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Structure‐Activity Relationships for Cumyl‐Containing Synthetic Cannabinoids to Induce Hypothermic, Cataleptic and Analgesic Effects in Mice
Author(s) -
Baumann Michael H.,
Garibay Nancy,
Partilla John S.,
Brandt Simon D.
Publication year - 2020
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2020.34.s1.03535
Subject(s) - catalepsy , chemistry , cannabinoid receptor , in vivo , pharmacology , synthetic cannabinoids , analgesic , cannabinoid , in vitro , designer drug , receptor , stereochemistry , medicine , biochemistry , drug , biology , antagonist , microbiology and biotechnology , haloperidol , dopamine
Synthetic cannabinoids (SCs), also known as “spice” or “K2”, are an evolving class of new psychoactive substances that pose public health risks. SCs exert their psychoactive effects by stimulating cannabinoid‐1 receptors (CB1) in the brain, yet few studies have systemically evaluated structure‐activity relationships (SAR) for newly‐emerging compounds. Here, we investigated the pharmacology of SCs which possess a fixed cumyl ‘head group’ but a variable N ‐alkyl ‘tail group’ which ranged from 3 to 7 carbons in length. Cumyl‐PINACA, which contains a 5‐carbon pentyl tail, served as a reference compound. In vitro CB1 binding was assessed by displacement of [ 3 H]SR141716 in mouse brain membranes. In vivo effects of subcutaneously (sc) administered drugs were examined in male C57Bl/6J mice bearing surgically‐implanted telemetric temperature transponders. Mice were subjected to a ‘triad’ test battery which assessed temperature, catalepsy, and analgesia every 30 min post‐injection for 2 h. Temperature was measured via a handheld receiver. Catalepsy was measured using the bar test, with a cut off of 60 sec, whereas analgesia was measured using a hot plate set at 52°C, with a cut off of 45 sec. Cumyl‐PINACA was the most potent inhibitor of CB1 binding with an IC 50 =1.8 nM. Decreasing N‐ alkyl chain length to a 3‐carbon propyl markedly reduced binding affinity (IC 50 =44.8 nM), as did increasing chain length to a 7‐carbon heptyl (IC 50 =124.0 nM). Consistent with the in vitro findings, cumyl‐PINACA was the most potent compound to induce cannabinoid‐like effects in the triad test battery, with ED 50 s ranging from 0.06–0.09 mg/kg, sc. Importantly, all cumyl compounds induced hypothermic, cataleptic, and analgesic effects with a rank order of potency that matched their IC 50 s for inhibition of CB1 binding. THC exhibited ED 50 s in the triad test ranging from 18.7–30.3 mg/kg, sc. Overall, our data reveal that certain cumyl‐containing SCs are more potent CB1 agonists than THC. Furthermore, N ‐alkyl chain length is a critical determinant for the pharmacological effects of cumyl SCs, with a 5‐carbon pentyl chain conferring optimal activity. More research examining the SAR for newly‐emerging SCs is needed to inform stakeholders involved with responding to the abuse of these compounds. Support or Funding Information This work was supported generously through IRP, NIDA, NIH.