Characterization of (R,S)‐5,7‐di‐tert‐butyl‐3‐hydroxy‐3‐trifluoromethyl‐3H‐benzofuran‐2‐one as a positive allosteric modulator of GABA_B receptors

Abstract

Background and purpose: As baclofen is active in patients with anxiety disorders, GABA B receptors have been implicated in the modulation of anxiety. To avoid the side effects of baclofen, allosteric enhancers of GABA B receptors have been studied to provide an alternative therapeutic avenue for modulation of GABA B receptors. The aim of this study was to characterize derivatives of (R,S)-5,7-di-tert-butyl-3-hydroxy-3-trifluoromethyl-3H-benzofuran-2-one (rac-BHFF) as enhancers of GABA B receptors. Experimental approach: Enhancing properties of rac-BHFF were assessed in the Chinese hamster ovary (CHO)-Ga16-hGABA B(1a,2a) cells by Fluorometric Imaging Plate Reader and GTPg[35 S]-binding assays, and in rat hippocampal slices by population spike (PS) recordings. In vivo activities of rac-BHFF were assessed using the loss of righting reflex (LRR) and stressinduced hyperthermia (SIH) models. Key results: In GTPg[35 S]-binding assays, 0.3 mM rac-BHFF or its pure enantiomer ( þ )-BHFF shifted the GABA concentrationresponse curve to the left, an effect that resulted in a large increase in both GABA potency (by 15.3-and 87.3-fold) and efficacy (149% and 181%), respectively. In hippocampal slices, rac-BHFF enhanced baclofen-induced inhibition of PS of CA1 pyramidal cells. In an in vivo mechanism-based model in mice, rac-BHFF increased dose-dependently the LRR induced by baclofen with a minimum effective dose of 3 mg kg À1 p.o. rac-BHFF (100 mg kg À1 p.o.) tested alone had no effect on LRR nor on spontaneous locomotor activity, but exhibited anxiolytic-like activity in the SIH model in mice. Conclusions and implications: rac-BHFF derivatives may serve as valuable pharmacological tools to elucidate the pathophysiological roles played by GABA B receptors in the central and peripheral nervous systems.

Effects of the GABAB Receptor-Positive Modulators CGP7930 and rac-BHFF in Baclofen- and γ-Hydroxybutyrate-Discriminating Pigeons

“…CGP7930 and rac-BHFF were synthesized by K. Cheng at the National Institute on Drug Abuse (Bethesda, MD), and CGP35348 was synthesized by J. Agyin at the University of Texas Health Science Center (San Antonio, TX). All compounds were dissolved in sterile water or saline, except diazepam, which was dissolved in sterile water with 70% Emulphor and 10% ethanol (by volume), CGP7930, which was suspended in sterile water with 0.6% methylcellulose, and rac-BHFF, which was suspended in a 4:1:15 mixture containing Cremophor EL, 1,2-propanediol, and distilled water (Malherbe et al, 2008). All compounds were injected intramuscularly in a volume of 0.1 to 1 ml, except CGP7930 and rac-BHFF, which were administered orally in a volume of 5 ml/kg.…”

“…CGP7939 and rac-BHFF increase loss of righting in mice induced by a subthreshold dose of the GABA B receptor agonist baclofen without producing loss of righting when given alone (Carai et al, 2004;Malherbe et al, 2008), which shows that they could have positive modulating properties at GABA B receptors in vivo. Recently, these properties were characterized in more detail by using shifts of dose-response curves for GABA B receptor agonists to compare the relative potency and effectiveness of the positive modulators (Koek et al, 2010).…”

“…Several compounds have been shown to have positive GABA B modulatory activity in vitro [2,6-di-tert-butyl-4-(3-hydroxy-2,2-dimethylpropyl)phenol (CGP7930) (Urwyler et al, 2001;Adams and Lawrence, 2007), N, (Urwyler et al, 2003), (R,S)-5,7-di-tert-butyl-3-hydroxy-3-trifluoromethyl-3H-benzofuran-2-one (rac-BHFF) (Malherbe et al, 2008), N- [(1R,2R,4S)bicyclo[2.2.1]hept-2-yl]-2-methyl-5-[4-(trifluoromethyl)phenyl]-4-pyrimidinamine (BHF177) (Guery et al, 2007;Maccioni et al, 2009), methyl-2-(1-adamantanecarboxamido)-4-ethyl-5-methylthiophene-3-carboxylate (COR627), and methyl-2-(cyclohexanecarboxamido)-4-ethyl-5-methylthiophene-3-carboxylate (COR628) (Castelli et al, 2012)], evidenced by enhancing GABA, and, for all compounds except BHF177, also by enhancing the GABA B receptor agonist baclofen. In vivo results suggest positive GABA B receptor modulators to have anxiolyticand antidepressant-like properties in elevated-maze and forced-swimming tests, respectively (Cryan et al, 2004;Frankowska et al, 2007;Jacobson and Cryan, 2008).…”

Structure and ligand recognition of class C GPCRs

“…In addition to CGP7930, a number of PAMs that target the GABA B receptor have been reported, such as GS39783 [87] . Several allosteric agonists have also been synthesized, including rac-BHFF and its analogs [88] . However, no NAMs that target the GABA B receptor have been described.…”

Metabotropic Receptors for Glutamate and GABA

“…As with many Class C GPCRs, there exist a number of allosteric modulators available for the GABA B receptor, yet all known modulators are PAMs, with no known NAMs, to date. Some PAMs of the GABA B receptor are CGP7930, GS39783 and the more recent, rac-BHFF (Malherbe et al, 2008;Pin and Prezeau, 2007) (Figure 6). These PAMs increase orthosteric agonist potency and maximal response in a system-dependent manner, whilst possessing partial agonism in their own right.…”