Towards functional selectivity for α6β3γ2 GABA_A receptors: a series of novel pyrazoloquinolinones

Abstract

Background and PurposeThe GABAA receptors are ligand‐gated ion channels, which play an important role in neurotransmission. Their variety of binding sites serves as an appealing target for many clinically relevant drugs. Here, we explored the functional selectivity of modulatory effects at specific extracellular α+/β− interfaces, using a systematically varied series of pyrazoloquinolinones.Experimental ApproachRecombinant GABAA receptors were expressed in Xenopus laevis oocytes and modulatory effects on GABA‐elicited currents by the newly synthesized and reference compounds were investigated by the two‐electrode voltage clamp method.Key ResultsWe identified a new compound which, to the best of our knowledge, shows the highest functional selectivity for positive modulation at α6β3γ2 GABAA receptors with nearly no residual activity at the other αxβ3γ2 (x = 1–5) subtypes. This modulation was independent of affinity for α+/γ− interfaces. Furthermore, we demonstrated for the first time a compound that elicits a negative modulation at specific extracellular α+/β− interfaces.Conclusion and ImplicationsThese results constitute a major step towards a potential selective positive modulation of certain α6‐containing GABAA receptors, which might be useful to elicit their physiological role. Furthermore, these studies pave the way towards insights into molecular principles that drive positive versus negative allosteric modulation of specific GABAA receptor isoforms.

Two Distinct Populations of α1α6-Containing GABAA-Receptors in Rat Cerebellum

“…Nonlinear regression analysis of the displacement curves used the equation: Y = Bottom + (Top-Bottom)/(1 + 10 ∧ ((LogIC50-X)*Hill-slope). IC50 values were converted into Ki values using the Cheng-Prusoff relationship (Cheng and Prusoff, 1973 ) Ki = IC50/(1 + (S/KD)) with S being the concentration of the radioligand (2 nM for 3 H-flunitrazepam or 5 nM for 3 H-Ro 15-4513) and the KD values as described previously [4.8 nM for 3 H-flunitrazepam (Simeone et al, 2017 ) and 1.4 nM for 3 H-Ro 15-4513 in the presence of diazepam (Treven et al, 2018 )].…”

Trigeminal neuropathic pain development and maintenance in rats are suppressed by a positive modulator of α6 GABAA receptors

“…Recently, pyrazoloquinolinones with specific substitution patterns were identified as the first ligands functionally selective for α6β2/3γ2 receptors; one of them was PZ‐II‐029 (presented as compound 6 in Varagic et al, ). Furthermore, LAU165, an inactive compound with similar chemical properties, was also identified (Treven et al, ).…”

International Union of Basic and Clinical Pharmacology. CVI: GABAAReceptor Subtype- and Function-selective Ligands: Key Issues in Translation to Humans

“…17; section V.D.10) (Christian et al, 2015), PZ-II-029 ( Fig. 34; section V. G.3) (Varagic et al, 2013a), LAU159 (Treven et al, 2018), ELB138 (imepitoin), or ELB139 (Rabe et al, 2007;Rundfeldt and Löscher, 2014), confirm this hypothesis in clinical investigations by demonstrating a wider separation of anxiolytic and sedative properties in humans, pharmaceutical companies might have to radically change their strategy for the development of more selective drugs: Instead of developing high potency, high efficacy drugs with receptor subtype selectivity, the development of low potency, low efficacy drugs with receptor subtype selectivity might be more promising for eliciting selective actions. Since drug efficacy plays a critical role in determining the degree of GABA A receptor uncoupling, and, perhaps in the development of tolerance and dependence (Primus et al, 1996), low efficacy drugs might have an added benefit in a long-term treatment of patients.…”

“…34), as well as other structurally related compounds, are high affinity null modulators at the benzodiazepine binding sites of various GABA A receptor subtypes but in addition also positively modulate a6b3g2 receptors with low potency and exceptionally high selectivity via the a6+b32 interface (Varagic et al, 2013a). Recently, the structurally related LAU159 (8-chloro-2-(3-methoxyphenyl)-2H-pyrazolo [4,3-c]quinolin-3(5H)-one) has been demonstrated to show the highest functional selectivity for positive modulation at a6b3g2 receptors with nearly no residual activity at the other a125b3g2 receptors up to 10 mM concentrations (Treven et al, 2018). PZ-II-029 and LAU159, together with LAU463 (7-bromo-2-(4-methoxyphenyl)-2,5-dihydro-3H-pyrazolo [4,3-c]quinolin-3-one), another a6b3g2 receptor-selective compound, were recently used as lead compounds for the development of a variety of deuterated a6b3g2 receptor-selective compounds with increased metabolic stability and bioavailability (Knutson et al, 2018).…”