Molecular Determinants Underlying Delta Selective Compound 2 Activity at -Containing GABA Receptors.

Delta selective compound 2 (DS2; 4-chloro--[2-(2-thienyl)imidazo[1,2-]pyridin-3-yl]benzamide) is one of the most widely used tools to study selective actions mediated by -subunit-containing GABA receptors. DS2 was discovered over 10 years ago, but despite great efforts, the precise molecular site of action has remained elusive. Using a combination of computational modeling, site-directed mutagenesis, and cell-based pharmacological assays, we probed three potential binding sites for DS2 and analogs at receptors: an interface site in the extracellular domain (ECD), equivalent to the diazepam binding site in receptors, and two sites in the transmembrane domain (TMD) - one in the and one in the interface, with the site corresponding to the binding site for etomidate and a recently disclosed low-affinity binding site for diazepam.

Structural Determinants for the Mode of Action of Imidazopyridine DS2 at δ-Containing γ-Aminobutyric Acid Type A Receptors.

Despite the therapeutic relevance of δ-containing γ-aminobutyric acid type A receptors (GABARs) and the need for δ-selective compounds, the structural determinants for the mode and molecular site of action of δ-selective positive allosteric modulator imidazo[1,2-a]pyridine DS2 remain elusive. To guide the quest for insight, we synthesized a series of DS2 analogues guided by a structural receptor model. Using a fluorescence-based fluorometric imaging plate reader membrane potential assay, we found that the δ-selectivity and the pharmacological profile are severely affected by substituents in the 5-position of the imidazopyridine core scaffold.