Jeffrey M. Schkeryantz

N-(4-((2-(trifluoromethyl)-3-hydroxy-4-(isobutyryl)phenoxy)methyl)benzyl)-1-methyl-1H-imidazole-4-carboxamide (THIIC), a Novel Metabotropic Glutamate 2 Potentiator with Potential Anxiolytic/Antidepressant Properties: In Vivo Profiling Suggests a Link between Behavioral and Central Nervous System Neurochemical Changes

The normalization of excessive glutamatergic neurotransmission through the activation of metabotropic glutamate 2 (mGlu2) receptors may have therapeutic potential in a variety of psychiatric disorders, including anxiety/depression and schizophrenia. Here, we characterize the pharmacological properties of N-(4-((2-(trifluoromethyl)-3-hydroxy-4-(isobutyryl)phenoxy)methyl)benzyl)-1-methyl-1H-imidazole-4-carboxamide (THIIC), a structurally novel, potent, and selective allosteric potentiator of human and rat mGlu2 receptors (EC50 = 23 and 13 nM, respectively). THIIC produced anxiolytic-like efficacy in the rat stress-induced hyperthermia assay and the mouse stress-induced elevation of cerebellar cGMP and marble-burying assays. THIIC also produced robust activity in three assays that detect antidepressant-like activity, including the mouse forced-swim test, the rat differential reinforcement of low rate 72-s assay, and the rat dominant-submissive test, with a maximal response similar to that of imipramine. Effects of THIIC in the forced-swim test and marble burying were deleted in mGlu2 receptor null mice. Analysis of sleep electroencephalogram (EEG) showed that THIIC had a sleep-promoting profile with increased non-rapid eye movement (REM) and decreased REM sleep. THIIC also decreased the dark phase increase in extracellular histamine in the medial prefrontal cortex and decreased levels of the histamine metabolite tele-methylhistamine (t-MeHA) in rat cerebrospinal fluid. Collectively, these results indicate that the novel mGlu2-positive allosteric modulator THIIC has robust activity in models used to predict anxiolytic/antidepressant efficacy, substantiating, at least with this molecule, differentiation in the biological impact of mGlu2 potentiation versus mGlu2/3 orthosteric agonism. In addition, we provide evidence that sleep EEG and CSF t-MeHA might function as viable biomarker approaches to facilitate the translational development of THIIC and other mGlu2 potentiators.

The pharmacology of LXR.

Liver X receptors (LXRs) are members of the nuclear hormone receptor superfamily of ligand-activated transcription factors. Two LXRs (LXRalpha and LXRbeta) were initially characterized as orphan members of this superfamily with disparate patterns of tissue expression. These two receptors later were recognized as sterol-responsive with the ability to directly bind several oxysterol metabolites. Many LXR target genes have been identified that implicate these receptors in a variety of physiological processes including cholesterol transport and metabolism, glucose metabolism, and inflammation. Synthetic LXR ligands have been designed with the potential to treat disorders such as atherosclerosis and diabetes. In this review, we describe the potential utility of LXR ligands in the treatment of disease.

Activation of metabotropic glutamate (mGlu)2 receptors suppresses histamine release in limbic brain regions following acute ketamine challenge

In the present study we demonstrated that ketamine, an NMDA antagonist and possible psychotomimetic, increases extracellular histamine (HA) in the rat brain. We then examined the ability of the group II mGlu receptor agonist LY379268 to modulate the ketamine evoked increases in HA release in three limbic brain regions. Ketamine (25 mg/kg) increased HA in the medial prefrontal cortex (mPFC), ventral hippocampus (vHipp) and the nucleus accumbens (NAc) shell. LY379268 administered alone was without effect on basal HA efflux in the mPFC or vHipp but modestly decreased HA efflux in the NAc shell. Administration of LY379268 (3 and 10 mg/kg) prior to ketamine significantly attenuated the HA response in the mPFC, vHipp and the NAc shell. The inhibitory effects of LY379268 in the mPFC were mimicked by the systemic administration of the mGlu2 receptor positive allosteric modulator CBiPES (60 mg/kg). Finally, local perfusion experiments revealed that the effects of LY379268 on ketamine evoked HA efflux appear to be mediated by mGlu2 receptors outside the PFC as the intra-mPFC perfusion of LY379268 (100 microM or 300 microM) failed to attenuate ketamine evoked increases in HA efflux. Together, these novel observations reveal an effect of ketamine on histaminergic transmission in limbic brain areas and provide further insight into the possible antipsychotic mechanism of action of mGlu2/3 receptor agonists.

Group II metabotropic glutamate receptor type 2 allosteric potentiators prevent sodium lactate-induced panic-like response in panic-vulnerable rats

Rats with chronic inhibition of GABA synthesis by infusion of l-allyglycine, a glutamic acid decarboxylase inhibitor, into their dorsomedial/perifornical hypothalamus are anxious and exhibit panic-like cardio-respiratory responses to treatment with intravenous (i.v.) sodium lactate (NaLac) infusions, in a manner similar to what occurs in patients with panic disorder. We previously showed that either NMDA receptor antagonists or metabotropic glutamate receptor type 2/3 receptor agonists can block such a NaLac response, suggesting that a glutamate mechanism is contributing to this panic-like state. Using this animal model of panic, we tested the efficacy of CBiPES and THIIC, which are selective group II metabotropic glutamate type 2 receptor allosteric potentiators (at 10–30mg/kg i.p.), in preventing NaLac-induced panic-like behavioral and cardiovascular responses. The positive control was alprazolam (3mg/kg i.p.), a clinically effective anti-panic benzodiazepine. As predicted, panic-prone rats given a NaLac challenge displayed NaLac-induced panic-like cardiovascular (i.e. tachycardia and hypertensive) responses and “anxiety” (i.e. decreased social interaction time) and “flight” (i.e. increased locomotion) -associated behaviors; however, systemic injection of the panic-prone rats with CBiPES, THIIC or alprazolam prior to the NaLac dose blocked all NaLac-induced panic-like behaviors and cardiovascular responses. These data suggested that in a rat animal model, selective group II metabotropic glutamate type 2 receptor allosteric potentiators show an anti-panic efficacy similar to alprazolam.

Molecular determinants of LXRα agonism

Liver X receptors (LXRs) are nuclear receptors that participate in the regulation of cholesterol, bile acid, and glucose metabolism. Despite the identification of the natural oxysterol and nonsteroidal ligands for LXRalpha, little is known about the structure of the LXRalpha ligand-binding domain (LBD). We constructed a three-dimensional (3D) homology model of the LBD of LXRalpha based on the crystal structure of the retinoic acid receptor gamma (RARgamma) and all-trans retinoic acid complex. We combined molecular modeling and classical structure-function techniques to define the interactions between the LBD and three structurally diverse ligands, 22(R)-hydroxycholesterol (22RHC), N-(2,2,2-trifluoro-ethyl)-N-[4-(2,2,2-trifluoro-1-hydroxy-1-trifluoromethyl-ethyl)-phenyl]-benzenesulfonamide (T0901317) and (3-[3-[(2-chloro-3-trifluoromethyl-benzyl)-(2,2-diphenyl-ethyl)-amino]-propoxy]-phenyl)-acetic acid (GW3965). Sixteen individual amino acid point mutations were made in the predicted ligand-binding cavity of the LBD, and each of these mutant receptors was assessed for their ability to be activated by these three ligands. The majority of individual mutations resulted in lack of activation by all three ligands. Two residues were identified that resulted in a significant increase in basal activity while retaining responsiveness to the ligands. Interestingly, a number of residues were identified that appear to be selective in their response to a particular ligand, indicating that these three ligands recognize distinct structural components within the ligand-binding cavity. These data, together with our docking study, enable us to identify the amino acids that coordinate the interaction of both steroidal and non-steroidal ligands in the ligand-binding pocket of LXRalpha.

Synthesis of (−)-11-O-Debenzoyltashironin: Neurotrophic Sesquiterpenes Cause Hyperexcitation

11-O-Debenzoyltashironin (1) is a member of the neurotrophic sesquiterpenes, trace plant metabolites that enhance neurite outgrowth in cultured neurons. We report its synthesis in six steps from a butenolide heterodimer via its likely biosynthetic precursor, 3,6-dideoxy-10-hydroxypseudoanisatin, here identified as the chain tautomer of 1. Access to the tashironin chemotype fills a gap in a comparison set of convulsive and neurotrophic sesquiterpenes, which we hypothesized to share a common target. Here we show that both classes mutually hyperexcite rat cortical neurons, consistent with antagonism of inhibitory channels and a mechanism of depolarization-induced neurite outgrowth.

Further evaluation of the potential anxiolytic activity of imidazo[1,5-a][1,4]diazepin agents selective for α2/3-containing GABAA receptors

Abstract Positive allosteric modulators of GABAA receptors transduce a host of beneficial effects including anxiolytic actions. We have recently shown that bioavailability and anxiolytic‐like activity can be improved by eliminating the ester functionality in imidazo[1,5‐a][1,4]diazepines. In the present series of experiments, we further substantiate the value of heterocyle replacement of the ester for potential treatment of anxiety. None of three esters was active in a Vogel conflict test in rats that detects anxiolytic drugs like diazepam. Compounds 7 and 8, ester bioisosters, were selective for alpha 2 and 3 over alpha 1‐containing GABAA receptors but also had modest efficacy at GABAA alpha 5‐containing receptors. Compound 7 was efficacious and potent in this anxiolytic‐detecting assay without affecting non‐punished responding. The efficacies of the esters and of compound 7 were predicted from their efficacies as anticonvulsants against the GABAA antagonist pentylenetetrazole (PTZ). In contrast, the related structural analog, compound 8, did not produce anxiolytic‐like effects in rats despite anticonvulsant efficacy. These data thus support the following conclusions: 1) ancillary pharmacological actions of compound 8 might be responsible for its lack of anxiolytic‐like efficacy despite its efficacy as an anticonvulsant 2) esters of imidazo[1,5‐a][1,4]diazepines do not demonstrate anxiolytic‐like effects in rats due to their low bioavailability and 3) replacement of the ester function with suitable heterocycles markedly improves bioavailability and engenders molecules with the opportunity to have potent and efficacious effects in vivo that correspond to human anxiolytic actions. HighlightsNovel imidazo[1,5‐a][1,4]diazepines were explored as potential anxiolytic drugs.Three esters were not active in a Vogel conflict test in rats that detects anxiolytic drugs like diazepam.Two new bioisosters were selective for alpha 2 and 3 over alpha 1‐containing GABAA receptors.Compound 7 was efficacious and potent in the Vogel conflict test.

Negative allosteric modulation of alpha 5-containing GABA A receptors engenders antidepressant-like effects and selectively prevents age-associated hyperactivity in tau-depositing mice

RationaleAssociated with frank neuropathology, patients with Alzheimer’s disease suffer from a host of neuropsychiatric symptoms that include depression, apathy, agitation, and aggression. Negative allosteric modulators (NAMs) of α5-containing GABAA receptors have been suggested to be a novel target for antidepressant action. We hypothesized that pharmacological modulation of this target would engender increased motivation in stressful environments.MethodsWe utilized electrophysiological recordings from Xenopus oocytes and behavioral measures in mice to address this hypothesis.ResultsIn the forced-swim assay in mice that detects antidepressant drugs, the α5β3γ2 GABAΑ receptor NAM, RY-080 produced a marked antidepressant phenotype. Another compound, PWZ-029, was characterized as an α5β3γ2 receptor NAM of lower intrinsic efficacy in electrophysiological studies in Xenopus oocytes. In contrast to RY-080, PWZ-029 was only moderately active in the forced-swim assay and the α5β3γ2 receptor antagonist, Xli-093, was not active at all. The effects of RY-080 were prevented by the non-selective benzodiazepine receptor antagonist flumazenil as well as by the selective ligands, PWZ-029 and Xli-093. These findings demonstrate that this effect of RY-080 is driven by negative allosteric modulation of α5βγ2 GABAA receptors. RY-080 was not active in the tail-suspension test. We also demonstrated a reduction in the age-dependent hyperactivity exhibited by transgenic mice that accumulate pathological tau (rTg4510 mice) by RY-080. The decrease in hyperactivity by RY-080 was selective for the hyperactivity of the rTg4510 mice since the locomotion of control strains of mice were not significantly affected by RY-080.Conclusionsα5βγ2 GABAA receptor NAMs might function as a pharmacological treatment for mood, amotivational syndromes, and psychomotor agitation in patients with Alzheimer’s and other neurodegenerative disorders.

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.

Bioisosteres of ethyl 8-ethynyl-6-(pyridin-2-yl)-4 H -benzo[ f ]imidazo [1,5- a ][1,4]diazepine-3-carboxylate (HZ-166) as novel alpha 2,3 selective potentiators of GABA A receptors: Improved bioavailability enhances anticonvulsant efficacy

&NA; HZ‐166 has previously been characterized as an &agr;2,3‐selective GABAA receptor modulator with anticonvulsant, anxiolytic, and anti‐nociceptive properties but reduced motor effects. We discovered a series of ester bioisosteres with reduced metabolic liabilities, leading to improved efficacy as anxiolytic‐like compounds in rats. In the present study, we evaluated the anticonvulsant effects KRM‐II‐81 across several rodent models. In some models we also evaluated key structural analogs. KRM‐II‐81 suppressed hyper‐excitation in a network of cultured cortical neurons without affecting the basal neuronal activity. KRM‐II‐81 was active against electroshock‐induced convulsions in mice, pentylenetetrazole (PTZ)‐induced convulsions in rats, elevations in PTZ‐seizure thresholds, and amygdala‐kindled seizures in rats with efficacies greater than that of diazepam. KRM‐II‐81 was also active in the 6 Hz seizure model in mice. Structural analogs of KRM‐II‐81 but not the ester, HZ‐166, were active in all models in which they were evaluated. We further evaluated KRM‐II‐81 in human cortical epileptic tissue where it was found to significantly‐attenuate picrotoxin‐ and AP‐4‐induced increases in firing rate across an electrode array. These molecules generally had a wider margin of separation in potencies to produce anticonvulsant effects vs. motor impairment on an inverted screen test than did diazepam. Ester bioisosters of HZ‐166 are thus presented as novel agents for the potential treatment of epilepsy acting via selective positive allosteric amplification of GABAA signaling through &agr;2/&agr;3‐containing GABA receptors. The in vivo data from the present study can serve as a guide to dosing parameters that predict engagement of central GABAA receptors. HighlightsKRM‐II‐81, a positive modulator of &agr; 2,3 GABAA receptors was characterized.KRM‐II‐81 was efficacious in multiple rodent anticonvulsant models.KRM‐II‐81 was also active in human cortical epileptic tissue.KRM‐II‐81 had a reduced motor impairing effects vs diazepam.KRM‐II‐81 and analogs are valuable new research tools.