Pharmacologic targeting of the CB2 cannabinoid receptor for application in centrally-mediated chronic pain

Cannabis preparations have been used for millennia for the treatment of pain and various ailments. However, psychotropic effects, mediated by the CB1 cannabinoid receptor in the central nervous system (CNS), limit their therapeutic use. Research to date suggests that selective activation of the CB2 cannabinoid receptor promotes analgesia without the occurrence of psychotropic effects. Cannabinoids, the principal active compounds in Cannabis sativa, lack the ability to selectively activate CB2. Glial cells of the CNS are known to play an important role in mediating certain forms of chronic pain through pro-inflammatory activity. Furthermore, CB2 receptors expressed by glia are now recognized as a potential therapeutic target for such disease states; however, the contribution of glial cell-mediated neuro-inflammation to the pathophysiology of chronic widespread musculoskeletal pain (CWP) disorders, such as fibromyalgia syndrome, remains unclear. An immunohistology investigation within the acidic saline model of CWP revealed significant up-regulation of Iba-1 and GFAP in the lumbar spinal cord, suggesting that gliosis may potentially mediate hyperalgesia in CWP disorders. Although further investigations are required, these data support that targeting of cannabinoid receptors expressed by glia may be a potentially viable approach for addressing CWP. To target cannabinoid receptors expressed by glia while minimizing the potential for CB1-associated CNS effects, compounds with selective CB2 agonist activity were designed, guided by CB2 molecular docking studies in silico, and synthesized for further investigation. β-caryophyllene, a naturally occurring sesquiterpene, along with two novel compounds, DML-3 and DML-4, were found to be full agonists at CB2 with 109, > 40 and >10,000 –fold selectivity over CB1, respectively. Furthermore, all three compounds significantly reduced activation of NF-κB, ERK1/2 and PI3K in U87MG astrocytes. Significant reductions in astrocyte IL-6 and IL-8 secretion occurred following treatment with β-caryophyllene (1 µM) and DML-4 (25 µM), with minor, non-significant reductions observed following treatment with DML-3 (25 µM). Based on the pharmacologic properties determined, each compound may be a potential candidate for therapeutically targeting pro-inflammatory glial cell activity. Further suggested investigations include quantification of β-arrestin recruitment, screening for off-target effects, testing for efficacy in research models of CWP, followed by in vivo pharmacokinetic and toxicological profiling.Pharmaceutical Sciences, Faculty ofGraduat