6SLN-lipo PGA specifically catches (coats) human influenza virus and synergizes neuraminidase-targeting drugs for human influenza therapeutic potential

Anti-influenza virus activity of the REV-ERBα agonist SR9009 and related analogues

REV-ERBα is a member of the nuclear receptor superfamily of transcription factors that aids in the regulation of many diseases. However, the prospect of using REV-ERBα for anti-influenza virus treatment remains poorly described, and there is an urgent need to develop effective anti-influenza agents due to the emergence of drug-resistant influenza viruses. In this study, eight SR9009 analogues were designed, synthesized, and evaluated for their biological activities against multiple influenza virus strains (H1N1, H3N2, adamantane- and oseltamivir-resistant H1N1 and influenza B virus), using ribavirin as the positive control. SR9009 and its analogues showed low micromolar or submicromolar EC₅₀ values and exhibited modestly improved antiviral potency compared to that of ribavirin. In particular, compound 5a possessed the most potent inhibitory activity (EC₅₀ = 0.471, 0.644, 1.644, 0.712 and 0.661 μM for A/PR/8/34, A/WSN/33, A/Wisconsin/67/2005, B/Yamagata/16/88 and Hebei/SWL1/2006, respectively). Cotransfection assays showed that all synthesized derivatives efficaciously suppressed transcription driven by the Bmal1 promoter. Mechanistic study results indicated that 5a efficiently inhibited IAV replication and interfered with the ealry stage of influenza virus life cycle. In addition, we found that 5a upregulated the key antiviral interferon-stimulated genes MxA, OAS2 and CH25H. Further in-depth transcriptome analysis revealed a series of upregulated genes that may contribute to the antiviral activities of 5a. These findings may provide an important direction for the development of new host-targeted broad-spectrum antiviral agents.

Significant role of host sialylated glycans in the infection and spread of severe acute respiratory syndrome coronavirus 2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been transmitted across all over the world, in contrast to the limited epidemic of genetically- and virologically-related SARS-CoV. However, the molecular basis explaining the difference in the virological characteristics among SARS-CoV-2 and SARS-CoV has been poorly defined. Here we identified that host sialoglycans play a significant role in the efficient spread of SARS-CoV-2 infection, while this was not the case with SARS-CoV. SARS-CoV-2 infection was significantly inhibited by α2-6-linked sialic acid-containing compounds, but not by α2–3 analog, in VeroE6/TMPRSS2 cells. The α2-6-linked compound bound to SARS-CoV-2 spike S1 subunit to competitively inhibit SARS-CoV-2 attachment to cells. Enzymatic removal of cell surface sialic acids impaired the interaction between SARS-CoV-2 spike and angiotensin-converting enzyme 2 (ACE2), and suppressed the efficient spread of SARS-CoV-2 infection over time, in contrast to its least effect on SARS-CoV spread. Our study provides a novel molecular basis of SARS-CoV-2 infection which illustrates the distinctive characteristics from SARS-CoV.

SARS-CoV-2, which has been highly transmissible and rapidly spreading worldwide, has caused approximately 458 million confirmed cases of COVID-19 with more than 6 million deaths by March 2022. Here we found that SARS-CoV-2 infection was significantly inhibited by α2-6-linked sialic acid-containing compounds and by depletion of cell surface sialic acid with only a minor effect on SARS-CoV infection. We identified that SARS-CoV-2 spike S1 subunit directly binds to α2-6-linked sialoglycans for efficient attachment to host cell surface. Our finding indicated that host sialoglycans play a significant role in the efficient infection of SARS-CoV-2, which provides a novel understanding of the molecular basis explaining the rapid spread of SARS-CoV-2 over SARS-CoV.

Synthesis and Neuraminidase Inhibitory Activity of Sialic Acid Analogues with Fluoro, Phosphono, and Sulfo Functionalities

Methods to synthesize influenza virus inhibitors with fluoro, phosphono, and/or sulfo functional groups are described. The resulting sialic acid analogues are produced from the natural substrate N-acetylneuraminic acid as starting material. Fluorescent assay methods for inhibition of influenza neuraminidase and virus proliferation are also provided.

Roles of Glycans and Non-glycans on the Epithelium and in the Immune System in H1-H18 Influenza A Virus Infections

The large variation of influenza A viruses (IAVs) in various susceptible hosts and their rapid evolution, which allows host/tissue switching, host immune escape, vaccine escape, and drug resistance, are difficult challenges for influenza control in all countries worldwide. Access and binding of the IAV to actual receptors at endocytic sites is critical for the establishment of influenza infection. In this chapter, the progress in identification of and roles of glycans and non-glycans on the epithelium and in the immune system in H1-H18 IAV infections are reviewed. The first part of the review is on current knowledge of H1-H16 IAV receptors on the epithelium including sialyl glycans, other negatively charged glycans, and annexins. The second part of the review focuses on H1-H16 IAV receptors in the immune system including acidic surfactant phospholipids, Sia on surfactant proteins, the carbohydrate recognition domain (CRD) of surfactant proteins, Sia on mucins, Sia and C-type lectins on macrophages and dendritic cells, and Sia on NK cells. The third part of the review is about a possible H17-H18 IAV receptor. Binding of these receptors to IAVs may result in inhibition or enhancement of IAV infection depending on their location, host cell type, and IAV strain. Among these receptors, host sialyl glycans are key determinants of viral hemagglutinin (HA) lectins for H1-H16 infections. HA must acquire mutations to bind to sialyl glycans that are dominant on a new target tissue when switching to a new host for efficient transmission and to bind to long sialyl glycans found in the case of seasonal HAs with multiple glycosylation sites as a consequence of immune evasion. Although sialyl receptors/C-type lectins on immune cells are decoy receptors/pathogen recognition receptors for capturing viral HA lectin/glycans protecting HA antigenic sites, some IAV strains do not escape, such as by release with neuraminidase, but hijack these molecules to gain entry and replication in immune cells. An understanding of the virus-host battle tactics at the receptor level might lead to the establishment of novel strategies for effective control of influenza.

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.

Identification and Screening of Natural Neuraminidase Inhibitors from Reduning Injection via One-Step High-Performance Liquid Chromatography-Fraction Collector and UHPLC/Q-TOF-MS

Neuraminidase plays an essential role in the spread of influenza viruses via cleaving sialic acids from the host cell receptors and virions. Neuraminidase has been regarded as an essential target for prevention and treatment of influenza infection. The one-step high-performance liquid chromatography-fraction collector (HPLC-FC) was selected to prepare fractions from Reduning (RDN) injection, while ultra-high-performance liquid chromatography/quadrupole-time-of-flight mass spectrometry (UHPLC/Q-TOF-MS) was used to identify fractions depending on their retention time and molecular ion. As a result, 75 fractions were prepared and 28 fractions out of them exhibited NA inhibitory effects with the dose-effect relationship. Exploring it further, six components including neochlorogenic acid, chlorogenic acid, cryptochlorogenic acid, isochlorogenic acid B, isochlorogenic acid A, and isochlorogenic acid C were the main components that accounted for almost 80% of inhibitory activity of RDN injection. Accordingly, these results demonstrated that this strategy could not only rapidly identify but also accurately screen active components from traditional Chinese medicine.

Advances in the development of entry inhibitors for sialic-acid-targeting viruses

Over the past decades, several antiviral drugs have been developed to treat a range of infections. Yet the number of treatable viral infections is still limited, and resistance to current drug regimens is an ever-growing problem. Therefore, additional strategies are needed to provide a rapid cure for infected individuals. An interesting target for antiviral drugs is the process of viral attachment and entry into the cell. Although most viruses use distinct host receptors for attachment to the target cell, some viruses share receptors, of which sialic acids are a common example. This review aims to give an update on entry inhibitors for a range of sialic-acid-targeting viruses and provides insight into the prospects for those with broad-spectrum potential.

Host Receptors of Influenza Viruses and Coronaviruses-Molecular Mechanisms of Recognition

Among the four genera of influenza viruses (IVs) and the four genera of coronaviruses (CoVs), zoonotic αIV and βCoV have occasionally caused airborne epidemic outbreaks in humans, who are immunologically naïve, and the outbreaks have resulted in high fatality rates as well as social and economic disruption and losses. The most devasting influenza A virus (IAV) in αIV, pandemic H1N1 in 1918, which caused at least 40 million deaths from about 500 million cases of infection, was the first recorded emergence of IAVs in humans. Usually, a novel human-adapted virus replaces the preexisting human-adapted virus. Interestingly, two IAV subtypes, A/H3N2/1968 and A/H1N1/2009 variants, and two lineages of influenza B viruses (IBV) in βIV, B/Yamagata and B/Victoria lineage-like viruses, remain seasonally detectable in humans. Both influenza C viruses (ICVs) in γIV and four human CoVs, HCoV-229E and HCoV-NL63 in αCoV and HCoV-OC43 and HCoV-HKU1 in βCoV, usually cause mild respiratory infections. Much attention has been given to CoVs since the global epidemic outbreaks of βSARS-CoV in 2002–2004 and βMERS-CoV from 2012 to present. βSARS-CoV-2, which is causing the ongoing COVID-19 pandemic that has resulted in 890,392 deaths from about 27 million cases of infection as of 8 September 2020, has provoked worldwide investigations of CoVs. With the aim of developing efficient strategies for controlling virus outbreaks and recurrences of seasonal virus variants, here we overview the structures, diversities, host ranges and host receptors of all IVs and CoVs and critically review current knowledge of receptor binding specificity of spike glycoproteins, which mediates infection, of IVs and of zoonotic, pandemic and seasonal CoVs.

Chemoreactive-Inspired Discovery of Influenza A Virus Dual Inhibitor to Block Hemagglutinin-Mediated Adsorption and Membrane Fusion

Owing to the emergence of drug resistance and high morbidity and mortality, the need for novel anti-influenza A virus (IAV) drugs with divergent targets is highly sought after. Herein, we reveal the discovery of an anti-IAV agent as a dual inhibitor to block hemagglutinin-mediated adsorption and membrane fusion using a chemoreactive ortho-quinone methide (o-QM) equivalent. Based on the o-QM equivalent nonenzymatically multipotent behavior, we created a series of clavatol-derived pseudo-natural products and found that penindolone (PND), a new diclavatol indole adduct, exhibited potent and broad-spectrum anti-IAV activities with low risk of inducing drug resistance. Distinct from current anti-IAV drugs, PND possesses a novel scaffold and is the first IAV inhibitor targeting both HA1 and HA2 subunits of virus hemagglutinin to dually block the IAV adsorption and membrane fusion process. More importantly, intranasal and oral administration of PND can protect mice against IAV-induced death and weight loss, superior to the effects of the clinical drug oseltamivir. Thus, the use of chemoreactive intermediates could expand our understanding of chemical diversity and aid in the development of anti-IAV drugs with novel targets.

Sialoglycovirology of Lectins: Sialyl Glycan Binding of Enveloped and Non-enveloped Viruses

On the cell sur "face", sialoglycoconjugates act as receptionists that have an important role in the first step of various cellular processes that bridge communication between the cell and its environment. Loss of Sia production can cause the developmental of defects and lethality in most animals; hence, animal cells are less prone to evolution of resistance to interactions by rapidly evolved Sia-binding viruses. Obligative intracellular viruses mostly have rapid evolution that allows escape from host immunity, leading to an epidemic variant, and that allows emergence of a novel strain, occasionally leading to pandemics that cause health-social-economic problems. Recently, much attention has been given to the mutual recognition systems via sialosugar chains between viruses and their host cells and there has been rapid growth of the research field "sialoglycovirology." In this chapter, the structural diversity of sialoglycoconjugates is overviewed, and enveloped and non-enveloped viruses that bind to Sia are reviewed. Also, interactions of viral lectins-host Sia receptors, which determine viral transmission, host range, and pathogenesis, are presented. The future direction of new therapeutic routes targeting viral lectins, development of easy-to-use detection methods for diagnosis and monitoring changes in virus binding specificity, and challenges in the development of suitable viruses to use in virus-based therapies for genetic disorders and cancer are discussed.

Hemagglutinin Inhibitors are Potential Future Anti-Influenza Drugs for Mono- and Combination Therapies

Infections by H1-H16 influenza A viruses require sufficient binding of viral hemagglutinins (HAs) to specific target receptors, glycoconjugates bearing sialyl sugar chains, on the host cell surface. Synthesized sialyl sugar chains targeting sialyl sugar-binding sites in HAs that are immutable as long as the virus does not switch to a different host species might therefore be highly effective candidate drugs for inhibition of the initial required step of virus entry. In this chapter, we describe the following aspects of updated sialyl sugar chains as influenza A virus HA inhibitors (HAIs): (1) mode of terminal sialyl-galactose linkage, (2) molecular length and structure of sialyl glycan receptors, (3) multivalent sialyl sugar chain dimension, (4) clustering of sialyl sugar chains on macromolecular scaffolds, and (5) enhancement of the stability of sialyl sugar chain HA inhibitors. We also discuss about the use of HAI-based combinations that should be considered for future influenza therapy.

Design, Synthesis, and Biological Evaluation of EdAP, a 4'-Ethynyl-2'-Deoxyadenosine 5'-Monophosphate Analog, as a Potent Influenza a Inhibitor

Influenza A viruses leading to infectious respiratory diseases cause seasonal epidemics and sometimes periodic global pandemics. Viral polymerase is an attractive target in inhibiting viral replication, and 4′-ethynyladenosine, which has been reported as a highly potent anti-human immunodeficiency virus (HIV) nucleoside derivative, can work as an anti-influenza agent. Herein, we designed and synthesized a 4′-ethynyl-2′-deoxyadenosine 5′-monophosphate analog called EdAP (5). EdAP exhibited potent inhibition against influenza virus multiplication in Madin–Darby canine kidney (MDCK) cells transfected with human α2-6-sialyltransferase (SIAT1) cDNA and did not show any toxicity toward the cells. Surprisingly, this DNA-type nucleic acid analog (5) inhibited the multiplication of influenza A virus, although influenza virus is an RNA virus that does not generate DNA.

N-glycan structures of human alveoli provide insight into influenza A virus infection and pathogenesis

The rapidly evolvable influenza A virus has caused pandemics linked to millions of deaths in the past century. Influenza A viruses are categorized by H (hemagglutinin; HA) and N (neuraminidase; NA) proteins expressed on the viral envelope surface. Analyses of past pandemics suggest that the HA gene segment comes from a nonhuman virus, which is then introduced into an immunologically naïve human population with potentially devastating consequences. As a prerequisite for infection, the nonhuman HA molecules of H1-H16 viruses must be able to bind to specific sialyl receptors on the host cell surface along the human respiratory tract. Thus, additional insight into the structures of host cell glycans and how different HAs interact with different glycans might provide new insight into the mechanisms underlying sustained infection and transmission in humans. In this work, we identified the sialyl N-glycans found in normal human alveoli and characterized the influenza viruses that preferentially bound to these different structures. We also determined the amino acid changes in HA that were linked to a switch of receptor-binding preference from nonhuman to pandemic, as well as pandemic to seasonal. Our data provide insight into why seasonal viruses are associated with reduced alveolar infection and damage and suggest new considerations for designing anti-HA vaccines and drugs. The results provide a better understanding of viral tropism and pathogenesis in humans that will be important for prediction and surveillance of zoonotic, pandemic, and epidemic influenza outbreaks.

DATABASE

The novel hemagglutinin nucleotide sequences reported here were deposited in GISAID under the accession numbers of EPI685738 for A/Yamaguchi/20/2006(H1N1) and EPI685740 for A/Kitakyushu/10/2006(H1N1).

Synthesis of Fucoidan-Mimetic Glycopolymers with Well-Defined Sulfation Patterns via Emulsion Ring-Opening Metathesis Polymerization

The approach developed here offers distinct and well-defined glycopolymers for deciphering the biological roles of natural bioactive polysaccharides. Fucose monomers were chemically synthesized and decorated with specific sulfation patterns including unsulfate, monosulfate, disulfate, and trisulfate groups. The six fucoidan-mimetic glycopolymers (18-23) were successfully fabricated through microwave-assisted ring-opening metathesis polymerization (ROMP) in an emulsion system. The molecular weight (M_w), polydispersity index (PDI), and multiple functional groups were fully characterized by SEC-MALLS-RI and NMR spectroscopy. Three glycopolymers (19, 21, 23) associated with 2-O-sulfation exhibited better inhibitory effects on the H1N1 virus, while glycopolymers (19, 20) with monosulfate groups were more effective against the H3N2 virus. These findings would promote the development of novel anti-influenza A virus (IAV) drugs based on natural fucoidans.

Inhibition effects of novel polyketide compound PPQ-B against influenza A virus replication by interfering with the cellular EGFR pathway

Development of anti-influenza A virus (IAV) drugs with novel targets and low toxicity is critical for preparedness against influenza outbreaks. In the current study, our results indicated that the novel polyketide compound purpurquinone B (PPQ-B) derived from acid-tolerant fungus Penicillium purpurogenum strain JS03-21 suppressed the replication of IAV in vitro with low toxicity, and may block some stages after virus adsorption. PPQ-B could inhibit H1N1 (A/Puerto Rico/8/34; PR8), H1N1 (A/California/04/2009; Cal09) and H3N2 (A/swine/Minnesota/02719/2009) virus replication in vitro, suggesting that PPQ-B possesses broad-spectrum anti-IAV activities. PPQ-B's antiviral activity may be largely related to its inhibition of some steps that occur 0-4 h after adsorption. Oral administration of PPQ-B could decrease pulmonary viral titers and improve survival rate in IAV infected mice. PPQ-B also significantly decreased the production of inflammatory factors TNF-α, IL-6, RANTES and KC in IAV infected lungs and A549 cells, suggesting that PPQ-B may also attenuate the inflammatory responses caused by IAV infection. PPQ-B may down-regulate the NF-κB and MAPK pathways to inhibit both virus replication and inflammatory responses. In summary, PPQ-B has the potential to be developed into a novel anti-IAV drug targeting host EGFR pathway in the future.

Boronic Acid Modifications Enhance the Anti-Influenza A Virus Activities of Novel Quindoline Derivatives

The unique glycan-binding ability of chemically synthesized boronic acid derivatives makes them emerging candidates for developing anti-influenza A virus (IAV) drugs. Herein we report the synthesis and the anti-IAV activities of three series of novel boronic acid-modified quindoline derivatives both in vitro and in vivo. Boronic acid-modified compounds 6a and 7a effectively prevented the entry of virus RNP into the nucleus, reduced virus titers in IAV infected cells, and also inhibited the activity of viral neuraminidase. Compound 7a possessed broad antiviral spectrum and was able to inhibit cellular NF-κB and MAPK signaling pathways to block IAV infection. More importantly, IAV infected mice treated with compound 7a showed better survival rates than mice treated with oseltamivir, a popular anti-IAV drug. Thus, our study provides not only an antiviral preclinical candidate but also useful information for further research and development of boronic acid-modified anti-IAV drugs.

Inhibition of Influenza A Virus Infection by Fucoidan Targeting Viral Neuraminidase and Cellular EGFR Pathway

Development of novel anti-influenza A virus (IAV) drugs with high efficiency and low toxicity is critical for preparedness against influenza outbreaks. Herein, we investigated the anti-IAV activities and mechanisms of fucoidan in vitro and in vivo. The results showed that a fucoidan KW derived from brown algae Kjellmaniella crassifolia effectively blocked IAV infection in vitro with low toxicity. KW possessed broad anti-IAV spectrum and low tendency of induction of viral resistance, superior to the anti-IAV drug amantadine. KW was capable of inactivating virus particles before infection and blocked some stages after adsorption. KW could bind to viral neuraminidase (NA) and inhibit the activity of NA to block the release of IAV. KW also interfered with the activation of EGFR, PKCα, NF-κB, and Akt, and inhibited both IAV endocytosis and EGFR internalization in IAV-infected cells, suggesting that KW may also inhibit cellular EGFR pathway. Moreover, intranasal administration of KW markedly improved survival and decreased viral titers in IAV-infected mice. Therefore, fucoidan KW has the potential to be developed into a novel nasal drop or spray for prevention and treatment of influenza in the future.

A Novel Potent and Highly Specific Inhibitor against Influenza Viral N1-N9 Neuraminidases: Insight into Neuraminidase-Inhibitor Interactions

People throughout the world continue to be at risk for death from influenza A virus, which is always creating a new variant. Here we present a new effective and specific anti-influenza viral neuraminidase (viNA) inhibitor, 9-cyclopropylcarbonylamino-4-guanidino-Neu5Ac2en (cPro-GUN). Like zanamivir, it is highly effective against N1-N9 avian and N1-N2 human viNAs, including H274Y oseltamivir-resistant N1 viNA, due to its C-6 portion still being anchored in the active site, different from the disruption of oseltamivir's C-6 anchoring by H274Y mutation. Unlike zanamivir, no sialidase inhibitory activity has been observed for cPro-GUN against huNeu1-huNeu4 enzymes. Broad efficacy of cPro-GUN against avian and human influenza viruses in cell cultures comparable to its sialidase inhibitory activities makes cPro-GUN ideal for further development for safe therapeutic or prophylactic use against both seasonal and pandemic influenza.