Development of 2-Aminotetralin-Type Serotonin 5-HT₁ Agonists: Molecular Determinants for Selective Binding and Signaling at 5-HT_1A, 5-HT_1B, 5-HT_1D, and 5-HT_1F Receptors

Abstract

The serotonin (5-hydroxytryptamine, 5-HT) 5-HT 1 G-protein coupled receptor subtypes (5-HT 1A/1B/1D/1E/1F ) share a high sequence homology, confounding development of subtype-specific ligands. This study used a 5-HT 1 structure-based ligand design approach to develop subtype-selective ligands using a 5-substituted-2-aminotetralin (5-SAT) chemotype, leveraging results from pharmacological, molecular modeling, and mutagenesis studies to delineate molecular determinants for 5-SAT binding and function at 5-HT 1 subtypes. 5-SATs demonstrated high affinity (K i ≤ 25 nM) and at least 50-fold stereoselective preference ([2S] > [2R]) at 5-HT 1A , 5-HT 1B, and 5-HT 1D receptors but essentially nil affinity (K i > 1 μM) at 5-HT 1F receptors. The 5-SATs tested were agonists with varying degrees of potency and efficacy, depending on chemotype substitution and 5-HT 1 receptor subtype. Models were built from the 5-HT 1A (cryo-EM), 5-HT 1B (crystal), and 5-HT 1D (cryo-EM) structures, and 5-SATs underwent docking studies with up to 1 μs molecular dynamics simulations. 5-SAT interactions observed at positions 3. 33, 5.38, 5.42, 5.43, and 7.39 of 5-HT 1 subtypes were confirmed with point mutation experiments. Additional 5-SATs were designed and synthesized to exploit experimental and computational results, yielding a new full efficacy 5-HT 1A agonist with 100-fold selectivity over 5-HT 1B/1D receptors. The results presented lay the foundation for the development of additional 5-HT 1 subtype selective ligands for drug discovery purposes.