In Silico Design of an Oseltamivir Derivative with Increased Affinity against Wild-Type and Mutant Variants of Neuraminidase and Hemagglutinin of Influenza A H1N1 Virus

Antiviral resistance has turned into a world concern nowadays. Influenza A H1N1 emerged as a problem at the world level due to the neuraminidase (NA) mutations. The NA mutants conferred resistance to oseltamivir and zanamivir. Several efforts were conducted to develop better anti-influenza A H1N1 drugs. Our research group combined in silico methods to create a compound derived from oseltamivir to be tested in vitro against influenza A H1N1. Here we show the results of a new compound derived from oseltamivir but with specific chemical modifications, with significant affinity either on NA (in silico and in vitro assays) or HA (in silico) from influenza A H1N1 strain. We include docking and molecular dynamics (MD) simulations of the oseltamivir derivative at the binding site onto NA and HA of influenza A H1N1. Additionally, the biological experimental results show that oseltamivir derivative decreases the lytic-plaque formation on viral susceptibility assays, and it does not show cytotoxicity. Finally, oseltamivir derivative assayed on viral NA showed a concentration-dependent inhibition behavior at nM, depicting a high affinity of the compound for the enzyme, corroborated with the MD simulations results, placing our designed oseltamivir derivative as a potential antiviral against influenza A H1N1.     

Coadministration of Hedera helix L. Extract Enabled Mice to Overcome Insufficient Protection against Influenza A/PR/8 Virus Infection under Suboptimal Treatment with Oseltamivir

Several anti-influenza drugs that reduce disease manifestation exist, and although these drugs provide clinical benefits in infected patients, their efficacy is limited by the emergence of drug-resistant influenza viruses. In the current study, we assessed the therapeutic strategy of enhancing the antiviral efficacy of an existing neuraminidase inhibitor, oseltamivir, by coadministering with the leaf extract from Hedera helix L, commonly known as ivy. Ivy extract has anti-inflammatory, antibacterial, antifungal, and antihelminthic properties. In the present study, we investigated its potential antiviral properties against influenza A/PR/8 (PR8) virus in a mouse model with suboptimal oseltamivir that mimics a poor clinical response to antiviral drug treatment. Suboptimal oseltamivir resulted in insufficient protection against PR8 infection. Oral administration of ivy extract with suboptimal oseltamivir increased the antiviral activity of oseltamivir. Ivy extract and its compounds, particularly hedrasaponin F, significantly reduced the cytopathic effect in PR8-infected A549 cells in the presence of oseltamivir. Compared with oseltamivir treatment alone, coadministration of the fraction of ivy extract that contained the highest proportion of hedrasaponin F with oseltamivir decreased pulmonary inflammation in PR8-infected mice. Inflammatory cytokines and chemokines, including tumor necrosis factor-alpha and chemokine (C-C motif) ligand 2, were reduced by treatment with oseltamivir and the fraction of ivy extract. Analysis of inflammatory cell infiltration in the bronchial alveolar of PR8-infected mice revealed that CD11b⁺Ly6G⁺ and CD11b⁺Ly6C^int cells were recruited after virus infection; coadministration of the ivy extract fraction with oseltamivir reduced infiltration of these inflammatory cells. In a model of suboptimal oseltamivir treatment, coadministration of ivy extract fraction that includes hedrasaponin F increased protection against PR8 infection that could be explained by its antiviral and anti-inflammatory activities.     

Combating influenza: natural products as neuraminidase inhibitors

The ever increasing threat of influenza pandemic outbreaks represents a serious concern for public health. Various therapeutic and prophylactic means are available which helps to counter viral infections including vaccines and curative such as zanamivir and oseltamivir. However, with the inception of unfamiliar strains which show resistance to the available drugs manifests the rapid demand for discovery of rational drug as antiviral agents. Neuraminidase, a crucial enzyme for viral replication is the most promising target for new drugs because of its highly conserved residues. Nature provides with a myriad of natural bioactive compounds constituting a plethora of chemical entities that can be useful in drug discovery against influenza. This review is an update on neuraminidase enzyme highlighting its structure, function, catalytic mechanism and its inhibition by natural products. Various approved neuraminidase inhibitors and neuraminidase inhibition assays along with their susceptibility have been described. A discussion on published reports about 267 plant secondary metabolites tested in the past 7 years (2011–2017) for their neuraminidase inhibition activity is presented. Moreover, the recent techniques using QSAR to develop third generation neuraminidase inhibitors have been described. This work summarizes the recent development in experimental and theoretical research based on neuraminidase inhibitors that will help in the discovery of antiviral agents in coming future.

     

Source of oseltamivir resistance in avian influenza H5N1 virus with the H274Y mutation

Molecular dynamics simulations were carried out for the mutant oseltamivir-NA complex, to provide detailed information on the oseltamivir-resistance resulting from the H274Y mutation in neuraminidase (NA) of avian influenza H5N1 viruses. In contrast with a previous proposal, the H274Y mutation does not prevent E276 and R224 from forming the hydrophobic pocket for the oseltamivir bulky group. Instead, reduction of the hydrophobicity and size of pocket in the area around an ethyl moiety at this bulky group were found to be the source of the oseltamivir-resistance. These changes were primarily due to the dramatic rotation of the hydrophilic –COO⁻ group of E276 toward the ethyl moiety. In addition, hydrogen-bonding interactions with N1 residues at the -NH₃ ⁺ and -NHAc groups of oseltamivir were replaced by a water molecule. The calculated binding affinity of oseltamivir to NA was significantly reduced from −14.6 kcal mol⁻¹ in the wild-type to −9.9 kcal mol⁻¹ in the mutant-type.     

Triple Combination of Amantadine,Ribavirin, and Oseltamivir Is Highly Active and Synergistic against Drug Resistant Influenza Virus Strains In Vitro

The rapid emergence and subsequent spread of the novel 2009 Influenza A/H1N1 virus (2009 H1N1) has prompted the World Health Organization to declare the first pandemic of the 21^st century, highlighting the threat of influenza to public health and healthcare systems. Widespread resistance to both classes of influenza antivirals (adamantanes and neuraminidase inhibitors) occurs in both pandemic and seasonal viruses, rendering these drugs to be of marginal utility in the treatment modality. Worldwide, virtually all 2009 H1N1 and seasonal H3N2 strains are resistant to the adamantanes (rimantadine and amantadine), and the majority of seasonal H1N1 strains are resistant to oseltamivir, the most widely prescribed neuraminidase inhibitor (NAI). To address the need for more effective therapy, we evaluated the in vitro activity of a triple combination antiviral drug (TCAD) regimen composed of drugs with different mechanisms of action against drug-resistant seasonal and 2009 H1N1 influenza viruses. Amantadine, ribavirin, and oseltamivir, alone and in combination, were tested against amantadine- and oseltamivir-resistant influenza A viruses using an in vitro infection model in MDCK cells. Our data show that the triple combination was highly synergistic against drug-resistant viruses, and the synergy of the triple combination was significantly greater than the synergy of any double combination tested (P<0.05), including the combination of two NAIs. Surprisingly, amantadine and oseltamivir contributed to the antiviral activity of the TCAD regimen against amantadine- and oseltamivir-resistant viruses, respectively, at concentrations where they had no activity as single agents, and at concentrations that were clinically achievable. Our data demonstrate that the TCAD regimen composed of amantadine, ribavirin, and oseltamivir is highly synergistic against resistant viruses, including 2009 H1N1. The TCAD regimen overcomes baseline drug resistance to both classes of approved influenza antivirals, and thus may represent a highly active antiviral therapy for seasonal and pandemic influenza.     

Mapping the sequence mutations of the 2009 H1N1 influenza A virus neuraminidase relative to drug and antibody binding sites

 

In this work, we study the consequences of sequence variations of the "2009 H1N1" (swine or Mexican flu) influenza A virus strain neuraminidase for drug treatment and vaccination. We find that it is phylogenetically more closely related to European H1N1 swine flu and H5N1 avian flu rather than to the H1N1 counterparts in the Americas. Homology-based 3D structure modeling reveals that the novel mutations are preferentially located at the protein surface and do not interfere with the active site. The latter is the binding cavity for 3 currently used neuraminidase inhibitors: oseltamivir (Tamiflu^®), zanamivir (Relenza^®) and peramivir; thus, the drugs should remain effective for treatment. However, the antigenic regions of the neuraminidase relevant for vaccine development, serological typing and passive antibody treatment can differ from those of previous strains and already vary among patients.

Reviewers

This article was reviewed by Sandor Pongor and L. Aravind.     

Synergistic effects in the designs of neuraminidase ligands: Analysis from docking and molecular dynamics studies

Docking and molecular dynamics were used to study the nine ligands (see Scheme 1) at the neuraminidase (NA) active sites. Their binding modes are structurally and energetically different, with details given in the text. Compared with 1A (oseltamivir carboxylate), the changes of core template or/and functional groups in the other ligands cause the reductions of interaction energies and numbers of H-bonds with the NA proteins. Nonetheless, all these ligands occupy the proximity space at the NA active sites and share some commonness in their binding modes. The fragment approach was then used to analyze and understand the binding specificities of the nine ligands. The contributions of each core template and functional group were evaluated. It was found that the core templates rather than functional groups play a larger role during the binding processes; in addition, the binding qualities are determined by the synergistic effects of the core templates and functional groups. Among the nine ligands, 1A (oseltamivir carboxylate) has the largest synergistic energy and its functional groups fit perfectly with the NA active site, consistent with the largest interaction energy, numerous H-bonds with the NA active-site residues as well as experimentally lowest IC₅₀ value. Owing to the poorer metabolizability than oseltamivir, large contribution of the benzene core template and fine synergistic effects of the functional groups, the 4-(N-acetylamino)-5-guanidino-3-(3-pentyloxy)benzoic acid should be an ideal lead compound for optimizing NA drugs.     

Computational study on new natural polycyclic compounds of H1N1 influenza virus neuraminidase

A new strain of influenza A (H1N1) virus is a major cause of morbidity and mortality around the world. The neuraminidase of the influenza virus has been the most potential target for the anti-influenza drugs such as oseltamivir and zanamivir. However, the emergence of drug-resistant variants of these drugs makes a pressing need for the development of new neuraminidase inhibitors for controlling illness and transmission. Here a 3D structure model of H1N1 avian influenza virus neuraminidase type 1 (N1) was constructed based on the structure of the template H5N1 avian influenza virus N1. Upon application of virtual screening technique for N1 inhibitors, two novel compounds (ZINC database ID: ZINC02128091, ZINC02098378) were found as the most favorable interaction energy with N1. Docking results showed that the compounds bound not only in the active pocket, but also in a new hydrophobic cave which contains Arg368, Trp399, Ile427, Pro431 and Lys432 of N1. Our result suggested that both of the screened compounds containing the hydrophobic group bring a strong conjugation effect with Arg293, Arg368 Lys432 of N1 by pi-pi interaction. However, the control inhibitors zanamivir and oseltamivir do not have this effect. The details of N1-compound binding structure obtained will be valuable for the development of a new anti-influenza virus agent.     

Design,synthesis, and neuraminidase inhibitory activity of GS-4071 analogues that utilize a novel hydrophobic paradigm

Structure-based design has led to the synthesis of a novel analogue of GS-4071, an influenza neuraminidase inhibitor, in which the basic amino group has been replaced by a hydrophobic vinyl group. An X-ray co-crystal structure of the new inhibitor (K(i)=45 nM) bound to the active site shows that the vinyl group occupies the same subsite as the amino group in GS-4071.     

Design,synthesis, and evaluation of carboxyl-modified oseltamivir derivatives with improved lipophilicity as neuraminidase inhibitors

In this study, a series of carboxyl-modified oseltamivir analogs with improved lipophilicity were designed and synthesized, and their inhibitory activities against neuraminidase from influenza A virus H5N1 subtype were evaluated. The results demonstrated that compound 5m exhibited potent inhibitory activity (IC₅₀?=?1.30?±?0.23?μM), and it targeted the recently discovered 430-cavity. Compound 5m (Log D?=??0.12) is more lipophilic than oseltamivir carboxylate (Log D?=??1.69) at pH 7.4, which is potentially propitious to improved membrane permeability and oral drug absorption. Meanwhile, 5m showed high stability in human liver microsomes. The findings of this study can be valuable in identifying neuraminidase inhibitors with optimal lipophilicity and in the exploration of 430-cavity.     

Insights from investigating the interaction of oseltamivir (Tamiflu) with neuraminidase of the 2009 H1N1 swine flu virus

The neuraminidase (NA) of influenza virus is the target of anti-flu drugs oseltamivir and zanamivir. Clinical practices showed that oseltamivir was effective to treat the 2009-H1N1 influenza but failed to the 2006-H5N1 avian influenza. To perform an in-depth analysis on such a drug-resistance problem, the 2009-H1N1-NA structure was developed. To compare it with the crystal 2006-H5N1-NA structure as well as the 1918 influenza virus H1N1-NA structure, the multiple sequential and structural alignments were performed. It has been revealed that the hydrophobic residue Try347 in H5N1-NA does not match with the hydrophilic carboxyl group of oseltamivir as in the case of H1N1-NA. This may be the reason why H5N1 avian influenza virus is drug-resistant to oseltamivir. The finding provides useful insights for how to modify the existing drugs, such as oseltamivir and zanamivir, making them not only become more effective against H1N1 virus but also effective against H5N1 virus.     

Molecular prediction of oseltamivir efficiency against probable influenza A (H1N1-2009) mutants: molecular modeling approach

To predict the susceptibility of the probable 2009 influenza A (H1N1-2009) mutant strains to oseltamivir, MD/LIE approach was applied to oseltamivir complexed with the most frequent drug-resistant strains of neuraminidase subtypes N1 and N2: two mutations on the framework residues (N294S and H274Y) and the two others on the direct-binding residues (E119V and R292K) of oseltamivir. Relative to those of the wild type (WT), loss of drug–target interaction energies, especially in terms of electrostatic contributions and hydrogen bonds were dominantly established in the E119V and R292K mutated systems. The inhibitory potencies of oseltamivir towards the WT and mutants were predicted according to the ordering of binding-free energies: WT (−12.3 kcal mol⁻¹) > N294S (−10.4 kcal mol⁻¹) > H274Y (−9.8 kcal mol⁻¹) > E119 V (−9.3 kcal mol⁻¹) > R292K (−7.7 kcal mol⁻¹), suggesting that the H1N1-2009 influenza with R292K substitution, perhaps, conferred a high level of oseltamivir resistance, while the other mutants revealed moderate resistance levels. This result calls for an urgent need to develop new potent anti-influenza agents against the next pandemic of potentially higher oseltamivir-resistant H1N1-2009 influenza.     

Structure,molecular genetics,and evolution of vacuolar H+-ATPases

Proton-ATPases can be divided into three classes denoted as P-, F-, and V-ATPases. The P-ATPases are evolutionarily distinct from the F- and V-type ATPases which have been shown to be related, probably evolved from a common ancestral enzyme. Like F-ATPases, V-ATPases are composed of two distinct structures: a catalytic sector that is hydrophilic in nature and a hydrophobic membrane sector which functions in proton conduction. Recent studies on the molecular biology of vacuolar H⁺-ATPases revealed surprising findings about the evolution of pronon pumps as well as important clues for the evolution of eukaryotic cells.     

Synthesis,spectroscopic characterization,molecular docking and theoretical studies (DFT) of N-(4-aminophenylsulfonyl)-2-(4-isobutylphenyl) propanamide having potential enzyme inhibition applications

A mutual prodrug (1) of ibuprofen and sulphanilamide has been synthesized with dual activity and improved toxicity profile. The synthesized compound has been characterized by elemental analysis, FT-IR, ¹HNMR, ¹³CNMR and ESI-MS. The molecular geometry of the compound (1) was optimized using density functional theory (DFT/B3LYP) method with the 6-311G(d,p) basis sets in ground state. Geometric parameters (bond lengths, bond angles, torsion angles), vibrational assignments, chemical shifts and thermodynamics of the compound (1) has been calculated theoretically and compared with the experimental data. Comparative AutoDock study of compound (1) with cyclooxygenase enzymes (COX-1 and COX-2) were performed involving docking for possible selectivity of our prodrug within the two Cox enzymes. The highest binding affinities of −8.7 Kcal/mol and −8.1 Kcal/mol has been obtained for COX-1 and COX-2 enzymes respectively. Compound (1) exhibited enhanced anti-inflammatory, anti-ulcer and free radical scavenging activities as compared with the parent drugs. Based on various in vitro and in vivo tests it is suggested that the Compound (1) is more active than the parent drugs. Moreover, LD₅₀ of compound (1) is higher than parent drug i.e. ibuprofen and sulphanilamide suggesting that the synthesized compound is much safer than its parent analogous.     

Bacillus licheniformis 749-C plasma membrane penicillinase, a hydrophobic polar protein

Plasma membrane penicillinase from Bacillus licheniformis 749/C is hydrophobic in nature, although it is virtually identical to its riydrophilic exoenzyme counterpart in amino acid composition and sequence. Unlike the exoenzyme, however, the purified membrane enzyme retains [³³P]phosphate and [³H]glycerol. By isoelectricfocusing the membrane enzyme is more acidic than the exoenzyme; it has a lower mobility in SDS gel electrophoresis, consistent with the presence of a very hydrophobic moiety. Unlike the exoenzyme, which binds no taurodeoxycholate, the membrane enzyme binds 10 molecules tightly and approximately 37 molecules in the presence of excess taurodeoxycholate (0.1% solution). The membrane enzyme is identical to the exoenzyme in its reaction with antibodies to exopenicillinase as determined by a radioimmune inhibition assay and immunodiffusion in agar. Heat stability studies indicate a slightly less stable conformation for the membrane enzyme, but this difference largely disappears in the presence of antibody to the exoenzyme. Conversion of membrane enzyme to exoenzyme has been achieved by brief treatment with trypsin, or by incubation of impure preparations at pH 9.0 in 25% potassium phosphate.Since the two forms of penicillinase are very similar in conformation, the hydrophobicity of the membrane form of the enzyme would seem to derive from combination with a hydrophobic moiety, probably phospholipid.     

Neuraminidase inhibitor R-125489--a promising drug for treating influenza virus: steered molecular dynamics approach

Two neuraminidase inhibitors, oseltamivir and zanamivir, are important drug treatments for influenza. Oseltamivir-resistant mutants of the influenza virus A/H1N1 and A/H5N1 have emerged, necessitating the development of new long-acting antiviral agents. One such agent is a new neuraminidase inhibitor R-125489 and its prodrug CS-8958. An atomic level understanding of the nature of this antiviral agents binding is still missing. We address this gap in our knowledge by applying steered molecular dynamics (SMD) simulations to different subtypes of seasonal and highly pathogenic influenza viruses. We show that, in agreement with experiments, R-125489 binds to neuraminidase more tightly than CS-8958. Based on results obtained by SMD and the molecular mechanics-Poisson–Boltzmann surface area method, we predict that R-125489 can be used to treat not only wild-type but also tamiflu-resistant N294S, H274Y variants of A/H5N1 virus as its binding affinity does not vary much across these systems. The high correlation level between theoretically determined rupture forces and experimental data on binding energies for the large number of systems studied here implies that SMD is a promising tool for drug design.     

Enteric absorption and pharmacokinetics of oseltamivir in critically ill patients with pandemic (H1N1) influenza

Background

Whether the enteric absorption of the neuraminidase inhibitor oseltamivir is impaired in critically ill patients is unknown. We documented the pharmacokinetic profile of oseltamivir in patients admitted to intensive care units (ICUs) with suspected or confirmed pandemic (H1N1) influenza.

Methods

We included 41 patients 18 years of age and older with suspected or confirmed pandemic (H1N1) influenza who were admitted for ventilatory support to nine ICUs in three cities in Canada and Spain. Using tandem mass spectrometry, we assessed plasma levels of oseltamivir free base and its active metabolite carboxylate at baseline (before gastric administration of the drug) and at 2, 4, 6, 9 and 12 hours after the fourth or later dose.

Results

Among the 36 patients who did not require dialysis, the median concentration of oseltamivir free base was 10.4 (interquartile range [IQR] 4.8–14.9) μg/L; the median concentration of the carboxylate metabolite was 404 (IQR 257–900) μg/L. The volume of distribution of the carboxylate metabolite did not increase with increasing body weight (R² = 0.00, p = 0.87). The rate of elimination of oseltamivir carboxylate was modestly correlated with estimations of creatinine clearance (R² = 0.27, p < 0.001). Drug clearance in the five patients who required continuous renal replacement therapy was about one-sixth that in the 36 patients with relatively normal renal function.

Interpretation

Oseltamivir was well absorbed enterically in critically ill patients admitted to the ICU with suspected or confirmed pandemic (H1N1) influenza. The dosage of 75 mg twice daily achieved plasma levels that were comparable to those in ambulatory patients and were far in excess of concentrations required to maximally inhibit neuraminidase activity of the virus. Adjustment of the dosage in patients with renal dysfunction requiring continuous renal replacement therapy is appropriate; adjustment for obesity does not appear to be necessary.A substantial number of cases of pandemic (H1N1) influenza have involved young adults and adolescents without serious comorbidities who present with severe viral pneumonia complicated by acute respiratory distress syndrome, rhabdomyolysis, renal failure and, occasionally, shock.^1,2 Antiviral therapy in such critically ill patients typically requires oral or nasogastric administration of the neuraminidase inhibitor oseltamivir. Current guidelines from the World Health Organization for the pharmacologic management of progressive or severe pandemic (H1N1) influenza recommend the consideration of high-dose therapy (≥ 150 mg twice daily).^3,4 Critically ill patients exhibit defects in gastrointestinal absorption because of impaired gut perfusion, edema of the bowel wall and ileus as a consequence of critical illness and shock.⁵ Whether the enteric absorption of oseltamivir is impaired in such patients is unknown.We undertook this study to document the pharmacokinetic profile of oseltamivir administered orally or by nasogastric tube in patients admitted to intensive care units (ICUs) with respiratory failure due to suspected or confirmed pandemic (H1N1) influenza.     

I222 Neuraminidase Mutations Further Reduce Oseltamivir Susceptibility of Indonesian Clade 2.1 Highly Pathogenic Avian Influenza A(H5N1) Viruses

We have tested the susceptibility to neuraminidase inhibitors of 155 clade 2.1 H5N1 viruses from Indonesia, isolated between 2006–2008 as well as 12 clade 1 isolates from Thailand and Cambodia from 2004–2007 using a fluorometric MUNANA-based enzyme inhibition assay. The Thailand and Cambodian clade 1 isolates tested here were all susceptible to oseltamivir and zanamivir, and sequence comparison indicated that reduced oseltamivir susceptibility we observed previously with clade 1 Cambodian isolates correlated with an S246G neuraminidase mutation. Eight Indonesian viruses (5%), all bearing I222 neuraminidase mutations, were identified as mild to extreme outliers for oseltamivir based on statistical analysis by box plots. IC₅₀s were from 50 to 500-fold higher than the reference clade 1 virus from Viet Nam, ranging from 43–75 nM for I222T/V mutants and from 268–349 nM for I222M mutants. All eight viruses were from different geographic locales; all I222M variants were from central Sumatra. None of the H5N1 isolates tested demonstrated reduced susceptibility to zanamivir (IC₅₀s all <5 nM). All I222 mutants showed loss of slow binding specifically for oseltamivir in an IC₅₀ kinetics assay. We identified four other Indonesian isolates with higher IC₅₀s which also demonstrated loss of slow binding, including one virus with an I117V mutation. There was a minimal effect on the binding of zanamivir and peramivir for all isolates tested. As H5N1 remains a potential pandemic threat, the incidence of mutations conferring reduced oseltamivir susceptibility is concerning and emphasizes the need for greater surveillance of drug susceptibility.     

A surface‐exposed neuraminidase affects complement resistance and virulence of the oral spirochaete Treponema denticola

Neuraminidases (sialidases) catalyse the removal of terminal sialic acid from glycoconjugates. Bacterial pathogens often utilize neuraminidases to scavenge host sialic acid, which can be utilized either as a nutrient or as a decorating molecule to disguise themselves from host immune attacks. Herein, a putative neuraminidase (TDE0471) was identified in Treponema denticola, an oral spirochaete associated with human periodontitis. TDE0471 is a cell surface‐exposed exo‐neuraminidase that removes sialic acid from human serum proteins; it is required for T. denticola to grow in a medium that mimics gingival crevice fluid, suggesting that the spirochaete may use sialic acid as a nutrient in vivo. TDE0471 protects T. denticola from serum killing by preventing the deposition of membrane attack complexes on the bacterial cell surface. Animal studies revealed that a TDE0471‐deficient mutant is less virulent than its parental wild‐type strain in BALB/C mice. However, it causes a level of tissue damage similar to the wild type in complement‐deficient B6.129S4‐C3^tm1Crr/J mice albeit the damage caused by both bacterial strains is more severe in these transgenic mice. Based on these results, we propose that T. denticola has evolved a strategy to scavenge host sialic acid using its neuraminidase, which allows the spirochaete to acquire nutrients and evade complement killing.     

Design,synthesis and biological evaluation of novel oseltamivir derivatives as potent neuraminidase inhibitors

Neuraminidase (NA) is one of the particular potential targets for novel antiviral therapy. In this work, a series of neuraminidase inhibitors with the cyclohexene scaffold were studied based upon the combination of 3D-QSAR, molecular docking, and molecular dynamics techniques. The results indicate that the built 3D-QSAR models yield reliable statistical information: the correlation coefficient (r²) and cross-validation coefficient (q²) of CoMFA (comparative molecular field analysis) are 0.992 and 0.819; the r² and q² of CoMSIA (comparative molecular similarity analysis) are 0.992 and 0.863, respectively. Molecular docking and MD simulations were conducted to confirm the detailed binding mode of enzyme-inhibitor system. The new NA inhibitors had been designed, synthesized, and their inhibitory activities against group-1 neuraminidase were determined. One agent displayed excellent neuraminidase inhibition, with IC₅₀ value of 39.6?μM against NA, while IC₅₀ value for oseltamivir is 61.1?μM. This compound may be further investigated for the treatment of infection by the new type influenza virus.