Apigenin Alleviates Autistic-like Stereotyped Repetitive Behaviors and Mitigates Brain Oxidative Stress in Mice

Studying the involvement of nicotinic acetylcholine receptors (nAChRs), specifically α7-nAChRs, in neuropsychiatric brain disorders such as autism spectrum disorder (ASD) has gained a growing interest. The flavonoid apigenin (APG) has been confirmed in its pharmacological action as a positive allosteric modulator of α7-nAChRs. However, there is no research describing the pharmacological potential of APG in ASD. The aim of this study was to evaluate the effects of the subchronic systemic treatment of APG (10-30 mg/kg) on ASD-like repetitive and compulsive-like behaviors and oxidative stress status in the hippocampus and cerebellum in BTBR mice, utilizing the reference drug aripiprazole (ARP, 1 mg/kg, i.p.). BTBR mice pretreated with APG (20 mg/kg) or ARP (1 mg/g, i.p.) displayed significant improvements in the marble-burying test (MBT), cotton-shredding test (CST), and self-grooming test (SGT) (all p < 0.05). However, a lower dose of APG (10 mg/kg, i.p.) failed to modulate behaviors in the MBT or SGT, but significantly attenuated the increased shredding behaviors in the CST of tested mice. Moreover, APG (10-30 mg/kg, i.p.) and ARP (1 mg/kg) moderated the disturbed levels of oxidative stress by mitigating the levels of catalase (CAT) and superoxide dismutase (SOD) in the hippocampus and cerebellum of treated BTBR mice. In patch clamp studies in hippocampal slices, the potency of choline (a selective agonist of α7-nAChRs) in activating fast inward currents was significantly potentiated following incubation with APG. Moreover, APG markedly potentiated the choline-induced enhancement of spontaneous inhibitory postsynaptic currents. The observed results propose the potential therapeutic use of APG in the management of ASD. However, further preclinical investigations in additional models and different rodent species are still needed to confirm the potential relevance of the therapeutic use of APG in ASD.

A Randomized Phase 2 KINETIC Trial Evaluating SAGE-324/BIIB124 in Individuals with Essential Tremor

BACKGROUND

SAGE-324/BIIB124 is an investigational positive allosteric modulator of GABAA receptors.

OBJECTIVE

KINETIC (NCT04305275), a double-blind, randomized, placebo-controlled, phase 2 study, evaluated SAGE-324/BIIB124 in individuals with essential tremor (ET).

METHODS

Individuals aged 18 to 80 years were randomly assigned 1:1 to orally receive 60 mg of SAGE-324/BIIB124 or placebo once daily for 28 days. The primary endpoint was change from baseline in The Essential Tremor Rating Assessment Scale-Performance Subscale (TETRAS-PS) Item 4 (upper-limb tremor) at day 29 with SAGE-324/BIIB124 versus placebo.

RESULTS

Between May 2020 and February 2021, 69 U.S. participants were randomly assigned to receive SAGE-324/BIIB124 (n = 34) or placebo (n = 35). There was a significant reduction from baseline in TETRAS-PS Item 4 at day 29 with SAGE-324/BIIB124 versus placebo (least squares mean [standard error]: -2.31 [0.401] vs. -1.24 [0.349], P = 0.0491). The most common treatment-emergent adverse events included somnolence, dizziness, fatigue, and balance disorder.

CONCLUSION

These results support further development of SAGE-324/BIIB124 for potential ET treatment. © 2024 Sage Therapeutics, Inc and The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Novel-Type GABAB PAMs: Structure-Activity Relationship in Light of the Protein Structure

Selecting a known HTS hit with the pyrazolo[1,5-a]pyrimidine core, our project was started from CMPPE, and its optimization was driven by a ligand-based pharmacophore model developed on the basis of published GABAB positive allosteric modulators (PAMs). Our primary goal was to improve the potency by finding new enthalpic interactions. Therefore, we included the lipophilic ligand efficiency (LLE or LipE) as an objective function in the optimization that led to a carboxylic acid derivative (34). This lead candidate offers the possibility to improve potency without drastically inflating the physicochemical properties. Although the discovery of the novel carboxyl feature was surprising, it turned out to be an important element of the GABAB PAM pharmacophore that can be perfectly explained based on the new protein structures. Rationalizing the binding mode of 34, we analyzed the intersubunit PAM binding site of GABAB receptor using the publicly available experimental structures.

Structural mechanisms of α7 nicotinic receptor allosteric modulation and activation

The α7 nicotinic acetylcholine receptor is a pentameric ligand-gated ion channel that plays an important role in cholinergic signaling throughout the nervous system. Its unique physiological characteristics and implications in neurological disorders and inflammation make it a promising but challenging therapeutic target. Positive allosteric modulators overcome limitations of traditional α7 agonists, but their potentiation mechanisms remain unclear. Here, we present high-resolution structures of α7-modulator complexes, revealing partially overlapping binding sites but varying conformational states. Structure-guided functional and computational tests suggest that differences in modulator activity arise from the stable rotation of a channel gating residue out of the pore. We extend the study using a time-resolved cryoelectron microscopy (cryo-EM) approach to reveal asymmetric state transitions for this homomeric channel and also find that a modulator with allosteric agonist activity exploits a distinct channel-gating mechanism. These results define mechanisms of α7 allosteric modulation and activation with implications across the pentameric receptor superfamily.

Efficacy and safety of Dimdazenil in the adult insomnia patients: a phase II randomized, multicenter, double-blind, placebo-controlled, and parallel-group study

STUDY OBJECTIVES

To evaluate the efficacy and safety of Dimdazenil, a positive allosteric modulator with selectivity for α1, α5 subunit-containing GABAA receptors, on sleep variables in patients with insomnia disorder.

METHODS

In this randomized, double-blind, placebo-controlled trial, adults (18-65 years) with insomnia disorder were randomized (1:1:1:1 to receive daily oral placebo, Dimdazenil (1.5, 2.5, or 5 mg) for 14 days. The primary efficacy outcome was the total sleep time (TST) on day 1/2 and day 13/14, measured by polysomnography. The secondary outcome measures included (1) latency to persistent sleep (LPS), sleep efficiency (SE), wake after sleep onset (WASO) and number of awakenings (NAW) on days 1/2 and day 13/14, and (2) the average subjective sleep latency (sSL), total sleep time (sTST), wake after sleep onset (sWASO) and number of awakenings (sNAW) recorded in sleep diary and sleep questionnaire, and the evaluation of insomnia severity index. Rebound insomnia, withdrawal, and treatment-emergent adverse events were also assessed.

RESULTS

Of 569 patients screened, 288 (76.4% female) were randomized and received one dose. For the primary outcomes, TST was significantly improved in the Dimdazenil 1.5, 2.5, and 5 mg group compared with the placebo group at day 1/2, and significantly improved in the Dimdazenil 2.5 and 5 mg groups compared with the placebo group at day 13/14. The Least Squares Means (standard errors) and 95% Confidence Intervals for the three active doses compared to placebo are 25.5 (8.31), (9.16, 41.89) for the 1.5 mg dose; 17.4 (8.19), (1.29, 33.55) for the 2.5 mg dose; 22.8 (8.15), (6.72, 38.80) for the 5 mg dose on day 1/2. Corresponding data on day 13/14 are 7.6 (8.07), (-8.24, 23.53) and 19.3 (8.06), (3.43, 35.17) and 18.2 (7.95), (2.49, 33.80). LPS was significantly reduced in the Dimdazenil 5 mg group compared with the placebo group on day 1/2. SE was significantly improved in the Dimdazenil 1.5 and 5 mg group compared with the placebo group at day 1/2. In the subjective sleep parameters, sSL on average was significantly lower in the Dimdazenil 1.5, 2.5, and 5 mg groups compared with the placebo group. sTST on average was significantly higher in the Dimdazenil 1.5, 2.5, and 5 mg groups compared with the placebo group. The most common TEAEs were dizziness, vertigo, and weakness with no clinically relevant treatment-related serious adverse events.

CONCLUSIONS

Dimdazenil of 1.5, 2.5, and 5 mg improved certain objective and subjective sleep outcomes in people with insomnia disorder, with a favorable safety profile. These findings suggested that Dimdazenil may represent a promising new treatment for insomnia disorder, a prevalent condition with limited effective and safe treatments available.

CLINICAL TRIAL INFORMATION

A multicenter, randomized, double-blind, multidose, placebo parallel controlled phase II clinical study of EVT201 in the treatment of insomnia disorders (http://www.chinadrugtrials.org), with the number of CTR20150664.

Identification of the Candidate mGlu2 Allosteric Modulator THRX-195518 through In Silico Method and Evaluation of Its Neuroprotective Potential against Glutamate-Induced Neurotoxicity in SH-SY5Y Cell Line

Glutamate (Glu) toxicity has been an important research topic in toxicology and neuroscience studies. In vitro and in vivo studies have shown that Group II metabotropic Glu2 (mGlu2) activators have cell viability effects. This study aims to determine a candidate ligand with high mGlu2 allosteric region activity among cytotoxicity-safe molecules using the in silico positioning method and to evaluate its cell viability effect in vitro. We investigated the candidate molecule's cell viability effect on the SH-SY5Y human neuroblastoma cell line by MTT analysis. In the study, LY 379268 (agonist) and JNJ-46281222 (positive allosteric modulator; PAM) were used as control reference molecules. Drug bank screening yielded THRX-195518 (docking score being -12.4 kcal/mol) as a potential novel drug candidate that has a high docking score and has not been mentioned in the literature so far. The orthosteric agonist LY 379268 exhibited a robust protective effect in our study. Additionally, our findings demonstrate that JNJ-46281222 and THRX-195518, identified as activating the mGlu2 allosteric region through in silico methods, preserve cell viability against Glu toxicity. Therefore, our study not only emphasizes the positive effects of this compound on cell viability against Glu toxicity but also sheds light on the potential of THRX-195518, acting as a mGlu2 PAM, based on in silico absorption, distribution, metabolism, excretion, and toxicity (ADMET) data, as a candidate drug molecule. These findings underscore the potential utility of THRX-195518 against both neurotoxicity and Central Nervous System (CNS) disorders, providing valuable insights.

The efficacy of zuranolone in postpartum depression and major depressive disorder: a review & number needed to treat (NNT) analysis

INTRODUCTION

Major depressive disorder (MDD) is a common and debilitating mental illness. Postpartum depression (PPD) impacts women globally and is one of the most common complications of childbirth that is underdiagnosed and undertreated, adversely impacting the mental health of women, children, and partners.Available antidepressant medications require weeks to months before showing effect. In this setting, zuranolone, an oral neuroactive steroid and a positive allosteric modulator of GABAA receptors, is an attractive alternative as a rapid-acting antidepressant treatment.

AREAS COVERED

This article reviews zuranolone (SAGE217), focusing on available clinical studies in individuals with PPD and MDD. This paper adds to the extant literature by presenting the efficacy data as Number Needed to Treat (NNT) to facilitate indirect comparisons with other antidepressants.

EXPERT OPINION

Zuranolone is a novel rapid-acting (i.e. two week course) oral antidepressant for the treatment of adults with PPD with ongoing clinical trials evaluating its efficacy in adults with MDD. Zuranolone is well tolerated with no significant safety concerns in any clinical trials completed to date. Zuranolone will be scheduled by the Drug Enforcement Agency (DEA).

2-Amino-5-arylethynyl-thiophen-3-yl-(phenyl)methanones as A1 Adenosine Receptor Positive Allosteric Modulators

A1 adenosine receptor (A1AR) agonists have cerebroprotective, cardioprotective, antinociceptive, and other pharmaceutical applications. We explored the structure-activity relationship of 5-arylethynyl aminothiophenes as A1AR positive allosteric modulators (PAMs). The derivatives were compared in binding and functional assays at the human A1AR, indicating that some fluoro-substituted analogues have enhanced PAM activity. We identified substitution of the terminal phenyl ring in 12 (2-F-Ph), 15 (3,4-F2-Ph, MRS7935), and 21 (2-CF3-Ph) as particularly enhancing the PAM activity. 15 was also shown to act as an A1 ago-PAM with EC50 ≈ 2 μM, without activity (30 μM) at other ARs. Molecular modeling indicated that both the 5-arylethynyl and the 4-neopentyl groups are located in a region outside the receptor transmembrane helix bundle that is in contact with the phospholipid bilayer, consistent with the preference for nonpolar substitution of the aryl moiety. Although they are hydrophobic, these PAMs could provide potential drug candidate molecules for engaging protective A1ARs.

A kinetic model for positive allosteric modulator (PAM)-antagonists for the type 1 cannabinoid (CB1 ) receptor

BACKGROUND AND PURPOSE

The cannabinoid (CB1 ) receptor is among the most abundant G protein-coupled receptors in brain. Allosteric ligands bind to a different site on receptors than the orthosteric ligand can have effects that are unique to the allosteric ligand and modulate orthosteric ligand activity. We propose a unified mathematical model describing the interaction effects of the allosteric ligand Org27569 and the orthosteric agonist CP55940 on CB1 receptor.

EXPERIMENTAL APPROACH

A ternary complex model was constructed, which incorporated kinetic properties to describe the time course of effects of Org27569 and CP55940 reported in the literature: (i) enhanced receptor binding of CP55940, (ii) reduced internalisation and (iii), time-dependent modulation of cAMP. Underlying mechanisms of time-dependent modulation by Org27569 were evaluated by simulation.

KEY RESULTS

A hypothetical transitional state of CP55940-CB1 -Org27569, which can internalise but cannot inhibit cAMP, was shown to be necessary and was sufficient to describe the allosteric modulation by Org27569, prior to receptors adopting an inactive conformation. The model indicated that the formation of this transitional CP55940-CB1 -Org27569 state and final inactive CP55940-CB1 -Org27569 state contributes to the enhanced CP55940 binding. The inactive CP55940-CB1 -Org27569 cannot internalise or inhibit cAMP, leading to reduced internalisation and cessation of cAMP inhibition.

CONCLUSIONS AND IMPLICATIONS

In conclusion, a kinetic mathematical model for CB1 receptor allosteric modulation was developed. However, a standard ternary complex model was not sufficient to capture the data and a hypothetical transitional state was required to describe the allosteric modulation properties of Org27569.

Side Groups Convert the α7 Nicotinic Receptor Agonist Ether Quinuclidine into a Type I Positive Allosteric Modulator

The quinuclidine scaffold has been extensively used for the development of nicotinic acetylcholine receptor (nAChR) agonists, with hydrophobic substituents at position 3 of the quinuclidine framework providing selectivity for α7 nAChRs. In this study, six new ligands (4-9) containing a 3-(pyridin-3-yloxy)quinuclidine moiety (ether quinuclidine) were synthesized to gain a better understanding of the structural-functional properties of ether quinuclidines. To evaluate the pharmacological activity of these ligands, two-electrode voltage-clamp and single-channel recordings were performed. Only ligand 4 activated α7 nAChR. Ligands 5 and 7 had no effects on α7 nAChR, but ligands 6, 8, and 9 potentiated the currents evoked by ACh. Ligand 6 was the most potent and efficacious of the potentiating ligands, with an estimated EC50 for potentiation of 12.6 ± 3.32 μM and a maximal potentiation of EC20 ACh responses of 850 ± 120%. Ligand 6 increased the maximal ACh responses without changing the kinetics of the current responses. At the single-channel level, the potentiation exerted by ligand 6 was evidenced in the low micromolar concentration range by the appearance of prolonged bursts of channel openings. Furthermore, computational studies revealed the preference of ligand 6 for an intersubunit site in the transmembrane domain and highlighted some putative key interactions that explain the different profiles of the synthesized ligands. Notably, Met276 in the 15' position of the transmembrane domain 2 almost abolished the effects of ligand 6 when mutated to Leu. We conclude that ligand 6 is a novel type I positive allosteric modulator (PAM-I) of α7 nAChR.

Synthesis and Receptor Binding Studies of α5 GABAAR Selective Novel Imidazodiazepines Targeted for Psychiatric and Cognitive Disorders

GABA mediates inhibitory actions through various GABA_A receptor subtypes, including 19 subunits in human GABAAR. Dysregulation of GABAergic neurotransmission is associated with several psychiatric disorders, including depression, anxiety, and schizophrenia. Selective targeting of α2/3 GABAARs can treat mood and anxiety, while α5 GABAA-Rs can treat anxiety, depression, and cognitive performance. GL-II-73 and MP-III-022, α5-positive allosteric modulators have shown promising results in animal models of chronic stress, aging, and cognitive disorders, including MDD, schizophrenia, autism, and Alzheimer's disease. Described in this article is how small changes in the structure of imidazodiazepine substituents can greatly impact the subtype selectivity of benzodiazepine GABAAR. To investigate alternate and potentially more effective therapeutic compounds, modifications were made to the structure of imidazodiazepine 1 to synthesize different amide analogs. The novel ligands were screened at the NIMH PDSP against a panel of 47 receptors, ion channels, including hERG, and transporters to identify on- and off-target interactions. Any ligands with significant inhibition in primary binding were subjected to secondary binding assays to determine their K_i values. The newly synthesized imidazodiazepines were found to have variable affinities for the benzodiazepine site and negligible or no binding to any off-target profile receptors that could cause other physiological problems.

A phase 1 randomized, placebo-controlled study to investigate potential interactions between ASP8062, a positive allosteric modulator of the GABAB receptor, and morphine in recreational opioid users

BACKGROUND

Recent increases in opioid use and subsequent opioid use disorder are a major public health crisis in the United States.

AIMS

This phase 1 randomized, placebo-controlled study investigated the safety, tolerability, and pharmacokinetics (PKs) of ASP8062, a γ-aminobutyric acid B receptor-positive allosteric modulator, with and without administration of morphine in participants who used opioids recreationally.

METHODS

Participants were randomly assigned (2:1) to daily dosing with ASP8062 25 mg or placebo on days 1-10. On day 10, all participants received morphine as a single oral dose of 45 mg; assessments were performed on days 11-16. The primary end point was safety, evaluated as the nature, frequency, and severity of adverse events, and end-tidal CO₂ levels. PK end points were a secondary outcome measure.

RESULTS

A total of 24 participants (aged 21-54 years) received ASP8062 (n = 16) or placebo (n = 8). There were no deaths or serious adverse events leading to treatment discontinuation during the study. Most adverse events were mild, with numerically lower absolute number of adverse events reported with ASP8062 plus morphine versus placebo plus morphine. ASP8062 plus morphine did not increase respiratory depression, potential drug abuse- or withdrawal-related adverse events. There were no significant PK interactions.

CONCLUSIONS

In this phase 1 study, we did not observe any unexpected safety signals or notable PK interactions with concomitant morphine administration. These data suggest a potentially low risk for an increase in drug abuse- or withdrawal-related adverse events or respiratory distress in participants exposed to ASP8062 and morphine.

Fumarate as positive modulator of allosteric transitions in the pentameric ligand-gated ion channel GLIC: Requirement of an intact vestibular pocket

GLIC is a prokaryotic orthologue of brain pentameric neurotransmitter receptors. Using whole-cell patch-clamp electrophysiology in a host cell line, we show that short-chain di-carboxylate compounds are positive modulators of pHo 5-evoked GLIC activity, with a rank order of action fumarate > succinate > malonate > glutarate. Potentiation by fumarate depends on intracellular pH, mainly as a result of a strong decrease of the pHo 5-evoked current when intracellular pH decreases. The modulating effect of fumarate also depends on extracellular pH, as fumarate is a weak inhibitor at pHo 6 and shows no agonist action at neutral pHo. A mutational analysis of residue-dependency for succinate and fumarate effects, based on two carboxylate-binding pockets previously identified by crystallography (Fourati et al. 2020), shows that positive modulation involves both the inter-subunit pocket, homologous to the neurotransmitter-binding orthotopic site, and the intra-subunit (also called vestibular) pocket. An almost similar pattern of mutational impact is observed for the effect of caffeate, a known negative modulator. We propose, for both di-carboxylate compounds and caffeate, a model where the inter-subunit pocket is the actual binding site, and the region corresponding to the vestibular pocket is required either for inter-subunit binding itself, or for binding-to-gating coupling during the allosteric transitions involved in pore gating modulation. KEY POINTS: Using a bacterial orthologue of brain pentameric neurotransmitter receptors, we show that the orthotopic/orthosteric agonist site and the adjacent vestibular region are functionally inter-dependent in mediating compound-elicited modulation. We propose that the two sites in the extracellular domain are involved "in series", a mechanism which may have relevance to Eukaryote receptors. We show that short-chain di-carboxylate compounds are positive modulators of GLIC. The most potent compound identified is fumarate, known to occupy the orthotopic/orthosteric site in previously published crystal structures. We show that intracellular pH modulates GLIC allosteric transitions, as previously known for extracellular pH. We report a caesium to sodium permeability ratio (PCs/PNa) of 0.54 for GLIC ion pore. Abstract figure legends We show that a low-pH intracellular solution negatively modulates allosteric transitions (see Legend to Fig. 3E for details), in the Prokaryote pentameric ligand-gated ion channel (pLGIC) GLIC, known to be activated by the agonist action of low-pH extracellular solutions. We use this property in the characterization of fumarate, and other compounds, as positive modulators of allosteric transitions. Data from a mutational analysis in two carboxylate binding pockets, together with published crystallographic data, shows that the modulator action of compounds binding at the conserved orthotopic site (homologous to the neurotransmitter / agonist binding site in brain pLGICs) is under the strict control of the adjacent intra-subunit vestibular region. We propose that both positive and negative modulators of allosteric transitions act by binding to the orthotopic main binding site. The 2-site "in series" mechanism proposed may have some relevance to Eukaryote pLGICs. This article is protected by copyright. All rights reserved.

2-(4-Fluorophenyl)-1H-benzo[d]imidazole as a Promising Template for the Development of Metabolically Robust, α1β2γ2GABA-A Receptor-Positive Allosteric Modulators

Modulation of α1β2γ2GABA-A receptor subpopulation expressed in the basal ganglia region is a conceptually novel mode of pharmacological strategy that offers prospects to tackle a variety of neurological dysfunction. Although clinical findings provided compelling evidence for the validity of this strategy, the current chemical space of molecules able to modulate the α1/γ2 interface of the GABA-A receptor is limited to imidazo[1,2-a]pyridine derivatives that undergo rapid biotransformation. In response to a deficiency in the chemical repertoire of GABA-A receptors, we identified a series of 2-(4-fluorophenyl)-1H-benzo[d]imidazoles as positive allosteric modulators (PAMs) with improved metabolic stability and reduced potential for hepatotoxicity, where lead molecules 9 and 23 displayed interesting features in a preliminary investigation. We further disclose that the identified scaffold shows a preference for interaction with the α1/γ2 interface of the GABA-A receptor, delivering several PAMs of the GABA-A receptor. The present work provides useful chemical templates to further explore the therapeutic potential of GABA-A receptor ligands and enriches the chemical space of molecules suitable for the interaction with the α1/γ2 interface.

Positive and negative allosteric modulation of GluK2 kainate receptors by BPAM344 and antiepileptic perampanel

Kainate receptors (KARs) are a subtype of ionotropic glutamate receptors that control synaptic transmission in the central nervous system and are implicated in neurological, psychiatric, and neurodevelopmental disorders. Understanding the regulation of KAR function by small molecules is essential for exploring these receptors as drug targets. Here, we present cryoelectron microscopy (cryo-EM) structures of KAR GluK2 in complex with the positive allosteric modulator BPAM344, competitive antagonist DNQX, and negative allosteric modulator, antiepileptic drug perampanel. Our structures show that two BPAM344 molecules bind per ligand-binding domain dimer interface. In the absence of an agonist or in the presence of DNQX, BPAM344 stabilizes GluK2 in the closed state. The closed state is also stabilized by perampanel, which binds to the ion channel extracellular collar sites located in two out of four GluK2 subunits. The molecular mechanisms of positive and negative allosteric modulation of KAR provide a guide for developing new therapeutic strategies.

PET imaging studies to investigate functional expression of mGluR2 using [11C]mG2P001

Metabotropic glutamate receptor 2 (mGluR2) has been extensively studied for the treatment of various neurological and psychiatric disorders. Understanding of the mGluR2 function is pivotal in supporting the drug discovery targeting mGluR2. Herein, the positive allosteric modulation of mGluR2 was investigated via the in vivo positron emission tomography (PET) imaging using 2-((4-(2-[11C]methoxy-4-(trifluoromethyl)phenyl)piperidin-1-yl)methyl)-1-methyl-1H-imidazo[4,5-b]pyridine ([11C]mG2P001). Distinct from the orthosteric compounds, pretreatment with the unlabeled mG2P001, a potent mGluR2 positive allosteric modulator (PAM), resulted in a significant increase instead of decrease of the [11C]mG2P001 accumulation in rat brain detected by PET imaging. Subsequent in vitro studies with [3H]mG2P001 revealed the cooperative binding mechanism of mG2P001 with glutamate and its pharmacological effect that contributed to the enhanced binding of [3H]mG2P001 in transfected CHO cells expressing mGluR2. The in vivo PET imaging and quantitative analysis of [11C]mG2P001 in non-human primates (NHPs) further validated the characteristics of [11C]mG2P001 as an imaging ligand for mGluR2. Self-blocking studies in primates enhanced accumulation of [11C]mG2P001. Altogether, these studies show that [11C]mG2P001 is a sensitive biomarker for mGluR2 expression and the binding is affected by the tissue glutamate concentration.

Recent Advances in the Discovery of Nicotinic Acetylcholine Receptor Allosteric Modulators

Positive allosteric modulators (PAMs), negative allosteric modulators (NAMs), silent agonists, allosteric activating PAMs and neutral or silent allosteric modulators are compounds capable of modulating the nicotinic receptor by interacting at allosteric modulatory sites distinct from the orthosteric sites. This survey is focused on the compounds that have been shown or have been designed to interact with nicotinic receptors as allosteric modulators of different subtypes, mainly α7 and α4β2. Minimal chemical changes can cause a different pharmacological profile, which can then lead to the design of selective modulators. Experimental evidence supports the use of allosteric modulators as therapeutic tools for neurological and non-neurological conditions.

Mechanism of Action and Structure-Activity Relationships of Tetracyclic Small Molecules Acting as Universal Positive Allosteric Modulators of the Cholecystokinin Receptor

As part of an ongoing effort to develop a drug targeting the type 1 cholecystokinin receptor (CCK1R) to help prevent and/or treat obesity, we recently performed a high throughput screening effort of small molecules seeking candidates that enhanced the action of the natural agonist, CCK, thus acting as positive allosteric modulators without exhibiting intrinsic agonist action. Such probes would be expected to act in a temporally finite way to enhance CCK action to induce satiety during and after a meal and potentially even modulate activity at the CCK1R in a high cholesterol environment present in some obese patients. The current work focuses on the best scaffold, representing tetracyclic molecules identified through high throughput screening we previously reported. Extensive characterization of the two top "hits" from the previous effort demonstrated them to fulfill the desired pharmacologic profile. We undertook analog-by-catalog expansion of this scaffold using 65 commercially available analogs. In this effort, we were able to eliminate an off-target effect observed for this scaffold while retaining its activity as a positive allosteric modulator of CCK1R in both normal and high cholesterol membrane environments. These insights should be useful in the rational medicinal chemical enhancement of this scaffold and in the future development of candidates to advance to pre-clinical proof-of-concept and to clinical trials.

Neurotoxic/Neuroprotective Effects of Clozapine and the Positive Allosteric Modulator of mGluR2 JNJ-46356479 in Human Neuroblastoma Cell Cultures

Current antipsychotics (APs) effectively control positive psychotic symptoms, mainly by blocking dopamine (DA) D2 receptors, but have little effect on negative and cognitive symptoms. Increased glutamate (GLU) release would trigger neurotoxicity, leading to apoptosis and synaptic pruning, which is involved in the pathophysiology of schizophrenia. New pharmacological strategies are being developed such as positive allosteric modulators (PAMs) of the metabotropic GLU receptor 2 (mGluR2) that inhibit the presynaptic release of GLU. We previously reported that treatment of adult mice with JNJ-46356479 (JNJ), a recently developed mGluR2 PAM, partially improved neuropathological deficits and schizophrenia-like behavior in a postnatal ketamine mouse model. In the present study, we evaluated, for the first time, the putative neuroprotective and antiapoptotic activity of JNJ in a human neuroblastoma cell line and compared it with the effect of clozapine (CLZ) as a clinical AP with the highest efficacy and with apparent utility in managing negative symptoms. Specifically, we measured changes in cell viability, caspase 3 activity and apoptosis, as well as in the expression of key genes involved in survival and cell death, produced by CLZ and JNJ alone and in combination with a high DA or GLU concentration as apoptosis inducers. Our results suggest that JNJ is not neurotoxic and attenuates apoptosis, particularly by decreasing the caspase 3 activation induced by DA and GLU, as well as increasing and decreasing the number of viable and apoptotic cells, respectively, only when cultures were exposed to GLU. Its effects seem to be less neurotoxic and more neuroprotective than those observed with CLZ. Moreover, JNJ partially normalized altered expression levels of glycolytic genes, which could act as a protective factor and be related to its putative neuroprotective effect. More studies are needed to define the mechanisms of action of this GLU modulator and its potential to become a novel therapeutic agent for schizophrenia.

GABA-A Alpha 2/3 but Not Alpha 1 Receptor Subunit Ligand Inhibits Harmaline and Pimozide-Induced Tremor in Rats

Treatment of tremors, such as in essential tremor (ET) and Parkinson's disease (PD) is mostly ineffective. Exact tremor pathomechanisms are unknown and relevant animal models are missing. GABA-A receptor is a target for tremorolytic medications, but current non-selective drugs produce side effects and have safety liabilities. The aim of this study was a search for GABA-A subunit-specific tremorolytics using different tremor-generating mechanisms. Two selective positive allosteric modulators (PAMs) were tested. Zolpidem, targeting GABA-A α1, was not effective in models of harmaline-induced ET, pimozide- or tetrabenazine-induced tremulous jaw movements (TJMs), while the novel GABA-A α2/3 selective MP-III-024 significantly reduced both the harmaline-induced ET tremor and pimozide-induced TJMs. While zolpidem decreased the locomotor activity of the rats, MP-III-024 produced small increases. These results provide important new clues into tremor suppression mechanisms initiated by the enhancement of GABA-driven inhibition in pathways controlled by α2/3 but not α1 containing GABA-A receptors. Tremor suppression by MP-III-024 provides a compelling reason to consider selective PAMs targeting α2/3-containing GABA-A receptors as novel therapeutic drug targets for ET and PD-associated tremor. The possibility of the improved tolerability and safety of this mechanism over non-selective GABA potentiation provides an additional rationale to further pursue the selective α2/3 hypothesis.

Pharmacological evaluation of enantiomerically separated positive allosteric modulators of cannabinoid 1 receptor, GAT591 and GAT593

Positive allosteric modulation of the type 1 cannabinoid receptor (CB1R) has substantial potential to treat both neurological and immune disorders. To date, a few studies have evaluated the structure-activity relationship (SAR) for CB1R positive allosteric modulators (PAMs). In this study, we separated the enantiomers of the previously characterized two potent CB1R ago-PAMs GAT591 and GAT593 to determine their biochemical activity at CB1R. Separating the enantiomers showed that the R-enantiomers (GAT1665 and GAT1667) displayed mixed allosteric agonist-PAM activity at CB1R while the S-enantiomers (GAT1664 and GAT1666) showed moderate activity. Furthermore, we observed that the R and S-enantiomers had distinct binding sites on CB1R, which led to their distinct behavior both in vitro and in vivo. The R-enantiomers (GAT1665 and GAT1667) produced ago-PAM effects in vitro, and PAM effects in the in vivo behavioral triad, indicating that the in vivo activity of these ligands may occur via PAM rather than agonist-based mechanisms. Overall, this study provides mechanistic insight into enantiospecific interaction of 2-phenylindole class of CB1R allosteric modulators, which have shown therapeutic potential in the treatment of pain, epilepsy, glaucoma, and Huntington's disease.

A novel small positive allosteric modulator of neuropeptide receptor PAC1-R exerts neuroprotective effects in MPTP mouse Parkinson's disease model

As a neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP)-preferring receptor, PAC1-R mediates effective neuroprotective activity. Based on the finding that the antibiotic doxycycline (DOX) with clinical neuroprotective activity functions as a positive allosteric modulator (PAM) of neuropeptide PACAP receptor 1 (PAC1-R), we use virtual and laboratory screening to search for novel small molecule PAMs of PAC1-R. Virtual screening is carried out using a small-molecule library TargetMol. After two-level precision screening with Glide, the top five compounds with the best predicted affinities for PAC1-R are selected and named small positive allosteric modulator 1‒5 (SPAM1‒5). Our results show that only 4-{[4-(4-Oxo-3,4-2-yl)butanamido]methyl}benzoic acid (SPAM1) has stronger neuroprotective activity than DOX in the MPP+ PD cell model and MPTP PD mouse model. SPAM1 has a higher affinity for PAC1-R than DOX, but has no antibiotic activity. Moreover, both SPAM1 and DOX block the decrease of PAC1-R level in mouse brain tissues induced by MPTP. The successful screening of SPAM1 offers a novel drug for the treatment of neurodegenerative disease targeting the PAC1-R.

Pregnane-based steroids are novel positive NMDA receptor modulators that may compensate for the effect of loss-of-function disease-associated GRIN mutations

BACKGROUND AND PURPOSE

N-methyl-D-aspartate receptors (NMDARs) play a critical role in synaptic plasticity, and mutations in human genes encoding NMDAR subunits have been described in individuals with various neuropsychiatric disorders. Compounds with a positive allosteric effect are thought to compensate for reduced receptor function.

EXPERIMENTAL APPROACH

We have used whole-cell patch-clamp electrophysiology on recombinant rat NMDARs and human variants found in individuals with neuropsychiatric disorders, in combination with in silico modelling, to explore the site of action of novel epipregnanolone-based NMDAR modulators.

KEY RESULTS

Analysis of the action of 4-(20-oxo-5β-pregnan-3β-yl) butanoic acid (EPA-But) at the NMDAR indicates that the effect of this steroid with a "bent" structure is different from that of cholesterol and oxysterols and shares a disuse-dependent mechanism of NMDAR potentiation with the "planar" steroid 20-oxo-pregn-5-en-3β-yl sulfate (PE-S). The potentiating effects of EPA-But and PE-S are additive. Alanine scan mutagenesis identified residues that reduce the potentiating effect of EPA-But. No correlation was found between the effects of EPA-But and PE-S at mutated receptors that were less sensitive to either steroid. The relative degree of potentiation induced by the two steroids also differed in human NMDARs carrying rare variants of hGluN1 or hGluN2B subunits found in individuals with neuropsychiatric disorders, including intellectual disability, epilepsy, developmental delay, and autism spectrum disorder.

CONCLUSION AND IMPLICATIONS

Our results show novel sites of action for pregnanolones at the NMDAR and provide an opportunity for the development of new therapeutic neurosteroid-based ligands to treat diseases associated with glutamatergic system hypofunction.

A Randomized, Double-Blind, Controlled Phase II Study of Foliglurax in Parkinson's Disease

BACKGROUND

Agents targeting the metabotropic glutamate receptor 4 have emerged as a potentially attractive new class of drugs for the treatment of Parkinson's disease (PD).

OBJECTIVE

The objective of this study was to evaluate the efficacy and safety of foliglurax in reducing off time and dyskinesia in patients with PD.

METHODS

This was a 28-day, multicenter, randomized, placebo-controlled, double-blind clinical trial of foliglurax 10 and 30 mg as adjunct to levodopa in 157 randomly assigned patients with PD and motor complications.

RESULTS

Although dose-dependent decreases in daily awake off time were apparent following treatment with foliglurax, the change from baseline to day 28 in off time (primary endpoint) and dyskinesia (secondary endpoint) did not improve significantly compared with placebo for either foliglurax dose. Treatment with foliglurax was generally safe, and there were no relevant safety signals.

CONCLUSIONS

There was no evidence in this study that foliglurax has efficacy in improving levodopa-induced motor complications in PD. © 2022 International Parkinson and Movement Disorder Society.

Muscarinic M3 positive allosteric modulator ASP8302 enhances bladder contraction and improves voiding dysfunction in rats

OBJECTIVES

Muscarinic M₃ (M₃ ) receptors mediate cholinergic smooth muscle contraction of the bladder. Current drugs targeting bladder M₃ receptors for micturition disorders have a risk of cholinergic side effects due to excessive receptor activation and insufficient selectivity. We investigated the effect of ASP8302, a novel positive allosteric modulator (PAM) of M₃ receptors, on bladder function in rats.

METHODS

Modulation of carbachol-induced increases in intracellular Ca²⁺ was assessed in cells expressing rat muscarinic receptors. Potentiation of bladder contractions was evaluated using isolated rat bladder strips and by measuring intravesical pressure in anesthetized rats. Conscious cystometry was performed to investigate the effects on residual urine volume and voiding efficiency in rat voiding dysfunction models induced by the α₁ -adrenoceptor agonist midodrine and muscarinic receptor antagonist atropine, and bladder outlet obstruction. To assess potential side effects, the number of stools and tracheal insufflation pressure were measured in conscious and anesthetized rats, respectively.

RESULTS

ASP8302 demonstrated PAM effects on the rat M₃ receptor in cell assays, and augmented cholinergic bladder contractions both in vivo and in vitro. ASP8302 improved voiding efficiency and reduced residual urine volume in two voiding dysfunction models as effectively as distigmine bromide, but unlike distigmine bromide did not affect the number of stools or tracheal insufflation pressure.

CONCLUSIONS

Our results in rats indicate that ASP8302 improves voiding dysfunction by potentiating bladder contraction with fewer effects on cholinergic responses in other organs, and suggest a potential advantage over current cholinomimetic drugs for treating micturition disorders caused by insufficient bladder contraction.

Structural Features of Iperoxo-BQCA Muscarinic Acetylcholine Receptor Hybrid Ligands Determining Subtype Selectivity and Efficacy

Selective agonists for the human M₁ and M₄ muscarinic acetylcholine receptors (mAChRs) are attractive candidates for the treatment of cognitive disorders, such as Alzheimer's disease and schizophrenia. Past efforts to optimize a ligand for selective agonism at any one of the M₁-M₅ mAChR subtypes has proven to be a significant challenge. Recently, research efforts have demonstrated that hybrid ligands may offer a potential solution to the lack of selectivity at mAChRs. In an attempt to design M₁ mAChR selective agonists by hybridizing an M₁ mAChR selective positive allosteric modulator [1-(4-methoxybenzyl)-4-oxo-1,4-dihydroquinoline-3-carboxylic acid] and a potent agonist [(4-[(4,5-dihydro-3-isoxazolyl)oxy]-N,N,N-trimethyl-2-butyn-1-aminium iodide) (iperoxo)], we unexpectedly discovered that these ligands possessed noticeable M₂/M₄ mAChR selectivity. Evaluation of truncated derivatives of the hybrid ligands at the M₁-M₅ mAChR subtypes suggests that the allosteric pharmacophore of iperoxo-based mAChR hybrid ligands likely sterically disrupts the allosteric site of the mAChRs, attenuating the efficacy of M₁/M₃/M₅ mAChR responses compared to M₂/M₄ mAChRs, resulting in a preference for the M₂/M₄ mAChRs. However, at certain intermediate linker lengths, the effects of this apparent disruption of the allosteric site are diminished, restoring nonselective agonism and suggesting a possible allosteric interaction which is favorable to efficacy at all M₁-M₅ mAChRs.

The Novel Positive Allosteric Modulator of the GABAB Receptor, KK-92A, Suppresses Alcohol Self-Administration and Cue-Induced Reinstatement of Alcohol Seeking in Rats

Positive allosteric modulators (PAMs) of the GABA_B receptor (GABA_B PAMs) are of interest in the addiction field due to their ability to suppress several behaviors motivated by drugs of abuse. KK-92A is a novel GABA_B PAM found to attenuate intravenous self-administration of nicotine and reinstatement of nicotine seeking in rats. This present study was aimed at extending to alcohol the anti-addictive properties of KK-92A. To this end, Sardinian alcohol-preferring rats were trained to lever-respond for oral alcohol (15% v/v) or sucrose (0.7% w/v) under the fixed ratio (FR) 5 (FR5) schedule of reinforcement. Once lever-responding behavior had stabilized, rats were exposed to tests with acutely administered KK-92A under FR5 and progressive ratio schedules of reinforcement and cue-induced reinstatement of previously extinguished alcohol seeking. KK-92A effect on spontaneous locomotor activity was also evaluated. Treatment with 10 and 20 mg/kg KK-92A suppressed lever-responding for alcohol, amount of self-administered alcohol, and breakpoint for alcohol. Treatment with 20 mg/kg KK-92A reduced sucrose self-administration. Combination of per se ineffective doses of KK-92A (2.5 mg/kg) and the GABA_B receptor agonist, baclofen (1 mg/kg), reduced alcohol self-administration. Treatment with 5, 10, and 20 mg/kg KK-92A suppressed reinstatement of alcohol seeking. Only treatment with 80 mg/kg KK-92A affected spontaneous locomotor activity. These results demonstrate the ability of KK-92A to inhibit alcohol-motivated behaviors in rodents and confirm that these effects are common to the entire class of GABA_B PAMs. The remarkable efficacy of KK-92A is discussed in terms of its ago-allosteric properties.

Reprogramming CBX8-PRC1 function with a positive allosteric modulator

Canonical targeting of Polycomb repressive complex 1 (PRC1) to repress developmental genes is mediated by cell-type-specific, paralogous chromobox (CBX) proteins (CBX2, 4, 6, 7, and 8). Based on their central role in silencing and their dysregulation associated with human disease including cancer, CBX proteins are attractive targets for small-molecule chemical probe development. Here, we have used a quantitative and target-specific cellular assay to discover a potent positive allosteric modulator (PAM) of CBX8. The PAM activity of UNC7040 antagonizes H3K27me3 binding by CBX8 while increasing interactions with nucleic acids. We show that treatment with UNC7040 leads to efficient and selective eviction of CBX8-containing PRC1 from chromatin, loss of silencing, and reduced proliferation across different cancer cell lines. Our discovery and characterization of UNC7040 not only reveals the most cellularly potent CBX8-specific chemical probe to date, but also corroborates a mechanism of Polycomb regulation by non-specific CBX nucleotide binding activity.

Oxytocin Is a Positive Allosteric Modulator of κ-Opioid Receptors but Not δ-Opioid Receptors in the G Protein Signaling Pathway

Oxytocin (OT) influences various physiological functions such as uterine contractions, maternal/social behavior, and analgesia. Opioid signaling pathways are involved in one of the analgesic mechanisms of OT. We previously showed that OT acts as a positive allosteric modulator (PAM) and enhances μ-opioid receptor (MOR) activity. In this study, which focused on other opioid receptor (OR) subtypes, we investigated whether OT influences opioid signaling pathways as a PAM for δ-OR (DOR) or κ-OR (KOR) using human embryonic kidney-293 cells expressing human DOR or KOR, respectively. The CellKey^TM results showed that OT enhanced impedance induced by endogenous/exogenous KOR agonists on KOR-expressing cells. OT did not affect DOR activity induced by endogenous/exogenous DOR agonists. OT potentiated the KOR agonist-induced Gi/o protein-mediated decrease in intracellular cAMP, but did not affect the increase in KOR internalization caused by the KOR agonists dynorphin A and (-)-U-50488 hydrochloride (U50488). OT did not bind to KOR orthosteric binding sites and did not affect the binding affinities of dynorphin A and U50488 for KOR. These results suggest that OT is a PAM of KOR and MOR and enhances G protein signaling without affecting β-arrestin signaling. Thus, OT has potential as a specific signaling-biased PAM of KOR.

De Novo Design of Peptidic Positive Allosteric Modulators Targeting TRPV1 with Analgesic Effects

Transient receptor potential vanilloid 1 (TRPV1) ion channel is a nociceptor critically involved in pain sensation. Direct blockade of TRPV1 exhibits significant analgesic effects but also incurs severe side effects such as hyperthermia, causing failures of TRPV1 inhibitors in clinical trials. In order to selectively target TRPV1 channels that are actively involved in pain-sensing, peptidic positive allosteric modulators (PAMs) based on the high-resolution structure of the TRPV1 intracellular ankyrin-repeat like domain are de novo designed. The hotspot centric approach is optimized for protein design; its usage in Rosetta increases the success rate in protein binder design. It is demonstrated experimentally, with a combination of fluorescence resonance energy transfer (FRET) imaging, surface plasmon resonance, and patch-clamp recording, that the designed PAMs bind to TRPV1 with nanomolar affinity and allosterically enhance its response to ligand activation as it is designed. It is further demonstrated that the designed PAM exhibits long-lasting in vivo analgesic effects in rats without changing their body temperature, suggesting that they have potentials for developing into novel analgesics.

(E)-3-furan-2-yl-N-phenylacrylamide (PAM-4) decreases nociception and emotional manifestations of neuropathic pain in mice by α7 nicotinic acetylcholine receptor potentiation

Clinical intervention of pain is often accompanied by changes in affective behaviors, so both assays of affective and sensorial aspects of nociception play an important role in the development of novel analgesics. Although positive allosteric modulation (PAM) of α7 nicotinic acetylcholine receptors (nAChRs) has been recognized as a novel approach for the relief of sensorial aspects of pain, their effects on affective components of pain remain unclear. Therefore, we investigated whether PAM-4, a highly selective α7-nAChR PAM, attenuates inflammatory and neuropathic pain, as well as the concomitant depressive/anxiety comorbidities. The anti-nociceptive activity of PAM-4 was assessed in mice using the formalin test and chronic constriction injury (CCI)-induced neuropathic pain model. The anxiolytic- and antidepressant-like activity of PAM-4 was evaluated using the marble burying test and forced swimming test. Acute systemic administration of PAM-4 dose-dependently reversed formalin-induced paw licking behavior and CCI-induced mechanical allodynia without development of any motor impairment. PAM-4 reversed the decreased swimming time and number of buried marbles in CCI-treated mice, suggesting that this ligand attenuates chronic pain-induced depression-like behavior and anxiogenic-like effects. The effects of PAM-4 were inhibited by the α7-selective antagonist methyllycaconitine, indicating molecular mechanism mediated by α7-nAChRs. Indeed, electrophysiological recordings showed the PAM-4 enhances human α7 nAChRs with higher potency and efficacy compared to rat α7 nAChRs. These findings suggest that PAM-4 reduces both sensorial and affective behaviors induced by chronic pain in mice by α7-nAChR potentiation. PAM-4 deserves further investigations for the management of chronic painful conditions with comorbidities.

Curcumin Potentiates α7 Nicotinic Acetylcholine Receptors and Alleviates Autistic-Like Social Deficits and Brain Oxidative Stress Status in Mice

Autistic spectrum disorder (ASD) refers to a group of neurodevelopmental disorders characterized by impaired social interaction and cognitive deficit, restricted repetitive behaviors, altered immune responses, and imbalanced oxidative stress status. In recent years, there has been a growing interest in studying the role of nicotinic acetylcholine receptors (nAChRs), specifically α7-nAChRs, in the CNS. Influence of agonists for α7-nAChRs on the cognitive behavior, learning, and memory formation has been demonstrated in neuro-pathological condition such as ASD and attention-deficit hyperactivity disorder (ADHD). Curcumin (CUR), the active compound of the spice turmeric, has been shown to act as a positive allosteric modulator of α7-nAChRs. Here we hypothesize that CUR, acting through α7-nAChRs, influences the neuropathology of ASD. In patch clamp studies, fast inward currents activated by choline, a selective agonist of α7-nAChRs, were significantly potentiated by CUR. Moreover, choline induced enhancement of spontaneous inhibitory postsynaptic currents was markedly increased in the presence of CUR. Furthermore, CUR (25, 50, and 100 mg/kg, i.p.) ameliorated dose-dependent social deficits without affecting locomotor activity or anxiety-like behaviors of tested male Black and Tan BRachyury (BTBR) mice. In addition, CUR (50 and 100 mg/kg, i.p.) mitigated oxidative stress status by restoring the decreased levels of superoxide dismutase (SOD) and catalase (CAT) in the hippocampus and the cerebellum of treated mice. Collectively, the observed results indicate that CUR potentiates α7-nAChRs in native central nervous system neurons, mitigates disturbed oxidative stress, and alleviates ASD-like features in BTBR mice used as an idiopathic rodent model of ASD, and may represent a promising novel pharmacological strategy for ASD treatment.

Enantioenriched Positive Allosteric Modulators Display Distinct Pharmacology at the Dopamine D1 Receptor

(1) Background: Two first-in-class racemic dopamine D₁ receptor (D₁R) positive allosteric modulator (PAM) chemotypes (1 and 2) were identified from a high-throughput screen. In particular, due to its selectivity for the D₁R and reported lack of intrinsic activity, compound 2 shows promise as a starting point toward the development of small molecule allosteric modulators to ameliorate the cognitive deficits associated with some neuropsychiatric disease states; (2) Methods: Herein, we describe the enantioenrichment of optical isomers of 2 using chiral auxiliaries derived from (R)- and (S)-3-hydroxy-4,4-dimethyldihydrofuran-2(3H)-one (d- and l-pantolactone, respectively); (3) Results: We confirm both the racemate and enantiomers of 2 are active and selective for the D₁R, but that the respective stereoisomers show a significant difference in their affinity and magnitude of positive allosteric cooperativity with dopamine; (4) Conclusions: These data warrant further investigation of asymmetric syntheses of optically pure analogues of 2 for the development of D₁R PAMs with superior allosteric properties.

Novel positive allosteric modulator of protease-activated receptor 1 promotes skin wound healing in hairless mice

BACKGROUND AND PURPOSE

Protease-activated receptor 1 (PAR1) is a GPCR expressed in several skin cell types, including keratinocyte and dermal fibroblast. PAR1 activation plays a crucial role in the process of skin wound healing such as thrombosis, inflammation, proliferation and tissue repair. In the present study, we identified a novel positive allosteric modulator of PAR1, GB83, and investigated its effect on skin wound healing.

EXPERIMENTAL APPROACH

The enhancement of PAR1 activity by GB83 was measured using Fluo-4 calcium assay. In silico docking analysis of GB83 in PAR1 was performed using dock ligands method (CDOCKER) with CHARMm force field. Effects of GB83 on cell viability and gene expression were observed using MTS assay and quantitative real-time PCRs, respectively. SKH-1 hairless mice were used to investigate the wound healing effect of GB83.

KEY RESULTS

We demonstrated that GB83 did not activate PAR1 by itself but strongly enhanced PAR1 activation by thrombin and PAR1-activating peptide (AP). In silico docking analysis revealed that GB83 can bind to the PAR1 binding site of vorapaxar. GB83 significantly promoted PAR1-mediated cell viability and migration. In addition, the enhancement of PAR1 activity by GB83 strongly increased gene expression of TGF-β, fibronectin and type I collagen in vitro and promoted skin wound healing in vivo.

CONCLUSION AND IMPLICATIONS

Our results revealed that GB83 is the first positive allosteric modulator of PAR1 and it can be a useful pharmacological tool for studying PAR1 and a potential therapeutic agent for skin wound healing.

Apigenin and Structurally Related Flavonoids Allosterically Potentiate the Function of Human α7-Nicotinic Acetylcholine Receptors Expressed in SH-EP1 Cells

Phytochemicals, such as monoterpenes, polyphenols, curcuminoids, and flavonoids, are known to have anti-inflammatory, antioxidant, neuroprotective, and procognitive effects. In this study, the effects of several polyhydroxy flavonoids, as derivatives of differently substituted 5,7-dihydroxy-4H-chromen-4-one including apigenin, genistein, luteolin, kaempferol, quercetin, gossypetin, and phloretin with different lipophilicities (cLogP), as well as topological polar surface area (TPSA), were tested for induction of Ca²⁺ transients by α7 human nicotinic acetylcholine (α7 nACh) receptors expressed in SH-EP1 cells. Apigenin (10 μM) caused a significant potentiation of ACh (30 μM)-induced Ca²⁺ transients, but did not affect Ca²⁺ transients induced by high K⁺ (60 mM) containing solutions. Co-application of apigenin with ACh was equally effective as apigenin preincubation. However, the effect of apigenin significantly diminished by increasing ACh concentrations. The flavonoids tested also potentiated α₇ nACh mediated Ca²⁺ transients with descending potency (highest to lowest) by genistein, gossypetin, kaempferol, luteolin, phloretin, quercetin, and apigenin. The specific binding of α7 nACh receptor antagonist [¹²⁵I]-bungarotoxin remained unchanged in the presence of any of the tested polyhydroxy flavonoids, suggesting that these compounds act as positive allosteric modulators of the α7-nACh receptor in SH-EP1 cells. These findings suggest a clinical potential for these phytochemicals in the treatment of various human diseases from pain to inflammation and neural disease.

Design, Synthesis, and Structure-Activity Relationships Study of N-Pyrimidyl/Pyridyl-2-thiazolamine Analogues as Novel Positive Allosteric Modulators of M3 Muscarinic Acetylcholine Receptor

The M₃ muscarinic acetylcholine receptor (mAChR) plays an essential pharmacological role in mediating a broad range of actions of acetylcholine (ACh) released throughout the periphery and central nerve system (CNS). Nevertheless, its agonistic functions remain unclear due to the lack of available subtype-selective agonists or positive allosteric modulators (PAMs). In the course of our extended structure-activity relationships (SARs) study on 2-acylaminothiazole derivative 1, a previously reported PAM of the M₃ mAChR, we successfully identified N-pyrimidyl/pyridyl-2-thiazolamine analogues as new scaffolds. The SARs study was rationalized using conformational analyses based on intramolecular interactions. A comprehensive study of a series of analogues described in this paper suggests that a unique sulfur-nitrogen nonbonding interaction in the N-pyrimidyl/pyridyl-2-thiazolamine moiety enable conformations that are essential for activity. Further, a SARs study around the N-pyrimidyl/pyridyl-2-thiazolamine core culminated in the discovery of compound 3g, which showed potent in vitro PAM activity for the M₃ mAChR with excellent subtype selectivity. Compound 3g also showed a distinct pharmacological effect on isolated smooth muscle tissue from rat bladder and favorable pharmacokinetics profiles, suggesting its potential as a chemical tool for probing the M₃ mAChR in further research.

Non-peptide agonists and positive allosteric modulators of glucagon-like peptide-1 receptors: Alternative approaches for treatment of Type 2 diabetes

Glucagon-like peptide-1 (GLP-1) receptors belong to the pharmaceutically important Class B family of GPCRs and are involved in many biologically significant signalling pathways. Its incretin peptide ligand GLP-1 analogues are effective treatments for Type 2 diabetes. Although developing non-peptide low MW drugs targeting GLP-1 receptors remains elusive, considerable progress has been made in discovering non-peptide agonists and positive allosteric modulators (PAMs) of GLP-1 receptors with demonstrated efficacy. Many of these compounds induce biased signalling in GLP-1 receptor-mediated functional pathways. High-quality structures of GLP-1 receptors in both inactive and active states have been reported, revealing detailed molecular interactions between GLP-1 receptors and non-peptide agonists or PAMs. These progresses raise the exciting possibility of developing non-peptide drugs of GLP-1 receptors as alternative treatments for Type 2 diabetes. The insight into the interactions between the receptor and the non-peptide ligand is also useful for developing non-peptide ligands targeting other Class B GPCRs.

Ligand recognition and allosteric regulation of DRD1-Gs signaling complexes

Dopamine receptors, including D1- and D2-like receptors, are important therapeutic targets in a variety of neurological syndromes, as well as cardiovascular and kidney diseases. Here, we present five cryoelectron microscopy (cryo-EM) structures of the dopamine D1 receptor (DRD1) coupled to Gs heterotrimer in complex with three catechol-based agonists, a non-catechol agonist, and a positive allosteric modulator for endogenous dopamine. These structures revealed that a polar interaction network is essential for catecholamine-like agonist recognition, whereas specific motifs in the extended binding pocket were responsible for discriminating D1- from D2-like receptors. Moreover, allosteric binding at a distinct inner surface pocket improved the activity of DRD1 by stabilizing endogenous dopamine interaction at the orthosteric site. DRD1-Gs interface revealed key features that serve as determinants for G protein coupling. Together, our study provides a structural understanding of the ligand recognition, allosteric regulation, and G protein coupling mechanisms of DRD1.

Distinct GluN1 and GluN2 Structural Determinants for Subunit-Selective Positive Allosteric Modulation of N-Methyl-d-aspartate Receptors

N-Methyl-d-aspartate receptors (NMDARs) are ionotropic ligand-gated glutamate receptors that mediate fast excitatory synaptic transmission in the central nervous system (CNS). Several neurological disorders may involve NMDAR hypofunction, which has driven therapeutic interest in positive allosteric modulators (PAMs) of NMDAR function. Here we describe modest changes to the tetrahydroisoquinoline scaffold of GluN2C/GluN2D-selective PAMs that expands activity to include GluN2A- and GluN2B-containing recombinant and synaptic NMDARs. These new analogues are distinct from GluN2C/GluN2D-selective compounds like (+)-(3-chlorophenyl)(6,7-dimethoxy-1-((4-methoxyphenoxy)methyl)-3,4-dihydroisoquinolin-2(1H)-yl)methanone (CIQ) by virtue of their subunit selectivity, molecular determinants of action, and allosteric regulation of agonist potency. The (S)-enantiomers of two analogues (EU1180-55, EU1180-154) showed activity at NMDARs containing all subunits (GluN2A, GluN2B, GluN2C, GluN2D), whereas the (R)-enantiomers were primarily active at GluN2C- and GluN2D-containing NMDARs. Determination of the actions of enantiomers on triheteromeric receptors confirms their unique pharmacology, with greater activity of (S) enantiomers at GluN2A/GluN2D and GluN2B/GluN2D subunit combinations than (R) enantiomers. Evaluation of the (S)-EU1180-55 and EU1180-154 response of chimeric kainate/NMDA receptors revealed structural determinants of action within the pore-forming region and associated linkers. Scanning mutagenesis identified structural determinants within the GluN1 pre-M1 and M1 regions that alter the activity of (S)-EU1180-55 but not (R)-EU1180-55. By contrast, mutations in pre-M1 and M1 regions of GluN2D perturb the actions of only the (R)-EU1180-55 but not the (S) enantiomer. Molecular modeling supports the idea that the (S) and (R) enantiomers interact distinctly with GluN1 and GluN2 pre-M1 regions, suggesting that two distinct sites exist for these NMDAR PAMs, each of which has different functional effects.

Reversal of Age-Related Neuronal Atrophy by α5-GABAA Receptor Positive Allosteric Modulation

Aging is associated with reduced brain volume, altered neural activity, and neuronal atrophy in cortical-like structures, comprising the frontal cortex and hippocampus, together contributing to cognitive impairments. Therapeutic efforts aimed at reversing these deficits have focused on excitatory or neurotrophic mechanisms, although recent findings show that reduced dendritic inhibition mediated by α5-subunit containing GABA-A receptors (α5-GABAA-Rs) occurs during aging and contributes to cognitive impairment. Here, we aimed to confirm the beneficial effect on working memory of augmenting α5-GABAA-R activity in old mice and tested its potential at reversing age-related neuronal atrophy. We show that GL-II-73, a novel ligand with positive allosteric modulatory activity at α5-GABAA-R (α5-PAM), increases dendritic branching complexity and spine numbers of cortical neurons in vitro. Using old mice, we confirm that α5-PAM reverses age-related working memory deficits and show that chronic treatment (3 months) significantly reverses age-related dendritic shrinkage and spine loss in frontal cortex and hippocampus. A subsequent 1-week treatment cessation (separate cohort) resulted in loss of efficacy on working memory but maintained morphological neurotrophic effects. Together, the results demonstrate the beneficial effect on working memory and neurotrophic efficacy of augmenting α5-GABAA-R function in old mice, suggesting symptomatic and disease-modifying potential in age-related brain disorders.

Roles of Cholecystokinin in the Nutritional Continuum. Physiology and Potential Therapeutics

Cholecystokinin is a gastrointestinal peptide hormone with important roles in metabolic physiology and the maintenance of normal nutritional status, as well as potential roles in the prevention and management of obesity, currently one of the dominant causes of direct or indirect morbidity and mortality. In this review, we discuss the roles of this hormone and its receptors in maintaining nutritional homeostasis, with a particular focus on appetite control. Targeting this action led to the development of full agonists of the type 1 cholecystokinin receptor that have so far failed in clinical trials for obesity. The possible reasons for clinical failure are discussed, along with alternative pharmacologic strategies to target this receptor for prevention and management of obesity, including development of biased agonists and allosteric modulators. Cellular cholesterol is a natural modulator of the type 1 cholecystokinin receptor, with elevated levels disrupting normal stimulus-activity coupling. The molecular basis for this is discussed, along with strategies to overcome this challenge with a corrective positive allosteric modulator. There remains substantial scope for development of drugs to target the type 1 cholecystokinin receptor with these new pharmacologic strategies and such drugs may provide new approaches for treatment of obesity.

Development of a Testing Funnel for Identification of Small-Molecule Modulators Targeting Secretin Receptors

The secretin receptor (SCTR), a prototypical class B G protein-coupled receptor (GPCR), exerts its effects mainly by activating Gαs proteins upon binding of its endogenous peptide ligand secretin. SCTRs can be found in a variety of tissues and organs across species, including the pancreas, stomach, liver, heart, lung, colon, kidney, and brain. Beyond that, modulation of SCTR-mediated signaling has therapeutic potential for the treatment of multiple diseases, such as heart failure, obesity, and diabetes. However, no ligands other than secretin and its peptide analogs have been described to regulate SCTRs, probably due to inherent challenges in family B GPCR drug discovery. Here we report creation of a testing funnel that allowed targeted detection of SCTR small-molecule activators. Pursuing the strategy to identify positive allosteric modulators (PAMs), we established a unique primary screening assay employing a mixture of three orthosteric stimulators that was compared in a screening campaign testing 12,000 small-molecule compounds. Beyond that, we developed a comprehensive set of secondary assays, such as a radiolabel-free target engagement assay and a NanoBiT (NanoLuc Binary Technology)-based approach to detect β-arrestin-2 recruitment, all feasible in a high-throughput environment as well as capable of profiling ligands and hits regarding their effect on binding and receptor function. This combination of methods enabled the discovery of five promising scaffolds, four of which have been validated and further characterized with respect to their allosteric activities. We propose that our results may serve as starting points for developing the first in vivo active small molecules targeting SCTRs.

Positive Allosteric Modulation of CB1 and CB2 Cannabinoid Receptors Enhances the Neuroprotective Activity of a Dual CB1R/CB2R Orthosteric Agonist

Preclinical studies highlighted that compounds targeting cannabinoid receptors could be useful for developing novel therapies against neurodegenerative disorders. However, the chronic use of orthosteric agonists alone has several disadvantages, limiting their usefulness as clinically relevant drugs. Positive allosteric modulators might represent a promising approach to achieve the potential therapeutic benefits of orthosteric agonists of cannabinoid receptors through increasing their activity and limiting their adverse effects. The aim of the present study was to show the effects of positive allosteric ligands of cannabinoid receptors on the activity of a potent dual orthosteric agonist for neuroinflammation and excitotoxic damage by excessive glutamate release. The results indicate that the combination of an orthosteric agonist with positive allosteric modulators could represent a promising therapeutic approach to the treatment of neurodegenerative disorders.

Allosteric Modulators of G Protein-Coupled Dopamine and Serotonin Receptors: A New Class of Atypical Antipsychotics

Schizophrenia was first described by Emil Krapelin in the 19th century as one of the major mental illnesses causing disability worldwide. Since the introduction of chlorpromazine in 1952, strategies aimed at modifying the activity of dopamine receptors have played a major role for the treatment of schizophrenia. The introduction of atypical antipsychotics with clozapine broadened the range of potential targets for the treatment of this psychiatric disease, as they also modify the activity of the serotoninergic receptors. Interestingly, all marketed drugs for schizophrenia bind to the orthosteric binding pocket of the receptor as competitive antagonists or partial agonists. In recent years, a strong effort to develop allosteric modulators as potential therapeutic agents for schizophrenia was made, mainly for the several advantages in their use. In particular, the allosteric binding sites are topographically distinct from the orthosteric pockets, and thus drugs targeting these sites have a higher degree of receptor subunit specificity. Moreover, “pure” allosteric modulators maintain the temporal and spatial fidelity of native orthosteric ligand. Furthermore, allosteric modulators have a “ceiling effect”, and their modulatory effect is saturated above certain concentrations. In this review, we summarize the progresses made in the identification of allosteric drugs for dopamine and serotonin receptors, which could lead to a new generation of atypical antipsychotics with a better profile, especially in terms of reduced side effects.

Species-Dependent Enhancement of Ovarian Cancer G Protein-Coupled Receptor 1 Activation by Ogerin

Ogerin is a positive allosteric modulator of human and mouse ovarian cancer G protein-coupled receptors (OGR1s). In the present study, we found that ogerin differentially enhances the activation of OGR1 in various animal species. Amino acid residues of OGR1 that are associated with ogerin are conserved among the species. This suggests that other amino acid residues may be involved in the action of ogerin. Chimeric receptors between human and zebrafish OGR1s showed that the amino acid residues that determine the species specificity of ogerin-induced enhancement reside in the transmembrane and/or intracellular regions of OGR1. This result highlights the importance of first verifying the effectiveness of ogerin to the OGR1 of the species of interest at the cellular level prior to analyzing the physiological and pathophysiological roles of OGR1 in the species.

Effects of the Positive Allosteric Modulator of Metabotropic Glutamate Receptor 5, VU-29, on Maintenance Association between Environmental Cues and Rewarding Properties of Ethanol in Rats

: Metabotropic glutamate subtype 5 (mGlu5) receptors are implicated in various forms of synaptic plasticity, including drugs of abuse. In drug-addicted individuals, associative memories can drive relapse to drug use. The present study investigated the potential of the mGlu5 receptor positive allosteric modulator (PAM), VU-29 (30 mg/kg, i.p.), to inhibit the maintenance of a learned association between ethanol and environmental context by using conditioned place preference (CPP) in rats. The ethanol-CPP was established by the administration of ethanol (1.0 g/kg, i.p. × 10 days) using an unbiased procedure. Following ethanol conditioning, VU-29 was administered at various post-conditioning times (ethanol free state at the home cage) to ascertain if there was a temporal window during which VU-29 would be effective. Our experiments indicated that VU-29 did not affect the expression of ethanol-induced CPP when it was given over two post-conditioning days. However, the expression of ethanol-CPP was inhibited by 10-day home cage administration of VU-29, but not by first 2-day or last 2-day injection of VU-29 during the 10-day period. These findings reveal that VU-29 can inhibit the maintenance of ethanol-induced CPP, and that treatment duration contributes to this effect of VU-29. Furthermore, VU-29 effect was reversed by pretreatment with either MTEP (the mGlu5 receptor antagonist), or MK-801 (the N-methyl-D-aspartate-NMDA receptor antagonist). Thus, the inhibitory effect of VU-29 is dependent on the functional interaction between mGlu5 and NMDA receptors. Because a reduction in ethanol-associated cues can reduce relapse, mGlu5 receptor PAM would be useful for therapy of alcoholism. Future research is required to confirm the current findings.

Water-soluble variant of human Lynx1 positively modulates synaptic plasticity and ameliorates cognitive impairment associated with α7-nAChR dysfunction

Lynx1 is a GPI-tethered protein colocalized with nicotinic acetylcholine receptors (nAChRs) in the brain areas important for learning and memory. Previously, we demonstrated that at low micromolar concentrations the water-soluble Lynx1 variant lacking GPI-anchor (ws-Lynx1) acts on α7-nAChRs as a positive allosteric modulator. We hypothesized that ws-Lynx1 could be used for improvement of cognitive processes dependent on nAChRs. Here we showed that 2 µM ws-Lynx1 increased the acetylcholine-evoked current at α7-nAChRs in the rat primary visual cortex L1 interneurons. At higher concentrations ws-Lynx1 inhibits α7-nAChRs expressed in Xenopus laevis oocytes with IC₅₀  ~ 50 µM. In mice, ws-Lynx1 penetrated the blood-brain barrier upon intranasal administration and accumulated in the cortex, hippocampus, and cerebellum. Chronic ws-Lynx1 treatment prevented the olfactory memory and motor learning impairment induced by the α7-nAChRs inhibitor methyllycaconitine (MLA). Enhanced long-term potentiation and increased paired-pulse facilitation ratio were observed in the hippocampal slices incubated with ws-Lynx1 and in the slices from ws-Lynx1-treated mice. Long-term potentiation blockade observed in MLA-treated mice was abolished by ws-Lynx1 co-administration. To understand the mechanism of ws-Lynx1 action, we studied the interaction of ws-Lynx1 and MLA at α7-nAChRs, measured the basal concentrations of endogenous Lynx1 and the α7 nAChR subunit and their association in the mouse brain. Our findings suggest that endogenous Lynx1 limits α7-nAChRs activation in the adult brain. Ws-Lynx1 partially displaces Lynx1 causing positive modulation of α7-nAChRs and enhancement of synaptic plasticity. Ws-Lynx1 and similar compounds may constitute useful hits for treatment of cognitive deficits associated with the cholinergic system dysfunction.

The nicotinic receptor alpha5 coding polymorphism rs16969968 as a major target in disease: Functional dissection and remaining challenges

Nicotinic acetylcholine receptors (nAChRs) are major signalling molecules in the central and peripheral nervous system. Over the last decade, they have been linked to a number of major human psychiatric and neurological conditions, like smoking, schizophrenia, Alzheimer's disease and many others. Human Genome-Wide Association Studies (GWAS) have robustly identified genetic alterations at a locus of chromosome 15q to several of these diseases. In this review, we discuss a major coding polymorphism in the alpha5 subunit, referred to as α5SNP, and its functional dissection in vitro and in vivo. Its presence at high frequency in many human populations lends itself to pharmaceutical intervention in the context of 'positive allosteric modulators' (PAMs). We will present the prospects of this novel treatment, and the remaining challenges to identify suitable molecules.

T-495, a novel low cooperative M1 receptor positive allosteric modulator, improves memory deficits associated with cholinergic dysfunction and is characterized by low gastrointestinal side effect risk

M₁ muscarinic acetylcholine receptor (M₁ R) activation can be a new therapeutic approach for the treatment of cognitive deficits associated with cholinergic hypofunction. However, M₁ R activation causes gastrointestinal (GI) side effects in animals. We previously found that an M₁ R positive allosteric modulator (PAM) with lower cooperativity (α-value) has a limited impact on ileum contraction and can produce a wider margin between cognitive improvement and GI side effects. In fact, TAK-071, a novel M₁ R PAM with low cooperativity (α-value of 199), improved scopolamine-induced cognitive deficits with a wider margin against GI side effects than a high cooperative M₁ R PAM, T-662 (α-value of 1786), in rats. Here, we describe the pharmacological characteristics of a novel low cooperative M₁ R PAM T-495 (α-value of 170), using the clinically tested higher cooperative M₁ R PAM MK-7622 (α-value of 511) as a control. In rats, T-495 caused diarrhea at a 100-fold higher dose than that required for the improvement of scopolamine-induced memory deficits. Contrastingly, MK-7622 showed memory improvement and induction of diarrhea at an equal dose. Combination of T-495, but not of MK-7622, and donepezil at each sub-effective dose improved scopolamine-induced memory deficits. Additionally, in mice with reduced acetylcholine levels in the forebrain via overexpression of A53T α-synuclein (ie, a mouse model of dementia with Lewy bodies and Parkinson's disease with dementia), T-495, like donepezil, reversed the memory deficits in the contextual fear conditioning test and Y-maze task. Thus, low cooperative M₁ R PAMs are promising agents for the treatment of memory deficits associated with cholinergic dysfunction.

Enhanced Akt/GSK-3β/CREB signaling mediates the anti-inflammatory actions of mGluR5 positive allosteric modulators in microglia and following traumatic brain injury in male mice

We have previously shown that treatment with a mGluR5 positive allosteric modulator (PAM) is neuroprotective after experimental traumatic brain injury (TBI), limiting post-traumatic neuroinflammation by reducing pro-inflammatory microglial activation and promoting anti-inflammatory and neuroprotective responses. However, the specific molecular mechanisms governing this anti-inflammatory shift in microglia remain unknown. Here we show that the mGluR5 PAM, VU0360172 (VuPAM), regulates microglial inflammatory responses through activation of Akt, resulting in the inhibition of GSK-3β. GSK-3β regulates the phosphorylation of CREB, thereby controlling the expression of inflammation-related genes and microglial plasticity. The anti-inflammatory action of VuPAM in microglia is reversed by inhibiting Akt/GSK-3β/CREB signaling. Using a well-characterized TBI model and CX3CR1^gfp/+ mice to visualize microglia in vivo, we demonstrate that VuPAM enhances Akt/GSK-3β/CREB signaling in the injured cortex, as well as anti-inflammatory microglial markers. Furthermore, in situ analysis revealed that GFP + microglia in the cortex of VuPAM-treated TBI mice co-express pCREB and the anti-inflammatory microglial phenotype marker YM1. Taken together, our data show that VuPAM decreases pro-inflammatory microglial activation by modulating Akt/GSK-3β/CREB signaling. These findings serve to clarify the potential neuroprotective mechanisms of mGluR5 PAM treatment after TBI, and suggest novel therapeutic targets for post-traumatic neuroinflammation. Cover Image for this issue: https://doi.org/10.1111/jnc.15048.