Emergence of a multidrug-resistant pandemic influenza A (H1N1) virus

Nanostructures for prevention, diagnosis, and treatment of viral respiratory infections: from influenza virus to SARS-CoV-2 variants

Viruses are a major cause of mortality and socio-economic downfall despite the plethora of biopharmaceuticals designed for their eradication. Conventional antiviral therapies are often ineffective. Live-attenuated vaccines can pose a safety risk due to the possibility of pathogen reversion, whereas inactivated viral vaccines and subunit vaccines do not generate robust and sustained immune responses. Recent studies have demonstrated the potential of strategies that combine nanotechnology concepts with the diagnosis, prevention, and treatment of viral infectious diseases. The present review provides a comprehensive introduction to the different strains of viruses involved in respiratory diseases and presents an overview of recent advances in the diagnosis and treatment of viral infections based on nanotechnology concepts and applications. Discussions in diagnostic/therapeutic nanotechnology-based approaches will be focused on H1N1 influenza, respiratory syncytial virus, human parainfluenza virus type 3 infections, as well as COVID-19 infections caused by the SARS-CoV-2 virus Delta variant and new emerging Omicron variant.

Potential cross-species transmission of highly pathogenic avian influenza H5 subtype (HPAI H5) viruses to humans calls for the development of H5-specific and universal influenza vaccines

In recent years, highly pathogenic avian influenza H5 subtype (HPAI H5) viruses have been prevalent around the world in both avian and mammalian species, causing serious economic losses to farmers. HPAI H5 infections of zoonotic origin also pose a threat to human health. Upon evaluating the global distribution of HPAI H5 viruses from 2019 to 2022, we found that the dominant strain of HPAI H5 rapidly changed from H5N8 to H5N1. A comparison of HA sequences from human- and avian-derived HPAI H5 viruses indicated high homology within the same subtype of viruses. Moreover, amino acid residues 137A, 192I, and 193R in the receptor-binding domain of HA1 were the key mutation sites for human infection in the current HPAI H5 subtype viruses. The recent rapid transmission of H5N1 HPAI in minks may result in the further evolution of the virus in mammals, thereby causing cross-species transmission to humans in the near future. This potential cross-species transmission calls for the development of an H5-specific influenza vaccine, as well as a universal influenza vaccine able to provide protection against a broad range of influenza strains.

Mahuang Xixin Fuzi decoction protects the BALB/c-nude mice infected with influenza A virus by reducing inflammatory cytokines storm and weakly regulating SIgA immune response

ETHNOPHARMACOLOGICAL RELEVANCE

Mahuang Xixin Fuzi Decoction (MXF), as a classical prescription of traditional Chinese medicine (TCM), has been used to treat the immunocompromised individuals infected with influenza A virus (IAV).

AIM OF THE STUDY

The study aims to explore the regulatory of MXF on inflammation and secretory immunoglobulin A (SIgA) antibodies immune response in BALB/c-nude mice infected with IAV.

MATERIALS AND METHODS

The BALB/c-nude mice were infected with IAV, then different dosages of MXF were orally administrated to the mice. The weight, rectal temperature, spontaneous activity, spleen index, lung index, pathological changes of lung tissues, and the relative mRNA expression level of H1N1 M gene were measured for the purpose of valuing the antiviral effect of MXF. The expression levels of cytokines in lungs and immunoglobulin A (IgA) in serum of BALB/c-nude mice were determined with Cytometric Bead Array System (CBA). SIgA in bronchoalveolar lavage fluids (BALF) was detected with Enzyme-linked Immunosorbent Assay (ELISA). The mRNA and protein expression levels of B cell activating factor (BAFF), chemokine receptors 10 (CCR10), and polymeric immunoglobulin receptor (pIgR) in the lung tissues, which are related to the secretion of SIgA, were determined by using RT-PCR and Western blot.

RESULTS

MXF could alleviate the clinical features and reduce the severity of viral lung lesions, including improving the body weight, rectal temperature and spontaneous activity of nude mice infected with IAV, increasing spleen index, decreasing lung index, alleviating pathological damage, and decreasing the relative expression level of H1N1 M gene. Levels of pro-inflammatory cytokines, including interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), interleukin-2 (IL-2), interleukin-12p70 (IL-12p70), and interleukin-17A (IL-17A) were also significantly decreased after treatment with MXF. Interferon-γ (IFN-γ), an antiviral cytokine, was significantly up-regulated in high dose MXF (3.12 g/kg) group. Moreover, after MXF treatment, the expressions of SIgA in BALF and IgA in serum were both at relatively low levels. And the mRNA and protein expressions of BAFF, CCR10, and pIgR were significantly decreased after treatment with MXF.

CONCLUSIONS

MXF has obviously protective effects on BALB/c-nude mice infected with IAV by inhibiting virus replication, calming inflammatory cytokine storm, and regulating SIgA immune response weakly.

Evolutionary dynamics of influenza A/H1N1 virus circulating in India from 2011 to 2021

Influenza A viruses (IAV) are fast-evolving pathogens with a very high mutation rate (2.0 × 10^-6 to 2.0 × 10^-4) compared to the influenza B (IBV) and influenza C (ICV) viruses. Generally, the tropical regions are considered as the reservoir for the IAV's genetic and antigenic evolutionary modification to be reintroduced into the temperate region. Therefore, in connection to the above facts, the present study emphasized on the evolutionary dynamic of the pandemic-2009 H1N1 (pdmH1N1) influenza virus in India. A total of Ninety-two whole genome sequences of pdmH1N1 viruses circulating in India during the 2009 post-pandemic era were analysed. The temporal signal of the study, indicating strict molecular clock evolutionary process and the overall substitution rate is 2.21 × 10^-3/site/year. We are using the nonparametric Bayesian Skygrid coalescent model to estimates the effective past population dynamic or size over time. The study exhibits a strong relation between the genetic distances and collection dates of the Indian pdmH1N1 strain. The skygrid plot represents the highest exponential growth of IAV in rainy and winter seasons. All the genes of Indian pdmH1N1 were under purifying selective pressure. The Bayesian time-imprinted phylogenetic tree represents the following clade distributions in the country within the last 10 years; I) clade 6, 6C, and 7 were co-circulating between the 2011 to 2012 flu season; II) the clade 6B was introduced into circulation in the late seasons of 2012; III) lastly, the clade 6B remain existing in the circulation and segregated into subclade 6B.1 with five different subgroup (6B.1A, 6B.1A.1, 6B.1A.5a, 6B.1A.5a.2, 6B.1A.7). The recent circulating strain of Indian H1N1 strain represent the insertion of basic-amino acid arginine (R) in the cleavage site (325/K-R) of HA protein and amino acid mutation (314/I-M) on the lateral head surface domain of NA protein. Moreover, the study indicates the sporadic presence of the oseltamivir-resistant (275/H-Y) H1N1 variant in circulation. The present study suggests the purifying selective pressure and stochastic ecological factors for the existence and adaptation of a certain clade 6B in the host populations and additional information on the emergence of mutated strains in the circulation.

Lessons from resistance analysis in clinical trials of IV zanamivir

Influenza infection causes substantial morbidity and mortality during seasonal epidemics and pandemics. Antivirals, including neuraminidase inhibitors, play an important role in the treatment of severely ill patients infected with influenza. Resistance is a key factor that can affect the efficacy of neuraminidase inhibitors (NAIs). It is a recommendation by regulatory authorities to monitor for resistance during the development of anti-influenza medications. An additional requirement by regulators is to examine amino acid sequences for minority species harbouring resistance substitutions. In a Phase III study of intravenous (IV) zanamivir respiratory samples were analysed for the presence of resistant quasi species using Next Generation Sequencing (NGS). In this study ten resistance substitutions, two of which were treatment emergent, were detected by NGS that otherwise would not have been detectable by Sanger sequencing. None of the substitutions were present at any other timepoints analysed. The effect these mutations have on clinical response is difficult to characterize; in fact, all patients from which these variants were isolated had a successful clinical outcome and the effect on clinical response was therefore likely minimal. Although NGS is becoming a routine method for nucleic acid sequencing and will detect substitutions previously undetected by Sanger sequencing, the value of this technique in identifying minority species with resistance substitutions that are clinically meaningful remains to be demonstrated, particularly with acute infections such as influenza.

Leveraging the therapeutic, biological, and self-assembling potential of peptides for the treatment of viral infections

Peptides and peptide-based materials have an increasing role in the treatment of viral infections through their use as active pharmaceutical ingredients, targeting moieties, excipients, carriers, or structural components in drug delivery systems. The discovery of peptide-based therapeutic compounds, coupled with the development of new stabilization and formulation strategies, has led to a resurgence of antiviral peptide therapeutics over the past two decades. The ability of peptides to bind cell receptors and to facilitate membrane penetration and subsequent intracellular trafficking enables their use in various antiviral systems for improved targeting efficiency and treatment efficacy. Importantly, the self-assembly of peptides into well-defined nanostructures provides a vast library of discrete constructs and supramolecular biomaterials for systemic and local delivery of antiviral agents. We review here the recent progress in exploiting the therapeutic, biological, and self-assembling potential of peptides, peptide conjugates, and their supramolecular assemblies in treating human viral infections, with an emphasis on the treatment strategies for Human Immunodeficiency Virus (HIV).

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.

Multi-Target Approaches of Epigallocatechin-3-O-gallate (EGCG) and its Derivatives Against Influenza Viruses

Influenza viruses (INFV), Orthomyxoviridae family, are mainly transmitted among humans, via aerosols or droplets from the respiratory secretions. However, fomites could be a potential transmission pathway. Annually, seasonal INFV infections account for 290-650 thousand deaths worldwide. Currently, there are two classes of approved drugs to treat INFV infections, being neuraminidase (NA) inhibitors and blockers of matrix-2 (M2) ion channel. However, cases of resistance have been observed for both chemical classes, reducing the efficacy of treatment. The emergence of influenza outbreaks and pandemics calls for new antiviral molecules more effective and that could overcome the current resistance to anti-influenza drugs. In this context, polyphenolic compounds are found in various plants and these have displayed different multi-target approaches against diverse pathogens. Among these, green tea (Camellia sinensis) catechins, in special epigallocatechin-3-O-gallate (EGCG), have demonstrated significant activities against the two most relevant human INFV, subtypes A and lineages B. In this sense, EGCG has been found a promising multi-target agent against INFV since can act inhibiting NA, hemagglutination (HA), RNA-dependent RNA polymerase (RdRp), and viral entry/adsorption. In general, the lack of knowledge about potential multi-target natural products prevents an adequate exploration of them, increasing the time for developing multi-target drugs. Then, this review aimed to compile to most relevant studies showing the anti-INFV effects of EGCG and its derivatives, which could become antiviral drug prototypes in the future.

Multidrug Resistance (MDR): A Widespread Phenomenon in Pharmacological Therapies

Multidrug resistance is a leading concern in public health. It describes a complex phenotype whose predominant feature is resistance to a wide range of structurally unrelated cytotoxic compounds, many of which are anticancer agents. Multidrug resistance may be also related to antimicrobial drugs, and is known to be one of the most serious global public health threats of this century. Indeed, this phenomenon has increased both mortality and morbidity as a consequence of treatment failures and its incidence in healthcare costs. The large amounts of antibiotics used in human therapies, as well as for farm animals and even for fishes in aquaculture, resulted in the selection of pathogenic bacteria resistant to multiple drugs. It is not negligible that the ongoing COVID-19 pandemic may further contribute to antimicrobial resistance. In this paper, multidrug resistance and antimicrobial resistance are underlined, focusing on the therapeutic options to overcome these obstacles in drug treatments. Lastly, some recent studies on nanodrug delivery systems have been reviewed since they may represent a significant approach for overcoming resistance.

Covalent Antiviral Agents

Nowadays, many viral infections have emerged and are taking a huge toll on human lives globally. Meanwhile, viral resistance to current drugs has drastically increased. Hence, there is a pressing need to design potent broad-spectrum antiviral agents to treat a variety of viral infections and overcome viral resistance. Covalent inhibitors have the potential to achieve both goals owing to their biochemical efficiency, prolonged duration of action, and the capability to inhibit shallow, solvent-exposed substrate-binding domains. In this chapter, we review the structures, activities, and inhibition mechanisms of covalent inhibitors against severe acute respiratory syndrome coronavirus 2, dengue virus, enterovirus, hepatitis C virus, human immunodeficiency virus, and influenza viruses. We also discuss the application of in silico study in covalent inhibitor design.

Antivirals Targeting the Surface Glycoproteins of Influenza Virus: Mechanisms of Action and Resistance

Hemagglutinin and neuraminidase, which constitute the glycoprotein spikes expressed on the surface of influenza A and B viruses, are the most exposed parts of the virus and play critical roles in the viral lifecycle. As such, they make prominent targets for the immune response and antiviral drugs. Neuraminidase inhibitors, particularly oseltamivir, constitute the most commonly used antivirals against influenza viruses, and they have proved their clinical utility against seasonal and emerging influenza viruses. However, the emergence of resistant strains remains a constant threat and consideration. Antivirals targeting the hemagglutinin protein are relatively new and have yet to gain global use but are proving to be effective additions to the antiviral repertoire, with a relatively high threshold for the emergence of resistance. Here we review antiviral drugs, both approved for clinical use and under investigation, that target the influenza virus hemagglutinin and neuraminidase proteins, focusing on their mechanisms of action and the emergence of resistance to them.

Baloxavir Marboxil Treatment of Nude Mice Infected With Influenza A Virus

BACKGROUND

Immunocompromised patients infected with influenza virus require prolonged treatment with neuraminidase inhibitors, because these patients are not able to eradicate the virus from the respiratory tract, leading to the emergence of drug-resistant mutant viruses.

METHODS

In this study, we examined the efficacy of baloxavir marboxil in nude mice that were immunologically deficient.

RESULTS

Daily treatment with a suboptimal dose of baloxavir marboxil increased the survival time of the virus-infected nude mice but did not clear the virus from their respiratory organs, resulting in gradual body weight loss after termination of treatment.

CONCLUSIONS

Despite the prolonged baloxavir marboxil treatment, few resistant mutants were detected.

Development of A4 antibody for detection of neuraminidase I223R/H275Y-associated antiviral multidrug-resistant influenza virus

The emergence and spread of antiviral drug-resistant viruses have been a worldwide challenge and a great concern for patient care. We report A4 antibody specifically recognizing and binding to the mutant I223R/H275Y neuraminidase and prove the applicability of A4 antibody for direct detection of antiviral multidrug-resistant viruses in various sensing platforms, including naked-eye detection, surface-enhanced Raman scattering-based immunoassay, and lateral flow system. The development of the A4 antibody enables fast, simple, and reliable point-of-care assays of antiviral multidrug-resistant influenza viruses. In addition to current influenza virus infection testing methods that do not provide information on the antiviral drug-resistance of the virus, diagnostic tests for antiviral multidrug-resistant viruses will improve clinical judgment in the treatment of influenza virus infections, avoid the unnecessary prescription of ineffective drugs, and improve current therapies.

Structure of avian influenza hemagglutinin in complex with a small molecule entry inhibitor

The binding properties of fusion inhibitor CBS1117 to hemagglutinin by x-ray crystallography, NMR, and mutagenesis give insights into mechanism and guidance for chemical optimization.

HA plays a critical role in influenza infection and, thus HA is a potential target for antivirals. Recently, our laboratories have described a novel fusion inhibitor, termed CBS1117, with EC₅₀ ∼3 μM against group 1 HA. In this work, we characterize the binding properties of CBS1117 to avian H5 HA by x-ray crystallography, NMR, and mutagenesis. The x-ray structure of the complex shows that the compound binds near the HA fusion peptide, a region that plays a critical role in HA-mediated fusion. NMR studies demonstrate binding of CBS1117 to H5 HA in solution and show extensive hydrophobic contacts between the compound and HA surface. Mutagenesis studies further support the location of the compound binding site proximal to the HA fusion peptide and identify additional amino acids that are important to compound binding. Together, this work gives new insights into the CBS1117 mechanism of action and can be exploited to further optimize this compound and better understand the group specific activity of small-molecule inhibitors of HA-mediated entry.

Triple combination therapy of favipiravir plus two monoclonal antibodies eradicates influenza virus from nude mice

Prolonged treatment of immunocompromised influenza patients with viral neuraminidase (NA) inhibitors is required, because the immune system of such patients fails to eradicate the viruses. Here, we attempted to eradicate influenza virus from the respiratory organs of nude mice, which is a model of immunocompromised hosts, by using combination therapy of the viral polymerase inhibitor favipiravir and monoclonal antibodies (mAbs) against the receptor-binding site (RBS) and stem of viral hemagglutinin (HA). Although monotherapy or combination therapy of two antivirals (two mAbs or favipiravir plus a mAb) suppressed virus replication, they failed to eradicate viruses from nude mice. In contrast, the triple combination therapy of favipiravir plus anti-Stem and anti-RBS mAbs completely stopped virus replication in nude mice, resulting in virus clearance. Triple combination approaches should be considered for the treatment of human immunocompromised patients with severe influenza.

Optimization of 4-Aminopiperidines as Inhibitors of Influenza A Viral Entry That Are Synergistic with Oseltamivir

Vaccination is the most prevalent prophylactic means for controlling seasonal influenza infections. However, an effective vaccine usually takes at least 6 months to develop for the circulating strains. Therefore, new therapeutic options are needed for the acute treatment of influenza infections to control this virus and prevent epidemics/pandemics from developing. We have discovered fast-acting, orally bioavailable acylated 4-aminopiperidines with an effective mechanism of action targeting viral hemagglutinin (HA). Our data show that these compounds are potent entry inhibitors of influenza A viruses. We present docking studies that suggest an HA binding site for these inhibitors on H5N1. Compound 16 displayed a significant decrease of viral titer when evaluated in the infectious assays with influenza virus H1N1 (A/Puerto Rico/8/1934) or H5N1 (A/Vietnam/1203/2004) strains and the oseltamivir-resistant strain with the most common H274Y mutation. In addition, compound 16 showed significant synergistic activity with oseltamivir in vitro.

Influenza A Virus Hemagglutinin-Neuraminidase-Receptor Balance: Preserving Virus Motility

Influenza A viruses (IAVs) occasionally cross the species barrier and adapt to novel host species. This requires readjustment of the functional balance of the sialic acid receptor-binding hemagglutinin (HA) and the receptor-destroying neuraminidase (NA) to the sialoglycan-receptor repertoire of the new host. Novel techniques have revealed mechanistic details of this HA-NA-receptor balance, emphasizing a previously underappreciated crucial role for NA in driving the motility of receptor-associated IAV particles. Motility enables virion penetration of the sialylated mucus layer as well as attachment to, and uptake into, underlying epithelial cells. As IAVs are essentially irreversibly bound in the absence of NA activity, the fine-tuning of the HA-NA-receptor balance rather than the binding avidity of IAV particles per se is an important factor in determining host species tropism.

Combination Therapy With Neuraminidase and Polymerase Inhibitors in Nude Mice Infected With Influenza Virus

Background

Treatment of immunocompromised, influenza virus-infected patients with the viral neuraminidase inhibitor oseltamivir often leads to the emergence of drug-resistant variants. Combination therapy with compounds that target different steps in the viral life cycle may improve treatment outcomes and reduce the emergence of drug-resistant variants.

Methods

Here, we infected immunocompromised nude mice with an influenza A virus and treated them with neuraminidase (oseltamivir, laninamivir) or viral polymerase (favipiravir) inhibitors, or combinations thereof.

Results

Combination therapy for 28 days increased survival times compared with monotherapy, but the animals died after treatment was terminated. Mono- and combination therapies did not consistently reduce lung virus titers. Prolonged viral replication led to the emergence of neuraminidase inhibitor-resistant variants, although viruses remained sensitive to favipiravir. Overall, favipiravir provided greater benefit than neuraminidase inhibitors.

Conclusions

Collectively, our data demonstrate that combination therapy in immunocompromised hosts increases survival times, but does not suppress the emergence of neuraminidase inhibitor-resistant variants.

An I436N substitution confers resistance of influenza A(H1N1)pdm09 viruses to multiple neuraminidase inhibitors without affecting viral fitness

The resistance of influenza viruses to neuraminidase (NA) inhibitors (NAIs; i.e. oseltamivir, zanamivir, peramivir and laninamivir) can be associated with several NA substitutions, with differing effects on viral fitness. To identify novel molecular markers conferring multi-NAI resistance, the NA gene of oseltamivir-resistant (H275Y, N1 numbering) 2009 pandemic influenza [A(H1N1)pdm09] virus was enriched with random mutations. This randomly mutated viral library was propagated in Madin-Darby canine kidney (MDCK) cells under zanamivir pressure and gave rise to additional changes within NA, including an I436N substitution located outside the NA enzyme active site. We generated four recombinant A(H1N1)pdm09 viruses containing either wild-type NA or NA with single (I436N or H275Y) or double (H275Y-I436N) substitutions. The double H275Y-I436N mutation significantly reduced inhibition by oseltamivir and peramivir and reduced inhibition by zanamivir and laninamivir. I436N alone reduced inhibition by all NAIs, suggesting that it is a multi-NAI resistance marker. I436N did not affect viral fitness in vitro or in a murine model; however, H275Y and I436N together had a negative impact on viral fitness. Further, I436N alone did not have an appreciable impact on viral replication in the upper respiratory tract or transmissibility in ferrets. However, the rg-H275Y-I436N double mutant transmitted less efficiently than either single mutant via the direct contact and respiratory droplet routes in ferrets. Overall, these results highlight the usefulness of a random mutagenesis approach for identifying potential molecular markers of resistance and the importance of I436N NA substitution in A(H1N1)pdm09 virus as a marker for multi-NAI resistance.

Bovine Lactoferrin Prevents Influenza A Virus Infection by Interfering with the Fusogenic Function of Viral Hemagglutinin

Bovine lactoferrin (bLf) is an iron-binding glycoprotein folded in two symmetric globular lobes (N- and C-lobes) with potent antimicrobial and immunomodulatory activities. Recently, we have shown that bLf, and in particular its C-lobe, interacts with influenza A virus hemagglutinin and prevents infection by different H1 and H3 viral subtypes. Influenza virus hemagglutinin (HA), and in particular its highly conserved fusion peptide involved in the low-pH-mediated fusion process, plays a significant role in the early steps of viral infection and represents an attractive target for the development of anti-influenza drugs. In the present research, we further investigated the influence of low pH on the interactions between bLf and influenza A H1N1 virus by different techniques, such as enzyme-linked immunosorbent assay, electron microscopy, hemolysis inhibition assay, and time course assay. Our results demonstrate that lactoferrin interaction with influenza hemagglutinin at low pH induces alterations that stabilize the conformation of the hemagglutinin, resulting in the inhibition of the fusion peptide activity. Taken together, our data allowed to better characterize the HA-specific inhibiting activity of bLf and to confirm HA as a good target for drug development.

Workshop report: Experimental animal models for universal influenza vaccines

A major challenge in influenza research is the selection of an appropriate animal model that accurately reflects the disease and the protective immune response observed in humans. A workshop organised by the EDUFLUVAC consortium, a European Union funded project coordinated by the European Vaccine Initiative, brought together experts from the influenza vaccine community with the aim to discuss the current knowledge and future perspectives for testing broadly reactive influenza vaccines in animal models. The programme included a diversity of models from well-established and publicly accepted models to cutting edge, newly developed animal models as well as ex-vivo approaches and human models. The audience concluded that different vaccine approaches may require evaluation in different animal models, depending on the type of immune response induced by the vaccine. Safety is the main concern for transition to clinical development and influenza vaccine associated enhanced disease was specifically emphasised. An efficient animal model to evaluate this aspect of safety still needs to be identified. Working with animal models requires ethical compliance and consideration of the 3R principles. Development of alternative approaches such as ex-vivo techniques is progressing but is still at an early stage and these methods are not yet suitable for broader application for vaccine evaluation. The human challenge is the ultimate model to assess influenza vaccines. However this model is expensive and not largely applicable. The currently used pre-clinical models are not yet specifically focused on studying unique aspects of a universal influenza vaccine. Further collaboration, communication and effective networking are needed for success in establishment of harmonised and standardised pre-clinical models for evaluation of new influenza vaccines. This report does not provide a complete review of the field but discusses the data presented by the speakers and discussion points raised during the meeting.

An easy, rapid, and sensitive method for detection of drug-resistant influenza virus by using a sialidase fluorescent imaging probe, BTP3-Neu5Ac

Immunochromatographic kits and RT-PCR are widely used as diagnostic tools for influenza detection in clinical and hygiene fields. Immunochromatographic kits are useful for differential typing of influenza A and influenza B but cannot show if the detected virus strains have acquired drug resistance against neuraminidase inhibitors that target sialidase activity of viral neuraminidase. Although RT-PCR enables determination of drug-resistant mutants, its efficacy is limited to viruses carrying a known substitution in their neuraminidase genome sequence. In the present study, an easy, rapid and sensitive method for detection of drug-resistant influenza viruses regardless of major antigenic changes or genomic mutations was developed. By using the method in combination with virus-concentrated membranes in centrifugal filter units and a sialidase imaging probe, 2-(benzothiazol-2-yl)-4-bromophenyl-N-acetylneuraminic acid (BTP3-Neu5Ac), sialidase activity of influenza neuraminidase was visualized on membranes by the green fluorescence of produced hydrophobic BTP3 under UV irradiation with a handheld UV flashlight. Fluorescence images in the presence or absence of neuraminidase inhibitors clearly discriminated drug-resistant influenza viruses from drug-sensitive ones. The assay can be done within 15 min. The detection sensitivity was shown to be equal to or higher than the sensitivities of commercial immunochromatographic kits. The assay will be a powerful tool for screening and monitoring of emerging drug-resistant influenza viruses and would help clinicians decide effective antiviral treatment strategies when such mutants have become prevalent.

Impact of R152K and R368K neuraminidase catalytic substitutions on in vitro properties and virulence of recombinant A(H1N1)pdm09 viruses

Neuraminidase (NA) mutations conferring resistance to NA inhibitors (NAIs) are expected to occur at framework or catalytic residues of the NA enzyme. Numerous clinical and in vitro reports already described NAI-resistant A(H1N1)pdm09 variants harboring various framework NA substitutions. By contrast, variants with NA catalytic changes remain poorly documented. Herein, we investigated the effect of R152K and R368K NA catalytic mutations on the NA enzyme properties, in vitro replicative capacity and virulence of A(H1N1)pdm09 recombinant viruses. In NA inhibition assays, the R152K and R368K substitutions resulted in reduced inhibition [10- to 100-fold increases in IC₅₀ vs the wild-type (WT)] or highly reduced inhibition (>100-fold increases in IC₅₀) to at least 3 approved NAIs (oseltamivir, zanamivir, peramivir and laninamivir). Such resistance phenotype correlated with a significant reduction of affinity observed for the mutants in enzyme kinetics experiments [increased Km from 20 ± 1.77 for the WT to 200.8 ± 10.54 and 565.2 ± 135 μM (P < 0.01) for the R152K and R368K mutants, respectively]. The R152K and R368K variants grew at comparable or even higher titers than the WT in both MDCK and ST6GalI-MDCK cells. In experimentally-infected C57BL/6 mice, the recombinant WT and the R152K and R368K variants induced important signs of infection (weight loss) and resulted in mortality rates of 87.5%, 37.5% and 100%, respectively. The lung viral titers were comparable between the three infected groups. While the NA mutations were stable, an N154I substitution was detected in the HA2 protein of the R152K and R368K variants after in vitro passages as well as in lungs of infected mice. Due to the multi-drug resistance phenotypes and conserved fitness, the emergence of NA catalytic mutations accompanied with potential compensatory HA changes should be carefully monitored in A(H1N1)pdm09 viruses.

Identification of neuraminidase inhibitors against dual H274Y/I222R mutant strains

Influenza is an annual seasonal epidemic that has continually drawn public attentions, due to the potential death toll and drug resistance. Neuraminidase, which is essential for the spread of influenza virus, has been regarded as a valid target for the treatment of influenza infection. Although neuraminidase drugs have been developed, they are susceptible to drug-resistant mutations in the sialic-binding site. In this study, we established computational models (site-moiety maps) of H1N1 and H5N1 to determine properties of the 150-cavity, which is adjacent to the drug-binding site. The models reveal that hydrogen-bonding interactions with residues R118, D151, and R156 and van der Waals interactions with residues Q136, D151, and T439 are important for identifying 150-cavitiy inhibitors. Based on the models, we discovered three new inhibitors with IC₅₀ values <10 μM that occupies both the 150-cavity and sialic sites. The experimental results identified inhibitors with similar activities against both wild-type and dual H274Y/I222R mutant neuraminidases and showed little cytotoxic effects. Furthermore, we identified three new inhibitors situated at the sialic-binding site with inhibitory effects for normal neuraminidase, but lowered effects for mutant strains. The results suggest that the new inhibitors can be used as a starting point to combat drug-resistant strains.

The hydrophobic side chain of oseltamivir influences type A subtype selectivity of neuraminidase inhibitors

Neuraminidase, which plays a critical role in the influenza virus life cycle, is a target for new therapeutic agents. The study of structure-activity relationships revealed that the C-5 position amino group of oseltamivir was pointed to 150-cavity of the neuraminidase in group 1. This cavity is important for selectivity of inhibitors against N1 versus N2 NA. A serial of influenza neuraminidase inhibitors with the oseltamivir scaffold containing lipophilic side chains at the C-5 position have been synthesized and evaluated for their influenza neuraminidase inhibitory activity and selectivity. The results indicated that compound 13o (H5N1 IC₅₀  = 0.1 ± 0.04 μm, H3N2 IC₅₀  = 0.26 ± 0.18 μm) showed better inhibitory activity and selectivity against the group 1 neuraminidase. This study may provide a clue to design of better group 1 neuraminidase inhibitors.

Synthesis and In Vitro Anti-Influenza Virus Evaluation of Novel Sialic Acid (C-5 and C-9)-Pentacyclic Triterpene Derivatives

The emergence of drug resistant variants of the influenza virus has led to a great need to identify novel and effective antiviral agents. In our previous study, a series of sialic acid (C-2 and C-4)-pentacyclic triterpene conjugates have been synthesized, and a five-fold more potent antiviral activity was observed when sialic acid was conjugated with pentacyclic triterpene via C-4 than C-2. It was here that we further reported the synthesis and anti-influenza activity of novel sialic acid (C-5 and C-9)-pentacyclic triterpene conjugates. Their structures were confirmed by ESI-HRMS, ¹H-NMR, and ¹³C-NMR spectroscopic analyses. Two conjugates (26 and 42) showed strong cytotoxicity to MDCK cells in the CellTiter-Glo assay at a concentration of 100 μM. However, they showed no significant cytotoxicity to HL-60, Hela, and A549 cell lines in MTT assay under the concentration of 10 μM (except compound 42 showed weak cytotoxicity to HL-60 cell line (10 μM, ~53%)). Compounds 20, 28, 36, and 44 displayed weak potency to influenza A/WSN/33 (H1N1) virus (100 μM, ~20–30%), and no significant anti-influenza activity was found for the other conjugates. The data suggested that both the C-5 acetylamide and C-9 hydroxy of sialic acid were important for its binding with hemagglutinin during viral entry into host cells, while C-4 and C-2 hydroxy were not critical for the binding process and could be replaced with hydrophobic moieties. The research presented herein had significant implications for the design of novel antiviral inhibitors based on a sialic acid scaffold.

Combating mutations in genetic disease and drug resistance: understanding molecular mechanisms to guide drug design

INTRODUCTION

Mutations introduce diversity into genomes, leading to selective changes and driving evolution. These changes have contributed to the emergence of many of the current major health concerns of the 21st century, from the development of genetic diseases and cancers to the rise and spread of drug resistance. The experimental systematic testing of all mutations in a system of interest is impractical and not cost-effective, which has created interest in the development of computational tools to understand the molecular consequences of mutations to aid and guide rational experimentation. Areas covered: Here, the authors discuss the recent development of computational methods to understand the effects of coding mutations to protein function and interactions, particularly in the context of the 3D structure of the protein. Expert opinion: While significant progress has been made in terms of innovative tools to understand and quantify the different range of effects in which a mutation or a set of mutations can give rise to a phenotype, a great gap still exists when integrating these predictions and drawing causality conclusions linking variants. This often requires a detailed understanding of the system being perturbed. However, as part of the drug development process it can be used preemptively in a similar fashion to pharmacokinetics predictions, to guide development of therapeutics to help guide the design and analysis of clinical trials, patient treatment and public health policy strategies.

A Review of Clinical Influenza A and B Infections With Reduced Susceptibility to Both Oseltamivir and Zanamivir

Anti-influenza drugs play major roles in the management of severe influenza infections. Neuraminidase inhibitors (NAIs), which are active against all influenza A subtypes and the 2 major influenza B lineages, constitute the only class of antivirals recommended for the control of influenza epidemics and eventual pandemics. Thus, the emergence of NAI resistance could be a major clinical concern. Although most currently circulating influenza A and B strains are susceptible to NAIs, clinical cases of influenza viruses harboring single or multiple NA substitutions or deletions conferring a cross-resistance phenotype to the 2 main NAIs (oseltamivir and zanamivir) have been reported, mostly in immunocompromised individuals. Moreover, such events seem to be more frequent in A(H1N1)pdm09 viruses containing the H274Y substitution together with other NA changes (I222R, E119D/G). This review summarizes the therapeutic regimens leading to the emergence of NAI cross-resistant influenza A and B viruses as well as the virologic properties of such variants.

Molecular Mechanism Underlying the Action of Influenza A Virus Fusion Inhibitor MBX2546

Influenza A virus envelop protein hemagglutinin (HA) plays important roles in viral entry. We previously have reported that MBX2546, a novel influenza A virus inhibitor, binds to HA and inhibits HA-mediated membrane fusion. In this report, we show that (i) both binding and stabilization of HA by MBX2546 are required for the inhibition of viral infection and (ii) the binding of HA by MBX2546 represses the low-pH-induced conformational change in the HA, which is a prerequisite for membrane fusion. Mutations in MBX2546-resistant influenza A/PR/8/34 (H1N1) viruses are mapped in the HA stem region near the amino terminus of HA2. Finally, we have modeled the binding site of MBX2546 using molecular dynamics and find that the resulting structure is in good agreement with our results. Together, these studies underscore the importance of the HA stem loop region as a potential target for therapeutic intervention.

Inhibition of influenza virus infection by multivalent pentacyclic triterpene-functionalized per-O-methylated cyclodextrin conjugates

Multivalent ligands that exhibit high binding affinity to influenza hemagglutinin (HA) trimer can block the interaction of HA with its sialic acid receptor. In this study, a series of multivalent pentacyclic triterpene-functionalized per-O-methylated cyclodextrin (CD) derivatives were designed and synthesized using 1, 3-dipolar cycloaddition click reaction. A cell-based assay showed that three compounds (25, 28 and 31) exhibited strong inhibitory activity against influenza A/WSN/33 (H1N1) virus. Compound 28 showed the most potent anti-influenza activity with IC₅₀ of 4.7 μM. The time-of-addition assay indicated that compound 28 inhibited the entry of influenza virus into host cell. Further hemagglutination inhibition (HI) and surface plasmon resonance (SPR) assays indicated that compound 28 tightly bound to influenza HA protein with a dissociation constant (K_D) of 4.0 μM. Our results demonstrated a strategy of using per-O-methylated β-CD as a scaffold for designing multivalent compounds to disrupt influenza HA protein-host receptor protein interaction and thus block influenza virus entry into host cells.

Antiviral Resistance in Influenza Viruses: Clinical and Epidemiological Aspects

There are three classes of antiviral drugs approved for the treatment of influenza: the M2 ion channel inhibitors (amantadine, rimantadine), neuraminidase (NA) inhibitors (laninamivir, oseltamivir, peramivir, zanamivir), and the protease inhibitor (favipiravir); some of the agents are only available in selected countries [1, 2]. These agents are effective at treating the signs and symptoms of influenza in patients infected with susceptible viruses. Clinical failure has been demonstrated in patients infected with viruses with primary resistance, i.e., antivirals can be present in the virus initially infecting the patient, or resistance may emerge during the course of therapy [3–5]. NA inhibitors are active against all nine NA subtypes recognized in nature [6], including highly pathogenic avian influenza A/H5N1 and recent low-pathogenic avian influenza A/H7N9 viruses [7]. Since seasonal influenza is usually an acute, self-limited illness in which viral clearance usually occurs rapidly due to innate and adaptive host immune responses, the emergence of drug-resistant variants would be anticipated to have limited effect on clinical recovery in otherwise healthy patients, as has been demonstrated clinically [3, 8, 9]. Unfortunately, immunocompromised or immunologically naïve hosts, such as young children and infants or those exposed to novel strains, are more likely to have mutations that confer resistance emergence during therapy; such resistant variants may also result in clinically significant adverse outcomes [10–13].

The pharmacological management of severe influenza infection - 'existing and emerging therapies'

INTRODUCTION

Over the last century several influenza outbreaks have traversed the globe, most recently the influenza A(H1N1) 2009 pandemic. On each occasion, a highly contagious, virulent pathogen has emerged, leading to significant morbidity and mortality amongst those affected. Areas covered: Early antiviral therapy and supportive care is the mainstay of treatment. Treatment should be started as soon as possible and not delayed for the results of diagnostic testing. Whilst oseltamivir is still the first choice, in case of treatment failure, oseltamivir resistance should be considered, particularly in immunosuppressed patients. Here we review the antivirals currently used for management of influenza and explore a number of investigational agents that may emerge as effective antivirals including parenteral agents, combination antiviral therapy and novel agents in order to adequately target influenza virulence. Expert Commentary: New tools for rapid diagnosis and susceptible strains will help if a patient is not improving because of a resistant strain or an inadequate immune response. Further randomized control trials will be conducted to investigate the use of new antivirals and co-adjuvant therapies that will help to elucidate the process of immune modulation, particularly in immunocompetent patients.

Hemin ameliorates influenza pneumonia by attenuating lung injury and regulating the immune response

The anti-influenza activity of hemin, an inducer, activator and the substrate of heme oxygenase-1 (HO-1), was examined both in vitro and in vivo. The human lung carcinoma cell line A549 was used to evaluate the in vitro effect of hemin on influenza A virus (IAV) replication. A mouse model was used to examine the in vivo activity of hemin. Observation indexes included survival rate and body weight of mice, virus load and pathological examination of the lungs, and characterization of the systemic and local immune responses. The results showed that hemin could induce HO-1 expression in A549 cells and inhibit IAV replication in vitro. The in vivo results showed that injection of hemin could protect mice from death and body weight loss caused by IAV infection. Hemin was administered both at initial and progressive stages of influenza pneumonia (1 day and 4 days after virus infection, respectively) and showed significant anti-influenza activity under both conditions. However, the results showed that although hemin could induce HO-1 expression in vivo, it could not inhibit IAV replication in vivo. Pathological examination showed that hemin significantly attenuated lung tissue injury caused by IAV. Further study showed that hemin could regulate the immune response to IAV infection by reducing lymphocytopenia and local inflammatory cytokine increases caused by IAV infection. This study shows that hemin has the potential for the treatment of IAV infection and its effect may be due to attenuation of lung injury and regulation of the immune response.

Formulation and Evaluation of Antibacterial Creams and Gels Containing Metal Ions for Topical Application

Background. Skin infections occur commonly and often present therapeutic challenges to practitioners due to the growing concerns regarding multidrug-resistant bacterial, viral, and fungal strains. The antimicrobial properties of zinc sulfate and copper sulfate are well known and have been investigated for many years. However, the synergistic activity between these two metal ions as antimicrobial ingredients has not been evaluated in topical formulations. Objective. The aims of the present study were to (1) formulate topical creams and gels containing zinc and copper alone or in combination and (2) evaluate the in vitro antibacterial activity of these metal ions in the formulations. Method. Formulation of the gels and creams was followed by evaluating their organoleptic characteristics, physicochemical properties, and in vitro antibacterial activity against Escherichia coli and Staphylococcus aureus. Results. Zinc sulfate and copper sulfate had a strong synergistic antibacterial activity in the creams and gels. The minimum effective concentration was found to be 3 w/w% for both active ingredients against the two tested microorganisms. Conclusions. This study evaluated and confirmed the synergistic in vitro antibacterial effect of copper sulfate and zinc sulfate in a cream and two gels.

Distinct Effects of T-705 (Favipiravir) and Ribavirin on Influenza Virus Replication and Viral RNA Synthesis

T-705 (favipiravir) is a new antiviral agent in advanced clinical development for influenza therapy. It is supposed to act as an alternative substrate for the viral polymerase, causing inhibition of viral RNA synthesis or virus mutagenesis. These mechanisms were also proposed for ribavirin, an established and broad antiviral drug that shares structural similarity with T-705. We here performed a comparative analysis of the effects of T-705 and ribavirin on influenza virus and host cell functions. Influenza virus-infected cell cultures were exposed to T-705 or ribavirin during single or serial virus passaging. The effects on viral RNA synthesis and infectious virus yield were determined and mutations appearing in the viral genome were detected by whole-genome virus sequencing. In addition, the cellular nucleotide pools as well as direct inhibition of the viral polymerase enzyme were quantified. We demonstrate that the anti-influenza virus effect of ribavirin is based on IMP dehydrogenase inhibition, which results in fast and profound GTP depletion and an imbalance in the nucleotide pools. In contrast, T-705 acts as a potent and GTP-competitive inhibitor of the viral polymerase. In infected cells, viral RNA synthesis is completely inhibited by T-705 or ribavirin at ≥50 μM, whereas exposure to lower drug concentrations induces formation of noninfectious particles and accumulation of random point mutations in the viral genome. This mutagenic effect is 2-fold higher for T-705 than for ribavirin. Hence, T-705 and ribavirin both act as purine pseudobases but profoundly differ with regard to the mechanism behind their antiviral and mutagenic effects on influenza virus.

Risk of resistant avian influenza A virus in wild waterfowl as a result of environmental release of oseltamivir

Oseltamivir is the best available anti-influenza drug and has therefore been stockpiled worldwide in large quantities as part of influenza pandemic preparedness planning. The active metabolite oseltamivir carboxylate (OC) is stable and is not removed by conventional sewage treatment. Active OC has been detected in river water at concentrations up to 0.86 µg/L. Although the natural reservoir hosts of influenza A virus (IAV) are wild waterfowl that reside in aquatic environments, the ecologic risks associated with environmental OC release and its potential to generate resistant viral variants among wild birds has largely been unknown. However, in recent years a number of in vivo mallard (Anas platyrhynchos) studies have been conducted regarding the potential of avian IAVs to become resistant to OC in natural reservoir birds if these are drug exposed. Development of resistance to OC was observed both in Group 1 (N1) and Group 2 (N2, N9) neuraminidase subtypes, when infected ducks were exposed to OC at concentrations between 0.95 and 12 µg/L in their water. All resistant variants maintained replication and transmission between ducks during drug exposure. In an A(H1N1)/H274Y virus, the OC resistance mutation persisted without selective drug pressure, demonstrating the potential of an IAV with a permissive genetic background to acquire and maintain OC resistance, potentially allowing circulation of the resistant variant among wild birds. The experimental studies have improved the appreciation of the risks associated with the environmental release of OC related to resistance development of avian IAVs among wild birds. Combined with knowledge of efficient methods for improved sewage treatment, the observations warrant implementation of novel efficient wastewater treatment methods, rational use of anti-influenza drugs, and improved surveillance of IAV resistance in wild birds.

Platform for determining the inhibition profile of neuraminidase inhibitors in an influenza virus N1 background

Efforts to develop novel neuraminidase inhibitors (NAIs) for the treatment of influenza are ongoing. Novel NAIs should in particular be also effective against seasonal and/or pandemic N1 that carry a H274Y or N294S substitution (N2 numbering), which are most commonly linked to oseltamivir resistance. Here we report a platform for profiling the efficacy of novel NAIs in the N1 genetic background of influenza A virus. Employing reverse genetics, a set of influenza virus variants containing an amino acid substitution associated with oseltamivir resistance in N1 isolates (H274Y, N294S, Y155H or Q136L) was generated. In parallel, so far unreported mutations of I427 (I427Q and I427M) were investigated. These possibly interfere with the side chain orientation of R371 and alter the binding affinity of most relevant NAIs. The profiling platform was validated with both oseltamivir and zanamivir and exemplarily applied to three analogs with differing decorations at positions 4 and 5. Besides confirming the inhibition profile of zanamivir and oseltamivir, the distinct effect of I427Q/M on the activity of both NAIs was shown. For 5-amidino and 5-guanidino analogs of oseltamivir a significantly stronger inhibition of virus variants carrying a NA-H274Y was confirmed, and additionally shown for NA-N294S and NA-Y155H substitutions as compared to the parent compound. Hence, the herein presented profiling platform is a valid tool for defining the inhibition profile of novel NAIs in the N1 background.

Stabilization and Improvement of a Promising Influenza Antiviral: Making a PAIN PAINless

The viral envelope protein hemagglutinin (HA) plays a critical role in influenza entry and thus is an attractive target for novel therapeutics. The small molecule tert-butylhydroquinone (TBHQ) has previously been shown to bind to HA and inhibit HA-mediated entry with low micromolar potency. However, enthusiasm for the use of TBHQ has diminished due to the compound's antioxidant properties. In this work we show that the antioxidant properties of TBHQ are not responsible for the inhibition of HA-mediated entry. In addition, we have performed a structure-activity relationship (SAR) analysis of TBHQ derivatives. We find that the most promising compound, 3-tert-butyl-4-methoxyphenol, exhibits enhanced potency (IC₅₀ = 0.6 μM), decreased toxicity (CC₅₀ = 340 μM), and increased stability (t_1/2 > 48 h). Finally, we have characterized the binding properties of 3-tert-butyl-4-methoxyphenol using NMR and molecular dynamics to guide future efforts for chemical optimization.

The Influenza Virus Polymerase Complex: An Update on Its Structure, Functions, and Significance for Antiviral Drug Design

Influenza viruses cause seasonal epidemics and pandemic outbreaks associated with significant morbidity and mortality, and a huge cost. Since resistance to the existing anti‐influenza drugs is rising, innovative inhibitors with a different mode of action are urgently needed. The influenza polymerase complex is widely recognized as a key drug target, given its critical role in virus replication and high degree of conservation among influenza A (of human or zoonotic origin) and B viruses. We here review the major progress that has been made in recent years in unravelling the structure and functions of this protein complex, enabling structure‐aided drug design toward the core regions of the PA endonuclease, PB1 polymerase, or cap‐binding PB2 subunit. Alternatively, inhibitors may target a protein–protein interaction site, a cellular factor involved in viral RNA synthesis, the viral RNA itself, or the nucleoprotein component of the viral ribonucleoprotein. The latest advances made for these diverse pharmacological targets have yielded agents in advanced (i.e., favipiravir and VX‐787) or early clinical testing, besides several experimental inhibitors in various stages of development, which are all covered here.

Phenotypic and genotypic analysis of influenza viruses isolated from adult subjects during a phase II study of intravenous zanamivir in hospitalised subjects

Intravenous zanamivir (IVZ) is a neuraminidase (NA) inhibitor (NAI) under investigation for the treatment of subjects hospitalised with influenza. The study included 130 symptomatic, hospitalised adults with influenza. Subjects received IVZ for 5-10 days. Viruses were cultured and analysed for susceptibility to zanamivir. Mean IC₅₀s (n = 50) (±SD) for influenza A/H1N1pdm09, A/H3N2 and influenza B were 0.20 ± 0.06, 0.26 ± 0.07 and 1.61 ± 0.35 nM, respectively, and are comparable to data observed for sensitive isolates. A total of 185 NA and 180 haemagglutinin (HA) sequences were obtained from 123 subjects; the majority did not contain resistance substitutions. Four influenza A/H1N1pdm09 viruses from four subjects harboured NA resistance substitutions: three, Y155H, D199G and S247N, were present at Day 1 before IVZ exposure and the fourth, E119D/E, was detected at Post Treatment +5 Days but was not present at 5 other timepoints. Five subjects harboured virus with treatment-emergent NA substitutions not associated with resistance; N63D, V83A, W190C, M269K (A/H1N1pdm09) and R210K (A/H3N2). Viruses from fifteen subjects harboured HA resistance substitutions, (A/H1N1pdm09) one emerged during treatment: S162N (Day 5). Five viruses harboured treatment-emergent HA substitutions (A/H1N1pdm09) not associated with resistance: E81K, V108L, S164D, D168N and S185N. 10/92 subjects with A/H1N1pdm09 harboured a D222 HA substitution, which has been associated with increased virulence. The emergent substitutions are not associated with resistance but may have arisen due to selection pressure during IVZ treatment or by chance. In this study, there was evidence for resistance selection in a post treatment sample but the resistant variant did not persist in later visit samples.

Identification and Characterization of Influenza Virus Entry Inhibitors through Dual Myxovirus High-Throughput Screening

Influenza A virus (IAV) infections cause major morbidity and mortality, generating an urgent need for novel antiviral therapeutics. We recently established a dual myxovirus high-throughput screening protocol that combines a fully replication-competent IAV-WSN strain and a respiratory syncytial virus reporter strain for the simultaneous identification of IAV-specific, paramyxovirus-specific, and broad-spectrum inhibitors. In the present study, this protocol was applied to a screening campaign to assess a diverse chemical library with over 142,000 entries. Focusing on IAV-specific hits, we obtained a hit rate of 0.03% after cytotoxicity testing and counterscreening. Three chemically distinct hit classes with nanomolar potency and favorable cytotoxicity profiles were selected. Time-of-addition, minigenome, and viral entry studies demonstrated that these classes block hemagglutinin (HA)-mediated membrane fusion. Antiviral activity extends to an isolate from the 2009 pandemic and, in one case, another group 1 subtype. Target identification through biolayer interferometry confirmed binding of all hit compounds to HA. Resistance profiling revealed two distinct escape mechanisms: primary resistance, associated with reduced compound binding, and secondary resistance, associated with unaltered binding. Secondary resistance was mediated, unusually, through two different pairs of cooperative mutations, each combining a mutation eliminating the membrane-proximal stalk N-glycan with a membrane-distal change in HA1 or HA2. Chemical synthesis of an analog library combined with in silico docking extracted a docking pose for the hit classes. Chemical interrogation spotlights IAV HA as a major druggable target for small-molecule inhibition. Our study identifies novel chemical scaffolds with high developmental potential, outlines diverse routes of IAV escape from entry inhibition, and establishes a path toward structure-aided lead development.

IMPORTANCE

This study is one of the first to apply a fully replication-competent third-generation IAV reporter strain to a large-scale high-throughput screen (HTS) drug discovery campaign, allowing multicycle infection and screening in physiologically relevant human respiratory cells. A large number of potential druggable targets was thus chemically interrogated, but mechanistic characterization, positive target identification, and resistance profiling demonstrated that three chemically promising and structurally distinct hit classes selected for further analysis all block HA-mediated membrane fusion. Viral escape from inhibition could be achieved through primary and secondary resistance mechanisms. In silico docking predicted compound binding to a microdomain located at the membrane-distal site of the prefusion HA stalk that was also previously suggested as a target site for chemically unrelated HA inhibitors. This study identifies an unexpected chemodominance of the HA stalk microdomain for small-molecule inhibitors in IAV inhibitor screening campaigns and highlights a novel mechanism of cooperative resistance to IAV entry blockers.

Progress in Treatment of Viral Infections in Children with Acute Lymphoblastic Leukemia

In children, the most commonly encountered type of leukemia is acute lymphoblastic leukemia (ALL). An important source of morbidity and mortality in ALL are viral infections. Even though allogeneic transplantations, which are often applied also in ALL, carry a recognized risk for viral infections, there are multiple factors that make ALL patients susceptible to viral infections. The presence of those factors has an influence in the type and severity of infections. Currently available treatment options do not guarantee a positive outcome for every case of viral infection in ALL, without significant side effects. Side effects can have very serious consequences for the ALL patients, which include nephrotoxicity. For this reason a number of strategies for personalized intervention have been already clinically tested, and experimental approaches are being developed. Adoptive immunotherapy, which entails administration of ex vivo grown immune cells to a patient, is a promising approach in general, and for transplant recipients in particular. The ex vivo grown cells are aimed to strengthen the immune response to the virus that has been identified in the patients' blood and tissue samples. Even though many patients with weakened immune system can benefit from progress in novel approaches, a viral infection still poses a very significant risk for many patients. Therefore, preventive measures and supportive care are very important for ALL patients.

Zanamivir-resistant influenza viruses with Q136K or Q136R neuraminidase residue mutations can arise during MDCK cell culture creating challenges for antiviral susceptibility monitoring

Surveillance of circulating influenza strains for antiviral susceptibility is important to ensure patient treatment guidelines remain appropriate. Influenza A(H3N2) and A(H1N1)pdm09 virus isolates containing mutations at the Q136 residue of the neuraminidase (NA) that conferred reduced susceptibility to the NA inhibitor (NAI) zanamivir were detected during antiviral susceptibility monitoring. Interestingly, the mutations were not detectable in the viruses from respective clinical specimens, only in the cultured isolates. We showed that variant viruses containing the Q136K and Q136R NA mutations were preferentially selected in Madin-Darby canine kidney epithelial (MDCK) cells, but were less well supported in MDCK-SIAT1 cells and embryonated eggs. The effect of Q136K, Q136R, Q136H and Q136L substitutions in NA subtypes N1 and N2 on NAI susceptibility and in vitro viral fitness was assessed. This study highlights the challenges that cell culture derived mutations can pose to the NAI susceptibility analysis and interpretation and reaffirms the need to sequence viruses from respective clinical specimens to avoid misdiagnosis. However, we also demonstrate that NA mutations at residue Q136 can confer reduced zanamivir, peramivir or laninamivir susceptibility, and therefore close monitoring of viruses for mutations at this site from patients being treated with these antivirals is important.

Influenza: from zoonosis to pandemic

Probable epidemic influenza outbreaks have been described as early as the 5th century BC, as part of the Cough of Perinthus associated with the winter solstice, in Hippocrates' Corpus Hippocraticum “Of the Epidemics” [1]. The word “influenza” was first introduced in the 16th century, defining the illness of the cold season that in the early 1930s was shown to be caused by “filterable agents”, since then called influenza viruses. Three types or genera of influenza viruses have been recognised (influenza A, B and C viruses), while a fourth genus has been recently proposed [2]. Today, we distinguish three manifestations of influenza in humans, which may impose from mild to severe morbidity and mortality burdens: zoonotic, pandemic and seasonal influenza, all caused by an infection with an influenza virus. Although our arsenal of intervention strategies for influenza has advanced in the past decades and a growing public conception has arisen of influenza as a usually seasonal inconvenience, threats posed by influenza A viruses, with their different manifestations and associated complications, are continuously knocking on our door.

Global surveillance and advances in vaccine technology are essential to answer the threat of influenza pandemicshttp://ow.ly/Yt3e4