The interaction of a ß2 adrenoceptor agonist drug with biomimetic cell membrane models: The case of terbutaline sulphate.

Terbutaline sulphate (TS) is a selective short-acting ß2 adrenoceptor agonist used for asthma treatment. The pharmacological activity of TS depends on its binding to the transmembrane protein, ß2 adrenoceptor. Thus, the interactions of this drug with biological membranes are expected, affecting its pharmacological activity. Using in vitro models to study the interaction of TS with biological membranes can provide important information about the activity of the drug. Here, liposomes with different lipid compositions were used as biomimetic models of cell membranes to evaluate the effect of composition, complexity, and physical state of membranes on TS-membrane interactions. For that, liposomes containing dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and liposomes containing DMPC and cholesterol (CHOL) were prepared. For the study of TS-membrane interactions, the TS lipophilicity was evaluated in terms of i) partition coefficient; ii) the preferential location of the drug within the membrane; iii) and the effect of TS on the membrane fluidity. The obtained data suggest that TS has an affinity for the lipid membrane, partitioning from the aqueous to the lipid phase. The affinity was dependent on the liposomes' compositions, showing a greater affinity for DMPC membranes than for DMPC:CHOL model. Dynamic light scattering (DLS) results revealed that this is due to the rigidizing effect caused by CHOL molecules. These findings provide valuable insights in the understanding of the complex interaction of TS with biomembrane models as well as the relevance of lipid compositions and membrane structure in such interactions, which may be related to its pharmacological activity and side effects.

Photoswitchable Antagonists for a Precise Spatiotemporal Control of ß2-Adrenoceptors.

ß2-Adrenoceptors (ß2-AR) are prototypical G-protein-coupled receptors and important pharmacological targets with relevant roles in physiological processes and diseases. Herein, we introduce Photoazolol-1-3, a series of photoswitchable azobenzene ß2-AR antagonists that can be reversibly controlled with light. These new photochromic ligands are designed following the azologization strategy, with a p-acetamido azobenzene substituting the hydrophobic moiety present in many ß2-AR antagonists. Using a fluorescence resonance energy transfer (FRET) biosensor-based assay, a variety of photopharmacological properties are identified. Two of the light-regulated molecules show potent ß2-AR antagonism and enable a reversible and dynamic control of cellular receptor activity with light. Their photopharmacological properties are opposite, with Photoazolol-1 being more active in the dark and Photoazolol-2 demonstrating higher antagonism upon illumination. In addition, we provide a molecular rationale for the interaction of the different photoisomers with the receptor. Overall, we present innovative tools and a proof of concept for the precise control of ß2-AR by means of light.

A Focus on Unusual ECL2 Interactions Yields ß2 -Adrenergic Receptor Antagonists with Unprecedented Scaffolds.

The binding pockets of aminergic G protein-coupled receptors are often targeted by drugs and virtual screening campaigns. In order to find ligands with unprecedented scaffolds for one of the best-investigated receptors of this subfamily, the ß2 -adrenergic receptor, we conducted a docking-based screen insisting that molecules would address previously untargeted residues in extracellular loop 2. We here report the discovery of ligands with a previously undescribed coumaran-based scaffold. Furthermore, we provide an analysis of the added value that X-ray structures in different conformations deliver for such docking screens.

An Integrated Markov State Model and Path Metadynamics Approach To Characterize Drug Binding Processes.

Unveiling the mechanistic features of drug-target binding is of central interest in biophysics and drug discovery. Herein, we address this challenge by combining two major computational approaches, namely, Molecular Dynamics (MD) simulations and Markov State Models (MSM), with a Path Collective Variables (PCVs) description coupled with metadynamics. We apply our methodology to reconstruct the binding process of the antagonist alprenolol to the ß2-adrenergic receptor, a well-established pharmaceutical target. The devised protocol allowed us to estimate the binding free energy and identify the minimum free energy path leading to the protein-ligand complex. In summary, we show that MSM and PCVs can be efficiently integrated to shed light upon mechanistic and energetic details underlying complex recognition processes in biological systems.

Development of covalent antagonists for ß1- and ß2-adrenergic receptors.

The selective covalent tethering of ligands to a specific GPCR binding site has attracted considerable interest in structural biology, molecular pharmacology and drug design. We recently reported on a covalently binding noradrenaline analog (FAUC37) facilitating crystallization of the ß2-adrenergic receptor (ß2ARH2.64C) in an active state. We herein present the stereospecific synthesis of covalently binding disulfide ligands based on the pharmacophores of adrenergic ß1- and ß2 receptor antagonists. Radioligand depletion experiments revealed that the disulfide-functionalized ligands were able to rapidly form a covalent bond with a specific cysteine residue of the receptor mutants ß1ARI2.64C and ß2ARH2.64C. The propranolol derivative (S)-1a induced nearly complete irreversible blockage of the ß2ARH2.64C within 30 min incubation. The CGP20712A-based ligand (S)-4 showed efficient covalent blocking of the ß2ARH2.64C at very low concentrations. The analog (S)-5a revealed extraordinary covalent cross-linking at the ß1ARI2.64C and ß2ARH2.64C mutant while retaining a 41-fold selectivity for the ß1AR wild type over ß2AR. These compounds may serve as valuable molecular tools for studying ß1/ß2 subtype selectivity or investigations on GPCR trafficking and dimerization.

How Effectively Can Adaptive Sampling Methods Capture Spontaneous Ligand Binding?

Molecular dynamics (MD) simulations that capture the spontaneous binding of drugs and other ligands to their target proteins can reveal a great deal of useful information, but most drug-like ligands bind on time scales longer than those accessible to individual MD simulations. Adaptive sampling methods-in which one performs multiple rounds of simulation, with the initial conditions of each round based on the results of previous rounds-offer a promising potential solution to this problem. No comprehensive analysis of the performance gains from adaptive sampling is available for ligand binding, however, particularly for protein-ligand systems typical of those encountered in drug discovery. Moreover, most previous work presupposes knowledge of the ligand's bound pose. Here we outline existing methods for adaptive sampling of the ligand-binding process and introduce several improvements, with a focus on methods that do not require prior knowledge of the binding site or bound pose. We then evaluate these methods by comparing them to traditional, long MD simulations for realistic protein-ligand systems. We find that adaptive sampling simulations typically fail to reach the bound pose more efficiently than traditional MD. However, adaptive sampling identifies multiple potential binding sites more efficiently than traditional MD and also provides better characterization of binding pathways. We explain these results by showing that protein-ligand binding is an example of an exploration-exploitation dilemma. Existing adaptive sampling methods for ligand binding in the absence of a known bound pose vastly favor the broad exploration of protein-ligand space, sometimes failing to sufficiently exploit intermediate states as they are discovered. We suggest potential avenues for future research to address this shortcoming.

Ligand-binding affinity of alternative conformers of human ß2 -adrenergic receptor in the presence of intracellular loop 3 (ICL3) and their potential use in virtual screening studies.

This study investigates the structural distinctiveness of orthosteric ligand-binding sites of several human ß2 adrenergic receptor (ß2 -AR) conformations that have been obtained from a set of independent molecular dynamics (MD) simulations in the presence of intracellular loop 3 (ICL3). A docking protocol was established in order to classify each receptor conformation via its binding affinity to selected ligands with known efficacy. This work's main goal was to reveal many subtle features of the ligand-binding site, presenting alternative conformations, which might be considered as either active- or inactive-like but mostly specific for that ligand. Agonists, inverse agonists, and antagonists were docked to each MD conformer with distinct binding pockets, using different docking tools and scoring functions. Mostly favored receptor conformation persistently observed in all docking/scoring evaluations was classified as active or inactive based on the type of ligand's biological effect. Classified MD conformers were further tested for their ability to discriminate agonists from inverse agonists/antagonists, and several conformers were proposed as important targets to be used in virtual screening experiments that were often limited to a single X-ray structure.

Synthesis, biological evaluation and molecular modeling of 2-amino-2-phenylethanol derivatives as novel ß2-adrenoceptor agonists.

A novel series of 2-amino-2-phenylethanol derivatives were developed as ß2-adrenoceptor agonists. Among them, 2-amino-3-fluoro-5-(2-hydroxy-1-(isopropylamino)ethyl)benzonitrile (compound 2f) exhibited the highest activity (EC50 = 0.25 nM) in stimulating ß2-adrenoceptor-mediated cellular cAMP production with a 763.6-fold selectivity over the ß1-adrenoceptor. The (S)-isomer of 2f was subsequently found to be 8.5-fold more active than the (R)-isomer. Molecular docking was performed to determine the putative binding modes of this new class of ß2-adrenoceptor agonists. Taken together, these data show that compound 2f is a promising lead compound worthy of further study for the development of ß2-adrenoceptor agonists.

Design, synthesis, and functional assessment of Cmpd-15 derivatives as negative allosteric modulators for the ß2-adrenergic receptor.

The ß2-adrenergic receptor (ß2AR), a G protein-coupled receptor, is an important therapeutic target. We recently described Cmpd-15, the first small molecule negative allosteric modulator (NAM) for the ß2AR. Herein we report in details the design, synthesis and structure-activity relationships (SAR) of seven Cmpd-15 derivatives. Furthermore, we provide in a dose-response paradigm, the details of the effects of these derivatives in modulating agonist-induced ß2AR activities (G-protein-mediated cAMP production and ß-arrestin recruitment to the receptor) as well as the binding affinity of an orthosteric agonist in radio-ligand competition binding assay. Our results show that some modifications, including removal of the formamide group in the para-formamido phenylalanine region and bromine in the meta-bromobenzyl methylbenzamide region caused dramatic reduction in the functional activity of Cmpd-15. These SAR results provide valuable insights into the mechanism of action of the NAM Cmpd-15 as well as the basis for future development of more potent and selective modulators for the ß2AR based on the chemical scaffold of Cmpd-15.

Mechanism of intracellular allosteric ß2AR antagonist revealed by X-ray crystal structure.

G-protein-coupled receptors (GPCRs) pose challenges for drug discovery efforts because of the high degree of structural homology in the orthosteric pocket, particularly for GPCRs within a single subfamily, such as the nine adrenergic receptors. Allosteric ligands may bind to less-conserved regions of these receptors and therefore are more likely to be selective. Unlike orthosteric ligands, which tonically activate or inhibit signalling, allosteric ligands modulate physiologic responses to hormones and neurotransmitters, and may therefore have fewer adverse effects. The majority of GPCR crystal structures published to date were obtained with receptors bound to orthosteric antagonists, and only a few structures bound to allosteric ligands have been reported. Compound 15 (Cmpd-15) is an allosteric modulator of the ß2 adrenergic receptor (ß2AR) that was recently isolated from a DNA-encoded small-molecule library. Orthosteric ß-adrenergic receptor antagonists, known as beta-blockers, are amongst the most prescribed drugs in the world and Cmpd-15 is the first allosteric beta-blocker. Cmpd-15 exhibits negative cooperativity with agonists and positive cooperativity with inverse agonists. Here we present the structure of the ß2AR bound to a polyethylene glycol-carboxylic acid derivative (Cmpd-15PA) of this modulator. Cmpd-15PA binds to a pocket formed primarily by the cytoplasmic ends of transmembrane segments 1, 2, 6 and 7 as well as intracellular loop 1 and helix 8. A comparison of this structure with inactive- and active-state structures of the ß2AR reveals the mechanism by which Cmpd-15 modulates agonist binding affinity and signalling.

Mahuannin B an adenylate cyclase inhibitor attenuates hyperhidrosis via suppressing ß2-adrenoceptor/cAMP signaling pathway.

BACKGROUND: Based on the traditional application of traditional Chinese Medicines (TCMs), Ephedra Herba (EH) is used to cure cold fever by inducing sweating, whereas Ephedra Radix (ER) is used to treat hyperhidrosis. Although they come from the same plant, Ephedra sinica Stapf, but have play opposing roles in clinical applications. EH is known to contain ephedrine alkaloids, which is the driver of the physiological changes in sweating, heart rate and blood pressure. However, the active pharmacological ingredients (APIs) of ER and the mechanisms by which it restricts sweating remain unknown. PURPOSE: The current work aims to discover the hidroschesis APIs from ER, as well as to establish its action mechanism. METHODS: UPLC-Q/TOF-MS, PCA, and heat map were utilized for identifying the differences between EH and ER. HPLC integrated with a ß2-adrenoceptor (ß2-AR) activity luciferase reporter assay system was used to screen active inhibitors; molecular docking and a series of biological assays centered on ß2-AR-related signaling pathways were evaluated to understand the roles of APIs. RESULTS: The opposite effect on sweating of EH and ER can be attributed to the APIs of amphetamine-type alkaloids and flavonoid derivatives. Mahuannin B is an effective anti-hydrotic agent, inhibiting the production of cAMP via suppression of adenylate cyclase (AC) activity. CONCLUSION: The effects of EH and ER on sweat and ß2-AR-related signaling pathway are opposite due to different alkaloids and flavonoids of APIs in EH and ER. The present work not only sheds light on the hidroschesis action of mahuannin B, but also presents a potential target of AC in the treatment of hyperhidrosis.

The Principles of Ligand Specificity on beta-2-adrenergic receptor.

G protein-coupled receptors are recognized as one of the largest families of membrane proteins. Despite sharing a characteristic seven-transmembrane topology, G protein-coupled receptors regulate a wide range of cellular signaling pathways in response to various physical and chemical stimuli, and prevail as an important target for drug discovery. Notably, the recent progress in crystallographic methods led to a breakthrough in elucidating the structures of membrane proteins. The structures of ß2-adrenergic receptor bound with a variety of ligands provide atomic details of the binding modes of agonists, antagonists and inverse agonists. In this study, we selected four representative molecules from each functional class of ligands and investigated their impacts on ß2-adrenergic receptor through a total of 12 × 100 ns molecular dynamics simulations. From the obtained trajectories, we generated molecular fingerprints exemplifying propensities of protein-ligand interactions. For each functional class of compounds, we characterized and compared the fluctuation of the protein backbone, the volumes in the intracellular pockets, the water densities in the receptors, the domain interaction networks as well as the movements of transmembrane helices. We discovered that each class of ligands exhibits a distinct mode of interactions with mainly TM5 and TM6, altering the shape and eventually the state of the receptor. Our findings provide insightful prospective into GPCR targeted structure-based drug discoveries.

Accelerated molecular dynamics simulations of the octopamine receptor using GPUs: discovery of an alternate agonist-binding position.

Octopamine receptors (OARs) perform key biological functions in invertebrates, making this class of G-protein coupled receptors (GPCRs) worth considering for insecticide development. However, no crystal structures and very little research exists for OARs. Furthermore, GPCRs are large proteins, are suspended in a lipid bilayer, and are activated on the millisecond timescale, all of which make conventional molecular dynamics (MD) simulations infeasible, even if run on large supercomputers. However, accelerated Molecular Dynamics (aMD) simulations can reduce this timescale to even hundreds of nanoseconds, while running the simulations on graphics processing units (GPUs) would enable even small clusters of GPUs to have processing power equivalent to hundreds of CPUs. Our results show that aMD simulations run on GPUs can successfully obtain the active and inactive state conformations of a GPCR on this reduced timescale. Furthermore, we discovered a potential alternate active-state agonist-binding position in the octopamine receptor which has yet to be observed and may be a novel GPCR agonist-binding position. These results demonstrate that a complex biological system with an activation process on the millisecond timescale can be successfully simulated on the nanosecond timescale using a simple computing system consisting of a small number of GPUs. Proteins 2016; 84:1480-1489. © 2016 Wiley Periodicals, Inc.

Recruitment of ß-arrestin 1 and 2 to the ß2-adrenoceptor: analysis of 65 ligands.

UNLABELLED: Beyond canonical signaling via Gαs and cAMP, the concept of functional selectivity at ß2-adrenoceptors (ß2ARs) describes the ability of adrenergic drugs to stabilize ligand-specific receptor conformations to initiate further signaling cascades comprising additional G-protein classes or ß-arrestins (ßarr). A set of 65 adrenergic ligands including 40 agonists and 25 antagonists in either racemic or enantiopure forms was used for ßarr recruitment experiments based on a split-luciferase assay in a cellular system expressing ß2AR. Many agonists showed only (weak) partial agonism regarding ßarr recruitment. Potencies and/or efficacies increased depending on the number of chirality centers in (R) configuration; no (S)-configured distomer was more effective at inducing ßarr recruitment other than the eutomer. ßarr2 was recruited more effectively than ßarr1. The analysis of antagonists revealed no significant effects on ßarr recruitment. Several agonists showed preference for activation of Gαs GTPase relative to ßarr recruitment, and no ßarr-biased ligand was identified. IN CONCLUSION: 1) agonists show strong bias for Gαs activation relative to ßarr recruitment; 2) agonists recruit ßarr1 and ßarr2 with subtle differences; and 3) there is no evidence for ßarr recruitment by antagonists.

Mapping functional group free energy patterns at protein occluded sites: nuclear receptors and G-protein coupled receptors.

Occluded ligand-binding pockets (LBP) such as those found in nuclear receptors (NR) and G-protein coupled receptors (GPCR) represent a significant opportunity and challenge for computer-aided drug design. To determine free energies maps of functional groups of these LBPs, a Grand-Canonical Monte Carlo/Molecular Dynamics (GCMC/MD) strategy is combined with the Site Identification by Ligand Competitive Saturation (SILCS) methodology. SILCS-GCMC/MD is shown to map functional group affinity patterns that recapitulate locations of functional groups across diverse classes of ligands in the LBPs of the androgen (AR) and peroxisome proliferator-activated-γ (PPARγ) NRs and the metabotropic glutamate (mGluR) and ß2-adreneric (ß2AR) GPCRs. Inclusion of protein flexibility identifies regions of the binding pockets not accessible in crystal conformations and allows for better quantitative estimates of relative ligand binding affinities in all the proteins tested. Differences in functional group requirements of the active and inactive states of the ß2AR LBP were used in virtual screening to identify high efficacy agonists targeting ß2AR in Airway Smooth Muscle (ASM) cells. Seven of the 15 selected ligands were found to effect ASM relaxation representing a 46% hit rate. Hence, the method will be of use for the rational design of ligands in the context of chemical biology and the development of therapeutic agents.

Interaction of fenoterol stereoisomers with ß2-adrenoceptor-G sα fusion proteins: antagonist and agonist competition binding.

The specific interaction between G-protein-coupled receptors and ligand is the starting point for downstream signaling. Fenoterol stereoisomers were successfully used to probe ligand-specific activation (functional selectivity) of the ß2-adrenoceptor (ß2AR) (Reinartz et al. 2015). In the present study, we extended the pharmacological profile of fenoterol stereoisomers using ß2AR-Gsα fusion proteins in agonist and antagonist competition binding assays. Dissociations between binding affinities and effector potencies were found for (R,S')- and (S,S')-isomers of 4'-methoxy-1-naphthyl-fenoterol. Our data corroborate former studies on the importance of the aminoalkyl moiety of fenoterol derivatives for functional selectivity.

Ultra-trace analysis of 12 ß2-agonists in pork, beef, mutton and chicken by ultrahigh-performance liquid-chromatography-quadrupole-orbitrap tandem mass spectrometry.

This paper presents an application of ultrahigh-performance liquid-chromatography - quadrupole - orbitrap high resolution mass spectrometry (UHPLC-Q-Orbitrap HRMS) for the ultra-trace analysis of 12 ß2-agonists in pork, beef, mutton and chicken meat. The mass spectrometer was operated in Full MS/dd-MS(2) (data-dependent MS(2)) mode, under which a Full MS scan was followed by a dd-MS(2) scan with a fragmentation energy. The quantification was achieved using matrix-matched standard calibration curves with salbutamol-d3 and clenbuterol-d9 as the internal standards. The method validation included assessment of selectivity, sensitivity, calibration curve, accuracy, precision, recovery, matrix effect and stability. The results show an exceptional linear relationship with the concentrations of the analytes over wide concentration ranges (e.g., 0.01-50 µg/kg for clenbuterol) as all the fitting coefficients of determination r(2) are >0.9986. The detection limits (LODs) were in the range of 0.0033-0.01 µg/kg, which was much lower than the current reported methods. The recoveries were able to reach 73.0-88.7%, while the matrix effects ranged from 83.7% to 92.8%. Analysis of 400 pork, beef, mutton and chicken samples reveal that only 4.25% samples were positive for ß2-agonists. The detected ß2-agonists involved salbutamol, clenbuterol, ractopamine and clorprenaline. Overall, the novel Q-Orbitrap technique was demonstrated to have great performance for the screening, identification and quantification of ultra-trace ß2-agonists used in food animal muscles, which helps to ensure food safety and public health.

Discovery of high affinity ligands for ß2-adrenergic receptor through pharmacophore-based high-throughput virtual screening and docking.

Novel high affinity compounds for human ß2-adrenergic receptor (ß2-AR) were searched among the clean drug-like subset of ZINC database consisting of 9,928,465 molecules that satisfy the Lipinski's rule of five. The screening protocol consisted of a high-throughput pharmacophore screening followed by an extensive amount of docking and rescoring. The pharmacophore model was composed of key features shared by all five inactive states of ß2-AR in complex with inverse agonists and antagonists. To test the discriminatory power of the pharmacophore model, a small-scale screening was initially performed on a database consisting of 117 compounds of which 53 antagonists were taken as active inhibitors and 64 agonists as inactive inhibitors. Accordingly, 7.3% of the ZINC database subset (729,413 compounds) satisfied the pharmacophore requirements, along with 44 antagonists and 17 agonists. Afterwards, all these hit compounds were docked to the inactive apo form of the receptor using various docking and scoring protocols. Following each docking experiment, the best pose was further evaluated based on the existence of key residues for antagonist binding in its vicinity. After final evaluations based on the human intestinal absorption (HIA) and the blood brain barrier (BBB) penetration properties, 62 hit compounds have been clustered based on their structural similarity and as a result four scaffolds were revealed. Two of these scaffolds were also observed in three high affinity compounds with experimentally known Ki values. Moreover, novel chemical compounds with distinct structures have been determined as potential ß2-AR drug candidates.

Observed drug-receptor association rates are governed by membrane affinity: the importance of establishing "micro-pharmacokinetic/pharmacodynamic relationships" at the ß2-adrenoceptor.

Current pharmacological models for determining affinity and kinetics of drugs for membrane receptors assume the interacting molecules are homogeneously distributed in the bulk aqueous phase. The phospholipid membrane can, however, provide a second compartment into which drugs can partition, particularly lipophilic/basic compounds. In this study we measured the phospholipid affinity and receptor binding kinetics of several clinically relevant ß2-adrenoceptor agonists and antagonists and demonstrated that the degree of phospholipid interaction directly affects the observed kinetic association rate (k on) and dissociation constant (Kd), but not the dissociation rate (k off) from the target, by concentrating drug in the local environment around the receptor. When the local drug concentration was accounted for, the k on was comparable across the cohort and the corrected Kd was directly related to the k off. In conclusion, we propose a new approach to determining the pharmacology of drugs for membrane targets that accounts for differences in local drug concentration brought about by direct affinity for phospholipids, establishing "micro-pharmacokinetic/pharmacodynamic relationships" for drugs.

Foamy macrophage responses in the rat lung following exposure to inhaled pharmaceuticals: a simple, pragmatic approach for inhaled drug development.

Successes in the field of respiratory medicines are largely limited to three main target classes: ß2 -adrenergic receptor agonists, muscarinic antagonists and corticosteroids. A significant factor in attrition during the development of respiratory medicines is the induction of foamy macrophage responses, particularly, in rats. The term foamy macrophage describes a vacuolated cytoplasmic appearance, seen by light microscopy, which is ultrastructurally characterized by the presence of lysosomal lamellar bodies, neutral lipid droplets or drug particles. We propose a simple classification, based light-heartedly on the theme 'the good, the bad and the ugly', which allows important distinctions to be made between phenotypes, aetiologies and adversity. Foamy macrophages induced in rat lungs by exposure to inhaled ß2 -agonists, antimuscarinics and corticosteroids are simple aggregates of uniform cells without other associated pathologies. In contrast, macrophage reactions induced by some other inhaled drug classes are more complex, associated with neutrophilic or lymphocytic infiltrations with/without damage to the adjacent alveolar walls. Foamy macrophage responses induced by inhaled drugs may be ascribed to either phagocytosis of poorly soluble drug particles, or to pharmacology. Both corticosteroids and ß2 -agonists increase surfactant synthesis whereas muscarinic antagonists may decrease surfactant breakdown, due to inhibition of phospholipase C, both of which lead to phagocytosis of excess surfactant. Simple foamy macrophage responses are considered non-adverse, whereas ones that are more complex are designated as adverse. The development of foamy macrophage responses has led to confusion in interpretation and we hope this review helps clarify what is in fact a relatively simple, predictable, easily interpretable, commonly induced change.