In vitro and in vivo pharmacological characterization of two novel selective cannabinoid CB2 receptor inverse agonists

We have previously developed quinolone-3-carboxamides with the aim of obtaining new ligands for both cannabinoid receptors, CB₁ and CB₂. Our preliminary screening led to the identification of cannabinoid receptor ligands characterized by high affinity and, in some cases, also selectivity for CB₂ receptors. Specifically, three compounds, 1, 2 and 3 showed high affinity for CB₂ as well as high selectivity over CB₁ receptors. In addition, the activity shown by 1 against the formalin-induced nocifensive response in mice, reported in our previous paper, suggests that quinolone-3-carboxamides possess anti-nociceptive properties. In the present work, we have performed functional in vitro bioassays with the aim of investigating the functional activity in the [³⁵S]GTPγS binding assay of the other two compounds that, like 1, behave as CB₂ selective ligands, and their potential analgesic actions in vivo. We found that both 2 and 3 behave in vitro as CB₂ inverse agonists and are able to decrease nociceptive behaviour in the late phase of the formalin test only at the highest dose tested, although, at lower doses, they prevent the anti-nociceptive effects of a selective CB₂ partial agonist in the formalin test. These results identify in 2 and 3 two novel, potent and selective CB₂ antagonists/inverse agonists and confirm previous reports in the literature that, in addition to agonists at cannabinoid CB₂ receptors, also inverse agonists/antagonists at these receptors show promise as anti-inflammatory agents.