Discovery of (1R,2R)-N-(4-(6-isopropylpyridin-2-yl)-3-(2-methyl-2H-indazol-5-yl)isothiazol-5-yl)-2-methylcyclopropanecarboxamide, a potent and orally efficacious mGlu5 receptor negative allosteric modulator.

A novel series of selective negative allosteric modulators (NAMs) for metabotropic glutamate receptor 5 (mGlu5) was discovered from an isothiazole scaffold. One compound of this series, (1R,2R)-N-(4-(6-isopropylpyridin-2-yl)-3-(2-methyl-2H-indazol-5-yl)isothiazol-5-yl)-2-methylcyclopropanecarboxamide (24), demonstrated satisfactory pharmacokinetic properties and, following oral dosing in rats, produced dose-dependent and long-lasting mGlu5 receptor occupancy. Consistent with the hypothesis that blockade of mGlu5 receptors will produce analgesic effects in mammals, compound 24 produced a dose-dependent reduction in paw licking responses in the formalin model of persistent pain.

Targeting group II metabotropic glutamate (mGlu) receptors for the treatment of psychosis associated with Alzheimer's disease: selective activation of mGlu2 receptors amplifies beta-amyloid toxicity in cultured neurons, whereas dual activation of mGlu2 and mGlu3 receptors is neuroprotective.

Dual orthosteric agonists of metabotropic glutamate 2 (mGlu2) and mGlu3 receptors are being developed as novel antipsychotic agents devoid of the adverse effects of conventional antipsychotics. Therefore, these drugs could be helpful for the treatment of psychotic symptoms associated with Alzheimer's disease (AD). In experimental animals, the antipsychotic activity of mGlu2/3 receptor agonists is largely mediated by the activation of mGlu2 receptors and is mimicked by selective positive allosteric modulators (PAMs) of mGlu2 receptors. We investigated the distinct influence of mGlu2 and mGlu3 receptors in mixed and pure neuronal cultures exposed to synthetic ß-amyloid protein (Aß) to model neurodegeneration occurring in AD. The mGlu2 receptor PAM, N-4'-cyano-biphenyl-3-yl)-N-(3-pyridinylmethyl)-ethanesulfonamide hydrochloride (LY566332), devoid of toxicity per se, amplified Aß-induced neurodegeneration, and this effect was prevented by the mGlu2/3 receptor antagonist (2S,1'S,2'S)-2-(9-xanthylmethyl)-2-(2'-carboxycyclopropyl)glycine (LY341495). LY566332 potentiated Aß toxicity regardless of the presence of glial mGlu3 receptors, but it was inactive when neurons lacked mGlu2 receptors. The dual mGlu2/3 receptor agonist, (-)-2-oxa-4-aminobicyclo[3.1.0]exhane-4,6-dicarboxylic acid (LY379268), was neuroprotective in mixed cultures via a paracrine mechanism mediated by transforming growth factor-ß1. LY379268 lost its protective activity in neurons grown with astrocytes lacking mGlu3 receptors, indicating that protection against Aß neurotoxicity was mediated entirely by glial mGlu3 receptors. The selective noncompetitive mGlu3 receptor antagonist, (3S)-1-(5-bromopyrimidin-2-yl)-N-(2,4-dichlorobenzyl)pyrrolidin-3-amine methanesulfonate hydrate (LY2389575), amplified Aß toxicity on its own, and, interestingly, unmasked a neurotoxic activity of LY379268, which probably was mediated by the activation of mGlu2 receptors. These data indicate that selective potentiation of mGlu2 receptors enhances neuronal vulnerability to Aß, whereas dual activation of mGlu2 and mGlu3 receptors is protective against Aß-induced toxicity.

Metabotropic Glutamate2 Receptors Play a Key Role in Modulating Head Twitches Induced by a Serotonergic Hallucinogen in Mice.

There is substantial evidence that glutamate can modulate the effects of 5-hydroxytryptamine2A (5-HT2A) receptor activation through stimulation of metabotropic glutamate2/3 (mGlu2/3) receptors in the prefrontal cortex. Here we show that constitutive deletion of the mGlu2 gene profoundly attenuates an effect of 5-HT2A receptor activation using the mouse head twitch response (HTR). MGlu2 and mGlu3 receptor knockout (KO) as well as age-matched ICR (CD-1) wild type (WT) mice were administered (±)1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and observed for head twitch activity. DOI failed to produce significant head twitches in mGlu2 receptor KO mice at a dose 10-fold higher than the peak effective dose in WT or mGlu3 receptor KO mice. In addition, the mGlu2/3 receptor agonist LY379268, and the mGlu2 receptor positive allosteric modulator (PAM) CBiPES, potently blocked the HTR to DOI in WT and mGlu3 receptor KO mice. Conversely, the mGlu2/3 receptor antagonist LY341495 (10 mg/kg) increased the HTR produced by DOI (3 mg/kg) in mGlu3 receptor KO mice. Finally, the mGlu2 receptor potentiator CBiPES was able to attenuate the increase in the HTR produced by LY341495 in mGlu3 receptor KO mice. Taken together, all of these results are consistent with the hypothesis that that DOI-induced head twitches are modulated by mGlu2 receptor activation. These results also are in keeping with a critical autoreceptor function for mGlu2 receptors in the prefrontal cortex with differential effects of acute vs. chronic perturbation (e.g., constitutive mGlu2 receptor KO mice). The robust attenuation of DOI-induced head twitches in the mGlu2 receptor KO mice appears to reflect the critical role of glutamate in ongoing regulation of 5-HT2A receptors in the prefrontal cortex. Future experiments with inducible knockouts for the mGlu2 receptor and/or selective mGlu3 receptor agonists/PAMs/antagonists could provide an important tools in understanding glutamatergic modulation of prefrontal cortical 5-HT2A receptor function.

Discovery of (1S,2R,3S,4S,5R,6R)-2-Amino-3-[(3,4-difluorophenyl)sulfanylmethyl]-4-hydroxy-bicyclo[3.1.0]hexane-2,6-dicarboxylic Acid Hydrochloride (LY3020371·HCl): A Potent, Metabotropic Glutamate 2/3 Receptor Antagonist with Antidepressant-Like Activity.

As part of our ongoing efforts to identify novel ligands for the metabotropic glutamate 2 and 3 (mGlu2/3) receptors, we have incorporated substitution at the C3 and C4 positions of the (1S,2R,5R,6R)-2-amino-bicyclo[3.1.0]hexane-2,6-dicarboxylic acid scaffold to generate mGlu2/3 antagonists. Exploration of this structure-activity relationship (SAR) led to the identification of (1S,2R,3S,4S,5R,6R)-2-amino-3-[(3,4-difluorophenyl)sulfanylmethyl]-4-hydroxy-bicyclo[3.1.0]hexane-2,6-dicarboxylic acid hydrochloride (LY3020371·HCl, 19f), a potent, selective, and maximally efficacious mGlu2/3 antagonist. Further characterization of compound 19f binding to the human metabotropic 2 glutamate (hmGlu2) site was established by cocrystallization of this molecule with the amino terminal domain (ATD) of the hmGlu2 receptor protein. The resulting cocrystal structure revealed the specific ligand-protein interactions, which likely explain the high affinity of 19f for this site and support its functional mGlu2 antagonist pharmacology. Further characterization of 19f in vivo demonstrated an antidepressant-like signature in the mouse forced-swim test (mFST) assay when brain levels of this compound exceeded the cellular mGlu2 IC50 value.

Metabotropic glutamate 2 receptor potentiators: receptor modulation, frequency-dependent synaptic activity, and efficacy in preclinical anxiety and psychosis model(s).

RATIONALE: To increase subtype selectivity and provide a novel means to alter receptor function, we discovered and characterization potentiators for the metabotropic glutamate 2 receptor (mGlu2). METHODS AND RESULTS: A class of 3-pyridylmethylsulfonamides (e.g., 3-MPPTS; 2,2,2-trifluoro-N-[3-(2-methoxyphenoxy)phenyl]-N-(3-pyridinylmethyl)-ethanesulfonamide) were found to be potent, subtype-selective potentiators of human and rat mGlu2. The sulfonamides increased agonist potency in functional assays but did not displace orthosteric radiolabeled antagonist or agonist binding to cloned mGlu2 receptors. Rather, the modulators increased the affinity of most of the orthosteric agonists including glutamate, DCG-IV (2S,2'R,3'R)-2-(2',3'-dicarboxylcyclopropyl)glycine), and LY354740 (1S,2S,5R,6S-2-aminobicyclo[3.1.0]hexane-2,6-bicaroxylate monohydrate). In striatal brain slices, LY354740 inhibited evoked excitatory postsynaptic potentials (EPSPs) equally well following either a low- (0.06 Hz) or high (4 Hz)-frequency stimulation of corticostriatal afferents. In contrast, the mGlu2 potentiator cyPPTS (2,2,2-trifluoro-N-[3-(cyclopentyloxy)phenyl]-N-(3-pyridinylmethyl)-ethanesulfonamide) inhibited striatal EPSPs only at higher frequencies of stimulation (2 and 4 Hz). Several sulfonamides including 4-MPPTS, 4-APPES (N-[4-(4-carboxamidophenoxy)phenyl]-N-(3-pyridinylmethyl)-ethanesulfonamide hydrochloride monohydrate) and/or CBiPES N-[4'-cyano-biphenyl-3-yl)-N-(3-pyridinylmethyl)-ethanesulfonamide hydrochloride) were tested in mGlu2/3 agonist-sensitive rodent model(s) of anxiety and psychosis. As seen with LY354740, both 4-MPPTS and 4-APPES were efficacious in a rat fear-potentiated startle paradigm. Likewise in mice, CBiPES attenuated a stress-induced hyperthermia and PCP-induced hyperlocomotor activity. Furthermore, CBiPES mediated alteration in PCP-induced hyperlocomotor activity was sensitive to mGlu2/3 antagonist pretreatment. CONCLUSIONS: Taken together, the data indicate mGlu2 receptor potentiators have a unique use-dependent effect on presynaptic glutamate release, and show efficacy in several mGlu2/3-sensitive animal models of psychiatric disorders.

Discovery of allosteric potentiators for the metabotropic glutamate 2 receptor: synthesis and subtype selectivity of N-(4-(2-methoxyphenoxy)phenyl)-N-(2,2,2- trifluoroethylsulfonyl)pyrid-3-ylmethylamine.

This report describes recently discovered novel allosteric modulators of metabotropic glutamate2 (mGlu2) receptors. These pyridylmethylsulfonamides (e.g., 3) potentiate glutamate, shifting agonist potency by 2-fold. This effect was specific for mGlu2 (vs mGlu1,3-8 receptors). Also, 3 failed to potentiate a chimeric mGlu2/1 receptor, demonstrating the mGlu2 transmembrane region's critical involvement. In a fear-potentiated startle model, 3 showed anxiolytic activity that was prevented by mGlu2/3 antagonist pretreatment. Thus, these pyridylmethylsulfonamides represent the first mGlu2 receptor potentiators discovered.

SAR study of a subtype selective allosteric potentiator of metabotropic glutamate 2 receptor, N-(4-phenoxyphenyl)-N-(3-pyridinylmethyl)ethanesulfonamide.

The major excitatory neurotransmitter in the Central Nervous System is L-glutamic acid. As a result much attention has been given to the discovery of selective modulators of both the ionotropic glutamate receptors (iGluRs) and the metabotropic glutamate receptors (mGluRs). In this study we describe a novel class of subtype selective allosteric potentiators of the mGlu2 receptor. An active compound N-(4-phenoxyphenyl)-N-(3-pyridinylmethyl)ethanesulfonamide, LY181837, was identified in the course of compound screening. The synthesis of two series of analogs examined the structural requirements of the diaryl region of this compound. This SAR study also resulted in compounds with an increase in potency of over 100-fold where the most potent compound reported has EC(50)=14 nM.