Characterization of two distinct neuraminidases from avian-origin human-infecting H7N9 influenza viruses

Discovering Influenza Virus Neuraminidase Inhibitors via Computational and Experimental Studies

Influenza A and B viruses spread out worldwide, causing several global concerns. Discovering neuraminidase inhibitors to prevent influenza A and B viruses is thus of great interest. In this work, a machine learning model was trained and tested to evaluate the ligand-binding affinity to neuraminidase. The model was then used to predict the binding affinity of compounds from the CHEMBL database, which is a manually curated database of bioactive molecules with drug-like properties. The physical insights into the binding process of ligands to neuraminidase were clarified via molecular docking and molecular dynamics simulations. Experimental investigation on enzymatic activity validated our computational results and suggested that 2 compounds were potential inhibitors of neuraminidase of the influenza A and B viruses.

MedChemExpress compounds prevent neuraminidase N1 via physics- and knowledge-based methods

Influenza A viruses spread out worldwide, causing several global concerns. Hence, discovering neuraminidase inhibitors to prevent the influenza A virus is of great interest. In this work, a machine learning model was employed to evaluate the ligand-binding affinity of ca. 10 000 compounds from the MedChemExpress (MCE) database for inhibiting neuraminidase. Atomistic simulations, including molecular docking and molecular dynamics simulations, then confirmed the ligand-binding affinity. Furthermore, we clarified the physical insights into the binding process of ligands to neuraminidase. It was found that five compounds, including micronomicin, didesmethyl cariprazine, argatroban, Kgp-IN-1, and AY 9944, are able to inhibit neuraminidase N1 of the influenza A virus. Ten residues, including Glu119, Asp151, Arg152, Trp179, Gln228, Glu277, Glu278, Arg293, Asn295, and Tyr402, may be very important in controlling the ligand-binding process to N1.

Microsecond dynamics of H10N7 influenza neuraminidase reveals the plasticity of loop regions and drug resistance due to the R292K mutation

At the beginning of the last century, multiple pandemics caused by influenza (flu) viruses severely impacted public health. Despite the development of vaccinations and antiviral medications to prevent and control impending flu outbreaks, unforeseen novel strains and continuously evolving old strains continue to represent a serious threat to human life. Therefore, the recently identified H10N7, for which not much data is available for rational structure-based drug design, needs to be further explored. Here, we investigated the structural dynamics of neuraminidase N7 upon binding of inhibitors, and the drug resistance mechanisms against the oseltamivir (OTV) and laninamivir (LNV) antivirals due to the crucial R292K mutation on the N7 using the computational microscope, molecular dynamics (MD) simulations. In this study, each system underwent long 2 × 1 μs MD simulations to answer the conformational changes and drug resistance mechanisms. These long time-scale dynamics simulations and free energy landscapes demonstrated that the mutant systems showed a high degree of conformational variation compared to their wildtype (WT) counterparts, and the LNV-bound mutant exhibited an extended 150-loop conformation. Further, the molecular mechanics Poisson-Boltzmann surface area (MM/PBSA) calculation and MM/GBSA free energy decomposition were used to characterize the binding of OTV and LNV with WT, and R292K mutated N7, revealing the R292K mutation as drug-resistant, facilitated by a decline in binding interaction and a reduction in the dehydration penalty. Due to the broader binding pocket cavity of the smaller K292 mutant residue relative to the wildtype, the drug carboxylate to K292 hydrogen bonding was lost, and the area surrounding the K292 residue was more accessible to water molecules. This implies that drug resistance could be reduced by strengthening the hydrogen bond contacts between N7 inhibitors and altered N7, creating inhibitors that can form a hydrogen bond to the mutant K292, or preserving the closed cavity conformations.

Engineering of novel hemagglutinin biosensors for rapid detection and drug screening of Influenza A H7N9 virus

New pathogenic influenza virus strains are constantly emerging, posing a serious risk to both human health and economic growth. To effectively control the spread of this virus, there is an urgent need for early, rapid, sensitive, simple, and cost-effective detection technologies, as well as new and effective antiviral drugs. In this study, we have successfully achieved a significant milestone by successfully fusing the H7N9 influenza virus hemagglutinin (HA) protein with the nano-luciferase component, resulting in the development of a novel set of biosensors. This remarkable achievement marks the first instance of utilizing this biosensor technology for influenza antibody detection. Our biosensor technology also has the potential to facilitate the development of antiviral drugs targeting specific epitopes of the HA protein, providing a promising avenue for the treatment of H7N9 influenza virus infections. Furthermore, our biosensors have broad applications beyond H7N9 influenza virus detection, as they can be expanded for the detection of other pathogens and drug screening applications in the future. By providing a novel and effective solution to the detection and treatment of influenza viruses, our biosensors have the potential to revolutionize the field of infectious disease control.

Targeting the Human Influenza a Virus: The Methods, Limitations, and Pitfalls of Virtual Screening for Drug-like Candidates Including Scaffold Hopping and Compound Profiling

In this study, we describe the input data and processing steps to find antiviral lead compounds by a virtual screen. Two-dimensional and three-dimensional filters were designed based on the X-ray crystallographic structures of viral neuraminidase co-crystallized with substrate sialic acid, substrate-like DANA, and four inhibitors (oseltamivir, zanamivir, laninamivir, and peramivir). As a result, ligand-receptor interactions were modeled, and those necessary for binding were utilized as screen filters. Prospective virtual screening (VS) was carried out in a virtual chemical library of over half a million small organic substances. Orderly filtered moieties were investigated based on 2D- and 3D-predicted binding fingerprints disregarding the "rule-of-five" for drug likeness, and followed by docking and ADMET profiling. Two-dimensional and three-dimensional screening were supervised after enriching the dataset with known reference drugs and decoys. All 2D, 3D, and 4D procedures were calibrated before execution, and were then validated. Presently, two top-ranked substances underwent successful patent filing. In addition, the study demonstrates how to work around reported VS pitfalls in detail.

Detecting the Neuraminidase R294K Mutation in Avian Influenza A (H7N9) Virus Using Reverse Transcription Droplet Digital PCR Method

The R294K mutation in neuraminidase (NA) causes resistance to oseltamivir in the avian influenza virus H7N9. Reverse transcription droplet digital polymerase chain reaction (RT-dd PCR) is a novel technique for detecting single-nucleotide polymorphisms. This study aimed to develop an RT-dd PCR method for detecting the R294K mutation in H7N9. Primers and dual probes were designed using the H7N9 NA gene and the annealing temperature was optimized at 58.0 °C. The sensitivity of our RT-dd PCR method was not significantly different from that of RT-qPCR (p = 0.625), but it could specifically detect R294 and 294K in H7N9. Among 89 clinical samples, 2 showed the R294K mutation. These two strains were evaluated using a neuraminidase inhibition test, which revealed that their sensitivity to oseltamivir was greatly reduced. The sensitivity and specificity of RT-dd PCR were similar to those of RT-qPCR and its accuracy was comparable to that of NGS. The RT-dd PCR method had the advantages of absolute quantitation, eliminating the need for a calibration standard curve, and being simpler in both experimental operation and result interpretation than NGS. Therefore, this RT-dd PCR method can be used to quantitatively detect the R294K mutation in H7N9.

A systemic review on medicinal plants and their bioactive constituents against avian influenza and further confirmation through in-silico analysis

Background

Avian influenza or more commonly known as bird flu is a widespread infectious disease in poultry. This review aims to accumulate information of different natural plant sources that can aid in combating this disease. Influenza virus (IV) is known for its ability to mutate and infect different species (including humans) and cause fatal consequences.

Methods

Total 33 plants and 4 natural compounds were identified and documented. Molecular docking was performed against the target viral protein neuraminidase (NA), with some plant based natural compounds and compared their results with standard drugs Oseltamivir and Zanamivir to obtain novel drug targets for influenza in chickens.

Results

It was seen that most extracts exhibit their action by interacting with viral hemagglutinin or neuraminidase and inhibit viral entry or release from the host cell. Some plants also interacted with the viral RNA replication or by reducing proinflammatory cytokines. Ethanol was mostly used for extraction. Among all the plants Theobroma cacao, Capparis Sinaica Veil, Androgarphis paniculate, Thallasodendron cillatum, Sinularia candidula, Larcifomes officinalis, Lenzites betulina, Datronia molis, Trametes gibbose exhibited their activity with least concentration (below 10 μg/ml). The dockings results showed that some natural compounds (5,7- dimethoxyflavone, Aloe emodin, Anthocyanins, Quercetin, Hemanthamine, Lyocrine, Terpenoid EA showed satisfactory binding affinity and binding specificity with viral neuraminidase compared to the synthetic drugs.

Conclusion

This review clusters up to date information of effective herbal plants to bolster future influenza treatment research in chickens. The in-silico analysis also suggests some potential targets for future drug development but these require more clinical analysis.

pH Regulates Ligand Binding to an Enzyme Active Site by Modulating Intermediate Populations

Understanding the mechanism of ligands binding to their protein targets and the influence of various factors governing the binding thermodynamics is essential for rational drug design. The solution pH is one of the critical factors that can influence ligand binding to a protein cavity, especially in enzymes whose function is sensitive to the pH. Using computer simulations, we studied the pH effect on the binding of a guanidinium ion (Gdm⁺) to the active site of hen egg-white lysozyme (HEWL). HEWL serves as a model system for enzymes with two acidic residues in the active site and ligands with Gdm⁺ moieties, which can bind to the active sites of such enzymes and are present in several approved drugs treating various disorders. The computed free energy surface (FES) shows that Gdm⁺ binds to the HEWL active site using two dominant binding pathways populating multiple intermediates. We show that the residues close to the active site that can anchor the ligand could play a critical role in ligand binding. Using a Markov state model, we quantified the lifetimes and kinetic pathways connecting the different states in the FES. The protonation and deprotonation of the acidic residues in the active site in response to the pH change strongly influence the Gdm⁺ binding. There is a sharp jump in the ligand-binding rate constant when the pH approaches the largest pK_a of the acidic residue present in the active site. The simulations reveal that, at most, three Gdm⁺ can bind at the active site, with the Gdm⁺ bound in the cavity of the active site acting as a scaffold for the other two Gdm⁺ ions binding. These results can aid in providing greater insights into designing novel molecules containing Gdm⁺ moieties that can have high binding affinities to inhibit the function of enzymes with acidic residues in their active site.

Structural and inhibitor sensitivity analysis of influenza B-like viral neuraminidases derived from Asiatic toad and spiny eel

Influenza virus neuraminidase (NA) is an important target for antiviral development because it plays a crucial role in releasing newly assembled viruses. Two unique influenza-like virus genomes were recently reported in the Wuhan Asiatic toad and Wuhan spiny eel. Their NA genes appear to be highly divergent from all known influenza NAs, raising key questions as to whether the Asiatic toad influenza-like virus NA (tNA) and spiny eel NA (eNA) have canonical NA activities and structures and whether they show sensitivity to NA inhibitors (NAIs). Here, we found that both tNA and eNA have neuraminidase activities. A detailed structural analysis revealed that tNA and eNA present similar overall structures to currently known NAs, with a conserved calcium binding site. Inhibition assays indicated that tNA is resistant to NAIs, while eNA is still sensitive to NAIs. E119 is conserved in canonical NAs. The P119E substitution in tNA can restore sensitivity to NAIs, and, in contrast, the E119P substitution in eNA decreased its sensitivity to NAIs. The structures of NA-inhibitor complexes further provide a detailed insight into NA-inhibitor interactions at the atomic level. Moreover, tNA and eNA have unique N-glycosylation sites compared with canonical NAs. Collectively, the structural features, NA activities, and sensitivities to NAIs suggest that fish- and amphibian-derived influenza-like viruses may circulate in these vertebrates. More attention should be paid to these influenza-like viruses because their NA molecules may play roles in the emergence of NAI resistance.

In Silico Studies Reveal Peramivir and Zanamivir as an Optimal Drug Treatment Even If H7N9 Avian Type Influenza Virus Acquires Further Resistance

An epidemic of avian type H7N9 influenza virus, which took place in China in 2013, was enhanced by a naturally occurring R294K mutation resistant against Oseltamivir at the catalytic site of the neuraminidase. To cope with such drug-resistant neuraminidase mutations, we applied the molecular docking technique to evaluate the fitness of the available drugs such as Oseltamivir, Zanamivir, Peramivir, Laninamivir, L-Arginine and Benserazide hydrochloride concerning the N9 enzyme with single (R294K, R119K, R372K), double (R119_294K, R119_372K, R294_372K) and triple (R119_294_372K) mutations in the pocket. We found that the drugs Peramivir and Zanamivir score best amongst the studied compounds, demonstrating their high binding potential towards the pockets with the considered mutations. Despite the fact that mutations changed the shape of the pocket and reduced the binding strength for all drugs, Peramivir was the only drug that formed interactions with the key residues at positions 119, 294 and 372 in the pocket of the triple N9 mutant, while Zanamivir demonstrated the lowest RMSD value (0.7 Å) with respect to the reference structure.

Impact of the R292K Mutation on Influenza A (H7N9) Virus Resistance towards Peramivir: A Molecular Dynamics Perspective

In March 2013, a novel avian influenza A (H7N9) virus emerged in China. By March 2021, it had infected more than 1500 people, raising concerns regarding its epidemic potential. Similar to the highly pathogenic H5N1 virus, the H7N9 virus causes severe pneumonia and acute respiratory distress syndrome in most patients. Moreover, genetic analysis showed that this avian H7N9 virus carries human adaptation markers in the hemagglutinin and polymerase basic 2 (PB2) genes associated with cross-species transmissibility. Clinical studies showed that a single mutation, neuraminidase (NA) R292K (N2 numbering), induces resistance to peramivir in the highly pathogenic H7N9 influenza A viruses. Therefore, to evaluate the risk for human public health and understand the possible source of drug resistance, we assessed the impact of the NA-R292K mutation on avian H7N9 virus resistance towards peramivir using various molecular dynamics approaches. We observed that the single point mutation led to a distorted peramivir orientation in the enzyme active site which, in turn, perturbed the inhibitor's binding. The R292K mutation induced a decrease in the interaction among neighboring amino acid residues when compared to its wild-type counterpart, as shown by the high degree of fluctuations in the radius of gyration. MM/GBSA calculations revealed that the mutation caused a decrease in the drug binding affinity by 17.28 kcal/mol when compared to the that for the wild-type enzyme. The mutation caused a distortion of hydrogen bond-mediated interactions with peramivir and increased the accessibility of water molecules around the K292 mutated residue.

Emerging HxNy Influenza A Viruses

The continuous emergence and reemergence of diverse subtypes of influenza A viruses, which are known as "HxNy" and are mediated through the reassortment of viral genomes, account for seasonal epidemics, occasional pandemics, and zoonotic outbreaks. We summarize and discuss the characteristics of historic human pandemic HxNy viruses and diverse subtypes of HxNy among wild birds, mammals, and live poultry markets. In addition, we summarize the key molecular features of emerging infectious HxNy influenza viruses from the perspectives of the receptor binding of Hx, the inhibitor-binding specificities and drug-resistance features of Ny, and the matching of the gene segments. Our work enhances our understanding of the potential threats of novel reassortant influenza viruses to public health and provides recommendations for effective prevention, control, and research of this pathogen.

Substitution of I222L-E119V in neuraminidase from highly pathogenic avian influenza H7N9 virus exhibited synergistic resistance effect to oseltamivir in mice

That the high frequency and good replication capacity of strains with reduced susceptibility to neuraminidase inhibitors (NAIs) in highly pathogenic avian influenza H7N9 (HPAI H7N9) virus made it a significance to further study its drug resistance. HPAI H7N9 viruses bearing NA I222L or E119V substitution and two mutations of I222L-E119V as well as their NAIs-sensitive counterpart were generated by reverse genetics for NA inhibition test and replication capability evaluation in vitro. The attenuated H7N9/PR8 recombinant viruses were developed to study the pathogenicity and drug resistance brought by the above substitutions to mice. The IC₅₀ fold change of oseltamivir to HPAI H7N9 with NA222L-119V is 306.34 times than that of its susceptible strain, and 3.5 times than the E119V mutant virus. HPAI H7N9 bearing NA222L-119V had good replication ability with peak value of more than 6log₁₀ TCID₅₀/ml in MDCK cells. H7N9/PR8 virus bearing NA222L-119V substitutions leaded to diffuse pneumonia, significant weight loss and fatality in mice. NA E119V made H7N9/PR8 virus resistant to oseltamivir, and I222L-E119V had synergistic resistance to oseltamivir in mice. Due to the good fitness of drug resistant strains of HPAI H7N9 virus, it is necessary to strengthen drug resistance surveillance and new drug research.

Risk of Environmental Exposure to H7N9 Influenza Virus via Airborne and Surface Routes in a Live Poultry Market in Hebei, China

Environmental transmission of viruses to humans has become an early warning for potential epidemic outbreaks, such as SARS-CoV-2 and influenza virus outbreaks. Recently, an H7N9 virus, A/environment/Hebei/621/2019 (H7N9), was isolated by environmental swabs from a live poultry market in Hebei, China. We found that this isolate could be transmitted by direct contact and aerosol in mammals. More importantly, after 5 passages in mice, the virus acquired two adaptive mutations, PB1-H115Q and B2-E627K, exhibiting increased virulence and aerosol transmissibility. These results suggest that this H7N9 virus might potentially be transmitted between humans through environmental or airborne routes.

Adaptation of influenza viruses to human airway receptors

Through annual epidemics and global pandemics, influenza A viruses (IAVs) remain a significant threat to human health as the leading cause of severe respiratory disease. Within the last century, four global pandemics have resulted from the introduction of novel IAVs into humans, with components of each originating from avian viruses. IAVs infect many avian species wherein they maintain a diverse natural reservoir, posing a risk to humans through the occasional emergence of novel strains with enhanced zoonotic potential. One natural barrier for transmission of avian IAVs into humans is the specificity of the receptor-binding protein, hemagglutinin (HA), which recognizes sialic-acid-containing glycans on host cells. HAs from human IAVs exhibit “human-type” receptor specificity, binding exclusively to glycans on cells lining the human airway where terminal sialic acids are attached in the α2-6 configuration (NeuAcα2-6Gal). In contrast, HAs from avian viruses exhibit specificity for “avian-type” α2-3-linked (NeuAcα2-3Gal) receptors and thus require adaptive mutations to bind human-type receptors. Since all human IAV pandemics can be traced to avian origins, there remains ever-present concern over emerging IAVs with human-adaptive potential that might lead to the next pandemic. This concern has been brought into focus through emergence of SARS-CoV-2, aligning both scientific and public attention to the threat of novel respiratory viruses from animal sources. In this review, we summarize receptor-binding adaptations underlying the emergence of all prior IAV pandemics in humans, maintenance and evolution of human-type receptor specificity in subsequent seasonal IAVs, and potential for future human-type receptor adaptation in novel avian HAs.

Avian-to-Human Receptor-Binding Adaptation of Avian H7N9 Influenza Virus Hemagglutinin

Since 2013, H7N9 avian influenza viruses (AIVs) have caused more than 1,600 human infections, posing a threat to public health. An emerging concern is whether H7N9 AIVs will cause pandemics among humans. Molecular analysis of hemagglutinin (HA), which is a critical determinant of interspecies transmission, shows that the current H7N9 AIVs are still dual-receptor tropic, indicating limited human-to-human transmission potency. Mutagenesis and structural studies reveal that a G186V substitution is sufficient for H7N9 AIVs to acquire human receptor-binding capacity, and a Q226L substitution would favor binding to both avian and human receptors only when paired with A138/V186/P221 hydrophobic residues. These data suggest a different evolutionary route of H7N9 viruses compared to other AIV-subtype HAs.

Profile and generation of reduced neuraminidase inhibitor susceptibility in highly pathogenic avian influenza H7N9 virus from human cases in Mainland of China, 2016-2019

Human infections with highly pathogenic avian influenza (HPAI) H7N9 virus were detected in late 2016. We examined the drug resistance profile of 30 HPAI H7N9 isolates from Mainland of China (2016-2019). Altogether, 23% (7/30) carried neuraminidase inhibitors (NAIs) - resistance mutations, and 13% (4/30) displayed reduced susceptibility to NAIs in neuraminidase (NA) inhibition test. An HPAI H7N9 reassortment virus we prepared was passaged with NAIs for 10 passages. Passage with zanamivir induced an E119G substitution in NA, whereas passage with oseltamivir induced R292K and E119V substitutions that simulated that seen in oseltamivir -treated HPAI H7N9 cases, indicating that the high frequency of resistant strains in the HPAI H7N9 isolates is related to NAIs use. In presence of NAIs, R238I, A146E, G151E and G234T substitutions were found in HA1 region of HA. No amino acid mutations were found in the internal genes of the recombinant virus.

Plasticity of the 340-Loop in Influenza Neuraminidase Offers New Insight for Antiviral Drug Development

The recently discovered 340-cavity in influenza neuraminidase (NA) N6 and N7 subtypes has introduced new possibilities for rational structure-based drug design. However, the plasticity of the 340-loop (residues 342–347) and the role of the 340-loop in NA activity and substrate binding have not been deeply exploited. Here, we investigate the mechanism of 340-cavity formation and demonstrate for the first time that seven of nine NA subtypes are able to adopt an open 340-cavity over 1.8 μs total molecular dynamics simulation time. The finding that the 340-loop plays a role in the sialic acid binding pathway suggests that the 340-cavity can function as a druggable pocket. Comparing the open and closed conformations of the 340-loop, the side chain orientation of residue 344 was found to govern the formation of the 340-cavity. Additionally, the conserved calcium ion was found to substantially influence the stability of the 340-loop. Our study provides dynamical evidence supporting the 340-cavity as a druggable hotspot at the atomic level and offers new structural insight in designing antiviral drugs.

Peramivir binding affinity with influenza A neuraminidase and research on its mutations using an induced-fit docking approach

Influenza A virus (IAV) has caused epidemic infections worldwide, with many strains resistant to inhibitors of a surface protein, neuraminidase (NA), due to point mutations on its structure. A novel NA inhibitor named peramivir was recently approved, but no exhaustive computational research regarding its binding affinity with wild-type and mutant NA has been conducted. In this study, a thorough investigation of IAV-NA PDB entries of 9 subtypes is described, providing a list of residues constituting the protein-ligand binding sites. The results of induced-fit docking approach point out key residues of wild-type NA participating in hydrogen bonds and/or ionic interactions with peramivir, among which Arg 368 is responsible for a peramivir-NA ionic interaction. Mutations on this residue greatly reduced the binding affinity of peramivir with NA, with 3 mutations R378Q, R378K and R378L (NA6) capable of deteriorating the docking performance of peramivir by over 50%. 200 compounds from 6-scaffolds were docked into these 3 mutant versions, revealing 18 compounds giving the most promising results. Among them, CMC-2012-7-1527-56 (benzoic acid scaffold, IC50 = 32 nM in inhibitory assays with IAV) is deemed the most potential inhibitor of mutant NA resisting both peramivir and zanamivir, and should be further investigated.

Source of oseltamivir resistance due to single E119D and double E119D/H274Y mutations in pdm09H1N1 influenza neuraminidase

Influenza epidemics are responsible for an average of 3-5 millions of severe cases and up to 500,000 deaths around the world. One of flu pandemic types is influenza A(H1N1)pdm09 virus (pdm09H1N1). Oseltamivir is the antiviral drug used to treat influenza targeting at neuraminidase (NA) located on the viral surface. Influenza virus undergoes high mutation rates and leads to drug resistance, and thus the development of more efficient drugs is required. In the present study, all-atom molecular dynamics simulations were applied to understand the oseltamivir resistance caused by the single E119D and double E119D/H274Y mutations on NA. The obtained results in terms of binding free energy and intermolecular interactions in the ligand-protein interface showed that the oseltamivir could not be well accommodated in the binding pocket of both NA mutants and the 150-loop moves out from oseltamivir as an "open" state. A greater number of water molecules accessible to the binding pocket could disrupt the oseltamivir binding with NA target as seen be high mobility of oseltamivir at the active site. Additionally, our finding could guide to the design and development of novel NA inhibitor drugs.

Evolutionary dynamics of the H7N9 avian influenza virus based on large-scale sequence analysis

Since 2013, epidemics caused by novel H7N9 avian influenza A viruses (AIVs) have become a considerable public health issue. This study investigated the evolution of these viruses at the population level. Compared to H7 and N9 before 2013, there were 18 and 24 substitutions in the majority of novel H7N9 AIVs, respectively. Nine of these in HA and six in NA were rare before 2013, and four of these in HA and two in NA displayed host tropism. S136(128)N and A143(135)V are located on the receptor binding sites of the HA1 subunit and might be important factors in determining the host species of novel H7N9 AIV. On an overall scale, the evolution of H7 and N9, both in terms of time distribution and host species, is under negative selection. However, both in HA and NA, several sites were under positive selection. In both the overall epidemics and the human-derived H7N9 AIVs, eight positive selection sites were identified in HA1, with some located within the known antigen epitopes or the receptor binding site(RBS) domain. This may induce variations in H7N9 AIV with positive selection. It is necessary to strengthen the surveillance of novel H7N9 AIVs, both in human and bird population to determine whether a new virus has emerged through selection pressure and to prevent future epidemics from occurring.

The evolution and characterization of influenza A(H7N9) virus under the selective pressure of peramivir

Human infection with H7N9 virus has provoked global public health concern due to the substantial morbidity and mortality. Neuraminidase inhibitors (NAIs) are used as first-line drugs to treat the infection. However, virus quasispecies can evolve rapidly under drug pressure, which may alter various biological characteristics of virus. Using an in vitro evolution platform and next-generation sequencing, we found the presence of peramivir led to changes to the dominant populations of the virus. Two important amino acid substitutions were identified in NA, I222T and H274Y, which caused reduced susceptibilities to oseltamivir or both oseltamivir and peramivir as confirmed by enzyme- and cell-based assays. The NA-H274Y variant showed decreased replicative fitness at the early stage of infection accompanied with impaired NA function. The quasispecies evolution of H7N9 virus and the potential emergence of these two variants should be closely monitored, which may guide the adjustment of antiviral strategies.

Rapid isolation of a potent human antibody against H7N9 influenza virus from an infected patient

Influenza virus A H7N9 remains a serious threat to public health due to the lack of effective vaccines and drugs. In this study, a neutralizing human antibody named 3L11 was rapidly isolated from the switched memory B cells of a patient infected with H7N9. The antibody 3L11 was encoded by the heavy-chain VH1-8 gene and the light-chain VL2-13 gene that had undergone somatic mutations, and conferred high affinity binding to H7N9 hemagglutinins (HAs). It promoted killing of infected cells by antibody-dependent cell-mediated cytotoxicity (ADCC). Epitope mapping by mass spectroscopy (MS) indicated that 3L11 bound to the peptide 149-175 of HAs that contained the 150-loop of the receptor-binding site (RBS). Additionally, the 3L11 escape strains had G151R (Gly¹⁵¹→Arg¹⁵¹) and S152P (Ser¹⁵²→Pro¹⁵²) mutations within a conserved antigenic site A near the RBS that were not observed in field strains. Importantly, 3L11 fully protected mice against a lethal H7N9 virus challenge, in both pre- and postexposure administration regimens. Altogether, this work demonstrates the feasibility of rapid isolation of neutralizing H7N9 antibodies from infected patients and provides a potential prophylactic and therapeutic agent against H7N9 viruses.

Highly pathogenic avian influenza H7N9 viruses with reduced susceptibility to neuraminidase inhibitors showed comparable replication capacity to their sensitive counterparts

BACKGROUND

Human infection with avian influenza H7N9 virus was first reported in 2013. Since the fifth epidemic, a highly pathogenic avian influenza (HPAI) H7N9 virus has emerged and caused 33 human infections. Several potential NAI resistance sites have been found in human cases. However, the drug susceptibility and replication ability of HPAI H7N9 virus with such substitutions have not yet been studied.

METHODS

Thirty-three HPAI H7N9 virus strains were isolated from human cases in China, and then sequences were analyzed to identify potential NAI resistance sites. Recombinant influenza viruses were generated to evaluate the effect of NA amino acid substitutions on NAI (oseltamivir or zanamivir) susceptibility and viral replication efficiency in MDCK cells.

RESULTS

Four potential NAI resistance sites, R292 K, E119V, A246T or H274Y, were screened. All four substitutions conferred either reduced or highly reduced susceptibility to oseltamivir or zanamivir. 292 K not only highly reduced the susceptibility of HPAI H7N9 to oseltamivir but also induced an increase in the IC50 of zanamivir. 119 V or 274Y conferred reduced susceptibility of HPAI H7N9 to oseltamivir. Additionally, 246 T conferred reduced susceptibility to zanamivir. All tested NAI-resistant viruses were capable of replication in MDCK cells. The virus yields of rg006-NA292K were lower than those of rg006-NA292R at 24, 48, 72 and 96 h postinfection (P<0.05). Rg006-NA119V, rg006-NA246T or rg006-NA274Y showed comparable replication capacity to wild-type virus (except for rg006-NA274Y at 96 h, P<0.05).

CONCLUSIONS

All 4 amino acid substitutions (R292 K, E119V, A246T or H274Y) in NA reduced the susceptibility of HPAI H7N9 to NAIs. The NAI-resistant mutations in HPAI H7N9, in most cases, did not reduce the replication ability of the virus in mammalian cells. Special attention needs to be paid to these mutations, and the development of new anti-H7N9 drugs is of great importance.

Diverse biological characteristics and varied virulence of H7N9 from Wave 5

There was a substantial increase with infections of H7N9 avian influenza virus (AIV) in humans during Wave 5 (2016-2017). To investigate whether H7N9 had become more infectious/transmissible and pathogenic overall, we characterized the receptor binding and experimentally infected ferrets with highly pathogenic (HP)- and low pathogenic (LP)-H7N9 isolates selected from Wave 5, and compared their pathogenicity and transmissibility with a Wave 1 isolate from 2013. Studies show that A/Anhui/1/2013 (LP) and A/Chicken/Heyuan/16876/2016 (HP) were highly virulent in ferrets, A/Guangdong/Th008/2017 (HP) and A/Chicken/Huizhou/HZ-3/2017 (HP) had moderate virulence and A/Shenzhen/Th001/2016 (LP) was of low virulence in ferrets. Transmission was observed only in ferrets infected with A/Anhui/1/2013 and A/Chicken/Heyuan/16876/2016, consistent with the idea that sicker ferrets had a higher probability to transmit virus to naive animals. Given the Varied virulence and transmissibility observed in circulating H7N9 viruses from Wave 5, we conclude that the current public health risk of H7N9 has not substantially increased compared to 2013 and the circulating viruses are quite diverse.

Efficacy and safety of Chou-Ling-Dan granules in the treatment of seasonal influenza via combining Western and traditional Chinese medicine: protocol for a multicentre, randomised controlled clinical trial

INTRODUCTION

Chou-Ling-Dan (CLD) (Laggerapterodonta) granules are an ethnic herbal medicine from Yunnan province of China. CLD granules have been used for the treatment of inflammatory conditions and feverish diseases in China, including seasonal influenza, but few evidence-based medicine (EBM) clinical studies have been conducted to assess its efficacy and safety in the treatment of influenza. Here, we performed an EBM clinical trial combining Western Chinese medicine and traditional Chinese medicine (TCM) evaluation systems to evaluate the efficacy and safety of CLD granules in the treatment of seasonal influenza.

METHODS AND ANALYSIS

The study is designed as a multicentre, randomised, double-blinded, double-simulation, oseltamivir-controlled and placebo-controlled, parallel-design clinical trial. Eligible subjects (n=318) will be allocated after satisfying the criteria (Western medicine). Subjects will be randomised to receive CLD granules, oseltamivir, or a placebo for 5 days of treatment and with follow-up after treatment to record symptoms and signs and to collect pharyngeal/throat swabs and serum samples for detecting the virus and antibodies. At the same time, the syndrome differentiation criteria of TCM, such as tongue body, furred tongue and type of pulse, will be recorded as determined by doctors of both Western and Chinese medicine. Participants will be instructed to comply with the protocol and to keep a daily record of symptoms. The primary and secondary outcomes and safety indicators will be used to evaluate the efficacy and safety of CLD granules in the treatment of seasonal influenza based on both Western Chinese medicine and TCM evaluation systems.

ETHICS AND DISSEMINATION

The CLD granules clinical trial will be conducted in accordance with the Declaration of Helsinki and Good Clinical Practice and has been approved by the Ethics Committee of the First Affiliated Hospital of Guangzhou Medical University. All participants must provide written informed consent. The results obtained will be disseminated at international medical conferences and in peer-reviewed publications.

TRIAL REGISTRATION NUMBER

NCT02662426; Pre-results.

Comparison between human infections caused by highly and low pathogenic H7N9 avian influenza viruses in Wave Five: Clinical and virological findings

OBJECTIVE

The newly emerged highly pathogenic (HP) H7N9 avian influenza virus during Wave Five has caused 28 human infections, while differences in disease severity between low pathogenic (LP)- and HP-H7N9 human infections remain unclear.

METHODS

Clinical data, concentrations of serum cytokines, dynamics of virus shedding and PaO₂/FiO₂ from patients infected with LP-H7N9 (n = 7, LP group) and HP-H7N9 (n = 5, HP group) viruses during Wave Five were compared. In addition, critical mutations associated with H7N9 virulence in mammal/human were analyzed.

RESULTS

Lymphopenia, elevated aspartate aminotransferase, alanine aminotransferase, C-reactive protein and lactate dehydrogenase were common features, with higher incidences of leukopenia and thrombocytopenia in the LP group. The acute phase of both groups was accompanied with elevated cytokines associated with disease severity, including MIF, MCP-1 and IP-10. Diffuse exudation of the lungs and consolidation were observed from all patients. The dynamics of virus shedding and PaO₂/FiO₂ were similar between both groups. Notably, a higher prevalence of neuraminidase inhibitors (NAIs) resistance in the HP-H7N9 virus was found.

CONCLUSIONS

Our results indicate that this newly emerged HP-H7N9 virus caused similar disease severity in humans compared with LP-H7N9 virus, while higher case fatality rate and prevalence of NAI-resistance in human HP-H7N9 infections were of great concern.

Risk Assessment of Fifth-Wave H7N9 Influenza A Viruses in Mammalian Models

The fifth wave of the H7N9 influenza epidemic in China was distinguished by a sudden increase in human infections, an extended geographic distribution, and the emergence of highly pathogenic avian influenza (HPAI) viruses. Genetically, some H7N9 viruses from the fifth wave have acquired novel amino acid changes at positions involved in mammalian adaptation, antigenicity, and hemagglutinin cleavability. Here, several human low-pathogenic avian influenza (LPAI) and HPAI H7N9 virus isolates from the fifth epidemic wave were assessed for their pathogenicity and transmissibility in mammalian models, as well as their ability to replicate in human airway epithelial cells. We found that an LPAI virus exhibited a similar capacity to replicate and cause disease in two animal species as viruses from previous waves. In contrast, HPAI H7N9 viruses possessed enhanced virulence, causing greater lethargy and mortality, with an extended tropism for brain tissues in both ferret and mouse models. These HPAI viruses also showed signs of adaptation to mammalian hosts by acquiring the ability to fuse at a lower pH threshold than other H7N9 viruses. All of the fifth-wave H7N9 viruses were able to transmit among cohoused ferrets but exhibited a limited capacity to transmit by respiratory droplets, and deep sequencing analysis revealed that the H7N9 viruses sampled after transmission showed a reduced amount of minor variants. Taken together, we conclude that the fifth-wave HPAI H7N9 viruses have gained the ability to cause enhanced disease in mammalian models and with further adaptation may acquire the ability to cause an H7N9 pandemic.IMPORTANCE The potential pandemic risk posed by avian influenza H7N9 viruses was heightened during the fifth epidemic wave in China due to the sudden increase in the number of human infections and the emergence of antigenically distinct LPAI and HPAI H7N9 viruses. In this study, a group of fifth-wave HPAI and LPAI viruses was evaluated for its ability to infect, cause disease, and transmit in small-animal models. The ability of HPAI H7N9 viruses to cause more severe disease and to replicate in brain tissues in animal models as well as their ability to fuse at a lower pH threshold than LPAI H7N9 viruses suggests that the fifth-wave H7N9 viruses have evolved to acquire novel traits with the potential to pose a higher risk to humans. Although the fifth-wave H7N9 viruses have not yet gained the ability to transmit efficiently by air, continuous surveillance and risk assessment remain essential parts of our pandemic preparedness efforts.

Development of a quadruple qRT-PCR assay for simultaneous identification of highly and low pathogenic H7N9 avian influenza viruses and characterization against oseltamivir resistance

Background

During the fifth wave of human H7N9 infections, a novel highly pathogenic (HP) H7N9 variant emerged with an insertion of multiple basic amino acids in the HA cleavage site. Moreover, a neuraminidase inhibitor (NAI) resistance (R292K in NA) mutation was found in H7N9 isolates from humans, poultry and the environment. In this study, we set out to develop and validate a multiplex quantitative reverse transcript polymerase chain reaction (qRT-PCR) to simultaneously detect the presence of H7N9 and further identify the HP and NAI-resistance mutations.

Methods

A quadruple qRT-PCR to simultaneously detect the presence of H7N9 and further identify the HP and NAI-resistance mutations was designed based on the analyses of the HA and NA genes of H7N9. This assay was further tested for specificity and sensitivity, and validated using clinical samples.

Results

The assay was highly specific and able to detect low pathogenic (LP)- or HP-H7N9 with/without the NAI-resistance mutation. The detection limit of the assay was determined to be 50 genome-equivalent copies and 2.8 × 10^− 3 50% tissue culture infectious doses (TCID₅₀) of live H7N9 per reaction. Clinical validation was confirmed by commercial kits and Sanger sequencing with ten clinical samples.

Conclusions

We developed and validated a rapid, single-reaction, one-step, quadruple real-time qRT-PCR to simultaneously detect the presence of H7N9 and further identify the HP- and NAI-resistance strains with excellent performance in specificity and sensitivity. This assay could be used to monitor the evolution of H7N9 viruses in the laboratory, field and the clinic for early-warning and the prevention of H7N9 infections.

New Threats from H7N9 Influenza Virus: Spread and Evolution of High- and Low-Pathogenicity Variants with High Genomic Diversity in Wave Five

H7N9 virus has caused five infection waves since it emerged in 2013. The highest number of human cases was seen in wave 5; however, the underlying reasons have not been thoroughly elucidated. In this study, the geographical distribution, phylogeny, and genetic evolution of 240 H7N9 viruses in wave 5, including 35 new isolates from patients and poultry in nine provinces, were comprehensively analyzed together with strains from first four waves. Geographical distribution analysis indicated that the newly emerging highly pathogenic (HP) and low-pathogenicity (LP) H7N9 viruses were cocirculating, causing human and poultry infections across China. Genetic analysis indicated that dynamic reassortment of the internal genes among LP-H7N9/H9N2/H6Ny and HP-H7N9, as well as of the surface genes, between the Yangtze and Pearl River Delta lineages resulted in at least 36 genotypes, with three major genotypes (G1 [A/chicken/Jiangsu/SC537/2013-like], G3 [A/Chicken/Zhongshan/ZS/2017-like], and G11 [A/Anhui/40094/2015-like]). The HP-H7N9 genotype likely evolved from G1 LP-H7N9 by the insertion of a KRTA motif at the cleavage site (CS) and then evolved into 15 genotypes with four different CS motifs, including PKGKRTAR/G, PKGKRIAR/G, PKRKRAAR/G, and PKRKRTAR/G. Approximately 46% (28/61) of HP strains belonged to G3. Importantly, neuraminidase (NA) inhibitor (NAI) resistance (R292K in NA) and mammalian adaptation (e.g., E627K and A588V in PB2) mutations were found in a few non-human-derived HP-H7N9 strains. In summary, the enhanced prevalence and diverse genetic characteristics that occurred with mammalian-adapted and NAI-resistant mutations may have contributed to increased numbers of human infections in wave 5.IMPORTANCE The highest numbers of human H7N9 infections were observed during wave 5 from October 2016 to September 2017. Our results showed that HP-H7N9 and LP-H7N9 had spread virtually throughout China and underwent dynamic reassortment with different subtypes (H7N9/H9N2 and H6Ny) and lineages (Yangtze and Pearl River Delta lineages), resulting in totals of 36 and 3 major genotypes, respectively. Notably, the NAI drug-resistant (R292K in NA) and mammalian-adapted (e.g., E627K in PB2) mutations were found in HP-H7N9 not only from human isolates but also from poultry and environmental isolates, indicating increased risks for human infections. The broad dissemination of LP- and HP-H7N9 with high levels of genetic diversity and host adaptation and drug-resistant mutations likely accounted for the sharp increases in the number of human infections during wave 5. Therefore, more strategies are needed against the further spread and damage of H7N9 in the world.

Convergent Evolution of Human-Isolated H7N9 Avian Influenza A Viruses

BACKGROUND

Avian influenza A virus H7N9 has caused 5 epidemic waves of human infections in China since 2013. Avian influenza A viruses may face strong selection to adapt to novel conditions when establishing themselves in humans. In this study, we sought to determine whether adaptive evolution had occurred in human-isolated H7N9 viruses.

METHODS

We evaluated all available genomes of H7N9 avian influenza A virus. Maximum likelihood trees were separately reconstructed for all 8 genes. Signals of positive selection and convergent evolution were then detected on branches that lead to changes in host tropism (from avian to human).

RESULTS

We found that 3 genes had significant signals of positive selection (all of them P < .05). In addition, we detected 34 sites having significant signals for parallel evolution in 8 genes (all of them P < .05), including 7 well-known sites (Q591K, E627K, and D701N in PB2 gene; R156K, V202A, and L244Q in HA; and R289K in NA) that play roles in crossing species barriers for avian influenza A viruses.

CONCLUSION

Our study suggests that, during infection in humans, H7N9 viruses have undergone adaptive evolution to adapt to their new host environment and that the sites where parallel evolution occurred might play roles in crossing species barriers and respond to the new selection pressures arising from their new host environments.

The inhibitory effect of sodium baicalin on oseltamivir-resistant influenza A virus via reduction of neuraminidase activity

Baicalin was identified as a neuraminidase (NA) inhibitor displaying anti-influenza A virus (IAV) activity. However, its poor solubility in saline has limited its use in the clinic. We generated sodium baicalin and showed that it exhibited greatly increased solubility in saline. Its efficacy against oseltamivir-resistant mutant A/FM/1/47-H275Y (H1N1-H275Y) was evaluated in vitro and in vivo. Results showed that 10 μM of sodium baicalin inhibited A/FM/1/47 (H1N1), A/Beijing/32/92 (H3N2) and H1N1-H275Y in MDCK cells in a dose-dependent manner, with inhibitory rates of 83.9, 75.9 and 47.7%, respectively. Intravenous administration of sodium baicalin at 100 mg/kg/d enabled the survival of 20% of H1N1-H275Y-infected mice. The treatment alleviated body weight loss and lung injury. Moreover, sodium baicalin exerted a clear inhibitory effect on NAs. The IC₅₀ values of sodium baicalin against H1N1-H275Y and cells-expressing A/Anhui/1/2013-R294K (H7N9-R294K) NA protein (N9-R294K) were 214.4 μM and 216.3 μM. Direct interactions between sodium baicalin and NA were observed, and we simulated the interactions of sodium baicalin with N9-R294K and N9 near the active sites of OC-N9-R294K and OC-N9. The residues responsible for the sodium baicalin-N9-R294K and sodium baicalin-N9 interactions were the same, confirming that sodium baicalin exerts effects on wild-type and oseltamivir-resistant viral strains.

220 mutation in the hemagglutinin of avian influenza A (H7N9) virus alters antigenicity during vaccine strain development

Since the first confirmed case of H7N9 infection was reported in China, there have been five epidemic waves of human H7N9 infections between 2013 and 2017. The fifth wave differed from the previous four waves in that highly pathogenic avian influenza (HPAI) H7N9 viruses with multiple basic amino acids at the cleavage site were detected in humans, poultry and environmental samples. The HPAI H7N9 viruses were genetically and antigenically distinct from previous H7N9 viruses. Therefore, a new candidate vaccine virus(CVV) derived from a HPAI A/Guangdong/17SF003/2016-like virus was proposed by the World Health Organization(WHO). According to the WHO recommendations, we constructed a new CVV using reverse genetic technology, with a (6+2) gene constitution. The (6+2) reassortant virus possessed hemagglutinin(HA) with multiple basic amino acids removed and the neuraminidase from A/Guangdong/SF003/2016 in a high-yield A/Puerto Rico/8/34 virus backbone. Sequence analysis confirmed that no mutations had occurred in the HA of V1E1(the initial CVV rescued in Vero cells and followed by passage in eggs), but a mixture of arginine (R)/glycine (G)/isoleucine (I) was detected at position 220 (H3 numbering) in the HA of V1E2 to V1E5 with different percentages. Furthermore, V1E5 showed improved growth characteristics and immunogenicity compared with V1E1, and retained low pathogenicity in chickens and chicken embryos, but the mutation changed its antigenicity. Our study indicates that antigenic changes should be closely monitored during the development of H7N9 CVV in eggs. Additionally, although V1E5 changes the antigenicity, the antisera had some reactivity to previous H7N9 CVVs.

Exploration of the 150 cavity and the role of serendipity in the discovery of inhibitors of influenza virus A neuraminidase

Influenza pandemics are an ongoing threat for the human population, as the avian influenza viruses H5N1 and H7N9 continue to circulate in the bird population and the chance of avian to human transmission increases. Neuraminidase, a glycoprotein located on the surface of the influenza virus, plays a crucial role in the viral replication process and, hence, has proven to be a useful target enzyme for the treatment of influenza infections. The discovery that certain subtypes of influenza neuraminidase have an additional cavity, the 150 cavity, near the substrate binding site has triggered considerable interest in the design of influenza inhibitors that exploit this feature. Currently available antiviral drugs, neuraminidase inhibitors oseltamivir and zanamivir, were designed using crystal structures predating this discovery by some years. This mini review is aimed at summarizing our group’s efforts, together with related work from other groups, on neuraminidase inhibitors that are designed to exploit both the catalytic site and the 150 cavity. The design of a parent scaffold that yields a potent inhibitor that is active in cell culture assays and retains activity against several neuraminidases from mutant strains is also described. Finally, the role of serendipity in the discovery of a new class of potent neuraminidase inhibitors with a novel spirolactam scaffold is also highlighted.

Emergence and Adaptation of a Novel Highly Pathogenic H7N9 Influenza Virus in Birds and Humans from a 2013 Human-Infecting Low-Pathogenic Ancestor

Since its emergence in 2013, the H7N9 low-pathogenic avian influenza virus (LPAIV) has been circulating in domestic poultry in China, causing five waves of human infections. A novel H7N9 highly pathogenic avian influenza virus (HPAIV) variant possessing multiple basic amino acids at the cleavage site of the hemagglutinin (HA) protein was first reported in two cases of human infection in January 2017. More seriously, those novel H7N9 HPAIV variants have been transmitted and caused outbreaks on poultry farms in eight provinces in China. Herein, we demonstrate the presence of three different amino acid motifs at the cleavage sites of these HPAIV variants which were isolated from chickens and humans and likely evolved from the preexisting LPAIVs. Animal experiments showed that these novel H7N9 HPAIV variants are both highly pathogenic in chickens and lethal to mice. Notably, human-origin viruses were more pathogenic in mice than avian viruses, and the mutations in the PB2 gene associated with adaptation to mammals (E627K, A588V, and D701N) were identified by next-generation sequencing (NGS) and Sanger sequencing of the isolates from infected mice. No polymorphisms in the key amino acid substitutions of PB2 and HA in isolates from infected chicken lungs were detected by NGS. In sum, these results highlight the high degree of pathogenicity and the valid transmissibility of this new H7N9 variant in chickens and the quick adaptation of this new H7N9 variant to mammals, so the risk should be evaluated and more attention should be paid to this variant.IMPORTANCE Due to the recent increased numbers of zoonotic infections in poultry and persistent human infections in China, influenza A(H7N9) virus has remained a public health threat. Most of the influenza A(H7N9) viruses reported previously have been of low pathogenicity. Now, these novel H7N9 HPAIV variants have caused human infections in three provinces and outbreaks on poultry farms in eight provinces in China. We analyzed the molecular features and compared the relative characteristics of one H7N9 LPAIV and two H7N9 HPAIVs isolated from chickens and two human-origin H7N9 HPAIVs in chicken and mouse models. We found that all HPAIVs both are highly pathogenic and have valid transmissibility in chickens. Strikingly, the human-origin viruses were more highly pathogenic than the avian-origin viruses in mice, and dynamic mutations were confirmed by NGS and Sanger sequencing. Our findings offer important insight into the origin, adaptation, pathogenicity, and transmissibility of these viruses to both poultry and mammals.

Synthesis and biological evaluation of NH2-acyl oseltamivir analogues as potent neuraminidase inhibitors

Neuraminidase inhibitors can deter nascent viruses from infecting intact cells by preventing their release from host cells. Herein, a neuraminidase inhibitor 11b absent of basic moieties was discovered in the process of searching for inhibitors targeting 150 cavity. It exhibited potent inhibitions against wild-type neuraminidases from group 1 (H5N1 and H1N1) and group 2 (H7N9) subtypes with IC₅₀ values similar to those of oseltamivir carboxylate. Moreover, 11b showed moderate inhibitions against mutant neuraminidases from H5N1-H274Y and H1N1-H274Y with IC₅₀ values of 2075 nM and 1382 nM, which were inferior to those of oseltamivir carboxylate (6095 nM and 4071 nM). The results were not consistent with the recognized SARs that a basic moiety was an indispensable part of a potent inhibitor.

Drug Susceptibility Evaluation of an Influenza A(H7N9) Virus by Analyzing Recombinant Neuraminidase Proteins

Background

Neuraminidase (NA) inhibitors are the recommended antiviral medications for influenza treatment. However, their therapeutic efficacy can be compromised by NA changes that emerge naturally and/or following antiviral treatment. Knowledge of which molecular changes confer drug resistance of influenza A(H7N9) viruses (group 2NA) remains sparse.

Methods

Fourteen amino acid substitutions were introduced into the NA of A/Shanghai/2/2013(H7N9). Recombinant N9 (recN9) proteins were expressed in a baculovirus system in insect cells and tested using the Centers for Disease Control and Prevention standardized NA inhibition (NI) assay with oseltamivir, zanamivir, peramivir, and laninamivir. The wild-type N9 crystal structure was determined in complex with oseltamivir, zanamivir, or sialic acid, and structural analysis was performed.

Results

All substitutions conferred either reduced or highly reduced inhibition by at least 1 NA inhibitor; half of them caused reduced inhibition or highly reduced inhibition by all NA inhibitors. R292K conferred the highest increase in oseltamivir half-maximal inhibitory concentration (IC50), and E119D conferred the highest zanamivir IC50. Unlike N2 (another group 2NA), H274Y conferred highly reduced inhibition by oseltamivir. Additionally, R152K, a naturally occurring variation at the NA catalytic residue of A(H7N9) viruses, conferred reduced inhibition by laninamivir.

Conclusions

The recNA method is a valuable tool for assessing the effect of NA changes on drug susceptibility of emerging influenza viruses.

Evaluation of the absolute affinity of neuraminidase inhibitor using steered molecular dynamics simulations

The absolute free energy difference of binding (ΔG) between neuraminidase and its inhibitor was evaluated using fast pulling of ligand (FPL) method over steered molecular dynamics (SMD) simulations. The metric was computed through linear interaction approximation. Binding nature was described by free energy differences of electrostatic and van der Waals (vdW) interactions. The finding indicates that vdW metric is dominant over electrostatics in binding process. The computed values are in good agreement with experimental data with a correlation coefficient of R=0.82 and error of σΔG_exp=2.2kcal/mol. The results were observed using Amber99SB-ILDN force field in comparison with CHARMM27 and GROMOS96 43a1 force fields. Obtained results may stimulate the search for an Influenza therapy.

Synthesis of Sulfo-Sialic Acid Analogues: Potent Neuraminidase Inhibitors in Regards to Anomeric Functionality

The design, synthesis and application of N-acetylneuraminic acid-derived compounds bearing anomeric sulfo functional groups are described. These novel compounds, which we refer to as sulfo-sialic acid analogues, include 2-decarboxy-2-deoxy-2-sulfo-N-acetylneuraminic acid and its 4-deoxy-3,4-dehydrogenated pseudoglycal. While 2-decarboxy-2-deoxy-2-sulfo-N-acetylneuraminic acid contains no further modifications of the 2-deoxy-pyranose ring, it is still a more potent inhibitor of avian-origin H5N1 neuraminidase (NA) and drug-resistant His275Tyr NA as compared to the oxocarbenium ion transition state analogue 2,3-dehydro-2-deoxy-N-acetylneuraminic acid. The sulfo-sialic acid analogues described in this report are also more potent inhibitors of influenza NA (up to 40-fold) and bacterial NA (up to 8.5-fold) relative to the corresponding anomeric phosphonic acids. These results confirm that this novel anomeric sulfo modification offers great potential to improve the potency of next-generation NA inhibitors including covalent inhibitors.

Epidemiology, Evolution, and Pathogenesis of H7N9 Influenza Viruses in Five Epidemic Waves since 2013 in China

H7N9 influenza viruses were first isolated in 2013 and continue to cause human infections. H7N9 infections represent an ongoing public health threat that has resulted in 1344 cases with 511 deaths as of April 9, 2017. This highlights the continued threat posed by the current poultry trade and live poultry market system in China. Until now, there have been five H7N9 influenza epidemic waves in China; however, the steep increase in the number of humans infected with H7N9 viruses observed in the fifth wave, beginning in October 2016, the spread into western provinces, and the emergence of highly pathogenic (HP) H7N9 influenza outbreaks in chickens and infection in humans have caused domestic and international concern. In this review, we summarize and compare the different waves of H7N9 regarding their epidemiology, pathogenesis, evolution, and characteristic features, and speculate on factors behind the recent increase in the number of human cases and sudden outbreaks in chickens. The continuous evolution of the virus poses a long-term threat to public health and the poultry industry, and thus it is imperative to strengthen prevention and control strategies.

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.

Genesis, Evolution and Prevalence of H5N6 Avian Influenza Viruses in China

Constant surveillance of live poultry markets (LPMs) is currently the best way to predict and identify emerging avian influenza viruses (AIVs) that pose a potential threat to public health. Through surveillance of LPMs from 16 provinces and municipalities in China during 2014-2016, we identified 3,174 AIV-positive samples and isolated and sequenced 1,135 AIVs covering 31 subtypes. Our analysis shows that H5N6 has replaced H5N1 as one of the dominant AIV subtypes in southern China, especially in ducks. Phylogenetic analysis reveals that H5N6 arose from reassortments of H5 and H6N6 viruses, with the hemagglutinin and neuraminidase combinations being strongly lineage specific. H5N6 viruses constitute at least 34 distinct genotypes derived from various evolutionary pathways. Notably, genotype G1.2 virus, with internal genes from the chicken H9N2/H7N9 gene pool, was responsible for at least five human H5N6 infections. Our findings highlight H5N6 AIVs as potential threats to public health and agriculture.

Seeing is believing: anti-PD-1/PD-L1 monoclonal antibodies in action for checkpoint blockade tumor immunotherapy

Structural immunology, focusing on structures of host immune related molecules, enables the immunologists to see what the molecules look like, and more importantly, how they work together. Antibody-based PD-1/PD-L1 blockade therapy has achieved brilliant successes in clinical applications. The recent breakthrough of the complex structures of checkpoint blockade antibodies with their counterparts, pembrolizumab with PD-1 and avelumab with PD-L1, have made it clear how these monoclonal antibodies compete the binding of PD-1/PD-L1 and function to blockade the receptor-ligand interaction. Herein, we summarize the structural findings of these two reports and look into the future for how this information would facilitate the development of more efficient PD-1/PD-L1 targeting antibodies, small molecule drugs, and other protein or non-protein inhibitors.