A, F-dextran loaded liposomes were incubated with BAX, N/C-BID and BCL-XL and the indicated concentrations of ABT-737 or ABT-263 (0.04, 0.2, 1 or 5 μM) for 2.5 h at room temperature. Both ABT-737 and ABT-263 reversed BCL-XL mediated inhibition of BAX and N/C-BID liposome permeabilization. B, Purified CLL cells were treated with 0.05% digitonin to permeabilize the plasma membrane and the cells were washed and pelleted by centrifugation at 13000 rpm. The permeabilized cells were incubated with different concentrations of ABT-737 and ABT-263 for 1 h at 37°C. The release of cytochrome c (Cyt c) from the cell pellet into the supernatant (SN) was assessed after centrifugation by western blotting.