5-HT_2A receptor agonism by tert-leucinamide and valinamide synthetic cannabinoids: In vitro and in vivo evidence

New synthetic cannabinoid receptor agonists (SCRAs) are associated with severe adverse effects, including unexpected psychiatric symptoms. These compounds are mainly active through their potent agonism on the cannabinoid receptors CB₁ and CB₂. Recently, evidence of the direct interaction of some SCRAs with the serotonergic 5-HT receptors has emerged.

SCRAs were screened for in vitro 5-HT_2A receptor activity using AequoScreen® intracellular Ca²⁺ release and inositol monophosphate (IP₁) formation assays. The pharmaco-toxicological effects induced by the administration of the most effective compound in vitro (AB-5'F-BUTINACA) were investigated in male CD-1 mice with specific focus on its interaction with CB₁ and 5-HT_2A receptors.

Many SCRAs with a valinamide (AB) or tert-leucinamide (ADB) head moiety had in vitro activity at the 5-HT_2A receptor at high concentrations with AB-5'F-BUTINACA and ADB-BUTINACA amongst the most efficacious. In vivo studies showed that AB-5'F-BUTINACA caused neurological changes, sensorimotor alteration, antinociception, hypothermia, reduction in breath rate and hypolocomotion in mice. The neurological, sensorimotor, and thermal antinociceptive effects were mediated by CB₁ and 5-HT_2A receptors, as they were prevented by pretreatment with the selective CB₁ and 5-HT_2A receptor antagonists (NESS0327 and MDL100907, respectively).

This study demonstrated for the first time that SCRAs with a valinamide or tert-leucinamide head moiety activate the 5-HT_2A receptor. Agonism of the compound AB-5'F-BUTINACA at the 5-HT_2A receptors resulted in in vivo effects. Our data revealed potential risks related to SCRA consumption that could exacerbate unexpected psychiatric conditions.