TY - JOUR

T1 - Functional Properties and Mechanism of Action of PPTQ, an Allosteric Agonist and Low Nanomolar Positive Allosteric Modulator at GABAA Receptors

AU - Madjroh, Nawid

AU - Olander, Emma Rie

AU - Bundgaard, Christoffer

AU - Söderhielm, Pella Cecilia

AU - Jensen, Anders A

N1 - Copyright © 2017 Elsevier Inc. All rights reserved.

PY - 2018

Y1 - 2018

N2 - The former sedative-hypnotic and recreational drug methaqualone (Quaalude) is a moderately potent, non-selective positive allosteric modulator (PAM) at GABAA receptors (GABAARs) (Hammer et al., 2015). In the present study, we have identified a novel methaqualone analog, 2-phenyl-3-(p-tolyl)quinazolin-4(3H)-one (PPTQ), in a screening of 67 analogs at five αβ2γ2S GABAAR subtypes and delineated its functional properties and mechanism of action at wild-type and mutant GABAARs expressed in Xenopus oocytes by two-electrode voltage clamp electrophysiology. PPTQ was found to be allosteric agonist and PAM (ago-PAM) at human α1β2γ2S and α4β2δ GABAARs, exhibiting intrinsic activity at micromolar concentrations and potentiating the GABA-evoked signaling through the receptors at concentrations down to the low-nanomolar range. Whereas PPTQ exclusively increased the potency of GABA at the α1β2γ2S receptor, it increased both GABA potency and efficacy at α4β2δ and displayed modest potency-based preference for α4β2δ over α1β2γ2S. In elaborate mutagenesis and competition experiments PPTQ was found to act through the same or an overlapping site as etomidate in the transmembrane β(+)/α(-) subunit interfaces, whereas it did not seem to target the other three transmembrane interfaces in the GABAAR. Finally, the PPTQ site was shown to be allosterically linked with sites targeted by neurosteroids and barbiturates but not with the high-affinity benzodiazepine site in the α1β2γ2S receptor. In conclusion, the development of a highly potent, bioavailable GABAAR ago-PAM by subtle modifications to the methaqualone scaffold demonstrates that derivatization of this infamous drug from the past can lead to modulators with distinct functional characteristics at the receptors.

AB - The former sedative-hypnotic and recreational drug methaqualone (Quaalude) is a moderately potent, non-selective positive allosteric modulator (PAM) at GABAA receptors (GABAARs) (Hammer et al., 2015). In the present study, we have identified a novel methaqualone analog, 2-phenyl-3-(p-tolyl)quinazolin-4(3H)-one (PPTQ), in a screening of 67 analogs at five αβ2γ2S GABAAR subtypes and delineated its functional properties and mechanism of action at wild-type and mutant GABAARs expressed in Xenopus oocytes by two-electrode voltage clamp electrophysiology. PPTQ was found to be allosteric agonist and PAM (ago-PAM) at human α1β2γ2S and α4β2δ GABAARs, exhibiting intrinsic activity at micromolar concentrations and potentiating the GABA-evoked signaling through the receptors at concentrations down to the low-nanomolar range. Whereas PPTQ exclusively increased the potency of GABA at the α1β2γ2S receptor, it increased both GABA potency and efficacy at α4β2δ and displayed modest potency-based preference for α4β2δ over α1β2γ2S. In elaborate mutagenesis and competition experiments PPTQ was found to act through the same or an overlapping site as etomidate in the transmembrane β(+)/α(-) subunit interfaces, whereas it did not seem to target the other three transmembrane interfaces in the GABAAR. Finally, the PPTQ site was shown to be allosterically linked with sites targeted by neurosteroids and barbiturates but not with the high-affinity benzodiazepine site in the α1β2γ2S receptor. In conclusion, the development of a highly potent, bioavailable GABAAR ago-PAM by subtle modifications to the methaqualone scaffold demonstrates that derivatization of this infamous drug from the past can lead to modulators with distinct functional characteristics at the receptors.

KW - Journal Article

U2 - 10.1016/j.bcp.2017.11.006

DO - 10.1016/j.bcp.2017.11.006

M3 - Journal article

C2 - 29155148

VL - 147

SP - 153

EP - 169

JO - Biochemical Pharmacology

JF - Biochemical Pharmacology

SN - 0006-2952

ER -