Mechanisms of Osteoclastogenesis Inhibition by a Novel Class of Biphenyl-Type Cannabinoid CB2 Receptor Inverse Agonists Original Research Article

The cannabinoid CB2 receptor is known to modulate osteoclast function by poorly understood mechanisms. Here, we report that the natural biphenyl neolignan 4′-O-methylhonokiol (MH) is a CB2 receptor-selective antiosteoclastogenic lead structure (Ki < 50 nM). Intriguingly, MH triggers a simultaneous Gi inverse agonist response and a strong CB2 receptor-dependent increase in intracellular calcium. The most active inverse agonists from a library of MH derivatives inhibited osteoclastogenesis in RANK ligand-stimulated RAW264.7 cells and primary human macrophages. Moreover, these ligands potently inhibited the osteoclastogenic action of endocannabinoids. Our data show that CB2 receptor-mediated cAMP formation, but not intracellular calcium, is crucially involved in the regulation of osteoclastogenesis, primarily by inhibiting macrophage chemotaxis and TNF-α expression. MH is an easily accessible CB2 receptor-selective scaffold that exhibits a novel type of functional heterogeneity.