Pathway-selective signaling of serotonergic psychedelics at 5-HT receptors: Implications for psychoactivity, safety, and therapeutic potential

Serotonergic psychedelics primarily activate the serotonin 2A receptor, but their full effects involve multiple receptor subtypes and signaling pathways. Using stable cell lines and bioassays measuring phospholipase C activation via inositol monophosphate formation, phospholipase A2 activation, β-arrestin2 recruitment, and Gαi-protein dissociation across 5-HT2A, 5-HT2B, 5-HT2C, and 5-HT1A receptors, the study found that inositol monophosphate formation provides the most robust measure of 5-HT2 receptor activation and correlates strongly with known psychoactive doses. Most psychedelics showed signaling bias toward the PLC-IP1 or PLA2-AA pathway at the 5-HT2A receptor. The 5-HT2A/5-HT1A activation ratio may indicate seizure risk and therapeutic potential. Low activation at the 5-HT2B receptor suggests reduced cardiac risk with intermittent use, while strong 5-HT2C receptor activation aligns with low abuse potential.

Study at a glance

Abstract

Serotonergic psychedelics primarily exert their effects through activation of the serotonin (5-HT) 2A receptor (5-HT 2A R). However, the full pharmacological profiles of these substances involve multiple serotonin receptor subtypes and intracellular signaling pathways. This study characterized the signaling behavior of a panel of serotonergic psychedelics using stable cell lines and a series of bioassays targeting phospholipase C (PLC) activation via inositol monophosphate (IP1) formation, phospholipase A 2 (PLA 2 ) activation, β-arrestin2 recruitment, and Gα i -protein dissociation across 5-HT 2A , 5-HT 2B , 5-HT 2C , and 5-HT 1A receptors. The results of the study indicate that IP1 formation offers the most robust and reproducible measure of 5-HT 2 R receptor activation and aligns most closely with human dosing data. Particularly for the 5-HT 2A R, PLC-IP1 activation exhibited a strong correlation with known psychoactive doses, contrasting with assays that relied on Ca²⁺ release. The majority of psychedelics exhibited a signaling bias toward the PLC-IP1 or the PLA 2 -AA pathway at the 5-HT₂ A R. The 5-HT 2A /5-HT 1A activation ratio may provide information about seizure risk and therapeutic potential. Furthermore, the low activation efficacy at the 5-HT₂ B R potentially suggests reduced cardiac risk with intermittent use, and the strong activation of the 5-HT₂ C R is in accordance with the reported low abuse potential of serotonergic psychedelics. This study underscores the importance of pathway-specific profiling in understanding the pharmacology of serotonergic psychedelics. It provides a framework for predicting efficacy and adverse effect potential and lays the groundwork for the rational design of next-generation psychedelics with improved safety and efficacy.