Pierre Lestage

Effects of S 18986-1, a novel cognitive enhancer, on memory performances in an object recognition task in rats

(S)-2,3-dihydro-[3,4]cyclopentano-1,2,4-benzothiadiazine-1,1-dioxi de (S 18986-1) is a new compound that facilitates post-synaptic responses by modulating alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor-mediated synaptic responses and thus promotes long-term potentiation and potentiates (S)-AMPA-induced release of noradrenaline in rat brain slices. In the present study, the effects of S 18986-1 were evaluated on cognitive functions by using a one-trial object-recognition test in the Wistar rat, a test which measures a form of episodic memory in rodents. Recognition was measured by the ability of treated rats to discriminate between a familiar and a new object after a 24-h retention delay. Oral administrations with S 18986-1 (0.3 to 100 mg/kg) 1 h before each session of the test improved object recognition at concentrations as low as 0.3 mg/kg. Under the same conditions, the nootropic drug aniracetam was active at a dose of 10 mg/kg by i.p. route. S 18986-1 was still effective on the object-recognition test when it was administered 4 h before each of the three sessions. Furthermore, subchronic oral pretreatment (7 days) with S 18986-1 (0.3 to 30 mg/kg) also increased the recognition of the familiar object indicating that the animals failed to develop tolerance to repeated administrations with S 18986-1. Finally, the recognition of the familiar object was improved when S 18986-1 was administered before the recognition trial whereas the rats failed to recognise the familiar object when S 18986-1 was administered before the sample presentation trial only. Taken together, the results indicated that S 18986-1 facilitated a form of episodic memory in the rat, by improving the recognition of a familiar information (retention). Furthermore, S 18986-1 was long-acting and demonstrated a good oral bioavailability. These data confer on S 18986-1, a potential role in improving episodic memory impaired in neurodegenerative diseases and during aging.

New quinolinic derivatives as centrally active antioxidants

A series of new 1,2-dihydro and 1,2,3,4-tetrahydroquinolines, synthesized from the corresponding propargylaniline intermediates, have been developed as antioxidants for the potential treatment of pathologies implicating central oxidative stress.

Partial agonist and neuromodulatory activity of S 24795 for alpha7 nAChR responses of hippocampal interneurons

S 24795 evoked methyllycaconitine-sensitive inward currents in voltage-clamped hippocampal interneurons with maximum amplitude about 14% that of ACh-evoked responses. Experiments with rat alpha7 receptors expressed in Xenopus oocytes confirmed that S 24795 is a partial agonist of alpha7 nAChR with an EC(50) of 34+/-11 microM and I(max) of approximately 10% relative to ACh. When 60 microM ACh was co-applied to alpha7-expressing oocytes along with increasing concentrations of S 24795, there was a progressive decrease in response compared to the responses to 60 microM ACh alone (IC(50) 45+/-9 microM). The positive allosteric modulator 5-hydroxyindole potentiated ACh- and S 24795-evoked responses of alpha7 receptors in both oocytes and hippocampal interneurons. In hippocampal slice experiments, depending on the ACh concentrations in the application pipette and the ratio of ACh to S 24795, co-application of S 24795 with ACh variously increased, decreased, or had no effect on responses, compared to ACh alone. In order to estimate the effective dilution factor for the pressure application experiments, we tested alpha7 receptors in oocytes with ACh alone and in co-application with S 24795 at the same ratios as in the slice experiments, but at varying dilution factors. The pattern of interaction seen in the slice experiments was most closely matched under the conditions of a 3:100 dilution, suggesting that the pipette solution was diluted approximately 30-fold at the site of action. This dilution factor was consistent with the potency of ACh and S 24795 in the oocyte expression system (EC(50)s approximately 30 microM).

Synthesis, pharmacological and structural characterization, and thermodynamic aspects of GluA2-positive allosteric modulators with a 3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxide scaffold.

Positive allosteric modulators of ionotropic glutamate receptors are potential compounds for treatment of cognitive disorders, e.g., Alzheimers disease. The modulators bind within the dimer interface of the ligand-binding domain (LBD) and stabilize the agonist-bound conformation, thereby slowing receptor desensitization and/or deactivation. Here we describe the synthesis and pharmacological testing at GluA2 of a new generation of 3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxides. The most potent modulator 3 in complex with GluA2-LBD-L483Y-N754S was subjected to structural analysis by X-ray crystallography, and the thermodynamics of binding was studied by isothermal titration calorimetry. Compound 3 binds to GluA2-LBD-L483Y-N754S with a Kd of 0.35 μM (ΔH = -7.5 kcal/mol and -TΔS = -1.3 kcal/mol). This is the first time that submicromolar binding affinity has been achieved for this type of positive allosteric modulator. The major structural factor increasing the binding affinity of 3 seems to be interactions between the cyclopropyl group of 3 and the backbone of Phe495 and Met496.

Ring-Fused Thiadiazines as Core Structures for the Development of Potent AMPA Receptor Potentiators

Amongst ionotropic glutamatergic receptors, the AMPA receptor subtype has been recognized as a major contributor to the fast excitatory neurotransmission in the central nervous system and the expression and maintenance of longterm potentiation. This receptor subtype also represents an interesting target to develop innovative therapeutic drugs such as positive allosteric modulators (AMPA receptor potentiators) since the enhancement of AMPA signals is expected to be beneficial in the management of several neurological disorders such as depression, schizophrenia, Parkinsons disease and learning-memory deficits linked to Alzheimers disease. This article is dedicated to the use of (hetero) aromatic ring-fused thiadiazines (i.e. benzo- pyrido- and thienothiadiazines) as core structures for the discovery of new positive allosteric modulators of AMPA receptors. Recent advances exploring other chemotypes in the field of AMPA potentiators is the object of a separate review of the present issue.

Thermodynamic Characterization of New Positive Allosteric Modulators Binding to the Glutamate Receptor A2 Ligand-Binding Domain: Combining Experimental and Computational Methods Unravels Differences in Driving Forces

Positive allosteric modulation of the ionotropic glutamate receptor GluA2 presents a potential treatment of cognitive disorders, for example, Alzheimers disease. In the present study, we describe the synthesis, pharmacology, and thermodynamic studies of a series of monofluoro-substituted 3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxides. Measurements of ligand binding by isothermal titration calorimetry (ITC) showed similar binding affinities for the modulator series at the GluA2 LBD but differences in the thermodynamic driving forces. Binding of 5c (7-F) and 6 (no-F) is enthalpy driven, and 5a (5-F) and 5b (6-F) are entropy driven. For 5d (8-F), both quantities were equal in size. Thermodynamic integration (TI) and one-step perturbation (OSP) were used to calculate the relative binding affinity of the modulators. The OSP calculations had a higher predictive power than those from TI, and combined with the shorter total simulation time, we found the OSP method to be more effective for this setup. Furthermore, from the molecular dynamics simulations, we extracted the enthalpies and entropies, and along with the ITC data, this suggested that the differences in binding free energies are largely explained by the direct ligand-surrounding enthalpies. Furthermore, we used the OSP setup to predict binding affinities for a series of polysubstituted fluorine compounds and monosubstituted methyl compounds and used these predictions to characterize the modulator binding pocket for this scaffold of positive allosteric modulators.

Synthesis and Pharmacology of Mono-, Di-, and Trialkyl-Substituted 7-Chloro-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-Dioxides Combined with X-ray Structure Analysis to Understand the Unexpected Structure-Activity Relationship at AMPA Receptors

Positive allosteric modulators of 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA)-type ionotropic glutamate receptors are promising compounds for treatment of neurological disorders, for example, Alzheimers disease. Here, we report synthesis and pharmacological evaluation of a series of mono-, di-, or trialkyl-substituted 7-chloro-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxides, comprising in total 16 new modulators. The trisubstituted compounds 7b, 7d, and 7e revealed potent activity (EC2× = 2.7-4.3 μM; concentration of compound responsible for a 2-fold increase of the AMPA mediated response) as AMPA receptor potentiators in an in vitro cellular fluorescence assay (FLIPR). The 4-cyclopropyl compound 7f was found to be considerably less potent (EC2× = 60 μM), in contrast to previously described 4-monoalkyl-substituted benzothiadiazine dioxides for which the cyclopropyl group constitutes the best choice of substituent. 7b was subjected to X-ray structural analysis in complex with the GluA2 ligand-binding domain. We propose an explanation of the unexpected structure-activity relationship of this new series of mono-, di-, and trialkyl-substituted 1,2,4-benzothiadiazine 1,1-dioxide compounds. The methyl substituent in the 3-position directs the binding mode of the 1,2,4-benzothiadiazine 1,1-dioxide (BTD) scaffold. When a methyl substituent is present in the 3-position of the BTD, additional methyl substituents in both the 2- and 4-positions increase potency, whereas introduction of a 4-cyclopropyl group does not enhance potency of 2,3,4-alkyl-substituted BTDs. A hydrogen bond donor in the 2-position of the BTD is not necessary for modulator potency.

Effects of positive modulators of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors in a benzodiazepine-induced deficit of spatial discrimination in mice

Imbalance between GABAergic and glutamatergic neurotransmission has been recently hypothesized to trigger memory decline related either to ageing or to Alzheimer’s disease (AD). Thereby, benzodiazepine-induced anterograde amnesia has been construed as a model of hippocampal-related cognitive dysfunctions. Since spatial memory is altered both by ageing and by benzodiazepines such as alprazolam, we investigated the pharmacological sensitivity of alprazolam-induced deficit in a delayed spatial discrimination (SD) task, notably with positive allosteric modulators of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors. We showed that alprazolam (0.1 mg/kg intraperitoneally) induced memory impairments as compared with vehicle-treated mice. The oral administration of modulators of AMPA receptors (IDRA-21: 10 mg/kg; S18986: 3 and 10 mg/kg) reversed the alprazolam-induced deficits. This study is first to show evidence that reference treatments of AD, such as memantine (a NMDA receptor antagonist) at 3 mg/kg per os (po) and donepezil (an acetylcholinesterase inhibitor) at 1 mg/kg po, also reversed the alprazolam-induced amnesia. Given such results, the SD task emerges as a valuable novel task to screen pro-cognitive compounds. Thus, we highlight the efficacy of modulators of AMPA-type glutamate receptors to counteract alprazolam-induced spatial deficits. These results could be viewed alongside the imbalance between excitation and inhibition observed during normal and pathological ageing.

Involvement of nicotinergic mechanisms in thyrotropin-releasing hormone-induced neurologic recovery after concussive head injury in the mouse

A behavioral study was performed in an attempt to understand the neuronal mechanisms involved in the thyrotropin-releasing hormone (TRH)-induced improvement of consciousness after concussive head injury in the mouse. Intravenous administration of TRH dose dependently shortened the duration of unconsciousness after concussion in the mouse (ED50 = 3.2 mg/kg). The improvement of recovery evoked by TRH (3 mg/kg i.v.) after concussion was not affected by i.p. pretreatment with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine, alpha-methyl-para-tyrosine, p-chlorophenylalanine, scopolamine or methylscopolamine. However, mecamylamine or hexamethonium i.p. pretreatment completely inhibited the TRH-induced improvement of outcome in traumatic brain injury. The results imply that TRH-induced improvement of recovery after concussion is not associated with increased activity of monoaminergic neurons in the brain. These results suggest that the inhibitory effect of TRH upon unconsciousness after concussion in mice is mainly produced by activation of central cholinergic systems via nicotinic receptors whereas muscarinic receptors seem to be not implicated.