Neuraminidase inhibitor susceptibility profile of pandemic and seasonal influenza viruses during the 2009-2010 and 2010-2011 influenza seasons in Japan

Inhibition of cap-dependent endonuclease in influenza virus with ADC189: a pre-clinical analysis and phase I trial

ADC189 is a novel drug of cap-dependent endonuclease inhibitor. In our study, its antiviral efficacy was evaluated in vitro and in vivo, and compared with baloxavir marboxil and oseltamivir. A first-in-human phase I study in healthy volunteers included single ascending dose (SAD) and food effect (FE) parts. In the preclinical study, ADC189 showed potent antiviral activity against various types of influenza viruses, including H1N1, H3N2, influenza B virus, and highly pathogenic avian influenza, comparable to baloxavir marboxil. Additionally, ADC189 exhibited much better antiviral efficacy than oseltamivir in H1N1 infected mice. In the phase I study, ADC189 was rapidly metabolized to ADC189-I07, and its exposure increased proportionally with the dose. The terminal elimination half-life (T1/2) ranged from 76.69 to 98.28 hours. Of note, food had no effect on the concentration, clearance, and exposure of ADC189. It was well tolerated, with few treatment-emergent adverse events (TEAEs) reported and no serious adverse events (SAEs). ADC189 demonstrated excellent antiviral efficacy both in vitro and in vivo. It was safe, well-tolerated, and had favorable pharmacokinetic characteristics in healthy volunteers, supporting its potential for single oral dosing in clinical practice.

Molecular dynamics study on the effect of the N1 neuraminidase double mutant G147R/H274Y on oseltamivir sensitivity

Inhibition of neuraminidase is the most prominent target in influenza medication using oseltamivir as an inhibitor. However, the emerging resistance of neuraminidase toward oseltamivir due to mutation reduces the efficacy of oseltamivir. The generally reported mutation is a single mutation at H274Y, which declines the sensitivity of oseltamivir by almost 900 folds compared to the wild-type variant. Moreover, an additional mutation at G147R increases the resistance by more than 2000 folds. However, sufficient studies on the resistance mechanism of this variant have not yet been reported. Therefore, we simulated four neuraminidase proteins comprising wild-type (WT), G147R, H274Y, and G147R/H274Y using molecular dynamics simulation to disclose the binding mechanism of oseltamivir. Trajectory analysis was conducted to reveal structural stability and flexibility. Furthermore, end-point free binding energy calculations were conducted. The energy decomposition of each residue was also calculated. The end-point energy calculation showed a similar result to that of experimental data. The energy decomposition analysis revealed that G147R/H274Y showed significant reduction in oseltamivir (OST) interaction with R118. Salt-bridge disruption caused by R224-E276 was also observed. Modification to enhance the polarity of the inhibitor might be useful in overcoming these changes. However, it should be noted that such changes could worsen the pharmacokinetic property of the inhibitor. It is hoped that these findings will provide useful insights for the development of an anti-influenza drug that can withstand the mutant variant.

Duration of fever in children infected with influenza A(H1N1)pdm09, A(H3N2) or B virus and treated with baloxavir marboxil, oseltamivir, laninamivir, or zanamivir in Japan during the 2012-2013 and 2019-2020 influenza seasons

We compared the duration of fever in children infected with A(H1N1)pdm09, A(H3N2), or influenza B viruses following treatment with baloxavir marboxil (baloxavir) or neuraminidase inhibitors (NAIs) (oseltamivir, zanamivir, or laninamivir). This observational study was conducted at 10 outpatient clinics across 9 prefectures in Japan during the 2012-2013 and 2019-2020 influenza seasons. Patients with influenza rapid antigen test positive were treated with one of four anti-influenza drugs. The type/subtype of influenza viruses were identified from MDCK or MDCK SIAT1 cell-grown samples using two-step real-time PCR. Daily self-reported body temperature after treatment were used to evaluate the duration of fever by treatment group and various underlying factors. Among 1742 patients <19 years old analyzed, 452 (26.0%) were A(H1N1)pdm09, 827 (48.0%) A(H3N2), and 463 (26.0%) influenza B virus infections. Among fours treatment groups, baloxavir showed a shorter median duration of fever compared to oseltamivir in univariate analysis for A(H1N1)pdm09 virus infections (baloxavir, 22.0 h versus oseltamivir, 26.7 h, P < 0.05; laninamivir, 25.5 h, and zanamivir, 25.0 h). However, this difference was not significant in multivariable analyses. For A(H3N2) virus infections, there were no statistically significant differences observed (20.3, 21.0, 22.0, and 19.0 h) uni- and multivariable analyses. For influenza B, baloxavir shortened the fever duration by approximately 15 h than NAIs (20.3, 35.0, 34.3, and 34.1 h), as supported by uni- and multivariable analyses. Baloxavir seems to have comparable clinical effectiveness with NAIs on influenza A but can be more effective for treating pediatric influenza B virus infections than NAIs.

Genomic Analyses Uncover Evolutionary Features of Influenza A/H3N2 Viruses in Yunnan Province, China, from 2017 to 2022

Influenza A viruses evolve at a high rate of nucleotide substitution, thereby requiring continuous monitoring to determine the efficacy of vaccines and antiviral drugs. In the current study, we performed whole-genome sequencing analyses of 253 influenza A/H3N2 strains from Yunnan Province, China, during 2017-2022. The hemagglutinin (HA) segments of Yunnan A/H3N2 strains isolated during 2017-2018 harbored a high genetic diversity due to heterogeneous distribution across branches. The mutation regularity of the predominant antigenic epitopes of HA segments in Yunnan was inconsistent in different years. Some important functional mutations in gene segments associated with viral adaptation and drug tolerance were revealed. The rapid genomic evolution of Yunnan A/H3N2 strains from 2017 to 2022 mainly concentrated on segments, i.e., matrix protein 2 (M2), non-structural protein 1 (NS1), neuraminidase (NA), NS2, and HA, with a high overall non-synonymous/synonymous substitution ratio (dN/dS). Our results highlighted a decline in vaccine efficacy against the A/H3N2 circulating strains, particularly against the Yunnan 2021-2022 A/H3N2 strains. These findings aid our understanding of evolutionary characteristics and epidemiological monitoring of the A/H3N2 viruses and provide in-depth insights into the protective efficacy of influenza vaccines.

Effectiveness of intravenous peramivir for the treatment of influenza A/H3N2 and influenza B/Victoria in hospitalized children

OBJECTIVE

To optimize the medication administered to children with influenza, we evaluated the effectiveness of peramivir in hospitalized children with influenza A/H3N2 and influenza B/Victoria.

METHODS

A retrospective study was conducted from October 2019 to March 2020 in children aged 29 days to 18 years with influenza A/H3N2 or B/Victoria. A total of 97 patients were enrolled and treated with intravenous infusion of peramivir.

RESULTS

The duration of influenza virus nucleic acid positivity in the influenza A/H3N2 group (3 days) was shorter than that in the influenza B/Victoria group (4 days) (P = 0.008). The remission time of fever symptoms in the influenza A/H3N2 group was 14 h, which was significantly shorter than that in the influenza B/Victoria group (26 h) (P = 0.042). In the 6-18 years age group, the median duration of virus nucleic acid positivity for children with influenza B/Victoria (4 days) was longer than that for children with influenza A/H3N2 (2 days) (P = 0.005). The incidence of adverse drug reactions (ADRs) with peramivir in the influenza A/H3N2 group and the influenza B/Victoria group was 2.04% (n = 1/49) and 4.17% (n = 2/48), respectively (P = 0.617).

CONCLUSIONS

A difference in the effectiveness of peramivir against different subtypes of influenza was observed. Compared to those infected with influenza B/Victoria, the children infected with influenza A/H3N2 experienced a significantly shorter duration of influenza virus nucleic acid positivity and remission time of fever symptoms.

Potent SARS-CoV-2 neutralizing antibodies with therapeutic effects in two animal models

The use of therapeutic neutralizing antibodies against SARS-CoV-2 infection has been highly effective. However, there remain few practical antibodies against viruses that are acquiring mutations. In this study, we created 494 monoclonal antibodies from patients with COVID-19-convalescent, and identified antibodies that exhibited the comparable neutralizing ability to clinically used antibodies in the neutralization assay using pseudovirus and authentic virus including variants of concerns. These antibodies have different profiles against various mutations, which were confirmed by cell-based assay and cryo-electron microscopy. To prevent antibody-dependent enhancement, N297A modification was introduced. Our antibodies showed a reduction of lung viral RNAs by therapeutic administration in a hamster model. In addition, an antibody cocktail consisting of three antibodies was also administered therapeutically to a macaque model, which resulted in reduced viral titers of swabs and lungs and reduced lung tissue damage scores. These results showed that our antibodies have sufficient antiviral activity as therapeutic candidates.

Development of cycling probe based real-time PCR methodology for influenza A viruses possessing the PA/I38T amino acid substitution associated with reduced baloxavir susceptibility

Baloxavir marboxil has been used for influenza treatment since March 2018 in Japan. After baloxavir treatment, the most frequently detected substitution is Ile38Thr in polymerase acidic protein (PA/I38T), and this substitution reduces baloxavir susceptibility in influenza A viruses. To rapidly investigate the frequency of PA/I38T in influenza A (H1N1)pdm09 and A (H3N2) viruses in clinical samples, we established a rapid real-time system to detect single nucleotide polymorphisms in PA, using cycling probe real-time PCR. We designed two sets of probes that were labeled with either 6-carboxyfluorescein (FAM) or 6-carboxy-X-rhodamine (ROX) to identify PA/I38 (wild type strain) or PA/I38T, respectively. The established cycling probe real-time PCR system showed a dynamic linear range of 10¹ to 10⁶ copies with high sensitivity in plasmid DNA controls. This real-time PCR system discriminated between PA/I38T and wild type viruses well. During the 2018/19 season, 377 influenza A-positive clinical samples were collected in Japan before antiviral treatment. Using our cycling probe real-time PCR system, we detected no (0/129, 0.0%) influenza A (H1N1)pdm09 viruses with PA/I38T substitutions and four A (H3N2) (4/229, 1.7%) with PA/I38T substitution prior to treatment. In addition, we found PA/I38T variant in siblings who did not received baloxavir treatment during an infection caused by A (H3N2) that afflicted the entire family. Although human-to-human transmission of PA/I38T variant may have occurred in a closed environment, the prevalence of this variant in influenza A viruses was still limited. Our cycling probe-PCR system is thus useful for antiviral surveillance of influenza A viruses possessing PA/I38T.

Pharmacokinetic behavior of peramivir in the plasma and lungs of rats after trans-nasal aerosol inhalation and intravenous injection

Peramivir, a neuraminidase inhibitor, was approved globally and is indicated for the treatment of uncomplicated influenza in adults and children. However, the only approved intravenous formulation of peramivir limits its clinical application due to the need for the specialized dosing techniques and increases the risk of contracting influenza virus infection among healthcare professionals when dosing within a short distance to the patient. The purpose of this study was to investigate the pharmacokinetic profile of peramivir in plasma and the lung of rats and to compare the profiles following administration through trans-nasal aerosol inhalation (0.0888, 0.1776, and 0.3552 mg/kg) and intravenous injection (30 mg/kg). The plasma concentration reached the C_max within 1.0 h (upon inhalation) and decreased at a t_1/2 of 6.71 and 10.9 h after inhalation and injection, respectively. The absolute bioavailability of peramivir after inhalation was 78.2 %. Overall, the pharmacokinetic exposure of peramivir in the lungs was higher than that in the plasma after aerosol inhalation. After inhalation, the C_max of peramivir in the lung was achieved within 1.0 h, and the elimination of the drug was slower than in the case of intravenous injection with t_1/2 values 1.81 h for injection and 5.72, 53.5, and 32.1 h for low, middle, and high doses administered through inhalation. The C_max and AUC_0-t values for peramivir in the lungs increased linearly with the increased inhalation dose. The results elucidate the pharmacokinetic process of peramivir after trans-nasal aerosol inhalation to rats and provide useful information for further rational application of this drug formulation.

Impact of long-term parental exposure to Tamiflu metabolites on the development medaka offspring (Oryzias latipes)

Despite the widespread use of the antiviral drug, Tamiflu®, little is known about the long-term toxic effects of drug or its metabolites in an aquatic ecosystem. This study integrated epidemiological and ecotoxicological methods to determine environmentally relevant concentrations of Tamiflu. A model based on the species medaka (Oryzias latipes) was then used to determine the health status and reproductivity of adults exposed to the drug as well as the embryonic development of offspring. The proposed ecotoxicological model was also used to quantitatively and qualitatively evaluate the toxicodynamic parameters related to egg production, hatchability, and development. Our results revealed that at an environmentally relevant exposure, Tamiflu and its metabolites had no adverse effects on growth, survival, or fecundity of adult medaka. Nonetheless, we observed a reduction in hatchability under exposure to 300 μg L^-1 and a reduction in body length under exposure exceeding 90 μg L^-1. Under exposure to 300 μg L^-1, the estimated spawning time to reach 50% of the maximum percentage of cumulative egg production (ET50) far exceeded that of the control group (without exposure to Tamiflu). We also observed a ∼ 3-fold decrease in maximum egg hatching (E_max). Based on an integrated epidemiological and ecotoxicological model, predictions of environmental concentrations of Tamiflu and its metabolites revealed that the influenza subtypes associated with increases in environmental concentrations: A(H3N2) > A(H1N1) > type B (in order of their effects). We also determined that A(H3N2) posed a potential risk to hatchability and development. Note however, the environmental concentrations of Tamiflu and its metabolites in most countries are lower than the effect concentrations derived in this study, indicating no hazards for aquatic environments. We recommend the use of hatchability and embryonic development as indicators in assessing the effects of long-term parental exposure to Tamiflu metabolites.

Design, synthesis and biological evaluation of "Multi-Site"-binding influenza virus neuraminidase inhibitors

Encouraged by our earlier discovery of neuraminidase inhibitors targeting 150-cavity or 430-cavity, herein, to yield more potent inhibitors, we designed, synthesized, and biologically evaluated a series of novel oseltamivir derivatives via modification of C-1 and C5-NH2 of oseltamivir by exploiting 150-cavity and/or 430-cavity. Among the synthesized compounds, compound 15e, the most potent N1-selective inhibitor targeting 150-cavity, showed 1.5 and 1.8 times greater activity than oseltamivir carboxylate (OSC) against N1 (H5N1) and N1 (H5N1-H274Y). In cellular assays, 15e also exhibited greater potency than OSC against H5N1 with EC50 of 0.66 μM. In addition, 15e demonstrated low cytotoxicity in vitro and low acute toxicity in mice. Molecular docking studies provided insights into the high potency of 15e against N1 and N1-H274Y mutant NA. Overall, we envisioned that the significant breakthrough in the discovery of potent group-1-specific neuraminidase inhibitors may lead to further investigation of more potent anti-influenza agents.

Peramivir susceptibilities of recombinant influenza A and B variants selected with various neuraminidase inhibitors

BACKGROUND

Peramivir is a parenteral neuraminidase inhibitor (NAI) approved for treating influenza infections in a few countries. We determined peramivir susceptibilities of several uncharacterized influenza A and B neuraminidase (NA) and haemagglutinin (HA) mutants selected with different NAIs.

METHODS

Recombinant wild-type (WT) and mutant NA proteins were expressed in 293T cells and susceptibility to peramivir, oseltamivir and zanamivir was determined by NA inhibition assay using the MUNANA substrate. Recombinant/reassortant influenza A(H1N1), A(H3N2) and B HA mutants were rescued by reverse genetics and assessed by plaque size or viral yield assays for drug susceptibility.

RESULTS

Recombinant R152K, I222K/T, G248R+I266V, Q312R+I427T and R371K (A[H1N1]pdm09); E41G, 1222L/V, Q226H and S247P (A[H3N2]) and D198Y, A246D/S/T and G402S (B) mutant NA proteins (N2 numbering) were analysed. Peramivir exhibited the lowest IC₅₀ values against both influenza A and B WT NAs. Peramivir and oseltamivir generally shared similar phenotypes. Of note, peramivir retained activity against I222K/T (A[H1N1]pdm09), I222L/V (A[H3N2]) and A246T (B) mutants, which had reduced inhibition (RI) or highly RI (HRI) against oseltamivir. Cross-RI/HRI against the three NAIs was observed for R152K, R371K and Q312R+I427T (A[H1N1]pdm09); S247P (A[H3N2]) and D198Y (B) mutants. All tested recombinant/reassortant R208K (A/Puerto Rico/8/34 [H1N1]); A28T, R124M and K189E (A/Victoria/3/75 [H3N2]) and T139N (B/Phuket/3073/13) HA mutants were susceptible to peramivir in cell culture experiments.

CONCLUSIONS

Peramivir is highly active against seasonal influenza subtypes. Although peramivir and oseltamivir generally share similar phenotypes, peramivir still possesses activity against some variants with RI/HRI against oseltamivir. Finally, NAI-induced HA substitutions alone did not significantly impact NAI susceptibility.

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.

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

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

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

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

Structure-Based Optimization of N-Substituted Oseltamivir Derivatives as Potent Anti-Influenza A Virus Agents with Significantly Improved Potency against Oseltamivir-Resistant N1-H274Y Variant

Due to the emergence of highly pathogenic and oseltamivir-resistant influenza viruses, there is an urgent need to develop new anti-influenza agents. Herein, five subseries of oseltamivir derivatives were designed and synthesized to improve their activity toward drug-resistant viral strains by further exploiting the 150-cavity in the neuraminidases (NAs). The bioassay results showed that compound 21h exhibited antiviral activities similar to or better than those of oseltamivir carboxylate (OSC) against H5N1, H5N2, H5N6, and H5N8. Besides, 21h was 5- to 86-fold more potent than OSC toward N1, N8, and N1-H274Y mutant NAs in the inhibitory assays. Computational studies provided a plausible rationale for the high potency of 21h against group-1 and N1-H274Y NAs. In addition, 21h demonstrated acceptable oral bioavailability, low acute toxicity, potent antiviral activity in vivo, and high metabolic stability. Overall, the above excellent profiles make 21h a promising drug candidate for the treatment of influenza virus infection.

Optimization of N-Substituted Oseltamivir Derivatives as Potent Inhibitors of Group-1 and -2 Influenza A Neuraminidases, Including a Drug-Resistant Variant

On the basis of our earlier discovery of N1-selective inhibitors, the 150-cavity of influenza virus neuraminidases (NAs) could be further exploited to yield more potent oseltamivir derivatives. Among the synthesized compounds, 15b and 15c were exceptionally active against both group-1 and -2 NAs. Especially for 09N1, N2, N6, and N9 subtypes, they showed 6.80-12.47 and 1.20-3.94 times greater activity than oseltamivir carboxylate (OSC). They also showed greater inhibitory activity than OSC toward H274Y and E119V variant. In cellular assays, they exhibited greater potency than OSC toward H5N1, H5N2, H5N6, and H5N8 viruses. 15b demonstrated high metabolic stability, low cytotoxicity in vitro, and low acute toxicity in mice. Computational modeling and molecular dynamics studies provided insights into the role of R group of 15b in improving potency toward group-1 and -2 NAs. We believe the successful exploitation of the 150-cavity of NAs represents an important breakthrough in the development of more potent anti-influenza agents.

Molecular genetic characteristics of influenza A virus clinically isolated during 2011-2016 influenza seasons in Korea

BACKGROUND

The influenza virus is reportedly associated with 3-5 million cases of severe illness and 250 000-500 000 deaths annually worldwide.

OBJECTIVES

We investigated the variation of influenza A virus in Korea and examined the association with death.

METHODS

A total of 13 620 cases were enrolled in the Hospital-based Influenza Morbidity & Mortality surveillance system in Korea during 2011-2016. Among these cases, a total of 4725 were diagnosed with influenza using RT-PCR (influenza A; n = 3696, influenza B; n = 928, co-infection; n = 101). We used 254 viral sequences from the 3696 influenza A cases for phylogenetic analysis using the BioEdit and MEGA 6.06 programs.

RESULTS

We found that the sequences of A/H3N2 in the 2011-2012 season belong to subgroup 3C.1, whereas the sequences in the 2012-2013 season pertain to subgroup 3C.2. The sequences in the 2013-2014 and 2014-2015 seasons involve subgroups 3C.3a and 3C.2a. The A/H1N1pdm09 subtype belongs to subgroup 6 and contains two clusters. In addition, sequence analysis confirmed the several substitutions of internal genes and gene substitutions associated with drug resistance (I222V in NA and S31N in M2) in the fatal cases. While statistical analysis found no significant associations between genetic differences in the viruses and mortality, mortality was associated with certain host factors, such as chronic lung disease.

CONCLUSIONS

In conclusion, influenza A virus clade changes occurred in Korea during the 2011-2016 seasons. These data, along with antigenic analysis, can aid in selecting effective vaccine strains. We confirmed that fatality in influenza A cases was related to underlying patient diseases, such as chronic lung disease, and further studies are needed to confirm associations between mortality and viral genetic substitutions.

Clinical effectiveness of four neuraminidase inhibitors (oseltamivir, zanamivir, laninamivir, and peramivir) for children with influenza A and B in the 2014-2015 to 2016-2017 influenza seasons in Japan

The clinical effectiveness of four neuraminidase inhibitors (NAIs) (oseltamivir, zanamivir, laninamivir, and peramivir) for children aged 0 months to 18 years with influenza A and B were investigated in the 2014-2015 to 2016-2017 influenza seasons in Japan. A total of 1207 patients (747 with influenza A and 460 with influenza B) were enrolled. The Cox proportional-hazards model using all of the patients showed that the duration of fever after administration of the first dose of the NAI was shorter in older patients (hazard ratio = 1.06 per 1 year of age, p < 0.001) and that the duration of fever after administration of the first dose of the NAI was shorter in patients with influenza A infection than in patients with influenza B infection (hazard ratio = 2.21, p < 0.001). A logistic regression model showed that the number of biphasic fever episodes was 2.99-times greater for influenza B-infected patients than for influenza A-infected patients (p < 0.001). The number of biphasic fever episodes in influenza A- or B-infected patients aged 0-4 years was 2.89-times greater than that in patients aged 10-18 years (p = 0.010), and the number of episodes in influenza A- or B-infected patients aged 5-9 years was 2.13-times greater than that in patients aged 10-18 years (p = 0.012).

Duration of fever and other symptoms after the inhalation of laninamivir octanoate hydrate in the 2016/17 Japanese influenza season; comparison with the 2011/12 to 2015/16 seasons

The duration of fever and symptoms after laninamivir octanoate hydrate (laninamivir) inhalation were investigated in the Japanese 2016/17 influenza season and the results were compared with those of the 2011/12 to 2015/16 seasons. A total of 1278 patients were evaluated for the duration of fever and symptoms in the six studied seasons. In the 2016/17 season, the influenza types/subtypes of the patients were 6 A (H1N1)pdm09 (2.9%), 183 A (H3N2) (87.6%), and 20 B (9.6%). The respective median durations of fever for A (H1N1)pdm09, A (H3N2), and B were 38.0, 33.0, and 38.5 h, without significant difference (p = 0.9201), and the median durations of symptoms were 86.5, 73.0, and 99.0 h, with significant difference (p = 0.0342). The median durations of fever and symptoms after laninamivir inhalation were quite consistent for the six studied seasons for A (H1N1)pdm09, A (H3N2), and B, without any significant differences. The percentage of patients with unresolved fever patients displayed a similar pattern through the six studied seasons for all these virus types. There was no significant difference in the duration of fever or symptoms between the Victoria and Yamagata lineages in the 2016/17 season and those of the previous studied seasons. Over the seasons tested, ten adverse drug reactions (ADRs) were reported from 1341 patients. The most frequent ADR was diarrhea and all ADRs were self-resolving and not serious. These results indicate the continuing clinical effectiveness of laninamivir against influenza A (H1N1)pdm09, A (H3N2), and B, with no safety issues.

Discovery of C-1 modified oseltamivir derivatives as potent influenza neuraminidase inhibitors

Inspired by our initial discovery about a series of neuraminidase (NA) inhibitors targeting the 150-cavity, in present study, we designed, synthesized, and biologically tested a panel of novel oseltamivir derivatives with C-1 modification, targeting the 430-cavity, an additional binding site which widely and stably existed in both group-1 and group-2 NAs. Some of the synthesized compounds displayed robust anti-influenza potencies against H5N1 and H5N6 viruses. Among them, compound 8b exerted the greatest inhibition, with IC₅₀ values of 0.088 and 0.097 μM and EC₅₀ values of 4.26 and 1.31 μM against H5N1 and H5N6 strains, respectively, which are similar to those of oseltamivir carboxylate (OSC). And its potency against mutant H5N1-H274Y NA was just 7-fold weaker than OSC. Molecular modeling revealed the elongated group at C-1 position being projected toward the 430-cavity. Notably, although compound 8b was not sensitive toward H5N1 strain relative to OSC in the embryonated egg model, it displayed greater anti-influenza virus effect against H5N6 strain than OSC at the concentration of 10 mmol/L. Overall, this work provided unique insights in the discovery of potent inhibitors against both group-1 and group-2 NAs.

Pharmacodynamics, Pharmacokinetics, and Antiviral Activity of BAY 81-8781, a Novel NF-κB Inhibiting Anti-influenza Drug

Influenza is a respiratory disease that causes annual epidemics. Antiviral treatment options targeting the virus exist, but their efficiency is limited and influenza virus strains easily develop resistance. Thus, new treatment strategies are urgently needed. In the present study, we investigated the anti-influenza virus properties of D,L-lysine acetylsalicylate ⋅ glycine (BAY 81-8781; LASAG) that is approved as Aspirin i.v. for intravenous application. Instead of targeting the virus directly BAY 81-8781 inhibits the activation of the NF-κB pathway, which is required for efficient influenza virus propagation. Using highly pathogenic avian influenza virus strains we could demonstrate that BAY 81-8781 was able to control influenza virus infection in vitro. In the mouse infection model, inhalation of BAY 81-8781 resulted in reduced lung virus titers and protection of mice from lethal infection. Pharmacological studies demonstrated that the oral route of administration was not suitable to reach the sufficient concentrations of BAY 81-8781 for a successful antiviral effect in the lung. BAY 81-8781 treatment of mice infected with influenza virus started as late as 48 h after infection was still effective in protecting 50% of the animals from death. In summary, the data represent a successful proof of the novel innovative antiviral concept of targeting a host cell signaling pathway that is required for viral propagation instead of viral structures.

In vitro antiviral effects of Peganum harmala seed extract and its total alkaloids against Influenza virus

This research was aimed to evaluate the in vitro antiviral effect and the mechanism of the effect of Peganum. harmala seeds extract against influenza A virus infection using Madin-Darby canine kidney (MDCK) cells. In this research, ethyl alcohol extract of P. harmala seeds and its total alkaloids was prepared. The potential antiviral activity of the extract and its total alkaloids against influenza A/Puerto Rico/8/34 (H1N1; PR8) virus was assessed. The mode of action of the extract to inhibit influenza replication was investigated using virucidal activity, hemagglutination inhibition assay, time of addition assays, RNA replication, western blot analysis and RNA polymerase blocking assay. The crud extract of P. harmala seed and its total alkaloids showed the best inhibitory effect against influenza A virus replication in MDCK cells using MTT assay, TCID₅₀ method and hemagglutination assay. Our results indicated that the extract inhibits viral RNA replication and viral polymerase activity but did not effect on hemagglutination inhibition and virucidal activity. This study showed that, in vitro antiviral activity of P. harmala seed extract against influenza virus is most probably associated with inhibiting viral RNA transcription. Therefore, this extract and its total alkaloid should be further characterized to be developed as anti-influenza A virus agent.

Drug resistance in influenza A virus: the epidemiology and management

Influenza A virus (IAV) is the sole cause of the unpredictable influenza pandemics and deadly zoonotic outbreaks and constitutes at least half of the cause of regular annual influenza epidemics in humans. Two classes of anti-IAV drugs, adamantanes and neuraminidase (NA) inhibitors (NAIs) targeting the viral components M2 ion channel and NA, respectively, have been approved to treat IAV infections. However, IAV rapidly acquired resistance against both classes of drugs by mutating these viral components. The adamantane-resistant IAV has established itself in nature, and a majority of the IAV subtypes, especially the most common H1N1 and H3N2, circulating globally are resistant to adamantanes. Consequently, adamantanes have become practically obsolete as anti-IAV drugs. Similarly, up to 100% of the globally circulating IAV H1N1 subtypes were resistant to oseltamivir, the most commonly used NAI, until 2009. However, the 2009 pandemic IAV H1N1 subtype, which was sensitive to NAIs and has now become one of the dominant seasonal influenza virus strains, has replaced the pre-2009 oseltamivir-resistant H1N1 variants. This review traces the epidemiology of both adamantane- and NAI-resistant IAV subtypes since the approval of these drugs and highlights the susceptibility status of currently circulating IAV subtypes to NAIs. Further, it provides an overview of currently and soon to be available control measures to manage current and emerging drug-resistant IAV. Finally, this review outlines the research directions that should be undertaken to manage the circulation of IAV in intermediate hosts and develop effective and alternative anti-IAV therapies.

Community- and hospital-acquired infections with oseltamivir- and peramivir-resistant influenza A(H1N1)pdm09 viruses during the 2015-2016 season in Japan

We report five cases of community- and hospital-acquired infections with oseltamivir- and peramivir-resistant A(H1N1)pdm09 viruses possessing the neuraminidase (NA) H275Y mutation during January-February 2016 in Japan. One case was hospitalized and was receiving oseltamivir for prophylaxis. The remaining four cases were not taking antiviral drugs at the time of sampling. These cases were geographically distant and epidemiologically unrelated. The five viruses showed ~300-fold rise in IC50 values against oseltamivir and peramivir, defined as highly reduced inhibition according to the WHO definition. Overall, the prevalence of the H275Y A(H1N1)pdm09 viruses was 1.8 % (5/282). The resistant viruses possessed the V241I, N369 K, and N386 K substitutions in the NA that have been previously reported among A(H1N1)pdm09 to alter transmission fitness. Analysis of Michaelis constant (Km) revealed that two of the isolates had reduced NA affinity to MUNANA, while the other three isolates displayed a slightly decreased affinity compared to the sensitive viruses. Further studies are needed to monitor the community spread of resistant viruses and to assess their transmissibility.

Therapeutic efficacy of peramivir against H5N1 highly pathogenic avian influenza viruses harboring the neuraminidase H275Y mutation

High morbidity and mortality associated with human cases of highly pathogenic avian influenza (HPAI) viruses, including H5N1 influenza virus, have been reported. The purpose of the present study was to evaluate the antiviral effects of peramivir against HPAI viruses. In neuraminidase (NA) inhibition and virus replication inhibition assays, peramivir showed strong inhibitory activity against H5N1, H7N1 and H7N7 HPAI viruses with sub-nanomolar activity in enzyme assays. In H5N1 viruses containing the NA H275Y mutation, the antiviral activity of peramivir against the variant was lower than that against the wild-type. Evaluation of the in vivo antiviral activity showed that a single intravenous treatment of peramivir (10 mg/kg) prevented lethality in mice infected with wild-type H5N1 virus and also following infection with H5N1 virus with the H275Y mutation after a 5 day administration of peramivir (30 mg/kg). Furthermore, mice injected with peramivir showed low viral titers and low levels of proinflammatory cytokines in the lungs. These results suggest that peramivir has therapeutic activity against HPAI viruses even if the virus harbors the NA H275Y mutation.

Influenza Virus Shedding in Laninamivir-Treated Children upon Returning to School

The current School Health and Safety Act in Japan states that children with influenza infection should stay home until day 6(th) after symptoms onset. This was an amendment of a previous version recommending school return on day 3 after defervescence. Here, we investigated the duration of fever and virus shedding after laninamivir treatment in 7 children infected with influenza A(H3N2) virus and 21 children with influenza B virus in relation to the school return timing recommended by the School Health and Safety Act during the 2011-2012 influenza season. Nasal discharge was collected on the first, second, and third hospital visits and virus titers were assessed by virus culture and real-time PCR. Duration of fever after laninamivir treatment was 1 day longer for influenza B than for influenza A(H3N2). Virus detection rates with 50% tissue culture infectious dose and viral RNA were highest at the first visit and gradually decreased at subsequent visits. Virus positivity rates were detectable at the time of defervescence in less than half of the enrolled patients (14.3-42.9%). Virus shedding rates were similarly low (0.0-19.0%) on day 3 or later from defervescence and on day 6 or later from fever onset (school return dates per the old and current School Health and Safety Act) regardless of the influenza type. In conclusion, despite the higher efficacy of laninamivir against A(H3N2) viruses than B viruses, viral shedding is low after return to school for both types, regardless of the version of the School Health and Safety Act.

Peramivir injection in the treatment of acute influenza: a review of the literature

Influenza virus infection is a major cause of morbidity and mortality in children and adults globally. Seasonal epidemics are common due to the rapid virus evolution, whereas the frequent emergence of antigenic variants can result in pandemics and sporadic/endemic avian influenza virus infections. Although annual vaccination is the mainstay for influenza prevention and control, the use of antiviral agents must be considered for treatment and prophylaxis against influenza. Currently available antiviral drugs include neuraminidase inhibitors (NAIs), adamantanes, and a novel polymerase inhibitor (favipiravir). Peramivir is a recently US Food and Drug Administration-approved NAI for the treatment of acute uncomplicated influenza in adults. The chemical structure of peramivir allows it to bind to the influenza neuraminidase with much higher affinity than oseltamivir. Peramivir is effective against a variety of influenza A and B subtypes and has a lower half-maximal inhibitory concentration compared to other NAIs in in vitro studies. Peramivir can be administered intravenously, a route that is favorable for hospitalized, critically ill patients with influenza. The long half-life of peramivir allows for once-daily dosing. The drug is eliminated primarily by the kidneys, warranting dose adjustments in patients with renal dysfunction. Studies have assessed the clinical efficacy of peramivir for treatment of pandemic influenza A (H1N1). Although anecdotal evidence supports the use of peramivir in pediatric patients, pregnant women, and hospitalized patients with severe influenza receiving continuous renal replacement therapy and extracorporeal membrane oxygenation, well-designed, controlled clinical trials should be conducted in order to assess its clinical efficacy in these patient populations.

Drug-Resistant and Genetic Evolutionary Analysis of Influenza Virus from Patients During the 2013 and 2014 Influenza Season in Beijing

The study aimed to analyze drug resistance and mutations and genetic evolution of influenza A and influenza B viruses during the 2013 and 2014 influenza season in Beijing, China. RNA was extracted from pharyngeal or nasal swabs of 28 patients, and determination of influenza genotypes was performed by using real-time reverse-transcription polymerase chain reaction. Influenza A virus samples were sequenced with the neuraminidase (NA) gene and M2 matrix protein gene to determine the NA inhibitor (NAI) resistance and amantadine resistance mutations, and influenza B virus samples were sequenced with the NA gene and hemagglutinin (HA) gene to analyze NAI resistance mutations. As a result, the enrolled subjects consisted of 19 patients with the A(H1N1)pdm09 subtype, four with A(H3N2) subtype and five with influenza B virus. All of the 23 samples with influenza A viruses harbored amantadine resistance mutation S31N in M2 matrix protein. V241I, a compensatory NAI resistance mutation, was detected in all of the 19 A(H1N1)pdm09 viruses. No other NAI resistance mutation was observed in both influenza A and B viruses. The NA gene of the five influenza B virus strains was classified as B-Victoria lineage, while the HA gene of five strains was classified as B-Yamagata lineage. In summary, all influenza A viruses from patients in Beijing in the 2013-2014 season were resistant to amantadine agent. Both influenza A and B viruses kept sensitive to NAIs. Lineage recombination was detected in influenza B virus strains and may impair the efficacy of influenza vaccination.

Full Genome Characterization of Human Influenza A/H3N2 Isolates from Asian Countries Reveals a Rare Amantadine Resistance-Conferring Mutation and Novel PB1-F2 Polymorphisms

Influenza A viruses evolve at a high rate requiring continuous monitoring to maintain the efficacy of vaccines and antiviral drugs. We performed next generation sequencing analysis of 100 influenza A/H3N2 isolates collected in four Asian countries (Japan, Lebanon, Myanmar, and Vietnam) during 2012-2015. Phylogenetic analysis revealed several reassortment events leading to the circulation of multiple clades within the same season. This was particularly evident during the 2013 and 2013/2014 seasons. Importantly, our data showed that certain lineages appeared to be fitter and were able to persist into the following season. The majority of A/H3N2 viruses continued to harbor the M2-S31N mutation conferring amantadine-resistance. In addition, an S31D mutation in the M2-protein, conferring a similar level of resistance as the S31N mutation, was detected in three isolates obtained in Japan during the 2014/2015 season. None of the isolates possessed the NA-H274Y mutation conferring oseltamivir-resistance, though a few isolates were found to contain mutations at the catalytic residue 151 (D151A/G/N or V) of the NA protein. These variations did not alter the susceptibility to neuraminidase inhibitors and were not detected in the original clinical specimens, suggesting that they had been acquired during their passage in MDCK cells. Novel polymorphisms were detected in the PB1-F2 open-reading frame resulting in truncations in the protein of 24-34 aminoacids in length. Thus, this study has demonstrated the utility of monitoring the full genome of influenza viruses to allow the detection of the potentially fittest lineages. This enhances our ability to predict the strain(s) most likely to persist into the following seasons and predict the potential degree of vaccine match or mismatch with the seasonal influenza season for that year. This will enable the public health and clinical teams to prepare for any related healthcare burden, depending on whether the vaccine match is predicted to be good or poor for that season.

Influenza A(H7N9) virus acquires resistance-related neuraminidase I222T substitution when infected mallards are exposed to low levels of oseltamivir in water

Influenza A virus (IAV) has its natural reservoir in wild waterfowl, and new human IAVs often contain gene segments originating from avian IAVs. Treatment options for severe human influenza are principally restricted to neuraminidase inhibitors (NAIs), among which oseltamivir is stockpiled in preparedness for influenza pandemics. There is evolutionary pressure in the environment for resistance development to oseltamivir in avian IAVs, as the active metabolite oseltamivir carboxylate (OC) passes largely undegraded through sewage treatment to river water where waterfowl reside. In an in vivo mallard (Anas platyrhynchos) model, we tested if low-pathogenic avian influenza A(H7N9) virus might become resistant if the host was exposed to low levels of OC. Ducks were experimentally infected, and OC was added to their water, after which infection and transmission were maintained by successive introductions of uninfected birds. Daily fecal samples were tested for IAV excretion, genotype, and phenotype. Following mallard exposure to 2.5 μg/liter OC, the resistance-related neuraminidase (NA) I222T substitution, was detected within 2 days during the first passage and was found in all viruses sequenced from subsequently introduced ducks. The substitution generated 8-fold and 2.4-fold increases in the 50% inhibitory concentration (IC50) for OC (P < 0.001) and zanamivir (P = 0.016), respectively. We conclude that OC exposure of IAV hosts, in the same concentration magnitude as found in the environment, may result in amino acid substitutions, leading to changed antiviral sensitivity in an IAV subtype that can be highly pathogenic to humans. Prudent use of oseltamivir and resistance surveillance of IAVs in wild birds are warranted.

The neuraminidases of MDCK grown human influenza A(H3N2) viruses isolated since 1994 can demonstrate receptor binding

Background

The neuraminidases (NAs) of MDCK passaged human influenza A(H3N2) strains isolated since 2005 are reported to have dual functions of cleavage of sialic acid and receptor binding. NA agglutination of red blood cells (RBCs) can be inhibited by neuraminidase inhibitors (NAIs), thus distinguishing it from haemagglutinin (HA) binding. We wanted to know if viruses prior to 2005 can demonstrate this property.

Methods

Pairs of influenza A(H3N2) isolates ranging from 1993–2008 passaged in parallel only in eggs or in MDCK cells were tested for inhibition of haemagglutination by various NAIs.

Results

Only viruses isolated since 1994 and cultured in MDCK cells bound chicken RBCs solely through their NA. NAI inhibition of agglutination of turkey RBCs was seen for some, but not all of these same MDCK grown viruses. Efficacy of inhibition of enzyme activity and haemagglutination differed between NAIs. For many viruses lower concentrations of oseltamivir could inhibit agglutination compared to zanamivir, although they could both inhibit enzyme activity at comparable concentrations. An E119V mutation reduced sensitivity to oseltamivir and 4-aminoDANA for both the enzyme assay and inhibition of agglutination. Sequence analysis of the NAs and HAs of some paired viruses revealed mutations in the haemagglutinin of all egg passaged viruses. For many of the paired egg and MDCK cultured viruses we found no differences in their NA sequences by Sanger sequencing. However, deep sequencing of MDCK grown isolates revealed low levels of variant populations with mutations at either D151 or T148 in the NA, suggesting mutations at either site may be able to confer this property.

Conclusions

The NA active site of MDCK cultured human influenza A(H3N2) viruses isolated since 1994 can express dual enzyme and receptor binding functions. Binding correlated with either D151 or T148 mutations. The catalytic and receptor binding sites do not appear to be structurally identical since relative concentrations of the NAIs to inhibit enzyme activity and agglutination differ.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-015-0295-3) contains supplementary material, which is available to authorized users.

Polygonum cuspidatum and its active components inhibit replication of the influenza virus through toll-like receptor 9-induced interferon beta expression

Influenza virus infection is a global public health issue. The effectiveness of antiviral therapies for influenza has been limited by the emergence of drug-resistant viral strains. Therefore, there is an urgent need to identify novel antiviral therapies. Here we tested the effects of 300 traditional Chinese medicines on the replication of various influenza virus strains in a lung cell line, A549, using an influenza-specific luciferase reporter assay. Of the traditional medicines tested, Polygonum cuspidatum (PC) and its active components, resveratrol and emodin, were found to attenuate influenza viral replication in A549 cells. Furthermore, they preferentially inhibited the replication of influenza A virus, including clinical strains isolated in 2009 and 2011 in Taiwan and the laboratory strain A/WSN/33 (H1N1). In addition to inhibiting the expression of hemagglutinin and neuraminidase, PC, emodin, and resveratrol also increased the expression of interferon beta (IFN-β) through Toll-like receptor 9 (TLR9). Moreover, the anti-viral activity of IFN-β or resveratrol was reduced when the A549 cells were treated with neutralizing anti-IFN-β antibodies or a TLR9 inhibitor, suggesting that IFN-β likely acts synergistically with resveratrol to inhibit H1N1 replication. This potential antiviral mechanism, involving direct inhibition of virus replication and simultaneous activation of the host immune response, has not been previously described for a single antiviral molecule. In conclusion, our data support the use of PC, resveratrol or emodin for inhibiting influenza virus replication directly and via TLR-9–induced IFN-β production.

Molecular surveillance of antiviral drug resistance of influenza A/H3N2 virus in Singapore, 2009-2013

Adamantanes and neuraminidase inhibitors (NAIs) are two classes of antiviral drugs available for the chemoprophylaxis and treatment of influenza infections. To determine the frequency of drug resistance in influenza A/H3N2 viruses in Singapore, large-scale sequencing of neuraminidase (NA) and matrix protein (MP) genes was performed directly without initial culture amplification. 241 laboratory-confirmed influenza A/H3N2 clinical samples, collected between May 2009 and November 2013 were included. In total, 229 NA (95%) and 241 MP (100%) complete sequences were obtained. Drug resistance mutations in the NA and MP genes were interpreted according to published studies. For the NAIs, a visual inspection of the aligned NA sequences revealed no known drug resistant genotypes (DRGs). For the adamantanes, the well-recognised S31N DRG was identified in all 241 MP genes. In addition, there was an increasing number of viruses carrying the combination of D93G+Y155F+D251V (since May 2013) or D93G (since March 2011) mutations in the NA gene. However, in-vitro NAI testing indicated that neither D93G+Y155F+D251V nor D93G alone conferred any changes in NAI susceptibility. Lastly, an I222T mutation in the NA gene that has previously been reported to cause oseltamivir-resistance in influenza A/H1N1/2009, B, and A/H5N1, was detected from a treatment-naïve patient. Further in-vitro NAI testing is required to confirm the effect of this mutation in A/H3N2 virus.

Discovery of N-substituted oseltamivir derivatives as potent and selective inhibitors of H5N1 influenza neuraminidase

To discover group-1-specific neuraminidase (NA) inhibitors that are especially involved in combating the H5N1 virus, two series of oseltamivir derivatives were designed and synthesized by targeting the 150-cavity. Among these, compound 20l was the most potent N1-selective inhibitor, with IC50 values of 0.0019, 0.0038, and 0.0067 μM against NAs from three H5N1 viruses. These values are better than those of oseltamivir carboxylate. Compound 32 was another potent N1-selective inhibitor that exhibited a 12-fold increase in activity against the H274Y mutant relative to oseltamivir carboxylate. Molecular docking studies revealed that the 150-cavity was an auxiliary binding site that may contribute to the high selectivity of these compounds. The present work is a significant breakthrough in the discovery of potent group-1-specific neuraminidase inhibitors, which may be further investigated for the treatment of infection by the H5N1 virus.

Peramivir and laninamivir susceptibility of circulating influenza A and B viruses

Influenza viruses collected from regions of Asia, Africa and Oceania between 2009 and 2012 were tested for their susceptibility to two new neuraminidase inhibitors, peramivir and laninamivir. All viruses tested had normal laninamivir inhibition. However, 3·2% (19/599) of A(H1N1)pdm09 viruses had highly reduced peramivir inhibition (due to H275Y NA mutation) and <1% (6/1238) of influenza B viruses had reduced or highly reduced peramivir inhibition, with single occurrence of variants containing I221T, A245T, K360E, A395E, D432G and a combined G145R+Y142H mutation. These data demonstrate that despite an increase in H275Y variants in 2011, there was no marked change in the frequency of peramivir- or laninamivir-resistant variants following the market release of the drugs in Japan in 2010.

In vitro neuraminidase inhibitory activity of four neuraminidase inhibitors against clinical isolates of influenza virus in the Japanese 2012-2013 season

The neuraminidase inhibitors (NAIs) oseltamivir phosphate (Tamiflu(®)), zanamivir (Relenza(®)), laninamivir octanoate (Inavir(®)), and peramivir (Rapiacta(®)) have been available for the treatment of influenza in Japan since 2010. The emergence of resistant virus to any of the NAIs is a great concern for influenza treatment. To assess the extent of viral resistance, we measured the 50% inhibitory concentration (IC50) of each NAI for influenza virus isolates in the 2012-2013 influenza season and compared the results to those of the 2010-2011 and 2011-2012 influenza seasons. Viral isolation of specimens obtained prior to treatment was done using Madine-Darby canine kidney cells, and the type and subtype of influenza, A(H1N1)pdm09, A(H3N2), or influenza B, 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 329 influenza viruses were isolated:5 influenza A(H1N1)pdm09 (1.5%), 316 influenza A(H3N2) (96.1%), and 8 influenza B (2.4%). No isolate showed an IC50 value exceeding 50 nM for any of the neuraminidase inhibitors. The IC50 values for A(H3N2) and B were similar to those of the 2010-2011 and 2011-2012 seasons. No isolate showed an increased IC50 value for A(H1N1)pdm09. These results indicate that the currently epidemic influenza viruses are susceptible to all four neuraminidase inhibitors, with no trend for IC50 values to increase at present.

Identification of a broad-spectrum antiviral small molecule against severe acute respiratory syndrome coronavirus and Ebola, Hendra, and Nipah viruses by using a novel high-throughput screening assay

Severe acute respiratory syndrome coronavirus (SARS-CoV) and Ebola, Hendra, and Nipah viruses are members of different viral families and are known causative agents of fatal viral diseases. These viruses depend on cathepsin L for entry into their target cells. The viral glycoproteins need to be primed by protease cleavage, rendering them active for fusion with the host cell membrane. In this study, we developed a novel high-throughput screening assay based on peptides, derived from the glycoproteins of the aforementioned viruses, which contain the cathepsin L cleavage site. We screened a library of 5,000 small molecules and discovered a small molecule that can inhibit the cathepsin L cleavage of all viral peptides with minimal inhibition of cleavage of a host protein-derived peptide (pro-neuropeptide Y). The small molecule inhibited the entry of all pseudotyped viruses in vitro and the cleavage of SARS-CoV spike glycoprotein in an in vitro cleavage assay. In addition, the Hendra and Nipah virus fusion glycoproteins were not cleaved in the presence of the small molecule in a cell-based cleavage assay. Furthermore, we demonstrate that the small molecule is a mixed inhibitor of cathepsin L. Our broad-spectrum antiviral small molecule appears to be an ideal candidate for future optimization and development into a potent antiviral against SARS-CoV and Ebola, Hendra, and Nipah viruses.

IMPORTANCE

We developed a novel high-throughput screening assay to identify small molecules that can prevent cathepsin L cleavage of viral glycoproteins derived from SARS-CoV and Ebola, Hendra, and Nipah viruses that are required for their entry into the host cell. We identified a novel broad-spectrum small molecule that could block cathepsin L-mediated cleavage and thus inhibit the entry of pseudotypes bearing the glycoprotein derived from SARS-CoV or Ebola, Hendra, or Nipah virus. The small molecule can be further optimized and developed into a potent broad-spectrum antiviral drug.