A small-molecule fusion inhibitor of influenza virus is orally active in mice

Multiple antiviral mechanisms of Ephedrae Herba and Cinnamomi Cortex against influenza: inhibition of entry and replication

Maoto, a traditional herbal medicine widely prescribed in Japan, has been shown to be effective in the treatment of influenza virus infection, but the mechanisms of its antiviral action remain unclear. We previously demonstrated that maoto binds to respiratory syncytial virus (RSV) spike proteins, thereby inhibiting their entry into host cells. In this report, a similar experiment was done to determine if maoto and its components have an anti-infective effect on the influenza virus. Our results indicate that maoto binds to the hemagglutinin (HA) spike protein, inhibiting virus entry into host cells in a manner analogous to its antiviral effect on RSV. This hemagglutinin-binding effect was observed across influenza A(H1N1), A(H3N2), and B viruses, highlighting the broad-spectrum inhibitory potential of maoto against diverse viral strains. Furthermore, maoto, internalized by cells along with the influenza virus, binds to a cap-dependent endonuclease (polymerase acidic [PA] protein) that is crucial for viral replication and inhibits its nuclease activity. Among maoto's constituent crude drugs, Ephedrae Herba (EH) and Cinnamomi Cortex (CC) were found to bind to both hemagglutinin and PA, indicating that they are responsible for the anti-infective effect of maoto. Maoto is distinctive in its multiple points of antiviral action, exhibiting a broad spectrum of antiviral properties, which makes it a versatile therapeutic agent against various viral mutations.IMPORTANCEThe influenza virus is a formidable pathogen responsible for global pandemics that claim over 300,000 lives annually. Employing an ingenious evolutionary strategy, this virus undergoes constant mutation, deftly evading the action of therapeutic agents and sustaining its relentless impact. Maoto, a traditional herbal medicine, has long been known for its efficacy against viral infections and is frequently prescribed in Japan for the treatment of influenza; however, the precise mechanisms of its action remain unclear. Our study was done to elucidate the antiviral mechanisms of maoto against the influenza virus, presenting data that supports its unique potential as a therapeutic agent capable of flexibly adapting to mutations of the influenza virus. These findings pave the way for the development of new drugs and the expansion of therapeutic options.

Design, Synthesis and Anti-Influenza Virus Activity of 4-Tert-Butyl-N-(3-Oxo-1-Thia-4-Azaspiro[4.5]Dec-4-yl)Benzamide Derivatives That Target Hemagglutinin-Mediated Fusion

Hemagglutinin (HA) is a viral glycoprotein that mediates influenza virus entry into the host cell and is considered a relevant viral target. We here report the identification of a class of 4-tert-butylphenyl-substituted spirothiazolidinones as HA-mediated fusion inhibitors with specific activity against influenza A/H3N2 virus. The novel spirocyclic compounds were achieved by using one-pot cyclocondensation method and the chemical structures were characterized by IR, 1H NMR, 13C NMR, and elemental analysis. Compound 2c, bearing methyl substitutions at positions 2- and 8- of the spiro ring displayed an EC50 value against influenza A/H3N2 virus of 1.3 μM and an antiviral selectivity index of 30. The fusion-inhibiting effect of compound 2c was revealed in the polykaryon assay which is based on cell-cell fusion when influenza virus H3 HA-transfected cells are exposed to low pH. Computer-aided docking was performed to predict the possible binding pocket in the H3 HA trimer. Resistance data and in silico studies indicated that compound 2c has an overlapping binding pocket in the stem region of H3 HA with the known fusion inhibitors TBHQ and arbidol.

Allosteric inhibition of trypanosomatid pyruvate kinases by a camelid single-domain antibody

African trypanosomes are the causative agents of neglected tropical diseases affecting both humans and livestock. Disease control is highly challenging due to an increasing number of drug treatment failures. African trypanosomes are extracellular, blood-borne parasites that mainly rely on glycolysis for their energy metabolism within the mammalian host. Trypanosomal glycolytic enzymes are therefore of interest for the development of trypanocidal drugs. Here, we report the serendipitous discovery of a camelid single-domain antibody (sdAb aka Nanobody) that selectively inhibits the enzymatic activity of trypanosomatid (but not host) pyruvate kinases through an allosteric mechanism. By combining enzyme kinetics, biophysics, structural biology, and transgenic parasite survival assays, we provide a proof-of-principle that the sdAb-mediated enzyme inhibition negatively impacts parasite fitness and growth.

PA and PA-X: two key proteins from segment 3 of the influenza viruses

In recent years, the influenza viruses have posed an increasingly severe threat to public health. It is essential to analyze the virulence and pathogenesis of influenza viruses to prevent and control them, as well as create antiviral drugs. Previous studies have revealed that influenza virus segment 3 codes for not only the PA protein but also a novel protein, PA-X. PA protein is one subunit of the polymerase of influenza viruses and plays a critical role in its life cycle. PA presented endonuclease activity, the transcription and replication of the viral genome, viral virulence, protein degradation, and host immune response by interacting with viral proteins, including PB2, PB1, and host factors, including ANP32A, CHD6, HAX1, hCLE, HDAC6, MCM complex. PA mutations were involved in the viral replication, pathogenicity, and transmission of influenza viruses in poultry, mammals, and humans. PA-X is an open reading frame generated by +1 ribosomal code shift at the N-terminal amino acids of segment 3 and possesses the shutoff activity of host gene expression, regulating the host immune response, viral virulence and transmission. Therefore, PA is one ideal target for the development of antiviral drugs against influenza viruses. Baloxavir marboxil (BXM) and Favipiravir are two very effective anti-influenza virus drugs targeting the PA endonuclease domain of influenza A viruses. In this review, we summarized the structures, viral replication, virulent determinants and transmission, host factors, innate immunity, and antiviral drugs involved in PA and PA-X. The information is of great value for underlying the mechanism of viral replication and developing novel effective strategies to prevent and control influenza infection and the pandemic.

Occurrence, predictive models and potential health risk assessment of viable but non-culturable (VBNC) pathogens in drinking water

Viable but non-culturable (VBNC) pathogens are prevalent in drinking water systems and can resuscitate under favorable conditions, thereby posing significant public health risks. This study investigated the occurrence of VBNC Escherichia coli and Pseudomonas aeruginosa in source water, tap water, and potable water in eastern China, using propidium monoazide-quantitative PCR and culture-based methods. Multiple linear regression (MLR) and artificial neural network (ANN) models were developed based on conventional water quality indicators to predict VBNC pathogen concentrations. The results indicated that drinking water treatment plants effectively reduced VBNC pathogens by 1-3 log units, however, concentrations ranging from 100 to 102 CFU/100 mL remained in tap and potable water, with detection rates between 83.33% and 100%. Furthermore, potable water contained a higher concentration of VBNC pathogens than tap water, suggesting a potential risk of microbial leakage from water dispensers. The constructed ANN models outperformed than MLR models, with R values greater than 0.8, indicating a strong correlation between measured values and model predictions for VBNC pathogens. ANN models also demonstrated superior accuracy than MLR models in predicting VBNC pathogens across different type of drinking water, achieving accuracies of 88.89% for Escherichia coli and 77.78% for Pseudomonas aeruginosa. The QMRA revealed that annual infection risks and disease burdens from VBNC pathogens in potable water were greater than those in tap water, with both exceeding acceptable safety thresholds. This study emphasizes that the risks posed by VBNC pathogens deserve attention and model predictions provide critical evidence for health risk identification.

De Novo Design of Lipopeptide-Based β-Sheet-Like Self-Assemblies: A Strategy to Develop Fusion Inhibitors as Broad-Spectrum Antivirals

The recent surge in emerging viral infections warrants the design of broad-spectrum antivirals. We aim to develop a lead molecule that targets a common biochemical feature of many enveloped viruses, membrane fusion. To achieve the broad-spectrum ability, instead of targeting the fusion machinery, we plan to modulate the physicochemical properties of the host and viral membranes to block fusion. The approach is based on the Coronin-1 protein of Mycobacterium, which presumably inhibits the phagosome-lysosome fusion, and a unique Trp-Asp (WD) sequence is placed at the distorted β-meander motif. We designed a WD-based branched lipopeptide (Myr-D(WD)2) that supported the intermolecular interactions to create a β-sheet-like supramolecular assembly at the membrane surface. TEM and confocal fluorescence experiments also suggest that the lipopeptide self-assembled at the bilayer interface and modulated the interfacial order and the water penetration. We demonstrated that the supramolecular organization of Myr-D(WD)2 could block artificial membrane fusion completely and restrict pH-dependent influenza virus (H1N1, H9N2), and pH-independent mouse hepatitis virus, human coronavirus (HCoV-OC43) infections. The present study provided an evidence-based broad-spectrum antiviral potential of a designed self-assembled lipopeptide.

Antiviral strategies against influenza virus: an update on approved and innovative therapeutic approaches

Influenza viruses still represent a great concern for Public Health by causing yearly seasonal epidemics and occasionally worldwide pandemics. Moreover, spillover events at the animal-human interface are becoming more frequent nowadays, also involving animal species not previously found as reservoirs. To restrict the effects of influenza virus epidemics, especially in at-risk population, and to prepare a drug arsenal for possible future pandemics, researchers worldwide have been working on the development of antiviral strategies since the 80's of the last century. One of the main obstacles is the considerable genomic variability of influenza viruses, which constantly poses the issues of drug-resistance emergence and immune evasion. This review summarizes the approved therapeutics for clinical management of influenza, promising new anti-flu compounds and monoclonal antibodies currently undergoing clinical evaluation, and molecules with efficacy against influenza virus in preclinical studies. Moreover, we discuss some innovative anti-influenza therapeutic approaches such as combination therapies and targeted protein degradation. Given the limited number of drugs approved for influenza treatment, there is a still strong need for novel potent anti-influenza drugs endowed with a high barrier to drug resistance and broad-spectrum activity against influenza viruses of animal origin that may be responsible of future large outbreaks and pandemics.

Potential Broad-Spectrum Antiviral Agents: A Key Arsenal Against Newly Emerging and Reemerging Respiratory RNA Viruses

Respiratory viral infections present significant global health challenges, causing substantial morbidity and mortality, particularly among highly susceptible components of the population. The emergence of pandemics and epidemics, such as those caused by influenza viruses and coronaviruses, emphasizes the urgent need for effective antiviral therapeutics. In this review, we explore the potential of broad-spectrum antiviral agents targeting respiratory RNA viruses, including influenza viruses, coronaviruses, respiratory syncytial virus, human metapneumovirus, human parainfluenza viruses, and rhinoviruses. Various broad-spectrum direct-acting and host-targeting antivirals are discussed, including monoclonal antibodies targeting conserved regions of viral surface proteins, molecules interfering with host cell receptors or viral replication machinery, viral protease inhibitors, siRNA therapies, ribonuclease, and 3D8 scFv. Advancements in host-targeting approaches to reduce resistance and RNA-based therapeutics offer significant potential for combating respiratory viral threats. Despite challenges, broad-spectrum antiviral agents represent a crucial strategy, particularly when specific viral pathogens are unidentified or rapid intervention is essential, such as during pandemics or outbreaks.

Mining Druggable Sites in Influenza A Hemagglutinin: Binding of the Pinanamine-Based Inhibitor M090

Assessing the binding mode of drug-like compounds is key in structure-based drug design. However, this may be challenged by factors such as the structural flexibility of the target protein. In this case, state-of-the-art computational methods can be valuable to explore the linkages between structural and pharmacological data. Following this strategy, extended molecular dynamics simulations and thermodynamic integration calculations are used to examine the binding of the potent antiviral inhibitor M090 and related pinanamine-based analogues, covering a 250-fold difference in inhibitory potency to the influenza A hemagglutinin, which is essential for virus entry and membrane fusion. This analysis has disclosed the hydrophobic shielding effect played by the 3-cyclopropylthiophene moiety in M090. Furthermore, the results support the negative effect of the resistance-induced E742 → D mutation, which should weaken the binding by increasing the structural flexibility of the L2-BS loop. The results pave the way to exploration of the antiviral activity of novel compounds.

One-pot synthesis, characterization and antiviral properties of new benzenesulfonamide-based spirothiazolidinones

A novel series of benzenesulfonamide substituted spirothiazolidinone derivatives (3a-j) were synthesized, characterized and evaluated for their antiviral activity. The spirocyclic compounds were prepared by the condensation of 4-(aminosulfonyl)-2-methoxybenzohydrazide, appropriate cyclic ketones and 2-mercaptopropionic acid in a one-pot reaction. The structures of the new compounds were established by IR, 1H NMR, 13C NMR (APT), and elemental analysis. The new compounds were evaluated in vitro antiviral activity against influenza A/H1N1, A/H3N2 and B viruses, as well as herpes simplex virus type 1 (HSV-1), respiratory syncytial virus (RSV) and yellow fever virus (YFV). Two derivatives bearing propyl (3d) and tert-butyl (3e) substituents at position 8 of the spiro ring exhibited activity against influenza A/H1N1 virus with EC50 values in the range of 35-45 µM and no cytotoxicity at 100 μM, the highest concentration tested.

Ultrapotent influenza hemagglutinin fusion inhibitors developed through SuFEx-enabled high-throughput medicinal chemistry

Seasonal and pandemic-associated influenza strains cause highly contagious viral respiratory infections that can lead to severe illness and excess mortality. Here, we report on the optimization of our small-molecule inhibitor F0045(S) targeting the influenza hemagglutinin (HA) stem with our Sulfur-Fluoride Exchange (SuFEx) click chemistry-based high-throughput medicinal chemistry (HTMC) strategy. A combination of SuFEx- and amide-based lead molecule diversification and structure-guided design led to identification and validation of ultrapotent influenza fusion inhibitors with subnanomolar EC50 cellular antiviral activity against several influenza A group 1 strains. X-ray structures of six of these compounds with HA indicate that the appended moieties occupy additional pockets on the HA surface and increase the binding interaction, where the accumulation of several polar interactions also contributes to the improved affinity. The compounds here represent the most potent HA small-molecule inhibitors to date. Our divergent HTMC platform is therefore a powerful, rapid, and cost-effective approach to develop bioactive chemical probes and drug-like candidates against viral targets.

Modular Biomimetic Strategy Enables Discovery and SAR Exploration of Oxime Macrocycles as Influenza A Virus (H1N1) Inhibitors

Although vaccination remains the prevalent prophylactic means for controlling Influenza A virus (IAV) infections, novel structural antivirus small-molecule drugs with new mechanisms of action for treating IAV are highly desirable. Herein, we describe a modular biomimetic strategy to expeditiously achieve a new class of macrocycles featuring oxime, which might target the hemagglutinin (HA)-mediated IAV entry into the host cells. SAR analysis revealed that the size and linker of the macrocycles play an important role in improving potency. Particularly, as a 14-membered macrocyclic oxime, 37 exhibited potent inhibitory activity against IAV H1N1 with an EC50 value of 23 nM and low cytotoxicity, which alleviated cytopathic effects and protected cell survival obviously after H1N1 infection. Furthermore, 37 showed significant synergistic activity with neuraminidase inhibitor oseltamivir in vitro.

Retracted and republished from: "The current state of research on influenza antiviral drug development: drugs in clinical trial and licensed drugs"

Influenza viruses (IVs) threaten global human health due to the high morbidity, infection, and mortality rates. Currently, the influenza drugs recommended by the Food and Drug Administration are oseltamivir, zanamivir, peramivir, and baloxavir marboxil. These recommended antivirals are currently effective for major subtypes of IVs as the compounds target conserved domains in neuraminidase or polymerase acidic (PA) protein. However, this trend may gradually change due to the selection of antiviral drugs and the natural evolution of IVs. Therefore, there is an urgent need to develop drugs related to the treatment of influenza to deal with the next pandemic. Here, we summarized the cutting-edge research in mechanism of action, inhibitory activity, and clinical efficacy of drugs that have been approved and drugs that are still in clinical trials for influenza treatment. We hope this review will provide up-to-date and comprehensive information on influenza antivirals and generate hypotheses for screens and development of new broad-spectrum influenza drugs in the near future.

Neutralizing antibodies to block viral entry and for identification of entry inhibitors

Neutralizing antibodies (NAbs) are naturally produced by our immune system to combat viral infections. Clinically, neutralizing antibodies with potent efficacy and high specificity have been extensively used to prevent and treat a wide variety of viral infections, including Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), Human Immunodeficiency Virus (HIV), Dengue Virus (DENV) and Hepatitis B Virus (HBV). An overwhelmingly large subset of clinically effective NAbs operates by targeting viral envelope proteins to inhibit viral entry into the host cell. Binding of viral envelope protein to the host receptor is a critical rate limiting step triggering a cascade of downstream events, including endocytosis, membrane fusion and pore formation to allow viral entry. In recent years, improved structural knowledge on these processes have allowed researchers to also leverage NAbs as an indispensable tool in guiding discovery of novel antiviral entry inhibitors, providing drug candidates with high efficacy and pan-genus specificity. This review will summarize the latest progresses on the applications of NAbs as effective entry inhibitors and as important tools to develop antiviral therapeutics by high-throughput drug screenings, rational design of peptidic entry inhibitor mimicking NAbs and in silico computational modeling approaches.

Discovery of cyperenoic acid as a potent and novel entry inhibitor of influenza A virus

Influenza therapeutics with new targets and modes of action are urgently needed due to the frequent emergence of mutants resistant to currently available anti-influenza drugs. Here we report the in vitro and in vivo anti-influenza A virus activities of cyperenoic acid, a natural compound, which was isolated from a Chinese medicine Croton crassifolius Geise. Cyperenoic acid could potently suppress H1N1, H3N2 and H9N2 virus replication with IC50 values ranging from 0.12 to 15.13 μM, and showed a low cytotoxicity against MDCK cells (CC50 = 939.2 ± 60.0 μM), with selectivity index (SI) values ranging from 62 to 7823. Oral or intraperitoneal treatment of cyperenoic acid effectively protected mice against a lethal influenza virus challenge, comparable to the efficacy of Tamiflu. Additionally, cyperenoic acid also significantly reduced lung virus titers and alleviated influenza-induced acute lung injury in infected mice. Mechanism-of-action studies revealed that cyperenoic acid exhibited its anti-influenza activity during the entry stage of viral replication by inhibiting HA-mediated viral fusion. Simulation docking analyses of cyperenoic acid with the HA structures implied that cyperenoic acid binds to the stalk domain of HA in a cavity near the fusion peptide. Collectively, these results demonstrate that cyperenoic acid is a promising lead compound for the anti-influenza drug development and this research provides a useful small-molecule probe for studying the HA-mediated viral entry process.

Efficiency of membrane fusion inhibitors on different hemagglutinin subtypes: insight from a molecular dynamics simulation perspective

The challenge in vaccine development, along with drug resistance issues, has encouraged the search for new anti-influenza drugs targeting different viral proteins. Hemagglutinin (HA) glycoprotein, crucial in the viral replication cycle, has emerged as a promising therapeutic target. CBS1117 and JNJ4796 were reported to exhibit similar potencies against infectious group 1 influenza, which included H1 and H5 HAs; however, their potencies were significantly reduced against group 2 HA. This study aims to explore the molecular binding mechanisms and group specificity of these fusion inhibitors against both group 1 (H5) and group 2 (H3) HA influenza viruses using molecular dynamics simulations. CBS1117 and JNJ4796 exhibit stronger interactions with key residues within the H5 HA binding pocket compared to H3-ligand complexes. Hydrogen bonding and hydrophobic interactions involving residues, such as H381, Q401, T3251 (H5-CBS1117), T3181 (H5-JNJ4796), W212, I452, V482, and V522 predominantly contribute to stabilizing H5-ligand systems. In contrast, these interactions are notably weakened in H3-inhibitor complexes. Predicted protein-ligand binding free energies align with experimental data, indicating CBS1117 and JNJ4796's preference for heterosubtypic group 1 HA binding. Understanding the detailed atomistic mechanisms behind the varying potencies of these inhibitors against the two HA groups can significantly contribute to the development and optimization of effective HA fusion inhibitors. To accomplish this, the knowledge of the transition of HA from its pre- to post-fusion states, the molecular size of ligands, and their potential binding regions, could be carefully considered.

An orally active entry inhibitor of influenza A viruses protects mice and synergizes with oseltamivir and baloxavir marboxil

Seasonal or pandemic illness caused by influenza A viruses (IAVs) is a major public health concern due to the high morbidity and notable mortality. Although there are several approved drugs targeting different mechanisms, the emergence of drug resistance calls for new drug candidates that can be used alone or in combinations. Small-molecule IAV entry inhibitor, ING-1466, binds to hemagglutinin (HA) and blocks HA-mediated viral infection. Here, we show that this inhibitor demonstrates preventive and therapeutic effects in a mouse model of IAV with substantial improvement in the survival rate. When administered orally it elicits a therapeutic effect in mice, even after the well-established infection. Moreover, the combination of ING-1466 with oseltamivir phosphate or baloxavir marboxil enhances the therapeutic effect in a synergistic manner. Overall, ING-1466 has excellent oral bioavailability and in vitro absorption, distribution, metabolism, excretion, and toxicity profile, suggesting that it can be developed for monotherapy or combination therapy for the treatment of IAV infections.

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.

The current state of research on influenza antiviral drug development: drugs in clinical trial and licensed drugs

Influenza viruses (IVs) threaten global human health due to the high morbidity, infection, and mortality rates. Currently, the influenza drugs recommended by the FDA are oseltamivir, zanamivir, peramivir, and baloxavir marboxil. Notably, owing to the high variability of IVs, no drug exists that can effectively treat all types and subtypes of IVs. Moreover, the current trend of drug resistance is likely to continue as the viral genome is constantly mutating. Therefore, there is an urgent need to develop drugs related to the treatment of influenza to deal with the next pandemic. Here, we summarized the cutting-edge research in mechanism of action, inhibitory activity, and clinical efficacy of drugs that have been approved and drugs that are still in clinical trials for influenza treatment. We hope this review will provide up-to-date and comprehensive information on influenza antivirals and generate hypotheses for screens and development of new broad-spectrum influenza drugs in the near future.

Non-Steroidal Estrogens Inhibit Influenza Virus by Interacting with Hemagglutinin and Preventing Viral Fusion

Influenza virus is one of the main causes of respiratory infections worldwide. Despite the availability of seasonal vaccines and antivirals, influenza virus infections cause an important health and economic burden. Therefore, the need to identify alternative antiviral strategies persists. In this study, we identified non-steroidal estrogens as potent inhibitors of influenza virus due to their interaction with the hemagglutinin protein, preventing viral entry. This activity is maintained in vitro, ex vivo, and in vivo. Therefore, we found a new domain to target on the hemagglutinin and a class of compounds that could be further optimized for influenza treatment.

Viral Membrane Fusion: A Dance Between Proteins and Lipids

There are at least 21 families of enveloped viruses that infect mammals, and many contain members of high concern for global human health. All enveloped viruses have a dedicated fusion protein or fusion complex that enacts the critical genome-releasing membrane fusion event that is essential before viral replication within the host cell interior can begin. Because all enveloped viruses enter cells by fusion, it behooves us to know how viral fusion proteins function. Viral fusion proteins are also major targets of neutralizing antibodies, and hence they serve as key vaccine immunogens. Here we review current concepts about viral membrane fusion proteins focusing on how they are triggered, structural intermediates between pre- and postfusion forms, and their interplay with the lipid bilayers they engage. We also discuss cellular and therapeutic interventions that thwart virus-cell membrane fusion.

Nine-valent oleanolic acid conjugates as potent inhibitors blocking the entry of influenza A virus

The influenza pandemic remains a major public health challenge that endangers the lives of many vulnerable and immune-compromised individuals worldwide. The high infectivity and genetic variability of influenza virus make it particularly challenging to design effective drugs to inhibit the virus. In previous studies, we determined that oleanolic acid (OA) and its derivatives block interactions between influenza and host cells, thus endowing OA with anti-viral efficacy. Inspired by the role of cluster glycosides in the interactions between hemagglutinins (HA) and sialic acid receptors (SA), we designed and synthesized a series of OA nonamers via the CuAAC reaction, and evaluated their anti-viral activities in vitro. We determined that among these nonamers, compound 15 displayed the highest potency (IC₅₀ = 5.23 μM), equivalent to the antiviral drug oseltamivir which is routinely prescribed for influenza A virus strain A/WSN/33 (H1N1). In addition, these compounds also displayed antiviral activity against influenza B. Mechanistic experiments indicated that OA nonamers can effectively target the influenza HA protein. This study collectively demonstrates that multivalent structure-activity binding strategy is an effective method for designing influenza virus inhibitors.

Glycomimetics for the inhibition and modulation of lectins

Carbohydrates are essential mediators of many processes in health and disease. They regulate self-/non-self- discrimination, are key elements of cellular communication, cancer, infection and inflammation, and determine protein folding, function and life-times. Moreover, they are integral to the cellular envelope for microorganisms and participate in biofilm formation. These diverse functions of carbohydrates are mediated by carbohydrate-binding proteins, lectins, and the more the knowledge about the biology of these proteins is advancing, the more interfering with carbohydrate recognition becomes a viable option for the development of novel therapeutics. In this respect, small molecules mimicking this recognition process become more and more available either as tools for fostering our basic understanding of glycobiology or as therapeutics. In this review, we outline the general design principles of glycomimetic inhibitors (Section 2). This section is then followed by highlighting three approaches to interfere with lectin function, i.e. with carbohydrate-derived glycomimetics (Section 3.1), novel glycomimetic scaffolds (Section 3.2) and allosteric modulators (Section 3.3). We summarize recent advances in design and application of glycomimetics for various classes of lectins of mammalian, viral and bacterial origin. Besides highlighting design principles in general, we showcase defined cases in which glycomimetics have been advanced to clinical trials or marketed. Additionally, emerging applications of glycomimetics for targeted protein degradation and targeted delivery purposes are reviewed in Section 4.

Molecular Modeling of Viral Type I Fusion Proteins: Inhibitors of Influenza Virus Hemagglutinin and the Spike Protein of Coronavirus

The fusion of viral and cell membranes is one of the basic processes in the life cycles of viruses. A number of enveloped viruses confer fusion of the viral envelope and the cell membrane using surface viral fusion proteins. Their conformational rearrangements lead to the unification of lipid bilayers of cell membranes and viral envelopes and the formation of fusion pores through which the viral genome enters the cytoplasm of the cell. A deep understanding of all the stages of conformational transitions preceding the fusion of viral and cell membranes is necessary for the development of specific inhibitors of viral reproduction. This review systematizes knowledge about the results of molecular modeling aimed at finding and explaining the mechanisms of antiviral activity of entry inhibitors. The first section of this review describes types of viral fusion proteins and is followed by a comparison of the structural features of class I fusion proteins, namely influenza virus hemagglutinin and the S-protein of the human coronavirus.

Antiviral Approaches against Influenza Virus

Preventing and controlling influenza virus infection remains a global public health challenge, as it causes seasonal epidemics to unexpected pandemics. These infections are responsible for high morbidity, mortality, and substantial economic impact. Vaccines are the prophylaxis mainstay in the fight against influenza. However, vaccination fails to confer complete protection due to inadequate vaccination coverages, vaccine shortages, and mismatches with circulating strains. Antivirals represent an important prophylactic and therapeutic measure to reduce influenza-associated morbidity and mortality, particularly in high-risk populations. Here, we review current FDA-approved influenza antivirals with their mechanisms of action, and different viral- and host-directed influenza antiviral approaches, including immunomodulatory interventions in clinical development. Furthermore, we also illustrate the potential utility of machine learning in developing next-generation antivirals against influenza.

Antiviral Effect of Ginsenosides rk1 against Influenza a Virus Infection by Targeting the Hemagglutinin 1-Mediated Virus Attachment

Influenza A virus (IAV) infections have been a serious hazard to public health everywhere. With the growing concern of drug-resistant IAV strains, there is an urgent need for novel anti-IAV medications, especially those with alternative mechanisms of action. Hemagglutinin (HA), an IAV glycoprotein, plays critical roles in the early stage of virus infection, including receptor binding and membrane fusion, making it a good target for developing anti-IAV drugs. Panax ginseng is a widely used herb in traditional medicine with extensive biological effects in various disease models, and its extract was reported to show protection in IAV-infected mice. However, the main effective anti-IAV constituents in panax ginseng remain unclear. Here, we report that ginsenoside rk1 (G-rk1) and G-rg5, out of the 23 screened ginsenosides, exhibit significant antiviral effects against 3 different IAV subtypes (H1N1, H5N1, and H3N2) in vitro. Mechanistically, G-rk1 blocked IAV binding to sialic acid in a hemagglutination inhibition (HAI) assay and an indirect ELISA assay; more importantly, we showed that G-rk1 interacted with HA1 in a dose-dependent manner in a surface plasmon resonance (SPR) analysis. Furthermore, G-rk1 treatment by intranasal inoculation effectively reduced the weight loss and mortality of mice challenged with a lethal dose of influenza virus A/Puerto Rico/8/34 (PR8). In conclusion, our findings reveal for the first time that G-rk1 possesses potent anti-IAV effects in vitro and in vivo. We have also identified and characterized with a direct binding assay a novel ginseng-derived IAV HA1 inhibitor for the first time, which could present potential approaches to prevent and treat IAV infections.

Analysis of the conserved protective epitopes of hemagglutinin on influenza A viruses

The conserved protective epitopes of hemagglutinin (HA) are essential to the design of a universal influenza vaccine and new targeted therapeutic agents. Over the last 15 years, numerous broadly neutralizing antibodies (bnAbs) targeting the HA of influenza A viruses have been isolated from B lymphocytes of human donors and mouse models, and their binding epitopes identified. This work has brought new perspectives for identifying conserved protective epitopes of HA. In this review, we succinctly analyzed and summarized the antigenic epitopes and functions of more than 70 kinds of bnAb. The highly conserved protective epitopes are concentrated on five regions of HA: the hydrophobic groove, the receptor-binding site, the occluded epitope region of the HA monomers interface, the fusion peptide region, and the vestigial esterase subdomain. Our analysis clarifies the distribution of the conserved protective epitope regions on HA and provides distinct targets for the design of novel vaccines and therapeutics to combat influenza A virus infection.

5-(Perylen-3-ylethynyl)uracil as an antiviral scaffold: Potent suppression of enveloped virus reproduction by 3-methyl derivatives in vitro

Amphipathic nucleoside and non-nucleoside derivatives of pentacyclic aromatic hydrocarbon perylene are known as potent non-cytotoxic broad-spectrum antivirals. Here we report 3-methyl-5-(perylen-3-ylethynyl)-uracil-1-acetic acid and its amides, a new series of compounds based on a 5-(perylen-3-ylethynyl)-uracil scaffold. The compounds demonstrate pronounced in vitro activity against arthropod-borne viruses, namely tick-borne encephalitis virus (TBEV) and yellow fever virus (YFV), in plaque reduction assays with EC₅₀ values below 1.9 and 1.3 nM, respectively, and Chikungunya virus (CHIKV) in cytopathic effect inhibition test with EC₅₀ values below 3.2 μM. The compounds are active against respiratory viruses as well: severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) in cytopathic effect inhibition test and influenza A virus (IAV) in virus titer reduction experiments are inhibited - EC₅₀ values below 51 nM and 2.2 μM, respectively. The activity stems from the presence of a hydrophobic perylene core, and all of the synthesized compounds exhibit comparable ¹O₂ generation rates. Nonetheless, activity can vary by orders of magnitude depending on the hydrophilic part of the molecule, suggesting a complex mode of action. A time-of-addition experiment and fluorescent imaging indicate that the compounds inhibit viral fusion in a dose-dependent manner. The localization of the compound in the lipid bilayers and visible damage to the viral envelope suggest the membrane as the primary target. Dramatic reduction of antiviral activity with limited irradiation or under treatment with antioxidants further cements the idea of photoinduced ROS-mediated viral envelope damage being the mode of antiviral action.

Stabilisation of Viral Membrane Fusion Proteins in Prefusion Conformation by Structure-Based Design for Structure Determination and Vaccine Development

The membrane surface of enveloped viruses contains dedicated proteins enabling the fusion of the viral with the host cell membrane. Working with these proteins is almost always challenging because they are membrane-embedded and naturally metastable. Fortunately, based on a range of different examples, researchers now have several possibilities to tame membrane fusion proteins, making them amenable for structure determination and immunogen generation. This review describes the structural and functional similarities of the different membrane fusion proteins and ways to exploit these features to stabilise them by targeted mutational approaches. The recent determination of two herpesvirus membrane fusion proteins in prefusion conformation holds the potential to apply similar methods to this group of viral fusogens. In addition to a better understanding of the herpesviral fusion mechanism, the structural insights gained will help to find ways to further stabilise these proteins using the methods described to obtain stable immunogens that will form the basis for the development of the next generation of vaccines and antiviral drugs.

Discovery of Pentacyclic Triterpenoid PROTACs as a Class of Effective Hemagglutinin Protein Degraders

Influenza hemagglutinin that drives viral entry into cells via the membrane fusion process is an up-and-coming antiviral drug target. Herein, we described for the first time the design, synthesis, and biological characteristics of a new class of pentacyclic triterpenoid-based proteolysis targeting chimeras (PROTACs) to enhance the degradation of hemagglutinin target. Among these PROTACs, V3 showed the best degradation effect on the hemagglutinin with a median degradation concentration of 1.44 μM in a ubiquitin and proteasome-dependent manner and broad-spectrum anti-influenza A virus activity but not affected the entry of influenza virus. Moreover, intravenous injection of V3 protected mice against influenza A virus-induced toxic effects. Further diazirine-containing photo-crosslinking mass spectrometric analysis of hemagglutinin complexes indicated crosslinking to Asn15, Thr31, and Asn27, a novel target of hemagglutinin. Taken together, our data revealed that oleanolic acid-based PROTACs could degrade hemagglutinin protein, providing a new direction toward the discovery of potential anti-influenza drugs.

Design of protein-binding proteins from the target structure alone

The design of proteins that bind to a specific site on the surface of a target protein using no information other than the three-dimensional structure of the target remains a challenge1-5. Here we describe a general solution to this problem that starts with a broad exploration of the vast space of possible binding modes to a selected region of a protein surface, and then intensifies the search in the vicinity of the most promising binding modes. We demonstrate the broad applicability of this approach through the de novo design of binding proteins to 12 diverse protein targets with different shapes and surface properties. Biophysical characterization shows that the binders, which are all smaller than 65 amino acids, are hyperstable and, following experimental optimization, bind their targets with nanomolar to picomolar affinities. We succeeded in solving crystal structures of five of the binder-target complexes, and all five closely match the corresponding computational design models. Experimental data on nearly half a million computational designs and hundreds of thousands of point mutants provide detailed feedback on the strengths and limitations of the method and of our current understanding of protein-protein interactions, and should guide improvements of both. Our approach enables the targeted design of binders to sites of interest on a wide variety of proteins for therapeutic and diagnostic applications.

Novel β-Cyclodextrin-Based Heptavalent Glycyrrhetinic Acid Conjugates: Synthesis, Characterization, and Anti-Influenza Activity

In our continuing efforts toward the design of novel pentacyclic triterpene derivatives as potential anti-influenza virus entry inhibitors, a series of homogeneous heptavalent glycyrrhetinic acid derivatives based on β-cyclodextrin scaffold were designed and synthesized by click chemistry. The structure was unambiguously characterized by NMR, IR, and MALDI-TOF-MS measurements. Seven conjugates showed sufficient inhibitory activity against influenza virus infection based on the cytopathic effect reduction assay with IC50 values in the micromolar range. The interactions of conjugate 37, the most potent compound (IC50 = 2.86 μM, CC50 > 100 μM), with the influenza virus were investigated using the hemagglutination inhibition assay. Moreover, the surface plasmon resonance assay further confirmed that compound 37 bound to the influenza HA protein specifically with a dissociation constant of 5.15 × 10−7 M. Our results suggest the promising role of β-cyclodextrin as a scaffold for preparing a variety of multivalent compounds as influenza entry inhibitors.

Broad-Spectrum Activity of Small Molecules Acting against Influenza a Virus: Biological and Computational Studies

Influenza still represents a problematic disease, involving millions of people every year and causing hundreds of thousands of deaths. Only a few drugs are clinically available. The search for an effective weapon is still ongoing. In this scenario, we recently identified new drug-like compounds with antiviral activity toward two A/H1N1 Influenza virus strains, which were demonstrated to interfere with the processes mediated by hemagglutinin (HA). In the present work, the compound’s ability to act against the A/H3N2 viral strain has been evaluated in hemagglutination inhibition (HI) assays. Two of the five tested compounds were also active toward the A/H3N2 Influenza virus. To validate the scaffold activity, analogue compounds of two broad-spectrum molecules were selected and purchased for HI testing on both A/H1N1 and A/H3N2 Influenza viruses. Forty-three compounds were tested, and four proved to be active toward all three viral strains. A computational study has been carried out to depict the HA binding process of the most interesting compounds.

Polyanionic Amphiphilic Dendritic Polyglycerols as Broad-Spectrum Viral Inhibitors with a Virucidal Mechanism

Heparin has been known to be a broad-spectrum inhibitor of viral infection for almost 70 years, and it has been used as a medication for almost 90 years due to its anticoagulant effect. This nontoxic biocompatible polymer efficiently binds to many types of viruses and prevents their attachment to cell membranes. However, the anticoagulant properties are limiting their use as an antiviral drug. Many heparin-like compounds have been developed throughout the years; however, the reversible nature of the virus inhibition mechanism has prevented their translation to the clinics. In vivo, such a mechanism requires the unrealistic maintenance of the concentration above the binding constant. Recently, we have shown that the addition of long hydrophobic linkers to heparin-like compounds renders the interaction irreversible while maintaining the low-toxicity and broad-spectrum activity. To date, such hydrophobic linkers have been used to create heparin-like gold nanoparticles and β-cyclodextrins. The former achieves a nanomolar inhibition concentration on a non-biodegradable scaffold. The latter, on a fully biodegradable scaffold, shows only a micromolar inhibition concentration. Here, we report that the addition of hydrophobic linkers to a new type of multifunctional scaffold (dendritic polyglycerol, dPG) creates biocompatible compounds endowed with nanomolar activity. Furthermore, we present an in-depth analysis of the molecular design rules needed to achieve irreversible virus inhibition. The most active compound (dPG-5) showed nanomolar activity against herpes simplex virus 2 (HSV-2) and respiratory syncytial virus (RSV), giving a proof-of-principle for broad-spectrum while keeping low-toxicity. In addition, we demonstrate that the virucidal activity leads to the release of viral DNA upon the interaction between the virus and our polyanionic dendritic polymers. We believe that this paper will be a stepping stone toward the design of a new class of irreversible nontoxic broad-spectrum antivirals.

pH-Dependent Mechanisms of Influenza Infection Mediated by Hemagglutinin

Influenza hemagglutinin (HA) is a viral membrane bound protein that plays a critical role in the viral life cycle by mediating entry into target cells. HA exploits the lowering of the pH in the endosomal compartment to initiate a series of conformational changes that promote access of the viral genetic material to the cytoplasm, and hence viral replication. In this review we will first discuss what is known about the structural properties of HA as a function of pH. Next, we will discuss the dynamics and intermediate states of HA. We will then discuss the specific residues that are thought to be titrated by the change in pH and possible mechanisms for the pH triggered conformational changes. Finally, we will discuss small molecules that disrupt the pH trigger and thus serve as potential therapeutic strategies to prevent influenza infection.

Understanding the regioselectivity of 5-substituted 1H-tetrazoles alkylation

A novel rational to account for the selectivity of 5-substituted 1H-tetrazole alkylation.

Peering into Avian Influenza A(H5N8) for a Framework towards Pandemic Preparedness

2014 marked the first emergence of avian influenza A(H5N8) in Jeonbuk Province, South Korea, which then quickly spread worldwide. In the midst of the 2020-2021 H5N8 outbreak, it spread to domestic poultry and wild waterfowl shorebirds, leading to the first human infection in Astrakhan Oblast, Russia. Despite being clinically asymptomatic and without direct human-to-human transmission, the World Health Organization stressed the need for continued risk assessment given the nature of Influenza to reassort and generate novel strains. Given its promiscuity and easy cross to humans, the urgency to understand the mechanisms of possible species jumping to avert disastrous pandemics is increasing. Addressing the epidemiology of H5N8, its mechanisms of species jumping and its implications, mutational and reassortment libraries can potentially be built, allowing them to be tested on various models complemented with deep-sequencing and automation. With knowledge on mutational patterns, cellular pathways, drug resistance mechanisms and effects of host proteins, we can be better prepared against H5N8 and other influenza A viruses.

Design and Synthesis of Oleanolic Acid Trimers to Enhance Inhibition of Influenza Virus Entry

Influenza is a major threat to millions of people worldwide. Entry inhibitors are of particular interest for the development of novel therapeutic strategies for influenza. We have previously discovered oleanolic acid (OA) to be a mild influenza hemagglutinin (HA) inhibitor. In this work, inspired by the 3D structure of HA as a homotrimeric receptor, we designed and synthesized 15 OA trimers with different linkers and central region via the copper-catalyzed azide-alkyne cycloaddition reaction. All of the OA trimers were evaluated for their antiviral activities in vitro, and 12c, 12e, 13c, and 13d were observed to exhibit robust potency (IC₅₀ in the submicromolar range) against influenza A/WSN/33 (H1N1) virus that was stronger than that observed with oseltamivir. In addition, these compounds also displayed strong biological activity against A/Hong Kong/4801/2014 and B/Sichuan/531/2018 (BV). The results of hemagglutination inhibition assays and surface plasmon resonance binding assays suggest that these OA trimers may interrupt the interaction between the HA protein of influenza virus and the host cell sialic acid receptor, thus blocking viral entry. These findings highlight the utility of multivalent OA conjugates to enhance the ligand-target interactions in anti-influenza virus drug design and are also helpful for studying antiviral drugs derived from natural products.

Hemagglutinin Structure and Activities

Hemagglutinins (HAs) are the receptor-binding and membrane fusion glycoproteins of influenza viruses. They recognize sialic acid-containing, cell-surface glycoconjugates as receptors but have limited affinity for them, and, as a consequence, virus attachment to cells requires their interaction with several virus HAs. Receptor-bound virus is transferred into endosomes where membrane fusion by HAs is activated at pH between 5 and 6.5, depending on the strain of virus. Fusion activity requires extensive rearrangements in HA conformation that include extrusion of a buried "fusion peptide" to connect with the endosomal membrane, form a bridge to the virus membrane, and eventually bring both membranes close together. In this review, we give an overview of the structures of the 16 genetically and antigenically distinct subtypes of influenza A HA in relation to these two functions in virus replication and in relation to recognition of HA by antibodies that neutralize infection.

Small-Molecule Inhibition of Viral Fusion Glycoproteins

Viral fusion glycoproteins catalyze membrane fusion during viral entry. Unlike most enzymes, however, they lack a conventional active site in which formation or scission of a specific covalent bond is catalyzed. Instead, they drive the membrane fusion reaction by cojoining highly regulated changes in conformation to membrane deformation. Despite the challenges in applying inhibitor design approaches to these proteins, recent advances in knowledge of the structures and mechanisms of viral fusogens have enabled the development of small-molecule inhibitors of both class I and class II viral fusion proteins. Here, we review well-validated inhibitors, including their discovery, targets, and mechanism(s) of action, while highlighting mechanistic similarities and differences. Together, these examples make a compelling case for small-molecule inhibitors as tools for probing the mechanisms of viral glycoprotein-mediated fusion and for viral glycoproteins as druggable targets.

Aryl Sulfonamide Inhibits Entry and Replication of Diverse Influenza Viruses via the Hemagglutinin Protein

Influenza viruses cause approximately half a million deaths every year worldwide. Vaccines are available but partially effective, and the number of antiviral medications is limited. Thus, it is crucial to develop therapeutic strategies to counteract this major pathogen. Influenza viruses enter the host cell via their hemagglutinin (HA) proteins. The HA subtypes of influenza A virus are phylogenetically classified into groups 1 and 2. Here, we identified an inhibitor of the HA protein, a tertiary aryl sulfonamide, that prevents influenza virus entry and replication. This compound shows potent antiviral activity against diverse H1N1, H5N1, and H3N2 influenza viruses encoding HA proteins from both groups 1 and 2. Synthesis of derivatives of this aryl sulfonamide identified moieties important for antiviral activity. This compound may be considered as a lead for drug development with the intent to be used alone or in combination with other influenza A virus antivirals to enhance pan-subtype efficacy.

Small Molecule Inhibitors of Influenza Virus Entry

Hemagglutinin (HA) plays a critical role during influenza virus receptor binding and subsequent membrane fusion process, thus HA has become a promising drug target. For the past several decades, we and other researchers have discovered a series of HA inhibitors mainly targeting its fusion machinery. In this review, we summarize the advances in HA-targeted development of small molecule inhibitors. Moreover, we discuss the structural basis and mode of action of these inhibitors, and speculate upon future directions toward more potent inhibitors of membrane fusion and potential anti-influenza drugs.

Optimization and SAR research at the piperazine and phenyl rings of JNJ4796 as new anti-influenza A virus agents, part 1

JNJ4796, a small molecule fuse inhibitor targeting the conserved stem region of hemagglutinin, effectively neutralized a broad spectrum of group 1 influenza A virus (IAV), and protected mice against lethal and sublethal influenza challenge after oral administration. In this study, we reported the modification and structure-activity relationship (SAR) of C (piperazine ring) and E (phenyl ring) rings of JNJ4796. Compound (R)-2c was identified to show excellent in vitro activity against IAV H1N1 and Oseltamivir-resistant IAV H1N1 stains (IC₅₀: 0.03-0.06 μM), low cytotoxicity (CC₅₀ > 200 μM), accepted oral PK profiles and low inhibition rate of hERG (13.2%, at 10 μM). Evaluation for the in vivo anti-IAV efficacy of (R)-2c will begin soon.

A simple cost-effective microfluidic platform for rapid synthesis of diverse metal nanoparticles: A novel approach towards fighting SARS-CoV-2

The latest addition to the family of Coronaviruses, SARS-CoV-2, unleashed its wrath across the globe. The outbreak has been so rapid and widespread that even the most developed countries are still struggling with ways to contain the spread of the virus. The virus began spreading from Wuhan in China in December 2019 and has currently affected more than200 countries worldwide. Nanotechnology has huge potential for killing viruses as severe as HIV, herpes, human papilloma virus, and viruses of the respiratory tract, both inside as well as outside the host. Metal-nanoparticles can be employed for biosensing methodology of viruses/bacteria, along with the development of novel drugs and vaccines for COVID-19 and future pandemics. It is thus required for the nanoparticles to be synthesized quickly along with precise control over their size distribution. In this study, we propose a simple microfluidic-reactor-platform for in-situ metal-nanoparticle synthesis to be used against the pandemic for the development of preventive, diagnostic, and antiviral drug therapies. The device has been fabricated using a customized standard photolithography process using a simple and cost-effective setup. The confirmation on standard silver and gold metal nanoparticle formation in the microfluidic reactor platform was analysed using optical fiber spectrophotometer. This novel microfluidic platform provides the advantage of in-situ synthesis, flow parameter control and reduced agglomeration of nanoparticles over the bulk synthesis due to segregation of nucleation and growth stages inside a microchannel. The results are highly reproducible and hence scaling up of the nanoparticle production is possible without involving complex instrumentation.

Structural Basis for the Understanding of Entry Inhibitors Against SARS Viruses

Outbreaks due to Severe Acute Respiratory Syndrome-Corona virus 2 (SARS-CoV-2) initiated in Wuhan city, China, in December 2019 which continued to spread internationally, posing a pandemic threat as declared by WHO and as of March 10, 2021, confirmed cases reached 118 million along with 2.6 million deaths worldwide. In the absence of specific antiviral medication, symptomatic treatment and physical isolation remain the options to control the contagion. The recent clinical trials on antiviral drugs highlighted some promising compounds such as umifenovir (haemagglutinin-mediated fusion inhibitor), remdesivir (RdRp nucleoside inhibitor), and favipiravir (RdRp Inhibitor). WHO launched a multinational clinical trial on several promising analogs as a potential treatment to combat SARS infection. This situation urges a holistic approach to invent safe and specific drugs as a prophylactic and therapeutic cure for SARS-related-viral diseases, including COVID-19. It is significant to note that researchers worldwide have been doing their best to handle the crisis and have produced an extensive and promising literature body. It opens a scope and allows understanding the viral entry at the molecular level. A structure-based approach can reveal the molecular-level understanding of viral entry interaction. The ligand profiling and non-covalent interactions among participating amino-acid residues are critical information to delineate a structural interpretation. The structural investigation of SARS virus entry into host cells will reveal the possible strategy for designing drugs like entry inhibitors. The structure-based approach demonstrates details at the 3D molecular level. It shows specificity about SARS-CoV-2 spike interaction, which uses human angiotensin-converting enzyme 2 (ACE2) as a receptor for entry, and the human protease completes the process of viral fusion and infection. The 3D structural studies reveal the existence of two units, namely S1 and S2. S1 is called a receptor-binding domain (RBD) and responsible for interacting with the host (ACE2), and the S2 unit participates in the fusion of viral and cellular membranes. TMPRSS2 mediates the cleavage at S1/S2 subunit interface in S-protein of SARS CoV-2, leading to viral fusion. Conformational difference associated with S1 binding alters ACE2 interaction and inhibits viral fusion. Overall, the detailed 3D structural studies help understand the 3D structural basis of interaction between viruses with host factors and available scope for the new drug discovery process targeting SARS-related virus entry into the host cell.

Macrocyclic peptides exhibit antiviral effects against influenza virus HA and prevent pneumonia in animal models

Most anti-influenza drugs currently used, such as oseltamivir and zanamivir, inhibit the enzymatic activity of neuraminidase. However, neuraminidase inhibitor-resistant viruses have already been identified from various influenza virus isolates. Here, we report the development of a class of macrocyclic peptides that bind the influenza viral envelope protein hemagglutinin, named iHA. Of 28 iHAs examined, iHA-24 and iHA-100 have inhibitory effects on the in vitro replication of a wide range of Group 1 influenza viruses. In particular, iHA-100 bifunctionally inhibits hemagglutinin-mediated adsorption and membrane fusion through binding to the stalk domain of hemagglutinin. Moreover, iHA-100 shows powerful efficacy in inhibiting the growth of highly pathogenic influenza viruses and preventing severe pneumonia at later stages of infection in mouse and non-human primate cynomolgus macaque models. This study shows the potential for developing cyclic peptides that can be produced more efficiently than antibodies and have multiple functions as next-generation, mid-sized biomolecules.

Genetic and biological properties of H7N9 avian influenza viruses detected after application of the H7N9 poultry vaccine in China

The H7N9 avian influenza virus (AIV) that emerged in China have caused five waves of human infection. Further human cases have been successfully prevented since September 2017 through the use of an H7N9 vaccine in poultry. However, the H7N9 AIV has not been eradicated from poultry in China, and its evolution remains largely unexplored. In this study, we isolated 19 H7N9 AIVs during surveillance and diagnosis from February 2018 to December 2019, and genetic analysis showed that these viruses have formed two different genotypes. Animal studies indicated that the H7N9 viruses are highly lethal to chicken, cause mild infection in ducks, but have distinct pathotypes in mice. The viruses bound to avian-type receptors with high affinity, but gradually lost their ability to bind to human-type receptors. Importantly, we found that H7N9 AIVs isolated in 2019 were antigenically different from the H7N9 vaccine strain that was used for H7N9 influenza control in poultry, and that replication of these viruses cannot, therefore, be completely prevented in vaccinated chickens. We further revealed that two amino acid mutations at positions 135 and 160 in the HA protein added two glycosylation sites and facilitated the escape of the H7N9 viruses from the vaccine-induced immunity. Our study provides important insights into H7N9 virus evolution and control.