Up-regulation of MCL1 is not sufficient to induce resistance to ABT-737. CLL cells were pretreated with either 50 ng/mL IL-4 or IFNγ for 4 hours (A,C) or 20 hours (B,D). (A,B) After cytokine treatment, proteins were prepared and analyzed by Western blotting for expression of MCL1, BCL2, or α-tubulin as a loading control. Data from cells of one representative patient typical of 9 examined are shown. MCL1 levels of all 9 patients were quantified by densitometric analysis of Western blots, and values shown are the ratio of MCL1 in treated compared with control cells. The EC50 of ABT-737 at 4 hours is also shown. (C,D) After cytokine treatment (control ♦, IL-4 ▲, IFNγ ■, IL-4 and IFNγ ×), CLL cells were exposed for 4 hours to ABT-737 and apoptosis assessed by PS externalization. Data are the mean plus SEM (n = 9).
