Recombinant CCN1 inhibits MM cell growth in vitro. (A) H929 MM cells were incubated for indicated times alone (control; black) with recombinant CCN1 at 1 μg/mL (green), 2 μg/mL (blue), or 5 μg/mL (red). Cells exposed to 2 μg/mL CCN1 at 24 hours and 5 μg/mL CCN1 at 24, 48, 72, and 96 hours had significantly lower cell numbers than untreated controls (P < .01 and P < .001, respectively) (B) Luciferase-expressing stroma-dependent MM cell lines were cocultured with MSCs with increasing doses (μg/mL) of recombinant CCN1 for 7 days, and MM cell growth was determined every 24 hours from bioluminescence intensity.