Evidence for Two Modes of Binding of the Negative Allosteric Modulator SB269,652 to the Dopamine D2 Receptor.

Richard Ågren,Kristoffer Sahlholm

doi:10.3390/biomedicines10010022

Richard Ågren, Kristoffer Sahlholm

Open Access

https://doi.org/10.3390/biomedicines10010022

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Journal: Biomedicines	Publication Date: Dec 23, 2021
Citations: 1	License type: CC BY 4.0

Affiliation: Karolinska Institutet, Umeå University

Abstract

SB269,652 has been described as the first negative allosteric modulator (NAM) of the dopamine D2 receptor (D2R), however, the binding mode and allosteric mechanism of action of this ligand remain incompletely understood. SB269,652 comprises an orthosteric, primary pharmacophore and a secondary (or allosteric) pharmacophore joined by a hydrophilic cyclohexyl linker and is known to form corresponding interactions with the orthosteric binding site (OBS) and the secondary binding pocket (SBP) in the D2R. Here, we observed a surprisingly low potency of SB269,652 to negatively modulate the D2R-mediated activation of G protein-coupled inward-rectifier potassium channels (GIRK) and decided to perform a more detailed investigation of the interaction between dopamine and SB269,652. The results indicated that the SB269,652 inhibitory potency is increased 6.6-fold upon ligand pre-incubation, compared to the simultaneous co-application with dopamine. Mutagenesis experiments implicated both S193 in the OBS and E95 in the SBP in the effect of pre-application. The present findings extend previous knowledge about how SB269,652 competes with dopamine at the D2R and may be useful for the development of novel D2R ligands, such as antipsychotic drug candidates.

Highlights

SB269,652 has been described as the first negative allosteric modulator (NAM) of the dopamine D2 receptor (D2 R), the binding mode and allosteric mechanism of action of this ligand remain incompletely understood
We set out to characterize SB269,652 in our GIRK activation assay in Xenopus oocytes [14,17], heterologously expressing D2 R and GIRK channel subunits together with the GTPase accelerating protein, regulators of G protein signaling 4 (RGS4)
We investigated whether the order of the application of SB269,652 and DA could have an impact on the inhibitory potency of the former ligand

Summary

Introduction

SB269,652 has been described as the first negative allosteric modulator (NAM) of the dopamine D2 receptor (D2 R), the binding mode and allosteric mechanism of action of this ligand remain incompletely understood. The older, first-generation antipsychotics are characterized by D2/3 R antagonism and generally have a higher propensity for motor and endocrine side effects These adverse reactions may be less common with newer second- and third-generation drugs due to action at additional sites including serotonin receptors and partial D2/3 R agonism, respectively [3]. Undesired collateral actions, as well as the suboptimal amelioration of cognitive deficits in schizophrenia, are still important limitations to existing therapy, warranting the development of novel therapeutic strategies [4]. One such strategy centers on the use of negative allosteric modulators (NAMs), which reduce DA potency and/or efficacy at D2/3 Rs rather than compete with DA for binding to the receptor

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