Novel Druggable Hot Spots in Avian Influenza Neuraminidase H5N1 Revealed by Computational Solvent Mapping of a Reduced and Representative Receptor Ensemble

The influenza virus subtype H5N1 has raised concerns of a possible human pandemic threat because of its high virulence and mutation rate. Although several approved anti-influenza drugs effectively target the neuraminidase, some strains have already acquired resistance to the currently available anti-influenza drugs. In this study, we present the synergistic application of extended explicit solvent molecular dynamics (MD) and computational solvent mapping (CS-Map) to identify putative ‘hot spots’ within flexible binding regions of N1 neuraminidase. Using representative conformations of the N1 binding region extracted from a clustering analysis of four concatenated 40-ns MD simulations, CS-Map was utilized to assess the ability of small, solvent-sized molecules to bind within close proximity to the sialic acid binding region. Mapping analyses of the dominant MD conformations reveal the presence of additional hot spot regions in the 150- and 430-loop regions. Our hot spot analysis provides further support for the feasibility of developing high-affinity inhibitors capable of binding these regions, which appear to be unique to the N1 strain

Susceptibility of highly pathogenic H5N1 influenza viruses to the neuraminidase inhibitor oseltamivir differs in vitro and in a mouse model

While the neuraminidase (NA) inhibitor oseltamivir is currently our first line of defense against a pandemic threat, there is little information about whether in vitro testing can predict the in vivo effectiveness of antiviral treatment. Using a panel of five H5N1 influenza viruses (H5 clades 1 and 2), we determined that four viruses were susceptible to the drug in vitro (mean 50% inhibitory concentration [IC50], 0.1 to 4.9 nM), and A/Turkey/65-1242/06 virus was slightly less susceptible (mean IC50, 10.8 nM). Two avian viruses showed significantly greater NA enzymatic activity (Vmax) than the human viruses, and the five viruses varied in their affinity for the NA substrate MUNANA (Km, 64 to 300 μM) and for oseltamivir carboxylate (Ki, 0.1 to 7.9 nM). The protection of mice provided by a standard oseltamivir regimen (20 mg/kg/day for 5 days) also varied among the viruses used. We observed (i) complete protection against the less virulent A/chicken/Jogjakarta/BBVET/IX/04 virus; (ii) moderate protection (60 to 80% survival) against three viruses, two of which are neurotropic; and (iii) no protection against A/Turkey/65-1242/06 virus, which induced high pulmonary expression of proinflammatory mediators (interleukin-1α [IL-1α], IL-6, alpha interferon, and monocyte chemotactic protein 1) and contained a minor subpopulation of drug-resistant clones (I117V and E119A NA mutations). We found no correlation between in vitro susceptibility and in vivo protection (Spearman rank correlation coefficient ρ = -0.1; P > 0.05). Therefore, the in vivo efficacy of oseltamivir against highly pathogenic H5N1 influenza viruses cannot be reliably predicted by susceptibility testing, and more prognostic ways to evaluate anti-influenza compounds must be developed. Multiple viral and host factors modulate the effectiveness of NA inhibitor regimens against such viruses and new, more consistently effective treatment options, including combination therapies, are needed. Copyright © 2009, American Society for Microbiology. All Rights Reserved

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. Copyright © 2007, American Society for Microbiology. All Rights Reserved

Competitive fitness of oseltamivir-sensitive and -resistant highly pathogenic H5N1 influenza viruses in a ferret model

The fitness of oseltamivir-resistant highly pathogenic H5N1 influenza viruses has important clinical implications. We generated recombinant human A/Vietnam/1203/04 (VN; clade 1) and A/Turkey/15/06 (TK; clade 2.2) influenza viruses containing the H274Y neuraminidase (NA) mutation, which confers resistance to NA inhibitors, and compared the fitness levels of the wild-type (WT) and resistant virus pairs in ferrets. The VN-H274Y and VN-WT viruses replicated to similar titers in the upper respiratory tract (URT) and caused comparable disease signs, and none of the animals survived. On days 1 to 3 postinoculation, disease signs caused by oseltamivir-resistant TK-H274Y virus were milder than those caused by TK-WT virus, and all animals survived. We then studied fitness by using a novel approach. We coinoculated ferrets with different ratios of oseltamivir-resistant and -sensitive H5N1 viruses and measured the proportion of clones in day-6 nasal washes that contained the H274Y NA mutation. Although the proportion of VN-H274Y clones increased consistently, that of TK-H274Y virus decreased. Mutations within NA catalytic (R292K) and framework (E119A/K, I222L, H274L, and N294S) sites or near the NA enzyme active site (V116I, I117T/V, Q136H, K150N, and A250T) emerged spontaneously (without drug pressure) in both pairs of viruses. The NA substitutions I254V and E276A could exert a compensatory effect on the fitness of VN-H274Y and TK-H274Y viruses. NA enzymatic function was reduced in both drug-resistant H5N1 viruses. These results show that the H274Y NA mutation affects the fitness of two H5N1 influenza viruses differently. Our novel method of assessing viral fitness accounts for both virus-host interactions and virus-virus interactions within the host. Copyright © 2010, American Society for Microbiology. All Rights Reserved

Intrinsic ferromagnetism in Hg1-xFexSe (0.00012 ≤ x ≤ 0.0013) diluted magnetic semiconductor bulk single crystals at room temperature: Role of hybridization of impurity electronic states

We investigate room-temperature structural properties and spontaneous magnetism in a series of Hg1-xFexSe (0.00012 ≤ x ≤ 0.0013) diluted magnetic semiconductor bulk single crystals grown by the Bridgman method. In order to elucidate the experimentally observed high-temperature magnetism in the studied systems, the dependencies of magnetization on magnetic field strength for the entire sample series were studied. Their detailed analysis revealed impurity contributions typical of ferromagnetic materials, which are described by magnetization curves with the parameters characterizing the spontaneous spin magnetism of the donor conduction electrons of the outer d-shells of the impurity atoms. According to the previously-developed theoretical concept, such a magnetic ordering mechanism stems from the direct exchange coupling of donor conduction electrons due to hybridization of impurity states, rather than from inter-impurity interactions. The results of optical emission spectroscopy and X-ray diffraction analysis confirmed the observed ferromagnetism to be intrinsic and linked directly to the d-electrons of iron impurity atoms

Sialic acid-binding protein Sp2CBMTD protects mice against lethal challenge with emerging influenza A (H7N9) virus

This study was supported by the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Department of Health and Human Services, under contract no. HHSN266200700005C and HHSN272201400006C, by the American Lebanese Syrian Associated Charities (ALSAC), and by the UK Medical Research Council Biomedical Catalyst grant MR/L012847/1.Compounds that target the cellular factors essential for influenza virus replication represent an innovative approach to antiviral therapy. Sp2CBMTD is a genetically engineered multivalent protein that masks sialic acid-containing cellular receptors on the respiratory epithelium, which are recognized by influenza viruses. Here, we evaluated the antiviral potential of Sp2CBMTD against lethal infection in mice with an emerging A/Anhui/1/2013 (H7N9) influenza virus and addressed the mechanistic basis of its activity in vivo. Sp2CBMTD was administered to mice intranasally as a single or repeated dose (0.1, 1, 10, or 100 μg) before (day −7, −3, and/or −1) or after (6 or 24 h) H7N9 virus inoculation. A single Sp2CBMTD dose (10 or 100 μg) protected 80% to 100% of the mice when administered 7 days before the H7N9 lethal challenge. Repeated Sp2CBMTD administration conferred the highest protection, resulting in 100% survival of the mice even at the lowest dose tested (0.1 μg). When treatment began 24 h after exposure to the H7N9 virus, a single administration of 100 μg of Sp2CBMTD protected 40% of the mice from death. The administration of Sp2CBMTD induced the pulmonary expression of proinflammatory mediators (interleukin-6 [IL-6], IL-1β, RANTES, monocyte chemotactic protein-1 [MCP-1], macrophage inflammatory protein-1α [MIP-1α], and inducible protein [IP-10]) and recruited neutrophils to the respiratory tract before H7N9 virus infection, which resulted in less pronounced inflammation and rapid virus clearance from mouse lungs. Sp2CBMTD administration did not affect the virus-specific adaptive immune response, which was sufficient to protect against reinfection with a higher dose of homologous H7N9 virus or heterologous H5N1 virus. Thus, Sp2CBMTD was effective in preventing H7N9 infections in a lethal mouse model and holds promise as a prophylaxis option against zoonotic influenza viruses.PostprintPeer reviewe