Search for novel neuraminidase inhibitors: Design, synthesis and interaction of oseltamivir derivatives with model membrane using docking, NMR and DSC methods

Oseltamivir phosphate interaction with model membranes

Oseltamivir belongs to the neuraminidase inhibitors, developed against the influenza virus, and registered under the trademark Tamiflu. Despite its long-term acquaintance, there is limited information in the literature about its physicochemical and structural properties in a lipid-water system. We present an experimentally determined partition coefficient with structural information on the interaction of oseltamivir with the model membrane, its possible location, and its effect on the membrane thermodynamics. The hydrophobic part of the lipid bilayer is affected to a moderate extent, which was proved by slight changes in thermal and structural properties. Hereby, interaction of oseltamivir with the phospholipid bilayer induces concentration dependent decrease of lateral pressure in the bilayer acyl chain region. Oseltamivir charges the bilayer surface positively, which results in the zeta potential increase and changes in anisotropic properties studied by the polarised light microscopy. At the highest oseltamivir concentrations studied, the multilamellar structure is extensively disturbed, likely due to electrostatic repulsion between the adjacent bilayers.

In quest of small-molecules as potent non-competitive inhibitors against influenza

A series of scaffolds namely aurones, 3-indolinones, 4-quinolones and cinnamic acid-piperazine hybrids, was designed, synthesized and investigated in vitro against influenza A/H1N1pdm09 virus. Designed molecules adopted different binding mode i.e., in 430-cavity of neuraminidase, unlike sialic acid and oseltamivir in molecular docking studies. All molecules reduced the viral titer and exhibited non-cytotoxicity along with cryo-protective property towards MDCK cells. Molecules (Z)-2-(3'-Chloro-benzylidene)-1,2-dihydro-indol-3-one (2f), (Z)-2-(4'-Chloro-benzylidene)-1,2-dihydro-indol-3-one (2g) and 2-(2'-Methoxy-phenyl)-1H-quinolin-4-one (3a) were the most interesting molecules identified in this research, endowed with robust potencies showing low-nanomolar EC₅₀ values of 4.0 nM, 6.7 nM and 4.9 nM, respectively, compared to reference competitive and non-competitive inhibitors: oseltamivir (EC₅₀ = 12.7 nM) and quercetin (EC₅₀ = 0.56 µM), respectively. Besides, 2f, 2g and 3a exhibited good neuraminidase inhibitory activity in sub-micromolar range (IC₅₀ = 0.52 µM, 3.5 µM, 1.3 µM respectively). Moreover, these molecules were determined as non-competitive inhibitors similar to reference non-competitive inhibitor quercetin unlike reference competitive inhibitor oseltamivir in kinetics studies.

Rosmarinic Acid as a Potent Influenza Neuraminidase Inhibitor: In Vitro and In Silico Study

BACKGROUND

Neuraminidase (NA), a major glycoprotein found on the surface of the influenza virus, is an important target for the prophylaxis and treatment of influenza virus infections. Recently, several plant-derived polyphenols, especially caffeic acid analogs, have been reported to exert the inhibitory activity against NA.

OBJECTIVE

Herein, we aimed to investigate the anti-influenza NA activity of caffeic acid and its hydroxycinnamate analogues, rosmarinic acid and salvianolic acid A, in comparison to a known NA inhibitor, oseltamivir.

METHODS

In vitro MUNANA-based NA inhibitory assay was used to evaluate the inhibitory activity of the three interested hydroxycinnamic compounds towards the influenza NA enzyme. Subsequently, allatom molecular dynamics (MD) simulations and binding free energy calculations were employed to elucidate the structural insights into the protein-ligand complexations.

RESULTS

Rosmarinic acid showed the highest inhibitory activity against NA with the IC50 of 0.40 μM compared to caffeic acid (IC50 of 0.81 μM) and salvianolic acid A (IC50 of >1 μM). From 100-ns MD simulations, the binding affinity, hot-spot residues, and H-bond formations of rosmarinic acid/NA complex were higher than those of caffeic acid/NA model, in which their molecular complexations was driven mainly by electrostatic attractions and H-bond formations from several charged residues (R118, E119, D151, R152, E227, E277, and R371). Notably, the two hydroxyl groups on both phenyl and phenylacetic rings of rosmarinic acid play a crucial role in stabilizing NA through a strongly formed Hbond( s).

CONCLUSION

Our findings shed light on the potentiality of rosmarinic acid as a lead compound for further development of a potential influenza NA inhibitor.

Source of oseltamivir resistance due to single E119D and double E119D/H274Y mutations in pdm09H1N1 influenza neuraminidase

Influenza epidemics are responsible for an average of 3-5 millions of severe cases and up to 500,000 deaths around the world. One of flu pandemic types is influenza A(H1N1)pdm09 virus (pdm09H1N1). Oseltamivir is the antiviral drug used to treat influenza targeting at neuraminidase (NA) located on the viral surface. Influenza virus undergoes high mutation rates and leads to drug resistance, and thus the development of more efficient drugs is required. In the present study, all-atom molecular dynamics simulations were applied to understand the oseltamivir resistance caused by the single E119D and double E119D/H274Y mutations on NA. The obtained results in terms of binding free energy and intermolecular interactions in the ligand-protein interface showed that the oseltamivir could not be well accommodated in the binding pocket of both NA mutants and the 150-loop moves out from oseltamivir as an "open" state. A greater number of water molecules accessible to the binding pocket could disrupt the oseltamivir binding with NA target as seen be high mobility of oseltamivir at the active site. Additionally, our finding could guide to the design and development of novel NA inhibitor drugs.

Potential New H1N1 Neuraminidase Inhibitors from Ferulic Acid and Vanillin: Molecular Modelling, Synthesis and in Vitro Assay

We report the computational and experimental efforts in the design and synthesis of novel neuraminidase (NA) inhibitors from ferulic acid and vanillin. Two proposed ferulic acid analogues, MY7 and MY8 were predicted to inhibit H1N1 NA using molecular docking. From these two analogues, we designed, synthesised and evaluated the biological activities of a series of ferulic acid and vanillin derivatives. The enzymatic H1N1 NA inhibition assay showed MY21 (a vanillin derivative) has the lowest IC50 of 50 μM. In contrast, the virus inhibition assay showed MY15, a ferulic acid derivative has the best activity with the EC50 of ~0.95 μM. Modelling studies further suggest that these predicted activities might be due to the interactions with conserved and essential residues of NA with ΔGbind values comparable to those of oseltamivir and zanamivir, the two commercial NA inhibitors.

A new role of neuraminidase (NA) in the influenza virus life cycle: implication for developing NA inhibitors with novel mechanism of action

The entire life cycle of influenza virus involves viral attachment, entry, replication, and release. Previous studies have demonstrated that neuraminidase (NA) is an essential glycoprotein on the surface of influenza virus and that it is responsible for release of progeny virions from the host cell to infect new cells. However, recent studies have also suggested that NA may play other roles in the early stages of the viral life cycle, that is, viral attachment and entry. This review focuses on the new role of NA in the early stages of influenza life cycle and the corresponding development of novel NA inhibitors. Copyright © 2016 John Wiley & Sons, Ltd.

Localization and interaction of hydroxyflavones with lipid bilayer model membranes: a study using DSC and multinuclear NMR

The localization and interaction of six naturally occurring flavones (FLV, 5HF, 6HF, 7HF, CHY and BLN) in DPPC bilayers were studied using DSC and multi-nuclear NMR. DSC results indicate that FLV and 6HF interact with alkyl chains. The (1)H NMR shows interaction of flavones with the sn-glycero region. Ring current induced chemical shifts indicate that 6HF and BLN acquire parallel orientation in bilayers. 2D NOESY spectra indicate partitioning of the B-ring into the alkyl chain region. The DSC, NMR and binding studies indicate that 5HF and 7HF are located near head group region, while 6HF, CHY and BLN are located in the vicinity of sn-glycero region, and FLV is inserted deepest in the membrane.

Intermolecular interaction of voriconazole analogues with model membrane by DSC and NMR, and their antifungal activity using NMR based metabolic profiling

The development of novel antifungal agents with high susceptibility and increased potency can be achieved by increasing their overall lipophilicity. To enhance the lipophilicity of voriconazole, a second generation azole antifungal agent, we have synthesized its carboxylic acid ester analogues, namely p-methoxybenzoate (Vpmb), toluate (Vtol), benzoate (Vbz) and p-nitrobenzoate (Vpnb). The intermolecular interactions of these analogues with model membrane have been investigated using nuclear magnetic resonance (NMR) and differential scanning calorimetric (DSC) techniques. The results indicate varying degree of changes in the membrane bilayer's structural architecture and physico-chemical characteristics which possibly can be correlated with the antifungal effects via fungal membrane. Rapid metabolite profiling of chemical entities using cell preparations is one of the most important steps in drug discovery. We have evaluated the effect of synthesized analogues on Candida albicans. The method involves real time (1)H NMR measurement of intact cells monitoring NMR signals from fungal metabolites which gives Metabolic End Point (MEP). This is then compared with Minimum Inhibitory Concentration (MIC) determined using conventional methods. Results indicate that one of the synthesized analogues, Vpmb shows reasonably good activity.