Profiling the Impact of mGlu/Elfn1 Protein Interactions on the Pharmacology of mGlu Allosteric Modulators.

The group III metabotropic glutamate receptors (mGlu receptors) are predominantly expressed presynaptically throughout the central nervous system (CNS) where they regulate the release of glutamate and GABA. These receptors have recently been shown to be anchored by transsynaptic expression of the laminin proteins ELFN1 and ELFN2. In particular, the mGlu receptor is localized at presynaptic active zones from pyramidal cells to somatostatin-containing interneurons with postsynaptic ELFN1, and this interaction drives the rapidly facilitating nature of these synapses in the hippocampus and cortex.

Discovery of a Novel sp‑Rich M Positive Allosteric Modulators (PAMs) Chemotype via Scaffold Hopping.

The M receptor has long been investigated as a promising CNS drug target, yet further research is essential to fully elucidate compound's Pharmacodynamic (PD) as well as Toxicokinetic (TK) effects. In this context, the development of structurally diverse and high-profile M PAM tool compounds remains highly valuable, as existing advanced tools exhibit notable structural similarity. One approach that can be considered during scaffold hopping exercise and can improve drug-like properties is to introduce additional sp carbon atoms and increase Fsp values; the fraction of sp hybridized carbons.

Overexpression of mGlu in Mice: Implications for Neurodevelopmental Disorders.

Metabotropic glutamate receptor 7 (mGlu) is a G protein-coupled receptor (GPCR) involved in neurotransmitter release throughout the central nervous system (CNS). Low levels of the receptor are correlated with intellectual disability, autism, repetitive behaviors, and seizures in patients with neurodevelopmental disorders (NDDs), including the disease Rett syndrome. These findings suggest that increasing mGlu activity may be of therapeutic benefit.

Profiling metabotropic glutamate receptor 7 expression in Rett syndrome: consequences for pharmacotherapy.

We have reported that levels of metabotropic glutamate receptor 7 (mGlu ) are dramatically decreased in brain samples from Rett syndrome patients carrying truncation mutations in the ( ) gene. Additionally, we identified decreases in mGlu levels in female mice and demonstrated that administration of a positive allosteric modulator (PAM) with activity at mGlu corrected deficits in cognitive, social, and respiratory domains. Here, we expanded our studies to a larger cohort of RTT samples covering a range of mutations and evaluated expression of the three widely expressed group III mGlu receptors (mGlu ).

Potentiation of group III metabotropic glutamate receptors positively affects neurophysiological features in a mouse model of Rett syndrome.

Rett syndrome (RTT) is a neurodevelopmental disorder primarily caused by loss-of-function mutations in the X-linked methyl-CpG-binding protein 2 (MECP2) gene. Genetic restoration of MECP2 in mice can reverse phenotypes, providing hope for disease-modifying therapies in the disease. Studies in people with and mouse models of RTT have identified neurophysiological features, such as auditory event-related potentials (AEPs), that correlate with disease severity, suggesting potential as translatable biomarkers.

Characterization of Novel and Known Activators of Cannabinoid Receptor Subtype 2 Reveals Mixed Pharmacology That Differentiates Mycophenolate Mofetil and GW-842,166X from MDA7.

CB and CB cannabinoid receptors are members of the GPCR superfamily that modulate the effects of endocannabinoids. CB is the most abundant CB receptor in the central nervous system, while CB is present both peripherally and in the brain. CB plays a role in inflammation, as well as neurodegenerative and psychiatric disorders.

Discovery of Pre-Clinical Candidate /: A Highly Selective, Orally Bioavailable, and Structurally Distinct Tricyclic M Muscarinic Acetylcholine Receptor Positive Allosteric Modulator (PAM) with Robust In Vivo Efficacy.

Herein, we report the structure-activity relationship to develop novel tricyclic M positive allosteric modulator scaffolds with improved pharmacological properties. This endeavor involved modifying a 5-amino-3,4-dimethylthieno[2,3-]pyridazine-6-carboxamide core via a "tie-back" strategy to discover a novel tricyclic 3,4-dimethylpyrimido[4',5':4,5]thieno[2,3-]pyridazine core. From this exercise, / was identified as a preclinical candidate, which displays low nanomolar potency against both human and rat M.

Discovery of Thieno[3,2-]pyridine-5-carboxamide and 2,3-Difluorobenzamide Negative Allosteric Modulators of Metabotropic Glutamate Receptor Subtype 5.

This Letter describes the discovery of novel mGlu NAMs and . Starting from previously reported picolinamide compounds, a structure-activity relationship study of various core isosteres was conducted, leading to the identification of thieno[3,2-]pyridine-5-carboxamide and 2,3-difluorobenzamide as competent core replacements. These compounds are highly potent as well as brain penetrant with an IVIVC agreement and improved oral bioavailability in rats.

Application of Deuterium in an M Positive Allosteric Modulator Back-Up Program: The Discovery of VU6045422.

Recently, we disclosed VU0467319, an M positive allosteric modulator (PAM) clinical candidate that had successfully completed a phase I single ascending dose clinical trial. Pharmacokinetic assessment revealed that, in humans upon increasing dose, a circulating, inactive metabolite constituted a major portion of the total drug-related area under the curve (AUC). One approach the team employed to reduce inactive metabolite formation in the back-up program was the kinetic isotope effect, replacing the metabolically labile C-H bonds with shorter, more stable C-D bonds.

Further Optimization of the mGlu PAM VU6024578/BI02982816: Discovery and Characterization of VU6033685.

Herein, we report the further chemical optimization of the metabotropic glutamate receptor subtype 1 (mGlu) positive allosteric modulator (PAM) VU6024578/BI02982816 and the discovery of VU6033685/BI1752. PAM VU6033685/BI1752 was developed through an iterative process wherein, after the furanyl moiety (a potential toxicophore) was replaced by an -linked pyrazole, a diversity screen identified a quinoline core, which was further truncated to a pyridine scaffold. PAM VU6033685/BI1752 proved to be a potent and selective mGlu PAM with efficacy in both amphetamine-induced hyperlocomotion (AHL) and novel object recognition (NOR) with a clear pharmacokinetic-pharmacodynamic (PK/PD) relationship.

Discovery of 4-(5-Membered)Heteroarylether-6-methylpicolinamide Negative Allosteric Modulators of Metabotropic Glutamate Receptor Subtype 5.

This Letter details our efforts to develop novel, non-acetylene-containing metabotropic glutamate receptor subtype 5 (mGlu) negative allosteric modulators (NAMs) with improved pharmacological properties. This endeavor involved replacing the ether-linked pyrimidine moiety, a metabolic liability, with various 5-membered heterocycles. From this exercise, we identified , a highly brain penetrant and selective mGlu NAM which displayed moderate potency against both human and rat mGlu.

Discovery of VU6024578/BI02982816: An mGlu Positive Allosteric Modulator with Efficacy in Preclinical Antipsychotic and Cognition Models.

Herein, we report progress toward a metabotropic glutamate receptor subtype 1 (mGlu) positive allosteric modulator (PAM) clinical candidate and the discovery of VU6024578/BI02982816. From a weak high-throughput screening hit (VU0538160, EC > 10 μM, 71% Glu), optimization efforts improved functional potency over 185-fold to deliver the selective (inactive on mGlu) and CNS penetrant (rat K = 0.99, K = 0.

Discovery of VU0467319: an M Positive Allosteric Modulator Candidate That Advanced into Clinical Trials.

Herein we detail the of VU0467319 (VU319), an M Positive Allosteric Modulator (PAM) clinical candidate that successfully completed a Phase I Single Ascending Dose (SAD) clinical trial. VU319 () is a moderately potent M PAM (M PAM EC = 492 nM ± 2.9 nM, 71.

The cannabinoid CB receptor positive allosteric modulator EC21a exhibits complicated pharmacology .

Schizophrenia is a complex disease involving the dysregulation of numerous brain circuits and patients exhibit positive symptoms (hallucinations, delusions), negative symptoms (anhedonia), and cognitive impairments. We have shown that the antipsychotic efficacy of positive allosteric modulators (PAMs) of both the M muscarinic receptor and metabotropic glutamate receptor 1 (mGlu) involve the retrograde activation of the presynaptic cannabinoid type-2 (CB) receptor, indicating that CB activation or potentiation could result in a novel therapeutic strategy for schizophrenia. We used two complementary assays, receptor-mediated phosphoinositide hydrolysis and GIRK channel activation, to characterize a CB PAM scaffold, represented by the compound EC21a, to explore its potential as a starting point to optimize therapeutics for schizophrenia.

Elucidating the molecular logic of a metabotropic glutamate receptor heterodimer.

Metabotropic glutamate (mGlu) receptor protomers can heterodimerize, leading to different pharmacology compared to their homodimeric counterparts. Here, we use complemented donor-acceptor resonance energy transfer (CODA-RET) technology that distinguishes signaling from defined mGlu heterodimers or homodimers, together with targeted mutagenesis of receptor protomers and computational docking, to elucidate the mechanism of activation and differential pharmacology in mGlu heteromers. We demonstrate that positive allosteric modulators (PAMs) that bind an upper allosteric pocket in the mGlu transmembrane domain are active at both mGlu homomers and mGlu heteromers, while those that bind a lower allosteric pocket within the same domain are efficacious in homomers but not heteromers.

Discovery of VU6016235: A Highly Selective, Orally Bioavailable, and Structurally Distinct Tricyclic M Muscarinic Acetylcholine Receptor Positive Allosteric Modulator (PAM).

Herein, we report structure-activity relationship (SAR) studies to develop novel tricyclic M PAM scaffolds with improved pharmacological properties. This endeavor involved a "tie-back" strategy to replace a 5-amino-2,4-dimethylthieno[2,3-]pyrimidine-6-carboxamide core, which led to the discovery of two novel tricyclic cores. While both tricyclic cores displayed low nanomolar potency against both human and rat M and were highly brain-penetrant, the 2,4-dimethylpyrido[4',3':4,5]thieno[2,3-]pyrimidine tricycle core provided lead compound, , with an overall superior pharmacological and drug metabolism and pharmacokinetics (DMPK) profile, as well as efficacy in a preclinical antipsychotic animal model.

Discovery of VU6007496: Challenges in the Development of an M Positive Allosteric Modulator Backup Candidate.

Herein we report progress toward a backup clinical candidate to the M positive allosteric modulator (PAM) VU319/ACP-319. Scaffold-hopping from the pyrrolo[2,3-]pyridine-based M PAM VU6007477 to isomeric pyrrolo[3,2-]pyridine and thieno[3,2-]pyridine congeners identified several backup contenders. Ultimately, VU6007496, a pyrrolo[3,2-]pyridine, advanced into late stage profiling, only to be plagued with unanticipated, species-specific metabolism and active/toxic metabolites which were identified in our phenotypic seizure liability screen, preventing further development.

Discovery of VU6008677: A Structurally Distinct Tricyclic M Positive Allosteric Modulator with Improved CYP450 Profile.

This Letter details our efforts to develop novel tricyclic muscarinic acetylcholine receptor subtype 4 (M) positive allosteric modulator (PAM) scaffolds with improved pharmacological properties. This endeavor involved a "tie-back" strategy to replace the 3-amino-5-chloro-4,6-dimethylthieno[2,3-]pyridine-2-carboxamide core, which led to the discovery of two novel tricyclic cores: an 8-chloro-9-methylpyrido[3',2':4,5]thieno[3,2-]pyrimidin-4-amine core and 8-chloro-7,9-dimethylpyrido[3',2':4,5]furo[3,2-]pyrimidin-4-amine core. Both tricyclic cores displayed low nanomolar potency against human M and greatly reduced cytochrome P450 inhibition when compared with parent compound .

Development of VU6036864: A Triazolopyridine-Based High-Quality Antagonist Tool Compound of the M Muscarinic Acetylcholine Receptor.

While the muscarinic acetylcholine receptor mAChR subtype 5 (M) has been studied over decades, recent findings suggest that more in-depth research is required to elucidate a thorough understanding of its physiological function related to neurological and psychiatric disorders. Our efforts to identify potent, selective, and pharmaceutically favorable next-generation M antagonist tool compounds have led to the discovery of a novel triazolopyridine-based series. In particular, () showed exquisite potency (human M IC = 20 nM), good subtype selectivity (>500 fold selectivity against human M), desirable brain exposure ( = 0.

Potentiation of the muscarinic acetylcholine receptor 1 modulates neurophysiological features in a mouse model of Rett syndrome.

Rett syndrome (RTT) is a neurodevelopmental disorder primarily caused by mutations in the X chromosome-linked gene Methyl-CpG Binding Protein 2 (MECP2). Restoring MeCP2 expression after disease onset in a mouse model of RTT reverses phenotypes, providing hope for development of treatments for RTT. Translatable biomarkers of improvement and treatment responses have the potential to accelerate both preclinical and clinical evaluation of targeted therapies in RTT.

MeCP2 gene therapy ameliorates disease phenotype in mouse model for Pitt Hopkins syndrome.

The neurodevelopmental disorder Pitt Hopkins syndrome (PTHS) causes clinical symptoms similar to Rett syndrome (RTT) patients. However, RTT is caused by MECP2 mutations whereas mutations in the TCF4 gene lead to PTHS. The mechanistic commonalities underling these two disorders are unknown, but their shared symptomology suggest that convergent pathway-level disruption likely exists.

Novel pharmacological targets for GABAergic dysfunction in ADHD.

Attention deficit/hyperactivity disorder (ADHD) is a neurodevelopment disorder that affects approximately 5% of the population. The disorder is characterized by impulsivity, hyperactivity, and deficits in attention and cognition, although symptoms vary across patients due to the heterogenous and polygenic nature of the disorder. Stimulant medications are the standard of care treatment for ADHD patients, and their effectiveness has led to the dopaminergic hypothesis of ADHD in which deficits in dopaminergic signaling, especially in cortical brain regions, mechanistically underly ADHD pathophysiology.

Therapeutic Potential for Metabotropic Glutamate Receptor 7 Modulators in Cognitive Disorders.

Metabotropic glutamate receptor 7 (mGlu) is the most highly conserved and abundantly expressed mGlu receptor in the human brain. The presynaptic localization of mGlu, coupled with its low affinity for its endogenous agonist, glutamate, are features that contribute to the receptor's role in modulating neuronal excitation and inhibition patterns, including long-term potentiation, in various brain regions. These characteristics suggest that mGlu modulation may serve as a novel therapeutic strategy in disorders of cognitive dysfunction, including neurodevelopmental disorders that cause impairments in learning, memory, and attention.

Activation of Metabotropic Glutamate Receptor 3 Modulates Thalamo-accumbal Transmission and Rescues Schizophrenia-Like Physiological and Behavioral Deficits.

Background: Polymorphisms in the gene encoding for metabotropic glutamate receptor 3 (mGlu) are associated with an increased likelihood of schizophrenia diagnosis and can predict improvements in negative symptoms following treatment with antipsychotics. However, the mechanisms by which mGlu can regulate brain circuits involved in schizophrenia pathophysiology are not clear.

Methods: We employed selective pharmacological tools and a variety of approaches including whole-cell patch-clamp electrophysiology, slice optogenetics, and fiber photometry to investigate the effects of mGlu activation on phencyclidine (PCP)-induced impairments in thalamo-accumbal transmission and sociability deficits.

Development of a Selective and High Affinity Radioligand, [H]VU6013720, for the M Muscarinic Receptor.

M muscarinic receptors are highly expressed in the striatum and cortex, brain regions that are involved in diseases such as Parkinson's disease, schizophrenia, and dystonia. Despite potential therapeutic advantages of specifically targeting the M receptor, it has been historically challenging to develop highly selective ligands, resulting in undesired off-target activity at other members of the muscarinic receptor family. Recently, we have reported first-in-class, potent, and selective M receptor antagonists.