Roles of the hemagglutinin of influenza A virus in viral entry and development of antiviral therapeutics and vaccines

Differential detection of H1N1 virus spiker proteins by two hexaphenylbutadiene isomers based on size-matching principle

As one of the high pathogenic influenza viruses, H1N1 virus easily induces to serious diseases, even leading to death. To date, all detection methods for H1N1 virus had shortcomings, including high equipment cost, time consumption, and etc. Therefore, a novel detection method should be established to achieve more convenient, rapid, and low-cost detection. In this work, an isomer of HPBmN-I with aggregation-induced emission characteristic was firstly synthesized on the basis of our previous reported HPBpN-I. The results showed that HPBmN-I only selectively binds to N1 in the presence of H1, while HPBpN-I can exhibit total fluorescence response to H1 and N1 in H1/N1 mixture. The limited of detection (LOD) of HPBmN-I to N1 was estimated to be 20.82 ng/mL in normal saline (NS) according to the IUPAC-based approach. The simulation calculations based on molecular docking revealed that four HPBmN-I molecules combine well with the hydrophobic cavity of N1 and achieve the fluorescence enhancement due to size matching with each other. The combination of HPBpN-I and HPBmN-I as probes was successfully used to quantitatively detect H1 and N1 in real H1N1 virus. Compared to enzyme-linked immunosorbent assay (ELISA) method, the established method not only showed the same detection accuracy but also had the advantages of real-time, ease of preparation, and low-cost, demonstrating potential market prospects.

Synthesis and pharmacodynamic evaluation of naphthalene derivatives against influenza A virus in vitro and in vivo

Influenza A virus is a highly mutable pathogenic pathogen that could cause a global pandemic. It is necessary to find new anti-influenza drugs to resist influenza epidemics due to the seasonal popularity of a certain area every year. Naphthalene derivatives had potential antiviral activity. A series of naphthalene derivatives were synthesized via the metal-free intramolecular hydroarylation reactions of alkynes. Evaluation of their biological efficacy showed that compound 2-aminonaphthalene 4d had better antiviral activity in vitro than ribavirin. By studying the mechanism of action of 2-aminonaphthalene 4din vivo and in vitro, we found that 4d had antiviral activity to three different subtype influenza viruses of A/Weiss/43 (H1N1), A/Virginia/ATCC2/2009 (H1N1) and A/California/2/2014 (H3N2). Compound 4d had the best effect after viral adsorption, and mainly played in the early stage of virus replication. 2-Aminonaphthalene 4d could reduce the replication of virus by inhibiting the NP and M proteins of virus. Compound 4d cut down ROS accumulation, autophagy and apoptosis induced by influenza virus. Inflammatory response mediated by RIG-1 pathway were suppressed in the cell and mice. In addition, the pathological changes of lung tissue and virus titer in mice were reduced by the administration of 4d. Therefore, naphthalene derivative 4d is a potential drug for the treatment of influenza A virus infection.

Synthesis of N-Acetyllactosamine and N-Acetyllactosamine-Based Bioactives

N-Acetyllactosamine (LacNAc) or more specifically β-d-galactopyranosyl-1,4-N-acetyl-d-glucosamine is a unique acyl-amino sugar and a key structural unit in human milk oligosaccharides, an antigen component of many glycoproteins, and an antiviral active component for the development of effective drugs against viruses. LacNAc is useful itself and as a basic building block for producing various bioactive oligosaccharides, notably because this synthesis may be used to add value to dairy lactose. Despite a significant amount of information in the literature on the benefits, structures, and types of different LacNAc-derived oligosaccharides, knowledge about their effective synthesis for large-scale production is still in its infancy. This work provides a comprehensive analysis of existing production strategies for LacNAc and important LacNAc-based structures, including sialylated LacNAc as well as poly- and oligo-LacNAc. We conclude that direct extraction from milk is too complex, while chemical synthesis is also impractical at an industrial scale. Microbial routes have application when multiple step reactions are needed, but the major route to large-scale biochemical production will likely lie with enzymatic routes, particularly those using β-galactosidases (for LacNAc synthesis), sialidases (for sialylated LacNAc synthesis), and β-N-acetylhexosaminidases (for oligo-LacNAc synthesis). Glycosyltransferases, especially for the biosynthesis of extended complex LacNAc structures, could also play a major role in the future. In these cases, immobilization of the enzyme can increase stability and reduce cost. Processing parameters, such as substrate concentration and purity, acceptor/donor ratio, water activity, and temperature, can affect product selectivity and yield. More work is needed to optimize these reaction parameters and in the development of robust, thermally stable enzymes to facilitate commercial production of these important bioactive substances.

Evolution of A(H1N1) pdm09 influenza virus masking by glycosylation

Introduction: As the pathogen that caused the first influenza virus pandemic in this century, the swine-origin A(H1N1) pdm09 influenza virus has caused continuous harm to human public health. The evolution of hemagglutinin protein glycosylation sites, including the increase in number and positional changes, is an important way for influenza viruses to escape host immune pressure. Based on the traditional influenza virus molecular monitoring, special attention should be paid to the influence of glycosylation evolution on the biological characteristics of virus antigenicity, transmission and pathogenicity. The epidemiological significance of glycosylation mutants should be analyzed as a predictive tool for early warning of new outbreaks and pandemics, as well as the design of vaccines and drug targets.Areas covered: We review on the evolutionary characteristics of glycosylation on the HA protein of the A(H1N1)pdm09 influenza virus in the last ten years.Expert opinion: We discuss the crucial impact of evolutionary glycosylation on the biological characteristics of the virus and the host immune responses, summarize studies revealing different roles of glycosylation play during host adaptation. Although these studies show the significance of glycosylation evolution in host-virus interaction, much remains to be discovered about the mechanism.

Intervention Strategies for Seasonal and Emerging Respiratory Viruses with Drugs and Vaccines Targeting Viral Surface Glycoproteins

Vaccines and therapeutics targeting viral surface glycoproteins are a major component of disease prevention for respiratory viral diseases. Over the years, vaccines have proven to be the most successful intervention for preventing disease. Technological advances in vaccine platforms that focus on viral surface glycoproteins have provided solutions for current and emerging pathogens like SARS-CoV-2, and our understanding of the structural basis for antibody neutralization is guiding the selection of other vaccine targets for respiratory viruses like RSV. This review discusses the role of viral surface glycoproteins in disease intervention approaches.

Development and Effects of Influenza Antiviral Drugs

Influenza virus is a highly contagious zoonotic respiratory disease that causes seasonal outbreaks each year and unpredictable pandemics occasionally with high morbidity and mortality rates, posing a great threat to public health worldwide. Besides the limited effect of vaccines, the problem is exacerbated by the lack of drugs with strong antiviral activity against all flu strains. Currently, there are two classes of antiviral drugs available that are chemosynthetic and approved against influenza A virus for prophylactic and therapeutic treatment, but the appearance of drug-resistant virus strains is a serious issue that strikes at the core of influenza control. There is therefore an urgent need to develop new antiviral drugs. Many reports have shown that the development of novel bioactive plant extracts and microbial extracts has significant advantages in influenza treatment. This paper comprehensively reviews the development and effects of chemosynthetic drugs, plant extracts, and microbial extracts with influenza antiviral activity, hoping to provide some references for novel antiviral drug design and promising alternative candidates for further anti-influenza drug development.

Specific Influenza Therapy: Current State and Prospects (Review)

Introduction. Respiratory infections are among the leaders in morbidity and mortality worldwide. The most severe cases of the disease are most often caused by the flu virus. Currently, there are many ways of specific prevention and treatment of influenza infection, but their effectiveness is far from ideal. This is due to the high variability of the influenza virus and the subsequent occurrence of resistance to the drugs used. In this regard, the improvement and development of antiviral drugs is an urgent task.

Text. Influenza virus is an RNA-containing virus that causes massive epidemics and pandemics. Specific influenza prophylaxis includes vaccination. However, antigenic variability of the virus reduces the effectiveness of the vaccine, which requires constant costly development of its more advanced modifications. Specific treatment for influenza infection includes several classes of drugs, such as neuraminidase (NA) inhibitors oseltamivir, zanamivir and M2 protein inhibitors amantadine, rimantadine. At one time, these drugs were quite effective. But the formed resistance of influenza viruses to these drugs requires the creation of new or modifications of existing antiviral agents. Among the new domestic developments of antiviral drugs, histidyl-1-adamantainethylamine, which is a modification of the rimantadine molecule, has shown sufficient antiviral activity at the stage of preclinical studies. A representative of another class of drugs is arbidol (umifenovir), an inhibitor of hemagglutinin (HA) of the influenza virus. According to studies, the drug has high profiles of efficacy and safety, but the recommendation of the World Health Organization is to continue clinical trials. Currently, clinical studies of new classes of drugs are underway – baloxavir marboxil and favipiravir. Baloxavir marboxyl is a prodrug that is converted in vivo to baloxavir, an inhibitor of cap-dependent endonuclease. Favipiravir is an inhibitor of RNA-dependent RNA polymerase. In vitro studies in cell culture and in vivo in laboratory animals have shown higher efficacy of these drugs than the above with minimal toxicity.

Conclusion. The rapid evolution of the influenza virus leads to a gradual decrease in the effectiveness of modern antiviral drugs. New compounds targeting targets important for virus reproduction are in clinical trials. The future of the fight against influenza depends on the outcome of these tests, according to which the compounds can become effective drugs for the prevention and treatment of influenza.

Zoonotic Potential of Influenza A Viruses: A Comprehensive Overview

Influenza A viruses (IAVs) possess a great zoonotic potential as they are able to infect different avian and mammalian animal hosts, from which they can be transmitted to humans. This is based on the ability of IAV to gradually change their genome by mutation or even reassemble their genome segments during co-infection of the host cell with different IAV strains, resulting in a high genetic diversity. Variants of circulating or newly emerging IAVs continue to trigger global health threats annually for both humans and animals. Here, we provide an introduction on IAVs, highlighting the mechanisms of viral evolution, the host spectrum, and the animal/human interface. Pathogenicity determinants of IAVs in mammals, with special emphasis on newly emerging IAVs with pandemic potential, are discussed. Finally, an overview is provided on various approaches for the prevention of human IAV infections.

A Combined NMR-Computational Study of the Interaction between Influenza Virus Hemagglutinin and Sialic Derivatives from Human and Avian Receptors on the Surface of Transfected Cells

The development of small-molecule inhibitors of influenza virus Hemagglutinin could be relevant to the opposition of the diffusion of new pandemic viruses. In this work, we made use of Nuclear Magnetic Resonance (NMR) spectroscopy to study the interaction between two derivatives of sialic acid, Neu5Ac-α-(2,6)-Gal-β-(1⁻4)-GlcNAc and Neu5Ac-α-(2,3)-Gal-β-(1⁻4)-GlcNAc, and hemagglutinin directly expressed on the surface of recombinant human cells. We analyzed the interaction of these trisaccharides with 293T cells transfected with the H5 and H1 variants of hemagglutinin, which thus retain their native trimeric conformation in such a realistic environment. By exploiting the magnetization transfer between the protein and the ligand, we obtained evidence of the binding event, and identified the epitope. We analyzed the conformational features of the glycans with an approach combining NMR spectroscopy and data-driven molecular dynamics simulations, thus obtaining useful information for an efficient drug design.

Cathepsin B plays a key role in optimal production of the influenza A virus

Background

Influenza A virus (IAV) is the etiologic agent of the febrile respiratory illness, commonly referred to as 'flu'. The lysosomal protease cathepsin B (CTSB) has shown to be involved in the lifecycle of various viruses. Here, we examined the role of CTSB in the IAV lifecycle.

Methods

CTSB-deficient (CTSB^-/-) macrophages and the human lung epithelial cell line A549 cells treated with CA-074Me were infected with the A/Puerto Rico/8/34 strain of IAV (IAV-PR8). Viral entry and propagation were measured through quantitative real-time RT-PCR; production and localization of hemagglutinin (HA) protein in the infected host cells were analysed by Western blots, flow cytometry and confocal microscopy; production of progeny viruses were measured by a hemagglutination assay.

Results

CTSB^-/- macrophages and CA-074Me-treated A549 cells had no defects in incorporating IAV-PR8 virions and permitting viral RNA synthesis. However, these cells produced significantly lower amounts of HA protein and progeny virions than wild-type or untreated cells.

Conclusion

These data indicate that CTSB is involved in the expression of IAV-PR8 HA protein and subsequent optimal production of IAV-PR8 progeny virions. Targeting CTSB can be a novel therapeutic strategy for treating IAV infection.

Potent influenza A virus entry inhibitors targeting a conserved region of hemagglutinin

Influenza A viruses (IAVs) induce acute respiratory disease and cause significant morbidity and mortality throughout the world. With the emergence of drug-resistant viral strains, new and effective anti-IAV drugs with different modes of action are urgently needed. In this study, by conjugating cholesterol to the N-terminus of the short peptide KKWK, a lipopeptide named S-KKWK was created. The anti-IAV test indicated that S-KKWK and its derivatives displayed potent antiviral activities against a broad variety of influenza A viral strains including oseltamivir-resistant strains and clinically relevant isolates with IC₅₀ values ranging from 0.7 to 3.0µM. An extensive mechanistic study showed that these peptides functioned as viral "entry blockers" by inhibiting the conformational rearrangements of HA2 subunit, thereby interrupting the fusion of virus-host cell membranes. Significantly, a computer-aided docking simulation and protein sequence alignment identified conserved residues in the stem region of HA2 as the possible binding site of S-KKWK, which may be employed as a potential drug target for designing anti-IAVs with a broad-spectrum of activity. By targeting this region, a potent anti-IAV agent was subsequently created. In addition, the anti-IAV activity of S-KKWK was assessed by experiments with influenza A virus-infected mice, in which S-KKWK reduced the mortality of infected animals and extended survival time significantly. Overall, in addition to providing a strategy for designing broad-spectrum anti-IAV agents, these results indicate that S-KKWK and its derivatives are prospective candidates for potent antivirals.

Recombinant Lactococcus lactis Expressing Haemagglutinin from a Polish Avian H5N1 Isolate and Its Immunological Effect in Preliminary Animal Trials

Lactic acid bacteria (LAB) are Gram-positive, nonpathogenic microorganisms that are gaining much interest as antigen producers for development of live vaccine vectors. Heterologous proteins of different origin have been successfully expressed in various LAB species, including Lactococcus lactis. Recombinant L. lactis strains have been shown to induce specific local and systemic immune responses against various antigens. Our study aimed at constructing a L. lactis strain expressing haemagglutinin of a Polish avian H5H1 influenza isolate and examining its effect on animals. Expression of the cloned H5 gene was achieved using the nisin-controlled gene expression system. Detection of the intracellular H5 antigen produced in L. lactis was performed by Western blot analysis and confirmed using mass spectrometry. The potential of L. lactis recombinant cells to induce an immune response was examined by setting up preliminary immunization trials on chickens and mice. Obtained sera were tested for specific antibodies by ELISA assays. The results of these studies are a promising step toward developing a vaccine against the bird flu using Lactococcus lactis cells as bioreactors for efficient antigen production and delivery to the mucosal surface.

Investigational hemagglutinin-targeted influenza virus inhibitors

INTRODUCTION

Seasonal influenza and pandemic outbreaks typically result in high mortality and morbidity associated with severe economic burdens. Vaccines and anti-influenza drugs have made great contributions to control the infection. However, antigenic drifts and shifts allow influenza viruses to easily escape immune neutralization and antiviral drug activity. Hemagglutinin (HA)is an important envelope protein for the entry of influenza viruses into host cells, thus, HA-targeted agents may be potential anti-influenza drugs. Areas covered: In this review, we describe arbidol, a unique licensed drug targeting HA; discuss and summarize HA-targeted anti-influenza agents been tested before or being tested currently in clinical trials, including monoclonal antibodies, small molecule inhibitors, proteins and peptides. Other small molecule inhibitors are also briefly introduced. Expert opinion: Exploring new clinical applications for existing drugs can provide additional anti-influenza candidates with promising safety and bioavailability, and largely shortened time and costs. To enhance therapeutic efficacy and avoid drug-resistance, combination therapy involving in HA-targeted anti-influenza agent is reasonable and attractive. For drug discovery, it is helpful to keep an eye on the development of methodology in organic synthesis and probe into the co-crystal structure of HA in complex with small molecule.

3DFlu: database of sequence and structural variability of the influenza hemagglutinin at population scale

The influenza virus type A (IVA) is an important pathogen which is able to cause annual epidemics and even pandemics. This fact is the consequence of the antigenic shifts and drifts capabilities of IVA, caused by the high mutation rate and the reassortment capabilities of the virus. The hemagglutinin (HA) protein constitutes the main IVA antigen and has a crucial role in the infection mechanism, being responsible for the recognition of host-specific sialic acid derivatives. Despite the relative abundance of HA sequence and serological studies, comparative structure-based analysis of HA are less investigated. The 3DFlu database contains well annotated HA representatives: 1192 models and 263 crystallographic structures. The relations between these proteins are defined using different metrics and are visualized as a network in the provided web interface. Moreover structural and sequence comparison of the proteins can be explored. Metadata information (e.g. protein identifier, IVA strain, year and location of infection) can enhance the exploration of the presented data. With our database researchers gain a useful tool for the exploration of high quality HA models, viewing and comparing changes in the HA viral subtypes at several information levels (sequence, structure, ESP). The complete and integrated view of those relations might be useful to determine the efficiency of transmission, pathogenicity and for the investigation of evolutionary tendencies of the influenza virus.

Database URL: http://nucleus3d.cent.uw.edu.pl/influenza

Novel hemagglutinin-based influenza virus inhibitors

Influenza virus has caused seasonal epidemics and worldwide pandemics, which caused tremendous loss of human lives and socioeconomics. Nowadays, only two classes of anti-influenza drugs, M2 ion channel inhibitors and neuraminidase inhibitors respectively, are used for prophylaxis and treatment of influenza virus infection. Unfortunately, influenza virus strains resistant to one or all of those drugs emerge frequently. Hemagglutinin (HA), the glycoprotein in influenza virus envelope, plays a critical role in viral binding, fusion and entry processes. Therefore, HA is a promising target for developing anti-influenza drugs, which block the initial entry step of viral life cycle. Here we reviewed recent understanding of conformational changes of HA in protein folding and fusion processes, and the discovery of HA-based influenza entry inhibitors, which may provide more choices for preventing and controlling potential pandemics caused by multi-resistant influenza viruses.

HASP server: a database and structural visualization platform for comparative models of influenza A hemagglutinin proteins

Background

Influenza A viruses possess RNA genomes that mutate frequently in response to immune pressures. The mutations in the hemagglutinin genes are particularly significant, as the hemagglutinin proteins mediate attachment and fusion to host cells, thereby influencing viral pathogenicity and species specificity. Large-scale influenza A genome sequencing efforts have been ongoing to understand past epidemics and pandemics and anticipate future outbreaks. Sequencing efforts thus far have generated nearly 9,000 distinct hemagglutinin amino acid sequences.

Description

Comparative models for all publicly available influenza A hemagglutinin protein sequences (8,769 to date) were generated using the Rosetta modeling suite. The C-alpha root mean square deviations between a randomly chosen test set of models and their crystallographic templates were less than 2 Å, suggesting that the modeling protocols yielded high-quality results. The models were compiled into an online resource, the Hemagglutinin Structure Prediction (HASP) server. The HASP server was designed as a scientific tool for researchers to visualize hemagglutinin protein sequences of interest in a three-dimensional context. With a built-in molecular viewer, hemagglutinin models can be compared side-by-side and navigated by a corresponding sequence alignment. The models and alignments can be downloaded for offline use and further analysis.

Conclusions

The modeling protocols used in the HASP server scale well for large amounts of sequences and will keep pace with expanded sequencing efforts. The conservative approach to modeling and the intuitive search and visualization interfaces allow researchers to quickly analyze hemagglutinin sequences of interest in the context of the most highly related experimental structures, and allow them to directly compare hemagglutinin sequences to each other simultaneously in their two- and three-dimensional contexts. The models and methodology have shown utility in current research efforts and the ongoing aim of the HASP server is to continue to accelerate influenza A research and have a positive impact on global public health.

Influenza A virus entry inhibitors targeting the hemagglutinin

Influenza A virus (IAV) has caused seasonal influenza epidemics and influenza pandemics, which resulted in serious threat to public health and socioeconomic impacts. Until now, only 5 drugs belong to two categories are used for prophylaxis and treatment of IAV infection. Hemagglutinin (HA), the envelope glycoprotein of IAV, plays a critical role in viral binding, fusion and entry. Therefore, HA is an attractive target for developing anti‑IAV drugs to block the entry step of IAV infection. Here we reviewed the recent progress in the study of conformational changes of HA during viral fusion process and the development of HA-based IAV entry inhibitors, which may provide a new choice for controlling future influenza pandemics.

A critical HA1 neutralizing domain of H5N1 influenza in an optimal conformation induces strong cross-protection

The highly pathogenic avian influenza (HPAI) H5N1 viruses, especially the laboratory-generated H5N1 mutants, have demonstrated the potential to cross the species barrier and infect mammals and humans. Consequently, the design of an effective and safe anti-H5N1 vaccine is essential. We previously demonstrated that the full-length hemagglutinin 1 (HA1) could induce significant neutralizing antibody response and protection. Here, we intended to identify the critical neutralizing domain (CND) in an optimal conformation that can elicit strong cross-neutralizing antibodies and protection against divergent H5N1 strains. We thus constructed six recombinant proteins covering different regions of HA1 of A/Anhui/1/2005(H5N1), each of which was fused with foldon (Fd) and Fc of human IgG. We found that the critical fragment fused with Fd/Fc (HA-13–263-Fdc, H5 numbering) that could elicit the strongest neutralizing antibody response is located in the N-terminal region of HA1 (residues 13–263), which covers the receptor-binding domain (RBD, residues 112–263). We then constructed three additional recombinants fused with Fd plus His tag (HA-13–263-Fd-His), Fc only (HA-13–263-Fc), and His tag only (HA-13–263-His), respectively. We found that the HA-13–263-Fdc, which formed an oligomeric conformation, induced the strongest neutralizing antibody response and cross-protection against challenges of two tested H5N1 virus strains covering clade 1: A/VietNam/1194/2004 (VN/1194) or clade 2.3.4: A/Shenzhen/406H/06 (SZ/406H), while HA-13–263-Fc dimer and HA-13–263-Fd-His trimer elicited higher neutralizing antibody response and protection than HA-13–263-His monomer. These results suggest that the oligomeric form of the CND containing the RBD can be further developed as an effective and safe vaccine for cross-protection against divergent strains of H5N1 viruses.

Potential strategies and biosafety protocols used for dual-use research on highly pathogenic influenza viruses

Influenza A viruses (IAVs), particularly the highly pathogenic avian influenza H5N1, have posed a substantial threat to public health worldwide. Although the laboratory generation of the mutant influenza virus H5N1 with airborne transmissibility among mammals, which has been considered as a dual-use research, may benefit the development of effective vaccines and therapeutics against the emerging infectious agents, it may also pose threats to national biosecurity, laboratory biosafety, and/or public health. This review introduces the classification and characterization of IAVs, pinpoints historic pandemics and epidemics caused by IAVs, emphasizes the significance and necessity of biosafety, summarizes currently established biosafety-related protocols for IAV research, and provides potential strategies to improve biosafety protocols for dual-use research on the highly pathogenic avian influenza viruses and other emerging infectious agents.

Acid-dependent viral entry

Virus infection of host cells requires that entry into the cell results in efficient genome release leading to translation and replication. These initial steps revolving around the entry and genomic release processes are crucial for viral progeny generation. Despite the variety of receptors used by viruses to initiate entry, evidence from both enveloped and non-enveloped viral infections is highlighting the important role played by intracellular acidic compartments in the entry of many viruses. These compartments provide connecting nodes within the endocytic network, presenting multiple viral internalization pathways. Endosomal compartments employing an internal acidic pH can trigger molecular mechanisms leading to disassembly of viral particles, thus providing appropriate genome delivery. Accordingly, viruses have evolved to select optimal intracellular conditions for promoting efficient genome release, leading to propagation of the infectious agent. This review will address the implications of cellular compartment involvement in virus infectious processes, and the roles played by the viruses' own machinery, including pH sensing mechanisms and the methodologies applied for studying acid-dependent viral entry into host cells.