Sensitivity of TCL1 leukemias to R406-induced apoptosis in vitro. (A) TCL1 leukemia cells were cultured for 48 hours with increasing concentrations of R406. The rate of apoptosis was determined by Annexin V/PI staining. Samples NB1, NB2, and NB3 are normal B cells that were purified by negative selection from the spleens of wild-type mice; samples NS1 and NS2 are mononuclear cells obtained from the spleens of the same animals. (B) Time-course analysis of in vitro sensitivity to R406. The percentage of viable cells relative to control (no R406) was determined in 2 TCL1 leukemias (TCL1-540 and TCL1-551) and 2 normal B-cell samples (NB4 and NB5) after 24, 48, and 72 hours incubation with the indicated concentrations of R406. (C) Human CLL cells and TCL1 leukemia cells were cultured for 48 hours in the presence of the indicated concentrations of R406. Protein extracts were analyzed for changes in the expression of Mcl-1 and Bim by immunoblotting. Actin served as a loading control.