Inhibition of Syk activity induces cell death in tumor B cells. Cells were treated with R406 in vitro. (A) A representative plot of cell viability as determined by MTS assay by concentration of the Syk inhibitor R406 (n = 4). (B) Representative plots of PI stains of TBL-1 and DBL-114 tumor B cells treated with DMSO (gray shaded) or 2 μM R406 (black trace). The bar is gated on subdiploid DNA for apoptotic cells. The bottom percentage is for DMSO treatment and the top for R406. (C) A bar graph depicting percent positive 7-AAD (top panel) or PI (bottom panel) after 24-hour treatment with DMSO (■) or 2 μM R406 (□).