1′-Acetoxychavicol Acetate Inhibits RANKL–Induced Osteoclastic Differentiation of RAW 264.7 Monocytic Cells by Suppressing Nuclear Factor-κB Activation

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Abstract
Osteoclastogenesis is commonly associated with various age-related diseases, including cancer. A member of the tumor necrosis factor superfamily, receptor activator of nuclear factor-κB (NF-κB) ligand (RANKL), has been shown to play a critical role in osteoclast formation and bone resorption. Thus, agents that suppress RANKL signaling have a potential to suppress bone loss. In this report, we investigated the effect of 1′-acetoxychavicol acetate (ACA), a component of Alpina galanga, on RANKL signaling and consequent osteoclastogenesis in RAW 264.7 cells, a murine monocytic cell line. Treatment of these cells with RANKL activated NF-κB, and coexposure of the cells to ACA completely suppressed RANKL-induced NF-κB activation in a time- and concentration-dependent manner. The suppression of NF-κB by ACA was mediated through suppression of RANKL-induced activation of IκBα kinase, IκBα phosphorylation, and IκBα degradation. Furthermore, incubation of monocytic cells with RANKL induced osteoclastogenesis, and ACA suppressed it. Inhibition of osteoclastogenesis was maximal when cells were simultaneously exposed to ACA and RANKL and minimum when ACA was added 2 days after RANKL. ACA also inhibited the osteoclastogenesis induced by human breast cancer MCF-7 cells, multiple myeloma MM1 cells, and head and neck squamous cell carcinoma LICR-LON-HN5 cells. These results indicate that ACA is an effective blocker of RANKL-induced NF-κB activation and of osteoclastogenesis induced by RANKL and tumor cells, suggesting its potential as a therapeutic agent for osteoporosis and cancer-associated bone loss. (Mol Cancer Res 2006;4(4):275–81)