CCR6 as a Potential Target for Therapeutic Antibodies for the Treatment of Inflammatory Diseases

The CC chemokine receptor 6 (CCR6) is a G protein-coupled receptor (GPCR) involved in a wide range of biological processes. When CCR6 binds to its sole ligand CCL20, a signaling network is produced. This pathway is implicated in mechanisms related to many diseases, such as cancer, psoriasis, multiple sclerosis, HIV infection or rheumatoid arthritis. The CCR6/CCL20 axis plays a fundamental role in immune homeostasis and activation. Th17 cells express the CCR6 receptor and inflammatory cytokines, including IL-17, IL-21 and IL-22, which are involved in the spread of inflammatory response. The CCL20/CCR6 mechanism plays a crucial role in the recruitment of these pro-inflammatory cells to local tissues. To date, there are no drugs against CCR6 approved, and the development of small molecules against CCR6 is complicated due to the difficulty in screenings. This review highlights the potential as a therapeutic target of the CCR6 receptor in numerous diseases and the importance of the development of antibodies against CCR6 that could be a promising alternative to small molecules in the treatment of CCR6/CCL20 axis-related pathologies.

Genetic Ablation and Pharmacological Blockade of Bradykinin B1 Receptor Unveiled a Detrimental Role for the Kinin System in Chagas Disease Cardiomyopathy

Chagas disease, the parasitic infection caused by Trypanosoma cruzi, afflicts about 6 million people in Latin America. Here, we investigated the hypothesis that T. cruzi may fuel heart parasitism by activating B1R, a G protein-coupled (brady) kinin receptor whose expression is upregulated in inflamed tissues. Studies in WT and B1R^-/- mice showed that T. cruzi DNA levels (15 days post infection-dpi) were sharply reduced in the transgenic heart. FACS analysis revealed that frequencies of proinflammatory neutrophils and monocytes were diminished in B1R^-/- hearts whereas CK-MB activity (60 dpi) was exclusively detected in B1R^+/+ sera. Since chronic myocarditis and heart fibrosis (90 dpi) were markedly attenuated in the transgenic mice, we sought to determine whether a pharmacological blockade of the des-Arg⁹-bradykinin (DABK)/B1R pathway might alleviate chagasic cardiomyopathy. Using C57BL/6 mice acutely infected by a myotropic T. cruzi strain (Colombian), we found that daily treatment (15-60 dpi) with R-954 (B1R antagonist) reduced heart parasitism and blunted cardiac injury. Extending R-954 treatment to the chronic phase (120-160 dpi), we verified that B1R targeting (i) decreased mortality indexes, (ii) mitigated chronic myocarditis, and (iii) ameliorated heart conduction disturbances. Collectively, our study suggests that a pharmacological blockade of the proinflammatory KKS/DABK/B1R pathway is cardioprotective in acute and chronic Chagas disease.

NanoB2 to monitor interactions of ligands with membrane proteins by combining nanobodies and NanoBRET

The therapeutic potential of ligands targeting disease-associated membrane proteins is predicted by ligand-receptor binding constants, which can be determined using NanoLuciferase (NanoLuc)-based bioluminescence resonance energy transfer (NanoBRET) methods. However, the broad applicability of these methods is hampered by the restricted availability of fluorescent probes. We describe the use of antibody fragments, like nanobodies, as universal building blocks for fluorescent probes for use in NanoBRET. Our nanobody-NanoBRET (NanoB2) workflow starts with the generation of NanoLuc-tagged receptors and fluorescent nanobodies, enabling homogeneous, real-time monitoring of nanobody-receptor binding. Moreover, NanoB2 facilitates the assessment of receptor binding of unlabeled ligands in competition binding experiments. The broad significance is illustrated by the successful application of NanoB2 to different drug targets (e.g., multiple G protein-coupled receptors [GPCRs] and a receptor tyrosine kinase [RTK]) at distinct therapeutically relevant binding sites (i.e., extracellular and intracellular).

Ablation of GPR56 Causes β-Cell Dysfunction by ATP Loss through Mistargeting of Mitochondrial VDAC1 to the Plasma Membrane

The activation of G Protein-Coupled Receptor 56 (GPR56), also referred to as Adhesion G-Protein-Coupled Ceceptor G1 (ADGRG1), by Collagen Type III (Coll III) prompts cell growth, proliferation, and survival, among other attributes. We investigated the signaling cascades mediating this functional effect in relation to the mitochondrial outer membrane voltage-dependent anion Channel-1 (VDAC1) expression in pancreatic β-cells. GPR56KD attenuated the Coll III-induced suppression of P70S6K, JNK, AKT, NFκB, STAT3, and STAT5 phosphorylation/activity in INS-1 cells cultured at 20 mM glucose (glucotoxicity) for 72 h. GPR56-KD also increased Chrebp, Txnip, and Vdac1 while decreasing Vdac2 mRNA expression. In GPR56-KD islet β-cells, Vdac1 was co-localized with SNAP-25, demonstrating its plasma membrane translocation. This resulted in ATP loss, reduced cAMP production and impaired glucose-stimulated insulin secretion (GSIS) in INS-1 and human EndoC βH1 cells. The latter defects were reversed by an acute inhibition of VDAC1 with an antibody or the VDAC1 inhibitor VBIT-4. We demonstrate that Coll III potentiates GSIS by increasing cAMP and preserving β-cell functionality under glucotoxic conditions in a GPR56-dependent manner by attenuating the inflammatory response. These results emphasize GPR56 and VDAC1 as drug targets in conditions with impaired β-cell function.

Cryo-EM structure of the human chemerin receptor 1-Gi protein complex bound to the C-terminal nonapeptide of chemerin

Chemerin is a processed protein that acts on G protein-coupled receptors (GPCRs) for its chemotactic and adipokine activities. The biologically active chemerin (chemerin 21-157) results from proteolytic cleavage of prochemerin and uses its C-terminal peptide containing the sequence YFPGQFAFS for receptor activation. Here we report a high-resolution cryo-electron microscopy (cryo-EM) structure of human chemerin receptor 1 (CMKLR1) bound to the C-terminal nonapeptide of chemokine (C9) in complex with Gi proteins. C9 inserts its C terminus into the binding pocket and is stabilized through hydrophobic interactions involving its Y1, F2, F6, and F8, as well as polar interactions between G4, S9, and several amino acids lining the binding pocket of CMKLR1. Microsecond scale molecular dynamics simulations support a balanced force distribution across the whole ligand-receptor interface that enhances thermodynamic stability of the captured binding pose of C9. The C9 interaction with CMKLR1 is drastically different from chemokine recognition by chemokine receptors, which follow a two-site two-step model. In contrast, C9 takes an "S"-shaped pose in the binding pocket of CMKLR1 much like angiotensin II in the AT1 receptor. Our mutagenesis and functional analyses confirmed the cryo-EM structure and key residues in the binding pocket for these interactions. Our findings provide a structural basis for chemerin recognition by CMKLR1 for the established chemotactic and adipokine activities.

Cholesterol in Class C GPCRs: Role, Relevance, and Localization

G-protein coupled receptors (GPCRs), one of the largest superfamilies of cell-surface receptors, are heptahelical integral membrane proteins that play critical roles in virtually every organ system. G-protein-coupled receptors operate in membranes rich in cholesterol, with an imbalance in cholesterol level within the vicinity of GPCR transmembrane domains affecting the structure and/or function of many GPCRs, a phenomenon that has been linked to several diseases. These effects of cholesterol could result in indirect changes by altering the mechanical properties of the lipid environment or direct changes by binding to specific sites on the protein. There are a number of studies and reviews on how cholesterol modulates class A GPCRs; however, this area of study is yet to be explored for class C GPCRs, which are characterized by a large extracellular region and often form constitutive dimers. This review highlights specific sites of interaction, functions, and structural dynamics involved in the cholesterol recognition of the class C GPCRs. We summarize recent data from some typical family members to explain the effects of membrane cholesterol on the structural features and functions of class C GPCRs and speculate on their corresponding therapeutic potential.

Gβγ subunits colocalize with RNA polymerase II and regulate transcription in cardiac fibroblasts

Gβγ subunits mediate many different signaling processes in various compartments of the cell, including the nucleus. To gain insight into the functions of nuclear Gβγ signaling, we investigated the functional role of Gβγ signaling in the regulation of GPCR-mediated gene expression in primary rat neonatal cardiac fibroblasts. We identified a novel, negative, regulatory role for the Gβ₁γ dimer in the fibrotic response. Depletion of Gβ₁ led to derepression of the fibrotic response at the mRNA and protein levels under basal conditions and an enhanced fibrotic response after sustained stimulation of the angiotensin II type I receptor. Our genome-wide chromatin immunoprecipitation experiments revealed that Gβ₁ colocalized and interacted with RNA polymerase II on fibrotic genes in an angiotensin II-dependent manner. Additionally, blocking transcription with inhibitors of Cdk9 prevented association of Gβγ with transcription complexes. Together, our findings suggest that Gβ₁γ is a novel transcriptional regulator of the fibrotic response that may act to restrict fibrosis to conditions of sustained fibrotic signaling. Our work expands the role for Gβγ signaling in cardiac fibrosis and may have broad implications for the role of nuclear Gβγ signaling in other cell types.

The Role of Genetics in the Development and Pharmacotherapy of Depression and Its Impact on Drug Discovery

Complex disorders, such as depression, remain a mystery for scientists. Although genetic factors are considered important for the prediction of one's vulnerability, it is hard to estimate the exact risk for a patient to develop depression, based only on one category of vulnerability criteria. Genetic factors also regulate drug metabolism, and when they are identified in a specific combination, may result in increased drug resistance. A proper understanding of the genetic basis of depression assists in the development of novel promising medications and effective disorder management schemes. This review aims to analyze the recent literature focusing on the correlation between specific genes and the occurrence of depression. Moreover, certain aspects targeting a high drug resistance identified among patients suffering from major depressive disorder were highlighted in this manuscript. An expected direction of future drug discovery campaigns was also discussed.

Allosteric binding cooperativity in a kinetic context

Allosteric modulators are of prime interest in drug discovery. These drugs regulate the binding and function of endogenous ligands, with some advantages over orthosteric ligands. A typical pharmacological parameter in allosteric modulation is binding cooperativity. This property can yield unexpected but illuminating results when decomposed into its kinetic parameters. Using two reference models (the allosteric ternary complex receptor model and a heterodimer receptor model), a relationship has been derived for the cooperativity rate constant parameters. This relationship allows many combinations of the cooperativity kinetic parameters for a single binding cooperativity value obtained under equilibrium conditions. This assessment may help understand striking experimental results involving allosteric modulation and suggest further investigations in the field.

Non-canonical Golgi-compartmentalized Gβγ signaling: mechanisms, functions, and therapeutic targets

G protein Gβγ subunits are key mediators of G protein-coupled receptor (GPCR) signaling under physiological and pathological conditions; their inhibitors have been tested for the treatment of human disease. Conventional wisdom is that the Gβγ complex is activated and subsequently exerts its functions at the plasma membrane (PM). Recent studies have revealed non-canonical activation of Gβγ at intracellular organelles, where the Golgi apparatus is a major locale, via translocation or local activation. Golgi-localized Gβγ activates specific signaling cascades and regulates fundamental cell processes such as membrane trafficking, proliferation, and migration. More recent studies have shown that inhibiting Golgi-compartmentalized Gβγ signaling attenuates cardiomyocyte hypertrophy and prostate tumorigenesis, indicating new therapeutic targets. We review novel activation mechanisms and non-canonical functions of Gβγ at the Golgi, and discuss potential therapeutic interventions by targeting Golgi-biased Gβγ-directed signaling.

Ligands selectively tune the local and global motions of neurotensin receptor 1 (NTS1)

Nuclear magnetic resonance (NMR) studies have revealed that fast methyl sidechain dynamics can report on entropically-driven allostery. Yet, NMR applications have been largely limited to the super-microsecond motional regimes of G protein-coupled receptors (GPCRs). We use ¹³C^ε-methionine chemical shift-based global order parameters to test if ligands affect the fast dynamics of a thermostabilized GPCR, neurotensin receptor 1 (NTS₁). We establish that the NTS₁ solution ensemble includes substates with lifetimes on several, discrete timescales. The longest-lived states reflect those captured in agonist- and inverse agonist-bound crystal structures, separated by large energy barriers. We observe that the rapid fluctuations of individual methionine residues, superimposed on these long-lived states, respond collectively with the degree of fast, global dynamics correlating with ligand pharmacology. This approach lends confidence to interpreting spectra in terms of local structure and methyl dihedral angle geometry. The results suggest a role for sub-microsecond dynamics and conformational entropy in GPCR ligand discrimination.

Structures of the entire human opioid receptor family

Opioids are effective analgesics, but their use is beset by serious side effects, including addiction and respiratory depression, which contribute to the ongoing opioid crisis. The human opioid system contains four opioid receptors (μOR, δOR, κOR, and NOPR) and a set of related endogenous opioid peptides (EOPs), which show distinct selectivity toward their respective opioid receptors (ORs). Despite being key to the development of safer analgesics, the mechanisms of molecular recognition and selectivity of EOPs to ORs remain unclear. Here, we systematically characterize the binding of EOPs to ORs and present five structures of EOP-OR-Gi complexes, including β-endorphin- and endomorphin-bound μOR, deltorphin-bound δOR, dynorphin-bound κOR, and nociceptin-bound NOPR. These structures, supported by biochemical results, uncover the specific recognition and selectivity of opioid peptides and the conserved mechanism of opioid receptor activation. These results provide a structural framework to facilitate rational design of safer opioid drugs for pain relief.

2-{N-[(2,4,5-trichlorophenoxy) acetyl]-N-methylamino}-3-pyrrolidinepropanamide analogs as potential antagonists of Urotensin II receptor

THE PURPOSE OF THE ARTICLE

To identify novel small molecule antagonists of Urotensin II receptor with acceptable pharmacological profile.

MATERIALS AND METHODS

Structure-activity-relationship (SAR) studies on 2-{N-[(2,4,5-trichlorophenoxy) acetyl]-N-methylamino}-3-pyrrolidinepropanamide series were conducted and shortlisted compounds were synthesized and evaluated in in vitro cell-based assays. Human and mouse Urotensin II receptor overexpressing CHO cells were used for calcium release and radioligand binding assays. Initial molecules in this series had solubility and inter-species variability issue in the calcium release assay. We, therefore, conducted SAR to overcome these 2 issues and molecules with accepted in vitro profile were evaluated further in mouse pressor response model to generate the in vivo proof of concept for UII receptor antagonization.

RESULTS AND CONCLUSIONS

We report herewith identification of 2-{N-[(2,4,5-trichlorophenoxy)acetyl]-N-methylamino}-3-pyrrolidinepropanamides series to obtain novel small molecule antagonists of Urotensin II receptor with acceptable pharmacological profile.

Essential Role of Adhesion GPCR, GPR123, for Human Pluripotent Stem Cells and Reprogramming towards Pluripotency

G-protein-coupled receptors (GPCRs) are the largest family of cell surface receptors. They modulate key physiological functions and are required in diverse developmental processes including embryogenesis, but their role in pluripotency maintenance and acquisition during the reprogramming towards hiPSCs draws little attention. Meanwhile, it is known that more than 106 GPCRs are overexpressed in human pluripotent stem cells (hPSCs). Previously, to identify novel effectors of reprogramming, we performed a high-throughput RNA interference (RNAi) screening assay and identified adhesion GPCR, GPR123, as a potential reprogramming effector. Its role has not been explored before. Herein, by employing GPR123 RNAi we addressed the role of GPR123 for hPSCs. The suppression of GPR123 in hPSCs leads to the loss of pluripotency and differentiation, impacted colony morphology, accumulation of cells at the G2 phase of the cell cycle, and absence of the scratch closure. Application of the GPR123 RNAi at the initiation stage of reprogramming leads to a decrease in the percentage of the "true" hiPSC colonies, a drop in E-cadherin expression, a decrease in the percentage of NANOG+ nuclei, and the absence of actin cytoskeleton remodeling. Together this leads to the absence of the alkaline-phosphatase-positive hiPSCs colonies on the 18th day of the reprogramming process. Overall, these data indicate for the first time the essential role of GPR123 in the maintenance and acquisition of pluripotency.

psnGPCRdb: The Structure-network Database of G Protein Coupled Receptors

G protein coupled receptors (GPCRs) are critical eukaryotic signal transduction gatekeepers and represent the largest protein superfamily in the human proteome, with more than 800 members. They share seven transmembrane helices organized in an up-down bundle architecture. GPCR-mediated signaling pathways have been linked to numerous human diseases, and GPCRs are the targets of approximately 35% of all drugs currently on the market. Structure network analysis, a graph theory-based approach, represents a cutting-edge tool to deeply understand GPCR function, which strongly relies on communication between the extracellular and intracellular poles of their structure. psnGPCRdb stores the structure networks (i.e., linked nodes, hubs, communities and communication pathways) computed on all updated GPCR structures in the Protein Data Bank, in their isolated states or in complex with extracellular and/or intracellular molecules. The structure communication signatures of a sub-family or family of GPCRs as well as of their small-molecule activators or inhibitors are stored as consensus networks. The database stores also all meaningful structure network-based comparisons (i.e., difference networks) of functionally different states (i.e., inactive or active) of a given receptor sub-type, or of consensus networks representative of a receptor sub-type, type, sub-family or family. Single or consensus GPCR networks hold also information on amino acid conservation. The database allows to graphically analyze 3D structure networks together with interactive data-tables. Ligand-centric networks can be analyzed as well. psnGPCRdb is unique and represents a powerful resource to unravel GPCR function with important implications in cell signaling and drug design. psnGPCRdb is freely available at: http://webpsn.hpc.unimo.it/psngpcr.php.

Selection and Comparative Gene Expression of Midgut-Specific Targets for Drosophila suzukii

Spotted-wing drosophila (SWD), Drosophila suzukii, is a destructive and invasive pest that attacks most small fruits and cherries. The current management for SWD involves the use of conventional insecticides. In an effort to develop a biologically based control option, the application of RNA interference (RNAi) has been investigated. To develop an RNAi approach, suitable targets must be identified, and an efficient delivery method must be developed for introducing the double-stranded RNA (dsRNA) in the midgut. In D. suzukii, we previously found that dsRNA nucleases actively degrade dsRNA molecules in the midgut. In this study, we focused on identifying biological targets focused on the midgut membrane. The profile of midgut-specific genes was analyzed and compared with the genes expressed in the whole-body using transcriptome analysis. Differential gene expression analysis revealed that 1921 contigs were upregulated and 1834 contigs were downregulated in the midgut when compared to genes from other body tissues. We chose ten midgut-specifically upregulated genes and empirically confirmed their expressions. We are particularly interested in the midgut membrane proteins, including G protein-coupled receptors (GPCRs) such as diuretic hormone 31 (DH31) receptor, neuropeptide F (NPF) recepror, toll-9, adhesion receptors, methuselah (mth), and gustatory receptor, because insect GPCRs have been offered great potential for next-generation pest management.

Solving an Old Puzzle: Elucidation and Evaluation of the Binding Mode of Salvinorin A at the Kappa Opioid Receptor

The natural product Salvinorin A (SalA) was the first nitrogen-lacking agonist discovered for the opioid receptors and exhibits high selectivity for the kappa opioid receptor (KOR) turning SalA into a promising analgesic to overcome the current opioid crisis. Since SalA's suffers from poor pharmacokinetic properties, particularly the absence of gastrointestinal bioavailability, fast metabolic inactivation, and subsequent short duration of action, the rational design of new tailored analogs with improved clinical usability is highly desired. Despite being known for decades, the binding mode of SalA within the KOR remains elusive as several conflicting binding modes of SalA were proposed hindering the rational design of new analgesics. In this study, we rationally determined the binding mode of SalA to the active state KOR by in silico experiments (docking, molecular dynamics simulations, dynophores) in the context of all available mutagenesis studies and structure-activity relationship (SAR) data. To the best of our knowledge, this is the first comprehensive evaluation of SalA's binding mode since the determination of the active state KOR crystal structure. SalA binds above the morphinan binding site with its furan pointing toward the intracellular core while the C2-acetoxy group is oriented toward the extracellular loop 2 (ECL2). SalA is solely stabilized within the binding pocket by hydrogen bonds (C210^ECL2, Y312^7.35, Y313^7.36) and hydrophobic contacts (V118^2.63, I139^3.33, I294^6.55, I316^7.39). With the disruption of this interaction pattern or the establishment of additional interactions within the binding site, we were able to rationalize the experimental data for selected analogs. We surmise the C2-substituent interactions as important for SalA and its analogs to be experimentally active, albeit with moderate frequency within MD simulations of SalA. We further identified the non-conserved residues 2.63, 7.35, and 7.36 responsible for the KOR subtype selectivity of SalA. We are confident that the elucidation of the SalA binding mode will promote the understanding of KOR activation and facilitate the development of novel analgesics that are urgently needed.

Layer-Wise Relevance Analysis for Motif Recognition in the Activation Pathway of the β2-Adrenergic GPCR Receptor

G-protein-coupled receptors (GPCRs) are cell membrane proteins of relevance as therapeutic targets, and are associated to the development of treatments for illnesses such as diabetes, Alzheimer's, or even cancer. Therefore, comprehending the underlying mechanisms of the receptor functional properties is of particular interest in pharmacoproteomics and in disease therapy at large. Their interaction with ligands elicits multiple molecular rearrangements all along their structure, inducing activation pathways that distinctly influence the cell response. In this work, we studied GPCR signaling pathways from molecular dynamics simulations as they provide rich information about the dynamic nature of the receptors. We focused on studying the molecular properties of the receptors using deep-learning-based methods. In particular, we designed and trained a one-dimensional convolution neural network and illustrated its use in a classification of conformational states: active, intermediate, or inactive, of the β2-adrenergic receptor when bound to the full agonist BI-167107. Through a novel explainability-oriented investigation of the prediction results, we were able to identify and assess the contribution of individual motifs (residues) influencing a particular activation pathway. Consequently, we contribute a methodology that assists in the elucidation of the underlying mechanisms of receptor activation-deactivation.

Phosphoproteomic Analysis of Dopamine D2 Receptor Signaling Reveals Interplay of G Protein- and β-Arrestin-Mediated Effects

Leveraging biased signaling of G protein-coupled receptors has been proposed as a promising strategy for the development of drugs with higher specificity. However, the consequences of selectively targeting G protein- or β-arrestin-mediated signaling on cellular functions are not comprehensively understood. In this study, we utilized phosphoproteomics to gain a systematic overview of signaling induced by the four biased and balanced dopamine D2 receptor (D₂R) ligands MS308, BM138, quinpirole, and sulpiride in an in vitro D₂R transfection model. Quantification of 14,160 phosphosites revealed a low impact of the partial G protein agonist MS308 on cellular protein phosphorylation, as well as surprising similarities between the balanced agonist quinpirole and the inverse agonist sulpiride. Analysis of the temporal profiles of ligand-induced phosphorylation events showed a transient impact of the G protein-selective agonist MS308, whereas the β-arrestin-preferring agonist BM138 elicited a delayed, but more pronounced response. Functional enrichment analysis of ligand-impacted phosphoproteins and treatment-linked kinases confirmed multiple known functions of D₂R signaling while also revealing novel effects, for example of MS308 on sterol regulatory element-binding protein-related gene expression. All raw data were deposited in MassIVE (MSV000089457).

Bromophenols from Symphyocladia latiuscula (Harvey) Yamada as Novel Cholecystokinin 2 Receptor Antagonists

BACKGROUND

Cholecystokinin (CCK) is one of the most abundant peptides in the central nervous system and is believed to function as a neurotransmitter as well as a gut hormone with an inverse correlation of its level to anxiety and depression. Therefore, CCK receptors (CCKRs) could be a relevant target for novel antidepressant therapy.

METHODS

In silico target prediction was first employed to predict the probability of the bromophenols interacting with key protein targets based on a model trained on known bioactivity data and chemical similarity considerations. Next, we tested the functional effect of natural bromophenols from Symphyocladia latiuscula on the CCK2 receptor followed by a molecular docking simulation to predict interactions between a compound and the binding site of the target protein.

RESULTS

Results of cell-based functional G-protein coupled receptor (GPCR) assays demonstrate that bromophenols 2,3,6-tribromo-4,5-dihydroxybenzyl alcohol (1), 2,3,6-tribromo-4,5-dihydroxybenzyl methyl ether (2), and bis-(2,3,6-tribromo-4,5-dihydroxybenzyl) ether (3) are full CCK2 antagonists. Molecular docking simulation of 1‒3 with CCK2 demonstrated strong binding by means of interaction with prime interacting residues: Arg356, Asn353, Val349, His376, Phe227, and Pro210. Simulation results predicted good binding scores and interactions with prime residues, such as the reference antagonist YM022.

CONCLUSIONS

The results of this study suggest bromophenols 1-3 are CCK2R antagonists that could be novel therapeutic agents for CCK2R-related diseases, especially anxiety and depression.

Small Molecule Tools to Study Cellular Target Engagement for the Intracellular Allosteric Binding Site of GPCRs

A conserved intracellular allosteric binding site (IABS) has recently been identified at several G protein-coupled receptors (GPCRs). Ligands targeting the IABS, so-called intracellular allosteric antagonists, are highly promising compounds for pharmaceutical intervention and currently evaluated in several clinical trials. Beside co-crystal structures that laid the foundation for the structure-based development of intracellular allosteric GPCR antagonists, small molecule tools that enable an unambiguous identification and characterization of intracellular allosteric GPCR ligands are of utmost importance for drug discovery campaigns in this field. Herein, we discuss recent approaches that leverage cellular target engagement studies for the IABS and thus play a critical role in the evaluation of IABS-targeted ligands as potential therapeutic agents.

Synthesis, Structural and Behavioral Studies of Indole Derivatives D2AAK5, D2AAK6 and D2AAK7 as Serotonin 5-HT1A and 5-HT2A Receptor Ligands

Serotonin receptors are involved in a number of physiological functions and regulate aggression, anxiety, appetite, cognition, learning, memory, mood, nausea, sleep, and thermoregulation. Here we report synthesis and detailed structural and behavioral studies of three indole derivatives: D2AAK5, D2AAK6, and D2AAK7 as serotonin 5-HT_1A and 5-HT_2A receptor ligands. X-ray studies revealed that the D2AAK5 compound crystallizes in centrosymmetric triclinic space group with one molecule in the asymmetric unit. The main interaction between the ligands and the receptors is the salt bridge between the protonatable nitrogen atom of the ligands and the conserved Asp (3.32) of the receptors. The complexes were stable in the molecular dynamic simulations. MD revealed that the studied ligands are relatively stable in their binding sites, with the exception of D2AAK7 in the serotonin 5-HT_1A receptor. D2AAK7 exerts anxiolytic activity in the EPM test, while D2AAK5 has a beneficial effect on the memory processes in the PA test.

Internalization of somatostatin receptors in brain and periphery

Somatostatin (SRIF) is a neuropeptide that acts as an important regulator of both endocrine and exocrine secretion and modulates neurotransmission in the central nervous system (CNS). SRIF also regulates cell proliferation in normal tissues and tumors. The physiological actions of SRIF are mediated by a family of five G protein-coupled receptors, called somatostatin receptor (SST) SST₁, SST₂, SST₃, SST₄, SST₅. These five receptors share similar molecular structure and signaling pathways but they display marked differences in their anatomical distribution, subcellular localization and intracellular trafficking. The SST subtypes are widely distributed in the CNS and peripheral nervous system, in many endocrine glands and tumors, particularly of neuroendocrine origin. In this review, we focus on the agonist-dependent internalization and recycling of the different SST subtypes in vivo in the CNS, peripheral organs and tumors. We also discuss the physiological, pathophysiological and potential therapeutic effects of the intracellular trafficking of SST subtypes.