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

## TL;DR

This study identifies compounds that bind to the GABAB receptor's main site and act as antagonists, potentially useful for treating neurological disorders.

## Contribution

A novel combination of virtual screening and in vitro validation successfully identified orthosteric GABAB receptor ligands.

## Key findings

- Two compounds confirmed to bind to the orthosteric site of GABAB-R.
- The compounds act as antagonists at the GABAB receptor.
- Virtual screening proved effective in identifying functional ligands.

## Abstract

The GABAB receptor (GABAB-R) is
a heterodimeric
class C G-protein coupled receptor (GPCR) associated with numerous
neurological and neuropsychiatric disorders and is an interesting
target for drug development. Each subunit has an extracellular part
called the Venus flytrap domain (VFT), and the VFT of the GABAB1a/b subunit contains the orthosteric γ-aminobutyric
acid (GABA) binding site. In the present study, we have used a combined
ligand- and structure-based virtual screening (VS) campaign to identify
putative compounds binding to the orthosteric binding site. Based
on the VS, 34 ligands were purchased and tested in vitro using the functional Hit Hunter cAMP assay in Chinese hamster ovary
(CHO)-K1 cells stably overexpressing the human GABAB(1b,2)-R and in wild-type CHO-K1 cells. Based on the initial testing, two
compounds were selected for studies in the [35S]­GTPγS
binding assays and a competition binding assay using the GABAB-R antagonist [3H]­CGP54626 as the radioligand.
In addition, their effects on the dose–response curve of GABA
were further evaluated in the Hit Hunter cAMP assay. The experimental
testing confirmed that both compounds bind to the orthosteric site
of GABAB-R and are antagonists.