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HIV-reverse transcriptase inhibition: inclusion of ligand-induced fit by cross-docking studies.

Nonnucleoside reverse transcriptase inhibitors (NNRTIs) have, in addition to the nucleoside reverse transcriptase inhibitors (NRTIs) and protease inhibitors (PIs), a definitive role in the treatment of HIV-1 infections. Since the appearance of HEPT and TIBO, more than 30 structurally different classes of compounds have been reported as NNRTIs, which are specific inhibitors of HIV-1 replication, targeting the HIV-1 reverse transcriptase (RT). Nevirapine and delavirdine are the first formally licensed for clinical use, and others have been licensed afterward, while several are in preclinical or clinical development. The NNRTIs interact with a specific site of HIV-1 RT (nonnucleoside binding site, NNBS) that is close to, but distinct from, the NRTI binding site. In this work we report the application of the Autodock program assessing its usability through reproduction of 41 NNRTI experimental bound conformations. Moreover, cross-docking experiments on the wild-type and mutated RT forms were conducted to take into account the enzyme flexibility as a valuable tool for structure-based drug design (SBDD) studies and to gain insight on the mode of action of new anti-HIV agents active against both wild-type and resistant strains.

Binding Sites↗

Improving binding mode predictions by docking into protein-specifically adapted potential fields.

The development of a protein-specifically adapted objective function for docking is described. Structural and energetic information about known protein-ligand complexes is exploited to tailor knowledge-based potentials using a "reverse", protein-based CoMFA-type (=AFMoC) approach. That way, effects due to protein flexibility and information about multiple solvation schemes can be implicitly incorporated. Compared to the application of AFMoC for binding affinity predictions, a Shannon entropy based column filtering of the descriptor matrix and the capping of adapted repulsive potentials within the binding site have turned out to be crucial for the success of this method. The new developed approach (AFMoC(obj)) was validated on a data set of 66 HIV-1 protease inhibitors, for which experimental structural information was available. Convincingly, for ligands with up to 20 rotatable bonds, in more than 75% of all cases a binding mode below 2 A rmsd has been identified on the first scoring rank when AFMoC(obj)-based potentials were used as the objective function in AutoDock. With respect to nonadapted DrugScore or AutoDock fields, the binding mode prediction accuracy was significantly improved by 14%. Noteworthy, very similar results were obtained for training and test set compounds, demonstrating the strength and robustness of this method. Implications of our findings for binding affinity predictions and its usage in virtual screening are further discussed.

Binding Sites↗

Identification of novel extracellular signal-regulated kinase docking domain inhibitors.

The extracellular signal regulated kinase (ERK1 and ERK2) signal transduction pathways play a critical role in cell proliferation. Hyperactivation of the ERK proteins either through increased expression of membrane-bound growth factor receptors or genetic mutations of upstream proteins is thought to be involved in the pathogenesis of many human cancers. Thus, targeted inhibition of ERK signaling is viewed as a potential approach to prevent cancer cell proliferation. Currently, no specific inhibitors of the ERK proteins exist. Moreover, most kinase inhibitors lack specificity because they target the ATP binding region, which is well conserved among the protein kinase families. Taking advantage of recently identified ERK docking domains, which are reported to facilitate substrate protein interactions, we have used computer-aided drug design (CADD) to identify novel small molecular weight ERK inhibitors. Following a CADD screen of over 800 000 molecules, 80 potential compounds were selected and tested for activity in biological assays. Several compounds inhibited ERK-specific phosphorylation of ribosomal S6 kinase-1 (Rsk-1) or the ternary complex factor Elk-1 (TCF/Elk-1), both of which are involved in promoting cell proliferation. Active compounds showed a dose-dependent reduction in the proliferation of several cancer cell lines as measured by colony survival assays. Direct binding between the active compounds and ERK2 was indicated by fluorescence quenching. These active compounds may serve as lead candidates for development of novel specific inhibitors of ERK-substrate interactions involved in cell proliferation.

Binding Sites↗

Computational elucidation of the structural basis of ligand binding to the dopamine 3 receptor through docking and homology modeling.

The dopamine subtype 3 receptor (D3) is a promising therapeutic target for the treatment of cocaine addiction, schizophrenia, Parkinson's disease, and other disorders, but little is known about the binding of ligands to D3 at the atomic level. In the present study, binding of 29 known ligands to the D3 receptor was modeled computationally using four D3 receptor models which were obtained from homology modeling. The predicted binding models were validated with experimental data from site-directed mutagenesis, structure-activity relationship studies, and affinity labeling studies. Docking scores calculated for these 29 ligands correlate reasonably well with the experimentally determined binding affinities. A pharmacophore model is proposed that describes the binding of ligands at a single D3 receptor binding site and offers insights into the binding of structurally diverse D3 ligands to this receptor.

Binding Sites↗

A new lead for nonpeptidic active-site-directed inhibitors of the severe acute respiratory syndrome coronavirus main protease discovered by a combination of screening and docking methods.

The coronavirus main protease, M(pro), is considered to be a major target for drugs suitable for combating coronavirus infections including severe acute respiratory syndrome (SARS). An HPLC-based screening of electrophilic compounds that was performed to identify potential M(pro) inhibitors revealed etacrynic acid tert-butylamide (6a) as an effective nonpeptidic inhibitor. Docking studies suggested a binding mode in which the phenyl ring acts as a spacer bridging the inhibitor's activated double bond and its hydrophobic tert-butyl moiety. The latter is supposed to fit into the S4 pocket of the target protease. Furthermore, these studies revealed etacrynic acid amide (6b) as a promising lead for nonpeptidic active-site-directed M(pro) inhibitors. In a fluorimetric enzyme assay using a novel fluorescence resonance energy transfer (FRET) pair labeled substrate, compound 6b showed a K(i) value of 35.3 muM. Since the novel lead compound does not target the S1', S1, and S2 subsites of the enzyme's substrate-binding pockets, there is room for improvement that underlines the lead character of compound 6b.

Amides↗

Ligand docking in the gastric H+/K+-ATPase: homology modeling of reversible inhibitor binding sites.

Using the recent high-resolution X-ray structures determined for the Ca2+-ATPase, we have generated two homology models of the gastric H+/K+-ATPase reflecting the E1 and E2 conformations adopted by P-type ATPases in their catalytic cycle. In regimes where the in situ solid-state NMR-determined structure for 1,2,3-trimethyl-8-(pentafluorophenylmethoxy)imidazo[1,2-a]pyridinium iodide (TMPFPIP), a reversible inhibitor of the gastric H+/K+-ATPase, was retained in its predefined conformation and was allowed full torsional flexibility in docking, the ligands localized to discrete binding volumes in the E1 model and to a single central binding space, together with secondary peripheral locations, in the E2 conformation. The results of these binding studies are in good agreement with current site-directed mutagenesis data and support the suggestion that the binding site is proximal to the loop between TM5 and TM6 and TM8, the transmembrane (TM) region considered important for cation translocation. Furthermore, the results of the simulation with the flexible ligand complement the solid-state NMR structural constraints of this inhibitor when bound in situ to the protein.

Binding Sites↗

Pharmacophore modeling, docking, and principal component analysis based clustering: combined computer-assisted approaches to identify new inhibitors of the human rhinovirus coat protein.

The development and application of a sophisticated virtual screening and selection protocol to identify potential, novel inhibitors of the human rhinovirus coat protein employing various computer-assisted strategies are described. A large commercially available database of compounds was screened using a highly selective, structure-based pharmacophore model generated with the program Catalyst. A docking study and a principal component analysis were carried out within the software package Cerius and served to validate and further refine the obtained results. These combined efforts led to the selection of six candidate structures, for which in vitro anti-rhinoviral activity could be shown in a biological assay.

Antiviral Agents↗

Classification of chemical compounds by protein-compound docking for use in designing a focused library.

We developed a new method for the classification of chemical compounds and protein pockets and applied it to a random screening experiment for macrophage migration inhibitory factor (MIF). The principal component analysis (PCA) method was applied to the protein-compound interaction matrix, which was given by thorough docking calculations between a set of many protein pockets and chemical compounds. Each compound and protein pocket was depicted as a point in the PCA spaces of compounds and proteins, respectively. This method was applied to distinguish active compounds from negative compounds of MIF. A random screening experiment for MIF was performed, and our method revealed that the active compounds were localized in the PCA space of compounds, while the negative compounds showed a wide distribution. Furthermore, protein pockets, which bind similar compounds, were classified and were found to form a cluster in the PCA space.

Binding Sites↗

Discovery of cell-permeable non-peptide inhibitors of beta-secretase by high-throughput docking and continuum electrostatics calculations.

A fragment-based docking procedure followed by substructure search were used to identify active-site beta-secretase inhibitors from a composite set of about 300 000 and a library of nearly 180 000 small molecules, respectively. EC(50) values less than 10 microM were measured in at least one of two different mammalian cell-based assays for 12 of the 72 purchased compounds. In particular, the phenylureathiadiazole 2 and the diphenylurea derivative 3 are promising lead compounds for beta-secretase inhibition.

Amyloid Precursor Protein Secretases↗

Modeling water molecules in protein-ligand docking using GOLD.

We implemented a novel approach to score water mediation and displacement in the protein-ligand docking program GOLD. The method allows water molecules to switch on and off and to rotate around their three principal axes. A constant penalty, sigma(p), representing the loss of rigid-body entropy, is added for water molecules that are switched on, hence rewarding water displacement. We tested the methodology in an extensive validation study. First, sigma(p) is optimized against a training set of 58 protein-ligand complexes. For this training set, our algorithm correctly predicts water mediation/displacement in approximately 92% of the cases. We observed small improvements in the quality of the predicted binding modes for water-mediated complexes. In the second part of this work, an entirely independent set of 225 complexes is used. For this test set, our algorithm correctly predicts water mediation/displacement in approximately 93% of the cases. Improvements in binding mode quality were observed for individual water-mediated complexes.

Algorithms↗

Indol-1-yl acetic acids as peroxisome proliferator-activated receptor agonists: design, synthesis, structural biology, and molecular docking studies.

A series of novel indole-based PPAR agonists is described leading to discovery of 10k, a highly potent PPAR pan-agonist. The structural biology and molecular docking studies revealed that the distances between the acidic group and the linker, when a ligand was complexed with PPARgamma protein, were important for the potent activity. The hydrophobic tail part of 10k makes intensive hydrophobic interaction with the PPARgamma protein resulting in potent activity.

Binding Sites↗

A theoretical study to investigate D2DAR/D4DAR selectivity: receptor modeling and molecular docking of dopaminergic ligands.

Molecular modeling methods have been applied to construct three-dimensional models for dopaminergic ligand complexes with D2 and D4 receptor subtypes (D2DAR and D4DAR), using the bovine rhodopsin crystal structure as a template for the modeling study. Different dopaminergic ligands, in particular the N-n-propyl-substituted 3-aryl- and 3-cyclohexylpiperidines, were docked into the D2DAR and the D4DAR, to evaluate the agreement between theoretical and experimental results as regards their D2/D4 selectivity. The different position of an aromatic region in the two receptors might explain the structural basis of this biological property.

Amino Acid Sequence↗

Molecular docking-based study of vasopressin analogues modified at positions 2 and 3 with N-methylphenylalanine: influence on receptor-bound conformations and interactions with vasopressin and oxytocin receptors.

In this study, four cyclic vasopressin (CYFQNCPRG-NH(2), AVP) analogues substituted at positions 2 and 3 with four combinations of enantiomers of N-methylphenylalanine have been investigated. Three-dimensional structures of analogues have been formerly determined using NMR spectroscopy in dimethyl sulfoxide. Three-dimensional models of the vasopressin and oxytocin receptors were constructed by combining the multiple sequence alignment and the RD crystal structure as a template. The analogues have been docked into the receptor using the AutoDock program. The relaxation of the receptor-ligand complexes using energy minimization, followed by the constrained simulated annealing protocols (CSA), has been performed. The receptor-bound conformations of the investigated analogues have been proposed. We concluded that the N-methylated residues at positions 2 and 3 act as a structural restraint, determining the conformation of analogues, their location inside the receptor cavity, and mutual arrangement of the aromatic side chains. The conserved polar residues constitute the handles keeping the biologically active analogues inside the binding cavity. The Arg(8)-D(2.65) salt bridge might be responsible for analogue-selective binding in OTR and V1aR versus V2R, where the positively charged K(2.65) 100 is present at the equivalent position.

Amino Acid Sequence↗

New efficient substrates for semicarbazide-sensitive amine oxidase/VAP-1 enzyme: analysis by SARs and computational docking.

Structure activity relationships for semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 (SSAO/VAP-1) were studied using a library of arylalkylamine substrates, with the aim of contributing to the discovery of more efficient SSAO substrates. Experimental data were contrasted with computational docking studies, thereby allowing us to examine the mechanism and substrate-binding affinity of SSAO and thus contribute to the discovery of more efficient SSAO substrates and provide a structural basis for their interactions. We also built a model of the mouse SSAO structure, which provides several structural rationales for interspecies differences in SSAO substrate selectivity and reveals new trends in SSAO substrate recognition. In this context, we identified novel efficient substrates for human SSAO that can be used as a lead for the discovery of antidiabetic agents.

Adipocytes↗

Structure-based optimization of azole antifungal agents by CoMFA, CoMSIA, and molecular docking.

In a continuing effort to develop highly potent azole antifungal agents, the three-dimensional quantitative structure-activity relationship methods, CoMFA and CoMSIA, were applied using a set of novel azole antifungal compounds. The binding mode of the compounds at the active site of lanosterol 14alpha-demethylase was further explored using the flexible docking method. Various hydrophobic, van der Waals, pi-pi stacking, and hydrogen bonding interactions were observed between the azoles and the enzyme. Based on results from the molecular modeling, a receptor-based pharmacophore model was established to guide the rational optimization of the azole antifungal agents. Thus, a total of 57 novel azoles were designed and synthesized by a three-step optimization process. In vitro antifungal assay revealed that the antifungal activities of these novel azoles were greatly improved, which confirmed the reliability of the model from molecular modeling.

Antifungal Agents↗

Accurate prediction of the relative potencies of members of a series of kinase inhibitors using molecular docking and MM-GBSA scoring.

The ability of molecular docking, using the program Glide and an MM-GBSA postdocking scoring protocol, to correctly rank a number of congeneric kinase inhibitors was assessed. The approach was successful for the cases considered and suggests that this may be useful for the design of inhibitors in the lead optimization phase of drug discovery.

Aniline Compounds↗

Clarification of the binding mode of teleocidin and benzolactams to the Cys2 domain of protein kinase Cdelta by synthesis of hydrophobically modified, teleocidin-mimicking benzolactams and computational docking simulation.

Phorbol esters (12-O-tetradecanoylphorbol 13-acetate; TPA) and teleocidins are known to be potent tumor promoters and to activate protein kinase C (PKC) by binding competitively to the enzyme. The relationship between the chemical structures and the activities of these compounds has attracted much attention because of the marked structural dissimilarities. The benzolactam 5, with an eight-membered lactam ring and benzene ring instead of the nine-membered lactam ring and indole ring of teleocidins, reproduces the active ring conformation and biological activities of teleocidins. Herein we describe the synthesis of benzolactams with hydrophobic substituents at various positions. Structure-activity data indicate that the existence of a hydrophobic region between C-2 and C-9 and the steric factor at C-8 play critical roles in the appearance of biological activities. We also computationally simulated the docking of teleocidin and the modified benzolactam molecules to the Cys2 domain structure observed in the crystalline complex of PKCdelta with phorbol 13-acetate. Teleocidin and benzolactams fitted well into the same cavity as phorbol 13-acetate. Of the three functional groups hydrogen-bonding to the protein, two hydrogen-bonded with protein atoms in common with phorbol 13-acetate, but the third one hydrogen-bonded with a different protein atom from that in the case of phorbol 13-acetate. The model explains well the remarkable difference in activity between 5 and its analogue having a bulky substituent at C-8.

Binding Sites↗

Synthesis, CoMFA analysis, and receptor docking of 3,5-diacyl-2, 4-dialkylpyridine derivatives as selective A3 adenosine receptor antagonists.

3,5-Diacyl-2,4-dialkyl-6-phenylpyridine derivatives have been found to be selective antagonists at both human and rat A3 adenosine receptors (Li et al. J. Med. Chem. 1998, 41, 3186-3201). In the present study, ring-constrained, fluoro, hydroxy, and other derivatives in this series have been synthesized and tested for affinity at adenosine receptors in radioligand binding assays. Ki values at recombinant human and rat A3 adenosine receptors were determined using [125I]AB-MECA (N6-(4-amino-3-iodobenzyl)-5'-N-methylcarbamoyladenosine). Selectivity for A3 adenosine receptors was determined vs radioligand binding at rat brain A1 and A2A receptors, and structure-activity relationships at various positions of the pyridine ring (the 3- and 5-acyl substituents and the 2- and 4-alkyl substituents) were probed. At the 5-position inclusion of a beta-fluoroethyl (7) or a gamma-fluoropropyl ester (26) was favorable for human A3 receptor affinity, resulting in Ki values of 4.2 and 9.7 nM, respectively, while the pentafluoropropyl analogue was clearly less potent at human A3 receptors. At the 2-, 3-, and 4-positions, fluoro or hydroxy substitution failed to enhance potency and selectivity at human A3 receptors. Several analogues were nearly equipotent at rat and human A3 receptors. To further define the pharmacophore conformationally, a lactam, a lactone, and thiolactones were tested in adenosine receptor binding. The most potent analogue in this group was compound 34, in which a thiolactone was formed between 3- and 4-positions and which had a Ki value of 248 nM at human A3 receptors. Using affinity data and a general pharmacophore model for A3 adenosine receptor antagonists recently proposed, we applied comparative molecular field analysis (CoMFA) to obtain a three-dimensional quantitative structure-activity relationship for pyridine derivatives, having good predictability (r2pred = 0.873) for compounds in the test set. A rhodopsin-based model of the human A3 receptor was built, and the pyridine reference ligand 2,3,4, 5-tetraethyl-6-phenyl-pyridine-3-thiocarboxylate-5-carboxylate (MRS 1476) was docked in the putative ligand binding site. Interactions between receptor transmembrane domains and the steric and the electrostatic contour plots obtained from the CoMFA analysis were analyzed.

Animals↗