Influenza virus resistance to neuraminidase inhibitors

Herbal Medicines with Antiviral Activity Against the Influenza Virus, a Systematic Review

The rapidly changing influenza virus has remained a consistent threat to the well-being of a variety of species on the planet. Influenza virus' high mutation rate has allowed the virus to rapidly and continuously evolve, as well as generate new strains that are resistant to the current commercially available antivirals. Thus, the increased resistance has compelled the scientific community to explore alternative compounds that have antiviral effects against influenza virus. In this paper, the authors systematically review numerous herbal extracts that were shown to have antiviral effects against the virus. Specifically, the herbal antiviral targets mainly include hemagglutinin, neuraminidase and matrix 2 proteins. In some instances, herbal extracts inhibited the replication of oseltamivir-resistant strains and certain pentacyclic triterpenes exhibited higher antiviral activity than oseltamivir. This paper also explores the possibility of targeting various host-cell signaling pathways that are utilized by the virus during its replication process. Infected cell pathways are hijacked by intracellular signaling cascades such as NF-kB signaling, PI3K/Akt pathway, MAPK pathway and PKC/PKR signaling cascades. Herbal antivirals have been shown to target these pathways by suppressing nuclear export of influenza vRNP and thus inhibiting the phosphorylation signaling cascade. In conclusion, copious amounts of herbal antivirals have been shown to inhibit influenza virus, however further studies are needed for these new compounds to be up to modern pharmacological standards.

In Vitro Properties and Virulence of Contemporary Recombinant Influenza B Viruses Harboring Mutations of Cross-Resistance to Neuraminidase Inhibitors

Three neuraminidase inhibitors (NAIs: Oseltamivir, zanamivir and peramivir) are currently approved in many countries for the treatment of influenza A and B infections. The emergence of influenza B viruses (IBVs) containing mutations of cross-resistance to these NAIs constitutes a serious clinical threat. Herein, we used a reverse genetics system for the current B/Phuket/3073/2013 vaccine strain to investigate the impact on in vitro properties and virulence of H136N, R152K, D198E/N, I222T and N294S NA substitutions (N2 numbering), reported by the World Health Organization (WHO) as clinical markers of reduced or highly-reduced inhibition (RI/HRI) to multiple NAIs. Recombinant viruses were tested by NA inhibition assays. Their replicative capacity and virulence were evaluated in ST6GalI-MDCK cells and BALB/c mice, respectively. All NA mutants (excepted D198E/N) showed RI/HRI phenotypes against ≥ 2 NAIs. These mutants grew to comparable titers of the recombinant wild-type (WT) IBV in vitro, and some of them (H136N, I222T and N294S mutants) induced more weight loss and mortality in BALB/c mice in comparison to the recombinant WT IBV. These results demonstrate that, in contemporary IBVs, some NA mutations may confer RI/HRI phenotypes to existing NAIs without altering the viral fitness. This reinforces the need for development of novel antiviral strategies with different mechanisms of action.

2D-SAR, Topomer CoMFA and molecular docking studies on avian influenza neuraminidase inhibitors

Avian influenza is a serious zoonotic infectious disease with huge negative impacts on local poultry farming, human health and social stability. Therefore, the design of new compounds against avian influenza has been the focus in this field. In this study, computational methods were applied to investigate the compounds with neuraminidase inhibitory activity. First, 2D-SAR model was built to recognize neuraminidase inhibitors (NAIs). As a result, the accuracy of 10 cross-validation and independent tests is 96.84% and 98.97%, respectively. Then, the Topomer CoMFA model was constructed to predict the inhibitory activity and analyses molecular fields. Two models were obtained by changing the cutting methods. The second model is employed to predict the activity (q2 = 0.784 and r2 = 0.982). Molecular docking was also used to further analyze the binding sites between NAIs and neuraminidase from human and avian virus. As a result, it is found that same binding Total Score has some differences, but the binding sites are basically the same. At last, some potential NAIs were screened and some optimal opinions were taken. It is expected that our study can assist to study and develop new types of NAIs.

Incidence of antiviral drug resistance markers among human influenza A viruses in the Eastern Mediterranean Region, 2005-2016

BACKGROUND

Two classes of antiviral drugs are available for influenza antiviral therapy: the adamantanes and the neuraminidase inhibitors (NAIs). Due to the emergence of adamantane-resistant variants, the use of these drugs has been largely limited in the world. The NAIs became the drugs of choice for treatment of influenza A infections. However, amino acid substitutions in the NA protein might lead to reduced sensitivity to NAIs.

METHODS

The frequency and distribution of matrix protein 2 (M2) and neuraminidase (NA) variants which confer resistance to antiviral drugs was investigated in the Eastern Mediterranean Region (EMR) between 2005 and 2016. A total of 314 M2 and 1209 NA protein sequences from influenza A/H1N1, A/H1N1pdm09, A/H3N2, and A/H5N1 available in the public database were analyzed.

RESULTS

Eighty-six percent of the influenza A viruses detected in the EMR were resistant to adamantanes, among which, H3 strains exhibited the highest (95.32%) level of adamantane resistance. Approximately 98.51% (265/269) of influenza A/H1N1 and H3N2 resistant viruses had the S31N substitution in their M2 sequences. The V27A mutation was the only resistance marker found in A/H5N1 viruses and was detected at a frequency of 7.40% among the investigated viruses. Other resistant mutations L26F, A30T, G34E, and L38F were not detected in any of the variants. We found that 2.81% (n = 34) of the detected NA sequences from influenza A viruses possessed at least one NAI-resistant mutation and the vast majority of resistant viruses 79.41% (27/34) bear the H274Y mutation. The frequency of NAI-resistant viruses was 3.29% (24/729) for the H1N1pdm09, 10.64% (5/47) for the seasonal H1N1, and 4.06% (5/123) for H5N1 viruses. None of the H3N2 viruses analyzed during the study period were resistant to NAIs.

CONCLUSION

Our study reveals the emergence and spread of antiviral drug resistant influenza A viruses in the EMR and emphasizes the importance of continuous surveillance to maintain the effective use of the current antivirals.

Synthesis and structure-activity relationship study of arylsulfonamides as novel potent H5N1 inhibitors

H5N1 virus, one subtype of highly pathogenic influenza A virus in human infection, has recently received attention due to its unpredictable and high mortality. In this study, a series of arylsulfonamide derivatives were identified as improved H5N1 inhibitors for the influenza treatment by systematic structure-activity relationship investigation. Among them, the most potent H5N1 inhibitor 3h exhibited excellent antiviral activity against H5N1 virus with EC₅₀ value of 0.006 μM and selectivity index 33543.3. Moreover, the molecular docking of 3h with M2 proton channel protein provides practical way for understanding the inhibition of H5N1 with this kind of compounds.

Comparison of early and recent influenza A(H1N1)pdm09 isolates harboring or not the H275Y neuraminidase mutation, in vitro and in animal models

After 6 years of circulation in humans, a novel antigenic variant of influenza A(H1N1)pdm09 (i.e., A/Michigan/45/2015) emerged in 2015-16 and has predominated thereafter worldwide. Herein, we compared in vitro and in vivo properties of 2016 wild-type (WT) A/Michigan/45/15-like isolate and its H275Y neuraminidase (NA) variant to the original A/California/07/09-like counterparts. The H275Y mutation induced comparable levels of resistance to oseltamivir and peramivir without altering zanamivir susceptibility in both 2009 and 2016 isolates. In vitro, the two WT isolates had comparable replicative properties. The 2016-H275Y isolate had lower titers at 36 h post-inoculation (PI) (P < 0.05) while the 2009-H275Y titers were lower at both 24 h (P < 0.01) and 36 h PI (P < 0.001) vs the respective WTs. In mice, the 2016-WT isolate caused less weight losses (P < 0.001) and lower lung viral titers (LVTs) (P < 0.01) vs the 2009-WT. The LVTs of 2016-WT and 2016-H275Y groups were comparable whereas the 2009-H275Y LVTs were lower vs the respective WT (P < 0.01). Ferrets infected with the 2016-WT isolate and their contacts had higher nasal viral titers (NVTs) at early time points vs the 2009-WT group (P < 0.01). Also, NVTs of 2016-H275Y animals were lower vs the 2016-WT group at early time points in both infected (P < 0.01) and contact animals (P < 0.001). In conclusion, while the H275Y mutation similarly impacts the A/California/07/2009- and A/Michigan/45/2015-like A(H1N1)pdm09 NAs, the fitness of these isolates differs according to animal models with the 2016 virus being less virulent in mice but slightly more virulent in ferrets, potentially reflecting a period of cumulative changes in surface and internal genes.

Structure-activity relationship studies of lipophilic teicoplanin pseudoaglycon derivatives as new anti-influenza virus agents

Six series of semisynthetic lipophilic glycopeptide antibiotic derivatives were evaluated for in vitro activity against influenza A and B viruses. The new teicoplanin pseudoaglycon-derived lipoglycopeptides were prepared by coupling one or two side chains to the N-terminus of the glycopeptide core, using various conjugation methods. Three series of derivatives bearing two lipophilic groups were synthesized by attaching bis-alkylthio maleimides directly or through linkers of different lengths to the glycopeptide. Access to the fourth and fifth series of compounds was achieved by click chemistry, introducing single alkyl/aryl chains directly or through a tetraethylene glycol linker to the same position. A sixth group of semisynthetic derivatives was obtained by sulfonylation of the N-terminus. Of the 42 lipophilic teicoplanin pseudoaglycon derivatives tested, about half showed broad activity against influenza A and B viruses, with some of them having reasonable or no cytotoxicity. Minor differences in the side chain length as well as lipophilicity appeared to have significant impact on antiviral activity and cytotoxicity. Several lipoglycopeptides were also found to be active against human coronavirus.

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Multiple series of lipophilic teicoplanin pseudoaglycon derivatives were prepared.

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Alkyl or aryl chains were coupled to the N-terminus by various conjugation methods.

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The activity of new antibiotic derivatives was evaluated against influenza viruses.

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Half of the 42 derivatives showed high activity against influenza A and B viruses.

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The length and lipophilicity of the side chains influence the antiviral activity.

Optimization of N-Substituted Oseltamivir Derivatives as Potent Inhibitors of Group-1 and -2 Influenza A Neuraminidases, Including a Drug-Resistant Variant

On the basis of our earlier discovery of N1-selective inhibitors, the 150-cavity of influenza virus neuraminidases (NAs) could be further exploited to yield more potent oseltamivir derivatives. Among the synthesized compounds, 15b and 15c were exceptionally active against both group-1 and -2 NAs. Especially for 09N1, N2, N6, and N9 subtypes, they showed 6.80-12.47 and 1.20-3.94 times greater activity than oseltamivir carboxylate (OSC). They also showed greater inhibitory activity than OSC toward H274Y and E119V variant. In cellular assays, they exhibited greater potency than OSC toward H5N1, H5N2, H5N6, and H5N8 viruses. 15b demonstrated high metabolic stability, low cytotoxicity in vitro, and low acute toxicity in mice. Computational modeling and molecular dynamics studies provided insights into the role of R group of 15b in improving potency toward group-1 and -2 NAs. We believe the successful exploitation of the 150-cavity of NAs represents an important breakthrough in the development of more potent anti-influenza agents.

An easy, rapid, and sensitive method for detection of drug-resistant influenza virus by using a sialidase fluorescent imaging probe, BTP3-Neu5Ac

Immunochromatographic kits and RT-PCR are widely used as diagnostic tools for influenza detection in clinical and hygiene fields. Immunochromatographic kits are useful for differential typing of influenza A and influenza B but cannot show if the detected virus strains have acquired drug resistance against neuraminidase inhibitors that target sialidase activity of viral neuraminidase. Although RT-PCR enables determination of drug-resistant mutants, its efficacy is limited to viruses carrying a known substitution in their neuraminidase genome sequence. In the present study, an easy, rapid and sensitive method for detection of drug-resistant influenza viruses regardless of major antigenic changes or genomic mutations was developed. By using the method in combination with virus-concentrated membranes in centrifugal filter units and a sialidase imaging probe, 2-(benzothiazol-2-yl)-4-bromophenyl-N-acetylneuraminic acid (BTP3-Neu5Ac), sialidase activity of influenza neuraminidase was visualized on membranes by the green fluorescence of produced hydrophobic BTP3 under UV irradiation with a handheld UV flashlight. Fluorescence images in the presence or absence of neuraminidase inhibitors clearly discriminated drug-resistant influenza viruses from drug-sensitive ones. The assay can be done within 15 min. The detection sensitivity was shown to be equal to or higher than the sensitivities of commercial immunochromatographic kits. The assay will be a powerful tool for screening and monitoring of emerging drug-resistant influenza viruses and would help clinicians decide effective antiviral treatment strategies when such mutants have become prevalent.

Kinetic, Thermodynamic, and Structural Analysis of Drug Resistance Mutations in Neuraminidase from the 2009 Pandemic Influenza Virus

Neuraminidase is the main target for current influenza drugs. Reduced susceptibility to oseltamivir, the most widely prescribed neuraminidase inhibitor, has been repeatedly reported. The resistance substitutions I223V and S247N, alone or in combination with the major oseltamivir-resistance mutation H275Y, have been observed in 2009 pandemic H1N1 viruses. We overexpressed and purified the ectodomain of wild-type neuraminidase from the A/California/07/2009 (H1N1) influenza virus, as well as variants containing H275Y, I223V, and S247N single mutations and H275Y/I223V and H275Y/S247N double mutations. We performed enzymological and thermodynamic analyses and structurally examined the resistance mechanism. Our results reveal that the I223V or S247N substitution alone confers only a moderate reduction in oseltamivir affinity. In contrast, the major oseltamivir resistance mutation H275Y causes a significant decrease in the enzyme’s ability to bind this drug. Combination of H275Y with an I223V or S247N mutation results in extreme impairment of oseltamivir’s inhibition potency. Our structural analyses revealed that the H275Y substitution has a major effect on the oseltamivir binding pose within the active site while the influence of other studied mutations is much less prominent. Our crystal structures also helped explain the augmenting effect on resistance of combining H275Y with both substitutions.

Evolution of Therapeutic Antibodies, Influenza Virus Biology, Influenza, and Influenza Immunotherapy

This narrative review article summarizes past and current technologies for generating antibodies for passive immunization/immunotherapy. Contemporary DNA and protein technologies have facilitated the development of engineered therapeutic monoclonal antibodies in a variety of formats according to the required effector functions. Chimeric, humanized, and human monoclonal antibodies to antigenic/epitopic myriads with less immunogenicity than animal-derived antibodies in human recipients can be produced in vitro. Immunotherapy with ready-to-use antibodies has gained wide acceptance as a powerful treatment against both infectious and noninfectious diseases. Influenza, a highly contagious disease, precipitates annual epidemics and occasional pandemics, resulting in high health and economic burden worldwide. Currently available drugs are becoming less and less effective against this rapidly mutating virus. Alternative treatment strategies are needed, particularly for individuals at high risk for severe morbidity. In a setting where vaccines are not yet protective or available, human antibodies that are broadly effective against various influenza subtypes could be highly efficacious in lowering morbidity and mortality and controlling unprecedented epidemic/pandemic. Prototypes of human single-chain antibodies to several conserved proteins of influenza virus with no Fc portion (hence, no ADE effect in recipients) are available. These antibodies have high potential as a novel, safe, and effective anti-influenza agent.

Host-directed combinatorial RNAi improves inhibition of diverse strains of influenza A virus in human respiratory epithelial cells

Influenza A virus infections are important causes of morbidity and mortality worldwide, and currently available prevention and treatment methods are suboptimal. In recent years, genome-wide investigations have revealed numerous host factors that are required for influenza to successfully complete its life cycle. However, only a select, small number of influenza strains were evaluated using this platform, and there was considerable variation in the genes identified across different investigations. In an effort to develop a universally efficacious therapeutic strategy with limited potential for the emergence of resistance, this study was performed to investigate the effect of combinatorial RNA interference (RNAi) on inhibiting the replication of diverse influenza A virus subtypes and strains. Candidate genes were selected for targeting based on the results of multiple previous independent genome-wide studies. The effect of single and combinatorial RNAi on the replication of 12 diverse influenza A viruses, including three strains isolated from birds and one strain isolated from seals, was then evaluated in primary normal human bronchial epithelial cells. After excluding overly toxic siRNA, two siRNA combinations were identified that reduced mean viral replication by greater than 79 percent in all mammalian strains, and greater than 68 percent in all avian strains. Host-directed combinatorial RNAi effectively prevents growth of a broad range of influenza virus strains in vitro, and is a potential therapeutic candidate for further development and future in vivo studies.

Impact of R152K and R368K neuraminidase catalytic substitutions on in vitro properties and virulence of recombinant A(H1N1)pdm09 viruses

Neuraminidase (NA) mutations conferring resistance to NA inhibitors (NAIs) are expected to occur at framework or catalytic residues of the NA enzyme. Numerous clinical and in vitro reports already described NAI-resistant A(H1N1)pdm09 variants harboring various framework NA substitutions. By contrast, variants with NA catalytic changes remain poorly documented. Herein, we investigated the effect of R152K and R368K NA catalytic mutations on the NA enzyme properties, in vitro replicative capacity and virulence of A(H1N1)pdm09 recombinant viruses. In NA inhibition assays, the R152K and R368K substitutions resulted in reduced inhibition [10- to 100-fold increases in IC₅₀ vs the wild-type (WT)] or highly reduced inhibition (>100-fold increases in IC₅₀) to at least 3 approved NAIs (oseltamivir, zanamivir, peramivir and laninamivir). Such resistance phenotype correlated with a significant reduction of affinity observed for the mutants in enzyme kinetics experiments [increased Km from 20 ± 1.77 for the WT to 200.8 ± 10.54 and 565.2 ± 135 μM (P < 0.01) for the R152K and R368K mutants, respectively]. The R152K and R368K variants grew at comparable or even higher titers than the WT in both MDCK and ST6GalI-MDCK cells. In experimentally-infected C57BL/6 mice, the recombinant WT and the R152K and R368K variants induced important signs of infection (weight loss) and resulted in mortality rates of 87.5%, 37.5% and 100%, respectively. The lung viral titers were comparable between the three infected groups. While the NA mutations were stable, an N154I substitution was detected in the HA2 protein of the R152K and R368K variants after in vitro passages as well as in lungs of infected mice. Due to the multi-drug resistance phenotypes and conserved fitness, the emergence of NA catalytic mutations accompanied with potential compensatory HA changes should be carefully monitored in A(H1N1)pdm09 viruses.

The emerging influenza virus threat: status and new prospects for its therapy and control

Influenza A viruses (IAVs) are zoonotic pathogens that cause yearly outbreaks with high rates of morbidity and fatality. The virus continuously acquires point mutations while circulating in several hosts, ranging from aquatic birds to mammals, including humans. The wide range of hosts provides influenza A viruses greater chances of genetic re-assortment, leading to the emergence of zoonotic strains and occasional pandemics that have a severe impact on human life. Four major influenza pandemics have been reported to date, and health authorities worldwide have shown tremendous progress in efforts to control epidemics and pandemics. Here, we primarily discuss the pathogenesis of influenza virus type A, its epidemiology, pandemic potential, current status of antiviral drugs and vaccines, and ways to effectively manage the disease during a crisis.

In silico study of carvone derivatives as potential neuraminidase inhibitors

Recent outbreaks of highly pathogenic influenza strains have highlighted the need to develop new anti-influenza drugs. Here, we report an in silico study of carvone derivatives to analyze their binding modes with neuraminidase (NA) active sites. Two proposed carvone analogues, CV(A) and CV(B), with 36 designed ligands were predicted to inhibit NA (PDB ID: 3TI6) using molecular docking. The design is based on structural resemblance with the commercial inhibitor, oseltamivir (OTV), ligand polarity, and amino acid residues in the NA active sites. Docking simulations revealed that ligand A18 has the lowest energy binding (∆G_bind) value of -8.30 kcal mol^-1, comparable to OTV with ∆G_bind of -8.72 kcal mol^-1. A18 formed seven hydrogen bonds (H-bonds) at residues Arg292, Arg371, Asp151, Trp178, Glu227, and Tyr406, while eight H-bonds were formed by OTV with amino acids Arg118, Arg292, Arg371, Glu119, Asp151, and Arg152. Molecular dynamics (MD) simulation was conducted to compare the stability between ligand A18 and OTV with NA. Our simulation study showed that the A18-NA complex is as stable as the OTV-NA complex during the MD simulation of 50 ns through the analysis of RMSD, RMSF, total energy, hydrogen bonding, and MM/PBSA free energy calculations.

Predicting Displaceable Water Sites Using Mixed-Solvent Molecular Dynamics

Water molecules are an important factor in protein-ligand binding. Upon binding of a ligand with a protein's surface, waters can either be displaced by the ligand or may be conserved and possibly bridge interactions between the protein and ligand. Depending on the specific interactions made by the ligand, displacing waters can yield a gain in binding affinity. The extent to which binding affinity may increase is difficult to predict, as the favorable displacement of a water molecule is dependent on the site-specific interactions made by the water and the potential ligand. Several methods have been developed to predict the location of water sites on a protein's surface, but the majority of methods are not able to take into account both protein dynamics and the interactions made by specific functional groups. Mixed-solvent molecular dynamics (MixMD) is a cosolvent simulation technique that explicitly accounts for the interaction of both water and small molecule probes with a protein's surface, allowing for their direct competition. This method has previously been shown to identify both active and allosteric sites on a protein's surface. Using a test set of eight systems, we have developed a method using MixMD to identify conserved and displaceable water sites. Conserved sites can be determined by an occupancy-based metric to identify sites which are consistently occupied by water even in the presence of probe molecules. Conversely, displaceable water sites can be found by considering the sites which preferentially bind probe molecules. Furthermore, the inclusion of six probe types allows the MixMD method to predict which functional groups are capable of displacing which water sites. The MixMD method consistently identifies sites which are likely to be nondisplaceable and predicts the favorable displacement of water sites that are known to be displaced upon ligand binding.

Two reassortant types of highly pathogenic H5N8 avian influenza virus from wild birds in Central China in 2016

Since 2016, the highly pathogenic avian influenza H5N8 virus has emerged in the Central Asian flyway and Europe, causing massive deaths in poultry and wild birds. In this study, we isolated and identified three H5N8 viruses from swan goose and black swans in Hubei province during the 2016/2017 winter season. Whole-genome sequencing and phylogenetic analysis revealed that the three viruses clustered into a group of H5N8 viruses from Qinghai Lake and Europe. A novel reassortment virus from swan goose was distinguished from that of black swans, in that its PA and NP genes were distinct from those of Qinghai Lake viruses. Molecular dating revealed that the ancestral strain of these H5N8 viruses emerged around July 2015. From sequence comparison, we discovered eight amino acid substitutions in HA and NA during the adaption process from poultry to wild birds. The three viruses were isolated from wild birds in the East Asian-Australasian flyway; however, the viral genomes were similar to H5N8 viruses circulating along the Central Asian flyway. From these data, we conclude that wetlands and lakes in Central China may play a key role in disseminating H5N8 viruses between the East Asian-Australasian and Central Asian flyways.

Pandemic Influenza: A Comparative Ethical Approach

Community-networks such as families and schools may foster and propagate some types of public health disasters. For such disasters, a communitarian-oriented ethical lens offers useful perspectives into the underlying relational nexus that favors the spread of infection. This chapter compares two traditional bioethical lenses—the communitarian and care ethics framework—vis-à-vis their capacities to engage the moral quandaries elicited by pandemic influenza. It argues that these quandaries preclude the analytical lens of ethical prisms that are individual-oriented but warrant a people-oriented approach. Adopting this dual approach offers both a contrastive and a complementary way of rethinking the underlying socioethical tensions elicited by pandemic influenza in particular and other public health disasters generally.

Aniline-Based Inhibitors of Influenza H1N1 Virus Acting on Hemagglutinin-Mediated Fusion

Two series of easily accessible anilines were identified as inhibitors of influenza A virus subtype H1N1, and extensive chemical synthesis and analysis of the structure-activity relationship were performed. The compounds were shown to interfere with low pH-induced membrane fusion mediated by the H1 and H5 (group 1) hemagglutinin (HA) subtypes. A combination of virus resistance, HA interaction, and molecular dynamics simulation studies elucidated the binding site of these aniline-based influenza fusion inhibitors, which significantly overlaps with the pocket occupied by some H3 HA-specific inhibitors, indicating the high relevance of this cavity for drug design.

The inhibitory performance of flavonoid cyanidin-3-sambubiocide against H274Y mutation in H1N1 influenza virus

Oseltamivir (Tamiflu) is the most accepted antiviral drug that targets the neuraminidase (NA) protein to inhibit the viral release from the host cell. Few H1N1 influenza strains with the H274Y mutation creates drug resistance to oseltamivir. In this study, we report that flavonoid cyanidin-3-sambubiocide (C3S) compound acts as a potential inhibitor against H274Y mutation. The drug resistance mechanism and inhibitory activity of C3S and oseltamivir against wild-type (WT) and H274Y mutant-type (MT) have been studied and compared based on the results of molecular docking, molecular dynamics, and quantum chemical methods. Oseltamivir has been found less binding affinity with MT. C3S has more binding affinity with WT and MT proteins. From the dynamical study, the 150th loop of the MT protein has found more deformation than WT. A single H274Y mutation induces the conformational changes in the 150th loop which leads to produce more resistance to oseltamivir. The 150th cavity is more attractive target for C3S to stop the conformational changes in the MT, than 430th cavity of NA protein. The C3S is stabilized with MT by more number of hydrogen bonds than oseltamivir. The electrostatic interaction energy shows a stronger C3S binding with MT and this compound may be more effective against oseltamivir-resistant virus strains.

Monitoring influenza virus susceptibility to oseltamivir using a new rapid assay, iART

A new rapid assay for detecting oseltamivir resistance in influenza virus, iART, was used to test 149 clinical specimens. Results were obtained for 132, with iART indicating 41 as ‘resistant’. For these, sequence analysis found known and suspected markers of oseltamivir resistance, while no such markers were detected for the remaining 91 samples. Viruses isolated from the 41 specimens showed reduced or highly reduced inhibition by neuraminidase inhibition assay. iART may facilitate broader antiviral resistance testing.

Screening for Neuraminidase Inhibitor Resistance Markers among Avian Influenza Viruses of the N4, N5, N6, and N8 Neuraminidase Subtypes

Several subtypes of avian influenza viruses (AIVs) are emerging as novel human pathogens, and the frequency of related infections has increased in recent years. Although neuraminidase (NA) inhibitors (NAIs) are the only class of antiviral drugs available for therapeutic intervention for AIV-infected patients, studies on NAI resistance among AIVs have been limited, and markers of resistance are poorly understood. Previously, we identified unique NAI resistance substitutions in AIVs of the N3, N7, and N9 NA subtypes. Here, we report profiles of NA substitutions that confer NAI resistance in AIVs of the N4, N5, N6, and N8 NA subtypes using gene-fragmented random mutagenesis. We generated libraries of mutant influenza viruses using reverse genetics (RG) and selected resistant variants in the presence of the NAIs oseltamivir carboxylate and zanamivir in MDCK cells. In addition, two substitutions, H274Y and R292K (N2 numbering), were introduced into each NA gene for comparison. We identified 37 amino acid substitutions within the NA gene, 16 of which (4 in N4, 4 in N5, 4 in N6, and 4 in N8) conferred resistance to NAIs (oseltamivir carboxylate, zanamivir, or peramivir) as determined using a fluorescence-based NA inhibition assay. Substitutions conferring NAI resistance were mainly categorized as either novel NA subtype specific (G/N147V/I, A246V, and I427L) or previously reported in other subtypes (E119A/D/V, Q136K, E276D, R292K, and R371K). Our results demonstrate that each NA subtype possesses unique NAI resistance markers, and knowledge of these substitutions in AIVs is important in facilitating antiviral susceptibility monitoring of NAI resistance in AIVs.IMPORTANCE The frequency of human infections with avian influenza viruses (AIVs) has increased in recent years. Despite the availability of vaccines, neuraminidase inhibitors (NAIs), as the only available class of drugs for AIVs in humans, have been constantly used for treatment, leading to the inevitable emergence of drug-resistant variants. To screen for substitutions conferring NAI resistance in AIVs of N4, N5, N6, and N8 NA subtypes, random mutations within the target gene were generated, and resistant viruses were selected from mutant libraries in the presence of individual drugs. We identified 16 NA substitutions conferring NAI resistance in the tested AIV subtypes; some are novel and subtype specific, and others have been previously reported in other subtypes. Our findings will contribute to an increased and more comprehensive understanding of the mechanisms of NAI-induced inhibition of influenza virus and help lead to the development of drugs that bind to alternative interaction motifs.

In vivo mallard experiments indicate that zanamivir has less potential for environmental influenza A virus resistance development than oseltamivir

Neuraminidase inhibitors are a cornerstone of influenza pandemic preparedness before vaccines can be mass-produced and thus a neuraminidase inhibitor-resistant pandemic is a serious threat to public health. Earlier work has demonstrated the potential for development and persistence of oseltamivir resistance in influenza A viruses exposed to environmentally relevant water concentrations of the drug when infecting mallards, the natural influenza reservoir that serves as the genetic base for human pandemics. As zanamivir is the major second-line neuraminidase inhibitor treatment, this study aimed to assess the potential for development and persistence of zanamivir resistance in an in vivo mallard model; especially important as zanamivir will probably be increasingly used. Our results indicate less potential for development and persistence of resistance due to zanamivir than oseltamivir in an environmental setting. This conclusion is based on: (1) the lower increase in zanamivir IC₅₀ conferred by the mutations caused by zanamivir exposure (2-17-fold); (2) the higher zanamivir water concentration needed to induce resistance (at least 10 µg l^-1); (3) the lack of zanamivir resistance persistence without drug pressure; and (4) the multiple resistance-related substitutions seen during zanamivir exposure (V116A, A138V, R152K, T157I and D199G) suggesting lack of one straight-forward evolutionary path to resistance. Our study also adds further evidence regarding the stability of the oseltamivir-induced substitution H275Y without drug pressure, and demonstrates the ability of a H275Y-carrying virus to acquire secondary mutations, further boosting oseltamivir resistance when exposed to zanamivir. Similar studies using influenza A viruses of the N2-phylogenetic group of neuraminidases are recommended.

Emergence of Oseltamivir-Resistant H7N9 Influenza Viruses in Immunosuppressed Cynomolgus Macaques

Antiviral compounds (eg, the neuraminidase inhibitor oseltamivir) are invaluable for the treatment of individuals infected with influenza A viruses of the H7N9 subtype (A[H7N9]), which have infected and killed hundreds of persons. However, oseltamivir treatment often leads to the emergence of resistant viruses in immunocompromised individuals. To better understand the emergence and properties of oseltamivir-resistant A(H7N9) viruses in immunosuppressed individuals, we infected immunosuppressed cynomolgus macaques with an A(H7N9) virus and treated them with oseltamivir. Disease severity and mortality were higher in immunosuppressed than in immunocompetent animals. Oseltamivir treatment at 2 different doses reduced A(H7N9) viral titers in infected animals, but even high-dose oseltamivir did not block viral replication sufficiently to suppress the emergence of resistant variants. Some resistant variants were not appreciably attenuated in cultured cells, but an oseltamivir-resistant A(H7N9) virus did not transmit among ferrets. These findings are useful for the control of A(H7N9) virus infections in clinical settings.

Biological Evaluation of Uridine Derivatives of 2-Deoxy Sugars as Potential Antiviral Compounds against Influenza A Virus

Influenza virus infection is a major cause of morbidity and mortality worldwide. Due to the limited ability of currently available treatments, there is an urgent need for new anti-influenza drugs with broad spectrum protection. We have previously shown that two 2-deoxy sugar derivatives of uridine (designated IW3 and IW7) targeting the glycan processing steps during maturation of viral glycoproteins show good anti-influenza virus activity and may be a promising alternative approach for the development of new anti-influenza therapy. In this study, a number of IW3 and IW7 analogues with different structural modifications in 2-deoxy sugar or uridine parts were synthesized and evaluated for their ability to inhibit influenza A virus infection in vitro. Using the cytopathic effect (CPE) inhibition assay and viral plaque reduction assay in vitro, we showed that compounds 2, 3, and 4 exerted the most inhibitory effect on influenza virus A/ostrich/Denmark/725/96 (H5N2) infection in Madin-Darby canine kidney (MDCK) cells, with 50% inhibitory concentrations (IC₅₀) for virus growth ranging from 82 to 100 (μM) without significant toxicity for the cells. The most active compound (2) showed activity of 82 μM with a selectivity index value of 5.27 against type A (H5N2) virus. Additionally, compound 2 reduced the formation of HA glycoprotein in a dose-dependent manner. Moreover, an analysis of physicochemical properties of studied compounds demonstrated a significant linear correlation between lipophilicity and antiviral activity. Therefore, inhibition of influenza A virus infection by conjugates of uridine and 2-deoxy sugars is a new promising approach for the development of new derivatives with anti-influenza activities.

Discovery of dapivirine, a nonnucleoside HIV-1 reverse transcriptase inhibitor, as a broad-spectrum antiviral against both influenza A and B viruses

The emergence of multidrug-resistant influenza viruses poses a persistent threat to public health. The current prophylaxis and therapeutic interventions for influenza virus infection have limited efficacy due to the continuous antigenic drift and antigenic shift of influenza viruses. As part of our ongoing effort to develop the next generation of influenza antivirals with broad-spectrum antiviral activity and a high genetic barrier to drug resistance, in this study we report the discovery of dapivirine, an FDA-approved HIV nonnucleoside reverse transcriptase inhibitor, as a broad-spectrum antiviral against multiple strains of influenza A and B viruses with low micromolar efficacy. Mechanistic studies revealed that dapivirine inhibits the nuclear entry of viral ribonucleoproteins at the early stage of viral replication. As a result, viral RNA and protein synthesis were inhibited. Furthermore, dapivirine has a high in vitro genetic barrier to drug resistance, and its antiviral activity is synergistic with oseltamivir carboxylate. In summary, the in vitro antiviral results of dapivirine suggest it is a promising candidate for the development of the next generation of dual influenza and HIV antivirals.

Data-driven interdisciplinary mathematical modelling quantitatively unveils competition dynamics of co-circulating influenza strains

BACKGROUND

Co-circulation of influenza strains is common to seasonal epidemics and pandemic emergence. Competition was considered involved in the vicissitudes of co-circulating influenza strains but never quantitatively studied at the human population level. The main purpose of the study was to explore the competition dynamics of co-circulating influenza strains in a quantitative way.

METHODS

We constructed a heterogeneous dynamic transmission model and ran the model to fit the weekly A/H1N1 influenza virus isolation rate through an influenza season. The construction process started on the 2007-2008 single-clade influenza season and, with the contribution from the clade-based A/H1N1 epidemiological curves, advanced to the 2008-2009 two-clade influenza season. Pearson method was used to estimate the correlation coefficient between the simulated epidemic curve and the observed weekly A/H1N1 influenza virus isolation rate curve.

RESULTS

The model found the potentially best-fit simulation with correlation coefficient up to 96% and all the successful simulations converging to the best-fit. The annual effective reproductive number of each co-circulating influenza strain was estimated. We found that, during the 2008-2009 influenza season, the annual effective reproductive number of the succeeding A/H1N1 clade 2B-2, carrying H275Y mutation in the neuraminidase, was estimated around 1.65. As to the preceding A/H1N1 clade 2C-2, the annual effective reproductive number would originally be equivalent to 1.65 but finally took on around 0.75 after the emergence of clade 2B-2. The model reported that clade 2B-2 outcompeted for the 2008-2009 influenza season mainly because clade 2C-2 suffered from a reduction of transmission fitness of around 71% on encountering the former.

CONCLUSIONS

We conclude that interdisciplinary data-driven mathematical modelling could bring to light the transmission dynamics of the A/H1N1 H275Y strains during the 2007-2009 influenza seasons worldwide and may inspire us to tackle the continually emerging drug-resistant A/H1N1pdm09 strains. Furthermore, we provide a prospective approach through mathematical modelling to solving a seemingly unintelligible problem at the human population level and look forward to its application at molecular level through bridging the resolution capacities of related disciplines.

Respiratory RNA Viruses

Acute upper and lower respiratory infections are a major public health problem and a leading cause of morbidity and mortality worldwide. At greatest risk are young children, the elderly, the chronically ill, and those with suppressed or compromised immune systems. Viruses are the predominant cause of respiratory tract illnesses and include RNA viruses such as respiratory syncytial virus, influenza virus, parainfluenza virus, metapneumovirus, rhinovirus, and coronavirus. Laboratory testing is required for a reliable diagnosis of viral respiratory infections, as a clinical diagnosis can be difficult since signs and symptoms are often overlapping and not specific for any one virus. Recent advances in technology have resulted in the development of newer diagnostic assays that offer great promise for rapid and accurate detection of respiratory viral infections. This chapter emphasizes the fundamental characteristics and clinical importance of the various RNA viruses that cause upper and lower respiratory tract diseases in the immunocompromised host. It highlights the laboratory methods that can be used to make a rapid and definitive diagnosis for the greatest impact on the care and management of ill patients, and the prevention and control of hospital-acquired infections and community outbreaks.

Evolutionary conservation of influenza A PB2 sequences reveals potential target sites for small molecule inhibitors

The influenza A basic polymerase protein 2 (PB2) functions as part of a heterotrimer to replicate the viral RNA genome. To investigate novel PB2 antiviral target sites, this work identified evolutionary conserved regions across the PB2 protein sequence amongst all sub-types and hosts, as well as ligand binding hot spots which overlap with highly conserved areas. Fifteen binding sites were predicted in different PB2 domains; some of which reside in areas of unknown function. Virtual screening of ~50,000 drug-like compounds showed binding affinities of up to -10.3kcal/mol. The highest affinity molecules were found to interact with conserved residues including Gln138, Gly222, Ile529, Asn540 and Thr530. A library containing 1738 FDA approved drugs was screened additionally and revealed Paliperidone as a top hit with a binding affinity of -10kcal/mol. Predicted ligands are ideal leads for new antivirals as they were targeted to evolutionary conserved binding sites.

Chimeric Hemagglutinin Constructs Induce Broad Protection against Influenza B Virus Challenge in the Mouse Model

Seasonal influenza virus epidemics represent a significant public health burden. Approximately 25% of all influenza virus infections are caused by type B viruses, and these infections can be severe, especially in children. Current influenza virus vaccines are an effective prophylaxis against infection but are impacted by rapid antigenic drift, which can lead to mismatches between vaccine strains and circulating strains. Here, we describe a broadly protective vaccine candidate based on chimeric hemagglutinins, consisting of globular head domains from exotic influenza A viruses and stalk domains from influenza B viruses. Sequential vaccination with these constructs in mice leads to the induction of broadly reactive antibodies that bind to the conserved stalk domain of influenza B virus hemagglutinin. Vaccinated mice are protected from lethal challenge with diverse influenza B viruses. Results from serum transfer experiments and antibody-dependent cell-mediated cytotoxicity (ADCC) assays indicate that this protection is antibody mediated and based on Fc effector functions. The present data suggest that chimeric hemagglutinin-based vaccination is a viable strategy to broadly protect against influenza B virus infection.IMPORTANCE While current influenza virus vaccines are effective, they are affected by mismatches between vaccine strains and circulating strains. Furthermore, the antiviral drug oseltamivir is less effective for treating influenza B virus infections than for treating influenza A virus infections. A vaccine that induces broad and long-lasting protection against influenza B viruses is therefore urgently needed.

A Review of Clinical Influenza A and B Infections With Reduced Susceptibility to Both Oseltamivir and Zanamivir

Anti-influenza drugs play major roles in the management of severe influenza infections. Neuraminidase inhibitors (NAIs), which are active against all influenza A subtypes and the 2 major influenza B lineages, constitute the only class of antivirals recommended for the control of influenza epidemics and eventual pandemics. Thus, the emergence of NAI resistance could be a major clinical concern. Although most currently circulating influenza A and B strains are susceptible to NAIs, clinical cases of influenza viruses harboring single or multiple NA substitutions or deletions conferring a cross-resistance phenotype to the 2 main NAIs (oseltamivir and zanamivir) have been reported, mostly in immunocompromised individuals. Moreover, such events seem to be more frequent in A(H1N1)pdm09 viruses containing the H274Y substitution together with other NA changes (I222R, E119D/G). This review summarizes the therapeutic regimens leading to the emergence of NAI cross-resistant influenza A and B viruses as well as the virologic properties of such variants.

An activity-integrated strategy of the identification, screening and determination of potential neuraminidase inhibitors from Radix Scutellariae

Small molecules isolated from herbal medicines (HMs) were identified as the potential neuraminidase inhibitors which are effective in influenza prevention and treatment. Unfortunately, current available screen methods of small molecules isolated from HMs are inefficient and insensitive. Here a novel Ultra Performance Liquid Chromatography coupled with diode-array detectors and auto-fraction collector / time-of-flight mass spectrometry (UPLC-DAD-FC/Q-TOF-MS) screening method with high efficiency was developed and validated to separate, collect, enrich, identify and quantify potential neuraminidase inhibitors from Radix Scutellariae. The results showed that 26 components with neuraminidase inhibitory activity were identified from Radix Scutellariae extracts. It was also found that the influence of origins on the quality of RS was more than that of cultivated time on the basis of the concentration of the effective components. These results brought novel insights into quality evaluation of Radix Scutellariae. It was demonstrated that new activity-integrated strategy was a suitable technique for the identification, screening and determination of potential neuraminidase inhibitors in herbal medicine and will provide novel potential strategies in other drug screening from herbal medicine.

Sequence analysis of haemagglutinin and neuraminidase of H1N1 strain from a patient coinfected with Mycobacterium tuberculosis

The 2009 H1N1 pandemic (H1N1pdm09) was associated with a considerable influenza-related morbidity and mortality. Among the complications, Mycobacterial tuberculosis was recorded as a coinfection with influenza in rare cases. The full-length sequences of the viral haemagglutinin and neuraminidase of H1N1pdm09 influenza A virus were analyzed from a recently infected patient. The patient was chronically infected with Mycobacterium tuberculosis. Molecular modelling and in-silico docking of the virus, and other selected strains with the drug oseltamivir were conducted and compared. Sequence analysis of the viral haemagglutinin revealed it to be closely related to the 6B.1 clade, with high identity to the circulating H1N1pdm09 strains, and confirmed that the virus still harbouring high affinity to the α-2,6-sialic acid human receptor. The viral neuraminidase showed high identity to the neuraminidase of the recently circulating strains of the virus with no evidence of the development of oseltamivir-resistant mutants. Regular monitoring of the circulating strains is recommended to screen for a possible emergence of drug-resistant strains.

Linear antimicrobial peptides with activity against herpes simplex virus 1 and Aichi virus

Viruses are the major cause of disease and mortality worldwide. Nowadays there are treatments based on antivirals or prophylaxis with vaccines. However, the rising number of reports of viral resistance to current antivirals and the emergence of new types of virus has concerned the scientific community. In this scenario, the search for alternative treatments has led scientists to the discovery of antimicrobial peptides (AMPs) derived from many different sources. Since some of them have shown antiviral activities, here we challenged 10 synthetic peptides from different animal and plant sources against, herpes simplex virus 1 (HSV-1), and Aichi virus. Among them, the highlight was Pa-MAP from the polar fish Pleuronectes americanus, which caused around 90% of inhibition of the HSV with a selectivity index of 5 and a virucidal mechanism of action. Moreover, LL-37 from human neutrophils showed 96% of inhibition against the Aichi virus, showing a selectivity index of 3.4. The other evaluated peptides did not show significant antiviral activity. In conclusion, the present study demonstrated that Pa-MAP seems to be a reliable candidate for a possible alternative drug to treat HSV-1 infections. © 2016 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 108: 1-6, 2017.

Prospective surveillance of antiviral resistance in hospitalized infants less than 12 months of age with A(H3N2) influenza infection and treated with oseltamivir

BACKGROUND

Infants exhibit elevated influenza virus loads and prolonged viral shedding, which may increase the risk for resistance development, especially in cases of suboptimal exposure to antiviral therapy.

METHODS

We performed a prospective surveillance of hospitalized infants undergoing oseltamivir therapy during the 2008-2009 and 2011-2012 influenza seasons at two paediatric hospitals in Germany. A total of 37 infants less than 1 year of age with laboratory confirmed influenza A(H3N2) infection received oseltamivir as per physician's order for 5 days (2008-2009 season: 2 mg/kg twice daily; 2011-2012 season: 2.0 mg/kg; 2.5 mg/kg and 3.0 mg/kg twice daily for infants <1 month; 2-3 months and 4-12 months, respectively). Virus load, the susceptibility to neuraminidase inhibitors (NAIs), and the presence of molecular markers of resistance to NAIs was assessed for influenza viruses recovered from respiratory samples collected at baseline and during follow-up visits.

RESULTS

Overall, 73% of the infants continued to shed viral RNA detectable by reverse transcription (RT)-PCR after dose number 10 of oseltamivir; 12 infants shed viruses, 2 of them (both 9 months of age) shed resistant viruses. Resistance was characterized by ≥1,000-fold increase of 50% inhibitory concentration (IC₅₀) for oseltamivir, up to 50-fold for zanamivir and elevated Km values when compared to susceptible A(H3N2) strains. Sanger sequencing revealed the selection of the NA-R292K substitution in both instances (after dose number 10 on day 6).

CONCLUSIONS

Our data suggest that it may be relevant to monitor antiviral resistance systematically in all infants, considering that the European Medicines Agency has recently extended the licensure for oseltamivir to include full-term infants.

Randomized, double-blind, placebo-controlled clinical trial to assess the safety and effectiveness of a novel dual-action oral topical formulation against upper respiratory infections

Background

Current prevention options for upper respiratory infections (URIs) are not optimal. We conducted a randomized, double-blinded, placebo-controlled pilot clinical trial to evaluate the safety and efficacy of ARMS-I™ (currently marketed as Halo™) in the prevention of URIs.

Methods

ARMS-I is patented novel formulation for the prevention and treatment of influenza, comprising a broad-spectrum antimicrobial agent (cetylpyridinium chloride, CPC) and components (glycerin and xanthan gum) that form a barrier on the host mucosa, thus preventing viral contact and invasion. Healthy adults (18–45 years of age) were randomized into ARMS-I or placebo group (50 subjects each). The drug was sprayed intra-orally (3× daily) for 75 days. The primary objectives were to establish whether ARMS-I decreased the frequency, severity or duration of URIs. Secondary objectives were to evaluate safety, tolerability, rate of virus detection, acceptability and adherence; effect on URI-associated absenteeism and medical visits; and effect of prior influenza vaccination on study outcomes.

Results

Of the 94 individuals who completed the study (placebo: n = 44, ARMS-I: n = 50), six presented with confirmed URI (placebo: 4, ARMS-I: 2), representing a 55% relative reduction, albeit this was statistically not significant). Influenza, coronavirus or rhinovirus were detected in three participants; all in the placebo group. Moreover, frequency of post-treatment exit visits was reduced by 55% in ARMS-I compared to the placebo group (N = 4 and 2, respectively). Fever was reported only in the placebo group. ARMS-I significantly reduced the frequency and severity of cough and sore throat, and duration of cough (P ≤ .019 for all comparisons). ARMS-I was safe, well tolerated, had high acceptability and high adherence to medication use. Medical visits occurred only in the placebo group while absenteeism did not differ between the two arms. Prior influenza vaccination had no effect on study outcome.

Conclusions

This randomized proof-of-concept clinical trial demonstrated that ARMS-I tended to provide protection against URIs in the enrolled study participants, while reducing severity and duration of cough and sore throat. A clinical trial with a larger number of study participants is warranted.

Trial registration

ClinicalTrials.gov NCT02644135 (retrospectively registered).

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-016-2177-8) contains supplementary material, which is available to authorized users.

Potential of marine natural products against drug-resistant fungal, viral, and parasitic infections

Antibiotics have revolutionised medicine in many aspects, and their discovery is considered a turning point in human history. However, the most serious consequence of the use of antibiotics is the concomitant development of resistance against them. The marine environment has proven to be a very rich source of diverse natural products with significant antibacterial, antifungal, antiviral, antiparasitic, antitumour, anti-inflammatory, antioxidant, and immunomodulatory activities. Many marine natural products (MNPs)-for example, neoechinulin B-have been found to be promising drug candidates to alleviate the mortality and morbidity rates caused by drug-resistant infections, and several MNP-based anti-infectives have already entered phase 1, 2, and 3 clinical trials, with six approved for usage by the US Food and Drug Administration and one by the EU. In this Review, we discuss the diversity of marine natural products that have shown in-vivo efficacy or in-vitro potential against drug-resistant infections of fungal, viral, and parasitic origin, and describe their mechanism of action. We highlight the drug-like physicochemical properties of the reported natural products that have bioactivity against drug-resistant pathogens in order to assess their drug potential. Difficulty in isolation and purification procedures, toxicity associated with the active compound, ecological impacts on natural environment, and insufficient investments by pharmaceutical companies are some of the clear reasons behind market failures and a poor pipeline of MNPs available to date. However, the diverse abundance of natural products in the marine environment could serve as a ray of light for the therapy of drug-resistant infections. Development of resistance-resistant antibiotics could be achieved via the coordinated networking of clinicians, microbiologists, natural product chemists, and pharmacologists together with pharmaceutical venture capitalist companies.

Molecular Basis for Differential Patterns of Drug Resistance in Influenza N1 and N2 Neuraminidase

Neuraminidase (NA) inhibitors are used for the prevention and treatment of influenza A virus infections. Two subtypes of NA, N1 and N2, predominate in viruses that infect humans, but differential patterns of drug resistance have emerged in each subtype despite highly homologous active sites. To understand the molecular basis for the selection of these drug resistance mutations, structural and dynamic analyses on complexes of N1 and N2 NA with substrates and inhibitors were performed. Comparison of dynamic substrate and inhibitor envelopes and interactions at the active site revealed how differential patterns of drug resistance have emerged for specific drug resistance mutations, at residues I222, S246, and H274 in N1 and E119 in N2. Our results show that the differences in intermolecular interactions, especially van der Waals contacts, of the inhibitors versus substrates at the NA active site effectively explain the selection of resistance mutations in the two subtypes. Avoiding such contacts that render inhibitors vulnerable to resistance by better mimicking the dynamics and intermolecular interactions of substrates can lead to the development of novel inhibitors that avoid drug resistance in both subtypes.

Influenza Neuraminidase Inhibitors: Synthetic Approaches, Derivatives and Biological Activity

Despite being a common viral disease, influenza has very negative consequences, causing the death of around half a million people each year. A neuraminidase located on the surface of the virus plays an important role in viral reproduction by contributing to the release of viruses from infected host cells. The treatment of influenza is mainly based on the administration of neuraminidase inhibitors. The neuraminidase inhibitors zanamivir, laninamivir, oseltamivir and peramivir have been commercialized and have been demonstrated to be potent influenza viral neuraminidase inhibitors against most influenza strains. In order to create more potent neuraminidase inhibitors and fight against the surge in resistance resulting from naturally-occurring mutations, these anti-influenza drugs have been used as templates for the development of new neuraminidase inhibitors through structure-activity relationship studies. Here, we review the synthetic routes to these commercial drugs, the modifications which have been performed on these structures and the effects of these modifications on their inhibitory activity.

Distinct Effects of T-705 (Favipiravir) and Ribavirin on Influenza Virus Replication and Viral RNA Synthesis

T-705 (favipiravir) is a new antiviral agent in advanced clinical development for influenza therapy. It is supposed to act as an alternative substrate for the viral polymerase, causing inhibition of viral RNA synthesis or virus mutagenesis. These mechanisms were also proposed for ribavirin, an established and broad antiviral drug that shares structural similarity with T-705. We here performed a comparative analysis of the effects of T-705 and ribavirin on influenza virus and host cell functions. Influenza virus-infected cell cultures were exposed to T-705 or ribavirin during single or serial virus passaging. The effects on viral RNA synthesis and infectious virus yield were determined and mutations appearing in the viral genome were detected by whole-genome virus sequencing. In addition, the cellular nucleotide pools as well as direct inhibition of the viral polymerase enzyme were quantified. We demonstrate that the anti-influenza virus effect of ribavirin is based on IMP dehydrogenase inhibition, which results in fast and profound GTP depletion and an imbalance in the nucleotide pools. In contrast, T-705 acts as a potent and GTP-competitive inhibitor of the viral polymerase. In infected cells, viral RNA synthesis is completely inhibited by T-705 or ribavirin at ≥50 μM, whereas exposure to lower drug concentrations induces formation of noninfectious particles and accumulation of random point mutations in the viral genome. This mutagenic effect is 2-fold higher for T-705 than for ribavirin. Hence, T-705 and ribavirin both act as purine pseudobases but profoundly differ with regard to the mechanism behind their antiviral and mutagenic effects on influenza virus.

Risk of resistant avian influenza A virus in wild waterfowl as a result of environmental release of oseltamivir

Oseltamivir is the best available anti-influenza drug and has therefore been stockpiled worldwide in large quantities as part of influenza pandemic preparedness planning. The active metabolite oseltamivir carboxylate (OC) is stable and is not removed by conventional sewage treatment. Active OC has been detected in river water at concentrations up to 0.86 µg/L. Although the natural reservoir hosts of influenza A virus (IAV) are wild waterfowl that reside in aquatic environments, the ecologic risks associated with environmental OC release and its potential to generate resistant viral variants among wild birds has largely been unknown. However, in recent years a number of in vivo mallard (Anas platyrhynchos) studies have been conducted regarding the potential of avian IAVs to become resistant to OC in natural reservoir birds if these are drug exposed. Development of resistance to OC was observed both in Group 1 (N1) and Group 2 (N2, N9) neuraminidase subtypes, when infected ducks were exposed to OC at concentrations between 0.95 and 12 µg/L in their water. All resistant variants maintained replication and transmission between ducks during drug exposure. In an A(H1N1)/H274Y virus, the OC resistance mutation persisted without selective drug pressure, demonstrating the potential of an IAV with a permissive genetic background to acquire and maintain OC resistance, potentially allowing circulation of the resistant variant among wild birds. The experimental studies have improved the appreciation of the risks associated with the environmental release of OC related to resistance development of avian IAVs among wild birds. Combined with knowledge of efficient methods for improved sewage treatment, the observations warrant implementation of novel efficient wastewater treatment methods, rational use of anti-influenza drugs, and improved surveillance of IAV resistance in wild birds.

Delivery of RNAi Therapeutics to the Airways-From Bench to Bedside

RNA interference (RNAi) is a potent and specific post-transcriptional gene silencing process. Since its discovery, tremendous efforts have been made to translate RNAi technology into therapeutic applications for the treatment of different human diseases including respiratory diseases, by manipulating the expression of disease-associated gene(s). Similar to other nucleic acid-based therapeutics, the major hurdle of RNAi therapy is delivery. Pulmonary delivery is a promising approach of delivering RNAi therapeutics directly to the airways for treating local conditions and minimizing systemic side effects. It is a non-invasive route of administration that is generally well accepted by patients. However, pulmonary drug delivery is a challenge as the lungs pose a series of anatomical, physiological and immunological barriers to drug delivery. Understanding these barriers is essential for the development an effective RNA delivery system. In this review, the different barriers to pulmonary drug delivery are introduced. The potential of RNAi molecules as new class of therapeutics, and the latest preclinical and clinical studies of using RNAi therapeutics in different respiratory conditions are discussed in details. We hope this review can provide some useful insights for moving inhaled RNAi therapeutics from bench to bedside.

Tautomeric and non-tautomeric N-substituted 2-iminobenzimidazolines as new lead compounds for the design of anti-influenza drugs: An in vitro study

A series of 1,3-disubstituted 2-iminobenzimidazolines as well as a number of their tautomeric analogs were synthesized. The synthesized compounds were tested for their cytotoxicity against MDCK cells and for inhibiting activity against influenza virus A/California/07/09 (H1N1)pdm09. Based on the results obtained, 50% cytotoxic concentration (CC₅₀), 50% inhibiting concentration (IC₅₀) and selectivity index (SI) were calculated for each compound. It was found that some of synthesized benzimidazole derivatives (7 of 22, 32%) possess strong virus-inhibiting activity against pandemic influenza virus (IC₅₀'s in low micromolar range) with quite moderate cytotoxicity (CC₅₀ in the range of thousands micromoles). Due to their high selectivity (highest SI's=50-83) these compounds are of significant interest for further in vivo experiments as well as for further structural optimization and drug development.