The interactions of apamin and tetraethylammonium are differentially affected by single mutations in the pore mouth of small conductance calcium-activated potassium (SK) channels

in Biochemical Pharmacology (2013), 85

Valine residues in the pore region of SK2 (V366) and SK3 (V520) were replaced by either an alanine or a phenylalanine to evaluate the impact on the interactions with the allosteric blocker apamin. Unlike ... [more ▼]

Valine residues in the pore region of SK2 (V366) and SK3 (V520) were replaced by either an alanine or a phenylalanine to evaluate the impact on the interactions with the allosteric blocker apamin. Unlike TEA which showed high sensitivity to phenylalanine mutated channels, the binding affinity of apamin to the phenylalanine mutants was strongly reduced. In addition, currents from phenylalanine mutants were largely resistant to block by apamin. On the other hand, when the valine residue was replaced by an alanine residue, an increase of the binding affinity and the amount of block by apamin was observed for alanine mutated SK2 channels, but not for mutated SK3 channels. Interestingly, the VA mutation reduced the sensitivity to TEA. In silico data confirmed these experimental results. Therefore, such mutations in the pore region of SK channels show that the three-dimensional structure of the SK tetramers can be disorganized in the outer pore region leading to reduced interaction of apamin with its target. [less ▲]

PHARMACOMODULATIONS DU WAY-100635 : DE NOUVELLES PISTES DANS LA CONCEPTION D’ANTAGONISTES SÉLECTIFS DES RÉCEPTEURS 5-HT1A

Poster (2012, May 24)

Le composé WAY-100635 est un outil pharmacologique abondamment utilisé dans l’exploration des récepteurs sérotoninergiques 5-HT1A. Dès lors, cette molécule de référence devrait présenter une sélectivité ... [more ▼]

Le composé WAY-100635 est un outil pharmacologique abondamment utilisé dans l’exploration des récepteurs sérotoninergiques 5-HT1A. Dès lors, cette molécule de référence devrait présenter une sélectivité importante pour sa cible. Cependant, des travaux récents ont démontré que, à côté de son activité antagoniste des récepteurs 5-HT1A, le WAY-100635 possédait également une affinité et activité conséquentes vis-à-vis des récepteurs dopaminergiques D4, ce qui pourrait limiter son utilisation comme outil pharmacologique. Dans ce contexte, nous avons entrepris diverses modulations structurales de cette molécule de manière à augmenter sa sélectivité vis-à-vis des récepteurs 5-HT1A. Cette sélectivité a été augmentée de manière significative lors du remplacement de la chaîne latérale basique par un groupement 4-phénylpipérazine ou 4-phényl-1,2,3,6-tétrahydropyridine. Une évaluation biologique plus approfondie des deux composés comprenant un profil d’affinité élargi à d’autres récepteurs a confirmé leur sélectivité vis-à-vis des récepteurs 5-HT1A. De plus, des expériences électrophysiologiques sur tranches de cerveau. [less ▲]

Interactions of apamin with pore mutated SK3 channels

Poster (2012, March 16)

In the present work, we have tested the impact of the replacement of valine residues in the pore region of SK3 (520) by either an alanine or a phenylalanine residue in terms of the interactions of apamin ... [more ▼]

In the present work, we have tested the impact of the replacement of valine residues in the pore region of SK3 (520) by either an alanine or a phenylalanine residue in terms of the interactions of apamin with these mutants in comparison with the corresponding native channels. Replacing valine residue at position 520 of the SK3 channel by a phenylalanine significantly increased the sensitivity of the channel to be blocked by tetraethylammonium (TEA) as previously reported. Indeed, an aromatic residue, such as a phenylalanine or a tyrosine, is frequently found in the pore region of several potassium channels more sensitive to TEA than SK channels. We measured the affinity (Kd) of apamin in saturation experiments and studied SK currents in transfected cells using patch clamp techniques. In parallel, molecular modelling techniques were used to examine the impact of these local modifications on the interaction of apamin with the corresponding channels. The presence of a phenylalanine in the pore region of potassium channels led to a higher sensitivity for TEA by creating more hydrophobic interactions as found by the docking procedure. In the in vitro binding experiments, the phenylalanine mutant (SK3VF) displayed a very low affinity for apamin. In patch clamp experiments, the SK current was only very partially blocked by apamin in the SK3VF mutant. Furthermore, apamin displayed an affinity and a blocking activity for the alanine mutant close to that for the corresponding native channels. In conclusion, the presence of a bulky and hydrophobic residue at a position near the pore mouth of SK3 channels has a negative impact on their interactions with apamin. [less ▲]

New pyridobenzoxazepine derivatives derived from 5-(4-methylpiperazin-1-yl)-8-chloro-pyrido[2,3-b][1,5]benzoxazepine (JL13): chemical synthesis and pharmacological evaluation

in Journal of Medicinal Chemistry (2012), 55(1572), 1582

A series of new pyridobenzoxazepine derivatives with various heterocyclic amine side chains were synthesized in order to explore two main parameters related to the distal basic nitrogen. These compounds ... [more ▼]

A series of new pyridobenzoxazepine derivatives with various heterocyclic amine side chains were synthesized in order to explore two main parameters related to the distal basic nitrogen. These compounds were tested for their affinity for dopamine D2L, D4, serotonin 5-HT1A, 5-HT2A and adrenergic 2A receptors in comparison with 5-(4-methylpiperazin-1-yl)-8-chloro-pyrido[2,3-b][1,5]benzoxazepine, JL13 (1) and other diarylazepine derivatives. In terms of multi-receptor target strategy, 2 and 5 present the most promising in vitro binding profile. Bulky, polar and more flexible side chains are not favourable in this context. 2 and 5 were tested in adult rats to evaluate their long-term effects on dopamine and serotonin receptors density in different brain areas. Similar to 1 and other second-generation antipsychotic drugs, repeated treatment with 2 significantly increased D1 and D4 receptors in nucleus accumbens and caudate putamen, and D2 receptors in medial prefrontal cortex and hippocampus while 5 significantly increased D2 and D4 receptors in nucleus accumbens. In addition, 2 increased 5-HT1A and decreased 5-HT2A receptors in cerebral cortex. In contrast, 5 did not alter levels of any 5-HT receptor subtype in any brain region examined. These results encourage further development of 2 as a novel second-generation antipsychotic agent. [less ▲]

Ion channel modulators: more diversity than previously thought

in Chembiochem : A European Journal of Chemical Biology (2011), 12(12), 1808-1812

Ion channel function can be modified in various ways. For example, numerous studies have shown that currents through voltage-gated ion channels are affected by pore block or modification of voltage ... [more ▼]

Ion channel function can be modified in various ways. For example, numerous studies have shown that currents through voltage-gated ion channels are affected by pore block or modification of voltage-dependence of activation/inactivation. Recent experiments performed on various ion channels show that allosteric modulation is an important mechanism to affect channel function. For instance, in KCa2 (formerly SK) channels, the prototypic “blocker” apamin prevents conduction by an allosteric mechanism, while TRPV1 channels are prevented from closing by a tarantula toxin, DkTx, through an interaction with residues located away from the selectivity filter. The recent evidence therefore suggests that, in several ion channels, the region around the outer mouth of the pore is rich in binding sites which may be exploited therapeutically. These discoveries also suggest that the pharmacological vocabulary should be adapted to define these various actions. [less ▲]

Crucial role of a shared extracellular loop in apamin sensitivity and maintenance of pore shape of small-conductance calcium-activated potassium (SK) channel

in Proceedings of the National Academy of Sciences of the United States of America (2011), 108(45), 18488-18493

Interaction of clozapine and its nitrenium ion with rat D2 dopamine receptors: in vitro binding and computational study

in Journal of Computer-Aided Molecular Design (2011), 25(2), 163-169

The interaction of diazepine analogues like clozapine or olanzapine with D2 receptor was greatly affected by a mixture of HRP/H2O2 known to induce the formation of nitrenium ion. Unlike diazepine ... [more ▼]

The interaction of diazepine analogues like clozapine or olanzapine with D2 receptor was greatly affected by a mixture of HRP/H2O2 known to induce the formation of nitrenium ion. Unlike diazepine derivatives, the oxidative mixture had low impact on the affinity of oxa- and thiazepine derivatives such as loxapine, clothiapine or JL13 for the D2 receptor. Molecular docking simulations revealed a huge difference between the mode of interaction of clozapine nitrenium ion and the parent drug. Electronic and geometric changes of the tricyclic ring system caused by the oxidation appeared to prevent the compound finding the correct binding mode and could therefore explain the difference observed in binding affinities. [less ▲]

Binding properties of clozapine and related compounds on native D2 dopamine receptors in normal and oxidative medium

Poster (2010, November 16)

Despite the presence of several side effects, clozapine remains a valuable drug in treating schizophrenia. The presence of haematological toxicity was proposed to be related to the formation of nitrenium ... [more ▼]

Despite the presence of several side effects, clozapine remains a valuable drug in treating schizophrenia. The presence of haematological toxicity was proposed to be related to the formation of nitrenium species (1). Indeed, nitrogen derivatives like clozapine or olanzapine are very sensitive to oxidation while oxygen or sulphur isosteres such as loxapine, clothiapine and JL13, possess a very low sensitivity to oxidation (2-4). In the present study, we explore the impact of oxidation conditions on the binding of these drugs on native rat dopamine D2 receptors. Rats brains were quickly removed after cerebral dislocation and dissected on ice to get striata. After weighting, tissues were homogenized in buffer and washed three times by centrifugation. The final pellet was dispersed in the appropriate volume of incubation buffer (Tris 50 mM, MgCl2 5 mM, EDTA (Na2) 1 mM buffered at pH 7.4 with 4N HCl) depending on the experimental conditions. In oxidative conditions, horseradish peroxidase (1.25 µg/tube) and H2O2 (50 µM) were added to the incubation buffer. [3H]-Spiperone was used as radioligand and the non specific binding was determined in the presence of haloperidol (10 µM). Incubation temperature and time were 27°C and 60 min respectively. Competition experiments were done with different molecules such as haloperidol and various tricyclic derivatives. In our previous studies (2,3), we had observed that compounds like clozapine or olanzapine are significantly affected by oxidative conditions. In the present report, we show that this sensitivity is also associated with a dramatic decrease of binding affinity. Unlike such diazepine analogues, the binding of loxapine and JL13, two oxygen isosteres is slightly affected in oxidative conditions. Firstly, these results show that the distal nitrogen is not affected by the oxidative conditions. Secondly, the nitrenium formation (1) might lead to a tridimensional change that would reduce the interactions in the binding pocket. The oxidative effect of HRP/H2O2 mixture can be prevented by addition of ascorbic acid to the incubation medium. Thus depending on the oxidant character of the extracellular medium in physiological or pathophysiological conditions, interaction of molecules with different targets can be modified significantly. [less ▲]

Etude du mode de liaison des canaux potassiques de type SK et l’apamine par modélisation moléculaire

Poster (2010, May 20)

Parmi les canaux ioniques impliqués dans le contrôle de l'activité neuronale, les canaux potassiques calcium-dépendants de basse conductance, dénommés canaux SK, constituent une cible thérapeutique ... [more ▼]

Parmi les canaux ioniques impliqués dans le contrôle de l'activité neuronale, les canaux potassiques calcium-dépendants de basse conductance, dénommés canaux SK, constituent une cible thérapeutique intéressante. En effet, ils sous-tendent la posthyperpolarisation ("AfterHyperPolarization") de durée moyenne (mAHP) qui limite l'excitabilité de divers types de neurones du système nerveux central (SNC). A ce jour, 3 types de sous-unités, SK1, SK2 et SK3, ont été identifiés dans différentes régions du cerveau. Le blocage sélectif de ces canaux pourrait être bénéfique dans le traitement de divers troubles du SNC comme la maladie de Parkinson (SK3), la dépression (SK3) ou encore les désordres cognitifs (SK2) (Liégeois et al., 2003 ; Pedarzani et al., 2008). Jusqu’à présent, le site d’interaction entre les canaux SK et leurs bloqueurs n’a pas encore été précisément élucidé. Dans ce contexte, nous avons entrepris la modélisation de ces canaux par homologie comparative en se basant sur la structure cristalline du canal potassique KCSA (Doyle et al., 1998). La construction de ces canaux constitue la première étape dans la détermination des requis structuraux essentiels à l’affinité de bloqueurs et à la compréhension des modes de liaison de ces ligands. Le mode de liaison de l’apamine, bloqueur peptidique issu du venin d’abeille, a été ensuite exploré par « docking ». Afin de confirmer ce site de liaison potentiel, des expériences de mutagénèse dirigée ont été réalisées. Les premiers canaux mutants testés dans des expériences électrophysiologiques par la technique de « patch clamp » ont permis de valider certaines données théoriques. Grâce à cette stratégie, nous espérons préciser le mécanisme d'action des bloqueurs des canaux SK et, idéalement, découvrir des pistes pour concevoir des bloqueurs sélectifs. [less ▲]

Synthesis and in vitro binding studies of piperazine-alkyl-naphthamides: Impact of homology and sulphonamide/carboxamide bioisosteric replacement on the affinity for 5-HT1A, alpha(2A), D4.2, D3 and D2L receptors

in Bioorganic & Medicinal Chemistry Letters (2010), 20