Discovery of 2-(Imidazo[1,2-b]pyridazin-2-yl)acetic Acid as a New Class of Ligands Selective for the γ-Hydroxybutyric Acid (GHB) High-Affinity Binding Sites.

Gabazine, a GABAA receptor antagonist, has previously been reported to inhibit the binding of [3H]NCS-382, a representative ligand of the high-affinity binding site for the neuroactive substance GHB. We herein report a study on the structural determinants of gabazine for binding to i) the orthosteric binding site of the GABAA receptor and ii) the high-affinity GHB binding site. Expanding the structural diversity of available ligands for the high-affinity GHB binding sites, this study identified 2-(imidazo[1,2-b]pyridazin-2-yl)acetic acid as a novel ligand-scaffold leading to analogs with relatively high affinity (Ki 0.19-2.19 µM) and >50 times selectivity for the [3H]NCS-382 over [3H]muscimol binding sites. These results highlight that gabazine interacts with the high-affinity GHB and orthosteric GABAA receptor binding sites differently, and that distinct analogs can be generated to select between them. To facilitate further in vivo studies a promising prodrug candidate for brain delivery was identified.