The Syk inhibitor R406 induces CLL cell apoptosis and abrogates BCR-derived survival signals. (A) Presented are contour plots that depict the relative green (DiOC6) and red (PI) fluorescence intensities of CLL cells from a representative patient on the horizontal and vertical axes, respectively. The viability was determined after 24 and 48 hours (as indicated on the left side) after incubation of CLL cells in medium alone (control), medium supplemented with 5 μM R406, medium with 10 μg/mL anti-IgM mAbs, or medium with anti-IgM mAbs and 5 μM R406, as indicated above the plots. The viable cell population is characterized by bright DiOC6 staining and PI exclusion, and is gated in the lower right corner of each contour plot. The percentage of viable cells is displayed above each of these gates. In this case, R406 reduced CLL cell viability from 54.8% to 44%. Anti-IgM stimulation increased CLL cell viability to 84.1%, which was completely abrogated by coincubation with anti-IgM plus R406, reducing CLL cell viability to 45% at 24 hours. Similar results were obtained at 48 hours (bottom row). (B-C) The bar diagrams represent the mean relative viabilities of CLL cells cultured in complete medium (control), or medium supplemented with 5 μM R406, 10 μg/mL anti-IgM, or the combination of 5 μM R406 and 10 μg/mL anti-IgM. Viabilities were normalized to the relative viability of control samples at the respective time points (100%), to account for differences in spontaneous apoptosis in samples from different patients. Displayed are the means (± SEM) from 11 different patient samples, assessed after 24 hours (B) and 48 hours (C). * and ** indicate P < .05.
