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Constitutive receptor activity/inverse agonism and functional selectivity/biased agonism are 2 concepts in contemporary pharmacology that have major implications for the use of drugs in medicine and research as well as for the processes of new drug development. Traditional receptor theory postulated that receptors in a population are quiescent unless activated by a ligand. Within this framework ligands could act as agonists with various degrees of intrinsic efficacy, or as antagonists with zero intrinsic efficacy. We now know that receptors can be active without an activating ligand and thus display \"constitutive\" activity. As a result, a new class of ligand was discovered that can reduce the constitutive activity of a receptor. These ligands produce the opposite effect of an agonist and are called inverse agonists. The second topic discussed is functional selectivity, also commonly referred to as biased agonism. Traditional receptor theory also posited that intrinsic efficacy is a single drug property independent of the system in which the drug acts. However, we now know that a drug, acting at a single receptor subtype, can have multiple intrinsic efficacies that differ depending on which of the multiple responses coupled to a receptor is measured. Thus, a drug can be simultaneously an agonist, an antagonist, and an inverse agonist acting at the same receptor. This means that drugs have an additional level of selectivity (signaling selectivity or \"functional selectivity\") beyond the traditional receptor selectivity. Both inverse agonism and functional selectivity need to be considered when drugs are used as medicines or as research tools.

The neuromodulator melatonin synchronizes circadian rhythms and related physiological functions through the actions of two G-protein-coupled receptors: MT 1 and MT 2 . Circadian release of melatonin at night from the pineal gland activates melatonin receptors in the suprachiasmatic nucleus of the hypothalamus, synchronizing the physiology and behaviour of animals to the light–dark cycle 1 – 4 . The two receptors are established drug targets for aligning circadian phase to this cycle in disorders of sleep 5 , 6 and depression 1 – 4 , 7 – 9 . Despite their importance, few in vivo active MT 1 -selective ligands have been reported 2 , 8 , 10 – 12 , hampering both the understanding of circadian biology and the development of targeted therapeutics. Here we docked more than 150 million virtual molecules to an MT 1 crystal structure, prioritizing structural fit and chemical novelty. Of these compounds, 38 high-ranking molecules were synthesized and tested, revealing ligands with potencies ranging from 470 picomolar to 6 micromolar. Structure-based optimization led to two selective MT 1 inverse agonists—which were topologically unrelated to previously explored chemotypes—that acted as inverse agonists in a mouse model of circadian re-entrainment. Notably, we found that these MT 1 -selective inverse agonists advanced the phase of the mouse circadian clock by 1.3–1.5 h when given at subjective dusk, an agonist-like effect that was eliminated in MT 1 - but not in MT 2 -knockout mice. This study illustrates the opportunities for modulating melatonin receptor biology through MT 1 -selective ligands and for the discovery of previously undescribed, in vivo active chemotypes from structure-based screens of diverse, ultralarge libraries. A computational screen of an ultra-large virtual library against the structure of the melatonin receptor found nanomolar ligands, and ultimately two selective MT 1 inverse agonists that induced phase advancement of the mouse circadian clock when given at subjective dusk.

Frequently referred to as the ‘magic methyl effect’, the installation of methyl groups—especially adjacent (α) to heteroatoms—has been shown to dramatically increase the potency of biologically active molecules 1 – 3 . However, existing methylation methods show limited scope and have not been demonstrated in complex settings 1 . Here we report a regioselective and chemoselective oxidative C( sp 3 )–H methylation method that is compatible with late-stage functionalization of drug scaffolds and natural products. This combines a highly site-selective and chemoselective C–H hydroxylation with a mild, functional-group-tolerant methylation. Using a small-molecule manganese catalyst, Mn(CF 3 PDP), at low loading (at a substrate/catalyst ratio of 200) affords targeted C–H hydroxylation on heterocyclic cores, while preserving electron-neutral and electron-rich aryls. Fluorine- or Lewis-acid-assisted formation of reactive iminium or oxonium intermediates enables the use of a mildly nucleophilic organoaluminium methylating reagent that preserves other electrophilic functionalities on the substrate. We show this late-stage C( sp 3 )–H methylation on 41 substrates housing 16 different medicinally important cores that include electron-rich aryls, heterocycles, carbonyls and amines. Eighteen pharmacologically relevant molecules with competing sites—including drugs (for example, tedizolid) and natural products—are methylated site-selectively at the most electron rich, least sterically hindered position. We demonstrate the syntheses of two magic methyl substrates—an inverse agonist for the nuclear receptor RORc and an antagonist of the sphingosine-1-phosphate receptor-1—via late-stage methylation from the drug or its advanced precursor. We also show a remote methylation of the B-ring carbocycle of an abiraterone analogue. The ability to methylate such complex molecules at late stages will reduce synthetic effort and thereby expedite broader exploration of the magic methyl effect in pursuit of new small-molecule therapeutics and chemical probes. A manganese-catalysed oxidative C( sp 3 )–H methylation method allows a methyl group to be selectively installed into medicinally important heterocycles, providing a way to improve pharmaceuticals and better understand the ‘magic methyl effect’.

Muscarinic M1–M5 acetylcholine receptors are G-protein-coupled receptors that regulate many vital functions of the central and peripheral nervous systems. In particular, the M1 and M4 receptor subtypes have emerged as attractive drug targets for treatments of neurological disorders, such as Alzheimer’s disease and schizophrenia, but the high conservation of the acetylcholine-binding pocket has spurred current research into targeting allosteric sites on these receptors. Here we report the crystal structures of the M1 and M4 muscarinic receptors bound to the inverse agonist, tiotropium. Comparison of these structures with each other, as well as with the previously reported M2 and M3 receptor structures, reveals differences in the orthosteric and allosteric binding sites that contribute to a role in drug selectivity at this important receptor family. We also report identification of a cluster of residues that form a network linking the orthosteric and allosteric sites of the M4 receptor, which provides new insight into how allosteric modulation may be transmitted between the two spatially distinct domains. X-ray crystal structures of the M1 and M4 muscarinic acetylcholine receptors, revealing differences in the orthosteric and allosteric binding sites that help to explain the subtype selectivity of drugs targeting this family of receptors. M1 and M4 muscarinic acetylcholine receptor structures Arthur Christopoulos and colleagues present the first X-ray crystal structures of the M1 and M4 muscarinic acetylcholine receptors, G-protein-coupled receptors (GPCRs) that regulate many vital functions of the central and peripheral nervous systems. The structures reveal differences in the orthosteric and allosteric binding sites that help to explain the subtype selectivity of drugs targeting this family of receptors. The M1 and M4 receptor subtypes are potential drug targets for treatments of neurological disorders, such as Alzheimer's disease and schizophrenia.

The MRGPRX family of receptors (MRGPRX1–4) is a family of mas-related G-protein-coupled receptors that have evolved relatively recently 1 . Of these, MRGPRX2 and MRGPRX4 are key physiological and pathological mediators of itch and related mast cell-mediated hypersensitivity reactions 2 – 5 . MRGPRX2 couples to both G i and G q in mast cells 6 . Here we describe agonist-stabilized structures of MRGPRX2 coupled to G i1 and G q in ternary complexes with the endogenous peptide cortistatin-14 and with a synthetic agonist probe, respectively, and the development of potent antagonist probes for MRGPRX2. We also describe a specific MRGPRX4 agonist and the structure of this agonist in a complex with MRGPRX4 and G q . Together, these findings should accelerate the structure-guided discovery of therapeutic agents for pain, itch and mast cell-mediated hypersensitivity. Structural studies of the itch receptors MRGPRX2 and MRGPRX4 in complex with endogenous and synthetic ligands provide a basis for the development of therapeutic compounds for pain, itch and mast cell-mediated hypersensitivity.

Narcolepsy is a life-long disorder characterised by excessive daytime sleepiness and cataplexy, often arising in childhood or adolescence. Pitolisant, a selective histamine H3 receptor inverse agonist, has been approved in Europe and USA for adults with narcolepsy with or without cataplexy, with a favourable safety profile. This phase 3 study aimed to assess the safety and efficacy of pitolisant in children with narcolepsy with or without cataplexy. For this double-blind, randomised, placebo-controlled, multisite study, we recruited patients aged 6–17 years with narcolepsy with or without cataplexy in 11 sleep centres in five countries (Italy, France, Netherlands, Russia, and Finland). Participants were required to have a Pediatric Daytime Sleepiness Scale score of 15 or greater and to have not received psychostimulants for at least 14 days before enrolment; participants who needed anticataplectics (including sodium oxybate) were required to have been on a stable dose for at least 1 month. Participants were randomly assigned to treatment with pitolisant or placebo in a 2:1 ratio at the end of screening. Randomisation was stratified by study centre and treatment was allocated using an interactive web response system. After a 4-week screening period including a 2-week baseline period, patients entered in a 4-week individual up-titration scheme from 5 mg a day to a maximum of 40 mg a day of pitolisant or placebo; treatment was administered at a stable dose for 4 weeks, followed by a 1-week placebo period. For the primary analysis, we assessed pitolisant versus placebo using change in the Ullanlinna Narcolepsy Scale (UNS) total score from baseline to the end of double-blind period in the full analysis set, defined as all randomly allocated patients who received at least one dose of treatment and who had at least one baseline UNS value. A decrease in the UNS total score reflects a reduction in both excessive daytime sleepiness and cataplexy. All adverse events were assessed in the safety population, defined as all participants who took at least one dose of study medication. An open-label follow-up is ongoing. This study is registered at ClinicalTrials.gov, NCT02611687. Between June 6, 2016, and April 3, 2021, we screened 115 participants and 110 were randomly assigned (mean age 12·9 [SD 3·0] years, 61 [55%] male, and 90 [82%] with cataplexy; 72 assigned to pitolisant and 38 to placebo); 107 (70 receiving pitolisant and 37 receiving placebo) completed the double-blind period. The mean adjusted difference in UNS total score from baseline to the end of the double-blind period was –6·3 (SE 1·1) in the pitolisant group and –2·6 (1·4) in the placebo group (least squares mean difference –3·7; 95% CI –6·4 to –1·0, p=0·007). Treatment-emergent adverse events were reported in 22 (31%) of 72 patients in the pitolisant group and 13 (34%) of 38 patients in the placebo group. The most frequently reported adverse events (affecting ≥5% of patients) in either group were headache (14 [19%] in the pitolisant group and three [8%] in the placebo group) and insomnia (five [7%] in the pitolisant group and one [3%] in the placebo group). Pitolisant treatment resulted in an improvement in narcolepsy symptoms in children, although the UNS was not validated for use in children with narcolepsy when our study began. The safety profile was similar to that reported in adults but further studies are needed to confirm long-term safety. Bioprojet.

Abstract Background Schizophrenia is a disabling disorder that profoundly affects functioning and quality of life. While available antipsychotics have improved outcomes for patients with schizophrenia, they are relatively ineffective for negative and cognitive symptoms and are associated with a range of troublesome side effects. A significant unmet medical need for more effective and better-tolerated therapies remains. Methods A roundtable consisting of 4 experts in the treatment of patients with schizophrenia convened to discuss the current treatment landscape, unmet needs from patient and societal perspectives, and the potential of emerging therapies with novel mechanisms of action (MOAs). Results Key areas of unmet need include optimal implementation of available treatments, effective treatment of negative and cognitive symptoms, improvements in medication adherence, novel MOAs, avoidance of postsynaptic dopamine blockade–related adverse effects, and individualized approaches to treatment. With the possible exception of clozapine, all currently available antipsychotics primarily act by blocking dopamine D2 receptors. Agents with novel MOAs are urgently needed to effectively target the full range of symptoms in schizophrenia and facilitate an individualized treatment approach. Discussion focused on promising novel MOAs that have demonstrated potential in phase 2 and 3 trials include muscarinic receptor agonism, trace amine-associated receptor 1 agonism, serotonin receptor antagonism/inverse agonism, and glutamatergic modulation. Conclusions Results from early clinical trials of agents with novel MOAs are encouraging, particularly for muscarinic and trace amine-associated receptor 1 agonists. These agents offer renewed hope for meaningful improvement in the management of patients with schizophrenia.

The orphan nuclear receptor, estrogen-related receptor γ (ERRγ) is a constitutively active transcription factor involved in mitochondrial metabolism and energy homeostasis. GSK5182, a specific inverse agonist of ERRγ that inhibits transcriptional activity, induces a conformational change in ERRγ, resulting in a loss of coactivator binding. However, the molecular mechanism underlying the stabilization of the ERRγ protein by its inverse agonist remains largely unknown. In this study, we found that GSK5182 inhibited ubiquitination of ERRγ, thereby stabilizing the ERRγ protein, using cell-based assays and confocal image analysis. Y326 of ERRγ was essential for stabilization by GSK5182, as ligand-induced stabilization of ERRγ was not observed with the ERRγ-Y326A mutant. GSK5182 suppressed ubiquitination of ERRγ by the E3 ligase Parkin and subsequent degradation. The inhibitory activity of GSK5182 was strong even when the ERRγ protein level was elevated, as ERRγ bound to GSK5182 recruited a corepressor, small heterodimer partner-interacting leucine zipper (SMILE), through the activation function 2 (AF-2) domain, without alteration of the nuclear localization or DNA-binding ability of ERRγ. In addition, the AF-2 domain of ERRγ was critical for the regulation of protein stability. Mutants in the AF-2 domain were present at higher levels than the wild type in the absence of GSK5182. Furthermore, the ERRγ-L449A/L451A mutant was no longer susceptible to GSK5182. Thus, the AF-2 domain of ERRγ is responsible for the regulation of transcriptional activity and protein stability by GSK5182. These findings suggest that GSK5182 regulates ERRγ by a unique molecular mechanism, increasing the inactive form of ERRγ via inhibition of ubiquitination.

The G protein-coupled receptors 3, 6, and 12 (GPR3, GPR6, and GPR12) comprise a family of closely related orphan receptors with no confirmed endogenous ligands. These receptors are constitutively active and capable of signaling through G protein-mediated and non-G protein-mediated mechanisms. These orphan receptors have previously been reported to play important roles in many normal physiological functions and to be involved in a variety of pathological conditions. Although they are orphans, GPR3, GPR6, and GPR12 are phylogenetically most closely related to the cannabinoid receptors. Using β-arrestin2 recruitment and cAMP accumulation assays, we recently found that the nonpsychoactive phytocannabinoid cannabidiol (CBD) is an inverse agonist for GPR3, GPR6, and GPR12. This discovery highlights these orphan receptors as potential new molecular targets for CBD, provides novel mechanisms of action, and suggests new therapeutic uses of CBD for illnesses such as Alzheimer’s disease, Parkinson’s disease, cancer, and infertility. Furthermore, identification of CBD as a new inverse agonist for GPR3, GPR6, and GPR12 provides the initial chemical scaffolds upon which potent and efficacious agents acting on these receptors can be developed, with the goal of developing chemical tools for studying these orphan receptors and ultimately new therapeutic agents.

A target for boosting stroke recovery Stroke is a leading cause of disability because of the brain's limited capacity for recovery. The functional recovery that does occur derives in part from the transfer of brain function to the tissue bordering the stroke site. A study in a mouse model shows that stroke reduces excitation in neurons adjacent to the stroke site by impairing transport of GABA, leading to a build-up of this inhibitory neurotransmitter. Genetic or pharmacological blockade of extrasynaptic GABA A receptors improves behavioural recovery. Critically, the treatment remains successful when there is a delay between stroke and therapy. This work identifies novel pharmacological targets for neural recovery after stroke and possibly other brain injuries. Following a stroke, there is generally limited functional recovery, but plasticity in adjacent intact areas may be critical to rehabilitation. These authors report that tonic GABA A inhibition is elevated in cortex immediately surrounding the stroke site. Furthermore, genetically or pharmacologically reducing tonic GABA A receptor signalling leads to improved functional and motor recovery in a mouse model of stroke, suggesting that this could be a new pharmacological target for stroke therapy. Stroke is a leading cause of disability, but no pharmacological therapy is currently available for promoting recovery. The brain region adjacent to stroke damage—the peri-infarct zone—is critical for rehabilitation, as it shows heightened neuroplasticity, allowing sensorimotor functions to re-map from damaged areas 1 , 2 , 3 . Thus, understanding the neuronal properties constraining this plasticity is important for the development of new treatments. Here we show that after a stroke in mice, tonic neuronal inhibition is increased in the peri-infarct zone. This increased tonic inhibition is mediated by extrasynaptic GABA A receptors and is caused by an impairment in GABA (γ-aminobutyric acid) transporter (GAT-3/GAT-4) function. To counteract the heightened inhibition, we administered in vivo a benzodiazepine inverse agonist specific for α5-subunit-containing extrasynaptic GABA A receptors at a delay after stroke. This treatment produced an early and sustained recovery of motor function. Genetically lowering the number of α5- or δ-subunit-containing GABA A receptors responsible for tonic inhibition also proved beneficial for recovery after stroke, consistent with the therapeutic potential of diminishing extrasynaptic GABA A receptor function. Together, our results identify new pharmacological targets and provide the rationale for a novel strategy to promote recovery after stroke and possibly other brain injuries.