Structure-Activity Assessment and In-Depth Analysis of Biased Agonism in a Set of Phenylalkylamine 5-HT2A Receptor Agonists.

Serotonergic psychedelics primarily activate the serotonin 2A receptor (5-HT2A), but the molecular basis for their psychedelic effects is not fully understood. A leading hypothesis is biased agonism, where certain signaling pathways are preferentially activated. This study tested a series of 4-position-substituted phenylalkylamines for their ability to recruit β-arrestin2 or miniGαq to the 5-HT2A receptor. All compounds acted as agonists with varying potency and efficacy. Lipophilicity of the 2C-X phenethylamines correlated more strongly with efficacy in the miniGαq assay than the β-arrestin2 assay. Molecular docking suggested that the 4-substituent fits into a hydrophobic pocket between transmembrane helices 4 and 5, potentially explaining this differential effect. Using serotonin and LSD as reference agonists, both benchmark and physiology bias were estimated, and qualitative structure-activity relationships remained consistent across different activation profiles.

Study at a glance

Abstract

Serotonergic psychedelics are described to have activation of the serotonin 2A receptor (5-HT2A) as their main pharmacological action. Despite their relevance, the molecular mechanisms underlying the psychedelic effects induced by certain 5-HT2A agonists remain elusive. One of the proposed hypotheses is the occurrence of biased agonism, defined as the preferential activation of certain signaling pathways over others. This study comparatively monitored the efficiency of a diverse panel of 4-position-substituted (and N-benzyl-derived) phenylalkylamines to induce recruitment of β-arrestin2 (βarr2) or miniGαq to the 5-HT2A, allowing us to assess structure-activity relationships and biased agonism. All test compounds exhibited agonist properties with a relatively large range of both EC50 and Emax values. Interestingly, the lipophilicity of the 2C-X phenethylamines was correlated with their efficacy in both assays but yielded a stronger correlation in the miniGαq- than in the βarr2-assay. Molecular docking suggested that accommodation of the 4-substituent of the 2C-X analogues in a hydrophobic pocket between transmembrane helices 4 and 5 of 5-HT2A may contribute to this differential effect. Aside from previously used standard conditions (lysergic acid diethylamide (LSD) as a reference agonist and a 2 h activation profile to assess a compound's activity), serotonin was included as a second reference agonist, and the compounds' activities were also assessed using the first 30 min of the activation profile. Under all assessed circumstances, the qualitative structure-activity relationships remained unchanged. Furthermore, the use of two reference agonists allowed for the estimation of both "benchmark bias" (relative to LSD) and "physiology bias" (relative to serotonin).