Dual resistance to adamantanes and oseltamivir among seasonal influenza A(H1N1) viruses: 2008-2010

UiO-66 nanoparticles combat influenza A virus in mice by activating the RIG-I-like receptor signaling pathway

The Influenza A virus (IAV) is a zoonotic pathogen that infects humans and various animal species. Infection with IAV can cause fever, anorexia, and dyspnea and is often accompanied by pneumonia characterized by an excessive release of cytokines (i.e., cytokine storm). Nanodrug delivery systems and nanoparticles are a novel approach to address IAV infections. Herein, UiO-66 nanoparticles (NPs) are synthesized using a high-temperature melting reaction. The in vitro and in vivo optimal concentrations of UiO-66 NPs for antiviral activity are 200 μg mL-1 and 60 mg kg-1, respectively. Transcriptome analysis revealed that UiO-66 NPs can activate the RIG-I-like receptor signaling pathway, thereby enhancing the downstream type I interferon antiviral effect. These NPs suppress inflammation-related pathways, including the FOXO, HIF, and AMPK signaling pathways. The inhibitory effect of UiO-66 NPs on the adsorption and entry of IAV into A549 cells is significant. This study presents novel findings that demonstrate the effective inhibition of IAV adsorption and entry into cells via UiO-66 NPs and highlights their ability to activate the cellular RIG-I-like receptor signaling pathway, thereby exerting an anti-IAV effect in vitro or in mice. These results provide valuable insights into the mechanism of action of UiO-66 NPs against IAV and substantial data for advancing innovative antiviral nanomedicine.

Recombinant A(H6N1)-H274Y avian influenza virus with dual drug resistance does not require permissive mutations to retain the replicative fitness in vitro and in ovo

The possible emergence of drug-resistant avian flu raises concerns over the limited effectiveness of currently approved antivirals (neuraminidase inhibitors - NAIs) in the hypothetical event of a zoonotic spillover. Our study demonstrated that the recombinant avian A(H6N1) viruses showed reduced inhibition (RI) by multiple NAI drugs following the introduction of point mutations found predominantly in the neuraminidase gene (NA) of NAI-resistant human influenza strains (E119V, R292K and H274Y; N2 numbering). Moreover, A(H6N1)-H274Y showed increased replication efficiency in vitro, and a fitness advantage over wild-type (WT) when co-inoculated into embryonated hen's eggs. The results presented in our study together with the zoonotic potential of the A(H6N1) virus as evidenced by the human infection from 2013, highlight the need for enhanced monitoring of NAI resistance-associated signatures in circulating LPAI (low pathogenic avian influenza) globally.

Naturally Occurring Mutations of SARS-CoV-2 Main Protease Confer Drug Resistance to Nirmatrelvir

The SARS-CoV-2 main protease (Mpro) is the drug target of Pfizer's oral drug nirmatrelvir. The emergence of SARS-CoV-2 variants with mutations in Mpro raised the alarm of potential drug resistance. To identify potential clinically relevant drug-resistant mutants, we systematically characterized 102 naturally occurring Mpro mutants located at 12 residues at the nirmatrelvir-binding site, among which 22 mutations in 5 residues, including S144M/F/A/G/Y, M165T, E166 V/G/A, H172Q/F, and Q192T/S/L/A/I/P/H/V/W/C/F, showed comparable enzymatic activity to the wild-type (kcat/Km < 10-fold change) while being resistant to nirmatrelvir (Ki > 10-fold increase). X-ray crystal structures were determined for six representative mutants with and/or without GC-376/nirmatrelvir. Using recombinant SARS-CoV-2 viruses generated from reverse genetics, we confirmed the drug resistance in the antiviral assay and showed that Mpro mutants with reduced enzymatic activity had attenuated viral replication. Overall, our study identified several drug-resistant hotspots in Mpro that warrant close monitoring for possible clinical evidence of nirmatrelvir resistance, some of which have already emerged in independent viral passage assays conducted by others.

Picolinic acid is a broad-spectrum inhibitor of enveloped virus entry that restricts SARS-CoV-2 and influenza A virus in vivo

The COVID-19 pandemic highlights an urgent need for effective antivirals. Targeting host processes co-opted by viruses is an attractive antiviral strategy with a high resistance barrier. Picolinic acid (PA) is a tryptophan metabolite endogenously produced in mammals. Here, we report the broad-spectrum antiviral activity of PA against enveloped viruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), influenza A virus (IAV), flaviviruses, herpes simplex virus, and parainfluenza virus. Mechanistic studies reveal that PA inhibits enveloped virus entry by compromising viral membrane integrity, inhibiting virus-cellular membrane fusion, and interfering with cellular endocytosis. More importantly, in pre-clinical animal models, PA exhibits promising antiviral efficacy against SARS-CoV-2 and IAV. Overall, our data establish PA as a broad-spectrum antiviral with promising pre-clinical efficacy against pandemic viruses SARS-CoV-2 and IAV.

The Envelope (E) Protein of SARS-CoV-2 as a Pharmacological Target

The COVID-19 pandemic caused by the SARS-CoV-2 virus is still a global health concern. Several spike (S) protein-based vaccines have been developed that efficiently protect the human population against severe forms of COVID-19. However, some SARS-CoV-2 variants of concern (VOCs) have emerged that evade the protective effect of vaccine-induced antibodies. Therefore, efficient and specific antiviral treatments to control COVID-19 are indispensable. To date, two drugs have been approved for mild COVID-19 treatment; nevertheless, more drugs, preferably broad-spectrum and ready-to-use therapeutic agents for new pandemics, are needed. Here, I discuss the PDZ-dependent protein-protein interactions of the viral E protein with host proteins as attractive alternatives for the development of antivirals against coronavirus.

Anti-inflammatory effects of theaflavin-3'-gallate during influenza virus infection through regulating the TLR4/MAPK/p38 pathway

Severe pathological damage caused by the influenza virus is one of the leading causes of death. However, the prevention and control strategies for influenza virus infection have certain limitations, and the exploration for new influenza antiviral drugs has become the major research direction. This study evaluated the antiviral activities of four theaflavin derivatives (TFs). Cytopathic effect (CPE) reduction assay revealed that theaflavin-3'-gallate (TF2b) and theaflavin (TF1) could effectively inhibit the replication of influenza viruses H1N1-UI182, H1N1-PR8, H3N2, and H5N1, and TF2b exhibited the most significant antiviral activity in vivo. Intraperitoneal injection of TF2b at 40 mg/kg/d effectively alleviated viral pneumonia, maintained body weight, and improved the survival rate of mice infected with a lethal dose of H1N1-UI182 to 55.56%. Hematological analysis of peripheral blood further showed that TF2b increased the number of lymphocytes and decreased the number of neutrophils, monocytes, and platelets in the blood of infected mice. RT-qPCR results showed that TF2b reduced the mRNA expression levels of inflammatory cytokines (IL-6, TNF-α, and IL-1β), chemokines (CXCL-2 and CCL-3), and interferons (IFN-α and IFN-γ) after influenza virus infection. In addition, TF2b significantly down-regulated the expression levels of TLR4, p-p38, p-ERK, and cytokines IL-6, TNF-α, IL-1β, and IL-10. These results suggest that TF2b not only significantly inhibits viral replication and proliferation in vitro, but also alleviates pneumonia injury in vivo. Its antiviral effect might be attributed to the down-regulation of influenza virus-induced inflammatory cytokines by regulating the TLR4/MAPK/p38 signaling pathway.

Synthesis and Crystal Structure of Adamantylated 4,5,6,7-Tetrahalogeno-1H-benzimidazoles Novel Multi-Target Ligands (Potential CK2, M2 and SARS-CoV-2 Inhibitors); X-ray/DFT/QTAIM/Hirshfeld Surfaces/Molecular Docking Study

A series of new congeners, 1-[2-(1-adamantyl)ethyl]-1H-benzimidazole (AB) and 1-[2-(1-adamantyl)ethyl]-4,5,6,7-tetrahalogeno-1H-benzimidazole (Hal=Cl, Br, I; tClAB, tBrAB, tIAB), have been synthesized and studied. These novel multi-target ligands combine a benzimidazole ring known to show antitumor activity and an adamantyl moiety showing anti-influenza activity. Their crystal structures were determined by X-ray, while intermolecular interactions were studied using topological Bader's Quantum Theory of Atoms in Molecules, Hirshfeld Surfaces, CLP and PIXEL approaches. The newly synthesized compounds crystallize within two different space groups, P-1 (AB and tIAB) and P2₁/c (tClAB and tBrAB). A number of intramolecular hydrogen bonds, C-H⋯Hal (Hal=Cl, Br, I), were found in all halogen-containing congeners studied, but the intermolecular C-H⋯N hydrogen bond was detected only in AB and tIAB, while C-Hal⋯π only in tClAB and tBrAB. The interplay between C-H⋯N and C-H⋯Hal hydrogen bonds and a shift from the strong (C-H⋯Cl) to the very weak (C-H⋯I) attractive interactions upon Hal exchange, supplemented with Hal⋯Hal overlapping, determines the differences in the symmetry of crystalline packing and is crucial from the biological point of view. The hypothesis about the potential dual inhibitor role of the newly synthesized congeners was verified using molecular docking and the congeners were found to be pharmaceutically attractive as Human Casein Kinase 2, CK2, inhibitors, Membrane Matrix 2 Protein, M2, blockers and Severe Acute Respiratory Syndrome Coronavirus 2, SARS-CoV-2, inhibitors. The addition of adamantyl moiety seems to broaden and modify the therapeutic indices of the 4,5,6,7-tetrahalogeno-1H-benzimidazoles.

Synthesis, Optimization, and Structure-Activity Relationships of Imidazo[1,2-a]pyrimidines as Inhibitors of Group 2 Influenza A Viruses

The influenza A virus (IAV) is a highly contagious virus that causes pandemics and seasonal epidemics, which are major public health issues. Current anti-influenza therapeutics are limited partly due to the continuous emergence of drug-resistant IAV strains; thus, there is an unmet need to develop novel anti-influenza therapies. Here, we present a novel imidazo[1,2-a]pyrimidine scaffold that targets group 2 IAV entry. We have explored three different regions of the lead compound, and we have developed a series of small molecules that have nanomolar activity against oseltamivir-sensitive and -resistant forms of group 2 IAVs. These small molecules target hemagglutinin (HA), which mediates the viral entry process. Mapping a known small-molecule-binding cavity of the HA structure with resistant mutants suggests that these molecules bind to that cavity and block HA-mediated membrane fusion.

An anti-influenza A virus microbial metabolite acts by degrading viral endonuclease PA

The emergence of new highly pathogenic and drug-resistant influenza strains urges the development of novel therapeutics for influenza A virus (IAV). Here, we report the discovery of an anti-IAV microbial metabolite called APL-16-5 that was originally isolated from the plant endophytic fungus Aspergillus sp. CPCC 400735. APL-16-5 binds to both the E3 ligase TRIM25 and IAV polymerase subunit PA, leading to TRIM25 ubiquitination of PA and subsequent degradation of PA in the proteasome. This mode of action conforms to that of a proteolysis targeting chimera which employs the cellular ubiquitin-proteasome machinery to chemically induce the degradation of target proteins. Importantly, APL-16-5 potently inhibits IAV and protects mice from lethal IAV infection. Therefore, we have identified a natural microbial metabolite with potent in vivo anti-IAV activity and the potential of becoming a new IAV therapeutic. The antiviral mechanism of APL-16-5 opens the possibility of improving its anti-IAV potency and specificity by adjusting its affinity for TRIM25 and viral PA protein through medicinal chemistry.

Nuclear magnetic resonance reveals a two hairpin equilibrium near the 3'-splice site of influenza A segment 7 mRNA that can be shifted by oligonucleotides

Influenza A kills hundreds of thousands of people globally every year and has the potential to generate more severe pandemics. Influenza A's RNA genome and transcriptome provide many potential therapeutic targets. Here, nuclear magnetic resonance (NMR) experiments suggest that one such target could be a hairpin loop of 8 nucleotides in a pseudoknot that sequesters a 3' splice site in canonical pairs until a conformational change releases it into a dynamic 2 × 2-nt internal loop. NMR experiments reveal that the hairpin loop is dynamic and able to bind oligonucleotides as short as pentamers. A 3D NMR structure of the complex contains 4 and likely 5 bp between pentamer and loop. Moreover, a hairpin sequence was discovered that mimics the equilibrium of the influenza hairpin between its structure in the pseudoknot and upon release of the splice site. Oligonucleotide binding shifts the equilibrium completely to the hairpin secondary structure required for pseudoknot folding. The results suggest this hairpin can be used to screen for compounds that stabilize the pseudoknot and potentially reduce splicing.

Protein Disulfide Isomerase A3 Regulates Influenza Neuraminidase Activity and Influenza Burden in the Lung

Influenza (IAV) neuraminidase (NA) is a glycoprotein required for the viral exit from the cell. NA requires disulfide bonds for proper function. We have recently demonstrated that protein disulfide isomerase (PDI)A3 is required for oxidative folding of IAV hemagglutinin (HA), and viral propagation. However, it not known whether PDIs are required for NA maturation or if these interactions represent a putative target for the treatment of influenza infection. We sought to determine whether PDIA3 is required for disulfide bonds of NA, its activity, and propagation of the virus. Requirement of disulfides for NA oligomerization and activity were determined using biotin switch and redox assays in WT and PDIA3^−/− in A549 cells. A PDI specific inhibitor (LOC14) was utilized to determine the requirement of PDIs in NA activity, IAV burden, and inflammatory response in A549 and primary mouse tracheal epithelial cells. Mice were treated with the inhibitor LOC14 and subsequently examined for IAV burden, NA activity, cytokine, and immune response. IAV-NA interacts with PDIA3 and this interaction is required for NA activity. PDIA3 ablation or inhibition decreased NA activity, viral burden, and inflammatory response in lung epithelial cells. LOC14 treatment significantly attenuated the influenza-induced inflammatory response in mice including the overall viral burden. These results provide evidence for PDIA3 inhibition suppressing NA activity, potentially providing a novel platform for host-targeted antiviral therapies.

Two phytocompounds from Schinopsis brasiliensis show promising antiviral activity with multiples targets in Influenza A virus

Influenza A virus, the main flu agent, affects billions of people worldwide. Conventional treatments still present limitations related to drug-resistance and severe side effects. As a result, natural product-derived molecules have been increasingly investigated as prospect drug candidates. Therefore, the aim of this study was to investigate the possible anti-flu activity and to evaluate the toxicity and pharmacokinetic parameters, by in silico approaches, of the Schinopsis brasiliensis Engl. phytochemical compounds. Nine phytocompounds and six antiviral drugs (Amantadine, Umifenovir, Favipiravir, Nitazoxanide, Oseltamivir, Zanamivir) were selected for the analyses against four Influenza A proteins: neuraminidase, polymerase basic protein 2, hemagglutinin and M2 ion channel protein. The molecular docking, the predicted antiviral activity, the predicted toxicity and the pharmacokinetics investigations were conducted. The obtained results demonstrated that Syringaresinol and Cycloartenone display promising in silico antiviral activity (binding energy < 5.0 and ≥ 9.0 kcal/mol) and safety (low toxicity than commercial anti-flu drugs). Overall, this study corroborated the hypothesis that S. brasiliensis barks extract has a biological activity against Influenza A virus. Additionally, Syringaresinol and Cycloartenone have multiple targets in Influenza A virus and showed themselves as the most promising phytocompounds to be isolated and considered for the therapeutic arsenal against the flu.

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.

Quercetin and its derivates as antiviral potentials: A comprehensive review

Quercetin, widely distributed in fruits and vegetables, is a flavonoid known for its antioxidant, antiviral, antimicrobial, and antiinflammatory properties. Several studies highlight the potential use of quercetin as an antiviral, due to its ability to inhibit the initial stages of virus infection, to be able to interact with proteases important for viral replication, and to reduce inflammation caused by infection. Quercetin could also be useful in combination with other drugs to potentially enhance the effects or synergistically interact with them, in order to reduce their side effects and related toxicity. Since there is no comprehensive compilation about antiviral activities of quercetin and derivates, the aim of this review is providing a summary of their antiviral activities on a set of human viral infections along with mechanisms of action. Thus, the following family of viruses are examined: Flaviviridae, Herpesviridae, Orthomyxoviridae, Coronaviridae, Hepadnaviridae, Retroviridae, Picornaviridae, Pneumoviridae, and Filoviridae.

The Natural Oligoribonucleotides Functionalized by D-Mannitol Affected Interactions of Hemagglutinin with Glycan Receptor Indicating Anti-Influenza Activity

Hemagglutinin (HA), the class I influenza A virus protein is responsible for the attachment of virus particles to the cell by binding to glycan receptors, subsequent virion internalization, and cell entry. Consequently, the importance of HA makes it a primary target for the development of anti-influenza drugs. The natural oligoribonucleotides (ORNs) as well as their derivatives functionalized with D-mannitol (ORNs-D-M) possess anti-influenza properties in vitro and in vivo due to interaction with HA receptor sites. This activity suppresses the viral infection in host cells. In the present work, the complexes of ORNs and ORNs-D-M with HA protein were studied by agglutination assay, fluorescence spectroscopy, as well as molecular docking simulations. Acquired experimental data exhibited a decrease in HA titer by 32 times after incubation with the ORNs-D-M for 0.5–24 h. Quenching fluorescence intensity of the HA suggests that titration by ORNs and ORNs-D-M probably leads to changes in the HA structure. Detailed structural data were obtained with the molecular docking simulations performed for ORNs and ORNs-D-M ligands containing three and six oligoribonucleotides. The results reveal that a majority of the ORNs and ORNs-D-M bind in a non-specific way to the receptor-binding domain of the HA protein. The ligand’s affinity to the hemagglutinin was estimated at the micromolar level. Presented experimental data confirmed that both natural ORNs and functionalized ORNs-D-M inhibit the interactions between HA and glycan receptors and demonstrate anti-influenza activity.

Influenza polymerase inhibitor resistance: Assessment of the current state of the art - A report of the isirv Antiviral group

It is more than 20 years since the neuraminidase inhibitors, oseltamivir and zanamivir were approved for the treatment and prevention of influenza. Guidelines for global surveillance and methods for evaluating resistance were established initially by the Neuraminidase Inhibitor Susceptibility Network (NISN), which merged 10 years ago with the International Society for influenza and other Respiratory Virus Diseases (isirv) to become the isirv-Antiviral Group (isirv-AVG). With the ongoing development of new influenza polymerase inhibitors and recent approval of baloxavir marboxil, the isirv-AVG held a closed meeting in August 2019 to discuss the impact of resistance to these inhibitors. Following this meeting and review of the current literature, this article is intended to summarize current knowledge regarding the clinical impact of resistance to polymerase inhibitors and approaches for surveillance and methods for laboratory evaluation of resistance, both in vitro and in animal models. We highlight limitations and gaps in current knowledge and suggest some strategies for addressing these gaps, including the need for additional clinical studies of influenza antiviral drug combinations. Lessons learned from influenza resistance monitoring may also be helpful for establishing future drug susceptibility surveillance and testing for SARS-CoV-2.

Discovery of a Novel Specific Inhibitor Targeting Influenza A Virus Nucleoprotein with Pleiotropic Inhibitory Effects on Various Steps of the Viral Life Cycle

Influenza A viruses (IAVs) continue to pose an imminent threat to humans due to annual influenza epidemic outbreaks and episodic pandemics with high mortality rates. In this context, the suboptimal vaccine coverage and efficacy, coupled with recurrent events of viral resistance against a very limited antiviral portfolio, emphasize an urgent need for new additional prophylactic and therapeutic options, including new antiviral targets and drugs with new mechanisms of action to prevent and treat influenza virus infection. Here, we characterized a novel influenza A virus nucleoprotein (NP) inhibitor, FA-6005, that inhibited a broad spectrum of human pandemic and seasonal influenza A and B viruses in vitro and protects mice against lethal influenza A virus challenge. The small molecule FA-6005 targeted a conserved NP I41 domain and acted as a potentially broad, multimechanistic anti-influenza virus therapeutic since FA-6005 suppressed influenza virus replication and perturbed intracellular trafficking of viral ribonucleoproteins (vRNPs) from early to late stages. Cocrystal structures of the NP/FA-6005 complex reconciled well with concurrent mutational studies. This study provides the first line of direct evidence suggesting that the newly identified NP I41 pocket is an attractive target for drug development that inhibits multiple functions of NP. Our results also highlight FA-6005 as a promising candidate for further development as an antiviral drug for the treatment of IAV infection and provide chemical-level details for inhibitor optimization.IMPORTANCE Current influenza antivirals have limitations with regard to their effectiveness and the potential emergence of resistance. Therefore, there is an urgent need for broad-spectrum inhibitors to address the considerable challenges posed by the rapid evolution of influenza viruses that limit the effectiveness of vaccines and lead to the emergence of antiviral drug resistance. Here, we identified a novel influenza A virus NP antagonist, FA-6005, with broad-spectrum efficacy against influenza viruses, and our study presents a comprehensive study of the mode of action of FA-6005 with the crystal structure of the compound in complex with NP. The influenza virus inhibitor holds promise as an urgently sought-after therapeutic option offering a mechanism of action complementary to existing antiviral drugs for the treatment of influenza virus infection and should further aid in the development of universal therapeutics.

Astragaloside IV attenuates IL-1β secretion by enhancing autophagy in H1N1 infection

Excessive secretion of inflammatory factors (cytokine storm) plays a significant role in H1N1-induced acute pneumonia, and autophagy acts as a cell-intrinsic mechanism to regulate inflammation. Astragaloside IV (AS-IV), originating from the astragalus root, possesses multiple pharmacological activities, such as anti-inflammation. However, the influences of AS-IV on H1N1-induced autophagy and inflammation have remained elusive. It has been reported that H1N1 infection leads to the accumulation of autophagosomes but obstructs autophagosomes incorporating into lysosomes, whereas the present study showed that AS-IV enhanced autophagy activation in H1N1 infection. Furthermore, we found that AS-IV promoted H1N1-triggered formation of autophagosomes and autolysosomes. Additionally, it was noted that AS-IV did not affect viral replication, mRNA level of interleukin-1 beta (IL-1β) and pro-IL-1β protein level, but significantly decreased secretion of IL-1β, and chloroquine (CQ, as an inhibitor of autophagy) increased secretion of IL-1β in H1N1 infection. In conclusion, AS-IV stimulates the formation of autophagosomes and the fusion of autophagosomes and lysosomes in H1N1 infection and may lead to decreased IL-1β secretion.

An influenza A hemagglutinin small-molecule fusion inhibitor identified by a new high-throughput fluorescence polarization screen

Influenza hemagglutinin (HA) glycoprotein is the primary surface antigen targeted by the host immune response and a focus for development of novel vaccines, broadly neutralizing antibodies (bnAbs), and therapeutics. HA enables viral entry into host cells via receptor binding and membrane fusion and is a validated target for drug discovery. However, to date, only a very few bona fide small molecules have been reported against the HA. To identity new antiviral lead candidates against the highly conserved fusion machinery in the HA stem, we synthesized a fluorescence-polarization probe based on a recently described neutralizing cyclic peptide P7 derived from the complementarity-determining region loops of human bnAbs FI6v3 and CR9114 against the HA stem. We then designed a robust binding assay compatible with high-throughput screening to identify molecules with low micromolar to nanomolar affinity to influenza A group 1 HAs. Our simple, low-cost, and efficient in vitro assay was used to screen H1/Puerto Rico/8/1934 (H1/PR8) HA trimer against ∼72,000 compounds. The crystal structure of H1/PR8 HA in complex with our best hit compound F0045(S) confirmed that it binds to pockets in the HA stem similar to bnAbs FI6v3 and CR9114, cyclic peptide P7, and small-molecule inhibitor JNJ4796. F0045 is enantioselective against a panel of group 1 HAs and F0045(S) exhibits in vitro neutralization activity against multiple H1N1 and H5N1 strains. Our assay, compound characterization, and small-molecule candidate should further stimulate the discovery and development of new compounds with unique chemical scaffolds and enhanced influenza antiviral capabilities.

Clinical Practice Guidelines by the Infectious Diseases Society of America: 2018 Update on Diagnosis, Treatment, Chemoprophylaxis, and Institutional Outbreak Management of Seasonal Influenzaa

These clinical practice guidelines are an update of the guidelines published by the Infectious Diseases Society of America (IDSA) in 2009, prior to the 2009 H1N1 influenza pandemic. This document addresses new information regarding diagnostic testing, treatment and chemoprophylaxis with antiviral medications, and issues related to institutional outbreak management for seasonal influenza. It is intended for use by primary care clinicians, obstetricians, emergency medicine providers, hospitalists, laboratorians, and infectious disease specialists, as well as other clinicians managing patients with suspected or laboratory-confirmed influenza. The guidelines consider the care of children and adults, including special populations such as pregnant and postpartum women and immunocompromised patients.

X-ray Crystal Structures of the Influenza M2 Proton Channel Drug-Resistant V27A Mutant Bound to a Spiro-Adamantyl Amine Inhibitor Reveal the Mechanism of Adamantane Resistance

The V27A mutation confers adamantane resistance on the influenza A matrix 2 (M2) proton channel and is becoming more prevalent in circulating populations of influenza A virus. We have used X-ray crystallography to determine structures of a spiro-adamantyl amine inhibitor bound to M2(22-46) V27A and also to M2(21-61) V27A in the Inwardclosed conformation. The spiro-adamantyl amine binding site is nearly identical for the two crystal structures. Compared to the M2 "wild type" (WT) with valine at position 27, we observe that the channel pore is wider at its N-terminus as a result of the V27A mutation and that this removes V27 side chain hydrophobic interactions that are important for binding of amantadine and rimantadine. The spiro-adamantyl amine inhibitor blocks proton conductance in the WT and V27A mutant channels by shifting its binding site in the pore depending on which residue is present at position 27. Additionally, in the structure of the M2(21-61) V27A construct, the C-terminus of the channel is tightly packed relative to that of the M2(22-46) construct. We observe that residues Asp44, Arg45, and Phe48 face the center of the channel pore and would be well-positioned to interact with protons exiting the M2 channel after passing through the His37 gate. A 300 ns molecular dynamics simulation of the M2(22-46) V27A-spiro-adamantyl amine complex predicts with accuracy the position of the ligands and waters inside the pore in the X-ray crystal structure of the M2(22-46) V27A complex.

Development of effective anti-influenza drugs: congeners and conjugates - a review

Influenza is a long-standing health problem. For treatment of seasonal flu and possible pandemic infections, there is a need to develop new anti-influenza drugs that have good bioavailability against a broad spectrum of influenza viruses, including the resistant strains. Relenza™ (zanamivir), Tamiflu™ (the phosphate salt of oseltamivir), Inavir™ (laninamivir octanoate) and Rapivab™ (peramivir) are four anti-influenza drugs targeting the viral neuraminidases (NAs). However, some problems of these drugs should be resolved, such as oral availability, drug resistance and the induced cytokine storm. Two possible strategies have been applied to tackle these problems by devising congeners and conjugates. In this review, congeners are the related compounds having comparable chemical structures and biological functions, whereas conjugate refers to a compound having two bioactive entities joined by a covalent bond. The rational design of NA inhibitors is based on the mechanism of the enzymatic hydrolysis of the sialic acid (Neu5Ac)-terminated glycoprotein. To improve binding affinity and lipophilicity of the existing NA inhibitors, several methods are utilized, including conversion of carboxylic acid to ester prodrug, conversion of guanidine to acylguanidine, substitution of carboxylic acid with bioisostere, and modification of glycerol side chain. Alternatively, conjugating NA inhibitors with other therapeutic entity provides a synergistic anti-influenza activity; for example, to kill the existing viruses and suppress the cytokines caused by cross-species infection.

Focusing on the Influenza Virus Polymerase Complex: Recent Progress in Drug Discovery and Assay Development

Influenza viruses are severe human pathogens that pose persistent threat to public health. Each year more people die of influenza virus infection than that of breast cancer. Due to the limited efficacy associated with current influenza vaccines, as well as emerging drug resistance from small molecule antiviral drugs, there is a clear need to develop new antivirals with novel mechanisms of action. The influenza virus polymerase complex has become a promising target for the development of the next-generation of antivirals for several reasons. Firstly, the influenza virus polymerase, which forms a heterotrimeric complex that consists of PA, PB1, and PB2 subunits, is highly conserved. Secondly, both individual polymerase subunit (PA, PB1, and PB2) and inter-subunit interactions (PA-PB1, PB1- PB2) represent promising drug targets. Lastly, growing insight into the structure and function of the polymerase complex has spearheaded the structure-guided design of new polymerase inhibitors. In this review, we highlight recent progress in drug discovery and assay development targeting the influenza virus polymerase complex and discuss their therapeutic potentials.

X-ray Crystal Structure of the Influenza A M2 Proton Channel S31N Mutant in Two Conformational States: An Open and Shut Case

The amantadine-resistant S31N mutant of the influenza A M2 proton channel has become prevalent in currently circulating viruses. Here, we have solved an X-ray crystal structure of M2(22-46) S31N that contains two distinct conformational states within its asymmetric unit. This structure reveals the mechanism of adamantane resistance in both conformational states of the M2 channel. In the Inward_open conformation, the mutant Asn31 side chain faces the channel pore and sterically blocks the adamantane binding site. In the Inward_closed conformation, Asn31 forms hydrogen bonds with carbonyls at the monomer-monomer interface, which twists the monomer helices and constricts the channel pore at the drug binding site. We also examine M2(19-49) WT and S31N using solution NMR spectroscopy and show that distribution of the two conformational states is dependent on both detergent choice and experimental pH.

Peptide Antiviral Strategies as an Alternative to Treat Lower Respiratory Viral Infections

Lower respiratory infection caused by human pathogens such as influenza and respiratory syncytial virus (RSV) is a significant healthcare burden that must be addressed. The preferred options to achieve this goal are usually to develop vaccines for prophylaxis and to develop antiviral small molecules to treat infected patients with convenient, orally administrable drugs. However, developing a vaccine against RSV poses special challenges with the diminished immune system of infants and the elderly, and finding a universal flu vaccine is difficult because the product must target a large array of viral strains. On the other hand, the use of small-molecule antivirals can result in the emergence of resistant viruses as it has well-been reported for HIV, influenza, and hepatitis C virus (HCV). This paper reviews peptide antiviral strategies as an alternative to address these challenges. The discovery of influenza and RSV peptidic fusion inhibitors will be discussed and compared to small molecules in view of escape mutations. The importance of constraining peptides into macrocycles to improve both their inhibitory activity and pharmacological properties will be highlighted.

Clinical Practice Guidelines by the Infectious Diseases Society of America: 2018 Update on Diagnosis, Treatment, Chemoprophylaxis, and Institutional Outbreak Management of Seasonal Influenzaa

These clinical practice guidelines are an update of the guidelines published by the Infectious Diseases Society of America (IDSA) in 2009, prior to the 2009 H1N1 influenza pandemic. This document addresses new information regarding diagnostic testing, treatment and chemoprophylaxis with antiviral medications, and issues related to institutional outbreak management for seasonal influenza. It is intended for use by primary care clinicians, obstetricians, emergency medicine providers, hospitalists, laboratorians, and infectious disease specialists, as well as other clinicians managing patients with suspected or laboratory-confirmed influenza. The guidelines consider the care of children and adults, including special populations such as pregnant and postpartum women and immunocompromised patients.

An Overview of the Most Significant Zoonotic Viral Pathogens Transmitted from Animal to Human in Saudi Arabia

Currently, there has been an increasing socioeconomic impact of zoonotic pathogens transmitted from animals to humans worldwide. Recently, in the Arabian Peninsula, including in Saudi Arabia, epidemiological data indicated an actual increase in the number of emerging and/or reemerging cases of several viral zoonotic diseases. Data presented in this review are very relevant because Saudi Arabia is considered the largest country in the Peninsula. We believe that zoonotic pathogens in Saudi Arabia remain an important public health problem; however, more than 10 million Muslim pilgrims from around 184 Islamic countries arrive yearly at Makkah for the Hajj season and/or for the Umrah. Therefore, for health reasons, several countries recommend vaccinations for various zoonotic diseases among preventive protocols that should be complied with before traveling to Saudi Arabia. However, there is a shortage of epidemiological data focusing on the emerging and reemerging of zoonotic pathogens transmitted from animal to humans in different densely populated cities and/or localities in Saudi Arabia. Therefore, further efforts might be needed to control the increasing impacts of zoonotic viral disease. Also, there is a need for a high collaboration to enhance the detection and determination of the prevalence, diagnosis, control, and prevention as well as intervention and reduction in outbreaks of these diseases in Saudi Arabia, particularly those from other countries. Persons in the health field including physicians and veterinarians, pet owners, pet store owners, exporters, border guards, and people involved in businesses related to animal products have adopted various preventive strategies. Some of these measures might pave the way to highly successful prevention and control results on the different transmission routes of these viral zoonotic diseases from or to Saudi Arabia. Moreover, the prevention of these viral pathogens depends on socioeconomic impacts, available data, improved diagnosis, and highly effective therapeutics or prophylaxis.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Complexes of Oligoribonucleotides with d-Mannitol Modulate the Innate Immune Response to Influenza A Virus H1N1 (A/FM/1/47) In Vivo

Rapid replication of the influenza A virus and lung tissue damage caused by exaggerated pro-inflammatory host immune responses lead to numerous deaths. Therefore, novel therapeutic agents that have anti-influenza activities and attenuate excessive pro-inflammatory responses that are induced by an influenza virus infection are needed. Oligoribonucleotides-d-mannitol (ORNs-d-M) complexes possess both antiviral and anti-inflammatory activities. The current research was aimed at studying the ORNs-d-M effects on expression of innate immune genes in mice lungs during an influenza virus infection. Expression of genes was determined by RT-qPCR and Western blot assays. In the present studies, we found that the ORNs-d-M reduced the influenza-induced up-expression of Toll-like receptors (TLRs) (tlr3, tlr7, tlr8), nuclear factor NF-kB (nfkbia, nfnb1), cytokines (ifnε, ifnk, ifna2, ifnb1, ifnγ, il6, il1b, il12a, tnf), chemokines (ccl3, ccl4, сcl5, cxcl9, cxcl10, cxcl11), interferon-stimulated genes (ISGs) (oas1a, oas2, oas3, mx1), and pro-oxidation (nos2, xdh) genes. The ORNs-d-M inhibited the mRNA overexpression of tlr3, tlr7, and tlr8 induced by the influenza virus, which suggests that they impair the upregulation of NF-kB, cytokines, chemokines, ISGs, and pro-oxidation genes induced by the influenza virus by inhibiting activation of the TLR-3, TLR-7, and TLR-8 signaling pathways. By impairing activation of the TLR-3, TLR-7, and TLR-8 signaling pathways, the ORNs-d-M can modulate the innate immune response to an influenza virus infection.

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

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

Cirsimaritin inhibits influenza A virus replication by downregulating the NF-κB signal transduction pathway

Background

Artemisia scoparia Waldst and Kit is a famous traditional Chinese medicine widely distributed in Xinjiang, China. Flavonoids extracted from it exhibits inhibitory activities against several influenza virus strains. Despite this fact, the antiviral properties of CST, one of such flavonoids, against the influenza virus has not been reported. Thus, the aim of this study is to investigate the anti-influenza virus efficacy and antiviral mechanism of CST.

Methods

The inhibitory activity of CST against influenza viruses was assessed by using viral titers and performing Western blot, qRT-PCR, and immunofluorescence assays in Madin–Darby canine kidney (MDCK) cells and a human monocytic cell line (THP-1). The mechanism of CST against influenza virus was analyzed by hemagglutination inhibition (HI) assay, neuraminidase (NA) inhibition assay, and Western blot.

Results

CST reduced viral titers and influenza A virus (IAV) RNA and protein synthesis in a dose-dependent manner. Mechanistically, CST had no inhibitory effect on the attachment and release processes of the viral life cycle, as indicated by the HI and NA assays. Conversely, the CST-mediated inhibition of IAV is possibly linked to the inactivation of the NF-κB/p65 signal pathway. CST also suppressed the activation of JNK MAPK and P38 MAPK in vitro. In line with NF-κB/p65 inhibition, the expression levels of proinflammatory cytokines (TNF-α, IL-1β, IL-8, and IL-10) and the inflammation-related protein COX-2 were downregulated by CST.

Conclusions

CST inhibited IAV replication by downregulating the NF-κB signal transduction pathway. CST may be a potential agent or supplement against IAV infection.

Pre-Clinical and Clinical Efficiency of Complexes of Oligoribonucleotides with D-Mannitol against Respiratory Viruses

Oligoribonucleotides-D-mannitol (ORNs-D-M) complexes possess antiviral, anti-inflammatory, and immunomodulatory actions. The aim of the present study was to evaluated an antiviral effect of ORNs-D-M against parainfluenza virus type 3 (PIV3); influenza CA709, PR834; avian influenza virus H5N2 (AIV) in vitro by a TCID₅₀; hemadsorption and neuraminidase activity assays; and clinical efficiency of ORNs-D-M in patients with acute respiratory infections (ARIs) of various etiologies by PCR assay and AmpliSens test systems. It was observed that ORNs-D-M have an antiviral activity against the influenza CA709, PR834, PIV3, and AIV in vitro. The injectable dosage form of ORNs-D-M was shown to have a stronger antiviral effect compared to capsule form. It was also detected that the injectable form of ORNs-D-M significantly reduced the neuraminidase activity of influenza PR834. A complex treatment of patients with ORNs-D-M had a positive effect on the course of the disease, it accelerated patients’ recovery. Treatment with ORNs-D-M caused eradication of adeno- and influenza viruses in patients with ARI. This drug contributed to significant decrease in duration of febrile period and cough. Comprehensive treatment with ORNs-D-M improved the disease clinical findings significantly. Collectively, these results suggested that ORNs-D-M may be used at co-infection with influenza and other respiratory viruses as a medical antiviral drug.

A small-molecule fragment that emulates binding of receptor and broadly neutralizing antibodies to influenza A hemagglutinin

The influenza virus hemagglutinin (HA) glycoprotein mediates receptor binding and membrane fusion during viral entry in host cells. Blocking these key steps in viral infection has applications for development of novel antiinfluenza therapeutics as well as vaccines. However, the lack of structural information on how small molecules can gain a foothold in the small, shallow receptor-binding site (RBS) has hindered drug design against this important target on the viral pathogen. Here, we report on the serendipitous crystallization-based discovery of a small-molecule N-cyclohexyltaurine, commonly known as the buffering agent CHES, that is able to bind to both group-1 and group-2 HAs of influenza A viruses. X-ray structural characterization of group-1 H5N1 A/Vietnam/1203/2004 (H5/Viet) and group-2 H3N2 A/Hong Kong/1/1968 (H3/HK68) HAs at 2.0-Å and 2.57-Å resolution, respectively, revealed that N-cyclohexyltaurine binds to the heart of the conserved HA RBS. N-cyclohexyltaurine mimics the binding mode of the natural receptor sialic acid and RBS-targeting bnAbs through formation of similar hydrogen bonds and CH-π interactions with the HA. In H3/HK68, N-cyclohexyltaurine also binds to a conserved pocket in the stem region, thereby exhibiting a dual-binding mode in group-2 HAs. These long-awaited structural insights into RBS recognition by a noncarbohydrate-based small molecule enhance our knowledge of how to target this important functional site and can serve as a template to guide the development of novel broad-spectrum small-molecule therapeutics against influenza virus.

Chinese herbal medicine compound Yi-Zhi-Hao pellet inhibits replication of influenza virus infection through activation of heme oxygenase-1

As a leading cause of respiratory disease, influenza A virus (IAV) presents a pandemic threat in annual seasonal outbreaks. Given the limitation of existing anti-influenza therapies, there remains to be a requirement for new drugs. Compound Yi-Zhi-Hao pellet (CYZH) is a famous traditional Chinese medicine (TCM) used in the clinic, whose formula has been recorded in Complication of National Standard for Traditional Chinese Medicine to treat common cold. In this study, we found that CYZH exhibited a broad-spectrum anti-influenza activity and inhibited the expression of viral RNA and proteins in vitro. Mechanistically, CYZH had no inhibitory activities against viral protein hemagglutinin and IAV RNA-dependent RNA polymerase. Instead, it induced activation of erythroid 2-related factor 2 (Nrf2) and nuclear factor kappa B (NF-κB), which subsequently upregulated heme oxygenase-1 (HO-1) expression. Also, CYZH protected cells from oxidative damage induced by reactive oxygen series. In conclusions, CYZH inhibits IAV replication in vitro, at least partly by activating expression of the Nrf2/HO-1 pathway.

Characterization of the neuraminidase genes from human influenza A viruses circulating in Iran from 2010 to 2015

BACKGROUND

Characterization of influenza viruses is critical for detection of new emerging variants. Herein, we analyzed the genetic diversity and drug susceptibility of the neuraminidase gene (NAs) expressed by influenza A/H1N1pdm09 and A/H3N2 viruses circulating in Iran from 2010 to 2015.

METHODS

We genetically analyzed the NAs of 38 influenza A/H1N1pdm09 and 35 A/H3N2 isolates.

RESULTS

The Iranian A/H1N1pdm09 viruses belonged to seven genogroups/subgenogroups, with the dominant groups being genogroups 6B and 6C. The A/H3N2 isolates fell into six gneogroups/subgenogroups, with the dominant genogroups being 3C and 3C.2a. The most common mutations detected among the A/H1N1pdm09 viruses included N44S, V106I, N200S, and N248D. All H1N1pdm09 viruses were genetically susceptible to the NAIs. However, one A/H1N1pdm09 virus from the 2013-2014 season possessed an NA-S247N mutation, which reduces the susceptibility to oseltamivir. In case of H3N2, none of the analyzed Iranian strains carried a substitution that might affect its susceptibility to NAIs.

CONCLUSION

The ongoing evolution of influenza viruses and the detect of influenza viruses with reduced susceptibility to NAIs warrants continuous monitoring of the circulating strains.

Potent peptidic fusion inhibitors of influenza virus

Influenza therapeutics with new targets and mechanisms of action are urgently needed to combat potential pandemics, emerging viruses, and constantly mutating strains in circulation. We report here on the design and structural characterization of potent peptidic inhibitors of influenza hemagglutinin. The peptide design was based on complementarity-determining region loops of human broadly neutralizing antibodies against the hemagglutinin (FI6v3 and CR9114). The optimized peptides exhibit nanomolar affinity and neutralization against influenza A group 1 viruses, including the 2009 H1N1 pandemic and avian H5N1 strains. The peptide inhibitors bind to the highly conserved stem epitope and block the low pH-induced conformational rearrangements associated with membrane fusion. These peptidic compounds and their advantageous biological properties should accelerate the development of new small molecule- and peptide-based therapeutics against influenza virus.

Chemical Genomics Approach Leads to the Identification of Hesperadin, an Aurora B Kinase Inhibitor, as a Broad-Spectrum Influenza Antiviral

Influenza viruses are respiratory pathogens that are responsible for annual influenza epidemics and sporadic influenza pandemics. Oseltamivir (Tamiflu^®) is currently the only FDA-approved oral drug that is available for the prevention and treatment of influenza virus infection. However, its narrow therapeutic window, coupled with the increasing incidence of drug resistance, calls for the next generation of influenza antivirals. In this study, we discovered hesperadin, an aurora B kinase inhibitor, as a broad-spectrum influenza antiviral through forward chemical genomics screening. Hesperadin inhibits multiple human clinical isolates of influenza A and B viruses with single to submicromolar efficacy, including oseltamivir-resistant strains. Mechanistic studies revealed that hesperadin inhibits the early stage of viral replication by delaying the nuclear entry of viral ribonucleoprotein complex, thereby inhibiting viral RNA transcription and translation as well as viral protein synthesis. Moreover, a combination of hesperadin with oseltamivir shows synergistic antiviral activity, therefore hesperadin can be used either alone to treat infections by oseltamivir-resistant influenza viruses or used in combination with oseltamivir to delay resistance evolution among oseltamivir-sensitive strains. In summary, the discovery of hesperadin as a broad-spectrum influenza antiviral offers an alternative to combat future influenza epidemics and pandemics.

Susceptibility of influenza A(H1N1)/pdm2009, seasonal A(H3N2) and B viruses to Oseltamivir in Guangdong, China between 2009 and 2014

Nasopharyngeal swabs were collected from patients through the influenza surveillance network of the CDC of Guangdong. All specimens between 2009 and 2014 were checked for influenza virus using MDCK cells and further subtyped. Of those collected, 542 H1N1pdm09, 230 A(H3N2)and 448 B viruses selected at random were subjected to fluorescence-based NAI assays. Viral RNA was extracted from resistant isolates, and their NA genes were amplified by RT-PCR. Alignment of nucleotides and amino acids was performed. We performed structural modelling and simulations of mutants using Modeller 9.x and AutoDock and analyzed conformations and binding affinities. All tested seasonal type B and H3N2 viruses from 2009 to 2014 remained sensitive to oseltamivir. However, there were five strains (out of 198 tested isolates acquired between June and September 2013) that were resistant to oseltamivir. Another three resistant strains were identified among isolates from March to April 2014. We found that 2013/2014 oseltamivir-resistant strains and 2012/2013/2014 oseltamivir-sensitive strains had all or some of the following mutations: N44S, N200S,V241I, I321V,N369K, N386 K and K432E. MutationsV241I, N369K, N386K and K432E, alone or in conjunction with H275Y, had a significant impact on the binding pattern and affinity of oseltamivir for neuraminidase, rendering neuraminidase less susceptible.

Structure-based optimization and synthesis of antiviral drug Arbidol analogues with significantly improved affinity to influenza hemagglutinin

Influenza is a highly contagious respiratory viral infection responsible for up to 50,000 deaths per annum in the US alone. The need for new therapeutics with novel modes of action is of paramount importance. We determined the X-ray structure of Arbidol with influenza hemagglutinin and found it was located in a distinct binding pocket. Herein, we report a structure-activity relationship study based on the co-complex combined with bio-layer interferometry to assess the binding of our compounds. Addition of a meta-hydroxy group to the thiophenol moiety of Arbidol to replace a structured water molecule in the binding pocket resulted in a dramatic increase in affinity against both H3 (1150-fold) and H1 (98-fold) hemagglutinin subtypes. Our analogues represent novel leads to yield more potent compounds against hemagglutinin that block viral entry.

Complexes of Oligoribonucleotides with D-Mannitol Inhibit Hemagglutinin-Glycan Interaction and Suppress Influenza A Virus H1N1 (A/FM/1/47) Infectivity In Vitro

The influenza virus hemagglutinin (HA) mediates both receptor (glycan) binding and membrane fusion for cell entry and has been the basis for subtyping influenza viruses. The oligoribonucleotides-d-mannitol (ORNs-d-M) complexes possess an anti-influenza activity in vitro and in vivo. In the present studies, we have found that ORNs-d-M interferes with hemagglutinin (HA)–glycan interaction and suppress viral infection in host cells. HA–glycan interactions were evaluated to indirectly quantify the amount of influenza virus titer by an agglutination assay. Influenza virus infectivity was determined by TCID₅₀ assay. The direct virucidal action of the complexes was evaluated by both cytopathic effects (CPE) reduction assay and cell MTT assay. We found that ORNs-d-M hinders interaction between HA and glycan. These complexes decreased the infectivity of influenza virus and had a direct virucidal action. ORNs-d-M reduces influenza virus infectivity, affecting the HA–glycan interaction in vitro. By suppressing the influenza viral infection, the ORNs-d-M can have direct virucidal action.

Nature nominee quercetin's anti-influenza combat strategy-Demonstrations and remonstrations

Nature's providences are rather the choicest remedies for human health and welfare. One such is quercetin, which is nature's nominee for cancer cure and recently demonstrated against influenza attack. Quercetin is highly recognized for its anticancer applications. This review emphasizes on yet another gift that this compound has to offer for mankind, which is none other than combating the deadly evasive influenza virus. The chemistry of this natural bioflavonoid and its derivatives and its modus operandi against influenza virus is consolidated into this review. The advancements and achievements made in the anti-influenza clinical history are also documented. Further, the challenges facing the progress of this compound to emerge as a predominant anti-influenza drug are discussed, and the future perspective for breaking its limitations through integration with nanoplatforms is envisioned.

Design and expeditious synthesis of organosilanes as potent antivirals targeting multidrug-resistant influenza A viruses

The efficacy of current influenza vaccines and small molecule antiviral drugs is curtailed by the emerging of multidrug-resistant influenza viruses. As resistance to the only FDA-approved oral influenza antiviral, oseltamivir (Tamiflu), continues to rise, there is a clear need to develop the next-generation of antiviral drugs. Since more than 95% of current circulating influenza A viruses carry the S31N mutation in their M2 genes, the AM2-S31N mutant proton channel represents an attractive target for the development of broad-spectrum antivirals. In this study we report the design and synthesis of the first class of organosilanes that have potent antiviral activity against a panel of human clinical isolates of influenza A viruses, including viruses that are resistant to amantadine, oseltamivir, or both.

A New Strategy to Reduce Influenza Escape: Detecting Therapeutic Targets Constituted of Invariance Groups

The pathogenicity of the different flu species is a real public health problem worldwide. To combat this scourge, we established a method to detect drug targets, reducing the possibility of escape. Besides being able to attach a drug candidate, these targets should have the main characteristic of being part of an essential viral function. The invariance groups that are sets of residues bearing an essential function can be detected genetically. They consist of invariant and synthetic lethal residues (interdependent residues not varying or slightly varying when together). We analyzed an alignment of more than 10,000 hemagglutinin sequences of influenza to detect six invariance groups, close in space, and on the protein surface. In parallel we identified five potential pockets on the surface of hemagglutinin. By combining these results, three potential binding sites were determined that are composed of invariance groups located respectively in the vestigial esterase domain, in the bottom of the stem and in the fusion area. The latter target is constituted of residues involved in the spring-loaded mechanism, an essential step in the fusion process. We propose a model describing how this potential target could block the reorganization of the hemagglutinin HA2 secondary structure and prevent viral entry into the host cell.

Structural basis of influenza virus fusion inhibition by the antiviral drug Arbidol

The broad-spectrum antiviral drug Arbidol shows efficacy against influenza viruses by targeting the hemagglutinin (HA) fusion machinery. However, the structural basis of the mechanism underlying fusion inhibition by Arbidol has remained obscure, thereby hindering its further development as a specific and optimized influenza therapeutic. We determined crystal structures of Arbidol in complex with influenza virus HA from pandemic 1968 H3N2 and recent 2013 H7N9 viruses. Arbidol binds in a hydrophobic cavity in the HA trimer stem at the interface between two protomers. This cavity is distal to the conserved epitope targeted by broadly neutralizing stem antibodies and is ∼16 Å from the fusion peptide. Arbidol primarily makes hydrophobic interactions with the binding site but also induces some conformational rearrangements to form a network of inter- and intraprotomer salt bridges. By functioning as molecular glue, Arbidol stabilizes the prefusion conformation of HA that inhibits the large conformational rearrangements associated with membrane fusion in the low pH of the endosome. This unique binding mode compared with the small-molecule inhibitors of other class I fusion proteins enhances our understanding of how small molecules can function as fusion inhibitors and guides the development of broad-spectrum therapeutics against influenza virus.