Elucidating Anti‐Inflammatory SAR at the 5‐HT2A Receptor
Authors: Billac Gerald Bernard , Flanagan Thomas Wayne , Nichols Charles David 
Published: April 2020

IntroductionDysregulated or maladaptive inflammatory signaling is a major component of many modern human diseases, such as allergic asthma, coronary artery disease, inflammatory bowel disease, diabetes, neurodegenerative diseases, depression, and addiction. Current pharmacological therapies individually target specific enzymatic pathways involved in the synthesis of certain pro‐inflammatory mediators, cell‐cell immune signal propagation by sequestration of pro‐inflammatory mediators, or broad suppression of the immune response. Previously published data from our laboratory suggests including psychedelics, a class of serotonin (5‐hydroxytryptamine; 5‐HT) 2A (5‐HT2A) receptor agonists, as a new category of anti‐inflammatory drugs. Whereas whole organism models will provide insight into the physiological and behavioral response profile, the mechanism of action and structural basis mediating the anti‐inflammatory and behavioral activity of psychedelics have yet to be elucidated on a molecular level. This knowledge can be used to optimize the therapeutic response by informing structure‐activity relationship (SAR) studies and drug candidate selection matrices for development of novel, small molecule anti‐inflammatory compounds.ObjectivesWe sought to evaluate the relationship of in vitro functional selectivity at the 5‐HT2A receptor on the efficacy of an in vivo anti‐inflammatory response.MethodsWe utilized human embryonic kidney cells stably expressing the 5‐HT2A receptor to evaluate real‐time calcium mobilization as a proxy measure of Gαq pathway activation. Further, we evaluated Arrestin‐3 recruitment using the PRESTO‐Tango luciferase reporter gene assay. Concurrent studies in our laboratory measured in vivo anti‐inflammatory activity using an airways hyperresponsiveness assay in a rat model of acute allergic asthma. All assays were completed using a comprehensive panel of ligands comprising four chemical classes: tryptamines, ergolines, phenethylamines, and phenisopropylamines.ResultsWhile there are differential responses for each ligand to activate individual signaling pathways, results from examination of the canonical Gαq pathway and recruitment of the multi‐adaptor protein Arrestin‐3 exhibited no significant correlation between potency and efficacy for either pathway with in vivo measures of anti‐inflammatory activity.ConclusionThis data illustrates that small modifications on the molecular structure of recognized pharmacophores can impart unique conformational changes of the receptor protein, which will alter the interaction with downstream effectors. Ongoing studies are examining additional GPCR‐mediated signaling. With this data, the varying degree of effector pathway bias can be determined for each ligand which supports better understanding of adverse and favorable therapeutic activities, as well as informs structure‐activity studies and drug candidate selection matrices. The collective analysis of a comprehensive panel of 5HT2A receptor ligands has never been examined in this fashion; thus, we aim to elucidate the SAR to inform drug design for novel molecules that are biased to pathways targeting a biologically therapeutic response.Support or Funding InformationSupport from this work was provided by the Eleusis Public Benefit Corporation.