Dissecting Serotonergic Mechanisms and Therapeutic Potential in Novel Psychedelics: An Integrative SAR and Behavioral Study of 5-Ring-Substituted DMT Analogs

[eng] The rapid emergence of novel psychoactive substances (NPS), including synthetic tryptamines – which are known by their ability to induce hallucinations – poses an increasing challenge for public health and regulatory authorities due to their unpredictable pharmacological effects, potential toxicity, and lack of thorough scientific characterization. Concurrently, psychedelics have re-emerged as promising candidates for treating several mental disorders, including depression, due to their ability to promote rapid and sustained therapeutic effects – potentially through mechanisms involving neuroplasticity. However, their clinical adoption is limited by the presence of hallucinogenic effects and an incomplete understanding of their mechanism of action. Through an integrative approach, combining chemical synthesis, in vitro assays, in silico modelling and behavioral studies in mouse models, this work elucidates the structure–activity relationships (SAR) of novel synthetic tryptamines across key serotonergic targets. Specifically, N-alkyl/allyl modifications to the amino group of 5-MeO-DMT and halogen substitutions on the indole ring of DMT were shown to influence binding affinity and selectivity for key serotonin receptors (5-HT1AR, 5-HT2AR, 5-HT2BR, 5-HT2CR), as well as their interaction with the serotonin transporter (SERT). In vitro functional assays revealed distinct agonist profiles and receptor signaling biases, while in vivo experiments in mice demonstrated divergent behavioral effects across the tested analogs, including variation in head twitch response (HTR), thermoregulatory changes, and locomotor activity. These findings also provided a mechanistic explanation into the opposing roles of 5-HT1AR and 5-HT2AR in mediating hallucinogenic and thermoregulatory responses. Among the studied compounds, 5-Br-DMT stood out as a non-hallucinogenic 5-HT2AR ligand with robust psychoplastogenic properties. Notably, it significantly increased expression of immediate early genes associated with neuroplasticity (e.g. Egr-1/2/3 and Arc) in the mouse prefrontal cortex and/or hippocampus, promoted dendritogenesis in cortical neurons, and exhibited rapid antidepressant-like effects in a mouse model of stress-induced depression. Furthermore, the study identifies 5-MeO-pyr-T and related analogs as compounds with high affinity and selectivity for 5-HT1AR with reduced hallucinogenic potential, warranting further investigation for assessing their therapeutic potential. Collectively, this work contributes foundational knowledge to the fields of psychopharmacology and drug regulation, providing predictive tools to anticipate public health risks while advancing therapeutic innovation. These findings lay groundwork for the rational design of safer, targeted serotonergic agents that retain therapeutic efficacy while minimizing hallucinogenic liability.