Structure–Activity Relationships for Psilocybin, Baeocystin, Aeruginascin, and Related Analogues to Produce Pharmacological Effects in Mice

Abstract

4-Phosphoryloxy-N,N-dimethyltryptamine (psilocybin) is a naturally occurring tertiary amine found in many mushroom species. Psilocybin is a prodrug for 4-hydroxy-N,N-dimethyltryptamine (psilocin), which induces psychedelic effects via agonist activity at the serotonin (5-HT) 2A receptor (5-HT2A). Several other 4-position ring-substituted tryptamines are present in psilocybin-containing mushrooms, including the secondary amine 4-phosphoryloxy-N-methyltryptamine (baeocystin) and the quaternary ammonium 4-phosphoryloxy-N,N,N-trimethyltryptamine (aeruginascin), but these compounds are not well studied. Here, we investigated the structure–activity relationships for psilocybin, baeocystin, and aeruginascin, as compared to their 4-acetoxy and 4-hydroxy analogues, using in vitro and in vivo methods. Broad receptor screening using radioligand binding assays in transfected cells revealed that secondary and tertiary tryptamines with either 4-acetoxy or 4-hydroxy substitutions display nanomolar affinity for most human 5-HT receptor subtypes tested, including the 5-HT2A and the serotonin 1A receptor (5-HT1A). The same compounds displayed affinity for 5-HT2A and 5-HT1A in mouse brain tissue in vitro and exhibited agonist efficacy in assays examining 5-HT2A-mediated calcium mobilization and β-arrestin 2 recruitment. In mouse experiments, only the tertiary amines psilocin, psilocybin, and 4-acetoxy-N,N-dimethyltryptamine (psilacetin) induced head twitch responses (ED50 0.11–0.29 mg/kg) indicative of psychedelic-like activity. Head twitches were blocked by 5-HT2A antagonist pretreatment, supporting 5-HT2A involvement. Both secondary and tertiary amines decreased body temperature and locomotor activity at higher doses, the effects of which were blocked by 5-HT1A antagonist pretreatment. Across all assays, the pharmacological effects of 4-acetoxy and 4-hydroxy compounds were similar, and these compounds were more potent than their 4-phosphoryloxy counterparts. Importantly, psilacetin appears to be a prodrug for psilocin that displays substantial serotonin receptor activities of its own.

Receptor Binding Profiles for Tryptamine Psychedelics and Effects of 4-Propionoxy-N,N-dimethyltryptamine in Mice

“…These data are generally consistent with other reports of agonist activities of these tryptamines at 5-HT 2 receptors in the G q -calcium mobilization assay . Agonist activity of 4-PrO-DMT has not previously been reported but is consistent with agonist actions of related compounds in this assay. , As predicted by the present primary binding screen and previously reported by others, , 4-HO-DiPT had weak (EC 50 ≈ 6,400 nM) potency and/or partial agonist efficacy (∼72%) at 5-HT 2C relative to 5-HT and the other psychedelic tryptamines tested.…”

“…Inhibition constants for 5-HT receptors assessed are shown in Table , while inhibition constants for the most common non-5-HT receptor targets are listed in Table and Table . Many of the compounds displayed affinity for all 5-HT receptors assessed, similar to the findings for psilocin and psilacetin. − In general, the receptor binding results show that 4-hydroxy compounds have higher affinity across all 5-HT receptor targets when compared to 4-acetoxy analogues with the same N -alkyl groups. We previously demonstrated that 4-hydroxy and 4-acetoxy analogues of psilocybin display higher affinity for more 5-HT receptor subtypes when compared to their 4-phosphoryloxy counterparts .…”

The Bright Side of Psychedelics: Latest Advances and Challenges in Neuropharmacology

“…However, psilocin is considered a partial agonist of the 5-HT2A receptor ( Figure 12 ). Indeed, compared with serotonin, psilocin shows an efficiency of less than 40% in the Ca 2+ mobilization assay [ 188 ]. The link with the 5-HT2A receptor is responsible for the “mystical” hallucinatory effects induced by psilocin [ 185 ].…”

“…However, a certain psilocin receptor non-specificity common to many psychedelics has been confirmed. In increasing order of affinity, psilocin can also bind to 5-HT2B, 5-HT1D, dopamine D1, 5-HT1E, 5-HT1A, 5-HT5A, 5-HT7, 5-HT6, D3, 5-HT2C and 5-HT1B receptors [ 185 , 188 ].…”

Psilocybin for Depression: From Credibility to Feasibility, What’s Missing?

“…The commonly referenced overarching mechanistic neurobiological principle is that psilocybin acts as an agonist of the 5-Hydroxytryptamine 2A receptor (5-HT2AR), which has been convincingly demonstrated as necessary for psychedelic drug effects [ 10 , 11 , 12 ], specifically for the propensity to visual hallucinations associated with psilocybin [ 13 ]. However, it is not entirely clear which signaling pathways are predictive of the therapeutic effect [ 14 ].…”