Characterization of a Cannabinoid CB₂Receptor-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

Abstract

Studies demonstrating the antihyperalgesic and antiallodynic effects of cannabinoid CB 2 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 CB 2 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 CB 2 receptors and selectivity over CB 1 receptors in both human and rat. Likewise, A-836339 exhibits high potencies at CB 2 and selectivity over CB 1 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 CB 2 receptor-mediated antihyperalgesic effect that is independent of CB 1 or -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 CB 1 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 CB 2 receptor pharmacology and for investigation of the role of CB 2 receptor modulation for treatment of pain in preclinical animal models.It is estimated that as high as 50% of the population will experience chronic pain during their lifetime, and the prevalence is likely to rise with the continued aging of the population (Markman and Philip, 2007). As a consequence, there exists an ever-growing demand for new therapies to provide safe and effective pain management. Despite intensive research to identify novel therapeutic approaches, there have been few major advances in pain therapy over the past sev-

Reduced Antinociceptive Effect of Repeated Treatment with a Cannabinoid Receptor Type 2 Agonist in Cannabinoid-Tolerant Rats Following Spinal Nerve Transection

“…administration of the CB2 receptor agonist JWH015 effectively reverses L5 nerve transection-induced behavioral hypersensitivity without antinociceptive tolerance through at least five days of treatment (Romero-Sandoval and Eisenach, 2007). Similar findings have been described with another CB2 receptor agonist, A-836339 (Yao et al, 2009). Taken together, these previous findings suggest that CB1 rather than CB2 receptor agonism is responsible for the antinociceptive tolerance observed in response to CP55940 administration in the current study.…”

“…Furthermore, sustained spinal or subcutaneous administration of the CB1 receptor agonist, WIN 55,212-2 has been shown to induce hypersensitivity and antinociceptive tolerance in naive mice and rats. In contrast, we (Romero-Sandoval and Eisenach, 2007;Romero-Sandoval et al, 2008a) and others (Yao et al, 2009) have shown that spinal CB2 receptor agonists (such as JWH015) relieve postoperative and neuropathic pain in rodent models without inducing neurological side effects or antinociceptive tolerance. Despite advancements in the molecular mechanisms involved in cannabinoid tolerance (Martini et al, 2010), a better understanding of the respective roles of CB1 and CB2 receptors is required to design effective therapies that do not induce tolerance.…”

Dynamic changes to the endocannabinoid system in models of chronic pain

“…The role of CB2 receptors in modulating peripheral nerves innervating the arthritic joint appear to be complex; close arterial (peripheral) administration of CB2 receptor agonists increased vasodilatation in the inflamed knee joints of rats [75] and facilitated peripheral nerve responses in rats with OA joint damage [52]. Nevertheless, systemic administration of the CB2 receptor agonist A-796260 reversed decreases in grip strength, a surrogate measure of pain, in the monosodium iodoacetate (MIA) model of osteoarthritis pain [76]. Our current lack of knowledge about how arthritis joint pathology impacts on the expression of cannabinoid receptors, both on peripheral nerves and on local cells within the knee joint, hinders the further interpretation of these studies at this point in time.…”

CB1 Knockout Mice Unveil Sustained CB2-Mediated Antiallodynic Effects of the Mixed CB1/CB2 Agonist CP55,940 in a Mouse Model of Paclitaxel-Induced Neuropathic Pain

“…By contrast, chronic CP55,940, at a dose that produced CB 2 -mediated antiallodynic efficacy, failed to decrease body temperature in CB 1 KO mice, documenting that prolonged activation of CB 2 receptors does not result in hypothermia (Malan et al, 2001;Valenzano et al, 2005;Yao et al, 2009;Elliott et al, 2011;Kinsey et al, 2011;Amenta et al, 2012). Chronic CP55,940-treated WT, but not CB 1 KO mice, showed profound withdrawal signs when challenged with the CB 1 antagonist rimonabant, suggesting precipitation at CB 1 receptors produces withdrawal symptoms (Tsou et al, 1995;Aceto et al, 1996;Cook et al, 1998;Rubino et al, 1998;Lichtman et al, 2001).…”