5-HT(1A) serotonin and D1 dopamine receptor agonists have been postulated to be able to improve negative and cognitive impairment symptoms of schizophrenia, while partial agonists and antagonists of the D2 and 5-HT(2A) receptors have been reported to be effective in reducing positive symptoms. There is therefore a need for well-defined homology models for the design of more selective antipsychotic agents, since no three-dimensional (3D) crystal structures of these receptors are currently available. In this study, homology models were built based on the high-resolution crystal structure of the β(2)-adrenergic receptor (2RH1) and further refined via molecular dynamics simulations in a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid bilayer system with the GROMOS96 53A6 united atom force field. Docking evaluations with representative agonists and antagonists using AutoDock 4.2 revealed binding modes in agreement with experimentally determined site-directed mutagenesis data and significant correlations between the computed and experimental pK (i) values. The models are also able to distinguish between antipsychotic agents with different selectivities and binding affinities for the four receptors, as well as to differentiate active compounds from decoys. Hence, these human 5-HT(1A), 5-HT(2A), D1 and D2 receptor homology models are capable of predicting the activities of novel ligands, and can be used as 3D templates for antipsychotic drug design and discovery.
Muscarinic acetylcholine receptor-active compounds have potential for the treatment of Alzheimer's disease. In this study, a series of natural and synthetic flavones and flavonols was assayed in vitro for their ability to inhibit radioligand binding at human cloned M1 muscarinic receptors. Several compounds were found to possess competitive binding affinity (Ki=40-110 µM), comparable to that of acetylcholine (Ki=59 µM). Despite the fact that these compounds lack a positively-charged ammonium group under physiological conditions, molecular modelling studies suggested that they bind to the orthosteric site of the receptor, mainly through non-polar interactions.
Selective blockade of the serotonin 5-HT(2A) receptor is a useful therapeutic approach for a number of disorders, including schizophrenia, insomnia and ischaemic heart disease. A series of aporphines were docked into a homology model of the rat 5-HT(2A) receptor using AutoDock. Selected compounds with high in silico binding affinities were screened in vitro using radioligand-binding assays against rat serotonin (5-HT(1A) and 5-HT(2A)) and dopamine (D1 and D2) receptors. (R)-Roemerine and (±)-nuciferine were found to have high affinity for the 5-HT(2A) receptor (K(i) = 62 and 139 nM, respectively), with (R)-roemerine showing 20- to 400-fold selectivity for the 5-HT(2A) receptor over the 5-HT(1A), D1 and D2 receptors. Investigation into the ligand-receptor interactions suggested that the selectivity of (R)-roemerine is due to it having stronger H-bonding and dipole-dipole interactions with several of the key residues in the 5-HT(2A) receptor-binding site.
Various works have been carried out in developing therapeutics against dengue. However, to date, no effective vaccine or anti-dengue agent has yet been discovered. The development of protease inhibitors is considered as a promising option, but most previous works have involved competitive inhibition. In this study, we focused on rational discovery of potential anti-dengue agents based on non-competitive inhibition of DEN-2 NS2B/NS3 protease. A homology model of the DEN-2 NS2B/NS3 protease (using West Nile Virus NS2B/NS3 protease complex, 2FP7, as the template) was used as the target, and pinostrobin, a flavanone, was used as the standard ligand. Virtual screening was performed involving a total of 13 341 small compounds, with the backbone structures of chalcone, flavanone, and flavone, available in the ZINC database. Ranking of the resulting compounds yielded compounds with higher binding affinities compared with the standard ligand. Inhibition assay of the selected top-ranking compounds against DEN-2 NS2B/NS3 proteolytic activity resulted in significantly better inhibition compared with the standard and correlated well with in silico results. In conclusion, via this rational discovery technique, better inhibitors were identified. This method can be used in further work to discover lead compounds for anti-dengue agents.
Bacopa monnieri has been used in Ayurvedic medicine to improve memory and cognition. The active constituent responsible for its pharmacological effects is bacoside A, a mixture of dammarane-type triterpenoid saponins containing sugar chains linked to a steroid aglycone skeleton. Triterpenoid saponins have been reported to be transformed in vivo to metabolites that give better biological activity and pharmacokinetic characteristics. Thus, the activities of the parent compounds (bacosides), aglycones (jujubogenin and pseudojujubogenin) and their derivatives (ebelin lactone and bacogenin A1) were compared using a combination of in silico and in vitro screening methods. The compounds were docked into 5-HT1A, 5-HT2A, D1, D2, M1 receptors and acetylcholinesterase (AChE) using AutoDock and their central nervous system (CNS) drug-like properties were determined using Discovery Studio molecular properties and ADMET descriptors. The compounds were screened in vitro using radioligand receptor binding and AChE inhibition assays. In silico studies showed that the parent bacosides were not able to dock into the chosen CNS targets and had poor molecular properties as a CNS drug. In contrast, the aglycones and their derivatives showed better binding affinity and good CNS drug-like properties, were well absorbed through the intestines and had good blood brain barrier (BBB) penetration. Among the compounds tested in vitro, ebelin lactone showed binding affinity towards M1 (Ki = 0.45 μM) and 5-HT2A (4.21 μM) receptors. Bacoside A and bacopaside X (9.06 μM) showed binding affinity towards the D1 receptor. None of the compounds showed any inhibitory activity against AChE. Since the stimulation of M1 and 5-HT2A receptors has been implicated in memory and cognition and ebelin lactone was shown to have the strongest binding energy, highest BBB penetration and binding affinity towards M1 and 5-HT2A receptors, we suggest that B. monnieri constituents may be transformed in vivo to the active form before exerting their pharmacological activity.
Structure-based virtual screening offers a good opportunity for the discovery of selective M1 muscarinic acetylcholine receptor (mAChR) agonists for the treatment of Alzheimer's disease. However, no 3-D structure of an M1 mAChR is yet available and the homology models that have been previously reported are only able to identify antagonists in virtual screening experiments. In this study, we generated a homology model of the human M1 mAChR, based on the crystal structure of an M3 mAChR as the template. This initial model was modified, using the agonist-bound crystal structure of a β2-adrenergic receptor as a guide, to give two possible activated structures. The T192 side chain was adjusted in both structures and one of the structures also had the whole of transmembrane (TM) 5 rotated and tilted toward the inner channel of the transmembrane region. The binding sites of all three structures were then refined by induced-fit docking (IFD) with acetylcholine. Virtual screening experiments showed that all three refined models could efficiently differentiate agonists from decoy molecules, with the TM5-modified models also giving good agonist/antagonist selectivity. The whole range of agonists and antagonists was observed to bind within the orthosteric site of the structure obtained by IFD refinement alone, implying that it has inactive state character. In contrast, the two TM5-modified structures were unable to accommodate the antagonists, supporting the proposition that they possess activated state character.
Various clinical symptoms are caused by dengue virus ranging from mild fever to severe hemorrhagic fever while there is no successful anti-dengue therapeutics available. Among different strategies towards identifying and developing anti-dengue therapeutics, testing anti-dengue properties of known drugs could represent an efficient strategy for which information of its medical approval, toxicity and side effects is readily available. In this study, we evaluated the antiviral activity of some medical compounds towards dengue NS2B-NS3 protease (DENV2 NS2B-NS3pro) as a target to inhibit dengue virus replication. Mefenamic acid, a non-steroid anti inflammatory drug and doxycycline, a derivative antibiotic of tetracycline both showed significant inhibition potential against DENV2 NS2B-NS3pro Ki values 32 ± 2 μM and 55 ± 5 μM respectively. The effective cytotoxic concentrations of 50% (CC50) against Vero cells were evaluated for mefenamic acid (150 ± 5 μM) and doxycycline (125 ± 4 μM). Concentrations lower than CC50 were used to test the inhibition potential of these compounds against DENV2 replication in Vero cells. The results showed significant reduction in viral load after applying mefenamic acid and doxycyline in concentration dependent manner. Mefenamic acid reduced viral RNA at EC50 of 32 ± 4 μM whilst doxycycline EC50 was 40 ± 3 μM. Mefenamic acid showed higher selectivity against dengue virus replication in vitro compared to doxycycline. These findings underline the need for further experimental and clinical studies on these drugs utilizing its anti-dengue and anti-inflammatory activities to attenuate the clinical symptoms of dengue infection.
A series of 2'-hydroxy- and 2'-hydroxy-4',6'-dimethoxychalcones was synthesised and evaluated as inhibitors of human acetylcholinesterase (AChE). The majority of the compounds were found to show some activity, with the most active compounds having IC50 values of 40-85 µM. Higher activities were generally observed for compounds with methoxy substituents in the A ring and halogen substituents in the B ring. Kinetic studies on the most active compounds showed that they act as mixed-type inhibitors, in agreement with the results of molecular modelling studies, which suggested that they interact with residues in the peripheral anionic site and the gorge region of AChE.
Some novel Schiff bases derived from 1-(2-ketoiminoethyl)piperazines were synthesized and characterized by mass spectroscopy, FTIR, UV-Visible, 1H and 13C-NMR. The compounds were tested for inhibitory activities on human acetylcholinesterase (hAChE), antioxidant activities, acute oral toxicity and further studied by molecular modeling techniques. The study identified the compound (DHP) to have the highest activity among the series in hAChE inhibition and DPPH assay while the compound LP revealed the highest activity in the FRAP assay. The hAChE inhibitory activity of DHP is comparable with that of propidium, a known AChE inhibitor. This high activity of DHP was checked by molecular modeling which showed that DHP could not be considered as a bivalent ligand due to its incapability to occupy the esteratic site (ES) region of the 3D crystal structure of hAChE. The antioxidant study unveiled varying results in 1,1-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays. This indicates mechanistic variations of the compounds in the two assays. The potential therapeutic applications and safety of these compounds were suggested for use as human acetylcholinesterase inhibitors and antioxidants.
Boesenbergia rotunda (Roxb.) Schlecht (family zingiberaceae) is a rhizomatous herb that is distributed from north-eastern India to south-east Asia, especially in Indonesia, Thailand and Malaysia. Previous research has shown that the crude extract of this plant has cytotoxic properties. The current study examines the cytotoxic properties of boesenbergin A isolated from Boesenbergia rotunda.
Alzheimer's disease (AD) is the most common form of dementia among older people and the pathogenesis of this disease is associated with oxidative stress. Acetylcholinesterase inhibitors with antioxidant activities are considered potential treatments for AD. Some novel ketone derivatives of gallic hydrazide-derived Schiff bases were synthesized and examined for their antioxidant activities and in vitro and in silico acetyl cholinesterase inhibition. The compounds were characterized using spectroscopy and X-ray crystallography. The ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays revealed that all the compounds have strong antioxidant activities. N-(1-(5-bromo-2-hydroxyphenyl)-ethylidene)-3,4,5-trihydroxybenzohydrazide (2) was the most potent inhibitor of human acetyl cholinesterase, giving an inhibition rate of 77% at 100 μM. Molecular docking simulation of the ligand-enzyme complex suggested that the ligand may be positioned in the enzyme's active-site gorge, interacting with residues in the peripheral anionic subsite (PAS) and acyl binding pocket (ABP). The current work warrants further preclinical studies to assess the potential for these novel compounds for the treatment of AD.