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The 5-hydroxytryptamine (5-HT) and dopamine (DA) receptors have emerged as significant targets for therapeutic intervention in psychiatric disorders. Currently, the efficacy of psychiatric drugs is limited by challenges in achieving desired outcomes, the occurrence of adverse effects, dependence, and withdrawal reactions. Consequently, there is a pressing need for the development of safe and effective therapeutic agents for psychiatric disorders. To explore the potential effects of natural product extracts as therapeutic agents for psychiatric disorders, 73 active ingredients from natural medicine extracts were screened to identify potential inhibitors of the serotonin 2A receptor (5-HT2AR) and dopamine D2 receptor (DRD2) using computerized virtual molecular docking. The most effective inhibitor of 5-HT2AR and DRD2 among these natural extracts was then evaluated for its drug-like properties using ADMET analysis, and its mechanisms of antagonism on DRD2 and 5-HT2AR were studied through molecular dynamics simulation. Risperidone was used as a positive control drug. The results showed that ruscogenin (RUS) was the most effective inhibitor of 5-HT2AR and DRD2, possessing favorable drug-like properties (most values of ADMET analysis were within the optimal range). When compared to risperidone, RUS exhibited more stable root mean square deviation (RMSD) plots, lower root mean square fluctuation (RMSF) values from residues 50 to 260, stronger hydrogen bonding interactions, higher compactness, a smaller solvent-accessible surface area (SASA) value, and lower binding free energy (-43.81 kcal/mol vs. -35.68 kcal/mol). RUS also demonstrated inhibitory effects on DRD2, as indicated by stable RMSD plots, low RMSF values from residues 50 to 250, strong hydrogen bonding interactions, high compactness, a small SASA value, and low binding free energy (-35.00 kcal/mol). Consequently, this research suggests that RUS, a natural pharmaceutical extract, is a promising candidate for further validation through clinical studies, representing a potential development of a therapeutic agent targeting psychiatric disorders., Competing Interests: The authors declare no conflicts of interest., (Copyright: This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.)

The ability of oxytocin (OT) to interact with the dopaminergic system through facilitatory D2-OT receptor (OTR) receptor-receptor interaction in the limbic system is increasingly considered to play roles in social or emotional behavior, and suggested to serve as a potential therapeutic target. Although roles of astrocytes in the modulatory effects of OT and dopamine in the central nervous system are well recognized, the possibility of D2-OTR receptor-receptor interaction in astrocytes has been neglected. In purified astrocyte processes from adult rat striatum, we assessed OTR and dopamine D2 receptor expression by confocal analysis. The effects of activation of these receptors were evaluated in the processes through a neurochemical study of glutamate release evoked by 4-aminopyridine; D2-OTR heteromerization was assessed by co-immunoprecipitation and proximity ligation assay (PLA). The structure of the possible D2-OTR heterodimer was estimated by a bioinformatic approach. We found that both D2 and OTR were expressed on the same astrocyte processes and controlled the release of glutamate, showing a facilitatory receptor-receptor interaction in the D2-OTR heteromers. Biochemical and biophysical evidence confirmed D2-OTR heterodimers on striatal astrocytes. The residues in the transmembrane domains four and five of both receptors are predicted to be mainly involved in the heteromerization. In conclusion, roles for astrocytic D2-OTR in the control of glutamatergic synapse functioning through modulation of astrocytic glutamate release should be taken into consideration when considering interactions between oxytocinergic and dopaminergic systems in striatum.

D3/D2 sub-specificity is a complex problem to solve. Indeed, in the absence of easy structural biology of the G-protein coupled receptors, and despite key progresses in this area, the systematic knowledge of the ligand/receptor relationship is difficult to obtain. Due to these structural biology limitations concerning membrane proteins, we favored the use of directed mutagenesis to document a rational towards the discovery of markedly specific D3 ligands over D2 ligands together with basic binding experiments. Using our methodology of stable expression of receptors in HEK cells, we constructed the gene encoding for 24 mutants and 4 chimeras of either D2 or D3 receptors and expressed them stably. Those cell lines, expressing a single copy of one receptor mutant each, were stably constructed, selected, amplified and the membranes from them were prepared. Binding data at those receptors were obtained using standard binding conditions for D2 and D3 dopamine receptors. We generated 26 new molecules derived from D2 or D3 ligands. Using 8 reference compounds and those 26 molecules, we characterized their binding at those mutants and chimeras, exemplifying an approach to better understand the difference at the molecular level of the D2 and D3 receptors. Although all the individual results are presented and could be used for minute analyses, the present report does not discuss the differences between D2 and D3 data. It simply shows the feasibility of the approach and its potential., (© 2022 The Protein Society.)

Dopamine is one of the crucial neurotransmitters in the human brain. Its out-of-range concentration can lead to various neurological diseases with special interest for dopamine D 2 and D 3 receptor subtypes. Although BODIPY is a highly versatile structural moiety for fluorescence labeling, we have looked out for structurally related pyridine-based moieties. We used BOPPY labelling of well-described D 2 R/D 3 R pharmacophores to obtain ligands with moderate to low nanomolar binding affinities as well as low to excellent quantum yields for bright fluorescence ligands. To best of our knowledge, this is the first report on the application of BOPPY fluorophores to GPCR ligands. This approach offers a general applicable way for fluorescence labelling via primary aliphatic amine elements., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The application of deep learning to generative molecule design has shown early promise for accelerating lead series development. However, questions remain concerning how factors like training, data set, and seed bias impact the technology's utility to medicinal and computational chemists. In this work, we analyze the impact of seed and training bias on the output of an activity-conditioned graph-based variational autoencoder (VAE). Leveraging a massive, labeled data set corresponding to the dopamine D2 receptor, our graph-based generative model is shown to excel in producing desired conditioned activities and favorable unconditioned physical properties in generated molecules. We implement an activity-swapping method that allows for the activation, deactivation, or retention of activity of molecular seeds, and we apply independent deep learning classifiers to verify the generative results. Overall, we uncover relationships between noise, molecular seeds, and training set selection across a range of latent-space sampling procedures, providing important insights for practical AI-driven molecule generation.

The dopamine D 2 receptor, belonging to the class A G protein-coupled receptors (GPCRs), is an important drug target for several diseases, including schizophrenia and Parkinson's disease. The D 2 receptor can be activated by the natural neurotransmitter dopamine or by synthetic ligands, which in both cases leads to the receptor coupling with a G protein. In addition to receptor modulation by orthosteric or allosteric ligands, it has been shown that lipids may affect the behaviour of membrane proteins. We constructed a model of a D 2 receptor with a long intracellular loop (ICL3) coupled with G iα1 or G iα2 proteins, embedded in a complex asymmetric membrane, and simulated it in complex with positive, negative or neutral allosteric ligands. In this study, we focused on the influence of ligand binding and G protein coupling on the membrane-receptor interactions. We show that there is a noticeable interplay between the cell membrane, G proteins, D 2 receptor and its modulators.

DRD2 is a neuronal cell surface protein involved in brain development and function. Variations in the Drd2 gene have clinical significance since DRD2 is a pharmacotherapeutic target for treating psychiatric disorders like ADHD and schizophrenia. Despite numerous studies on the disease association of single nucleotide polymorphisms (SNPs) in the intronic regions, investigation into the coding regions is surprisingly limited. In this study, we aimed at identifying potential functionally and pharmaco-therapeutically deleterious non-synonymous SNPs of Drd2. A wide array of bioinformatics tools was used to evaluate the impact of nsSNPs on protein structure and functionality. Out of 260 nsSNPs retrieved from the dbSNP database, initially 9 were predicted as deleterious by 15 tools. Upon further assessment of their domain association, conservation profile, homology models and inter-atomic interaction, the mutant F389V was considered as the most impactful. In-depth analysis of F389V through Molecular Docking and Dynamics Simulation revealed a decline in affinity for its native agonist dopamine and an increase in affinity for the antipsychotic drug risperidone. Remarkable alterations in binding interactions and stability of the protein-ligand complex in simulated physiological conditions were also noted. These findings will improve our understanding of the consequence of nsSNPs in disease-susceptibility and therapeutic efficacy., (© 2021. The Author(s).)

ONC201 is a first-in-class imipridone compound that is in clinical trials for the treatment of high-grade gliomas and other advanced cancers. Recent studies identified that ONC201 antagonizes D2-like dopamine receptors at therapeutically relevant concentrations. In the current study, characterization of ONC201 using radioligand binding and multiple functional assays revealed that it was a full antagonist of the D2 and D3 receptors (D2R and D3R) with low micromolar potencies, similar to its potency for antiproliferative effects. Curve-shift experiments using D2R-mediated β -arrestin recruitment and cAMP assays revealed that ONC201 exhibited a mixed form of antagonism. An operational model of allostery was used to analyze these data, which suggested that the predominant modulatory effect of ONC201 was on dopamine efficacy with little to no effect on dopamine affinity. To investigate how ONC201 binds to the D2R, we employed scanning mutagenesis coupled with a D2R-mediated calcium efflux assay. Eight residues were identified as being important for ONC201's functional antagonism of the D2R. Mutation of these residues followed by assessing ONC201 antagonism in multiple signaling assays highlighted specific residues involved in ONC201 binding. Together with computational modeling and simulation studies, our results suggest that ONC201 interacts with the D2R in a bitopic manner where the imipridone core of the molecule protrudes into the orthosteric binding site, but does not compete with dopamine, whereas a secondary phenyl ring engages an allosteric binding pocket that may be associated with negative modulation of receptor activity. SIGNIFICANCE STATEMENT: ONC201 is a novel antagonist of the D2 dopamine receptor with demonstrated efficacy in the treatment of various cancers, especially high-grade glioma. This study demonstrates that ONC201 antagonizes the D2 receptor with novel bitopic and negative allosteric mechanisms of action, which may explain its high selectivity and some of its clinical anticancer properties that are distinct from other D2 receptor antagonists widely used for the treatment of schizophrenia and other neuropsychiatric disorders., (U.S. Government work not protected by U.S. copyright.)

In this pilot study, a series of new 3,4-dihydroquinolin-2(1 H )-one derivatives as potential dopamine receptor D 2 (D 2 R) modulators were synthesized and evaluated in vitro. The preliminary structure-activity relationship disclosed that compound 5e exhibited the highest D 2 R affinity among the newly synthesized compounds. In addition, 5e showed a very low cytotoxic profile and a high probability to cross the blood-brain barrier, which is important considering the observed affinity. However, molecular modelling simulation revealed completely different binding mode of 5e compared to USC-D301, which might be the culprit of the reduced affinity of 5e toward D 2 R in comparison with USC-D301.

We previously proposed that the dopamine D2 receptor-interacting protein S100B binds to a putative S100B-binding motif at residues R233-L240 toward the N terminus of the third intracellular loop. We used in vitro pull-down assays with FLAG-tagged fragments of the rat dopamine D2 receptor third intracellular loop (D2-IC3) and in vitro-synthesized S100B to evaluate this hypothesis. Our results indicate that the putative S100B-binding motif is neither necessary nor sufficient for strong binding of S100B to D2-IC3. Instead, two residues at the junction of the fifth membrane-spanning domain and the cytoplasmic extension of that α -helical domain, K211-I212, are required for robust, calcium-sensitive binding of S100B. This is also the approximate location of previously identified determinants for the binding of arrestin and calmodulin. A D2 receptor mutation converting I212 to phenylalanine has been described in patients with a hyperkinetic movement disorder. SIGNIFICANCE STATEMENT: S100B is a small calcium-binding protein that modulates signaling by the dopamine D2 receptor. New data suggest that the previous hypothesis about the involvement of an S100B-binding motif is incorrect, and that an important determinant of S100B binding includes a residue that is mutated in patients with a hyperkinetic movement disorder., (U.S. Government work not protected by U.S. copyright.)

Psychosis is one of the psychiatric disorders that is controlled by dopaminergic drugs such as antipsychotics that have affinity for the dopamine D2 receptor (DRD2). In this investigation we perform quantum chemical calculations of two molecules [dopamine and risperidone] within a large cavity of DRD2 that represents the binding site of the receptor. Dopamine is an endogenous neurotransmitter and risperidone is a second-generation antipsychotic. Non-covalent interactions of dopamine and risperidone with DRD2 are analyzed using the Quantum Theory of Atoms in Molecules (QTAIM) and the Non-Covalent Interaction index (NCI). The QTAIM results show that these molecules strongly interact with the receptor. There are 22 non-covalent interactions for dopamine and 54 for risperidone. The electron density evaluated at each critical binding point is small in both systems but it is higher for dopamine than for risperidone, indicating that the interactions of DRD2 with the first are stronger than with the second molecule. However, the binding energy is higher for risperidone (-72.6 kcal mol-1) than for dopamine (-22.8 kcal mol-1). Thus, the strength of the binding energy is due to the number of contacts rather than the strength of the interactions themselves. This could be related to the ability of risperidone to block DRD2 and may explain the efficacy of this drug for controlling the symptoms of schizophrenia, but likewise its secondary effects.

N- phenylpiperazine analogs can bind selectively to the D3 versus the D2 dopamine receptor subtype despite the fact that these two D2-like dopamine receptor subtypes exhibit substantial amino acid sequence homology. The binding for a number of these receptor subtype selective compounds was found to be consistent with their ability to bind at the D3 dopamine receptor subtype in a bitopic manner. In this study, a series of the 3-thiophenephenyl and 4-thiazolylphenyl fluoride substituted N -phenylpiperazine analogs were evaluated. Compound 6a was found to bind at the human D3 receptor with nanomolar affinity with substantial D3 vs. D2 binding selectivity (approximately 500-fold). Compound 6a was also tested for activity in two in-vivo assays: (1) a hallucinogenic-dependent head twitch response inhibition assay using DBA/2J mice and (2) an L-dopa-dependent abnormal involuntary movement (AIM) inhibition assay using unilateral 6-hydroxydopamine lesioned (hemiparkinsonian) rats. Compound 6a was found to be active in both assays. This compound could lead to a better understanding of how a bitopic D3 dopamine receptor selective ligand might lead to the development of pharmacotherapeutics for the treatment of levodopa-induced dyskinesia (LID) in patients with Parkinson's disease.

More recently, there has been a paradigm shift toward selective drug targeting in the treatment of neurological disorders, including drug addiction, schizophrenia, and Parkinson's disease mediated by the different dopamine receptor subtypes. Antagonists with higher selectivity for D 3 dopamine receptor (D3DR) over D 2 dopamine receptor (D2DR) have been shown to attenuate drug-seeking behavior and associated side effects compared to non-subtype selective antagonists. However, high conservations among constituent residues of both proteins, particularly at the ligand-binding pockets, remain a challenge to therapeutic drug design. Recent studies have reported the discovery of two small-molecules R-VK4-40 and Y-QA31 which substantially inhibited D3DR with >180-fold selectivity over D2DR. Therefore, in this study, we seek to provide molecular and structural insights into these differential binding mechanistic using meta-analytic computational simulation methods. Findings revealed that R-VK4-40 and Y-QA31 adopted shallow binding modes and were more surface-exposed at D3DR while on the contrary, they exhibited deep hydrophobic pocket binding at D2DR. Also, two non-conserved residues; Tyr36 1.39 and Ser182 45.51 were identified in D3DR, based on their crucial roles and contributions to the selective binding of R-VK4-40 and Y-QA31. Importantly, both antagonists exhibited high affinities in complex with D3DR compared to D2DR, while van der Waals energies contributed majorly to their binding and stability. Structural analyses also revealed the distinct stabilizing effects of both compounds on D3DR secondary architecture relative to D2DR. Therefore, findings herein pinpointed the origin and mechanistic of selectivity of the compounds, which may assist in the rational design of potential small molecules of the D 2 -like dopamine family receptor subtype with improved potency and selectivity., (© 2021 John Wiley & Sons Ltd.)

The forward (k on ) and reverse (k off ) rate constants of drug-target interactions have important implications for therapeutic efficacy. Hence, time-resolved assays capable of measuring these binding rate constants may be informative to drug discovery efforts. Here, we used an ion channel activation assay to estimate the k on s and k off s of four dopamine D 2 receptor (D 2 R) agonists; dopamine (DA), p-tyramine, (R)- and (S)-5-OH-dipropylaminotetralin (DPAT). We further probed the role of the conserved serine S193 5.42 by mutagenesis, taking advantage of the preferential interaction of (S)-, but not (R)-5-OH-DPAT with this residue. Results suggested similar k off s for the two 5-OH-DPAT enantiomers at wild-type (WT) D 2 R, both being slower than the k off s of DA and p-tyramine. Conversely, the k on of (S)-5-OH-DPAT was estimated to be higher than that of (R)-5-OH-DPAT, in agreement with the higher potency of the (S)-enantiomer. Furthermore, S193 5.42 A mutation lowered the k on of (S)-5-OH-DPAT and reduced the potency difference between the two 5-OH-DPAT enantiomers. Kinetic K d s derived from the k off and k on estimates correlated well with EC 50 values for all four compounds across four orders of magnitude, strengthening the notion that our assay captured meaningful information about binding kinetics. The approach presented here may thus prove valuable for characterizing D 2 R agonist candidate drugs.

D2 dopamine receptors (DRD2s) belong to a family of G protein-coupled receptors that modulate synaptic dopaminergic tone via regulation of dopamine synthesis, storage, and synaptic release. DRD2s are the primary target for traditional antipsychotic medications; dysfunctional DRD2 signaling has been linked to major depressive disorder, attention-deficit hyperactivity disorder, addiction, Parkinson's, and schizophrenia. DRD2 lateral diffusion appears to be an important post-translational regulatory mechanism; however, the dynamic response of DRD2s to ligand-induced activation is poorly understood. Dynamic imaging of the long isoform of DRD2 (D2L) fused to an N-terminal antihemagglutinin (HA) epitope and transiently expressed in HEK-293 cells was achieved through a combination of a high-affinity biotinylated anti-HA antigen-binding fragment (Fab) and streptavidin-conjugated quantum dots (QD). Significant reduction (∼40%) in the rate of lateral diffusion of QD-tagged D2L proteins was observed under agonist (quinpirole; QN)-stimulated conditions compared to basal conditions. QN-induced diffusional slowing was accompanied by an increase in frequency, lifetime, and confinement of temporary arrest of lateral diffusion (TALL), an intrinsic property of single receptor lateral motion. The role of the actin cytoskeleton in QN-induced diffusional slowing of D2L was also explored. The observed dynamic changes appear to be a sensitive indicator of the receptor activity status and might also spatially and temporally shape the receptor-mediated downstream signaling. This dynamic information could potentially be useful in informing drug discovery efforts based on single-molecule pharmacology.

The D1- and D2-dopamine receptors (D1R and D2R), which signal through G s and G i , respectively, represent the principal stimulatory and inhibitory dopamine receptors in the central nervous system. D1R and D2R also represent the main therapeutic targets for Parkinson's disease, schizophrenia, and many other neuropsychiatric disorders, and insight into their signaling is essential for understanding both therapeutic and side effects of dopaminergic drugs. Here, we report four cryoelectron microscopy (cryo-EM) structures of D1R-G s and D2R-G i signaling complexes with selective and non-selective dopamine agonists, including two currently used anti-Parkinson's disease drugs, apomorphine and bromocriptine. These structures, together with mutagenesis studies, reveal the conserved binding mode of dopamine agonists, the unique pocket topology underlying ligand selectivity, the conformational changes in receptor activation, and potential structural determinants for G protein-coupling selectivity. These results provide both a molecular understanding of dopamine signaling and multiple structural templates for drug design targeting the dopaminergic system., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Background: Depression and stress-related disorders are leading causes of death worldwide. Standard treatments elevating serotonin or noradrenaline levels are not sufficiently effective and cause adverse side effects. A connection between dopamine pathways and stress-related disorders has been suggested. Compounds derived from herbal medicine could be a promising alternative. We examined the neuroprotective effects of ursolic acid (UA) by focusing on dopamine signalling., Methods: Trolox equivalent capacity assay was used to determine the antioxidant activities of UA in vitro. C. elegans N2 wildtype and dopamine receptor-knockout mutants (dop1-deficient RB665 and dop3-deficient LX703 strains) were used as in vivo models. H 2 DCFDA and acute juglone assays were applied to determine the antioxidant activity in dependency of dopamine pathways in vivo. Stress was assessed by heat and acute osmotic stress assays. The influence of UA on overall survival was analyzed by a life span assay. The dop1 and dop3 mRNA expression was determined by real time RT-PCR. We also examined the binding affinity of UA towards C. elegans Dop1 and Dop3 receptors as well as human dopamine receptors D1 and D3 by molecular docking., Results: Antioxidant activity assays showed that UA exerts strong antioxidant activity. UA increased resistance towards oxidative, osmotic and heat stress. Additionally, UA increased life span of nematodes. Moreover, dop1 and dop3 gene expression was significantly enhanced upon UA treatment. Docking analysis revealed stronger binding affinity of UA to C. elegans and human dopamine receptors than the natural ligand, dopamine. Binding to Dop1 was stronger than to Dop3., Conclusion: UA reduced stress-dependent ROS generation and acted through Dop1 and to a lesser extent through Dop3 to reduce stress and prolong life span in C. elegans. These results indicate that UA could be a promising lead compound for the development of new antidepressant medications., (Copyright © 2020. Published by Elsevier GmbH.)

In addition to the serotonin 5-HT 2A receptor (5-HT 2A R), the dopamine D 2 receptor (D 2 R) is a key therapeutic target of antipsychotics for the treatment of schizophrenia. The inactive state structures of D 2 R have been described in complex with the inverse agonists risperidone (D 2 R ris ) and haloperidol (D 2 R hal ). Here we describe the structure of human D 2 R in complex with spiperone (D 2 R spi ). In D 2 R spi , the conformation of the extracellular loop (ECL) 2, which composes the ligand-binding pocket, was substantially different from those in D 2 R ris and D 2 R hal , demonstrating that ECL2 in D 2 R is highly dynamic. Moreover, D 2 R spi exhibited an extended binding pocket to accommodate spiperone's phenyl ring, which probably contributes to the selectivity of spiperone to D 2 R and 5-HT 2A R. Together with D 2 R ris and D 2 R hal , the structural information of D 2 R spi should be of value for designing novel antipsychotics with improved safety and efficacy.

In medicinal chemistry, it is extremely important to evaluate, as accurately as possible, the molecular interactions involved in the formation of different ligand-receptor (L-R) complexes. Evaluating the different molecular interactions by quantum mechanics calculations is not a simple task, since formation of an L-R complex is a dynamic process. In this case, the use of combined techniques of molecular dynamics (MD) and quantum calculations is one the best possible approaches. In this work we report a comparative study using combined MD and QTAIM (Quantum Theory of Atoms In Molecules) calculations for five biological systems with different levels of structural complexity. We have studied Acetylcholinesterase (AChE), D2 Dopamine Receptor (D2DR), beta Secretase (BACE1), Dihydrofolate Reductase (DHFR) and Sphingosine Kinase 1 (SphK1). In these molecular targets, we have analyzed different ligands with diverse structural characteristics. The inhibitory activities of most of them have been previously measured in our laboratory. Our results indicate that QTAIM calculations can be extremely useful for in silico studies. It is possible to obtain very accurate information about the strength of the molecular interactions that stabilize the formation of the different L-R complexes. Better correlations can be obtained between theoretical and experimental data by using QTAIM calculations, allowing us to discriminate among ligands with similar affinities. QTAIM analysis gives fairly accurate information for weak interactions which are not well described by MD simulations. QTAIM study also allowed us to evaluate and determine which parts of the ligand need to be modified in order to increase its interactions with the molecular target. In this study we have discussed the importance of combined MD/QTAIM calculations for this type of simulations, showing their scopes and limitations., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Masson SAS. All rights reserved.)

Fluorescent ligands are versatile tools for the study of G protein-coupled receptors. Depending on the fluorophore, they can be used for a range of different applications, including fluorescence microscopy and bioluminescence or fluorescence resonance energy transfer (BRET or FRET) assays. Starting from phenylpiperazines and indanylamines, privileged scaffolds for dopamine D 2 -like receptors, we developed dansyl-labeled fluorescent ligands that are well accommodated in the binding pockets of D 2 and D 3 receptors. These receptors are the target proteins for the therapy for several neurologic and psychiatric disorders, including Parkinson's disease and schizophrenia. The dansyl-labeled ligands exhibit binding affinities up to 0.44 nM and 0.29 nM at D 2 R and D 3 R, respectively. When the dansyl label was exchanged for sterically more demanding xanthene or cyanine dyes, fluorescent ligands 10a-c retained excellent binding properties and, as expected from their indanylamine pharmacophore, acted as agonists at D 2 R. While the Cy3B-labeled ligand 10b was used to visualize D 2 R and D 3 R on the surface of living cells by total internal reflection microscopy, ligand 10a comprising a rhodamine label showed excellent properties in a NanoBRET binding assay at D 3 R.

Significant advancement of chemoproteomics has contributed to uncovering the mechanism of action (MoA) of small-molecule drugs by characterizing drug-protein interactions in living systems. However, cell-membrane proteins such as G protein-coupled receptors (GPCRs) and ion channels, due to their low abundance and unique biophysical properties associated with multiple transmembrane domains, can present challenges for proteome-wide mapping of drug-receptor interactions. Herein, we describe the development of novel tetrafunctional probes, consisting of (1) a ligand of interest, (2) 2-aryl-5-carboxytetrazole (ACT) as a photoreactive group, (3) a hydrazine-labile cleavable linker, and (4) biotin for enrichment. In live cell labeling studies, we demonstrated that the ACT-based probe showed superior reactivity and selectivity for labeling on-target GPCR by mass spectrometry analysis compared with control probes including diazirine-based probes. By leveraging ACT-based cleavable probes, we further identified a set of representative ionotropic receptors, targeted by CNS drugs, with remarkable selectivity and precise binding site information from mouse brain slices. We anticipate that the robust chemoproteomic platform using the ACT-based cleavable probe coupled with phenotypic screening should promote identification of pharmacologically relevant target receptors of drug candidates and ultimately development of first-in-class drugs with novel MoA.

Purpose: Dopamine D2-like receptors (D2) mediate various effects of dopamine. Characterizing the structural and functional regions can contribute to understanding the mechanism of biological effects of dopamine., Methods: A large scale phylogeny was utilized to construct a comprehensive dataset of D2 receptor, the evolutionary conserved residues were calculated at both super-family and sub-family (included human D2clade) levels, and then 3D structure of human D2 receptor (DRD2) was modeled to evaluate the significance of these conserved residues and motifs linked with structural stability, genetic variants, functional activation, protein interaction and drug binding., Results: All the drug binding sites and important protein-complex binding motifs showed evolutionary super-family conservation. However, genetic variants linked to different diseases all belonged to sub-family conservation. The extra cellular loop (ECL3) domain consisted of both super-family and sub-family conserved residues., Conclusions: Sub-family conserved residues probably play a vital role in the incidence and progression of diseases., Competing Interests: Declaration of Competing Interest There are no potential conflicts of interest to disclose., (Copyright © 2020 Elsevier B.V. All rights reserved.)

We report an exhaustive conformational and electronic study on dopamine (DA) interacting with the D 2 dopamine receptor (D 2 DR). For the first time, the complete surface of the conformational potential energy of the complex DA/D 2 DR is reported. Such a surface was obtained through the use of QM/MM calculations. A detailed study of the molecular interactions that stabilize and destabilize the different molecular complexes was carried out using two techniques: Quantum Theory of Atoms in Molecules computations and nuclear magnetic shielding constants calculations. A comparative study of the behavior of DA in the gas phase, aqueous solution, and in the active site of D 2 DR has allowed us to evaluate the degree of deformation suffered by the ligand and, therefore, analyze how rustic are the lock-key model and the induced fit theory in this case. Our results allow us to propose one of the conformations obtained as the "biologically relevant" conformation of DA when it is interacting with the D 2 DR., (© 2020 Wiley Periodicals LLC.)

The D2 dopamine receptor (DRD2) is a therapeutic target for Parkinson's disease 1 and antipsychotic drugs 2 . DRD2 is activated by the endogenous neurotransmitter dopamine and synthetic agonist drugs such as bromocriptine 3 , leading to stimulation of G i and inhibition of adenylyl cyclase. Here we used cryo-electron microscopy to elucidate the structure of an agonist-bound activated DRD2-G i complex reconstituted into a phospholipid membrane. The extracellular ligand-binding site of DRD2 is remodelled in response to agonist binding, with conformational changes in extracellular loop 2, transmembrane domain 5 (TM5), TM6 and TM7, propagating to opening of the intracellular G i -binding site. The DRD2-G i structure represents, to our knowledge, the first experimental model of a G-protein-coupled receptor-G-protein complex embedded in a phospholipid bilayer, which serves as a benchmark to validate the interactions seen in previous detergent-bound structures. The structure also reveals interactions that are unique to the membrane-embedded complex, including helix 8 burial in the inner leaflet, ordered lysine and arginine side chains in the membrane interfacial regions, and lipid anchoring of the G protein in the membrane. Our model of the activated DRD2 will help to inform the design of subtype-selective DRD2 ligands for multiple human central nervous system disorders.

The high functional plasticity of the glutamatergic synapse of the vestibular epithelium is supported by a delicate balance of excitatory and inhibitory interactions. One of the peptides co-localized with acetylcholine (ACh) in the efferent fibers is dopamine. Using external perfusion of the synaptic zone and multiunit recording of an afferent fibers activity the effect of dopamine antagonists on the background firing rate of the semicircular canal sensory fibers was studied on the isolated frog vestibular. The present research revealed that the dopamine receptor antagonist (D1) SCH-23390 significantly reduced the level of background activity at high concentrations. In contrast, D2 antagonist eticlopride caused positive-negative answer of the background activity of the sensory fibers in dose-depending manner. The data confirm the hypothesis that dopamine, being tonic released from the efferent fibers, realizes neuroprotective inhibitory control over the afferent glutamatergic synapse activity in the vestibular epithelium via D1 and D2 receptors.

Cell adhesion molecule close homolog of L1 (CHL1) and the dopamine receptor D2 (DRD2) are associated with psychiatric and mental disorders. We here show that DRD2 interacts with CHL1 in mouse brain, as evidenced by co-immunostaining, proximity ligation assay, co-immunoprecipitation, and pull-down assay with recombinant extracellular CHL1 domain fused to Fc (CHL1-Fc). Direct binding of CHL1-Fc to the first extracellular loop of DRD2 was shown by ELISA. Using HEK cells transfected to co-express CHL1 and the short (DRD2-S) or long (DRD2-L) DRD2 isoforms, co-localization of CHL1 and both isoforms was observed by immunostaining and proximity ligation assay. Moreover, CHL1 inhibited agonist-triggered internalization of DRD2-S. Proximity ligation assay showed close interaction between CHL1 and DRD2 in neurons expressing dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP32) or tyrosine hydroxylase (TH) in tissue sections of adult mouse striatum. In cultures of striatum or ventral midbrain, CHL1 was also closely associated with DRD2 in DARPP32- or TH-immunopositive cells, respectively. In the dorsal striatum of CHL1-deficient mice, lower levels of DRD2 and phosphorylated TH were observed, when compared to wild-type littermates. In the ventral striatum of CHL1-deficient mice, levels of phosphorylated DARPP32 were reduced. We propose that CHL1 regulates DRD2-dependent presynaptic and postsynaptic functions., (© 2020 The Authors. The FASEB Journal published by Wiley Periodicals, Inc. on behalf of Federation of American Societies for Experimental Biology.)

By analyzing and simulating inactive conformations of the highly homologous dopamine D 2 and D 3 receptors (D 2 R and D 3 R), we find that eticlopride binds D 2 R in a pose very similar to that in the D 3 R/eticlopride structure but incompatible with the D 2 R/risperidone structure. In addition, risperidone occupies a sub-pocket near the Na + binding site, whereas eticlopride does not. Based on these findings and our experimental results, we propose that the divergent receptor conformations stabilized by Na + -sensitive eticlopride and Na + -insensitive risperidone correspond to different degrees of inverse agonism. Moreover, our simulations reveal that the extracellular loops are highly dynamic, with spontaneous transitions of extracellular loop 2 from the helical conformation in the D 2 R/risperidone structure to an extended conformation similar to that in the D 3 R/eticlopride structure. Our results reveal previously unappreciated diversity and dynamics in the inactive conformations of D 2 R. These findings are critical for rational drug discovery, as limiting a virtual screen to a single conformation will miss relevant ligands., Competing Interests: JL, AA, PA, AK, KL, JS, RV, HL, HY, JJ, LS No competing interests declared

The dopamine D 2 receptor belongs to rhodopsin-like G protein-coupled receptors (GPCRs) and it is an important molecular target for the treatment of many disorders, including schizophrenia and Parkinson's disease. Here, computational methods were used to construct the full models of the dopamine D 2 receptor short (D 2S ) and long (D 2L ) isoforms (differing with 29 amino acids insertion in the third intracellular loop, ICL3) and to study their coupling with G i1 and G i2 proteins. It was found that the D 2L isoform preferentially couples with the G i2 protein and D 2S isoform with the G i1 protein, which is in accordance with experimental data. Our findings give mechanistic insight into the interplay between isoforms of dopamine D 2 receptors and G i proteins subtypes, which is important to understand signaling by these receptors and their mediation by pharmaceuticals, in particular psychotic and antipsychotic agents., Competing Interests: The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Membrane receptors sense and transduce extracellular stimuli into intracellular signaling responses but the molecular underpinnings remain poorly understood. We report a computational approach for designing protein allosteric signaling functions. By combining molecular dynamics simulations and design calculations, the method engineers amino-acid 'microswitches' at allosteric sites that modulate receptor stability or long-range coupling, to reprogram specific signaling properties. We designed 36 dopamine D2 receptor variants, whose constitutive and ligand-induced signaling agreed well with our predictions, repurposed the D2 receptor into a serotonin biosensor and predicted the signaling effects of more than 100 known G-protein-coupled receptor (GPCR) mutations. Our results reveal the existence of distinct classes of allosteric microswitches and pathways that define an unforeseen molecular mechanism of regulation and evolution of GPCR signaling. Our approach enables the rational design of allosteric receptors with enhanced stability and function to facilitate structural characterization, and reprogram cellular signaling in synthetic biology and cell engineering applications.

Haloperidol is a typical antipsychotic drug (APD) associated with an increased risk of extrapyramidal side effects (EPSs) and hyperprolactinemia relative to atypical APDs such as clozapine. Both drugs are dopamine D 2 receptor (D 2 R) antagonists, with contrasting kinetic profiles. Haloperidol displays fast association/slow dissociation at the D 2 R, whereas clozapine exhibits relatively slow association/fast dissociation. Recently, we have provided evidence that slow dissociation from the D 2 R predicts hyperprolactinemia, whereas fast association predicts EPS. Unfortunately, clozapine can cause severe side effects independent of its D 2 R action. Our results suggest an optimal kinetic profile for D 2 R antagonist APDs that avoids EPS. To begin exploring this hypothesis, we conducted a structure-kinetic relationship study of haloperidol and revealed that subtle structural modifications dramatically change binding kinetic rate constants, affording compounds with a clozapine-like kinetic profile. Thus, optimization of these kinetic parameters may allow development of novel APDs based on the haloperidol scaffold with improved side-effect profiles.

Dopamine receptors constitute a unique class of G-protein coupled receptors that mediate the activities of dopamine, a neurotransmitter implicated in diverse neurological diseases when dysregulated. Over the years, antipsychotic drugs have been primarily directed towards D 2 dopamine receptor (DRD2) while associable adverse effects have been centred on non-selective targeting. The recent crystal structure of DRD2 in complex with atypical antipsychotic could further aid the structure-based design of highly DRD2-selective antipsychotics. Therefore, in this study, we comprehensively investigate the molecular recognition and differential binding landscapes of class-I and II DRD2 atypical antipsychotics, using membrane-bilayer molecular dynamics simulation and binding free energy techniques. Findings revealed that selected class-I antipsychotics exhibited binding dynamics and poses dissimilar to the class-II types with different interactive mechanisms at the binding cavity of DRD2. More interestingly, the class-II drugs established a highly coordinated binding at the DRD2 active site with a pertinent and recurrent involvement of Asp114 via strong hydrogen interactions. Furthermore, while these compounds exert distinct effects on DRD2 structure, findings revealed that the class-II types favourably engaged the deep hydrophobic pocket of DRD2 compared to the class-I drugs. We speculate that these findings will be fundamental to the discovery of highly selective DRD2 antipsychotics., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Background: H3 K27M-mutant diffuse midline glioma is a fatal malignancy with no proven medical therapies. The entity predominantly occurs in children and young adults. ONC201 is a small molecule selective antagonist of dopamine receptor D2/3 (DRD2/3) with an exceptional safety profile. Following up on a durable response in the first H3 K27M-mutant diffuse midline glioma patient who received ONC201 (NCT02525692), an expanded access program was initiated., Methods: Patients with H3 K27M-mutant gliomas who received at least prior radiation were eligible. Patients with leptomeningeal spread were excluded. All patients received open-label ONC201 orally once every week. Safety, radiographic assessments, and overall survival were regularly assessed at least every 8 weeks by investigators. As of August 2018, a total of 18 patients with H3 K27M-mutant diffuse midline glioma or DIPG were enrolled to single patient expanded access ONC201 protocols. Among the 18 patients: seven adult (> 20 years old) and seven pediatric (< 20 years old) patients initiated ONC201 with recurrent disease and four pediatric patients initiated ONC201 following radiation, but prior to disease recurrence., Findings: Among the 14 patients with recurrent disease prior to initiation of ONC201, median progression-free survival is 14 weeks and median overall survival is 17 weeks. Three adults among the 14 recurrent patients remain on treatment progression-free with a median follow up of 49.6 (range 41-76.1) weeks. Among the 4 pediatric patients who initiated adjuvant ONC201 following radiation, two DIPG patients remain progression-free for at least 53 and 81 weeks. Radiographic regressions, including a complete response, were reported by investigators in a subset of patients with thalamic and pontine gliomas, along with improvements in disease-associated neurological symptoms., Interpretation: The clinical outcomes and radiographic responses in these patients provide the preliminary, and initial clinical proof-of-concept for targeting H3 K27M-mutant diffuse midline glioma with ONC201, regardless of age or location, providing rationale for robust clinical testing of the agent.

(+)-[ 11 C]PHNO, a dopamine D 2/3 receptor agonistic radiotracer, is applied for investigating the dopaminergic system via positron emission tomography (PET). An improved understanding of neuropsychiatric disorders associated with dysfunctions in the dopamine system and the underlying mechanism is a necessity in order to promote the development of new potential therapeutic drugs. In contrast to other broadly applied 11 C-radiopharmaceuticals, the production of this radiotracer requires a challenging four-step radiosynthesis involving harsh reaction conditions and reactants as well as an inert atmosphere. Consequently, the production is prone to errors and troubleshooting after failed radiosyntheses remains time consuming. Hence, we aimed to optimize the radiosynthesis of (+)-[ 11 C]PHNO for achieving better activity yields without loss of product quality. Therefore, we synthesized (+)-[ 11 C]PHNO and omitted all heating and cooling steps leading to higher activity yields. As a result, radiosynthesis fully conducted at room temperature led to a time-reduced production procedure that saves about 5 min, which is an appreciable decay-prevention of around 15% of the activity yield. Additionally, we established a troubleshooting protocol by investigating reaction intermediates, byproducts, and impurities. Indeed, partial runs enabled the assignment of byproducts to their associated error source. Finally, we were able to generate a decision tree facilitating error detection in (+)-[ 11 C]PHNO radiosynthesis., Competing Interests: The authors declare that there are no conflicts of interest., (Copyright © 2019 Sarah Pfaff et al.)

In order to search for novel antipsychotics acting through the D 2 receptor, it is necessary to know the structure-activity relationships for dopamine D 2 receptor antagonists. In this context, we constructed the universal three-dimensional quantitative structure-activity relationship (3D- QSAR) model for competitive dopamine D 2 receptor antagonists. We took 176 compounds from chemically different groups characterized by the half maximal inhibitory concentration (IC 50 )from the CHEMBL database and docked them to the X-ray structure of the human D 2 receptor in the inactive state. Selected docking poses were applied for Comparative Molecular Field Analysis (CoMFA) alignment. The obtained CoMFA model is characterized by a cross-validated coefficient Q 2 of 0.76 with an optimal component of 5, R 2 of 0.92, and an F value of 338.9. The steric and electrostatic field contributions are 67.4% and 32.6%, respectively. The statistics obtained prove that the CoMFA model is significant. Next, the IC 50 of the 16 compounds from the test set was predicted with R 2 of 0.95. Finally, a progressive scrambling test was carried out for additional validation. The CoMFA fields were mapped onto the dopamine D 2 receptor binding site, which enabled a discussion of the structure-activity relationship based on ligand-receptor interactions. In particular, it was found that one of the desired steric interactions covers the area of a putative common allosteric pocket suggested for some other G protein-coupled receptors (GPCRs), which would suggest that some of the known dopamine receptor antagonists are bitopic in their essence. The CoMFA model can be applied to predict the potential activity of novel dopamine D 2 receptor antagonists.

Partial agonists of the dopamine D 2 receptor (D 2 R) have been developed to treat the symptoms of schizophrenia without causing the side effects elicited by antagonists. The receptor-ligand interactions that determine the intrinsic efficacy of such drugs, however, are poorly understood. Aripiprazole has an extended structure comprising a phenylpiperazine primary pharmacophore and a 1,2,3,4-tetrahydroquinolin-2-one secondary pharmacophore. We combined site-directed mutagenesis, analytical pharmacology, ligand fragments, and molecular dynamics simulations to identify the D 2 R-aripiprazole interactions that contribute to affinity and efficacy. We reveal that an interaction between the secondary pharmacophore of aripiprazole and a secondary binding pocket defined by residues at the extracellular portions of transmembrane segments 1, 2, and 7 determines the intrinsic efficacy of aripiprazole. Our findings reveal a hitherto unappreciated mechanism for fine-tuning the intrinsic efficacy of D 2 R agonists.

The interplay between the dopamine (DA) and opioid systems in the brain is known to modulate the additive effects of substances of abuse. On one hand, opioids serve mankind by their analgesic properties, which are mediated via the mu opioid receptor (MOR), a Class A G protein-coupled receptor (GPCR), but on the other hand, they pose a potential threat by causing undesired side effects such as tolerance and dependence, for which the exact molecular mechanism is still unknown. Using human embryonic kidney 293T (HEK 293T) and HeLa cells transfected with MOR and the dopamine D 2 receptor (D 2 R), we demonstrate that these receptors heterodimerize, using an array of biochemical and biophysical techniques such as coimmunoprecipitation (co-IP), bioluminescence resonance energy transfer (BRET 1 ), Fӧrster resonance energy transfer (FRET), and functional complementation of a split luciferase. Furthermore, live cell imaging revealed that D 2L R, when coexpressed with MOR, slowed down internalization of MOR, following activation with the MOR agonist [D-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO)., Competing Interests: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Receptor-receptor interactions are essential to fine tune receptor responses and new techniques enable closer characterization of the interactions between involved proteins directly in the plasma membrane. Fluorescence cross-correlation spectroscopy (FCCS), which analyses concurrent movement of bound molecules with single-molecule detection limit, was here used to, in live N2a cells, study interactions between the Parkinson's disease (PD) associated orphan receptor GPR37, its homologue GPR37L1, and the two splice variants of the dopamine 2 receptor (D2R). An interaction between GPR37 and both splice forms of D2R was detected. 4-phenylbutyrate (4-PBA), a neuroprotective chemical chaperone known to increase GPR37 expression at the cell surface, increased the fraction of interacting molecules. The interaction was also increased by pramipexole, a D2R agonist commonly used in the treatment of PD, indicating a possible clinically relevance. Cross-correlation, indicating interaction between GPR37L1 and the short isoform of D2R, was also detected. However, this interaction was not changed with 4-PBA or pramipexole treatment. Overall, these data provide further evidence that heteromeric GPR37-D2R exist and can be pharmacologically modulated, which is relevant for the treatment of PD. This article is part of the Special Issue entitled 'Receptor heteromers and their allosteric receptor-receptor interactions'., (Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The dorsolateral striatum (DLS) is essential for motor and procedure learning, but the role of DLS spiny projection neurons (SPNs) of direct and indirect pathways, as marked, respectively, by D1 and D2 receptor (D1R and D2R) expression, remains to be clarified. Long-term two-photon calcium imaging of the same neuronal population during mouse learning of a cued lever-pushing task revealed a gradual emergence of distinct D1R and D2R neuronal ensembles that reproducibly fired in a sequential manner, with more D1R and D2R neurons fired during the lever-pushing period and intertrial intervals (ITIs), respectively. This sequential firing pattern was specifically associated with the learned motor behavior, because it changed markedly when the trained mice performed other cued motor tasks. Selective chemogenetic silencing of D1R and D2R neurons impaired the initiation of learned motor action and suppression of erroneous lever pushing during ITIs, respectively. Thus, motor learning involves reorganization of DLS neuronal activity, forming stable D1R and D2R neuronal ensembles that fired sequentially to regulate different aspects of the learned behavior., Competing Interests: The authors declare no conflict of interest.

Methiopropamine (MPA) is structurally categorized as a thiophene ring-based methamphetamine (MA) derivative. Although abusive potential of MPA was recognized, little is known about the neurotoxic potential of MPA up to now. We investigated whether MPA induces dopaminergic neurotoxicity, and whether MPA activates a specific dopamine receptor. Here, we observed that treatment with MPA resulted in dopaminergic neurotoxicity in a dose-dependent manner. MPA treatment potentiated oxidative parameters (i.e., increases in the level of reactive oxygen species, 4-hydroxynonenal, and protein carbonyl), M1 phenotype-related microglial activity, and pro-apoptotic property (i.e., increases in Bax- and cleaved caspase-3-expressions, while a decrease in Bcl-2-expression). Moreover, treatment with MPA resulted in significant impairments in dopaminergic parameters [i.e., changes in dopamine level, dopamine turnover rate, tyrosine hydroxylase (TH) levels, dopamine transporter (DAT) expression, and vesicular monoamine transporter-2 (VMAT-2) expression], and in behavioral deficits. Both dopamine D1 receptor antagonist SCH23390 and D2 receptor antagonist sulpiride protected from these neurotoxic consequences. Therefore, our results suggest that dopamine D1 and D2 receptors simultaneously mediate MPA-induced dopaminergic neurodegeneration in mice via oxidative burdens, microgliosis, and pro-apoptosis., (Copyright © 2019. Published by Elsevier B.V.)

Our previous findings indicate that A2A and D2 receptors are co-expressed on adult rat striatal astrocytes and on the astrocyte processes, and that A2A-D2 receptor⁻receptor interaction can control the release of glutamate from the processes. Functional evidence suggests that the receptor⁻receptor interaction was based on heteromerization of native A2A and D2 receptors at the plasma membrane of striatal astrocyte processes. We here provide biochemical and biophysical evidence confirming that receptor⁻receptor interaction between A2A and D2 receptors at the astrocyte plasma membrane is based on A2A-D2 heteromerization. To our knowledge, this is the first direct demonstration of the ability of native A2A and D2 receptors to heteromerize on glial cells. As striatal astrocytes are recognized to be involved in Parkinson's pathophysiology, the findings that adenosine A2A and dopamine D2 receptors can form A2A-D2 heteromers on the astrocytes in the striatum (and that these heteromers can play roles in the control of the striatal glutamatergic transmission) may shed light on the molecular mechanisms involved in the pathogenesis of the disease., Competing Interests: The authors declare no conflict of interest. The funding sources had no involvement in study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the article for publication.

Dopamine D1/D2 receptors are important targets for drug discovery in the treatment of central nervous system diseases. To discover new and potential D1/D2 ligands, 17 derivatives of tetrahydroprotoberberine (THPB) with various substituents were prepared by chemical synthesis or microbial transformation using Streptomyces griseus ATCC 13273. Their functional activities on D1 and D2 receptors were determined by cAMP assay and calcium flux assay. Seven compounds showed high activity on D1/D2 receptor with low IC 50 values less than 1 µM. Especially, top compound 5 showed strong antagonistic activity on both D1 and D2 receptor with an IC 50 of 0.391 and 0.0757 µM, respectively. Five compounds displayed selective antagonistic activity on D1 and D2 receptor. The SAR studies revealed that (1) the hydroxyl group at C-9 position plays an important role in keeping a good activity and small or fewer substituents on ring D of THPBs may also stimulate their effects, (2) the absence of substituents at C-9 position tends to be more selective for D2 receptor, and (3) hydroxyl substitution at C-2 position and the substitution at C-9 position may facilitate the conversion of D1 receptor from antagonist to agonist. Molecular docking simulations found that Asp 103/Asp 114, Ser 107/Cys 118, and Trp 285/ Trp 386 of D1/ D2 receptors are the key residues, which have strong interactions with the active D1/D2 compounds and may influence their functional profiles., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

We have synthesized 3 analogs of the dopamine D2 receptor (D2 DR) antagonist spiperone that can be conjugated to streptavidin-coated quantum dots via a pegylated biotin derivative. Using fluorescent imaging we demonstrate that substitution on the spiro position is tolerated, whilst the length and rigidity of a spacer arm attached to spiperone is important in controlling specific labeling as well as minimizing nonspecific labeling to cells and the surface of cell culture dishes. The ligand with the most rigid linker IDT772 (4) had the best binding profile and had high specific binding to D2 DR expressing HEK-293T cells with low nonspecific binding to plates and HEK-293T cells that lacked the D2 DR., (Copyright © 2019. Published by Elsevier Ltd.)

Dysfunction of the dopaminergic pathway is linked to numerous diseases of the nervous system. The D1-D2 receptor heteromer is known to play a role in certain neuropsychiatric disorders, such as depression. Here, we synthesized an eight amino acid residue peptide, EAARRAQE, derived from the third intracellular loop of the D2 receptor and show that the peptide binds to the D1 receptor with comparable efficiency as that of the full-length D2 receptor protein. Moreover, immunoprecipitation studies show the existence of a heteromeric complex formed both in vitro and in total protein derived from temporal and frontal lobe tissue from normal and depressed subjects. The efficiency of the peptide to block the D1-D2 heteromeric complex was comparable in all the samples tested., (© 2019 Federation of European Biochemical Societies.)

We tested the interactions with four different G protein-coupled receptors (GPCRs) of arrestin-3 mutants with substitutions in the four loops, three of which contact the receptor in the structure of the arrestin-1-rhodopsin complex. Point mutations in the loop at the distal tip of the N-domain (Glu157Ala), in the C-loop (Phe255Ala), back loop (Lys313Ala), and one of the mutations in the finger loop (Gly65Pro) had mild variable effects on receptor binding. In contrast, the deletion of Gly65 at the beginning of the finger loop reduced the binding to all GPCRs tested, with the binding to dopamine D2 receptor being affected most dramatically. Thus, the presence of a glycine at the beginning of the finger loop appears to be critical for the arrestin-receptor interaction., Competing Interests: The authors have declared that no competing interests exist.

1. The purpose of this study was to measure dopamine D 2/3 receptor occupancy (RO) as a marker of the clinical efficacy of ropinirole in rats via positron emission tomography (PET) using 18 F-fallypride as the radiotracer and to explore the relationship between dopamine RO and the plasma concentration of ropinirole via pharmacokinetic-pharmacodynamic modeling. 2. Plasma was collected from 16 rats treated with one of four doses of ropinirole. For the time-dependent study, the data of 16 rats in the 15 mg/kg dose group at four time points were averaged, and another 24 rats were divided into three dose groups (5 mg/kg, 30 mg/kg and 60 mg/kg) for the dose-dependent study; the animals were assessed via 18 F-fallypride PET scans. The correlation between dopamine RO and the ropinirole plasma concentration was investigated, and a pharmacokinetic-pharmacodynamic (PK-PD) model was established with WinNonlin 6.3 software. Both the plasma concentration and the binding potential changed in a time- and dose-dependent manner, and the plasma concentration that induces 50% RO (EC 50 ) as calculated by the PK-PD model was 1391 ng/mL. 3. 18 F-fallypride appeared to be a suitable radiotracer for ropinirole imaging, and its binding to the dopamine D 2 receptor has time- and concentration-dependent characteristics. A theory-based PK-PD model was developed to describe the relationship between the plasma ropinirole concentration and RO, providing a methodological foundation for noninvasive and in vivo clinical evaluations of ropinirole treatment.

Recently, a novel negative allosteric modulator (NAM) of the D 2 -like dopamine receptors 1 was identified through virtual ligand screening. This ligand comprises a thieno[2,3- d]pyrimidine scaffold that does not feature in known dopaminergic ligands. Herein, we provide pharmacological validation of an allosteric mode of action for 1, revealing that it is a NAM of dopamine efficacy and identify the structural determinants of this allostery. We find that key structural moieties are important for functional affinity and negative cooperativity, while functionalization of the thienopyrimidine at the 5- and 6-positions results in analogues with divergent cooperativity profiles. Successive compound iterations have yielded analogues exhibiting a 10-fold improvement in functional affinity, as well as enhanced negative cooperativity with dopamine affinity and efficacy. Furthermore, our study reveals a fragment-like core that maintains low μM affinity and robust negative cooperativity with markedly improved ligand efficiency.

SB269652 (1) is a negative allosteric modulator of the dopamine D 2 receptor. Herein, we present the design, synthesis, and pharmacological evaluation of "second generation" analogues of 1 whereby subtle modifications to the indole-2-carboxamide motif confer dramatic changes in functional affinity (5000-fold increase), cooperativity (100-fold increase), and a novel action to modulate dopamine efficacy. Thus, structural changes to this region of 1 allows the generation of a novel set of analogues with distinct pharmacological properties.

S100B is a dimeric EF-hand protein that undergoes a calcium-induced conformational change and interacts with a wide range of proteins to modulate their functions. The dopamine D2 receptor is one potential S100B binding partner that may play a key role in neurological processing. In this chapter, we describe the use of NMR spectroscopy to examine the interaction between calcium-bound S100B and the third intracellular loop (IC3) from the dopamine D2 receptor. We provide details that allow the strength of the interaction (K d ) between the two proteins to be determined and the IC3 site of interaction on the structure of S100B to be identified. Both these characteristics can be identified from a single series of nondestructive experiments.

Bivalent ligands have emerged as chemical tools to study G protein-coupled receptor dimers. Using a combination of computational, chemical, and biochemical tools, here we describe the design of bivalent ligand 13 with high affinity ( K DB1 = 21 pM) for the dopamine D 2 receptor (D 2 R) homodimer. Bivalent ligand 13 enhances the binding affinity relative to monovalent compound 15 by 37-fold, indicating simultaneous binding at both protomers. Using synthetic peptides with amino acid sequences of transmembrane (TM) domains of D 2 R, we provide evidence that TM6 forms the interface of the homodimer. Notably, the disturber peptide TAT-TM6 decreased the binding of bivalent ligand 13 by 52-fold and had no effect on monovalent compound 15, confirming the D 2 R homodimer through TM6 ex vivo. In conclusion, by using a versatile multivalent chemical platform, we have developed a precise strategy to generate a true bivalent ligand that simultaneously targets both orthosteric sites of the D 2 R homodimer.