemiology, pathogenesis and management

Enterovirus 71 (EV71) has emerged as a major cause of neurological threat in the world following the eradication of poliovirus. Most EV71 infections commonly result in hand-foot-mouth disease or herpangina, and some cases are associated with brainstem encephalitis and acute flaccid paralysis. Mortality was high in EV71 brainstem encephalitis complicated with pulmonary edema, particularly in children below 5 years of age. Destruction of vasomotor in the brainstem by EV71 produces autonomic nervous system dysregulation prior to the pulmonary edema. The pulmonary edema is the result of increased pulmonary vascular permeability caused by the direct brainstem lesions and/or a systemic inflammatory response syndrome produced by the release of cytokines and chemokines. There is currently no specific antiviral agent to treat or vaccine to prevent EV71 diseases. Treating severe EV71 brainstem encephalitis patients with intravenous IgG and milrinone is associated with significantly decreased mortality by attenuated sympathetic activity and cytokine production.