Characterization of a Cannabinoid CB2 Receptor-Selective Agonist, A-836339 [2,2,3,3-Tetramethyl-cyclopropanecarboxylic Acid [3-(2-Methoxy-ethyl)-4,5-dimethyl-3H-thiazol-(2Z)-ylidene]-amide], Using in Vitro Pharmacological Assays, in Vivo Pain Models, and Pharmacological Magnetic Resonance Imaging

[摘要]：

Studies demonstrating the antihyperalgesic and antiallodynic effects of cannabinoid CB2 receptor activation have been largely derived from the use of receptor-selective ligands. Here, we report the identification of A-836339 [2,2,3,3-tetramethyl-cyclopropanecarboxylic acid [3-(2-methoxy-ethyl)-4,5-dimethyl-3H-thiazol(2Z)-ylidene]-amide], a potent and selective CB2 agonist as characterized in in vitro pharmacological assays and in in vivo models of pain and central nervous system (CNS) behavior models. In radioligand binding assays, A-836339 displays high affinities at CB2 receptors and selectivity over CB1 receptors in both human and rat. Likewise, A-836339 exhibits high potencies at CB2 and selectivity over CB1 receptors in recombinant fluorescence imaging plate reader and cyclase functional assays. In addition A-836339 exhibits a profile devoid of significant affinity at other G-protein-coupled receptors and ion channels. A-836339 was characterized extensively in various animal pain models. In the complete Freund's adjuvant model of inflammatory pain, A-836339 exhibits a potent CB2 receptor-mediated antihyperalgesic effect that is independent of CB1 or mu-opioid receptors. A-836339 has also demonstrated efficacies in the chronic constrain injury (CCI) model of neuropathic pain, skin incision, and capsaicin-induced secondary mechanical hyperalgesia models. Furthermore, no tolerance was developed in the CCI model after subchronic treatment with A-836339 for 5 days. In assessing CNS effects, A-836339 exhibited a CB1 receptor-mediated decrease of spontaneous locomotor activities at a higher dose, a finding consistent with the CNS activation pattern observed by pharmacological magnetic resonance imaging. These data demonstrate that A-836339 is a useful tool for use of studying CB2 receptor pharmacology and for investigation of the role of CB2 receptor modulation for treatment of pain in preclinical animal models.

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