Inhibitors Oseltamivir Research Articles

Antiviral Chemistry & Chemotherapy's Current Antiviral Agents FactFile 2008 (2nd Edition): RNA Viruses

Among the RNA viruses, other than the retroviruses (that is, HIV), which are dealt with separately in the current FactFile, the most important targets for the development of antiviral agents at the moment are the orthomyxoviruses (that is, influenza), the hepaciviruses (that is, hepatitis C virus [HCV]) and, to a lesser extent, the picornaviruses. Although the uncoating inhibitors amantadine and rimantadine were the first known inhibitors of influenza A, the neuraminidase inhibitors oseltamivir, zanamivir and peramivir have now become the prime antiviral drugs for the treatment of influenza A and B virus infections. For HCV infections, standard treatment consists of the combination of pegylated interferon-alpha with ribavirin, but several other antivirals targeted at specific viral functions such as the HCV protease and/ or polymerase may be expected to soon take an important share of this important market. Still untapped is the potential of a variety of uncoating inhibitors, as well as protease and/or polymerase inhibitors against the wide spectrum of picornaviruses. While ribavirin has been available for 35 years as a broad-spectrum anti-RNA virus agent, relatively new and unexplored is favipiravir (T-705) accredited with activity against influenza as well as flaviviruses, bunyaviruses and arenaviruses.

Characterization of a trypsin-dependent avian influenza H5N1-pseudotyped HIV vector system for high throughput screening of inhibitory molecules

In this study, we have generated and characterized an avian influenza H5N1 hemagglutinin (HA), neuraminidase (NA) and M2 ion channel pseudotyped HIV-based vector system (HaNaM-pseudotyped HIV vector). The cleavage site of the HA protein was modified to necessitate trypsin-dependent maturation of the glycoprotein. HA, NA and M2 were efficiently incorporated in HIV vector particles which could transduce different cell lines in a trypsin-dependent manner. Results also showed that the presence of avian influenza M2 and NA proteins maximized both vector production and transduction and that transduction was highly sensitive to the specific NA inhibitor oseltamivir (Tamiflu). H5N1 HaNaM-pseudotyped HIV vector system was also adapted for cell-based high throughput screening of drug candidates against influenza virus infection, and its high sensitivity to the specific oseltamivir validates its potential utility in the identification of new influenza inhibitors. Overall, the trypsin-dependent H5N1-pseudotyped HIV vector can mimic avian influenza virus infection processes with sufficient precision to allow for the identification of new antivirals and to study avian influenza virus biology in a lower biosafety level laboratory environment.

Influenza A Virus Neuraminidase Limits Viral Superinfection

Enveloped viruses use multiple mechanisms to inhibit infection of a target cell by more than one virion. These mechanisms may be of particular importance for the evolution of segmented viruses, because superinfection exclusion may limit the frequency of reassortment of viral genes. Here, we show that cellular expression of influenza A virus neuraminidase (NA), but not hemagglutinin (HA) or the M2 proton pump, inhibits entry of HA-pseudotyped retroviruses. Cells infected with H1N1 or H3N2 influenza A virus were similarly refractory to HA-mediated infection and to superinfection with a second influenza A virus. Both HA-mediated entry and viral superinfection were rescued by the neuraminidase inhibitors oseltamivir carboxylate and zanamivir. These inhibitors also prevented the removal of alpha-2,3- and alpha-2,6-linked sialic acid observed in cells expressing NA or infected with influenza A viruses. Our data indicate that NA alone among viral proteins limits influenza A virus superinfection.

Increasing Influenza Virus Resistance to Neuraminidase Inhibitors

Because of high adamantine resistance rates, the neuraminidase inhibitors (NAIs) oseltamivir and zanamivir are the only antivirals recommended by the CDC for treatment and prophylaxis of influenza. Investigators recently reported the results of a surveillance study conducted using 4570 influenza isolates collected globally from October 2004 through …

Effect of a neuraminidase inhibitor (oseltamivir) on mouse jump-down behavior via stimulation of dopamine receptors

Oseltamivir (Tamiflu, Roche Laboratories, Inc.) is a neuraminidase inhibitor that can cause jumpdown behaviors in children. There is a mouse slip-down model, in which the dopamine D2 receptor activity is increased by serum sialoglycolipids and the mouse jump-down behavior appears in response to the dopamine D2 receptor agonist, PPHT. The present study examined the effect of oseltamivir on jump-down behavior in mice. Oseltamivir sialylates a serum glycolipid and this modified glycolipid induces jump-down behavior via the stimulation of dopamine D2 receptors. This mechanism may be involved in the abnormal behavior of children taking oseltamivir.

Desorption electrospray ionization reactions between host crown ethers and the influenza neuraminidase inhibitor oseltamivir for the rapid screening of Tamiflu®

Competitive host-guest chemistry on a desorption electrospray ionization mass spectrometry (DESI MS) platform is presented here as the basis for a rapid and quantitative screening method for assessing the quality of Tamiflu capsules with minimal sample preparation. Oseltamivir, the active ingredient in Tamiflu, is an orally active neuraminidase inhibitor antiviral. The high cost and demand for this drug has made it a target for counterfeiters, and reports of counterfeit Tamiflu capsules have already appeared. This urges the development of rapid and sensitive tools for Tamiflu authentication. The method presented here is based on the selective recognition of oseltamivir by crown ethers added to the DESI spray solvent. Crown ethers with various ring sizes were evaluated, all being observed to form stable host-guest complexes with protonated oseltamivir. The relative gas phase stability of each of the host-guest complexes was assessed and the results compared with dispersion-corrected density functional theory. Competive experiments with various pairs of crown ethers were used to assess the relative binding selectivities for oseltamivir. The abundance ratio of the formed complexes was observed to be dependent on the amount of analyte present on the surface of the sample, and independent of DESI geometric factors. These competitive reactions were then successfully tested as a means for the rapid quantitation of oseltamivir by reactive DESI MS without the need for an internal standard.

Do Antivirals Help Life-Threatening Influenza?

The neuraminidase inhibitor oseltamivir was FDA-approved for treatment of the flu based on studies showing efficacy primarily in healthy young adult outpatients. How well does the drug work for more complicated patients with more severe infection? In an industry-supported trial, Canadian researchers prospectively followed …

M2 Protein-A Proton Channel of Influenza A Virus

Recent outbreaks of highly pathogenic avian influenza A virus infections (H5 and H7 subtypes) in poultry and humans have raised concerns that a new influenza pandemic will occur in near future. Currently, four antivirals have proven efficacy in the treatment and prophylaxis of influenza A infections: two M2 inhibitors (amantadine and rimantadine) and two neuraminidase inhibitors (zanamivir and oseltamivir). Early treatment with antivirals reduces the duration of symptoms and the time to recovery by one to two days. However, when antivirals are used for the treatment the antiviral resistance develops rapidly, limiting their use. There is an urgent need for research on newer antiviral agents and "universal" vaccine against influenza virus. The M2 protein from the influenza A virus forms a proton channel in the virion and is essential for infection. As a relatively conserved protein, the M2 protein seems to be a suitable candidate for development of a new generation of vaccine or antiviral agents. This review describes the role of the M2 ion channel in virus replication and the structure-function relationship of the channel.

Synthesis of Tamiflu and its Phosphonate Congeners Possessing Potent Anti-Influenza Activity

Using d-xylose as an appropriate chiral precursor, we have synthesized active neuraminidase inhibitor oseltamivir, antiflu drug Tamiflu, and novel phosphonate congeners that exhibit even stronger antiflu activities by inhibiting the neuraminidases of the wild-type and H274Y mutant of H1N1 and H5N1 viruses. Molecular modeling of the neuraminidase−phosphonate complex indicates a pertinent binding mode of the phosphonate with three arginine residues in the active site. Discovery of such potent neuraminidase inhibitors will offer an opportunity to the development of new anti-influenza drugs.

Activity of the neuraminidase inhibitor A-315675 against oseltamivir-resistant influenza neuraminidases of N1 and N2 subtypes

Clinical use of the neuraminidase inhibitor (NAI) oseltamivir has been associated with the emergence of viral resistance resulting from subtype-specific neuraminidase (NA) mutations. In this study, we evaluated the impact of the most frequent oseltamivir-resistant NA mutations including E119V, H274Y, R292K and N294S on the susceptibility profile to a novel NAI (A-315675) using recombinant NA proteins of N1 and N2 subtypes and also selected oseltamivir-resistant influenza H1N1 and H3N2 viruses. In the N1 subtype, recombinant NA proteins containing mutations H274Y and N294S previously associated with resistance to oseltamivir (754- and 197-fold increases in IC(50) values, respectively, compared to WT) remained susceptible to A-315675 (2.5- and 2-fold increases in IC(50) values(,) respectively). In the N2 subtype, NA proteins harboring mutations E119V and R292K conferring high levels of resistance to oseltamivir (1016- and >10,000-fold increases in IC(50) values, respectively) had IC(50) values that increased by only 1.5- and 13-fold, respectively, against A-315675. Similar susceptibility patterns to A-315675 were obtained when testing recombinant H1N1 mutant viruses (H274Y and N294S) and clinical H3N2 mutants (E119V). The V116A and I117V mutations, previously associated with oseltamivir resistance in H5N1 viruses, were susceptible to oseltamivir when tested in the H1N1 background suggesting a strain-specific impact of these mutations. These results confirm the potent inhibitory effect of A-315675 against oseltamivir-resistant influenza viruses of the N1 and N2 subtypes and support the clinical development of its bioavailable prodrug A-322278.

Biological evaluation of anti-influenza viral activity of semi-synthetic catechin derivatives

Catechin derivatives with different alkyl chain length and aromatic ring substitutions at the 3-hydroxyl group were synthesized from epigallocatechin (EGC) and (+)-catechin (C) and their anti-influenza viral activity were evaluated in vitro and in ovo. Pronounced antiviral activity was observed for derivatives carrying moderate chain length (7–9 carbons) as compared to those with aromatic rings, whereas the 5′-hydroxyl group of the trihydroxy benzyl moiety did not significantly contribute to antiviral activity. The derivatives exerted inhibitory effects for all six influenza subtypes tested including three major types of currently circulating human influenza viruses (A/H1N1, A/H3N2 and B type), H2N2 and H9N2 avian influenza virus. The compounds strongly inhibited adsorption of the viruses on red blood cell (RBC). They also restricted the growth of avian influenza virus in ovo with minimum inhibition concentration (MIC) of 5–10 μM far exceeding the neuraminidase (NA) inhibitor oseltamivir or M2 proton channel inhibitor amantadine. The antiviral activity appears to be mediated by interaction with hemagglutinin (HA)/viral membrane rendering HA less fusogenic at the initial stage of infection. The broad spectrum activity against various subtypes of influenza viruses may complement the limitations of current antivirals and contribute for managing potentially emerging influenza pandemic. The structure-activity data of catechin derivatives may usefully guideline future research endeavors for applying green tea catechins as alternative anti-viral agents.

The critically ill avian influenza A (H5N1) patient*

This review examines perspectives of human infection with avian influenza A H5N1 (AI H5N1), specifically focusing on the presentation, diagnosis, and management of those critically ill with AI H5N1. PubMed (1966-2006), PubMed "related articles," publications and Web sites of the World Health Organization and the Centers for Disease Control and Prevention, personal files, abstract proceedings, and reference lists. We reviewed English-language publications pertaining to clinical presentation, diagnosis, and management of AI H5N1 and infection control expressly relating to the intensive care setting. The majority of reported patients with AI H5N1 are critically ill and require intensive care management. These patients progress rapidly to severe acute respiratory distress syndrome. Multiorgan failure occurs in a large proportion. Because of the nonspecific clinical, laboratory, and radiologic features, it is critical to seek a history of exposure to poultry or wild birds in suspected cases. Reverse transcription polymerase chain reaction performed on nasopharyngeal aspirate is the most reliable method for the laboratory diagnosis of AI H5N1. Treatment includes starting neuraminidase inhibitor oseltamivir as early as possible in addition to the standard supportive management. Aerosol generating procedures should be minimized to avoid nosocomial transmission. Strict infection control procedures are paramount to staff safety, although human-to-human transmission is rare as of this time. Many patients with AI H5N1 are critically ill either at presentation or shortly thereafter. Intensivists and intensive care units are therefore at the front line for this new cause of severe lung injury. Practitioners must be familiar with the nonspecific presentation of AI H5N1 and its diagnostic and therapeutic options. Although treating the infected patient with AI H5N1 is a priority, safeguarding healthcare workers and other patients must be considered of equal priority.

Graphical Representation and Numerical Characterization of H5N1 Avian Flu Neuraminidase Gene Sequence

The high degree of virulence and potential for development of a pandemic strain of the H5N1 avian flu has resulted in wide interest in characterization of the various genes of the H5N1 virus genome. We have considered for our analysis all 173 available complete sequences, as of February 2006, of the neuraminidase gene, which is the target of the most effective treatment regimen comprising the inhibitors oseltamivir and zanamivir. We have used a 2D graphical representation of the neuraminidase RNA sequences of H5N1 strains to identify a few distinct structural motifs. The H5N1 strains were split into two main classes: strains that were benign to human beings in the years up to 1996 and the period 1999-2002 and strains that were highly pathogenic to humans in the periods 1997 and 2003 to present. Comparisons with earlier H1N1 pandemic and epidemic strains have also been made to understand the current status of the gene. Our findings indicate that the base composition and distribution patterns are significantly different in the two periods, and this may be of interest in studying mutational changes in such viral genes.

Influenza antiviral susceptibility monitoring activities in relation to national antiviral stockpiles in Europe during the winter 2006/2007 season

Due to the influenza pandemic threat, many countries are stockpiling antivirals in the hope of limiting the impact of a future pandemic virus. Since resistance to antiviral drugs would probably significantly alter the effectiveness of antivirals, surveillance programmes to monitor the emergence of resistance are of considerable importance. During the 2006/2007 influenza season, an inventory was conducted by the European Surveillance Network for Vigilance against Viral Resistance (VIRGIL) in collaboration with the European Influenza Surveillance Scheme (EISS) to evaluate antiviral susceptibility testing by the National Influenza Reference Laboratories (NIRL) in relation to the national antiviral stockpile in 30 European countries that are members of EISS. All countries except Ukraine had a stockpile of the neuraminidase inhibitor (NAI) oseltamivir. Additionally, four countries had a stockpile of the NAI zanamivir and three of the M2 ion channel inhibitor rimantadine. Of 29 countries with a NAI stockpile, six countries'; NIRLs could determine virus susceptibility by 50% inhibitory concentration (IC50) and in 13 countries it could be done by sequencing. Only in one of the three countries with a rimantadine stockpile could the NIRL determine virus susceptibility, by sequencing only. However, including the 18 countries that had plans to introduce or extend antiviral susceptibility testing, the NIRLs of 21 of the 29 countries with a stockpile would be capable of susceptibility testing appropriate to the stockpiled drug by the end of the 2007/2008 influenza season. Although most European countries in this study have stockpiles of influenza antivirals, susceptibility surveillance capability by the NIRLs appropriate to the stockpiled antivirals is limited.

Antiviral Therapy and Prophylaxis for Influenza in Children

Antiviral agents are available that are safe and effective for the treatment and prophylaxis of influenza virus infections in children. The neuraminidase inhibitors (oseltamivir [Tamiflu] and zanamivir [Relenza]) are preferred agents because of current widespread resistance to the adamantanes (amantadine [Symmetrel] and rimantadine [Flumadine]). Therapy should be provided to children with influenza infection who are at high risk of severe infection and to children with moderate-to-severe influenza infection who may benefit from a decrease in the duration of symptoms. Prophylaxis should be provided (1) to high-risk children who have not yet received immunization and during the 2 weeks after immunization, (2) to unimmunized family members and health care professionals with close contact with high-risk unimmunized children or infants who are younger than 6 months, and (3) for control of influenza outbreaks in unimmunized staff and children in an institutional setting. Testing of current H5N1 avian influenza virus isolates, the potential agents of pandemic influenza, suggests susceptibility to oseltamivir and zanamivir. Because no prospective data exist on the efficacy of these agents in humans for H5N1 strains, the dosage and duration of therapy in adults and children may differ from those documented to be effective for epidemic influenza strains.

Cutting Edge: Oseltamivir Decreases T Cell GM1 Expression and Inhibits Clearance of Respiratory Syncytial Virus: Potential Role of Endogenous Sialidase in Antiviral Immunity

The sialoglycosphingolipid GM1 is important for lipid rafts and immune cell signaling. T cell activation in vitro increases GM1 expression and increases endogenous sialidase activity. GM1 expression has been hypothesized to be regulated by endogenous sialidase. We tested this hypothesis in vivo using a mouse model of respiratory syncytial virus (RSV) infection. RSV infection increased endogenous sialidase activity in lung mononuclear cells. RSV infection increased lung CD8+ T cell surface GM1 expression. Activated CD8+ T cells in the lungs of RSV-infected mice were GM1(high). Treatment of RSV-infected mice with the sialidase/neuraminidase inhibitor oseltamivir decreased T cell surface GM1 levels. Oseltamivir treatment decreased RSV-induced weight loss and inhibited RSV clearance. Our data indicate a novel role for an endogenous sialidase in regulating T cell GM1 expression and antiviral immunity. Also, oseltamivir, an important anti-influenza drug, inhibits the clearance of a respiratory virus that lacks a neuraminidase gene, RSV.

Efficacy of Oseltamivir Therapy in Ferrets Inoculated with Different Clades of H5N1 Influenza Virus

Highly pathogenic H5N1 influenza viruses have infected an increasing number of humans in Asia, with high mortality rates and the emergence of multiple distinguishable clades. It is not known whether antiviral drugs that are effective against contemporary human influenza viruses will be effective against systemically replicating viruses, such as these pathogens. Therefore, we evaluated the use of the neuraminidase (NA) inhibitor oseltamivir for early postexposure prophylaxis and for treatment in ferrets exposed to representatives of two clades of H5N1 virus with markedly different pathogenicities in ferrets. Ferrets were protected from lethal infection with the A/Vietnam/1203/04 (H5N1) virus by oseltamivir (5 mg/kg of body weight/day) given 4 h after virus inoculation, but higher daily doses (25 mg/kg) were required for treatment when it was initiated 24 h after virus inoculation. For the treatment of ferrets inoculated with the less pathogenic A/Turkey/15/06 (H5N1) virus, 10 mg/kg/day of oseltamivir was sufficient to reduce the lethargy of the animals, significantly inhibit inflammation in the upper respiratory tract, and block virus spread to the internal organs. Importantly, all ferrets that survived the initial infection were rechallenged with homologous virus after 21 days and were completely protected from infection. Direct sequencing of the NA or HA1 gene segments in viruses isolated from ferret after treatment showed no amino acid substitutions known to cause drug resistance in conserved residues. Thus, early oseltamivir treatment is crucial for protection against highly pathogenic H5N1 viruses and the higher dose may be needed for the treatment of more virulent viruses.

Design, synthesis, inhibitory activity, and SAR studies of pyrrolidine derivatives as neuraminidase inhibitors

A series of pyrrolidine derivatives were synthesized and evaluated for their ability to inhibit neuraminidase (NA) of influenza A virus (H3N2). All compounds were synthesized in good yields starting from commercially 4-hydroxy- l-proline using a suitable synthetic strategy. These compounds showed potent inhibitory activity against influenza A neuraminidase. Within this series, five compounds, 6e, 9c, 9e, 9f, and 10e, have good potency (IC 50 = 1.56–2.71 μM) which are compared to that the NA inhibitor Oseltamivir (IC 50 = 1.06 μM), and could be used as lead compoundS in the future.

Partial Resistance of Influenza B to Neuraminidase Inhibitors

Resistance of influenza A to neuraminidase inhibitors (oseltamivir and zanamivir) has been reported, but the prevalence of influenza B resistance is unknown, as is the potential transmissibility of resistant strains. Researchers used viral isolates from a 2004–2005 …

Questionnaire Survey on Efficacy and Safety of the Oral Neuraminidase Inhibitor Oseltamivir (Tamiflu) in Treatment of Influenza (2006 flu Season)

Oseltamivir (Tamiflu®),an oral neuraminidase inhibitor,has recently become the most common treatment for influenza in Japan.In the present study,we conducted a questionnaire survey to evaluate efficacy,adverse events and compliance in outpatients prescribed oseltamivir at the University of Fukui hospital during the period January to April 2006.The questionnaire was given to 221 patients,of whom 96 (43.4%) provided responses.The results obtained showed that 78 patients (81.3%) had influenza A and none had influenza B.Of the total 96 patients,29 (30.2%) were less than 10 years old and 29 (30.2%) were teenagers.Oseltamivir alleviated the fever of 79 of the patients (82.3%) within two days.Though almost all prescriptions for oseltamivir in our hospital were for five days,only 45.8 % of the patients replied that they took the drug for the full five days.Adverse events were reported by 24 patients (25.0 %).The most common were digestive system-related.Five patients (5.2%) reported neuropsychiatric symptoms which included hallucination and abnormal behavior.The results of our study showed that oseltamivir was effective in the treatment of influenza A,and suggested that some patients discontinue the regimen before completion.As it was a small scale study,further investigation will be needed in order to provide patients with adequate information on the proper use of oseltamivir.