Biased Ligands Research Articles

Functional competence of a partially engaged GPCR-β-arrestin complex.

G Protein-coupled receptors (GPCRs) constitute the largest family of cell surface receptors and drug targets. GPCR signalling and desensitization is critically regulated by β-arrestins (βarr). GPCR–βarr interaction is biphasic where the phosphorylated carboxyl terminus of GPCRs docks to the N-domain of βarr first and then seven transmembrane core of the receptor engages with βarr. It is currently unknown whether fully engaged GPCR–βarr complex is essential for functional outcomes or partially engaged complex can also be functionally competent. Here we assemble partially and fully engaged complexes of a chimeric β2V2R with βarr1, and discover that the core interaction is dispensable for receptor endocytosis, ERK MAP kinase binding and activation. Furthermore, we observe that carvedilol, a βarr biased ligand, does not promote detectable engagement between βarr1 and the receptor core. These findings uncover a previously unknown aspect of GPCR-βarr interaction and provide novel insights into GPCR signalling and regulatory paradigms.

PAR2 Modulators Derived from GB88.

PAR2 antagonists have potential for treating inflammatory, respiratory, gastrointestinal, neurological, and metabolic disorders, but few antagonists are known. Derivatives of GB88 (3) suggest that all four of its components bind at distinct PAR2 sites with the isoxazole, cyclohexylalanine, and isoleucine determining affinity and selectivity, while the C-terminal substituent determines agonist/antagonist function. Here we report structurally similar PAR2 ligands with opposing functions (agonist vs antagonist) upon binding to PAR2. A biased ligand AY117 (65) was found to antagonize calcium release induced by PAR2 agonists trypsin and hexapeptide 2f-LIGRLO-NH2 (IC50 2.2 and 0.7 μM, HT29 cells), but it was a selective PAR2 agonist in inhibiting cAMP stimulation and activating ERK1/2 phosphorylation. It showed anti-inflammatory properties both in vitro and in vivo.

Recent Developments in Group I Metabotropic Glutamate Receptor Allosteric Modulators for the Treatment of Psychiatric and Neurological Disorders (2014-May 2015).

In the last ~30 years, scientists have made great strides in understanding the biological function of group I metabotropic glutamate receptors (mGlu) in health and disease, as well as developing a broad array of potent and selective agents able to activate or inhibit these receptors. This article provides a comprehensive review of the most recent group I mGlu modulators published in patent and non-patent literatures from 2014 to May, 2015, including design, structure-activity relationship, in silico, in vitro and in vivo properties of key compounds. The current status of clinical mGlu5 negative allosteric modulators (NAMs) and the development of mGlu1 and mGlu5 PET ligands are also highlighted. While the therapeutic potential for group I mGlu modulating agents appears high, significant challenges remain. Strategies to reduce clinical development risks and mitigate important side effects, including psychotomimetic events observed with several mGlu5 NAMs and cellular toxicity associated with mGlu5 positive allosteric modulators (PAMs), while retaining therapeutic efficacy through approaches such as biased ligand signaling are discussed.

New therapeutic opportunities for 5-HT2 receptor ligands.

Serotonergic dysfunction is mainly associated with neuropsychiatric and cardiovascular disorders but has also been linked with many other pathological conditions. Serotonin (5-hydroxytryptamine, 5-HT) mediates numerous physiological functions in the brain and the periphery by activating a variety of receptors. 5-HT receptors are divided into four classes, three of which belong to the G protein-coupled receptor family. This review provides an overview of the recent pharmacological developments involving the Gq-coupled 5-HT2 receptor subfamily as well as the pathological implications of this receptor subfamily with regard to fibrosis, the central nervous system, cardiovascular disorders, and cancer. The final section highlights new therapeutic opportunities and emerging research revealing unexplored medical opportunities for this class of 5-HT receptors. The development of biased 5-HT2 receptor ligands appears to be an interesting topic in various areas. In light of recent discoveries, the need for the development of new and safer drugs should take into account the risk of cardiovascular side effects such as pulmonary hypertension and heart valve disease.

Biased small-molecule ligands for selective inhibition of HIV-1 cell entry via CCR5.

Since the discovery of HIV's use of CCR5 as the primary coreceptor in fusion, the focus on developing small‐molecule receptor antagonists for inhibition hereof has only resulted in one single drug, Maraviroc. We therefore investigated the possibility of using small‐molecule CCR5 agonists as HIV‐1 fusion inhibitors. A virus‐free cell‐based fusion reporter assay, based on mixing “effector cells” (expressing HIV Env and luciferase activator) with “target cells” (expressing CD4, CCR5 wild type or a selection of well‐described mutations, and luciferase reporter), was used as fusion readout. Receptor expression was evaluated by ELISA and fluorescence microscopy. On CCR5 WT, Maraviroc and Aplaviroc inhibited fusion with high potencies (EC 50 values of 91 and 501 nM, respectively), whereas removal of key residues for both antagonists (Glu283Ala) or Maraviroc alone (Tyr251Ala) prevented fusion inhibition, establishing this assay as suitable for screening of HIV entry inhibitors. Both ligands inhibited HIV fusion on signaling‐deficient CCR5 mutations (Tyr244Ala and Trp248Ala). Moreover, the steric hindrance CCR5 mutation (Gly286Phe) impaired fusion, presumably by a direct hindrance of gp120 interaction. Finally, the efficacy switch mutation (Leu203Phe) – converting small‐molecule antagonists/inverse agonists to full agonists biased toward G‐protein activation – uncovered that also small‐molecule agonists can function as direct HIV‐1 cell entry inhibitors. Importantly, no agonist‐induced receptor internalization was observed for this mutation. Our studies of the pharmacodynamic requirements for HIV‐1 fusion inhibitors highlight the possibility of future development of biased ligands with selective targeting of the HIV–CCR5 interaction without interfering with the normal functionality of CCR5.

Cardioprotective Angiotensin-(1-7) Peptide Acts as a Natural-Biased Ligand at the Angiotensin II Type 1 Receptor.

Hyperactivity of the renin-angiotensin-aldosterone system through the angiotensin II (Ang II)/Ang II type 1 receptor (AT1-R) axis constitutes a hallmark of hypertension. Recent findings indicate that only a subset of AT1-R signaling pathways is cardiodeleterious, and their selective inhibition by biased ligands promotes therapeutic benefit. To date, only synthetic biased ligands have been described, and whether natural renin-angiotensin-aldosterone system peptides exhibit functional selectivity at AT1-R remains unknown. In this study, we systematically determined efficacy and potency of Ang II, Ang III, Ang IV, and Ang-(1-7) in AT1-R-expressing HEK293T cells on the activation of cardiodeleterious G-proteins and cardioprotective β-arrestin2. Ang III and Ang IV fully activate similar G-proteins than Ang II, the prototypical AT1-R agonist, despite weaker potency of Ang IV. Interestingly, Ang-(1-7) that binds AT1-R fails to promote G-protein activation but behaves as a competitive antagonist for Ang II/Gi and Ang II/Gq pathways. Conversely, all renin-angiotensin-aldosterone system peptides act as agonists on the AT1-R/β-arrestin2 axis but display biased activities relative to Ang II as indicated by their differences in potency and AT1-R/β-arrestin2 intracellular routing. Importantly, we reveal Ang-(1-7) a known Mas receptor-specific ligand, as an AT1-R-biased agonist, selectively promoting β-arrestin activation while blocking the detrimental Ang II/AT1-R/Gq axis. This original pharmacological profile of Ang-(1-7) at AT1-R, similar to that of synthetic AT1-R-biased agonists, could, in part, contribute to its cardiovascular benefits. Accordingly, in vivo, Ang-(1-7) counteracts the phenylephrine-induced aorta contraction, which was blunted in AT1-R knockout mice. Collectively, these data suggest that Ang-(1-7) natural-biased agonism at AT1-R could fine-tune the physiology of the renin-angiotensin-aldosterone system.

Human DP and EP2 prostanoid receptors take on distinct forms depending on the diverse binding of different ligands.

Human D-type prostanoid (DP) and E-type prostanoid 2 (EP2) receptors are G protein-coupled receptors and are regarded as the most closely related receptors among prostanoid receptors because they are generated by tandem duplication. The DP receptor-cognate ligand, prostaglandin D2 (PGD2 ) has the ability to activate not only DP receptors but also EP2 receptors. Likewise, the EP2 receptor-cognate ligand, prostaglandin E2 (PGE2 ) has the ability to activate DP receptors in addition to EP receptors in order to stimulate cAMP formation. However, since PGD2 and/or PGE2 activate DP and EP2 receptors to similar maximal levels, that is, their similar efficacies, differences between the ligands in each receptor have not yet been determined in detail except for their different affinities. Herein we demonstrated, using an in silico simulation to predict binding patterns among DP or EP2 receptors and PGD2 , PGE2 , or prostaglandin F2α as the reference prostanoid, that DP and EP2 receptors plausibly take on distinct forms depending on the diverse binding of different ligands. Since these ligands have the potential to make these receptors form distinct conformations with discrete signaling pathways, they are consequently regarded as endogenous biased ligands. Moreover, by using functional assays, the susceptibilities of the DP receptors to the noncognate ligands were approximately 10 times lower than those of EP2 receptors. Thus, EP2 receptors seem to be able to distinguish endogenous ligands better than DP receptors, thereby both receptors are plausibly gaining role-sharing functions with respect to one another as the copies of duplicated gene.

Molecular Mechanism of Biased Ligand Conformational Changes in CC Chemokine Receptor 7.

Biased ligand binding to G protein-coupled receptors enables functional selectivity of intracellular effectors to mediate cellular function. Despite the significant advances made in characterizing the conformational states (transmembrane helical arrangements) capable of discriminating between G protein and arrestin binding, the role of the ligand in stabilizing such conformations remains unclear. To address this issue, we simulate microsecond dynamics of CC chemokine receptor 7 (CCR7) bound to its native biased ligands, CCL19 and CCL21, and detect a series of molecular switches that are mediated by various ligand-induced allosteric events. These molecular switches involve three tyrosine residues (Y112(3.32), Y255(6.51), and Y288(7.39)), three phenylalanine residues (F116(3.36), F208(5.47), and F248(6.44)), and a polar interaction between Q252(6.48) and R294(7.45) in the transmembrane domain of CCR7. Conformational changes within these switches, particularly hydrogen bond formation between Y112(3.32) and Y255(6.51), lead to global helical movements in the receptor's transmembrane helices and contribute to the transitioning of the receptor to distinct states. Ligand-induced helical movements in the receptor highlight the ability of biased ligands to stabilize the receptor in different states through a dynamic network of allosteric events.

Fibroblast growth factor 19 meets mammalian target of rapamycin: A mitogenic Tête‐à‐Tête under consideration

Fibroblast growth factor 19 meets mammalian target of rapamycin: A mitogenic Tête‐à‐Tête under consideration

Systematic analysis of factors influencing observations of biased agonism at the mu-opioid receptor

Biased agonism describes the ability of distinct G protein-coupled receptor (GPCR) ligands to stabilise distinct receptor conformations leading to the activation of different cell signalling pathways that can deliver different physiologic outcomes. This phenomenon is having a major impact on modern drug discovery as it offers the potential to design ligands that selectively activate or inhibit the signalling pathways linked to therapeutic effects with minimal activation or blockade of signalling pathways that are linked to the development of adverse on-target effects. However, the explosion in studies of biased agonism at multiple GPCR families in recombinant cell lines has revealed a high degree of variability on descriptions of biased ligands at the same GPCR and raised the question of whether biased agonism is a fixed attribute of a ligand in all cell types. The current study addresses this question at the mu-opioid receptor (MOP). Here, we have systematically assessed the impact of differential cellular protein complement (and cellular background), signalling kinetics and receptor species on our previous descriptions of biased agonism at MOP by several opioid peptides and synthetic opioids. Our results show that all these factors need to be carefully determined and reported when considering biased agonism. Nevertheless, our studies also show that, despite changes in overall signalling profiles, ligands that previously showed distinct bias profiles at MOP retained their uniqueness across different cell backgrounds.

Abstract 346: Manipulating P2Y2 Receptor Biased Signaling to Limit Pro-thrombotic Gene Expression in Human Coronary Artery Endothelial Cells

Recently we reported that in human coronary artery endothelial cells (HCAEC), the P2Y2 nucleotide receptor (P2Y2R) regulates the pro-thrombotic gene tissue factor (TF) expression through positive and negative signaling mechanisms. Here, we report the identification of a P2Y2R ligand JZS0312 which selectively activates the negative, but not the positive pathways, leading to decreased TF expression. Unlike the endogenous agonist UTP, JZS0312 alone had no effect on TF mRNA transcription, but it unexpectedly inhibited UTP-induced TF expression. Mechanistic study showed that JZS0312 induced intracellular Ca 2+ mobilization in HCAEC which exhibited the same efficacy as UTP and was inhibited by AR-C118925, a P2Y2R-selective antagonist. However, when evaluated in their activation of the MAPK pathways, JZS0312 only activated the ERK1/2, but not JNK and p38, whereas UTP activated all the three, suggesting JZS0312 as a biased ligand for the P2Y2R. This notion was supported by the fact that JZS0312-induced ERK1/2 activation was inhibited by AR-C1189258 and it had no effect on ERK1/2 in P2Y2R-null cells. In addition, JZS0312 selectively activated the TF gene repressor Fra-1, but not the positive AP-1 subunits c-Jun and ATF-2, whereas UTP activated all of them. Furthermore, luciferase activity assay indicates that JZS0312 suppressed TF gene promoter activity via ERK1/2 activation, while UTP increased overall TF promoter activity. These findings reveal that JZS0312 acts as a biased agonist in human endothelial P2Y2R, in which it selectively activates the ERK1/2-Fra1 pathway, leading to suppression of TF gene transcription. Thus, JZS0312 represents the first identified biased ligand in the P2Y receptor family, opening new avenue for potential drug discovery in relevant inflammatory and thrombotic diseases.

Delineating biased ligand efficacy at 7TM receptors from an experimental perspective

During the last 10 years, the concept of “biased agonism” also called “functional selectivity” swamped the pharmacology of 7 transmembrane receptors and paved the way for developing signaling pathway-selective drugs with increased efficacy and less adverse effects. Initially thought to select the activation of only a subset of the signaling pathways by the reference agonist, bias ligands revealed higher complexity as they have been shown to stabilize variable receptor conformations that associate with distinct signaling events from the reference. Today, one major challenge relies on the in vitro determination of the bias and classification of these ligands, as a prerequisite for future in vivo and clinical translation. In this review, current experimental considerations for the bias evaluation related to choice of the cellular model, of the signaling pathway as well as of the assays are presented and discussed.

Potent lipidated antagonists to protease‐activated receptor 2 (PAR2)

Protease‐activated receptor‐2 (PAR2) belongs to a four‐member family of G‐Protein coupled receptors (GPCRs) that contain internal ligands exposed following exogenous or endogenous protease cleavage of the extracellular amino terminus. PAR2 is associated with a variety of inflammatory conditions, including asthma and pain. The contributions of PAR2 signaling to disease has been hindered by the lack of potent, efficacious antagonists, and their potential for biased‐ligand signaling. We recently demonstrated that lipid tethering of known PAR2 peptidomimetic agonists based on the primary trypsin cleavage sequence (SLIGRL) increased their potency > 200 fold. In this study, we used lipid tethering (hexadecyl (Hdc) group with polyethylene glycol (PEG) spacers) and heterocycle (2‐aminothiazoyl; 2‐at) substitution of hexapeptide sequence derived from the primary cleavage site of kallikreins 4/16 (SSKGRS) to elucidate novel PAR2 antagonists. Compound 562 (C562), 2‐aminothiazol‐4yl‐SKGRS‐PEG3‐Hdc blocks PAR2 Ca2+ signaling elicited via peptidomimetics (2‐at‐LIGRL‐NH2) or via asthma associated protease activation (Alternaria alternata filtrates) in cultured human bronchial epithelial cells (16HBE14o‐). This compound was a biased‐signaling antagonist in that it had no effect on mitogen activated protein kinase (MAPK) signaling, the other major signaling pathway activated via PAR2. A shortened version of C562, 2‐at‐SKGR‐PEG3‐Hdc (C595), maintained antagonistic activity against peptidomimetic activation in an in vitro physiological signaling assay (xCELLigence). C595 is closely related to the previously described potent and specific PAR2 agonist, 2‐at‐LIGR‐PEG3‐Hdc. Thus, we screened a series of potential PAR2 ligands with a heterocycle serine substitute followed by four amino acids (XXGR) and the PEG3‐Hdc lipid tether. We describe several potent agonists, and one partial agonist (C608, 2‐at‐TIGR‐PEG3‐Hdc) that also acts as a potent, specific and biased signaling antagonist of PAR2. When used in nanomolar concentrations, C608 blocked PAR2‐dependent Ca2+ signaling via protease or peptidomimetics without effects on MAPK signaling. C562, C595 and C608 are novel pharmacological tools that can be used to evaluate the physiological consequences of PAR2 full and biased ligand signaling.Support or Funding InformationThis work was primarily funded by a multi‐PI grant (NS 073664 to SB, JV and TJP) from the National Institutes of Health. Additional support for this work was from the following grants: National Institute of Health training grants (T32 HL 007249 for ANF; T32 ES 007091 for CLS), National Institutes of Health R01NS 065926 (TJP) and R01AI083403 (SB; Michael O. Daines, PI), State of Arizona Technology and Research Initiative Fund Awarded through Bio5 (JV).

A biased mu‐opioid receptor positive allosteric modulator that does not alter receptor regulation

Currently used opioid analgesics compete with endogenous opioid peptide ligands by binding to the orthosteric site of the mu opioid receptor (MOPr). Activation of this G protein‐coupled receptor (GPCR) affords analgesia but also causes respiratory depression, sedation, constipation, and euphoria leading to a high addictive liability. Our lab is currently pursuing the idea that positive allosteric modulators of MOPr (mu‐PAMs) may be a way to treat pain with a better therapeutic profile. Such compounds, including the lead ligand BMS‐986122, enhance the affinity, potency, and efficacy of opioid agonists to bind MOPr and activate G protein. On the other hand, BMS‐986122 does not stimulate G protein activation, as measured by [35S]GTPγS binding in the absence of an orthosteric ligand. Here, we sought to determine if BMS‐986122 activates non‐G protein mediated pathways downstream of MOPr and to investigate the long‐term consequences of BMS‐986122 exposure on the regulation of MOPr in vitro using C6 rat glioma cells expressing rat MOPr. The results demonstrate that BMS‐986122 initiates phosphorylation of ERK1/2 in a pertussis‐toxin insensitive manner supporting a G protein‐independent mechanism. BMS‐986122 alone did not cause any long‐term adaptations in MOPr signaling. Moreover, in contrast to its ability to enhance agonist‐mediated activation of G protein, BMS‐986122 failed to enhance agonist‐induced desensitization of MOPr as measured by receptor downregulation, receptor phosphorylation, and loss of receptor‐mediated signaling following long‐term agonist exposure. Development of biased allosteric ligands at GPCRs represents a novel avenue for analgesic drug development. Future work will determine the physiological consequences of this biased PAM in mouse models of pain.Support or Funding InformationFunded by DA039997

A G Protein-biased Designer G Protein-coupled Receptor Useful for Studying the Physiological Relevance of Gq/11-dependent Signaling Pathways

Designerreceptorsexclusivelyactivated by adesignerdrug (DREADDs) are clozapine-N-oxide-sensitive designer G protein-coupled receptors (GPCRs) that have emerged as powerful novel chemogenetic tools to study the physiological relevance of GPCR signaling pathways in specific cell types or tissues. Like endogenous GPCRs, clozapine-N-oxide-activated DREADDs do not only activate heterotrimeric G proteins but can also trigger β-arrestin-dependent (G protein-independent) signaling. To dissect the relative physiological relevance of G protein-mediatedversusβ-arrestin-mediated signaling in different cell types or physiological processes, the availability of G protein- and β-arrestin-biased DREADDs would be highly desirable. In this study, we report the development of a mutationally modified version of a non-biased DREADD derived from the M3muscarinic receptor that can activate Gq/11with high efficacy but lacks the ability to interact with β-arrestins. We also demonstrate that this novel DREADD is activein vivoand that cell type-selective expression of this new designer receptor can provide novel insights into the physiological roles of G protein (Gq/11)-dependentversusβ-arrestin-dependent signaling in hepatocytes. Thus, this novel Gq/11-biased DREADD represents a powerful new tool to study the physiological relevance of Gq/11-dependent signaling in distinct tissues and cell types, in the absence of β-arrestin-mediated cellular effects. Such studies should guide the development of novel classes of functionally biased ligands that show high efficacy in various pathophysiological conditions but display a reduced incidence of side effects.

G Protein-Coupled Receptors (GPCRs) in Alzheimer's Disease: A Focus on BACE1 Related GPCRs.

The G protein coupled receptors (GPCRs) have been considered as one of the largest families of validated drug targets, which involve in almost overall physiological functions and pathological processes. Meanwhile, Alzheimer’s disease (AD), the most common type of dementia, affects thinking, learning, memory and behavior of elderly people, that has become the hotspot nowadays for its increasing risks and incurability. The above fields have been intensively studied, and the link between the two has been demonstrated, whereas the way how GPCRs perturb AD progress are yet to be further explored given their complexities. In this review, we summarized recent progress regarding the GPCRs interacted with β-site APP cleaving enzyme 1 (BACE1), a key secretase in AD pathogenesis. Then we discussed the current findings on the regulatory roles of GPCRs on BACE1, and the possibility for pharmaceutical treatment of AD patients by the allosteric modulators and biased ligands of GPCRs. We hope this review can provide new insights into the understanding of mechanistic link between GPCRs and BACE1, and highlight the potential of GPCRs as therapeutic target for AD.

Biased ligand quantification in drug discovery: from theory to high throughput screening to identify new biased μ opioid receptor agonists.

Biased GPCR ligands are able to engage with their target receptor in a manner that preferentially activates distinct downstream signalling and offers potential for next generation therapeutics. However, accurate quantification of ligand bias in vitro is complex, and current best practice is not amenable for testing large numbers of compound. We have therefore sought to apply ligand bias theory to an industrial scale screening campaign for the identification of new biased μ receptor agonists. μ receptor assays with appropriate dynamic range were developed for both Gαi -dependent signalling and β-arrestin2 recruitment. Δlog(Emax /EC50 ) analysis was validated as an alternative for the operational model of agonism in calculating pathway bias towards Gαi -dependent signalling. The analysis was applied to a high throughput screen to characterize the prevalence and nature of pathway bias among a diverse set of compounds with μ receptor agonist activity. A high throughput screening campaign yielded 440 hits with greater than 10-fold bias relative to DAMGO. To validate these results, we quantified pathway bias of a subset of hits using the operational model of agonism. The high degree of correlation across these biased hits confirmed that Δlog(Emax /EC50 ) was a suitable method for identifying genuine biased ligands within a large collection of diverse compounds. This work demonstrates that using Δlog(Emax /EC50 ), drug discovery can apply the concept of biased ligand quantification on a large scale and accelerate the deliberate discovery of novel therapeutics acting via this complex pharmacology.

G Protein-coupled Receptor Biased Agonism.

G protein-coupled receptors are the largest family of targets for current therapeutics. The classic model of their activation was binary, where agonist binding induced an active conformation and subsequent downstream signaling. Subsequently, the revised concept of biased agonism emerged, where different ligands at the same G protein-coupled receptor selectively activate one downstream pathway versus another. Advances in understanding the mechanism of biased agonism have led to the development of novel ligands, which have the potential for improved therapeutic and safety profiles. In this review, we summarize the theory and most recent breakthroughs in understanding biased signaling, examine recent laboratory investigations concerning biased ligands across different organ systems, and discuss the promising clinical applications of biased agonism.

Structural Studies of the Human Kappa Opioid Receptor Active State Conformations

The crystal structure of the human kappa opioid receptor (hKOR) in complex with antagonist JDTic had been previously solved to 2.9 A (Wu et al, 2012, Nature 485, 327-332). From this crystal structure, key receptor-ligand interactions were observed and extended via modeling to GNTI, β-NNTA, and other hKOR ligands. However, a major hurdle still remains in elucidating hKOR in different states of activation. Having this information would lead to a more comprehensive understanding of hKOR activation and function, informing design of more efficient analgesics with reduced side effects. Specifically, we seek to utilize selective hKOR ligands to trap hKOR in conformational states that correlate to the properties of each ligand. Here we present our work in progress on the design of novel hKOR constructs and their complexes with agonists, antagonists, and biased ligands.

ChemInform Abstract: Biased Agonism: An Emerging Paradigm in GPCR Drug Discovery

AbstractReview: 124 refs.