Development of 2-Aminotetralin-Type Serotonin 5-HT₁ Agonists: Molecular Determinants for Selective Binding and...

The serotonin (5-hydroxytryptamine, 5-HT) 5-HT₁ 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-HT₁ 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-HT₁ 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-HT₁ 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-HT₁ 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-HT₁ subtype selective ligands for drug discovery purposes.