Global update on the susceptibility of human influenza viruses to neuraminidase inhibitors, 2015-2016

Low antiviral resistance in Influenza A and B viruses isolated in Mexico from 2010 to 2023

The most widely used class of antivirals available for Influenza treatment are the neuraminidase inhibitors (NAI) Oseltamivir and Zanamivir. However, amino acid (AA) substitutions in the neuraminidase may cause reduced inhibition or high antiviral resistance. In Mexico, the current state of knowledge about NAI susceptibility is scarce, in this study we report the results of 14 years of Influenza surveillance by phenotypic and genotypic methods. A total of 255 isolates were assessed with the NAI assay, including Influenza A(H1N1)pdm09, A(H3N2) and Influenza B (IBV). Furthermore, 827 sequences contained in the GISAID platform were analyzed in search of relevant mutations.Overall, five isolates showed highly reduced inhibition or reduced inhibition to Oseltamivir, and two showed reduced inhibition to Zanamivir in the NAI assays. Additionally, five A(H1N1)pdm09 sequences from the GISAID possessed AA substitutions associated to reduced inhibition to Oseltamivir and none to Zanamivir. Oseltamivir resistant A(H1N1)pdm09 harbored the H275Y mutation. No genetic mutations were identified in Influenza A(H3N2) and IBV. Overall, these results show that in Mexico the rate of NAI resistance is low (0.6%), but it is essential to continue the Influenza surveillance in order to understand the drug susceptibility of circulating strains.

Optimization of an allelic discrimination real-time RT-PCR assay for detection of H275Y oseltamivir resistance gene mutation among influenza A(H1N1)pdm09 patients from 2020 to 2022

Influenza virus is known to cause mild to severe respiratory infections and is also prone to genetic mutations. Of all the mutations, neuraminidase (NA) gene mutations are a matter of concern, as most approved antivirals target this protein. During the 2020 influenza season, an emergence of mutation in the NA gene, affecting the binding of the World Health Organization (WHO)-recommended probes to the specific site of the NA gene, was reported by our group. As a result of this mutation, the WHO-recommended allelic discrimination real-time reverse transcriptase polymerase chain reaction (RT-PCR) assay was unable to detect wild-type (H275) or mutant oseltamivir-resistant (Y275) strains of influenza A(H1N1)pmd09 viruses. In the current study, the WHO-recommended probes were redesigned according to the mutation in the probe binding site. Fifty undetermined samples (2020-2021) from the previous study were retested with the newly designed probes and found to be positive for H275 and/or Y275. The results obtained were similar to the Sanger sequencing results from the previous study, suggesting that the redesigned probes were efficient in discriminating between wild-type and mutant-type viruses. Furthermore, 133 samples from 2022, making a total of 183 samples (2020-2022), were tested using improved allelic discrimination real-time RT-PCR, and the overall prevalence rate of oseltamivir resistance in 2020-2022 was found to be 0.54%.

Design of new chemical entities targeting both native and H275Y mutant influenza a virus by deep reinforcement learning

Influenza virus remains a major public health challenge due to its high morbidity and mortality and seasonal surge. Although antiviral drugs against the influenza virus are widely used as a first-line defense, the virus undergoes rapid genetic changes, resulting in the emergence of drug-resistant strains. Thus, new antiviral drugs that can outwit resistant strains are of significant importance. Herein, we used deep reinforcement learning (RL) algorithm to design new chemical entities (NCEs) that are able to bind to the native and H275Y mutant (oseltamivir-resistant) neuraminidases (NAs) of influenza A virus with better binding energy than oseltamivir. We generated more than 66211 NCEs, which were prioritized based on the filtering rules, structural alerts, and synthetic accessibility. Then, 18 NCEs with better MM/PBSA scores than oseltamivir were further analyzed in molecular dynamics (MD) simulations conducted for 100 ns. The MD experiments showed that 8 NCEs formed very stable complexes with the binding pocket of both native and H275Y mutant NAs of H1N1. Furthermore, most NCEs demonstrated much better binding affinity to group 2 (N2, N3, and N9) and influenza B virus NAs than oseltamivir. Although all 8 NCEs have non-sialic acid-like structures, they showed a similar binding mode as oseltamivir, indicating that it is possible to find new scaffolds with better binding and antiviral properties than sialic acid-like inhibitors. In conclusion, we have designed potential compounds as antiviral candidates for further synthesis and testing against wild and mutant influenza virus.Communicated by Ramaswamy H. Sarma.

Deep mutational scanning of influenza A virus neuraminidase facilitates the identification of drug resistance mutations in vivo

IMPORTANCE

NA is a crucial surface antigen and drug target of influenza A virus. A comprehensive understanding of NA's mutational effect and drug resistance profiles in vivo is essential for comprehending the evolutionary constraints and making informed choices regarding drug selection to combat resistance in clinical settings. In the current study, we established an efficient deep mutational screening system in mouse lung tissues and systematically evaluated the fitness effect and drug resistance to three neuraminidase inhibitors of NA single-nucleotide mutations. The fitness of NA mutants is generally correlated with a natural mutation in the database. The fitness of NA mutants is influenced by biophysical factors such as protein stability, complex formation, and the immune response triggered by viral infection. In addition to confirming previously reported drug-resistant mutations, novel mutations were identified. Interestingly, we identified an allosteric drug-resistance mutation that is not located within the drug-binding pocket but potentially affects drug binding by interfering with NA tetramerization. The dual assessments performed in this study provide a more accurate assessment of the evolutionary potential of drug-resistant mutations and offer guidance for the rational selection of antiviral drugs.

Aprotinin-Drug against Respiratory Diseases

Aprotinin (APR) was discovered in 1930. APR is an effective pan-protease inhibitor, a typical "magic shotgun". Until 2007, APR was widely used as an antithrombotic and anti-inflammatory drug in cardiac and noncardiac surgeries for reduction of bleeding and thus limiting the need for blood transfusion. The ability of APR to inhibit proteolytic activation of some viruses leads to its use as an antiviral drug for the prevention and treatment of acute respiratory virus infections. However, due to incompetent interpretation of several clinical trials followed by incredible controversy in the literature, the usage of APR was nearly stopped for a decade worldwide. In 2015-2020, after re-analysis of these clinical trials' data the restrictions in APR usage were lifted worldwide. This review discusses antiviral mechanisms of APR action and summarizes current knowledge and prospective regarding the use of APR treatment for diseases caused by RNA-containing viruses, including influenza and SARS-CoV-2 viruses, or as a part of combination antiviral treatment.

Characterization of Influenza A(H1N1)pdm09 Viruses Isolated in the 2018-2019 and 2019-2020 Influenza Seasons in Japan

The influenza A(H1N1)pdm09 virus that emerged in 2009 causes seasonal epidemic worldwide. The virus acquired several amino acid substitutions that were responsible for antigenic drift until the 2018-2019 influenza season. Viruses possessing mutations in the NA and PA proteins that cause reduced susceptibility to NA inhibitors and baloxavir marboxil, respectively, have been detected after antiviral treatment, albeit infrequently. Here, we analyzed HA, NA, and PA sequences derived from A(H1N1)pdm09 viruses that were isolated during the 2018-2019 and 2019-2020 influenza seasons in Japan. We found that A(H1N1)pdm09 viruses possessing the D187A and Q189E substitutions in HA emerged and dominated during the 2019-2020 season; these substitutions in the antigenic site Sb, a high potency neutralizing antibody-eliciting site for humans, changed the antigenicity of A(H1N1)pdm09 viruses. Furthermore, we found that isolates possessing the N156K substitution, which was predicted to affect the antigenicity of A(H1N1)pdm09 virus at the laboratory level, were detected at a frequency of 1.0% in the 2018-2019 season but 10.1% in the 2019-2020 season. These findings indicate that two kinds of antigenically drifted viruses-N156K and D187A/Q189E viruses-co-circulated during the 2019-2020 influenza season in Japan.

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

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

Low prevalence of influenza A strains with resistance markers in Brazil during 2017-2019 seasons

The influenza A virus (IAV) is of a major public health concern as it causes annual epidemics and has the potential to cause pandemics. At present, the neuraminidase inhibitors (NAIs) are the most widely used anti-influenza drugs, but, more recently, the drug baloxavir marboxil (BXM), a polymerase inhibitor, has also been licensed in some countries. Mutations in the viral genes that encode the antiviral targets can lead to treatment resistance. Worldwide, a low prevalence of antiviral resistant strains has been reported. Despite that, this situation can change rapidly, and resistant strain surveillance is a priority. Thus, the aim of this was to evaluate Brazilian IAVs antiviral resistance from 2017 to 2019 through the identification of viral mutations associated with reduced inhibition of the drugs and by testing the susceptibility of IAV isolates to oseltamivir (OST), the most widely used NAI drug in the country. Initially, we analyzed 282 influenza A(H1N1)pdm09 and 455 A(H3N2) genetic sequences available on GISAID. The amino acid substitution (AAS) NA:S247N was detected in one A(H1N1)pdm09 strain. We also identified NA:I222V (n = 6) and NA:N329K (n = 1) in A(H3N2) strains. In addition, we performed a molecular screening for NA:H275Y in 437 A(H1N1)pdm09 samples, by pyrosequencing, which revealed a single virus harboring this mutation. Furthermore, the determination of OST IC₅₀ values for 222 A(H1N1)pdm09 and 83 A(H3N2) isolates revealed that all isolates presented a normal susceptibility profile to the drug. Interestingly, we detected one A(H3N2) virus presenting with PA:E119D AAS. Moreover, the majority of the IAV sequences had the M2:S31N adamantanes resistant marker. In conclusion, we show a low prevalence of Brazilian IAV strains with NAI resistance markers, in accordance with what is reported worldwide, indicating that NAIs still remain an option for the treatment of influenza infections in Brazil. However, surveillance of influenza resistance should be strengthened in the country for improving the representativeness of investigated viruses and the robustness of the analysis.

Traditional Chinese Medicine Injections Combined With Oseltamivir for Influenza: Systematic Review and Network Meta-Analysis

Background: As a cause of respiratory tract infections in humans, influenza remains with high morbidity and mortality, with associated significant healthcare burden and increased financial burden. Traditional Chinese medicine injections (TCMIs) combined with oseltamivir (TCMIs + oseltamivir) are the representative therapeutic strategies for influenza, which is a compliant with clinical applications in China. The aim of this study was to describe the comparative efficacy and safety of TCMIs + oseltamivir in patients with influenza, based on the current evidence.

Methods: PubMed, Embase, Cochrane Library, Web of Science, China National Knowledge Infrastructure, Wanfang Data Knowledge Service Platform, VIP information resource integration service platform databases, and the Chinese biomedical literature service system were searched to find randomized controlled trials where TCMIs + oseltamivir are the representative therapeutic strategies for influenza, from inception until October 2021, without language restriction. Two investigators independently screened eligibility criteria, extracted data, and appraised the risk of bias with the same criteria. We conducted a network meta-analysis using the Bayesian random method for each outcome and performed the sensitivity analysis, meta-regression, and Egger’s and Begg’s tests for the reliability and robustness of our results.

Results: Thirty-one trials including 2,893 participants proved eligible and reported on four TCMIs + oseltamivir versus oseltamivir. Network meta-analysis showed Yanhuning (YHN) +oseltamivir (MD = −1.7, 95% CrI: −2.5 to −0.88; SUCRA = 0.89; low certainty of evidence) in fever disappearance time, Tanreqing (TRQ) +oseltamivir (MD = −1.9, 95% CrI: −2.8 to −1; SUCRA = 0.97; low certainty of evidence) in cough disappearance time, and Xiyanping (XYP) +oseltamivir (OR = 5.9, 95% CrI: 3.1 to 11; SUCRA = 0.82; very low certainty of evidence) in the response rate to be more efficacious than oseltamivir alone with the best SUCRA. Based on the combined SUCRA value for primary outcomes, TRQ + oseltamivir is probably better in cough disappearance time, and XYP + oseltamivir and YHN + oseltamivir may be better in fever disappearance time than others. No significant difference in safety between the treatments.

Conclusion: In patients with influenza, TCMIs + oseltamivir only partially improve flu symptoms. Overall therapeutic efficacy and safety are inconclusive, based on low to very low certainty of evidence. However, the safety remains uncertain, and TCMI treatments for influenza should be considered with caution. More high-quality studies examining the efficacy and safety of TCMIs are needed.

Systematic Review Registration:https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42021286994

Predicting Permissive Mutations That Improve the Fitness of A(H1N1)pdm09 Viruses Bearing the H275Y Neuraminidase Substitution

Oseltamivir-resistant influenza viruses arise due to amino acid mutations in key residues of the viral neuraminidase (NA). These changes often come at a fitness cost; however, it is known that permissive mutations in the viral NA can overcome this cost. This result was observed in former seasonal A(H1N1) viruses in 2007 which expressed the H275Y substitution (N1 numbering) with no apparent fitness cost and lead to widespread oseltamivir resistance. Therefore, this study aims to predict permissive mutations that may similarly enable fit H275Y variants to arise in currently circulating A(H1N1)pdm09 viruses. The first approach in this study utilized in silico analyses to predict potentially permissive mutations. The second approach involved the generation of a virus library which encompassed all possible NA mutations while keeping H275Y fixed. Fit variants were then selected by serially passaging the virus library either through ferrets by transmission or passaging once in vitro. The fitness impact of selected substitutions was further evaluated experimentally. The computational approach predicted three candidate permissive NA mutations which, in combination with each other, restored the replicative fitness of an H275Y variant. The second approach identified a stringent bottleneck during transmission between ferrets; however, three further substitutions were identified which may improve transmissibility. A comparison of fit H275Y variants in vitro and in experimentally infected animals showed a statistically significant correlation in the variants that were positively selected. Overall, this study provides valuable tools and insights into potential permissive mutations that may facilitate the emergence of a fit H275Y A(H1N1)pdm09 variant.

IMPORTANCE Oseltamivir (Tamiflu) is the most widely used antiviral for the treatment of influenza infections. Therefore, resistance to oseltamivir is a public health concern. This study is important as it explores the different evolutionary pathways available to current circulating influenza viruses that may lead to widespread oseltamivir resistance. Specifically, this study develops valuable experimental and computational tools to evaluate the fitness landscape of circulating A(H1N1)pmd09 influenza viruses bearing the H275Y mutation. The H275Y substitution is most commonly reported to confer oseltamivir resistance but also leads to loss of virus replication and transmission fitness, which limits its spread. However, it is known from previous influenza seasons that influenza viruses can evolve to overcome this loss of fitness. Therefore, this study aims to prospectively predict how contemporary A(H1N1)pmd09 influenza viruses may evolve to overcome the fitness cost of bearing the H275Y NA substitution, which could result in widespread oseltamivir resistance.

Characterization of influenza B viruses with reduced susceptibility to influenza neuraminidase inhibitors

A total of 3425 influenza B viruses collected from the Asia-Pacific region were tested against the four registered neuraminidase inhibitors (NAIs) (oseltamivir carboxylate, zanamivir, peramivir and laninamivir) as part of the routine surveillance work at the WHO Collaborating Centre for Research and Reference on Influenza, Melbourne between 2016 and 2020. Forty-five influenza B viruses with reduced susceptibility to one or more NAIs were identified. While the majority of these had neuraminidase (NA) mutations that were known to confer NAIs resistance, fifteen had NA mutations that had not been confirmed as being responsible for reduced NAIs susceptibility. Eleven of these NA mutations of concern were investigated using reverse genetics (RG) techniques to verify that these mutations were the cause of the reduced NAI susceptibility. All mutations were introduced separately into the NA of B/Brisbane/27/2016 (a B Victoria-lineage virus) or B/Yamanashi/166/98 (a B Yamagata-lineage virus) and the effects of these were analysed by an in vitro NAI assay. The T146K substitution in the NA of B Victoria and Yamagata-lineages resulted in a large increase in the IC₅₀ for peramivir (>1000-fold increase in the mean IC₅₀ of sensitive viruses with T146) with smaller increases for zanamivir and oseltamivir. A proline substitution (T146P) had a slightly lower (>700-fold) effect on the peramivir IC₅₀ and also on the other NAIs. The presence of a second NA mutation at N169S combined with the T146P further increased the IC₅₀ of peramivir (>7000-fold) and the other NAIs. A synergistic effect was also confirmed for dual NA mutations with G247D + I361V which showed a modest increase in the IC₅₀ for oseltamivir (6-fold). Only one of two RG-viruses with the mutation G108E could be rescued and it had a high IC₅₀ against zanamivir (>4000-fold) and laninamivir (>7000-fold), but a lower IC₅₀ against oseltamivir (>200-fold). NA mutations H101L, A200T, D432G, H439P and H439R were also confirmed to somewhat reduce the in vitro susceptibility of influenza B viruses to the NAIs. Overall, this study identifies the potential impact of selected mutations on the clinical performance of NAIs when used to treat influenza B infection in humans.

Global update on the susceptibilities of human influenza viruses to neuraminidase inhibitors and the cap-dependent endonuclease inhibitor baloxavir, 2018–2020

Global analysis of the susceptibility of influenza viruses to neuraminidase (NA) inhibitors (NAIs) and the polymerase acidic (PA) inhibitor (PAI) baloxavir was conducted by five World Health Organization Collaborating Centres for Reference and Research on Influenza during two periods (May 2018–May 2019 and May 2019–May 2020). Combined phenotypic and NA sequence-based analysis revealed that the global frequency of viruses displaying reduced or highly reduced inhibition (RI or HRI) or potential to show RI/HRI by NAIs remained low, 0.5% (165/35045) and 0.6% (159/26010) for the 2018–2019 and 2019–2020 periods, respectively. The most common amino acid substitution was NA-H275Y (N1 numbering) conferring HRI by oseltamivir and peramivir in A(H1N1)pdm09 viruses. Combined phenotypic and PA sequence-based analysis showed that the global frequency of viruses showing reduced susceptibility to baloxavir or carrying substitutions associated with reduced susceptibility was low, 0.5% (72/15906) and 0.1% (18/15692) for the 2018–2019 and 2019–2020 periods, respectively. Most (n = 61) of these viruses had I38→T/F/M/S/L/V PA amino acid substitutions. In Japan, where baloxavir use was highest, the rate was 4.5% (41/919) in the 2018–2019 period and most of the viruses (n = 32) had PA-I38T. Zoonotic viruses isolated from humans (n = 32) in different countries did not contain substitutions in NA associated with NAI RI/HRI phenotypes. One A(H5N6) virus had a dual substitution PA-I38V + PA-E199G, which may reduce susceptibility to baloxavir. Therefore, NAIs and baloxavir remain appropriate choices for the treatment of influenza virus infections, but close monitoring of antiviral susceptibility is warranted.

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.

Assays for Determining the Sialidase Activity of Influenza Viruses and Monitoring Influenza Virus Susceptibility to Neuraminidase Inhibitors

Three types of assays--colorimetric, fluorescent, and chemiluminescent--are used to determine the sialidase (neuraminidase: NA) activity of influenza viruses. The fluorescent assay is cost-effective and applicable for many laboratories and is, therefore, commonly used for global monitoring of the NA inhibitor susceptibility of influenza viruses. Here, I describe, in detail, protocols for the fluorescence-based NA activity assay and the NA inhibition assay, which are used to determine the NA activity and NA inhibitor susceptibility, respectively, of influenza viruses.

Anti-influenza virus activity of the elenolic acid rich olive leaf (Olea europaea L.) extract Isenolic®

Seasonal flu is caused by influenza infection, a virus that spreads easily in human population with periodical epidemic outbreaks. The high mutational rate of influenza viruses leads to the emergence of strains resistant to the current treatments. Due to that, scientific research is focusing on the development of new anti-influenza agents as alternative or complementary treatments. Olive tree (Olea europaea L.) has been a source of ancestral remedies due to its antimicrobial activity. Thus, the aim of this study was to test the anti-influenza activity of a standardized olive leaf extract rich in elenolic acid (EA), Isenolic^®, compared with oseltamivir. Isenolic^® extract was characterized by High Performance Liquid Chromatography (HPLC)-Mass Spectrometry and its content in EA was determined by HPLC. Cytotoxicity, viral neuraminidase inhibitor activity and cell viability protection against influenza infection of Isenolic^® were tested in vitro using sialic acid overexpressing Madin-Darby Canine Kidney cells. Isenolic^® formulations showed a 4% and 8% dry basis. Oseltamivir and Isenolic^® extracts showed anti-influenza activity. The 8% Isenolic^® formulation showed a dose-dependent neuraminidase inhibitor activity higher than the 4% formulation, and preserved cell viability under viral infection. Thus, Isenolic^® become a promising natural alternative to existing influenza treatments.

An Integrated Analysis Reveals Geniposide Extracted From Gardenia jasminoides J.Ellis Regulates Calcium Signaling Pathway Essential for Influenza A Virus Replication

Geniposide, an iridoid glycoside purified from the fruit of Gardenia jasminoides J.Ellis, has been reported to possess pleiotropic activity against different diseases. In particular, geniposide possesses a variety of biological activities and exerts good therapeutic effects in the treatment of several strains of the influenza virus. However, the molecular mechanism for the therapeutic effect has not been well defined. This study aimed to investigate the mechanism of geniposide on influenza A virus (IAV). The potential targets and signaling pathways of geniposide in the IAV infection were predicted using network pharmacology analysis. According to the result of network pharmacology analysis, we validated the calcium signaling pathway induced by IAV and investigated the effect of geniposide extracted from Gardenia jasminoides J.Ellis on this pathway. The primary Gene Ontology (GO) biological processes and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways KEGG enrichment analysis indicated that geniposide has a multi-target and multi-pathway inhibitory effect against influenza, and one of the mechanisms involves calcium signaling pathway. In the current study, geniposide treatment greatly decreased the levels of RNA polymerase in HEK-293T cells infected with IAV. Knocking down CAMKII in IAV-infected HEK-293T cells enhanced virus RNA (vRNA) production. Geniposide treatment increased CAMKII expression after IAV infection. Meanwhile, the CREB and c-Fos expressions were inhibited by geniposide after IAV infection. The experimental validation data showed that the geniposide was able to alleviate extracellular Ca2+ influx, dramatically decreased neuraminidase activity, and suppressed IAV replication in vitro via regulating the calcium signaling pathway. These anti-IAV effects might be related to the disrupted interplay between IAV RNA polymerase and CAMKII and the regulation of the downstream calcium signaling pathway essential for IAV replication. Taken together, the findings reveal a new facet of the mechanism by which geniposide fights IAV in a way that depends on CAMKII replication.

Reduced sialidase activity of influenza A(H3N2) neuraminidase associated with positively charged amino acid substitutions

Neuraminidase (NA) inhibitors (NAI), oseltamivir and zanamivir, are the main antiviral medications for influenza and monitoring of susceptibility to these antivirals is routinely done by determining 50 % inhibitory concentrations (IC₅₀) with MUNANA substrate. During 2010-2019, levels of A(H3N2) viruses presenting reduced NAI inhibition (RI) were low (~0.75 %) but varied year-on-year. The highest proportions of viruses showing RI were observed during the 2013-2014, 2016-2017 and 2017-2018 Northern Hemisphere seasons. The majority of RI viruses were found to contain positively charged NA amino acid substitutions of N329K, K/S329R, S331R or S334R, being notably higher during the 2016-2017 season. Sialidase activity kinetics were determined for viruses of RI phenotype and contemporary wild-type (WT) viruses showing close genetic relatedness and displaying normal inhibition (NI). RI phenotypes resulted from reduced sialidase activity compared to relevant WT viruses. Those containing S329R or N329K or S331R showed markedly higher K_m for the substrate and K_i values for NAIs, while those with S334R showed smaller effects. Substitutions at N329 and S331 disrupt a glycosylation sequon (NDS), confirmed to be utilised by mass spectrometry. However, gain of positive charge at all three positions was the major factor influencing the kinetic effects, not loss of glycosylation. Because of the altered enzyme characteristics NAs carrying these substitutions cannot be assessed reliably for susceptibility to NAIs using standard MUNANA-based assays due to reductions in the affinity of the enzyme for its substrate and the concentration of the substrate usually used.

Inhibitory effects of aprotinin on influenza A and B viruses in vitro and in vivo

Influenza viruses cause significant morbidity and mortality worldwide. Long-term or frequent use of approved anti-influenza agents has resulted in drug-resistant strains, thereby necessitating the discovery of new drugs. In this study, we found aprotinin, a serine protease inhibitor, as an anti-influenza candidate through screening of compound libraries. Aprotinin has been previously reported to show inhibitory effects on a few influenza A virus (IAV) subtypes (e.g., seasonal H1N1 and H3N2). However, because there were no reports of its inhibitory effects on the other types of influenza viruses, we investigated the inhibitory effects of aprotinin in vitro on a wide range of influenza viruses, including avian and oseltamivir-resistant influenza virus strains. Our cell-based assay showed that aprotinin had inhibitory effects on seasonal human IAVs (H1N1 and H3N2 subtypes), avian IAVs (H5N2, H6N5, and H9N2 subtypes), an oseltamivir-resistant IAV, and a currently circulating influenza B virus. We have also confirmed its activity in mice infected with a lethal dose of influenza virus, showing a significant increase in survival rate. Our findings suggest that aprotinin has the capacity to inhibit a wide range of influenza virus subtypes and should be considered for development as a therapeutic agent against influenza.

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.

Neuraminidase inhibitors are effective and safe in reducing influenza complications: meta-analysis of randomized controlled trials

BACKGROUND

There is scarce evidence verifying the impact of neuraminidase inhibitors (NAIs) in reducing influenza complications. The aim was to evaluate the available evidence from randomized-controlled trials (RCT) regarding the efficacy and safety of NAIs in reducing influenza complications.

METHODS

A systematic search of the literature was performed in the Cochrane Library, PubMed and Web of Science databases (2006-2019). Eligibility criteria were RCT that enrolled patients of any age or clinical severity with seasonal influenza (H₁N₁, H₃N_2, or B) or influenza-like syndrome and receiving NAIs comparing to placebo therapy.

RESULTS

Eighteen RCTs (9004 patients) were included: nine focused on oral oseltamivir, six on inhaled zanamivir, and three on intravenous peramivir. Administration of NAIs therapy significantly decreased the time to clinical resolution (median difference: -17.7 hours; and total influenza-related complications (OR: 0.64, 95%CI: 0.51-0.82). In addition, NAIs significantly decreased acute otitis media complication (OR: 0.50, 95%CI: 0.31-0.82) and need for antibiotic treatment (OR: 0.64, 95%CI: 0.46-0.90); and showed a trend towards a reduced occurrence of pneumonia (OR: 0.44, 95%CI: 0.10-2.00), bronchitis (OR: 0.80, 95%CI: 0.43-1.48), sinusitis (OR: 0.73, 95%CI: 0.40-1.32), asthma exacerbations (OR: 0.57, 95%CI: 0.28-1.16), and hospitalizations (OR: 0.57, 95%CI: 0.24-1.38). The overall proportion of AEs tend to increase with NAIs treatment (OR: 1.16, 95%CI: 0.92-1.47). Use of NAIs was associated with a significant increase of nausea and vomiting (OR: 1.61, 95%CI: 1.04-2.50) and a decrease on diarrhea (OR: 0.81, 95%CI: 0.65-1.00).

CONCLUSIONS

NAIs are effective in reducing time to clinical resolution, total influenza-related complications, otitis media, and need of antibiotic administration. Reductions on mortality, pneumonia, asthma exacerbations or hospitalization rates only did demonstrate a trend benefit in favor of NAIs. The only significant AE is the increased occurrence of nausea and vomiting.

Treatment of infections in cancer patients: an update from the neutropenia, infection and myelosuppression study group of the Multinational Association for Supportive Care in Cancer (MASCC)

INTRODUCTION

Patients with hematological and advanced solid malignancies have acquired immune dysfunction, often exacerbated by treatment, posing a significant risk for the development of infections. This review evaluates the utility of current clinical and treatment guidelines, in the setting of management of infections in cancer patients.

AREAS COVERED

These include causes of infection in cancer patients, management of patients with high-risk and low-risk febrile neutropenia, management of low-risk patients in an outpatient setting, the role of granulocyte colony-stimulating factor (G-CSF) in the prevention and treatment of neutropenia-related infections, management of lung infections in various clinical settings, and emerging challenges surrounding the risk of infection in cancer patients treated with novel treatments. The literature search was performed by accessing PubMed and other databases, focusing on published clinical trials of relevant anti-cancer agents and diseases, primarily covering the recent past, but also including several key studies published during the last decade and, somewhat earlier in a few cases.

EXPERT REVIEW

Notwithstanding the promise of gene therapy/gene editing in hematological malignancies and some types of solid cancers, innovations introduced in clinical practice include more discerning clinical management such as the generalized use of biosimilar formulations of G-CSF and the implementation of novel, innovative immunotherapies.

Indole - a promising pharmacophore in recent antiviral drug discovery

The bicyclic molecule indole has been in the limelight because of its numerous pharmacological potencies. It is used as an excellent scaffold in drug discovery of medicinal drugs such as antimicrobials, anticancer agents, antihypertensives, anti-proliferative agents and anti-inflammatory agents. In spite of its diverse therapeutic activity, it is used as a key pharmacophore in synthesizing the most potent biological agents. Besides, viral infections are ubiquitous and their prevention and cure have become a great challenge. In this regard, the design of indole-containing antiviral drugs is accomplished to combat viral infections. A lot of research is being carried out towards antiviral drug discovery by many researchers round the clock. Herein, the antiviral activity of recently discovered indole scaffolds is compiled and critically evaluated to give a meaningful summary. In addition, the structure-activity relationship of remarkable antiviral agents is discussed. Also, the structural motifs attributed to noteworthy antiviral properties are highlighted to guide future antiviral research.

In Vitro Characterization of Multidrug-Resistant Influenza A(H1N1)pdm09 Viruses Carrying a Dual Neuraminidase Mutation Isolated from Immunocompromised Patients

Influenza A(H1N1)pdm09 viruses carrying a dual neuraminidase (NA) substitution were isolated from immunocompromised patients after administration of one or more NA inhibitors. These mutant viruses possessed an H275Y/I223R, H275Y/I223K, or H275Y/G147R substitution in their NA and showed enhanced cross-resistance to oseltamivir and peramivir and reduced susceptibility to zanamivir compared to single H275Y mutant viruses. Baloxavir could be a treatment option against the multidrug-resistant viruses because these dual H275Y mutant viruses showed susceptibility to this drug. The G147R substitution appears to stabilize the NA structure, with the fitness of the H275Y/G147R mutant virus being similar or somewhat better than that of the wild-type virus. Since the multidrug-resistant viruses may be able to transmit between humans, surveillance of these viruses must continue to improve clinical management and to protect public health.

Substitutions at H134 and in the 430-loop region in influenza B neuraminidases can confer reduced susceptibility to multiple neuraminidase inhibitors

With the introduction of the influenza specific neuraminidase inhibitors (NAIs) in 1999, there were concerns about the emergence and spread of resistant viruses in the community setting. Surveillance and testing of community isolates for their susceptibility to the NAIs was initially carried out by the Neuraminidase Inhibitor Susceptibility Network (NISN) and has subsequently been taken on by the global WHO influenza network laboratories. During the NISN surveillance, we identified two Yamagata lineage influenza B viruses with amino acid substitutions of H134Y (B/Auckland/2/2001) or W438R (B/Yokohama/12/2005) which had slightly elevated IC₅₀ values for zanamivir and/or oseltamivir, but not sufficiently to be characterized as mild outliers at the time. As it has now been well demonstrated that mixed populations can mask the true magnitude of resistance of a mutant, we re-examined both of these isolates by plaque purification to see if the true susceptibilities were being masked due to mixed populations. Results confirmed that the B/Auckland isolate contained both wild type and H134Y mutant populations, with mutant IC₅₀ values > 250 nM for both oseltamivir and peramivir in the enzyme inhibition assay. The B/Yokohama isolate also contained both wild type and W438R mutant populations, the latter now demonstrating IC₅₀ values > 400 nM for zanamivir, oseltamivir and peramivir. In addition, plaque purification of the B/Yokohama isolate identified viruses with other single neuraminidase substitutions H134Y, H134R, H431R, or T436P. H134R and H431R viruses had IC₅₀ values > 400 nM and >250 nM respectively against all three NAIs. All changes conferred much greater resistance to peramivir than to zanamivir, and less to oseltamivir, and affected the kinetics of binding and dissociation of the NAIs. Most affected affinity (K_m) for the MUNANA substrate, but some had decreased while others had increased affinity. Despite resistance in the enzyme assay, no reduced susceptibility was seen in plaque reduction assays in MDCK cells for any of the mutant viruses. None of these substitutions was in the active site. Modelling suggests that these substitutions affect the 150 and 430-loop regions described for influenza A NAs, suggesting they may also be important for substrate and inhibitor binding for influenza B NAs.

Anti-neuraminidase activity of chemical constituents of Balanophora involucrata

Balanophora involucrata J. D. Hooker has been known to possess potential anti-inflammatory and antibacterial activities; however, its antiviral activity has not been evaluated so far. In order to find new neuraminidase inhibitors (NAIs), the neuraminidase (NA) inhibition activity of different B. involucrata extracts was evaluated. In this study, an in vitro NA inhibition assay was performed to identify which extract of B. involucrata exhibits (maximal) inhibitory activity against NA. Ultra high performance liquid chromatography/quadrupole time-of-flight-tandem mass spectroscopy (MS/MS) and molecular docking techniques were used to identify the specific compounds responsible for the anti-influenza activity of the extract, and to explore the potential natural NAIs. The ethyl acetate extract of B. involucrata exhibited significant inhibitory activity against NA with 50% inhibitory concentration (IC₅₀ ) value of 159.5 μg/mL. Twenty compounds were identified according to the MS/MS spectra; among them two compounds (quercitrin and phloridzin) showed obvious inhibitory activity against NA, with IC₅₀ of 311.76 and 347.32 μmol/L, respectively. This study suggested that B. involucrata can be a potential natural source of NAIs and may be useful in the fight against ferocious influenza viruses.

Successful treatment with baloxavir marboxil of a patient with peramivir-resistant influenza A/H3N2 with a dual E119D/R292K substitution after allogeneic hematopoietic cell transplantation: a case report

BACKGROUND

Extended use of oseltamivir in an immunocompromised host could reportedly induce neuraminidase gene mutation possibly leading to oseltamivir-resistant influenza A/H3N2 virus. To our knowledge, no report is available on the clinical course of a severely immunocompromised patient with a dual E119D/R292K neuraminidase mutated-influenza A/H3N2 during the administration of peramivir.

CASE PRESENTATION

A 49-year-old male patient was admitted for second allogeneic hematopoietic cell transplantation for active acute leukemia. The patient received 5 mg prednisolone and 75 mg cyclosporine and had severe lymphopenia (70/μL). At the time of hospitalization, the patient was diagnosed with upper tract influenza A virus infection, and oseltamivir treatment was initiated immediately. However, the patient was intolerant to oseltamivir. The following day, treatment was changed to peramivir. Despite a total period of neuraminidase-inhibitor administration of 16 days, the symptoms and viral shedding continued. Changing to baloxavir marboxil resolved the symptoms, and the influenza diagnostic test became negative. Subsequently, sequence analysis of the nasopharyngeal specimen revealed the dual E119D/R292K neuraminidase mutant influenza A/H3N2.

CONCLUSIONS

In a highly immunocompromised host, clinicians should take care when peramivir is used for extended periods to treat influenza virus A/H3N2 infection as this could potentially leading to a dual E119D/R292K substitution in neuraminidase protein. Baloxavir marboxil may be one of the agents that can be used to treat this type of mutated influenza virus infection.

5-(Perylen-3-ylethynyl)uracil Derivatives Inhibit Reproduction of Respiratory Viruses

In this work, we describe the synthesis of 5-(perylen-3-ylethynyl)uridine and its ability to effectively inhibit the replication of respiratory disease pathogens in cell culture, namely: influenza A virus (IVA); type 3 parainfluenza virus (PIV-3); and human respiratory syncytial virus (RSV). Related known compounds were also analyzed: 5-(perylen-3-ylethynyl)-2'-deoxy-uridine; 5-(perylen-3-ylethynyl)-arabino-uridine; and 1-carboxymethyl-3-pivaloyloxymethyl-5-(perylen-3-ylethynyl)uracil.

Utilising animal models to evaluate oseltamivir efficacy against influenza A and B viruses with reduced in vitro susceptibility

The neuraminidase (NA) inhibitor (NAI) oseltamivir (OST) is the most widely used influenza antiviral drug. Several NA amino acid substitutions are reported to reduce viral susceptibility to OST in in vitro assays. However, whether there is a correlation between the level of reduction in susceptibility in vitro and the efficacy of OST against these viruses in vivo is not well understood. In this study, a ferret model was utilised to evaluate OST efficacy against circulating influenza A and B viruses with a range of in vitro generated 50% inhibitory concentrations (IC50) values for OST. OST efficacy against an A(H1N1)pdm09 and an A(H1N1)pdm09 virus with the H275Y substitution in neuraminidase was also tested in the macaque model. The results from this study showed that OST had a significant impact on virological parameters compared to placebo treatment of ferrets infected with wild-type influenza A viruses with normal IC50 values (~1 nM). However, this efficacy was lower against wild-type influenza B and other viruses with higher IC50 values. Differing pathogenicity of the viruses made evaluation of clinical parameters difficult, although some effect of OST in reducing clinical signs was observed with influenza A(H1N1) and A(H1N1)pdm09 (H275Y) viruses. Viral titres in macaques were too low to draw conclusive results. Analysis of the ferret data revealed a correlation between IC50 and OST efficacy in reducing viral shedding but highlighted that the current WHO guidelines/criteria for defining normal, reduced or highly reduced inhibition in influenza B viruses based on in vitro data are not well aligned with the low in vivo OST efficacy observed for both wild-type influenza B viruses and those with reduced OST susceptibility.

Antivirals in medical biodefense

The viruses historically implicated or currently considered as candidates for misuse in bioterrorist events are poxviruses, filoviruses, bunyaviruses, orthomyxoviruses, paramyxoviruses and a number of arboviruses causing encephalitis, including alpha- and flaviviruses. All these viruses are of concern for public health services when they occur in natural outbreaks or emerge in unvaccinated populations. Recent events and intelligence reports point to a growing risk of dangerous biological agents being used for nefarious purposes. Public health responses effective in natural outbreaks of infectious disease may not be sufficient to deal with the severe consequences of a deliberate release of such agents. One important aspect of countermeasures against viral biothreat agents are the antiviral treatment options available for use in post-exposure prophylaxis. These issues were adressed by the organizers of the 16th Medical Biodefense Conference, held in Munich in 2018, in a special session on the development of drugs to treat infections with viruses currently perceived as a threat to societies or associated with a potential for misuse as biothreat agents. This review will outline the state-of-the-art methods in antivirals research discussed and provide an overview of antiviral compounds in the pipeline that are already approved for use or still under development.

Epidemic of influenza A(H1N1)pdm09 analyzed by full genome sequences and the first case of oseltamivir-resistant strain in Myanmar 2017

A community outbreak of human influenza A(H1N1)pdm09 virus strains was observed in Myanmar in 2017. We investigated the circulation patterns, antigenicity, and drug resistance of 2017 influenza A(H1N1)pdm09 viruses from Myanmar and characterized the full genome of influenza virus strains in Myanmar from in-patients and out-patients to assess the pathogenicity of the viruses. Nasopharyngeal swabs were collected from out-patients and in-patients with acute respiratory tract infections in Yangon and Pyinmana City in Myanmar during January-December 2017. A total of 215 out-patients and 18 in-patients infected with A(H1N1)pdm09 were detected by virus isolation and real-time RT-PCR. Among the positive patients, 90.6% were less than 14 years old. Hemagglutination inhibition (HI) antibody titers against A(H1N1)pdm09 viruses in Myanmar were similar to the recommended Japanese influenza vaccine strain for 2017-2018 seasons (A/Singapore/GP1908/2015) and WHO recommended 2017 southern hemisphere vaccine component (A/Michigan/45/2015). Phylogenetic analysis of the hemagglutinin sequence showed that the Myanmar strains belonged to the genetic subclade 6B.1, possessing mutations of S162N and S164T at potential antigenic sites. However, the amino acid mutation at position 222, which may enhance the severity of disease and mortality, was not found. One case with no prior history of oseltamivir treatment possessed H275Y mutated virus in neuraminidase (NA), which confers resistance to oseltamivir and peramivir with elevated IC50 values. The full genome sequence of Myanmar strains showed no difference between samples from in-patients and out-patients, suggesting no additional viral mutations associated with patient severity. Several amino acid changes were observed in PB2, PB1, and M2 of Myanmar strains when compared to the vaccine strain and other Asian strains. However, no mutations associated with pathogenicity were found in the Myanmar strains, suggesting that viral factors cannot explain the underlying reasons of the massive outbreak in Myanmar. This study reported the first detection of an oseltamivir-resistant influenza virus in Myanmar, highlighting the importance of continuous antiviral monitoring and genetic characterization of the influenza virus in Myanmar.

Global update on the susceptibilities of human influenza viruses to neuraminidase inhibitors and the cap-dependent endonuclease inhibitor baloxavir, 2017-2018

The global analysis of neuraminidase inhibitor (NAI) susceptibility of influenza viruses has been conducted since the 2012-13 period. In 2018 a novel cap-dependent endonuclease inhibitor, baloxavir, that targets polymerase acidic subunit (PA) was approved for the treatment of influenza virus infection in Japan and the United States. For this annual report, the susceptibilities of influenza viruses to NAIs and baloxavir were analyzed. A total of 15409 viruses, collected by World Health Organization (WHO) recognized National Influenza Centers and other laboratories between May 2017 and May 2018, were assessed for phenotypic NAI susceptibility by five WHO Collaborating Centers (CCs). The 50% inhibitory concentration (IC₅₀) was determined for oseltamivir, zanamivir, peramivir and laninamivir. Reduced inhibition (RI) or highly reduced inhibition (HRI) by one or more NAIs was exhibited by 0.8% of viruses tested (n = 122). The frequency of viruses with RI or HRI has remained low since this global analysis began (2012-13: 0.6%; 2013-14: 1.9%; 2014-15: 0.5%; 2015-16: 0.8%; 2016-17: 0.2%). PA gene sequence data, available from public databases (n = 13523), were screened for amino acid substitutions associated with reduced susceptibility to baloxavir (PA E23G/K/R, PA A36V, PA A37T, PA I38F/M/T/L, PA E119D, PA E199G): 11 (0.08%) viruses possessed such substitutions. Five of them were included in phenotypic baloxavir susceptibility analysis by two WHO CCs and IC₅₀ values were determined. The PA variant viruses showed 6-17-fold reduced susceptibility to baloxavir. Overall, in the 2017-18 period the frequency of circulating influenza viruses with reduced susceptibility to NAIs or baloxavir was low, but continued monitoring is important.

Antigenic variants of influenza B viruses isolated in Japan during the 2017-2018 and 2018-2019 influenza seasons

Background

Here, we genetically and antigenically analyzed influenza B viruses (IBVs) isolated in Japan during the 2017‐2018 and 2018‐2019 influenza seasons.

Methods

A total of 68 IBVs (61 B/Yamagata/16/88‐like [B/Yamagata]‐lineage and 7 B/Victoria/2/87‐like [B/Victoria]‐lineage) were antigenically and genetically characterized by using hemagglutination inhibition (HI) assays and phylogenetic analysis, respectively. The susceptibility of IBVs to neuraminidase (NA) inhibitors was assessed by using a fluorescence‐based NA inhibition assay.

Results

All 61 B/Yamagata‐lineage isolates were genetically closely related to B/Phuket/3073/2013, the vaccine strain for these two seasons. Eleven B/Yamagata‐lineage isolates tested were antigenically similar to B/Phuket/3073/2013 by the HI test. Seven B/Victoria‐lineage isolates were genetically closely related to B/Texas/02/2013, the WHO‐recommended vaccine strain for the 2017‐2018 season; however, they were antigenically distinct from B/Texas/02/2013 with an eightfold or 16‐fold difference in HI titer. Of these 7 isolates, 4 possessed a two‐amino‐acid deletion at positions 162 and 163 in hemagglutinin (HA) and the other 3 had a three‐amino‐acid deletion at positions 162‐164 in HA. Importantly, the variants with the three‐amino‐acid deletion appeared to be antigenically different from the B/Colorado/06/2017 virus with the two‐amino‐acid deletion, the vaccine strain for the 2018‐2019 season with a fourfold or eightfold difference in HI titer. One B/Yamagata‐lineage isolate carrying a G407S mutation in its NA showed a marked reduction in susceptibility to zanamivir, peramivir, and laninamivir.

Conclusions

These results highlight the need for continued monitoring for the prevalence of the antigenic variant with the three‐amino‐acid deletion and the variant with reduced NA inhibitor susceptibility.

Discovery of Influenza Polymerase PA-PB1 Interaction Inhibitors Using an In Vitro Split-Luciferase Complementation-Based Assay

The limited therapeutic options and increasing drug-resistance call for next-generation influenza antivirals. Due to the essential function in viral replication and high sequence conservation among influenza viruses, influenza polymerase PA-PB1 protein-protein interaction becomes an attractive drug target. Here, we developed an in vitro split luciferase complementation-based assay to speed up screening of PA-PB1 interaction inhibitors. By screening 10,000 compounds, we identified two PA-PB1 interaction inhibitors, R160792 and R151785, with potent and broad-spectrum antiviral activity against a panel of influenza A and B viruses, including amantadine-, oseltamivir-, or dual resistant strains. Further mechanistic study reveals that R151785 inhibits PA nuclear localization, reduces the levels of viral RNAs and proteins, and inhibits viral replication at the intermediate stage, all of which are in line with its antiviral mechanism of action. Overall, we developed a robust high throughput-screening assay for screening broad-spectrum influenza antivirals targeting PA-PB1 interaction and identified R151785 as a promising antiviral drug candidate.

Influenza A/H4N2 mallard infection experiments further indicate zanamivir as less prone to induce environmental resistance development than oseltamivir

Neuraminidase inhibitors (NAIs) are the gold standard treatment for influenza A virus (IAV). Oseltamivir is mostly used, followed by zanamivir (ZA). NAIs are not readily degraded in conventional wastewater treatment plants and can be detected in aquatic environments. Waterfowl are natural IAV hosts and replicating IAVs could thus be exposed to NAIs in the environment and develop resistance. Avian IAVs form the genetic basis for new human IAVs, and a resistant IAV with pandemic potential poses a serious public health threat, as NAIs constitute a pandemic preparedness cornerstone. Resistance development in waterfowl IAVs exposed to NAIs in the water environment has previously been investigated in an in vivo mallard model and resistance development was demonstrated in several avian IAVs after the exposure of infected ducks to oseltamivir, and in an H1N1 IAV after exposure to ZA. The N1 and N2 types of IAVs have different characteristics and resistance mutations, and so the present study investigated the exposure of an N2-type IAV (H4N2) in infected mallards to 1, 10 and 100 µg l^-1 of ZA in the water environment. Two neuraminidase substitutions emerged, H274N (ZA IC₅₀ increased 5.5-fold) and E119G (ZA IC₅₀ increased 110-fold) at 10 and 100 µg l^-1 of ZA, respectively. Reversion towards wild-type was observed for both substitutions in experiments with removed drug pressure, indicating reduced fitness of both resistant viruses. These results corroborate previous findings that the development of resistance to ZA in the environment seems less likely to occur than the development of resistance to oseltamivir, adding information that is useful in planning for prudent drug use and pandemic preparedness.

Influenza B viruses from different genetic backgrounds are variably impaired by neuraminidase inhibitor resistance-associated substitutions

Identifying evolutionary routes to antiviral resistance among influenza viruses informs molecular-based resistance surveillance and clinical decisions. To improve antiviral management and understand whether clinically identified neuraminidase (NA) inhibitor (NAI) resistance-associated markers affect influenza B viruses of the Victoria- or Yamagata-lineages differentially, we generated a panel of NAI-resistant viruses (carrying E105K, G145E, R150K, D197N, I221 L/N/T/V, H273Y, N294S, or G407S substitutions; B numbering) in B/Brisbane/60/2008 (BR/08) and B/Phuket/3073/2013 (PH/13). In both backgrounds, I221 L/N/T/V resulted in reduced or highly reduced inhibition (HRI) by one to three currently available NAIs. D197N reduced inhibition by all NAIs in BR/08 but only by oseltamivir and peramivir in PH/13; R150K caused HRI by all NAIs in PH/13. Although PH/13 generally retained or enhanced NA activity in the presence of the substitutions, enzymatic activity in BR/08 was detrimentally affected. Similarly, substrate affinity and catalysis were relatively stable in PH/13, but not in the BR/08 variants. E105K, R150K, and D197N attenuated replication efficiency of BR/08 in vitro and in mice; only E105K had this effect in PH/13. Notably, the I221 L/N/T/V substitutions did not severely impair replication, particularly in PH/13. Overall, our data show differential effects of NA substitutions in representative Victoria- and Yamagata-lineage viruses, suggesting distinct evolution of these viruses caused variable fitness and NAI susceptibility profiles when similar key NA substitutions arise. Because the viruses harboring the I221 NA substitutions displayed undiminished fitness and are commonly reported, this position is likely to be the most clinically relevant marker for NAI resistance among contemporary influenza B viruses.

Effect of Forsythiaside A on the RLRs Signaling Pathway in the Lungs of Mice Infected with the Influenza A Virus FM1 Strain

Forsythiaside A, a phenylethanoid glycoside monomer extracted from Forsythia suspensa, shows anti-inflammatory, anti-infective, anti-oxidative, and antiviral pharmacological effects. The precise mechanism underlying the antiviral action of forsythiaside A is not completely clear. Therefore, in this study, we aimed to determine whether the anti-influenza action of forsythiaside A occurs via the retinoic acid-inducible gene-I–like receptors (RLRs) signaling pathway in the lung immune cells. Forsythiaside A was used to treat C57BL/6J mice and MAVS^−/− mice infected with mouse-adapted influenza A virus FM1 (H1N1, A/FM1/1/47 strain), and the physical parameters (body weight and lung index) and the expression of key factors in the RLRs/NF-κB signaling pathway were evaluated. At the same time, the level of virus replication and the ratio of Th1/Th2 and Th17/Treg of T cell subsets were measured. Compared with the untreated group, the weight loss in the forsythiaside A group in the C57BL/6J mice decreased, and the histopathological sections showed less inflammatory damage after the infection with the influenza A virus FM1 strain. The gene and protein expression of retinoic acid-inducible gene-I (RIG-I), MAVS, and NF-κB were significantly decreased in the forsythiaside A group. Flow cytometry showed that Th1/Th2 and Th17/Treg differentiated into Th2 cells and Treg cells, respectively, after treatment with forsythiaside A. In conclusion, forsythiaside A reduces the inflammatory response caused by influenza A virus FM1 strain in mouse lungs by affecting the RLRs signaling pathway in the mouse lung immune cells.

Effect of aloin on viral neuraminidase and hemagglutinin-specific T cell immunity in acute influenza

BACKGROUND

Millions of people are infected by the influenza virus worldwide every year. Current selections of anti-influenza agents are limited and their effectiveness and drug resistance are still of concern.

PURPOSE

Investigation on in vitro and in vivo effect of aloin from Aloe vera leaves against influenza virus infection.

METHODS

In vitro antiviral property of aloin was measured by plaque reduction assay in which MDCK cells were infected with oseltamivir-sensitive A(H1N1)pdm09, oseltamivir-resistant A(H1N1)pdm09, H1N1 or H3N2 influenza A or with influenza B viruses in the presence of aloin. In vivo activity was tested in H1N1 influenza virus infected mice. Aloin-mediated inhibition of influenza neuraminidase activity was tested by MUNANA assay. Aloin treatment-mediated modulation of anti-influenza immunity was tested by the study of hemagglutinin-specific T cells in vivo.

RESULTS

Aloin significantly reduced in vitro infection by all the tested strains of influenza viruses, including oseltamivir-resistant A(H1N1)pdm09 influenza viruses, with an average IC₅₀ value 91.83 ± 18.97 μM. In H1N1 influenza virus infected mice, aloin treatment (intraperitoneal, once daily for 5 days) reduced virus load in the lungs and attenuated body weight loss and mortality. Adjuvant aloin treatment also improved the outcome with delayed oseltamivir treatment. Aloin inhibited viral neuraminidase and impeded neuraminidase-mediated TGF-β activation. Viral neuraminidase mediated immune suppression with TGF-β was constrained and influenza hemagglutinin-specific T cell immunity was increased. There was more infiltration of hemagglutinin-specific CD4+ and CD8+ T cells in the lungs and their production of effector cytokines IFN-γ and TNF-α was boosted.

CONCLUSION

Aloin from Aloe vera leaves is a potent anti-influenza compound that inhibits viral neuraminidase activity, even of the oseltamivir-resistant influenza virus. With suppression of this virus machinery, aloin boosts host immunity with augmented hemagglutinin-specific T cell response to the infection. In addition, in the context of compromised benefit with delayed oseltamivir treatment, adjuvant aloin treatment ameliorates the disease and improves survival. Taken together, aloin has the potential to be further evaluated for clinical applications in human influenza.

Neuraminidase inhibitor resistance in influenza: a clinical perspective

PURPOSE OF REVIEW

Neuraminidase inhibitors (NAIs), including oseltamivir, zanamivir, and peramivir, is the main class of antiviral available for clinical use. As such, development of resistance toward these agents is of great clinical and public health concern.

RECENT FINDINGS

At present, NAI resistance remains uncommon among the circulating viruses (oseltamivir <3.5%, zanamivir <1%). Resistance risk is slightly higher in A(H1N1) than A(H3N2) and B viruses. Resistance may emerge during drug exposure, particularly among young children (<5 years), the immunocompromised, and individuals receiving prophylactic regimens. H275Y A(H1N1) variant, showing high-level oseltamivir resistance, is capable of causing outbreaks. R294K A(H7N9) variant shows reduced inhibition across NAIs. Multi-NAI resistance has been reported in the immunocompromised.

SUMMARY

These findings highlight the importance of continuous surveillance, and assessment of viral fitness and transmissibility of resistant virus strains. Detection can be challenging, especially in a mix of resistant and wild-type viruses. Recent advances in molecular techniques (e.g. targeted mutation PCR, iART, ddPCR, pyrosequencing, next-generation sequencing) have improved detection and our understanding of viral dynamics. Treatment options available for oseltamivir-resistant viruses are limited, and susceptibility testing of other NAIs may be required, but non-NAI antivirals (e.g. polymerase inhibitors) that are active against these resistant viruses are in late-stage clinical development.

Molecular characterization of the influenza A(H1N1)pdm09 isolates collected in the 2015-2016 season and comparison of HA mutations detected in Turkey since 2009

Influenza A(H1N1)pdm09 pandemic virus causing the 2009 global outbreak moved into the post-pandemic period, but its variants continued to be the prevailing subtype in the 2015-2016 influenza season in Europe and Asia. To determine the molecular characteristics of influenza A(H1N1)pdm09 isolates circulating during the 2015-2016 season in Turkey, we identified mutations in the hemagglutinin (HA) genes and investigated the presence of H275Y alteration in the neuraminidase genes in the randomly selected isolates. The comparison of the HA nucleotide sequences revealed a very high homology (>99.5%) among the studied influenza A(H1N1)pdm09 isolates, while a relatively low homology (96.6%-97.2%), was observed between Turkish isolates and the A/California/07/2009 vaccine virus. Overall 14 common mutations were detected in HA sequences of all 2015-2016 influenza A(H1N1)pdm09 isolates with respect to the A/California/07/2009 virus, four of which located in three different antigenic sites. Eleven rare mutations in 12 HA sequences were also detected. Phylogenetic analysis revealed that all characterized influenza A(H1N1)pdm09 isolates formed a single genetic cluster, belonging to the genetic subclade 6B.1, defined by HA amino acid substitutions S84N, S162N, and I216T. Furthermore, all isolates showed an oseltamivir-sensitive genotype, suggesting that Tamiflu (Oseltamivir) could still be the drug of choice in Turkey.

Treatment-Emergent Influenza Variant Viruses With Reduced Baloxavir Susceptibility: Impact on Clinical and Virologic Outcomes in Uncomplicated Influenza

Background

Single-dose baloxavir rapidly reduces influenza virus titers and symptoms in patients with uncomplicated influenza, but viruses with reduced in vitro susceptibility due to amino acid substitutions at position 38 of polymerase acidic protein (PA/I38X) sometimes emerge.

Methods

We evaluated the kinetics, risk factors, and effects on clinical and virologic outcomes of emergence of PA/I38X-substituted viruses.

Results

Viruses containing PA/I38X substitutions were identified 3–9 days after baloxavir treatment in 9.7% (36/370) of patients, of whom 85.3% had transient virus titer rises. Median time to sustained cessation of infectious virus detection was 192, 48, and 96 hours in the baloxavir recipients with PA/I38X-substituted viruses, without PA/I38X-substituted viruses, and placebo recipients, respectively. The corresponding median times to alleviation of symptoms were 63.1, 51.0, and 80.2 hours, respectively. After day 5, symptom increases occurred in 11.5%, 8.0%, and 13.0%, respectively, and in 8.9% of oseltamivir recipients. Variant virus emergence was associated with lower baseline neutralizing antibody titers.

Conclusions

The emergence of viruses with PA/I38X substitutions following baloxavir treatment was associated with transient rises in infectious virus titers, prolongation of virus detectability, initial delay in symptom alleviation, and uncommonly with symptom rebound. The potential transmissibility of PA/I38X-substituted viruses requires careful study.

Clinical Trial Registration

NCT02954354.

Peramivir: A Review in Uncomplicated Influenza

Intravenous peramivir (Alpivab™; Rapivab^®; Rapiacta^®; PeramiFlu^®), the most recent globally approved inhibitor of influenza neuraminidase, is indicated for the treatment of uncomplicated influenza in adults and children from the age of 2 years. This article, written from an EU perspective, reviews the clinical use of peramivir in this indication and summarizes its pharmacological properties. In large, randomized, double-blind, multicentre trials in previously healthy adults with uncomplicated influenza, a single infusion of peramivir 600 mg significantly shortened the median time to resolution of influenza symptoms compared with placebo and was noninferior to the recommended oseltamivir regimen in terms of this primary outcome. Albeit data are limited, results from a noncomparative phase 3 trial in paediatric patients (≈ 95% of whom were aged ≥ 2 years) with acute uncomplicated influenza receiving the recommended dose of peramivir were generally consistent with those in adults. Peramivir was generally well tolerated in children and adults participating in these clinical trials, with most adverse events of mild to moderate intensity. Given its simple single-dose regimen and with intravenous administration offering a potential advantage over oral administration in individuals with nausea, vomiting or having difficulty in swallowing, peramivir provides an additional option for treating uncomplicated influenza infection in adults and children from the age of 2 years.

Passaging of an influenza A(H1N1)pdm09 virus in a difluoro sialic acid inhibitor selects for a novel, but unfit I106M neuraminidase mutant

An influenza A(H1N1)pdm09 and an influenza B virus were passaged in 3-fluoro(eq)-4-guanidino difluoro sialic acid (3Feq4Gu DFSA), an inhibitor of the influenza neuraminidase (NA) to determine whether resistant variants could be selected. 3Feq4Gu DFSA is a mechanism-based inhibitor, forming a covalent link to Y406 in the NA active site. Given its similarity to the natural substrate, sialic acid, we predicted resistant variants would be difficult to select. Yields of both viruses decreased with passaging, so that after 12 passages both viruses were only growing to low titers. Drug concentrations were decreased for another three passages. There was no difference in NA sensitivity in the MUNANA fluorescence-based assay, nor in plaque assays for the passaged virus stocks. All influenza B plaques were still wild type in all assays. There were isolated small diffuse plaques in the P15 pdm09 stock, which after purification had barely detectable NA or hemagglutinin (HA) activity. These had a novel non-active site I106M substitution in the NA gene, but unexpectedly no HA changes. The I106M may impact NA function through steric effects on the movement of the 150 and 430-loops. The I106M viruses had similar replication kinetics in MDCK cells as wild type viruses, but their ability to bind to and infect CHO-K1 cells expressing high levels of cell-bound mucin was compromised. The I106M substitution was unstable, with progeny rapidly reverting to wild type by three different mechanisms. Some had reverted to I106, some had V106, both with wild type NA and HA properties. A third group retained the I106M, but had a compensating R363K substitution, which regained almost wild type NA properties. These viruses now agglutinated chicken red blood cells (CRBCs) but unlike the I/V106, they rebound after elution at 37 °C. There were no mutations in the HA, but each phenotype correlated with the NA sequence. We propose that the activity in the I106M mutant is insufficient to remove carbohydrates from the virion HA and NA, sterically limiting HA access to CRBC receptors, thus resulting in poor HA binding.

Neuraminidase inhibitors as a strategy for influenza treatment: pros, cons and future perspectives

Introduction: Influenza represents a major public health threat worldwide. Implementation of good personal health and hygiene habits, together with vaccination, is the most effective tools to reduce influenza burden both in community and in healthcare setting. However, achieving adequate vaccination rates is challenging, and vaccination does not always guarantee complete protection. Neuraminidase inhibitors represent an important measure to reduce the risk of influenza-related complications among high-risk patients developing influenza infection. Areas covered: Neuraminidase inhibitors have been proven to be safe and effective in reducing influenza severity, duration of symptoms, hospitalizations, and influenza-related-mortality. Here the authors review the available data on neuraminidase inhibitors, including the mechanism of action, pharmacokinetics, efficacy, safety and current indications for their use in clinical practice. Expert opinion: Although vaccination is the most effective tool to reduce influenza-associated morbidity and mortality, neuraminidase inhibitors represent an important option for the treatment of patients with influenza infection, particularly in high-risk categories. Moreover, antivirals play an important role in influenza prevention and prophylaxis in selected settings.

Identification and in vivo Efficacy Assessment of Approved Orally Bioavailable Human Host Protein-Targeting Drugs With Broad Anti-influenza A Activity

The high genetic variability of influenza A viruses poses a continual challenge to seasonal and pandemic vaccine development, leaving antiviral drugs as the first line of defense against antigenically different strains or new subtypes. As resistance against drugs targeting viral proteins emerges rapidly, we assessed the antiviral activity of already approved drugs that target cellular proteins involved in the viral life cycle and were orally bioavailable. Out of 15 candidate compounds, four were able to inhibit infection by 10- to 100-fold without causing toxicity, in vitro. Two of the drugs, dextromethorphan and ketotifen, displayed a 50% effective dose between 5 and 50 μM, not only for the classic H1N1 PR8 strain, but also for a pandemic H1N1 and a seasonal H3N2 strain. Efficacy assessment in mice revealed that dextromethorphan consistently resulted in a significant reduction of viral lung titers and also enhanced the efficacy of oseltamivir. Dextromethorphan treatment of ferrets infected with a pandemic H1N1 strain led to a reduction in clinical disease severity, but no effect on viral titer was observed. In addition to identifying dextromethorphan as a potential influenza treatment option, our study illustrates the feasibility of a bioinformatics-driven rational approach for repurposing approved drugs against infectious diseases.

Characterization of substitutions in the neuraminidase of A(H7N9) influenza viruses selected following serial passage in the presence of different neuraminidase inhibitors

Avian A(H7N9) infections in humans have been reported in China since 2013 and are of public health concern due to their severity and pandemic potential. Oseltamivir and peramivir are neuraminidase inhibitors (NAIs) routinely used for the treatment of A(H7N9) infections, but variants with reduced sensitivity to these drugs can emerge in patients during treatment. Zanamivir and laninamivir are NAIs that are used less frequently. Herein, we performed in vitro serial passaging experiments with recombinant viruses, containing the neuraminidase (NA) from influenza A/Anhui/1/13 (H7N9) virus, in the presence of each NAI, to determine whether variants with reduced sensitivity would emerge. NA substitutions were characterized for their effect on the NA enzymatic activity and surface expression of the A/Anhui/1/13 (Anhui/1) NA, as well as NAs originating from contemporary A(H7N9) viruses of the Yangtze River Delta and Pearl River Delta lineages. In vitro passage in the presence of oseltamivir, peramivir and laninamivir selected for substitutions associated with reduced sensitivity (E119D, R292K and R152K), whereas passage in the presence of zanamivir did not select for any viruses with reduced sensitivity. All the NA substitutions significantly reduced activity, but not the expression of the Anhui/1 NA. In contemporary N9 NAs, all substitutions tested significantly reduced NA enzyme function in the Yangtze River lineage background, but not in the Pearl River Delta lineage background. Overall, these findings suggest that zanamivir may be less likely than the other NAIs to select for resistance in A(H7N9) viruses and that the impact of substitutions that reduce NAI susceptibility or enzyme function may be less in A(H7N9) viruses from the Pearl River lineage.

In vitro neuraminidase inhibitory concentration (IC50) of four neuraminidase inhibitors in the Japanese 2017-18 season: Comparison with the 2010-11 to 2016-17 seasons

To assess the extent of susceptibility to the four most commonly used neuraminidase inhibitors (NAIs) of the viruses epidemic in the 2017-18 Japanese influenza season, we measured the 50% inhibitory concentration (IC₅₀) for influenza virus isolates from patients and compared them with the results from the 2010-11 to 2016-17 seasons. Viral isolation was done with specimens obtained prior to treatment, and the type and subtype was determined by RT-PCR using type- and subtype-specific primers. The IC₅₀ was determined by a neuraminidase inhibition assay using a fluorescent substrate. A total of 237 virus isolates, 50 A(H1N1)pdm09, 92 A(H3N2), and 95 B were measured. No A(H1N1)pdm09 with highly reduced sensitivity for oseltamivir was found in the 2017-18 season. No isolates with highly reduced sensitivity to the four NAIs have been found for A(H3N2) or B from the 2010-11 to 2017-18 seasons. The geometric mean IC₅₀s of the four NAIs were quite consistent during the eight studied seasons. These results indicate that the sensitivity to the four commonly used NAIs has been maintained.

Population dynamics at neuraminidase position 151 of influenza A (H1N1)pdm09 virus in clinical specimens

Influenza A virus mutates rapidly, allowing it to escape natural and vaccine-induced immunity. Neuraminidase (NA) is a surface protein capable of cleaving the glycosidic linkages of neuraminic acids to release newly formed virions from infected cells. Genetic variants within a viral population can influence the emergence of pandemic viruses as well as drug susceptibility and vaccine effectiveness. In the present study, 55 clinical specimens from patients infected with the 2009 pandemic influenza A/H1N1 virus, abbreviated as A(H1N1)pdm09, during the 2015-2016 outbreak season in Taiwan were collected. Whole genomes were obtained through next-generation sequencing. Based on the published sequences from A(H1N1)pdm09 strains worldwide, a mixed population of two distinct variants at NA position 151 was revealed. We initially reasoned that such a mixed population may have emerged during cell culture. However, additional investigations confirmed that these mixed variants were detectable in the specimens of patients. To further investigate the role of the two NA-151 variants in a dynamic population, a reverse genetics system was employed to generate recombinant A(H1N1)pdm09 viruses. It was observed that the mixture of the two distinct variants was characterized by a higher replication rate compared to the recombinant viruses harbouring a single variant. Moreover, an NA inhibition assay revealed that a high frequency of the minor NA-151 variant in A(H1N1)pdm09 was associated with a reduced susceptibility to NA inhibitors. We conclude that two distinct NA-151 variants can be identified in patient specimens and that such variants may increase viral replication and NA activity.