Structure–Activity Assessment and In-Depth Analysis of Biased Agonism in a Set of Phenylalkylamine 5-HT_2A Receptor Agonists

Abstract

Serotonergic psychedelics are described to have activation of the serotonin 2A receptor (5-HT 2A ) as their main pharmacological action. Despite their relevance, the molecular mechanisms underlying the psychedelic effects induced by certain 5-HT 2A 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 4position-substituted (and N-benzyl-derived) phenylalkylamines to induce recruitment of β-arrestin2 (βarr2) or miniGα q to the 5-HT 2A , allowing us to assess structure−activity relationships and biased agonism. All test compounds exhibited agonist properties with a relatively large range of both EC 50 and E max values. Interestingly, the lipophilicity of the 2C-X phenethylamines was correlated with their efficacy in both assays but yielded a stronger correlation in the miniGα q -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-HT 2A 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).

Comparative Pharmacological Effects of Lisuride and Lysergic Acid Diethylamide Revisited

“…Results for reference agonists LSD, serotonin, and DOI align with previously published data obtained with the same assays and with data obtained using a cell line stably expressing the assay components of the βarr2 assay (Figures and S1). ,,− Specifically, low nanomolar EC 50 values were observed for LSD in both 5-HT 2A receptor recruitment assays. Serotonin exhibited a similar EC 50 value and a higher E max value in the βarr2 assay relative to LSD.…”

The mechanistic divide in psychedelic neuroscience: An unbridgeable gap?

“…However, the comparability of 5-HT 2A G q recruitment by classical psychedelics in humans and animals remains to be elucidated, as does comparability of psychedelic-induced β-arrestin 2 translocation and effects on tachyphylaxis/receptor down-regulation. Additional signaling pathways, e.g., arachidonic acid release, may be involved as well [ 19 , [30] , [31] , [32] ]. Classical psychedelics also bind with varying affinities to several other 5-HT receptors, including 5-HT 1A , 5-HT 2B , and 5-HT 2C , and they have varying agonist activity at dopamine and alpha-adrenergic receptors [ 33 , 34 ].…”

Bias translation: The final frontier?

“…In general, these ideas centre on the emphasis of beneficial signalling pathways—for example, β‐arrestin for PTH receptor in bone building in osteoporosis (Ferrari et al, 2005), β‐arrestin‐mediated glucagon‐like peptide‐1 (GLP1) for insulin secretion in diabetes (Sonoda et al, 2008), or the elimination of negative signalling (opioid‐mediated respiratory depression and/or negative behavioural effects mediated by β‐arrestin; Raehal & Bohn, 2011; Raehal et al, 2005; Bohn et al, 2003; Urs & Caron, 2014). There are many more recent proposals for improved drug candidates based on the biased concept including agonists for muscarinic acetylcholine receptors (McDonald et al, 2022; Randakova & Jakubic, 2021), opioid receptors (Che et al, 2021; Conibear et al, 2020), ghrelin receptors (Mende et al, 2018), neurotensin receptors (Krumm et al, 2023), glucocorticoid receptors (Mao et al, 2023), and 5‐HT 2A receptors (Allen et al, 2011; Pottie et al, 2023). Interestingly, efforts to achieve selectivity through allosteric modulation in studies for Alzheimer's disease and schizophrenia fall short of yielding the selectivity needed without added biased signalling (in this case, induced bias through allosteric modulation) (van der Westhuizen et al, 2021).…”