Identification of Orthosteric GABA_B Receptor Ligands by Virtual Screening and In Vitro Validation

Area of Science:

• Neuroscience
• Pharmacology
• Molecular Biology

Background:

• The GABA_B receptor (GABA_B-R), a class C G-protein coupled receptor (GPCR), is implicated in various neurological and neuropsychiatric disorders.
• Its heterodimeric structure, featuring Venus flytrap (VFT) domains, presents a significant target for therapeutic intervention.
• The VFT of the GABA_B1a/b subunit harbors the orthosteric binding site for γ-aminobutyric acid (GABA).

Purpose of the Study:

• To identify novel compounds that bind to the orthosteric binding site of the GABA_B receptor.
• To characterize the binding and functional activity of identified compounds as potential GABA_B-R modulators.

Main Methods:

• A combined virtual screening (VS) approach, integrating ligand- and structure-based methods, was employed to identify potential binders.
• 34 selected compounds underwent in vitro testing using the Hit Hunter cAMP assay in Chinese hamster ovary (CHO)-K1 cells overexpressing human GABA_B(1b,2)-R.
• Further characterization involved [³⁵S]-GTPγS binding assays, competition binding assays with [³H]-CGP54626, and evaluation of GABA dose-response curves.

Main Results:

• The virtual screening campaign successfully identified putative compounds targeting the GABA_B-R orthosteric binding site.
• In vitro assays confirmed that two selected compounds bind to the orthosteric site of the GABA_B receptor.
• Experimental data demonstrated that these two compounds function as antagonists of the GABA_B receptor.

Conclusions:

• The study successfully identified and validated two novel antagonists for the GABA_B receptor.
• These compounds bind to the orthosteric site, confirming their potential as therapeutic agents for GABA_B-R related conditions.
• The findings support the GABA_B receptor as a viable drug target for neurological and neuropsychiatric disorders.