Design and Synthesis of Selurampanel, a Novel Orally Active and Competitive AMPA Receptor Antagonist.

A series of potent quinazolinedione sulfonamide antagonists of the α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptor were designed and synthesized. The structure-activity relationships (SAR) and in vivo activity of the series were investigated. In particular, compound 1 S (selurampanel; N-[7-isopropyl-6-(2-methylpyrazol-3-yl)-2,4-dioxo-1H-quinazolin-3-yl]methanesulfonamide) has shown excellent oral potency against maximal electroshock seizure (MES)-induced generalized tonic-clonic seizures in rodents as well as significant activity in patients suffering from various forms of epilepsy. The X-ray crystal structure of selurampanel bound to the AMPA receptor hGluA was also obtained.

AQW051, a novel, potent and selective α7 nicotinic ACh receptor partial agonist: pharmacological characterization and phase I evaluation.

BACKGROUND AND PURPOSE: Activation of the α7 nicotinic ACh receptor (nACh receptor) is considered an attractive target for the treatment of cognitive impairment associated with neurological disorders. Here we describe the novel α7-nACh receptor agonist AQW051 as a promising drug candidate for this indication. EXPERIMENTAL APPROACH: AQW051 was functionally characterized in vitro and cognitive effects evaluated in rodent behavioural models. Pharmacokinetics and tolerability were evaluated in three phase I placebo-controlled studies in 180 healthy subjects. KEY RESULTS: In vitro, AQW051 bound with high affinity to α7-nACh receptors and stimulated calcium influx in cells recombinantly expressing the human α7-nACh receptor. In vivo, AQW051 demonstrated good oral bioavailability and rapid penetration into the rodent brain. AQW051 administered over a broad dose range facilitated learning/memory performance in the object recognition and social recognition test in mice and the water maze model in aged rats. Clinically, AQW051 was well tolerated in healthy young and elderly subjects, with an adverse event (AE) profile comparable with placebo. No serious AEs were reported and all AEs were either mild or moderate in severity at single oral doses up to 200 mg and multiple daily doses up to 75 mg. Once-daily oral administration of AQW051 resulted in continuous exposure and a two- to threefold accumulation compared with steady state was achieved by 1 week. CONCLUSIONS AND IMPLICATIONS: These data support further development of AQW051 as a cognitive-enhancing agent, as a therapeutic, for example, in Alzheimer's disease or schizophrenia.

Gastrin-releasing peptide signaling plays a limited and subtle role in amygdala physiology and aversive memory.

Links between synaptic plasticity in the lateral amygdala (LA) and Pavlovian fear learning are well established. Neuropeptides including gastrin-releasing peptide (GRP) can modulate LA function. GRP increases inhibition in the LA and mice lacking the GRP receptor (GRPR KO) show more pronounced and persistent fear after single-trial associative learning. Here, we confirmed these initial findings and examined whether they extrapolate to more aspects of amygdala physiology and to other forms of aversive associative learning. GRP application in brain slices from wildtype but not GRPR KO mice increased spontaneous inhibitory activity in LA pyramidal neurons. In amygdala slices from GRPR KO mice, GRP did not increase inhibitory activity. In comparison to wildtype, short- but not long-term plasticity was increased in the cortico-lateral amygdala (LA) pathway of GRPR KO amygdala slices, whereas no changes were detected in the thalamo-LA pathway. In addition, GRPR KO mice showed enhanced fear evoked by single-trial conditioning and reduced spontaneous firing of neurons in the central nucleus of the amygdala (CeA). Altogether, these results are consistent with a potentially important modulatory role of GRP/GRPR signaling in the amygdala. However, administration of GRP or the GRPR antagonist (D-Phe(6), Leu-NHEt(13), des-Met(14))-Bombesin (6-14) did not affect amygdala LTP in brain slices, nor did they affect the expression of conditioned fear following intra-amygdala administration. GRPR KO mice also failed to show differences in fear expression and extinction after multiple-trial fear conditioning, and there were no differences in conditioned taste aversion or gustatory neophobia. Collectively, our data indicate that GRP/GRPR signaling modulates amygdala physiology in a paradigm-specific fashion that likely is insufficient to generate therapeutic effects across amygdala-dependent disorders.

6-Amino quinazolinedione sulfonamides as orally active competitive AMPA receptor antagonists.

A new set of quinazolinedione sulfonamide derivatives as competitive AMPA receptor antagonist with improved properties compared to 1 is disclosed. By modulating physico-chemical properties, compound 29 was identified with a low ED(50) of 5.5mg/kg in an animal model of anticonvulsant activity after oral dosage.

Quinazolinedione sulfonamides: a novel class of competitive AMPA receptor antagonists with oral activity.

Quinazoline-2,4-diones with a sulfonamide group attached to the N(3) ring atom constitute a novel class of competitive AMPA receptor antagonists. One of the synthesized compounds, 28, shows nanomolar receptor affinity, whereas other examples of the series display oral anticonvulsant activity in animal models.

The selective nicotinic acetylcholine receptor alpha7 agonist JN403 is active in animal models of cognition, sensory gating, epilepsy and pain.

Several lines of evidence suggest that the nicotinic acetylcholine receptor alpha7 (nAChR alpha7) is involved in central nervous system disorders like schizophrenia and Alzheimer's disease as well as in inflammatory disorders like sepsis and pancreatitis. The present article describes the in vivo effects of JN403, a compound recently characterized to be a potent and selective partial nAChR alpha7 agonist. JN403 rapidly penetrates into the brain after i.v. and after p.o. administration in mice and rats. In the social recognition test in mice JN403 facilitates learning/memory performance over a broad dose range. JN403 shows anxiolytic-like properties in the social exploration model in rats and the effects are retained after a 6h pre-treatment period and after subchronic administration. The effect on sensory inhibition was investigated in DBA/2 mice, a strain with reduced sensory inhibition under standard experimental conditions. Systemic administration of JN403 restores sensory gating in DBA/2 mice, both in anaesthetized and awake animals. Furthermore, JN403 shows anticonvulsant potential in the audiogenic seizure paradigm in DBA/2 mice. In the two models of permanent pain tested, JN403 produces a significant reversal of mechanical hyperalgesia. The onset was fast and the duration lasted for about 6h. Altogether, the present set of data suggests that nAChR alpha7 agonists, like JN403 may be beneficial for improving learning/memory performance, restoring sensory gating deficits, and alleviating pain, epileptic seizures and conditions of anxiety.

JN403, in vitro characterization of a novel nicotinic acetylcholine receptor alpha7 selective agonist.

This report describes the in vitro features of a novel selective nicotinic acetylcholine receptor (nAChR) alpha7 agonist, JN403, (S)-(1-Aza-bicyclo[2.2.2]oct-3-yl)-carbamic acid (S)-1-(2-fluoro-phenyl)-ethyl ester. JN403 was evaluated in a number of in vitro systems of different species, at recombinant receptors using radioligand binding, signal transduction and electrophysiological studies. When using [(125)I] alpha-bungarotoxin (alpha-BTX) as a radioligand, JN403 has high affinity for human recombinant nAChR alpha7 (pK(D)=6.7). Functionally, JN403 is a partial and potent agonist at human nAChR alpha7. The compound stimulates calcium influx in GH3 cells recombinantly expressing the human nAChR with an pEC(50) of 7.0 and an E(max) of 85% (compared to the full agonist epibatidine). In Xenopus oocytes expressing human nAChR alpha7 JN403 induces inward currents with an pEC(50) of 5.7 and an E(max) of 55%. In both recombinant systems JN403 is a partial agonist and the agonistic effects are blocked after pre-administration of methyllycaconitine (MLA, 100nM), a nAChR alpha7 antagonist. In functional calcium influx assays, JN403 displays a significantly lower potency for other subtypes of human nAChRs like alpha4beta2, alpha3beta4, alpha1beta1gammadelta as well as 5HT(3) receptors when tested functionally as an antagonist (pIC(50)<4.8) and is devoid of agonistic activity (pEC(50)<4). Similarly, JN403 shows low binding activity at a wide panel of neurotransmitter receptors. Thus, JN403 is a potent and selective nAChR alpha7 agonist and will be a useful tool for the characterization of nAChR alpha7 mediated effects both in vitro and in vivo.

AMPA receptor antagonists: potential therapeutic applications.

The current review will focus on the recent patents for AMPA receptor antagonists and their claims, evidence for their therapeutic effectiveness in the treatment of epilepsy and their potential role in psychiatric and neurodegenerative disorders. It will also highlight the proposed mechanisms of action and the implications thereof for our current understanding of the biomolecular basis of these pathologies. It will conclude with a summary of what we know, but also point out the remaining uncertainties, especially as this relates to the claims in the patent under discussion.

Role of NMDA receptor subtypes in governing the direction of hippocampal synaptic plasticity.

Activation of N-methyl-d-aspartate subtype glutamate receptors (NMDARs) is required for long-term potentiation (LTP) and long-term depression (LTD) of excitatory synaptic transmission at hippocampal CA1 synapses, the proposed cellular substrates of learning and memory. However, little is known about how activation of NMDARs leads to these two opposing forms of synaptic plasticity. Using hippocampal slice preparations, we showed that selectively blocking NMDARs that contain the NR2B subunit abolishes the induction of LTD but not LTP. In contrast, preferential inhibition of NR2A-containing NMDARs prevents the induction of LTP without affecting LTD production. These results demonstrate that distinct NMDAR subunits are critical factors that determine the polarity of synaptic plasticity.

Behavioral characterization of the novel GABAB receptor-positive modulator GS39783 (N,N'-dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine): anxiolytic-like activity without side effects associated with baclofen or benzodiazepines.

The role of GABAB receptors in various behavioral processes has been largely defined using the prototypical GABAB receptor agonist baclofen. However, baclofen induces sedation, hypothermia and muscle relaxation, which may interfere with its use in behavioral paradigms. Although there is much evidence for a role of the inhibitory neurotransmitter GABA in the pathophysiology of anxiety, the role of GABAB receptors in these disorders is largely unclear. We recently identified GS39783 (N,N'-dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine) as a selective allosteric positive modulator at GABAB receptors. The aim of the present study was to broadly characterize the effects of GS39783 in well-validated rodent models for motor activity, cognition, and anxiety. The following tests were included: locomotor activity in rats and mice, rotarod and traction tests (including determinations of core temperature) in mice, passive avoidance in mice and rats, elevated plus maze in rats, elevated zero maze in mice and rats, stress-induced hyperthermia in mice, and pentobarbital- and ethanol-induced sleep in mice. Unlike baclofen and/or the benzodiazepine chlordiazepoxide, GS39783 had no effect in any of the tests for locomotion, cognition, temperature, or narcosis. Most interestingly, GS39783 had anxiolytic-like effects in all the tests used. Overall, the data obtained here suggest that positive modulation of GABAB receptors may serve as a novel therapeutic strategy for the development of anxiolytics, with a superior side effect profile to both baclofen and benzodiazepines.

N,N'-Dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine (GS39783) and structurally related compounds: novel allosteric enhancers of gamma-aminobutyric acidB receptor function.

N,N'-Dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine (GS39783) and structurally related compounds are described as novel allosteric enhancers of GABA(B) receptor function. They potentiate GABA-stimulated guanosine 5'-O-(3-[35S]thio)triphosphate ([35S]GTPgammaS) binding to membranes from a GABA(B)(1b/2)-expressing Chinese hamster ovary cell line at low micromolar concentrations, but do not stimulate [35S]GTPgammaS binding by themselves. Similar effects of GS39783 are seen on native GABA(B) receptors in rat brain membranes. Concentration-response curves with GABA in the presence of different fixed concentrations of GS39783 reveal an increase of both the potency and maximal efficacy of GABA at the GABA(B)(1b/2) heterodimer. In radioligand binding experiments, GS39783 reduces the kinetic rate constants of the association and dissociation of [3H]3-aminopropylphosphinic acid, resulting in a net increase in affinity for the agonist radioligand. In equilibrium binding experiments (displacement of the antagonist ligand [3H]CGP62349), GS39783 increases agonist affinities. Agonist displacement curves are biphasic, probably reflecting the G protein-coupled and uncoupled states of the receptor. The proportion of the high-affinity component is increased by GS39783, suggesting that the G protein coupling of the receptor is also promoted by the positive modulator. We also show that GS39783 has modulatory effects in cellular assays such as GABA(B) receptor-mediated activation of inwardly rectifying potassium channels in Xenopus oocytes and Ca2+ signaling in human embryonic kidney 293 cells. In a more physiological context, GS39783 is shown to suppress paired pulse inhibition in rat hippocampal slices. This effect is reversed by the competitive GABA(B) receptor antagonist CGP55845A and is produced most likely by enhancing the effect of synaptically released GABA at presynaptic GABA(B) receptors.

The anticonvulsant gabapentin (neurontin) does not act through gamma-aminobutyric acid-B receptors.

The actions of the anticonvulsant gabapentin [1-(aminomethyl)cyclohexaneacetic acid, Neurontin] have been somewhat enigmatic until recently, when it was claimed to be a gamma-aminobutyric acid-B (GABA(B)) receptor agonist acting exclusively at a heterodimeric complex containing the GABA(B(1a)) splice variant (Mol Pharmacol 2001;59:144-152). In this study, we have investigated the effects of gabapentin on recombinant GABA(B(1a)) and GABA(B(1b)) receptors coexpressed with GABA(B(2)) in five different functional recombinant assays, its ability to inhibit [(3)H]GABA binding in a GABA(B) receptor-selective binding assay using rat synaptic membranes, and its ability to inhibit transient lower esophageal sphincter relaxations in Labrador retriever dogs. Up to a concentration of 1 mM, gabapentin displayed no agonistic effects on either the GABA(B(1a,2)) or the GABA(B(1b,2)) heterodimer, when these were expressed in Xenopus laevis oocytes or mammalian cells and assayed by means of electrophysiology, calcium mobilization, inositol phosphate, and fluorometry assays. Gabapentin did not displace [(3)H]GABA from GABA(B) receptor sites in rat synaptic membranes. Finally, in contrast to the classic GABA(B) receptor agonist baclofen, gabapentin was unable to inhibit transient lower esophageal sphincter relaxations in dogs. Because of high levels of GABA(B(1a)) in the canine nodose ganglion, this finding indirectly supports the inactivity of gabapentin on the GABA(B(1a,2)) heterodimer demonstrated in various in vitro assays. In light of these results, we find it highly questionable that gabapentin is a GABA(B) receptor agonist. Hence, the anticonvulsive effects of the compound have to arise from GABA(B) receptor-independent mechanisms. This also implies that the first GABA(B) receptor splice variant-selective ligand remains to be discovered.

5-Phosphonomethylquinoxalinediones as competitive NMDA receptor antagonists with a preference for the human 1A/2A, rather than 1A/2B receptor composition.

NMDA antagonists derived from 5-phosphonomethyl-1,4-dihydroquinoxaline-2,3-dione (3a) are potent anticonvulsant agents, and display strong protective effects in the electroshock-induced convulsion assay in mice. Their preference for the human NMDAR 1A/2A over 1A/2B subunit composition was optimized, leading to (1RS,1'S)-PEAQX (9r), which shows a >100-fold selectivity.