AMPA Receptor Positive Modulators Research Articles

Tarps differentially affect the pharmacology of ampakines

Transmembrane AMPA receptor regulatory proteins (TARPs) govern AMPA receptor cell surface expression and distinct physiological properties including agonist affinity, desensitization and deactivation kinetics. The prototypical TARP, STG or γ2 and TARPs γ3, γ4, γ7 and γ8 are all expressed to varying degrees in the mammalian brain and differentially regulate AMPAR gating parameters. Positive allosteric AMPA receptor modulators or ampakines alter receptor rates of agonist binding/unbinding, channel opening and can offset receptor desensitization and deactivation. The effects of the two ampakines, CX614 and cyclothiazide (CTZ) were evaluated on homomeric GluR1-flip receptors and GluR2-flop receptors expressed on HEK293 cells by transient transfection with or without different TARPs γ2, γ3, γ4 or γ8 genes. γ4 was the most robust TARP in increasing the affinities of CX614 and CTZ on GluR1-flip receptors, but had no such effect on GluR2-flop receptors. However, γ8 gave the most significant increases in affinities of CX614 and CTZ on GluR2-flop. These data show that TARPs differentially affect the surface expression and kinetics of the AMPA receptor, as well as the pharmacology of ampakines for the AMPA receptor. The modulatory effects of TARPs on ampakine pharmacology are complex, being dependent on both the TARP subtype and the AMPA receptor subtypes/isoforms.

Novel positive allosteric modulator of AMPA-receptors based on tricyclic scaffold

Molecular modeling, synthesis, and activity evaluation of a novel positive allosteric modulator of the AMPA receptor, 6-[4-methoxy-3-(1H-pyrazol-1-ylmethyl)benzyl]-1,11-dimethyl-3,6,9-triazatricyclo[7.3.1.13,11]tetradecane-4,8,12-trione, are presented. The main point of the design was to fill the interdomain cavity of GluA2 ligand binding domains based on the cyclothiazide binding mode. Electrophysiological studies showed high potentiation of the kainate-induced currents (pECmax ∼ 12).

The reduction in glutamate release is predictive of cognitive and emotional alterations that are corrected by the positive modulator of AMPA receptors S 47445 in perinatal stressed rats

S 47445 is a positive modulator of glutamate AMPA-type receptors, possessing neurotrophic and enhancing synaptic plasticity effects as well as pro-cognitive and anti-stress properties. Here, the drug was assessed in the perinatal stress (PRS) rat model, known to have a high predictive validity with monoaminergic antidepressants. The effects of a chronic treatment (i.p.) with S 47445 were investigated on risk-taking, motivational and cognitive behavior. S 47445 (1 and 10 mg/kg) increased the exploration of the elevated-plus maze and light/dark box as well as the time spent grooming in the splash test, and improved social memory in PRS rats. Also, the effects of S 47445 were examined on the synaptic neurotransmission. The reduced depolarization-evoked glutamate release induced by PRS was corrected with S 47445 (10 mg/kg). Remarkably, the reduction in glutamate release induced by PRS and corrected by S 47445 chronic treatment was correlated with all the behavioral changes. S 47445 at 10 mg/kg also normalized the lower levels of synaptic vesicle-associated proteins in ventral hippocampus in PRS rats. Finally, S 47445 reversed the decrease of mGlu5 receptors, GR and OXTR induced by PRS. Collectively, in an animal model of stress-related disorders, S 47445 corrected the imbalance between excitatory and inhibitory neurotransmission by regulating glutamate-evoked release that is predictive of PRS behavioral alterations, and also normalized the reduction of trafficking of synaptic vesicles induced by PRS. These results support the interest of glutamatergic-based therapeutic strategies to alleviate stress-related disorders.

Stargazin differentially modulates ampakine gating kinetics and pharmacology

It was previously reported that Stargazin (STG) enhances the surface expression of AMPA receptors, controls receptor gating and slows channel desensitization as an auxiliary subunit of the receptors. Ampakines are a class of AMPA receptor positive allosteric modulators that modify rates of transmitter binding, channel activity and desensitization parameters. As such, they have shown efficacy in animal models of neurodegenerative diseases, where excitatory synaptic transmission is compromised. Given the functional similarities between STG and ampakines, the current study sought to probe interactions between STG and ampakine gating properties. The effects of the high impact ampakines, CX614 and cyclothiazide (CTZ), were compared with homomeric GluR1-flip (Glur1i) and GluR2-flop (Glur2o) receptors expressed in HEK293 cells by transient transfection with or without STG gene. STG dramatically enhanced the surface expression of AMPA receptors and increased glutamate-induced steady-state currents during desensitization. STG also increased ratios of 500 μM kainate and 500 μM glutamate activated steady-state currents. STG reduced association rates of ampakines and differentially affected the dissociation rates for both CX614 and CTZ on desensitized receptors. The estimated Kd value for CX614 was lowered from 340 μM to 70 μM, whereas that for CTZ was lowered from 170 μM to 6 μM by STG. The data suggest that Stargazin can dramatically alter the conformation of the receptor dimer interface where CX614 and CTZ are known to bind. This work also demonstrates the importance of considering STG interactions when developing ampakines to treat neurodegenerative diseases in which AMPAergic signaling is compromised.

Functional characterization of AMPA receptor positive allosteric modulators PF-04958242 and LY-451395

Functional characterization of AMPA receptor positive allosteric modulators PF-04958242 and LY-451395

Synergistic enhancing-memory effect of donepezil and S 47445, an AMPA positive allosteric modulator, in middle-aged and aged mice

Positive allosteric modulators of AMPA receptors (AMPA-PAMs) are described to facilitate cognitive processes in different memory-based models. Among them, S 47445 is a novel potent and selective AMPA-PAM. In order to assess its efficacy after repeated administration, S 47445 effect was evaluated in two aging-induced memory dysfunction tasks in old mice, one short-term working memory model evaluated in a radial maze task and one assessing contextual memory performance. S 47445 was shown to improve cognition in both models sensitive to aging. In fact, administration of S 47445 at 0.3 mg/kg (s.c.) reversed the age-induced deficits of the working memory model whatever the retention interval. Moreover, in the contextual task, S 47445 also reversed the age-induced deficit at all tested doses (from 0.03 to 0.3 mg/kg, p.o.). Since donepezil, an acetylcholinesterase inhibitor, induces only moderate symptomatic effects on memory in Alzheimer’s disease patients, an alternative strategy for treatment of cognitive symptoms could be to act simultaneously on both glutamatergic AMPA receptors and cholinergic pathways by combining pharmacological treatments. The present study further examined such effects by assessing combinations of S 47445 and donepezil given orally during 9 days in aged C57/Bl6J mice using contextual memory task (CSD) and the working memory model of serial alternation task (AT). Interestingly, a significant synergistic memory-enhancing effect was observed with the combination of donepezil at 0.1 mg/kg with S 47445 at 0.1 mg/kg p.o. in the CSD or with S 47445 at 0.1 and 0.3 mg/kg in AT in comparison to compounds given alone and without any pharmacokinetic interaction.

Structural requirements for molecular design of positive allosteric modulators of AMPA receptor

Positive allosteric modulators of AMPA receptor are prospective for the development of safe and efficacious agents for the correction of disruption of the central nervous system functions. Joint application of molecular docking, MFTA and CoMFA QSAR modelling, and pharmacophore analysis affords a consistent picture of structural requirements for molecular design of novel promising bivalent modulators with high activity, including overall twisted-staple shape of a molecule, hydrophobic central core, and polar hydrogen bond acceptor groups in peripheral parts of a molecule.

Upregulation of neurotrophins by S 47445, a novel positive allosteric modulator of AMPA receptors in aged rats

At molecular levels, it has been shown that aging is associated with alterations in neuroplastic mechanisms. In this study, it was examined if the altered expression of neurotrophins observed in aged rats could be corrected by a chronic treatment with S 47445 (1–3–10mg/kg, p.o.), a novel selective positive allosteric modulator of the AMPA receptors. Both the mRNA and the protein levels of the neurotrophins Bdnf, NT-3 and Ngf were specifically measured in the prefrontal cortex and hippocampus (ventral and dorsal) of aged rats. It was found that 2-week-treatment with S 47445 corrected the age-related deficits of these neurotrophins and/or positively modulated their expression in comparison to vehicle aged rats in the range of procognitive and antidepressant active doses in rodents.Collectively, the ability of S 47445 to modulate various neurotrophins demonstrated its neurotrophic properties in two major brain structures involved in cognition and mood regulation suggesting its therapeutic potential for improving several diseases such as Alzheimer’s disease and/or Major Depressive Disorders.

Comparative studies of AMPA receptor positive allosteric modulators PF‐04958242 and PF‐04531686

Fast excitatory transmission in the central nervous system is mediated by α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptors responding to the endogenous neurotransmitter L‐glutamate. Dysfunction of AMPA receptors has been associated with various neurological and neuropsychiatric disorders, but therapeutic targeting of these channels has proved difficult due to the preponderance of side effects associated with AMPA receptor agonists. Positive allosteric modulators (PAMs) of AMPA receptors are thus conceptually attractive therapeutics because they rely on endogenous glutamate signaling to potentiate excitatory signaling. The objective of this work is to study the effects of two PAMs, PF‐04958242 and PF‐04531686, on the biophysical properties of recombinant and native AMPA receptors, with the expectation that the comparative data will prove informative for pro‐cognitive preclinical or clinical studies with these small molecules.We expressed a wide variety of AMPA receptor constructs with and without auxiliary subunits in HEK293T/17 cells, and characterized the effects of PAMs on currents elicited by fast‐application of glutamate. Both PAMs increased glutamate‐evoked current amplitudes and completely eliminated desensitization of all AMPA receptors containing the flip splice isoform, whereas desensitization of currents from flop‐containing receptors was slowed to differing degrees. At saturating PAM concentrations, PF‐04531686 slowed deactivation of GluA1 and GluA4 receptors to a greater degree than PF‐04958242.Comparable effects were seen on deactivation of excitatory synaptic currents (EPSCs) recorded from hippocampal CA1 neurons in slice preparations from wildtype mice. Application (1 mM) of PF‐04531686 slowed both evoked and spontaneous EPSC decays by 3‐fold; in contrast, PF‐04958242 slowed EPSCs 1.5‐fold. At a lower concentration (300 nM), EPSCs were also slowed by PF‐04531686, but not PF‐04958242. There was no effect on paired‐pulse ratio at any concentration of either PAM. These results show that both PAMs slow the decay of EPSCs, resulting from their pharmacological actions on AMPA receptor decay rates. We predict from these data that both PAMs will impact cognition, but that PF‐04958242 might have less risk of unwanted mechanism‐mediated side‐effects due to its more modest modulatory action on synaptic AMPA receptor function.Support or Funding InformationThis project was supported by a contract from Pfizer Neuroscience.

Pharmacological characterization of N-[(2S)-5-(6-fluoro-3-pyridinyl)-2, 3-dihydro-1H-inden-2-yl]-2-propanesulfonamide: a novel, clinical AMPA receptor positive allosteric modulator.

AMPA receptor positive allosteric modulators represent a potential therapeutic strategy to improve cognition in people with schizophrenia. These studies collectively constitute the preclinical pharmacology data package used to build confidence in the pharmacology of this molecule and enable a clinical trial application. [N-[(2S)-5-(6-fluoro-3-pyridinyl)-2,3-dihydro 1H-inden-2-yl]-2-propanesulfonamide] (UoS12258) was profiled in a number of in vitro and in vivo studies to highlight its suitability as a novel therapeutic agent. We demonstrated that UoS12258 is a selective, positive allosteric modulator of the AMPA receptor. At rat native hetero-oligomeric AMPA receptors, UoS12258 displayed a minimum effective concentration of approximately 10nM in vitro and enhanced AMPA receptor-mediated synaptic transmission at an estimated free brain concentration of approximately 15nM in vivo. UoS12258 reversed a delay-induced deficit in novel object recognition in rats after both acute and sub-chronic dosing. Sub-chronic dosing reduced the minimum effective dose from 0.3 to 0.03mg·kg-1 . UoS12258 was also effective at improving performance in two other cognition models, passive avoidance in scopolamine-impaired rats and water maze learning and retention in aged rats. In side-effect profiling studies, UoS12258 did not produce significant changes in the maximal electroshock threshold test at doses below 10mg·kg-1 . We conclude that UoS12258 is a potent and selective AMPA receptor modulator exhibiting cognition enhancing properties in several rat behavioural models superior to other molecules that have previously entered clinical evaluation.

Neuropeptide cycloprolylglycine is an endogenous positive modulator of AMPA receptors.

We have previously shown that neuropeptide cycloprolylglycine (CPG) increases the content of brain-derived neurotrophic factor (BDNF) in the culture of neuronal cells under normal conditions and in pathology. This is the first study to show that CPG at a physiological concentration of 10-6 M significantly enhances the transmembrane AMPA currents in rat cerebellar Purkinje cells. Thus, CPG is a positive endogenous modulator of AMPA receptors. It was assumed that the neuropsychotropic effects of CPG are implemented as a result of BDNF accumulation after the activation of AMPA receptors by this neuropeptide.

The frontal cortex as a network hub controlling mood and cognition: Probing its neurochemical substrates for improved therapy of psychiatric and neurological disorders.

The highly-interconnected and neurochemically-rich frontal cortex plays a crucial role in the regulation of mood and cognition, domains disrupted in depression and other central nervous system disorders, and it is an important site of action for their therapeutic control. For improving our understanding of the function and dysfunction of the frontal cortex, and for identifying improved treatments, quantification of extracellular pools of neuromodulators by microdialysis in freely-moving rodents has proven indispensable. This approach has revealed a complex mesh of autoreceptor and heteroceptor interactions amongst monoaminergic pathways, and led from selective 5-HT reuptake inhibitors to novel classes of multi-target drugs for treating depression like the mixed α2-adrenoceptor/5-HT reuptake inhibitor, S35966, and the clinically-launched vortioxetine and vilazodone. Moreover, integration of non-monoaminergic actions resulted in the discovery and development of the innovative melatonin receptor agonist/5-HT2C receptor antagonist, Agomelatine. Melatonin levels, like those of corticosterone and the "social hormone", oxytocin, can now be quantified by microdialysis over the full 24 h daily cycle. Further, the introduction of procedures for measuring extracellular histamine and acetylcholine has provided insights into strategies for improving cognition by, for example, blockade of 5-HT6 and/or dopamine D3 receptors. The challenge of concurrently determining extracellular levels of GABA, glutamate, d-serine, glycine, kynurenate and other amino acids, and of clarifying their interactions with monoamines, has also been resolved. This has proven important for characterizing the actions of glycine reuptake inhibitors that indirectly augment transmission at N-methyl-d-aspartate receptors, and of "glutamatergic antidepressants" like ketamine, mGluR5 antagonists and positive modulators of AMPA receptors (including S47445). Most recently, quantification of the neurotoxic proteins Aβ42 and Tau has extended microdialysis studies to the pathogenesis of neurodegenerative disorders, and another frontier currently being broached is microRNAs. The present article discusses the above themes, focusses on recent advances, highlights opportunities for clinical "translation", and suggests avenues for further progress.

AMPA Receptor Positive Allosteric Modulators: Potential for the Treatment of Neuropsychiatric and Neurological Disorders.

The neurotransmitter glutamate and its receptors have long been of interest to scientists involved in pharmaceutical research since dysfunction of the glutamatergic signalling pathway has been associated with the pathophysiology of several psychiatric and neurological disorders. The research on AMPAR positive allosteric modulators offers opportunities to modulate fast excitatory synaptic transmission and identify new potential therapeutic agents for a range of neurodiseases. The field of AMPAR modulators continues to be a dynamic area of drug discovery with a pronounced diversification of the chemotypes explored in recent years. This article reviews literature published in this area in the last 6 years, focusing on the new core templates, some derived from high-throughput screens, with an emphasis on structure-activity relationships, drug metabolism and pharmacokinetics properties, and pharmacological profiles of these series.

P.2.e.003 - The positive modulator of AMPA receptors, S 47445, improved behavior, cognitive, neurochemical and synaptic proteins modifications induced by prenatal restraint stress

The aim of this study was to evaluate the efficacy and tolerability of lacosamide (LCM) both as add-on therapy and monotherapy in patients with temporal lobe epilepsy (TLE) based on an observational, prospective, multicenter study.We enrolled 100 patients (mean age: 43.4 ± 12.53 years, 57 females) with nonlesional TLE and TLE with hippocampal sclerosis (HS) that did not respond to the first drug and who were referred to epilepsy centers of the University of Catanzaro, University of Palermo, IRCSS Neuromed of Pozzilli, and Otto-von-Guericke University of Magdeburg. In this open-label, multicenter trial, patients were initiated on oral LCM as add-on therapy to first AED monotherapy or as a later add-on to two concomitant AEDs. Seizure frequency changes and adverse events were recorded for at least six months after LCM was added.Fourteen patients dropped out because of positive MRI findings other than HS. Patients received LCM at 200–400 mg/day. Fifty-eight out of these 86 patients with seizures that were previously drug-resistant had reduced seizure frequency after introduction of LCM. Forty-five out of 86 patients were classified as responders (12 were seizure-free, 33 achieved a reduction > 50%). Interestingly, five patients out of 86 achieved seizure freedom for at least one year and progressively switched to monotherapy with LCM, and all five remained seizure-free at follow-up (6–48 months).Our results may suggest that LCM at doses of 200 to 400 mg/day reduces seizure frequency in adults with TLE regardless of the presence of HS, and that it may be considered as a first add-on treatment for patients with pharmacoresistant TLE.

Pharmacophore analysis of positive allosteric modulators of AMPA receptors

A 3D QSAR study of a set of positive allosteric modulators of AMPA receptors was performed using the CoMFA approach. It was shown that the van der Waals component introduces the major contribution to the predicted pEC50 values, while the contribution of the electrostatic component is minor. The pharmacophore hypothesis for positive allosteric modulators was generated and validated.

Sensing Allosteric Modulator Binding to AMPA Receptors at the Glutamate-Binding Site

Positive allosteric modulators of AMPA receptors (GluAs) stabilize the activated GluA structure by binding to the glutamate-binding domain (LBD) dimer interface. By adding contacts across the dimer interface, allosteric modulators strengthen the LBD dimer and inhibit desensitization-linked dimer disruption. Structurally diverse molecules can occupy the interface to fill various pockets and act as LBD dimerizers. Functionally, allosteric modulators exert a primary allosteric effect by stabilizing the open channel; however, allosteric modulators with different dimer interface binding patterns lead to differing impacts on agonist site binding affinity. Here, we examine the secondary allosteric effects on the glutamate-binding site. Using nuclear magnetic resonance (NMR) spectroscopy, we observed the global backbone changes on the isolated GluA2 LBD as a result of allosteric modulator binding. Spectral changes at the dimer interface correlate well with allosteric modulator binding sites on bound X-ray crystal structures. The backbone residues near the agonist-binding site are also affected differently depending on the orientation of allosteric modulator binding. Further, allosteric modulator binding to the LBD induces local environmental changes at the agonist site as reported by NMR active nuclei on the LBD-bound agonist. By improving the molecular understanding of GluA allosteric modulators in the context of secondary agonist-site effects, our results provide further guidance for rational drug design.

Kinetic Contributions to Gating by Interactions Unique to N-methyl-d-aspartate (NMDA) Receptors

Among glutamate-gated channels, NMDA receptors produce currents that subside with unusually slow kinetics, and this feature is essential to the physiology of central excitatory synapses. Relative to the homologous AMPA and kainate receptors, NMDA receptors have additional intersubunit contacts in the ligand binding domain that occur at both conserved and non-conserved sites. We examined GluN1/GluN2A single-channel currents with kinetic analyses and modeling to probe these class-specific intersubunit interactions for their role in glutamate binding and receptor gating. We found that substitutions that eliminate such interactions at non-conserved sites reduced stationary gating, accelerated deactivation, and imparted sensitivity to aniracetam, an AMPA receptor-selective positive modulator. Abolishing unique contacts at conserved sites also reduced stationary gating and accelerated deactivation. These results show that contacts specific to NMDA receptors, which brace the heterodimer interface within the ligand binding domain, stabilize actively gating receptor conformations and result in longer bursts and slower deactivations. They support the view that the strength of the heterodimer interface modulates gating in both NMDA and non-NMDA receptors and that unique interactions at this interface are responsible in part for basic differences between the kinetics of NMDA and non-NMDA currents at glutamatergic synapses.

Novel bivalent positive allosteric modulators of AMPA receptor.

A positive allosteric modulator of AMPA receptors has been designed using computer-aided molecular modeling techniques. It possessed a record high experimentally confirmed potency in the picomolar concentration range and belongs to a new type of bivalent AMPA receptor ligands containing bicyclo[3.3.1]nonane scaffold. The suggested structure could serve as a basis for further optimization and development of drugs for the treatment of neurodegenerative diseases, cognition enhancement, and improvement of memory.

In vitro characterization of s44858: A positive allosteric modulator of ampa receptors and GluN2B selective non-competitive nmda receptors antagonist

In vitro characterization of s44858: A positive allosteric modulator of ampa receptors and GluN2B selective non-competitive nmda receptors antagonist

In vivo characterization of s44858, a positive allosteric modulator of ampa receptors and GluN2B selective non-competitive nmda antagonist

In vivo characterization of s44858, a positive allosteric modulator of ampa receptors and GluN2B selective non-competitive nmda antagonist