BHQ880 reverses the inhibitory effect of MM cells on osteoblastogenesis. (A) BMSC obtained from BM aspirate of MM patients were stimulated with OB differentiation media for 3 weeks in the presence of IgG1 isotype control antibody or 1 μg/mL BHQ880 and in the absence (top panel) or in the presence (bottom panel) of INA-6 MM cells. At the end of the culture period, the cells were fixed in 10% formaldehyde and stained with Alizarin Red for 30 minutes. (B) Calcium deposition was quantified in these cultures using osteogenesis assay kit. The amount of calcium deposits in differentiated BMSC treated with BHQ880 (red column) is expressed as percent of calcium deposition compared with differentiated BMSC treated with isotype control antibody (blue column) in the absence and presence of MM cells. (C) Supernatants from these assays were analyzed for huIL-6 level by ELISA. IL-6 production was suppressed after treatment with BHQ880 in supernatants from both cultures with and without MM cells.