Pharmacological profiles and psychedelic-like effects of 4-hydroxy-, 4-acetoxy-, and 4-methoxy-N-methyl-N-isopropyltryptamine

Abstract ID 92316 Poster Board 281 Background: A variety of tryptamine-based psychedelics induce psychoactive effects in humans and animals that are mediated by serotonin 2A receptors (5-HT_2A), but these compounds are generally non-selective and interact with other targets in the brain. For example, previous findings show that 4-hydroxy, 4-acetoxy- and 4-methoxy analogs of N-methyl-N-isopropyltryptamine (4-HO-MiPT, 4-AcO-MiPT, and 4-MeO-MiPT, respectively) interact with 5-HT transporters (SERT) in addition to acting as agonists at 5-HT_2A. Here we studied the in vitro receptor profiles, in vitro monoamine transporter activities, and in vivo pharmacological effects of 4-HO-MiPT, 4-AcO-MiPT, and 4-MeO-MiPT. Methods: Receptor and transporter affinities were determined using a comprehensive binding screen where inhibition constants and functional activities were determined in vitro. Next, the ability of the compounds to block [³H]neurotransmitter uptake at the dopamine transporter (DAT), norepinephrine transporter (NET), and SERT was examined in rat brain synaptosomes and transporter-transfected cells. Inhibition constants for drug binding to serotonin 1A receptors (5-HT_1A) and 5-HT_2A were determined in mouse brain. Lastly, we compared the dose-related effects of acute subcutaneous 4-HO-MiPT, 4-AcO-MiPT, and 4-MeO-MiPT (0.03–30 mg/kg) on 5-HT_2A-mediated head twitch responses (HTRs) in male C57BL/6J mice (n = 5 – 6/ dose) over 30 min test sessions. Videos of each session were analyzed using commercially available software. Locomotor activity and body temperature changes were also assessed. Results: The radioligand binding screen revealed that the MiPT analogs mainly targeted 5-HT receptors but also had notable inhibition constants at alpha-adrenergic receptors, sigma receptors, and SERT. Functional assays assessing Gα_q-mediated calcium release showed the compounds act as fully efficacious 5-HT_2A agonists (EC₅₀ range = 6–120 nM; E_max range = 90–102%), with reduced potency or efficacy at other 5-HT₂ subtypes. The compounds all displayed nM affinities at 5-HT_2A (K_i range = 269–991 nM) in mouse brain, but only 4-MeO-MiPT displayed nM affinity at 5-HT_1A (K_i = 347 nM). 4-MeO-MiPT also displayed potent and selective uptake inhibition at SERT (IC₅₀ = 57 nM) relative to the other two compounds (IC₅₀s = 423–1,398 nM) and cocaine (IC₅₀ = 326 nM). In mice, the compounds had similar potencies for inducing HTRs (ED₅₀ range = 0.75–0.97 mg/kg), with the rank order of 4-HO e 4-AcO e 4-MeO. Interestingly, 4-MeO-MiPT had reduced efficacy for inducing HTRs relative to the other compounds (E_max = 34 vs 77–80 HTRs/30 min). All compounds produced hypothermia (E_max = 4–7 °C) and hypolocomotion at the highest doses (i.e. 10 & 30 mg/kg). Conclusions: Overall, our data indicate that 4-position ring-substituted MiPT analogs interact mainly with 5-HT_2A and other 5-HT receptors, but they also have relevant effects at non-receptor targets such as SERT. 4-MeO-MiPT displays potent SERT uptake inhibition and higher affinity for 5-HT_1A when compared to its 4-HO and 4-AcO counterparts, which may underlie its reduced psychedelic-like effects in mice. Ongoing studies are evaluating the role of SERT and 5-HT_1A in modulating the psychedelic-like effects of 4-MeO-MiPT to better understand the pharmacology of hybrid SERT uptake blocker/psychedelic tryptamines. This work was supported by a NIDA IRP grant to M.H.B. (DA-000522-16) and a collaborative research and development agreement between NIDA IRP and CaaMTech.