Bone Abstracts

Tumour necrosis factor receptor-associated factor 6 (TRAF6) plays a key role in osteoclastogenesis through the regulation of RANK/CD40 TRAF6-mediated signaling. Mice deficient in TRAF6 exhibit high bone mass and were protected against inflammation-induced bone loss. Here we describe the effects of a small-molecule 6877002 that has been shown to prevent the binding of TRAF6 to its domain on RANK/CD40 receptor on osteoclast formation in vitro and in vivo and on ovariectomy-induced bone loss in vivo. The TRAF6 inhibitor 6877002 (1 μM) inhibited RANKL- and/or CD40L-induced osteoclast formation (86%, P<0.001) and survival (57%, P<0.001) without affecting pre-osteoclast viability. Moreover, this agent (1 μM) inhibited the ability of osteoblasts to induce osteoclast formation and activity in murine osteoblast-bone marrow co-cultures without affecting osteoblast viability. In human T cells, 6877002 (1 μM) completely prevented T cell-induced osteoclast formation (91%, P<0.001) and significantly reduced mature osteoclast survival (54%, P<0.001) without affecting T cell survival. Pretreatment of mature osteoclasts and their precursors generated in M-CSF and RANKL stimulated mouse bone marrow cultures or M-CSF dependent bone marrow macrophages with 6877002 (10 μM) for 60 min prior to stimulation with RANK-L (100 ng/ml) or CD40L (100 ng/ml), completely abolished the phosphorylation of IKKαβ and prevented NFκB activation. The TRAF6 inhibitor 6877002 (10 mg/kg per day) completely prevented the loss of trabecular bone (40% increase, P<0.01) following ovariectomy and preserved trabecular number and thickness (P<0.05), and increased trabecular connectivity in mice. Histomorphometric analysis showed that this was mainly due to a reduction in osteoclast number and activity (P<0.05) with no significant effect on osteoblast number. Altogether, these findings suggest that the small molecule TRAF6 inhibitor 6877002 and related compounds have great potential as a novel class of anti-resorptive agents, which may be of clinical value in the treatment of diseases characterized by excessive osteoclastic bone resorption such as postmenopausal osteoporosis, rheumatoid arthritis and cancer-associated bone disease.