Flavopiridol and shRNA decrease MCL-1 and BFL-1 levels and increase the response to ABT-737 in resistant CLL cell lines. (A) Mec-1, Mec-2, and PTA CLL cells were treated with flavopiridol for 4 hours, and then BCL-2, MCL-1, and BFL-1 levels were assessed by quantitative RT-PCR. (B) Mec-1, Mec-2, and PTA-3920 were treated with flavopiridol for 4 hours; then the drug was removed and cells were cultured without or with ABT-737 (100nM) for an additional 18 hours. (C) Quantitative RT-PCR analyses of BCL-2, MCL-1, and BFL-1 levels in Mec-1 parental, SHMCL-1, SHBFL-1, and as a control, scrambled shRNA (shControl)–expressing cells. (D) Mec-1 parental, shControl, SHMCL-1, and SHBFL-1–expressing cells were treated with ABT-737 (1000nM) for 18 hours. Cell viability was assayed by annexin-V/FITC and propidium iodide staining and analyzed by flow cytometry. Values are normalized to untreated cells, and DMSO treatment served as a negative control. P values were determined by the 2-tailed t test. The graphs presented are representative of 2 independent experiments with data shown as mean ± SD.