Peramivir for the treatment of influenza

Natural History of Influenza B Virus-Current Knowledge on Treatment, Resistance and Therapeutic Options

Influenza B virus (IBV) significantly impacts the health and the economy of the global population. WHO global health estimates project 1 billion flu cases annually, with 3 to 5 million resulting in severe disease and 0.3 to 0.5 million influenza-related deaths worldwide. Influenza B virus epidemics result in significant economic losses due to healthcare expenses, reduced workforce productivity, and strain on healthcare systems. Influenza B virus epidemics, such as the 1987-1988 Yamagata lineage outbreak and the 2001-2002 Victoria lineage outbreak, had a significant global impact. IBV's fast mutation and replication rates facilitate rapid adaptation to the environment, enabling the evasion of existing immunity and the development of resistance to virus-targeting treatments. This leads to annual outbreaks and necessitates the development of new vaccination formulations. This review aims to elucidate IBV's evolutionary genomic organization and life cycle and provide an overview of anti-IBV drugs, resistance, treatment options, and prospects for IBV biology, emphasizing challenges in preventing and treating IBV infection.

Repurposing of antiviral drugs for COVID-19 and impact of repurposed drugs on the nervous system

The recent pandemic, Coronavirus Disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has devastated humanity and is continuing to threaten us. Due to the high transmissibility of this pathogen, researchers are still trying to cope with the treatment and prevention of this disease. Few of them were successful in finding cure for COVID-19 by including repurposed drugs in the treatment. In such pandemic situations, when it is nearly impossible to design and implement a new drug target, previously designed antiviral drugs could help against novel viruses, referred to as drug repurposing/redirecting/repositioning or re-profiling. This review describes the current landscape of the repurposing of antiviral drugs for COVID-19 and the impact of these drugs on our nervous system. In some cases, specific antiviral therapy has been notably associated with neurological toxicity, characterized by peripheral neuropathy, neurocognitive and neuropsychiatric effects within the central nervous system (CNS).

Antiviral Drugs in Influenza

Flu is a serious health, medical, and economic problem, but no therapy is yet available that has satisfactory results and reduces the occurrence of these problems. Nearly 20 years after the registration of the previous therapy, baloxavir marboxil, a drug with a new mechanism of action, recently appeared on the market. This is a promising step in the fight against the influenza virus. This article presents the possibilities of using all available antiviral drugs specific for influenza A and B. We compare all currently recommended anti-influenza medications, considering their mechanisms of action, administration, indications, target groups, effectiveness, and safety profiles. We demonstrate that baloxavir marboxil presents a similar safety and efficacy profile to those of drugs already used in the treatment of influenza. Further research on combination therapy is highly recommended and may have promising results.

Zanamivir aqueous solution in severe influenza: A global Compassionate Use Program, 2009-2019

BACKGROUND

Zanamivir is a neuraminidase inhibitor effective against influenza A and B viruses. In 2009, GlaxoSmithKline (GSK) began clinical development of intravenous (IV) zanamivir and initiated a global Compassionate Use Program (CUP) in response to the evolving H1N1 global pandemic. The goal of the CUP was to provide zanamivir to critically ill patients with limited treatment options.

METHODS

Zanamivir was administered to patients with suspected or confirmed influenza infection who were not suitable for other approved antiviral treatments. Reporting of serious adverse events (SAEs) was mandatory and recorded in the GSK safety database. A master summary tracking sheet captured requests and patient characteristics. A case report form was available for detailing medical conditions, dosing, treatment duration, and clinical outcomes.

RESULTS

In total, 4,033 requests were made for zanamivir treatment of hospitalized patients from 38 countries between 2009 and 2019; ≥95% patients received zanamivir via the IV route. Europe had the highest number of requests (n = 3,051) followed by North America (n = 713). At least 20 patients were aged ≤6 months, of whom 12 were born prematurely. The GSK safety database included 466 patients with ≥1 SAE, of whom 374 (80%) had a fatal outcome. Drug-related SAEs were reported in 41 (11%) patients, including hepatic failure (n = 6 [2%]) and acute kidney injury (n = 5 [1%)].

CONCLUSIONS

The CUP facilitated global access to zanamivir prior to product approval. No new safety concerns were identified in the CUP compared with IV zanamivir clinical studies.

Development of 6E3 antibody-mediated SERS immunoassay for drug-resistant influenza virus

Influenza viruses are responsible for several pandemics and seasonal epidemics and pose a major public health threat. Even after a major outbreak, the emergence of drug-resistant influenza viruses can pose disease control problems. Here we report a novel 6E3 monoclonal antibody capable of recognizing and binding to the H275Y neuraminidase (NA) mutation, which has been associated with reduced susceptibility of influenza viruses to NA inhibitors. The 6E3 antibody had a K_D of 72.74 μM for wild-type NA and 32.76 pM for H275Y NA, suggesting that it can identify drug-resistant pandemic H1N1 (pH1N1) influenza virus. Molecular modeling studies also suggest the high-affinity binding of this antibody to pH1N1 H275Y NA. This antibody was also subject to dot-blot, enzyme-linked immunosorbent assay, bare-eye detection, and lateral flow assay to demonstrate its specificity to drug-resistant pH1N1. Furthermore, it was immobilized on Au nanoplate and nanoparticles, enabling surface-enhanced Raman scattering (SERS)-based detection of the H275Y mutant pH1N1. Using 6E3 antibody-mediated SERS immunoassay, the drug-resistant influenza virus can be detected at a low concentration of 10² plaque-forming units/mL. We also detected pH1N1 in human nasopharyngeal aspirate samples, suggesting that the 6E3-mediated SERS assay has the potential for diagnostic application. We anticipate that this newly developed antibody and SERS-based immunoassay will contribute to the diagnosis of drug-resistant influenza viruses and improve treatment strategies for influenza patients.

Investigation of genetic variation: Neuraminidase gene of influenza A virus H1N1/pdm09, Shiraz, Iran (2015-2016)

Oseltamivir and antiviral agents are frequently used for the prevention and treatment of influenza infection. However, resistance to oseltamivir has been reported globally due to a mutation in the Influenza virus neuraminidase gene. Such resistance will be detected by genotyping and phenotyping studies of viral isolates. The recent study aimed to determine the genetic mutation of neuraminidase gene in influenza A (H1N1) viruses isolated from children referred to Shiraz tertiary hospitals during 1 year (2015-2016) with influenza-like symptoms. A total of 300 patients were registered and throat samples were taken. The throat swabs were used for viral RNA extraction. Detection of influenza A (H1N1) was performed using the one-step real-time polymerase chain reaction (qRT-PCR) method. From positive isolates for H1N1, 51 random samples were evaluated for neuraminidase gene mutation with the nested PCR-sequencing method. Of 300 cases, 102 (34%) isolates were detected as influenza A (H1N1) pdm09. Based on sequencing results, 2 of the 44 sequenced isolates exhibited H275Y substitution, which presented oseltamivir resistance. In comparison with reference strain, the phylogenetic analysis of sequenced isolates was classified in genogroup 6B. While this result is the first report of emerging oseltamivir-resistant in the southwest of Iran, it is highly recommended to perform these evaluations on the different geographical regions in any prevalence area to plan treatment strategies for influenza.

Traditional Chinese Medicine in Treating Influenza: From Basic Science to Clinical Applications

Influenza infection is a highly contagious, acute febrile respiratory disease caused by the influenza virus. Traditional Chinese Medicine (TCM) has dominated plenty of theoretical and practical approaches in the treatment of influenza. It is, therefore, important to highlight the effects of TCM in the clinical treatment of influenza and their impact on inhibiting the growth of this virus in laboratory experiments. We scrutinized existing evidence on whether TCM is effective in clinical applications. Moreover, we described the potential mechanisms of TCM against the influenza virus. Our findings provide analytical evidence that supports the effectiveness of TCM in treating influenza infections as well as their mechanisms against this virus.

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.

Boronate, trifluoroborate, sulfone, sulfinate and sulfonate congeners of oseltamivir carboxylic acid: Synthesis and anti-influenza activity

Tamiflu readily undergoes endogenous hydrolysis to give oseltamivir carboxylic acid (OC) as the active anti-influenza agent to inhibit the viral neuraminidase (NA). GOC is derived from OC by replacing the 5-amino group with a guanidino group. In this study, OC and GOC congeners with the carboxylic acid bioisosteres of boronic acid, trifluoroborate, sulfone, sulfinic acid, sulfonic acid and sulfonate ester were first synthesized, starting with conversion of OC to a Barton ester, followed by halodecarboxylation to give the iodocyclohexene, which served as a pivotal intermediate for palladium-catalyzed coupling reactions with appropriate diboron and thiol reagents. The enzymatic and cell-based assays indicated that the GOC congeners consistently displayed better NA inhibition and anti-influenza activity than the corresponding OC congeners. The GOC sulfonic acid congener (7a) was the most potent anti-influenza agent, showing EC₅₀ = 2.2 nM against the wild-type H1N1 virus, presumably because the sulfonic acid 7a was more lipophilic than GOC and exerted stronger interactions on the three arginine residues (R118, R292 and R371) in the NA active site. Although the trifluoroborates, sulfones and sulfonate esters did not have acidic proton, they still exhibited appreciable NA inhibitory activity, indicating that the polarized B-F and S→O bonds still made sufficient interactions with the tri-arginine motif.

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.

Carrier-Mediated Prodrug Uptake to Improve the Oral Bioavailability of Polar Drugs: An Application to an Oseltamivir Analogue

The goal of this study was to improve the intestinal mucosal cell membrane permeability of the poorly absorbed guanidino analogue of a neuraminidase inhibitor, oseltamivir carboxylate (GOC) using a carrier-mediated strategy. Valyl amino acid prodrug of GOC with isopropyl-methylene-dioxy linker (GOC-ISP-Val) was evaluated as the potential substrate for intestinal oligopeptide transporter, hPEPT1 in Xenopus laevis oocytes heterologously expressing hPEPT1, and an intestinal mouse perfusion system. The diastereomers of GOC-ISP-Val were assessed for chemical and metabolic stability. Permeability of GOC-ISP-Val was determined in Caco-2 cells and mice. Diastereomer 2 was about 2 times more stable than diastereomer 1 in simulated intestinal fluid and rapidly hydrolyzed to the parent drug in cell homogenates. The prodrug had a 9 times-enhanced apparent permeability (P(app)) in Caco-2 cells compared with the parent drug. Both diastereomer exhibited high effective permeability (P(eff)) in mice, 6.32 ± 3.12 and 5.20 ± 2.81 × 10(-5) cm/s for diastereomer 1 and 2, respectively. GOC-ISP-Val was found to be a substrate of hPEPT1. Overall, this study indicates that the prodrug, GOC-ISP-Val, seems to be a promising oral anti-influenza agent that has sufficient stability at physiologically relevant pHs before absorption, significantly improved permeability via hPEPT1 and potentially rapid activation in the intestinal cells.

Screening and evaluation of commonly-used anti-influenza Chinese herbal medicines based on anti-neuraminidase activity

Anti-influenza Chinese herbal medicines (anti-flu CHMs) have advantages in preventing and treating influenza virus infection. Despite various data on antiviral activities of some anti-flu CHMs have been reported, most of them could not be compared using the standard evaluation methods for antiviral activity. This situation poses an obstacle to a wide application of anti-flu CHMs. Thus, it was necessary to develop an evaluation method to estimate antiviral activities of anti-flu CHMs. In the present study, we searched for anti-flu CHMs, based on clinic usage, to select study objects from commonly-used patented anti-flu Chinese medicines. Then, a neuraminidase-based bioassay, optimized and verified by HPLC method by our research group, was adopted to detect antiviral activities of selected 26 anti-flu CHMs. Finally, eight of these herbs, including Coptidis Rhizoma, Isatidis Folium, Lonicerae Flos, Scutellaria Radix, Cyrtomium Rhizome, Houttuynia Cordata, Gardeniae Fructus, and Chrysanthemi Indici Flos, were shown to have strong antiviral activities with half maximal inhibitory concentration (IC₅₀) values being 2.02 to 6.78 mg·mL^-1 (expressed as raw materials). In contrast, the IC₅₀ value of positive control peramivir was 0.38 mg·mL^-1. Considering the extract yields of CHMs, the active component in these herbs may have a stronger antiviral activity than peramivir, suggesting that these herbs could be further researched for active compounds. Moreover, the proposed neuraminidase-based bioassay was high-throughput and simple and could be used for evaluation and screening of anti-flu CHMs as well as for their quality control.

Peramivir: A Novel Intravenous Neuraminidase Inhibitor for Treatment of Acute Influenza Infections

Peramivir is a novel cyclopentane neuraminidase inhibitor of influenza virus. It was approved by the Food and Drug Administration in December 2014 for treatment of acute uncomplicated influenza in patients 18 years and older. For several months prior to approval, the drug was made clinically available under Emergency Use authorization during the 2009 H1N1 influenza pandemic. Peramivir is highly effective against human influenza A and B isolates as well as emerging influenza virus strains with pandemic potential. Clinical trials demonstrated that the drug is well-tolerated in adult and pediatric populations. Adverse events are generally mild to moderate and similar in frequency to patients receiving placebo. Common side effects include gastrointestinal disorders and decreased neutrophil counts but are self-limiting. Peramivir is administered as a single-dose via the intravenous route providing a valuable therapeutic alternative for critically ill patients or those unable to tolerate other administration routes. Successful clinical trials and post-marketing data in pediatric populations in Japan support the safety and efficacy of peramivir in this population where administration of other antivirals might not be feasible.

Standardizing the influenza neuraminidase inhibition assay among United States public health laboratories conducting virological surveillance

BACKGROUND

Monitoring influenza virus susceptibility to neuraminidase (NA) inhibitors (NAIs) is vital for detecting drug-resistant variants, and is primarily assessed using NA inhibition (NI) assays, supplemented by NA sequence analysis. However, differences in NI testing methodologies between surveillance laboratories results in variability of 50% inhibitory concentration (IC50) values, which impacts data sharing, reporting and interpretation. In 2011, the Centers for Disease Control and Prevention (CDC), in collaboration with the Association for Public Health Laboratories (APHL) spearheaded efforts to standardize fluorescence-based NI assay testing in the United States (U.S.), with the goal of achieving consistency of IC50 data.

METHODS

For the standardization process, three participating state public health laboratories (PHLs), designated as National Surveillance Reference Centers for Influenza (NSRC-Is), assessed the NAI susceptibility of the 2011-12 CDC reference virus panel using stepwise procedures, with support from the CDC reference laboratory. Next, the NSRC-Is assessed the NAI susceptibility of season 2011-12 U.S. influenza surveillance isolates (n = 940), with a large subset (n = 742) tested in parallel by CDC. Subsequently, U.S. influenza surveillance isolates (n = 9629) circulating during the next three influenza seasons (2012-15), were independently tested by the three NSRC-Is (n = 7331) and CDC (n = 2298).

RESULTS

The NI assay IC50s generated by respective NSRC-Is using viruses and drugs prepared by CDC were similar to those obtained with viruses and drugs prepared in-house, and were uniform between laboratories. IC50s for U.S. surveillance isolates tested during four consecutive influenza seasons (2011-15) were consistent from season to season, within and between laboratories.

CONCLUSION

These results show that the NI assay is robust enough to be standardized, marking the first time IC50 data have been normalized across multiple laboratories, and used for U.S. national NAI susceptibility surveillance.

Highly Substituted Cyclopentane-CMP Conjugates as Potent Sialyltransferase Inhibitors

Sialylconjugates on cell surfaces are involved in many biological events such as cellular recognition, signal transduction, and immune response. It has been reported that aberrant sialylation at the nonreducing end of glycoconjugates and overexpression of sialyltransferases (STs) in cells are correlated with the malignance, invasion, and metastasis of tumors. Therefore, inhibitors of STs would provide valuable leads for the discovery of antitumor drugs. On the basis of the transition state of the enzyme-catalyzed sialylation reaction, we proposed that the cyclopentane skeleton in its two puckered conformations might mimic the planar structure of the donor (CMP-Neu5Ac) in the transition state. A series of cyclopentane-containing compounds were designed and synthesized by coupling different cyclopentane α-hydroxyphosphonates with cytidine phosphoramidite. Their inhibitory activities against recombinant human ST6Gal-I were assayed, and a potent inhibitor 48l with a Ki of 0.028 ± 0.006 μM was identified. The results show that the cyclopentanoid-type compounds could become a new type of sialyltransferase inhibitors as biological probes or drug leads.

Emergence of Multidrug-Resistant Influenza A(H1N1)pdm09 Virus Variants in an Immunocompromised Child Treated With Oseltamivir and Zanamivir

Prolonged treatment of an immunocompromised child with oseltamivir and zanamivir for A(H1N1)pdm09 virus infection led to the emergence of viruses carrying H275Y and/or E119G in the neuraminidase (NA). When phenotypically evaluated by NA inhibition, the dual H275Y-E119G substitution caused highly reduced inhibition by 4 NA inhibitors: oseltamivir, zanamivir, peramivir, and laninamivir.

Application of a seven-target pyrosequencing assay to improve the detection of neuraminidase inhibitor-resistant Influenza A(H3N2) viruses

National U.S. influenza antiviral surveillance incorporates data generated by neuraminidase (NA) inhibition (NI) testing of isolates supplemented with NA sequence analysis and pyrosequencing analysis of clinical specimens. A lack of established correlates for clinically relevant resistance to NA inhibitors (NAIs) hinders interpretation of NI assay data. Nonetheless, A(H3N2) viruses are commonly monitored for moderately or highly reduced inhibition in the NI assay and/or for the presence of NA markers E119V, R292K, and N294S. In 2012 to 2013, three drug-resistant A(H3N2) viruses were detected by NI assay among isolates (n = 1,424); all showed highly reduced inhibition by oseltamivir and had E119V. In addition, one R292K variant was detected among clinical samples (n = 1,024) by a 3-target pyrosequencing assay. Overall, the frequency of NAI resistance was low (0.16% [4 of 2,448]). To screen for additional NA markers previously identified in viruses from NAI-treated patients, the pyrosequencing assay was modified to include Q136K, I222V, and deletions encompassing residues 245 to 248 (del245-248) and residues 247 to 250 (del247-250). The 7-target pyrosequencing assay detected NA variants carrying E119V, Q136, and del245-248 in an isolate from an oseltamivir-treated patient. Next, this assay was applied to clinical specimens collected from hospitalized patients and submitted for NI testing but failed cell culture propagation. Of the 27 clinical specimens tested, 4 (15%) contained NA changes: R292K (n = 2), E119V (n = 1), and del247-250 (n = 1). Recombinant NAs with del247-250 or del245-248 conferred highly reduced inhibition by oseltamivir, reduced inhibition by zanamivir, and normal inhibition by peramivir and laninamivir. Our results demonstrated the benefits of the 7-target pyrosequencing assay in conducting A(H3N2) antiviral surveillance and testing for clinical care.

Safety and efficacy of peramivir for influenza treatment

Objective

This report presents a review of the efficacy and safety of peramivir, a neuraminidase inhibitor that was granted Emergency Use Authorization by the US Food and Drug Administration (FDA) from October 23, 2009 to June 23, 2010 during the 2009 H1N1 pandemic.

Methods

Literature was accessed via PubMed (January 2000–April 2014) using several search terms: peramivir; BCX-1812; RWJ 270201; H1N1, influenza; antivirals; and neuraminidase inhibitors. The peramivir manufacturers, Shionogi and Co Ltd and BioCryst Pharmaceuticals, were contacted to obtain unpublished data and information presented at recent scientific meetings. Information was obtained from the Centers for Disease Control and Prevention (CDC) and from US FDA websites. English-language and Japanese-language reports in the literature were reviewed and selected based on relevance, along with information from the CDC, US FDA, and the drug manufacturers.

Results

We obtained eleven clinical trial reports of intravenous peramivir, two of which described comparisons with oseltamivir. Seven of nine other recently reported published studies was a dose–response study. Clinical reports of critically ill patients and pediatric patients infected with pandemic H1N1 described that early treatment significantly decreased mortality. Peramivir administered at 300 mg once daily in adult patients with influenza significantly reduces the time to alleviation of symptoms or fever compared to placebo. It is likely to be as effective as other neuraminidase inhibitors.

Conclusion

Although peramivir shows efficacy for the treatment of seasonal and pH1N1 influenza, it has not received US FDA approval. Peramivir is used safely and efficiently in hospitalized adult and pediatric patients with suspected or laboratory-confirmed influenza. Peramivir might be a beneficial alternative antiviral treatment for many patients, including those unable to receive inhaled or oral neuraminidase inhibitors, or those requiring nonintravenous drug delivery.

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.

Characterization of drug-resistant influenza A(H7N9) variants isolated from an oseltamivir-treated patient in Taiwan

BACKGROUND

Patients contracting influenza A(H7N9) infection often developed severe disease causing respiratory failure. Neuraminidase (NA) inhibitors (NAIs) are the primary option for treatment, but information on drug-resistance markers for influenza A(H7N9) is limited.

METHODS

Four NA variants of A/Taiwan/1/2013(H7N9) virus containing a single substitution (NA-E119V, NA-I222K, NA-I222R, or NA-R292K) recovered from an oseltamivir-treated patient were tested for NAI susceptibility in vitro; their replicative fitness was evaluated in cell culture, mice, and ferrets.

RESULTS

NA-R292K led to highly reduced inhibition by oseltamivir and peramivir, while NA-E119V, NA-I222K, and NA-I222R caused reduced inhibition by oseltamivir. Mice infected with any virus showed severe clinical signs with high mortality rates. NA-I222K virus was the most virulent in mice, whereas virus lacking NA change (NA-WT) and NA-R292K virus seemed the least virulent. Sequence analysis suggests that PB2-S714N increased virulence of NA-I222K virus in mice; NS1-K126R, alone or in combination with PB2-V227M, produced contrasting effects in NA-WT and NA-R292K viruses. In ferrets, all viruses replicated to high titers in the upper respiratory tract but produced only mild illness. NA-R292K virus, showed reduced replicative fitness in this animal model.

CONCLUSIONS

Our data highlight challenges in assessment of the replicative fitness of H7N9 NA variants that emerged in NAI-treated patients.

Combination effects of peramivir and favipiravir against oseltamivir-resistant 2009 pandemic influenza A(H1N1) infection in mice

Antiviral drugs are being used for therapeutic purposes against influenza illness in humans. However, antiviral-resistant variants often nullify the effectiveness of antivirals. Combined medications, as seen in the treatment of cancers and other infectious diseases, have been suggested as an option for the control of antiviral-resistant influenza viruses. Here, we evaluated the therapeutic value of combination therapy against oseltamivir-resistant 2009 pandemic influenza H1N1 virus infection in DBA/2 mice. Mice were treated for five days with favipiravir and peramivir starting 4 hours after lethal challenge. Compared with either monotherapy, combination therapy saved more mice from viral lethality and resulted in increased antiviral efficacy in the lungs of infected mice. Furthermore, the synergism between the two antivirals, which was consistent with the survival outcomes of combination therapy, indicated that favipiravir could serve as a critical agent of combination therapy for the control of oseltamivir-resistant strains. Our results provide new insight into the feasibility of favipiravir in combination therapy against oseltamivir-resistant influenza virus infection.

The relationship between in vivo antiviral activity and pharmacokinetic parameters of peramivir in influenza virus infection model in mice

The purpose of this study was to investigate the relationship between pharmacokinetic (PK) parameters of intravenous (IV) peramivir and in vivo antiviral activity pharmacodynamic (PD) outcomes in a mouse model of influenza virus infection. Peramivir was administrated to mice in three dosing schedules; once, twice and four times after infection of A/WS/33 (H1N1). The survival rate at day 14 after virus infection was employed as the antiviral activity outcome for analysis. The relationship between day 14 survival and PK parameters, including area under the concentration-time curve (AUC), maximum concentration (Cmax) and time that drug concentration exceeds IC95 (T(>IC95)), was estimated using a logistic regression model, and model fitness was evaluated by calculation of the Akaike information criterion (AIC) index. The AIC indices of AUC, Cmax and T(>IC95) were about 114, 151 and 124, respectively. The AIC of AUC and T(>IC95) were smaller than that of Cmax. Therefore, both AUC and T(>IC95) were the PK parameters that correlated best with the antiviral activity of peramivir IV against influenza virus infection in mice.

Detection and management of antiviral resistance for influenza viruses

Neuraminidase inhibitors (NAIs) are first-line agents for the treatment and prevention of influenza virus infections. As for other antivirals, the development of resistance to NAIs has become an important concern particularly in the case of A(H1N1) viruses and oseltamivir. The most frequently reported change conferring oseltamivir resistance in that viral context is the H275Y neuraminidase mutation (N1 numbering). Recent studies have shown that, in the presence of the appropriate permissive mutations, the H275Y variant can retain virulence and transmissibility in some viral backgrounds. Most oseltamivir-resistant influenza A virus infections can be managed with the use of inhaled or intravenous zanamivir, another NAI. New NAI compounds and non-neuraminidase agents as well as combination therapies are currently in clinical evaluation for the treatment for severe influenza infections.

Influenza prevention and treatment in transplant recipients and immunocompromised hosts

The host immune response is critical for the control and clearance of influenza virus after initial infection. Unfortunately, key components of the innate and adaptive responses to influenza are compromised in solid organ and hematopoietic stem cell transplant recipients. As a result, influenza in these key patient populations is associated with prolonged viral shedding, more frequent complications, including bacterial and fungal superinfections and rejection, and increased mortality. While vaccine is the critical prophylaxis strategy in other populations, response rates are diminished, particularly early post-transplant, among immunocompromised patients. Prospective data suggest that antiviral prophylaxis represents an effective and safe alternative to vaccine in patients who would be predicted to have poor responses to influenza vaccine. While there have not been randomized, controlled studies of antiviral therapy completed in solid organ or hematopoietic stem cell patient populations, observational data suggest that early therapy is associated with reduced rates of progression to lower airway involvement, morbidity, and mortality. Further studies are needed to define the optimal regimen, dose, duration, and endpoint to define successful treatment.

Spread of viral infection to family members from influenza patients treated with a neuraminidase inhibitor

We compared the incidence rates of household secondary infection among influenza patients prescribed laninamivir, oseltamivir, or zanamivir (neuraminidase inhibitors), based on health-insurance claims data owned by Japan Medical Data Center (JMDC) which was consisting of medical information on patients who were prescribed an anti-influenza drug and their family members between October 2010 and July 2011. The date when an index case patient was prescribed laninamivir, oseltamivir or zanamivir for the first time was defined as "Day 1". If other members in the same family were prescribed laninamivir, oseltamivir, zanamivir, or peramivir during Days 3-8, we assumed any household secondary infection had occurred. The incidence rate was 11.0%, 14.3%, and 11.6% in index case patients prescribed laninamivir, oseltamivir, and zanamivir, respectively. The results of the logistic regression analysis revealed a significant difference between laninamivir and oseltamivir, while no significant difference was observed between laninamivir and zanamivir.

Autodisplay of an archaeal γ-lactamase on the cell surface of Escherichia coli using Xcc_Est as an anchoring scaffold and its application for preparation of the enantiopure antiviral drug intermediate (-) vince lactam

At present, autotransporter protein mediated surface display has opened a new dimension in the development of whole-cell biocatalysts. Here, we report the identification of a novel autotransporter Xcc_Est from Xanthomonas campestris pv campestris 8004 by bioinformatic analysis and application of Xcc_Est as an anchoring motif for surface display of γ-lactamase (Gla) from thermophilic archaeon Sulfolobus solfataricus P2 in Escherichia coli. The localization of γ-lactamase in the cell envelope was monitored by Western blot, activity assay and flow cytometry analysis. Either the full-length or truncated Xcc_Est could efficiently transport γ-lactamase to the cell surface. Compared with the free enzyme, the displayed γ-lactamase exhibited optimum temperature of 30 °C other than 90 °C, with a substantial decrease of 60 °C. Under the preparation system, the engineered E. coli with autodisplayed γ-lactamase converted 100 g racemic vince lactam to produce 49.2 g (-) vince lactam at 30 °C within 4 h. By using chiral HPLC, the ee value of the produced (-) vince lactam was determined to be 99.5 %. The whole-cell biocatalyst exhibited excellent stability under the operational conditions. Our results indicate that the E. coli with surface displayed γ-lactamase is an efficient and economical whole cell biocatalyst for preparing the antiviral drug intermediate (-) vince lactam at mild temperature, eliminating expensive energy cost performed at high temperature.

Drug susceptibility surveillance of influenza viruses circulating in the United States in 2011-2012: application of the WHO antiviral working group criteria

Background

Assessing susceptibility of influenza viruses to neuraminidase (NA) inhibitors (NAIs) is primarily done in NA inhibition (NI) assays, supplemented by NA sequence analysis. However, two factors present challenges for NI assay data interpretation: lack of established IC₅₀ values indicative of clinically relevant resistance and insufficient harmonization of NI testing methodologies among surveillance laboratories. In 2012, the WHO working group on influenza antiviral susceptibility (WHO-AVWG) developed criteria to facilitate consistent interpretation and reporting of NI assay data.

Methods

The WHO-AVWG classification criteria were applied in interpreting NI assay data for two FDA-licensed NAIs, oseltamivir and zanamivir, for viruses collected in the United States during the 2011–2012 winter season.

Results

All A (H1N1)pdm09 viruses (n = 449) exhibited normal inhibition by oseltamivir and zanamivir, with the exception of eight viruses (1·8%) with highly reduced inhibition by oseltamivir, which carried the H275Y marker of oseltamivir resistance. A (H3N2) viruses (n = 978) exhibited normal inhibition by both NAIs, except for one virus with highly reduced inhibition by zanamivir due to the cell culture-selected NA change, Q136K. Type B viruses (n = 343) exhibited normal inhibition by both drugs, except for an isolate with reduced inhibition by both NAIs that had the cell culture-selected A200T substitution.

Conclusions

WHO-AVWG classification criteria allowed the detection of viruses carrying the established oseltamivir resistance marker, as well as viruses whose susceptibility was altered during propagation. These criteria were consistent with statistical-based criteria for detecting outliers and will be useful in harmonizing NI assay data among surveillance laboratories worldwide and in establishing laboratory correlates of clinically relevant resistance.

Neuraminidase inhibitors for influenza B virus infection: efficacy and resistance

Many aspects of the biology and epidemiology of influenza B viruses are far less studied than for influenza A viruses, and one of these aspects is efficacy and resistance to the clinically available antiviral drugs, the neuraminidase (NA) inhibitors (NAIs). Acute respiratory infections are one of the leading causes of death in children and adults, and influenza is among the few respiratory infections that can be prevented and treated by vaccination and antiviral treatment. Recent data has suggested that influenza B virus infections are of specific concern to pediatric patients because of the increased risk of severe disease. Treatment of influenza B is a challenging task for the following reasons: This review presents current knowledge of the efficacy of NAIs for influenza B virus and antiviral resistance in clinical, surveillance, and experimental studies.

Bioluminescence-based neuraminidase inhibition assay for monitoring influenza virus drug susceptibility in clinical specimens

The QFlu prototype bioluminescence-based neuraminidase (NA) inhibition (NI) assay kit was designed to detect NA inhibitor (NAI)-resistant influenza viruses at point of care. Here, we evaluated its suitability for drug susceptibility assessment at a surveillance laboratory. A comprehensive panel of reference viruses (n = 14) and a set of 90 seasonal influenza virus A and B isolates were included for testing with oseltamivir and/or zanamivir in the QFlu assay using the manufacturer-recommended protocol and a modified version attuned to surveillance requirements. The 50% inhibitory concentrations (IC50s) generated were compared with those of NI assays currently used for monitoring influenza drug susceptibility, the fluorescent (FL) and chemiluminescent (CL) assays. To provide proof of principle, clinical specimens (n = 235) confirmed by real-time reverse transcription (RT)-PCR to contain influenza virus A(H1N1)pdm09 and prescreened for the oseltamivir resistance marker H275Y using pyrosequencing were subsequently tested in the QFlu assay. All three NI assays were able to discriminate the reference NA variants and their matching wild-type viruses based on the difference in their IC50s. Unless the antigenic types were first identified, certain NA variants (e.g., H3N2 with E119V) could be detected among seasonal viruses using the FL assays only. Notably, the QFlu assay identified oseltamivir-resistant A(H1N1)pdm09 viruses carrying the H275Y marker directly in clinical specimens, which is not feasible with the other two phenotypic assays, which required prior virus culturing in cells. Furthermore, The QFlu assay allows detection of the influenza virus A and B isolates carrying established and potential NA inhibitor resistance markers and may become a useful tool for monitoring drug resistance in clinical specimens.

Assays for monitoring susceptibility of influenza viruses to neuraminidase inhibitors

Close monitoring of drug susceptibility among human influenza viruses was necessitated by widespread resistance to M2 inhibitors in influenza H1N1 (pre-pandemic and 2009 pandemic) and H3N2 viruses, and of oseltamivir resistance in pre-pandemic H1N1 viruses. The FDA-approved neuraminidase (NA) inhibitors (NAIs), oseltamivir and zanamivir, as well as investigational NAIs, peramivir and laninamivir, are currently the principal treatment options for managing influenza infection. However, there are challenges associated with assessing virus susceptibility to this class of drugs. Traditional cell culture-based assays are not reliable for phenotypic testing of NAI susceptibility due to complexity in interpretation. Two types of laboratory assays are currently available for monitoring NAI susceptibility, phenotypic such as the neuraminidase inhibition (NI) assay and genotypic. The NI assay's requirement for propagated virus lengthens testing turnaround; therefore, the need for timely detection of molecular markers associated with NAI resistance (e.g., H275Y in H1N1) has spurred the development of rapid, high-throughput assays, such as real-time RT-PCR and pyrosequencing. The high sensitivity of genotypic assays allows testing of clinical specimens thus eliminating the need for virus propagation in cell culture. The NI assays are especially valuable when a novel virus emerges or a new NAI becomes available. Modifications continue to be introduced into NI assays, including optimization and data analysis criteria. The optimal assay of choice for monitoring influenza drug susceptibility varies widely depending on the needs of laboratories (e.g., surveillance purposes, clinical settings). Optimally, it is desirable to combine functional and genetic analyses of virus isolates and, when possible, the respective clinical specimens.

Neuraminidase inhibitor susceptibility surveillance of influenza viruses circulating worldwide during the 2011 Southern Hemisphere season

Background

Neuraminidase (NA) inhibitors (NAIs) are currently the only antivirals effective against influenza infections due to widespread resistance to M2 inhibitors.

Methods

Influenza A and B viruses (n = 1079) collected worldwide between April 01, 2011, and September 30, 2011, were assessed for susceptibility to FDA‐approved NAIs, oseltamivir and zanamivir, and investigational peramivir, using the fluorescent‐based NA‐Fluor™ Influenza Neuraminidase Assay Kit. A subset of viruses (n = 98) were tested for susceptibility to the investigational NAI, laninamivir.

Results

Influenza A(H1N1)pdm09 viruses (n = 326) were sensitive to all NAIs, except for two (0·6%) with H275Y (N1 numbering; H274Y in N2 numbering) substitution, which exhibited elevated IC₅₀s for oseltamivir and peramivir, and a third with previously unreported N325K substitution, exhibiting reduced susceptibility to oseltamivir. Influenza A(H3N2) viruses (n = 407) were sensitive to all NAIs. Influenza B viruses (n = 346) were sensitive to all NAIs, except two (0·6%) with H273Y (N1 numbering; H274Y in N2 numbering) substitution, exhibiting reduced susceptibility to oseltamivir and peramivir, and one with previously unreported G140R and N144K substitutions, exhibiting reduced susceptibility to oseltamivir, zanamivir, and peramivir. All influenza A and B viruses were sensitive to laninamivir. It is unknown whether substitutions N325K, G140R, and N144K were present in the virus prior to culturing because clinical specimens were unavailable for testing.

Conclusions

This study summarizes NAI susceptibility of influenza viruses circulating worldwide during the 2011 Southern Hemisphere (SH) season, assessed using the NA‐Fluor™ Kit. Despite low resistance to NAIs among tested influenza viruses, constant surveillance of influenza virus susceptibility to NAIs should be emphasized.

Influenza vaccines and vaccinations in Poland - past, present and future

Influenza causes seasonal infections worldwide that can lead to complications and deaths in every age group. The most effective and cheapest way to combat influenza is through vaccination. In many countries, including Poland, for each age group, the rate of vaccination against influenza is still at a very low level, which generates high social costs, not infrequently family tragedies in the case of irreversible complications of influenza, or death of a loved one. Regular vaccination should be part of good medical practice, as well as an individual’s engagement in their own health and in that of their family. Based on numerous studies, it is estimated that the effectiveness of current inactivated influenza vaccine in reducing morbidity and mortality in high-risk groups ranges from 50–70%. According to data from the National Institute of Public Health-National Institute of Hygiene, the rate of vaccination in children in 2008 in Poland was very low. In the group of children aged from 6 months to 14 years, only 1.1–1.6% were vaccinated. Although influenza vaccination for people aged over 65 years was free of charge in many provinces in this group, only 13.4% of this population was immunized, while in the case of people with chronic diseases, only 11.1% were immunized. The vaccination rate among health care employees is an embarrassing 6.4%. More educational activities addressed to both medical professionals and patients are required in order to increase influenza vaccine coverage in Poland.

Influenza virus resistance to neuraminidase inhibitors

In addition to immunization programs, antiviral agents can play a major role for the control of seasonal influenza epidemics and may also provide prophylactic and therapeutic benefits during an eventual pandemic. The purpose of this article is to review the mechanism of action, pharmacokinetics and clinical indications of neuraminidase inhibitors (NAIs) with an emphasis on the emergence of antiviral drug resistance. There are two approved NAIs compounds in US: inhaled zanamivir and oral oseltamivir, which have been commercially available since 1999-2000. In addition, two other NAIs, peramivir (an intravenous cyclopentane derivative) and laninamivir (a long-acting NAI administered by a single nasal inhalation) have been approved in certain countries and are under clinical evaluations in others. As for other antivirals, the development and dissemination of drug resistance is a significant threat to the clinical utility of NAIs. The emergence and worldwide spread of oseltamivir-resistant seasonal A(H1N1) viruses during the 2007-2009 seasons emphasize the need for continuous monitoring of antiviral drug susceptibilities. Further research priorities should include a better understanding of the mechanisms of resistance to existing antivirals, the development of novel compounds which target viral or host proteins and the evaluation of combination therapies for improved treatment of severe influenza infections, particularly in immunocompromised individuals. This article forms part of a symposium in Antiviral Research on "Treatment of influenza: targeting the virus or the host."

Efficacy of repeated intravenous injection of peramivir against influenza A (H1N1) 2009 virus infection in immunosuppressed mice

The efficacy of intravenous peramivir against influenza A (H1N1) 2009 virus infection was evaluated in mice in which the immune system was suppressed by cyclophosphamide (CP) treatment. The mortality rate of the vehicle control group was 100%, and the mice lost 20% of their body weight on average by day 13 postinfection (p.i.). Repeated administration of peramivir (40 mg/kg of body weight once a day, given intravenously for 20 days), starting at 1 h p.i., significantly reduced mortality, body weight loss, viral titers, and cytokine production in infected mice compared with results for administration of vehicle (P < 0.01). In addition, repeated administration of peramivir, starting at 24 h, 48 h, or 72 h p.i., also resulted in increases in survival rates and reduction of viral titers in the lungs (P < 0.01). The mean days to death (MDD) of the vehicle group was 14.5 days, while in the groups treated with peramivir starting at 24 h, 48 h, and 72 h p.i., the MDDs were >23.0, 20.9, and 21.8 days, respectively. In comparison, repeated administration of oseltamivir phosphate (5 mg/kg twice a day, given orally for 20 days), starting at 24 h, 48 h, and 72 h p.i., also significantly prevented body weight loss, whereas no significant differences in mortality rates and viral titers in the lungs were observed compared with results for the vehicle group. These data indicated that repeated administration of peramivir was effective in promoting the survival and reducing virus replication in immunosuppressed mice infected with influenza A (H1N1) 2009 virus.

Antiviral activity of Isatis indigotica root-derived clemastanin B against human and avian influenza A and B viruses in vitro

Clemastanin B, 7S,8R,8'R-(-)-lariciresinol-4,4'-bis-O-β-D-glucopyranoside, is one of the major lignans extracted from Isatis indigotica root (IIR). In this study, the anti-influenza activities of clemastanin B were evaluated in vitro. Clemastanin B was found to inhibit different subtypes of human (H1N1, including swine-origin H1N1; H3N2 and influenza B) and avian influenza viruses (H6N2, H7N3, H9N2) at different magnitudes of activity (IC50 0.087-0.72 mg/ml) while this compound was inactive against respiratory syncytial virus (RSV), adenovirus 3 (ADV3), parainfluenza virus 3 (PIV3), enterovirus 71 (EV71) and human rhinovirus (HRV). An apparent virus titer reduction was detected when MDCK cells were treated with clemastanin B after viral infection, particularly at the early stage, and the ribonucleoprotein (RNP) of the influenza virus was retained in the nucleus after treatment with clemastanin B. These results demonstrated that clemastanin B targets viral endocytosis, uncoating or RNP export from the nucleus. Furthermore, treatment with clemastanin B did not easily result in the emergence of viral drug resistance. The effects of clemastanin B demonstrated in this study may promote the antiviral study of IIR, but additional studies are required to define the anti-influenza mechanism(s).

Uronosyl phosphonate-based sialidase inhibitor synthesis and conformational analysis

With a view to development of novel sialidase inhibitors, mimetics of the natural inhibitor Neu5Ac2en have been prepared in which a phosphonate group replaces the sialic acid glycerol side chain. Different hex-4-en derivatives adopt half-chair conformations that place the glycosyl phosphonate in an equatorial position. For the α-L-threo-hex-4-en derivative this conformation is equivalent to that of Neu5Ac2en, and opposite to that seen for alkyl O-glycosides with the same overall stereochemistry.

A single E105K mutation far from the active site of influenza B virus neuraminidase contributes to reduced susceptibility to multiple neuraminidase-inhibitor drugs

Drugs inhibiting the enzymatic activity of influenza virus neuraminidase (NA) are the cornerstone of therapy for influenza virus infection. The emergence of drug-resistant variants may limit the benefits of antiviral therapy. Here we report the recovery of an influenza B virus with reduced susceptibilities to NA inhibitors from a human patient with no history of antiviral drug treatment. The virus, designated B/Kochi/61/2011, was isolated by inoculating Madin-Darby canine kidney (MDCK) cells with respiratory specimens from the patient. NA inhibition assays demonstrated that the B/Kochi/61/2011 isolate showed a remarkable reduction in susceptibility to peramivir. The isolate also exhibited low to moderately reduced sensitivity to oseltamivir, laninamivir, and zanamivir. A sequence analysis of viruses propagated in MDCK cells revealed that the isolate contained a mutation (E105K) not previously associated with reduced susceptibility to NA inhibitors. However, pyrosequencing analysis showed that the NA E105K mutation was below a detectable level in the original clinical specimens, suggesting that the mutant virus may be preferably selected during propagation in MDCK cells. Analysis of the three-dimensional model of E105 and K105 NAs with peramivir suggested that the E105K mutation at the monomer-monomer interface of the NA tetramer may destabilize the tetrameric form of NA, leading to decreased susceptibility to NA inhibitors. These results have implications for understanding the mechanism of resistance against NA-inhibitor drugs.

Exploring the interactions of unsaturated glucuronides with influenza virus sialidase

A series of C3 O-functionalized 2-acetamido-2-deoxy-Δ⁴-β-D-glucuronides were synthesized to explore noncharge interactions in subsite 2 of the influenza virus sialidase active site. In complex with A/N8 sialidase, the parent compound (C3 OH) inverts its solution conformation to bind with all substituents well positioned in the active site. The parent compound inhibits influenza virus sialidase at a sub-μM level; the introduction of small alkyl substituents or an acetyl group at C3 is also tolerated.

Therapeutic activity of intramuscular peramivir in mice infected with a recombinant influenza A/WSN/33 (H1N1) virus containing the H275Y neuraminidase mutation

The therapeutic activity of intramuscular (IM) peramivir was evaluated in mice infected with a recombinant influenza A/WSN/33 virus containing the H275Y neuraminidase (NA) mutation known to confer oseltamivir resistance. Regimens consisted of single (90 mg/kg of body weight) or multiple (45 mg/kg daily for 5 days) IM peramivir doses that were initiated 24 h or 48 h postinfection (p.i.). An oral oseltamivir regimen (1 or 10 mg/kg daily for 5 days) was used for comparison. Untreated animals had a mortality rate of 75% and showed a mean weight loss of 16.9% on day 5 p.i. When started at 24 h p.i., both peramivir regimens prevented mortality and significantly reduced weight loss (P < 0.001) and lung viral titers (LVT) (P < 0.001). A high dose (10 mg/kg) of oseltamivir initiated at 24 h p.i. also prevented mortality and significantly decreased weight loss (P < 0.05) and LVT (P < 0.001) compared to the untreated group results. In contrast, a low dose (1 mg/kg) of oseltamivir did not show any benefits. When started at 48 h p.i., both peramivir regimens prevented mortality and significantly reduced weight loss (P < 0.01) and LVT (P < 0.001) whereas low-dose or high-dose oseltamivir regimens had no effect on mortality rates, body weight loss, and LVT. Our results show that single-dose and multiple-dose IM peramivir regimens retain clinical and virological activities against the A/H1N1 H275Y variant despite some reduction in susceptibility when assessed in vitro using enzymatic assays. IM peramivir could constitute an alternative for treatment of oseltamivir-resistant A/H1N1 infections, although additional studies are warranted to support such a recommendation.