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Synthetic cannabinoid receptor agonists (SCRAs) are one of the largest and most structurally diverse classes of new psychoactive substances (NPS). Despite this, pharmacological data are often lacking following the identification of a new SCRA in drug markets. In this first of a three-part series, we describe the synthesis, analytical characterization, and binding affinity of a proactively generated, systematic library of 30 indole, indazole, and 7-azaindole SCRAs related to MMB-4en-PICA, MDMB-4en-PINACA, ADB-4en-PINACA, and MMB-4CN-BUTINACA featuring a 4-pentenyl (4en-P), butyl (B/BUT), or 4-cyanobutyl (4CN-B/BUT) tail and a methyl L-valinate (MMB), methyl L-tert-leucinate (MDMB), methyl L-phenylalaninate (MPP), L-valinamide (AB), L-tert-leucinamide (ADB), L-phenylalaninamide (APP), adamantyl (A), or cumyl head group. Competitive radioligand binding assays demonstrated that the indazole core conferred the highest CB 1 binding affinity (K i = 0.17-39 nM), followed by indole-(K i = 0.95-160 nM) and then 7-azaindole-derived SCRAs (K i = 5.4-271 nM). Variation of the head group had the greatest effect on binding, with tert-leucine amides and methyl esters (K i = 0.17-14 nM) generally showing the greatest affinities, followed by valine derivatives (K i = 0.72-180 nM), and then phenylalanine derivatives (K i = 2.5-271 nM). Adamantyl head groups (K i = 8.8-59 nM)

Background and Purpose: Corneal injury can result in dysfunction of corneal nociceptive signaling and corneal sensitization. Activation of the endocannabinoid system has been reported to be analgesic and anti-inflammatory. The purpose of this research was to investigate the antinociceptive and anti-inflammatory effects of cannabinoids with reported actions at cannabinoid 1 (CB1R) and cannabinoid 2 (CB2R) receptors and/or noncannabinoid receptors in an experimental model of corneal hyperalgesia.Methods: Corneal hyperalgesia (increased pain response) was generated using chemical cauterization of the corneal epithelium in wild-type (WT) and CB2R knockout (CB2R−/−) mice. Cauterized eyes were treated topically with the phytocannabinoids Δ8-tetrahydrocannabinol (Δ8THC) or cannabidiol (CBD), or the CBD derivative HU-308, in the presence or absence of the CB1R antagonist AM251 (2.0 mg/kg i.p.), or the 5-HT1A receptor antagonist WAY100635 (1 mg/kg i.p.). Behavioral pain responses to a topical capsaicin challenge at 6 h postinjury were quantified from video recordings. Mice were euthanized at 6 and 12 h postcorneal injury for immunohistochemical analysis to quantify corneal neutrophil infiltration.Results: Corneal cauterization resulted in hyperalgesia to capsaicin at 6 h postinjury compared to sham control eyes. Neutrophil infiltration, indicative of inflammation, was apparent at 6 and 12 h postinjury in WT mice. Application of Δ8THC, CBD, and HU-308 reduced the pain score and neutrophil infiltration in WT mice. The antinociceptive and anti-inflammatory actions of Δ8THC, but not CBD, were blocked by the CB1R antagonist AM251, but were still apparent, for both cannabinoids, in CB2R−/− mice. However, the antinociceptive and anti-inflammatory actions of HU-308 were absent in the CB2R−/− mice. The antinociceptive and anti-inflammatory effects of CBD were blocked by the 5-HT1A antagonist WAY100635.Conclusion: Topical cannabinoids reduce corneal hyperalgesia and inflammation. The antinociceptive and anti-inflammatory effects of Δ8THC are mediated primarily via CB1R, whereas that of the cannabinoids CBD and HU-308, involve activation of 5-HT1A receptors and CB2Rs, respectively. Cannabinoids could be a novel clinical therapy for corneal pain and inflammation resulting from ocular surface injury.

Synthetic cannabinoid receptor agonists (SCRAs) remain one the most prevalent classes of new psychoactive substances (NPS) worldwide, and examples are generally poorly characterised at the time of first detection. We...

Synthetic cannabinoid receptor agonists (SCRAs) are the second largest class of new psychoactive substances (NPS) and are associated with serious adverse effects and even death. Despite this, little pharmacological data are available for many of the most recent SCRAs. This study consists of three different parts, aiming to systematically evaluate a panel of 30 SCRAs using binding and different in vitro human cannabinoid 1 receptor (CB1) activation assays. The present Part II investigated the SCRA analogs for their CB1 activation via a β‐arrestin recruitment assay. The panel was systematically designed to include key structural sub‐features of recent SCRAs. Thus, the 4‐pentenyl tail of MMB‐4en‐PICA and MDMB‐4en‐PINACA was retained while incorporating varying head groups from other prevalent SCRAs, including amides and esters of L‐valine, L‐tert‐leucine, and L‐phenylalanine, and adamantyl and cumyl moieties. All 30 SCRAs activated CB1, with indazoles generally showing the greatest potency (EC50 = 1.88–281 nM), followed by indoles (EC50 = 11.5–2293 nM), and the corresponding 7‐azaindoles (EC50 = 62.4–9251 nM). Several subunit‐linked structure–activity relationships were identified: (i) tert‐leucine‐functionalized SCRAs were more potent than the corresponding valine derivatives; (ii) no major difference in potency or efficacy was observed between tert‐leucine/valine‐derived amides and the corresponding methyl esters; however, phenylalanine analogs were affected by this change; and (iii) minor structural changes to the 4‐pentenyl substituent had little influence on activity. These findings elucidate structural features that modulate the CB1 activation potential of currently prevalent SCRAs and a systematic panel of analogs, some of which may appear in NPS markets in future.