Synthesis and molecular docking of novel non-competitive antagonists of GluK2 receptor.

Here we present the synthesis, pharmacological activity, and molecular docking of novel non-competitive antagonists of GluK2 receptor. The compounds concerned are derivatives of indole and carbazole and are the second reported series of non-competitive antagonists of the GluK2 receptor (the first one was also published by our group). The activity of the indole derivatives is in the micromolar range, as in the case of the first series of non-competitive GluK2 receptor antagonists. We have found that designed carbazole derivatives are devoid of activity. Active indole derivatives interact with the transduction domain of the GluK2 receptor, i.e., the domain which links the transmembrane region of the receptor with the agonist-binding domain. The binding pocket is situated within one receptor subunit.

Structural studies, homology modeling and molecular docking of novel non-competitive antagonists of GluK1/GluK2 receptors.

Non-competitive ligands of kainate receptors have focused significant attention as medicinal compounds because they seem to be better tolerated than competitive antagonists and uncompetitive blocker of these receptors. Here we present structural studies (X-ray structure determination, NMR and MS spectra) of novel indole-derived non-competitive antagonists of GluK1/GluK2 receptors, homology models of GluK1 and GluK2 receptors based on novel AMPA receptor template as well as molecular docking of ligands to their molecular targets. We find that the allosteric site is in the receptor transduction domain, in one receptor subunit, not between the two subunits as it was indicated by our earlier studies.

Modeling of glutamate GluR6 receptor and its interactions with novel noncompetitive antagonists.

The study proposes the first complete model of an ionotropic glutamate receptor (GluR6). The model is in accordance with available experimental data from single-particle electron microscopy images and exhibits correct shape and dimensions and the appropriate symmetry: 2-fold in the N-terminal domain (NTD), ligand-binding domain (LBD), and external part of the transmembrane region, whereas it is 4-fold deeper in the channel. The methodology applied for GluR6 receptor model building was validated in the docking procedure of competitive and uncompetitive antagonists. The constructed model was used to study molecular interactions of novel noncompetitive GluR6 antagonists with their molecular target. A new binding site in the GluR6 receptor transduction domain has been identified. It is situated between two subunits in the receptor dimer. The following residues were recognized as crucial for interactions: Arg663A, Arg663B (M3-S2 linker), Ser809B (S2-M4 linker), and Phe553A (S1-M1 linker).

New GABA-modulating 1,2,4-oxadiazole derivatives and their anticonvulsant activity.

A series of 3- and 5-aryl-1,2,4-oxadiazole derivatives were prepared and tested for anticonvulsant activity in a variety of models. These 1,2,4-oxadiazoles exhibit considerable activity in both pentylenetetrazole (PTZ) and maximal electroshock seizure (MES) models. Compound 10 was protective in the PTZ model in rats with an oral ED(50) of 25.5mg/kg and in the MES model in rats with an oral ED(50) of 14.6mg/kg. Neurotoxicity (rotarod) was observed with an ED(50) of 335mg/kg. We found several oxadiazoles that acted as selective GABA potentiating compounds with no interaction to the benzodiazepine binding site.

Synthesis, pharmacology, and structure-activity relationships of novel imidazolones and pyrrolones as modulators of GABAA receptors.

New series of imidazolones and pyrrolones were synthesized. The compounds were tested regarding their anxiolytic properties due to modulation of the GABAA receptor response. Several derivatives exhibit considerable pharmacological activity while lacking the typical side effects of benzodiazepine receptor agonists. 1-(4-chlorophenyl)-4-morpholin-1-yl-1,5-dihydro-imidazol-2-one (2) and 1-(4-chlorophenyl)-4-piperidin-1-yl-1,5-dihydro-imidazol-2-one (3) were protective in the pentylenetetrazole test in rats with oral ED50 of 27.4 and 12.8 mg/kg and TD50 (rotarod) of >500 and 265 mg/kg, respectively. The minimum effective dose in the Vogel conflict test was 3 mg/kg for both compounds. Common structure-activity relationship and comparative molecular field analysis models of the various series of derivatives could be established which are in accordance with a GABAA mediated pharmacological action. The findings fit well into an established pharmacophore model. This model is refined by an additional steric restriction feature.

Characterization in rats of the anxiolytic potential of ELB139 [1-(4-chlorophenyl)-4-piperidin-1-yl-1,5-dihydro-imidazol-2-on], a new agonist at the benzodiazepine binding site of the GABAA receptor.

Benzodiazepines are among the most effective drugs for the treatment of anxiety disorders. However, their use is limited by undesired side effects, including sedation, development of tolerance, and drug abuse. The aim of this study was to evaluate the pharmacological profile of ELB139 [1-(4-chlorophenyl)-4-piperidin-1-yl-1,5-dihydro-imidazol-2-on] in different models of anxiety and to correlate these effects with its activity in vitro. ELB139 binds with an IC(50) of 1390 nM to the flunitrazepam binding site in rat forebrain cortical membranes. In rat hippocampal neurons, ELB139 potentiated GABA-induced currents without reaching the maximum effect of diazepam, indicating a partial benzodiazepine agonism. The potentiation was antagonized by the benzodiazepine antagonist flumazenil. ELB139 (10 and 30 mg/kg p.o.) was active in three different animal models of anxiety, i.e., in the elevated plus-maze, the light and dark box, and the Vogel conflict test. The anxiolytic activity in the elevated plus-maze was almost completely reversed by flumazenil (5 mg/kg i.p.), indicating that interaction with the benzodiazepine binding site is central to the pharmacological activity. No hint of sedation was observed at the doses tested in the three anxiety models and the open field. Also, no development of tolerance was observed within 6 weeks b.i.d. treatment with ELB139 in the elevated plus-maze test. In summary, ELB139 elicits strong effects on anxiety-related behavior in rats mediated by its benzodiazepine-like activity without showing sedation or the development of tolerance, a major side effect of benzodiazepines. These characteristics make the compound a prime candidate for clinical development.