Thomas C. Britton

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

RationaleTo 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 resultsA 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.ConclusionsTaken 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.

Structure-activity relationship of a series of diaminoalkyl substituted benzimidazole as neuropeptide Y Y1 receptor antagonists

A series of benzimidazoles (4) was synthesized and evaluated in vitro as potent and selective NPY Y1 receptor antagonists. Substitution of the piperidine nitrogen of 4 with appropriate R groups resulted in compounds with more than 80-fold higher affinity at the Y receptor compared to the parent compound 5 (R = H). The most potent benzimidazole in this series was 21 (Ki = 0.052 nM).

Targeting group II Metabotropic Glutamate (mGlu) receptors for the treatment of psychosis associated with alzheimer's disease: Selective activation of mGlu2 receptors amplifies β-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 Alzheimers 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 β-amyloid protein (Aβ) 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 Aβ-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 Aβ 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-β1. LY379268 lost its protective activity in neurons grown with astrocytes lacking mGlu3 receptors, indicating that protection against Aβ 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 Aβ 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 Aβ, whereas dual activation of mGlu2 and mGlu3 receptors is protective against Aβ-induced toxicity.

Diphenylpyrazolidinone and benzodiazepine cholecystokinin antagonists: A case of convergent evolution in medicinal chemistry

Abstract Two recently described classes of nonpeptide cholecystokinin receptor antagonists contain diphenylpyrazolidinone and benzodiazepine substructures, respectively. Although the origins and development of these series were completely independent, the low energy conformations predicted by modeling showed remarkable three-dimensional homology between the structures.

Structure-activity relationships of a series of 1-substituted-4-methylbenzimidazole neuropeptide Y-1 receptor antagonists.

The characterization of a novel series of NPY-1 receptor antagonists derived from the 4-methylbenzimidazole 4 is described. Appropriate substitution on the piperidyl nitrogen of 4 led to systematic increases in Y-1 receptor affinity, to approximately 50-fold, and to the discovery of the importance of a second basic substituent.

Structure-activity relationships of A series of benzothiophene-derived NPY Y1 antagonists : Optimization of the C-2 side chain

A series of benzo[b]thiophene-derived NPY-1 receptor antagonists is described. Systematic modification of the C-2 substituent afforded a 1000-fold range in Y1 receptor affinity. Appropriate substitution at the ortho and para positions of the C-2 phenyl ether produced a synergistic effect on Y1 binding affinity, which led to the discovery of the most active ligands, 12t (K(i) = 15 nM), 12u (K(i) = 11 nM), and 12v (K(i) = 13 nM).

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.

Novel bicyclo[3.1.0]hexane analogs as antagonists of metabotropic glutamate 2/3 receptors for the treatment of depression

Negative modulators of metabotropic glutamate 2 & 3 receptors demonstrate antidepressant-like activity in animal models and hold promise as novel therapeutic agents for the treatment of major depressive disorder. Herein we describe our efforts to prepare and optimize a series of conformationally constrained 3,4-disubstituted bicyclo[3.1.0]hexane glutamic acid analogs as orthosteric (glutamate site) mGlu2/3 receptor antagonists. This work led to the discovery of a highly potent and efficacious tool compound 18 (hmGlu2 IC50 46±14.2nM, hmGlu3 IC50=46.1±36.2nM). Compound 18 showed activity in the mouse forced swim test with a minimal effective dose (MED) of 1mg/kg ip. While in rat EEG studies it exhibited wake promoting effects at 3 and 10mg/kg ip without any significant effects on locomotor activity. Compound 18 thus represents a novel tool molecule for studying the impact of blocking mGlu2/3 receptors both in vitro and in vivo.

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.