Dose-dependent inhibitory effects of RO9021 on osteoclastogenesis. (A) Representative images of tartrate-resistant acid phosphate (TRAP) staining showing receptor activator of nuclear factor kappa-B ligand (RANK-L) and monocyte colony-stimulating factor (M-CSF) mediated osteoclastogenesis from mouse bone marrow macrophages (BMM). Osteoclasts were shown as TRAP+ multinuclear cells. Negative and positive controls labeled as (–) RANK-L (upper left) and (+) RANK-L (upper right), respectively. The concentration of RO9021 was labeled on the upper right corner of each image. (B) TRAP+ multinuclear osteoclasts were counted under a microscope and percentage of inhibition on osteoclastogenesis was presented. Results were in triplicate and are plotted as mean ± standard deviation. IC50, half-maximal inhibitory concentration.