Ester to amide substitution improves selectivity, efficacy and kinetic behavior of a benzodiazepine positive modulator of GABAA receptors containing the ?5 subunit.

ABSTRACT: We have synthesized and characterized MP-III-022 ((R)-8-ethynyl-6-(2-fluorophenyl)-N,4-dimethyl-4H-benzo[f]imidazo[1,5-a][1,4]diazepine-3-carboxamide) in vitro and in vivo as a binding- and efficacy-selective positive allosteric modulator of GABAA receptors containing the ?5 subunit (?5GABAARs). By approximation of the electrophysiological responses which the estimated free rat brain concentrations can induce, we demonstrated that convenient systemic administration of MP-III-022 in the dose range 1-10mg/kg may result in a selective potentiation, over a wide range from mild to moderate to strong, of ?5??2 GABAA receptors. For eliciting a comparable range of potentiation, the widely studied parent ligand SH-053-2'F-R-CH3 containing an ester moiety needs to be administered over a much wider dose range (10-200mg/kg), but at the price of activating non-?5 GABAARs as well as the desired ?5GABAARs at the highest dose. At the dose of 10mg/kg, which elicits a strong positive modulation of ?5GABAARs, MP-III-022 caused mild, but significant muscle relaxation, while at doses 1-10mg/kg was devoid of ataxia, sedation or an influence on the anxiety level, characteristic for non-selective benzodiazepines. As an amide compound with improved stability and kinetic properties, MP-III-022 may represent an optimized tool to study the influence of ?5GABAARs on the neuronal pathways related to CNS disorders such as schizophrenia, Alzheimer's disease, Down syndrome or autism.

SUBMITTER: Stamenic TT 

PROVIDER: S-EPMC5107132 | biostudies-other | 2016 Nov

REPOSITORIES: biostudies-other