YM155 downregulated survivin expression, inhibited cell proliferation, and induced cell apoptosis in ATL leukemic cell lines ATL-43b and ATL-55(+). (A) ATL-43b and ATL-55(+) cells were cultured with medium alone or 1 nM, 10 nM, or 100 nM YM155 for 48 hours. Cells were harvested and analyzed for survivin expression by western blot analysis. (B) MTT cell proliferation assay of ATL-43b and ATL-55(+) cells treated with a serial dilution of concentrations of YM155 for 72 hours. (C) ATL-43b and ATL-55(+) cells were cultured with medium alone or 1 nM, 10 nM, 100 nM, or 1000 nM YM155 for 48 hours. The cells were then labeled with fluorochrome inhibitor of caspases reagent and analyzed by flow cytometry to detect cells with active caspase 3 and caspase 7. (D) ATL-43b and ATL-55(+) cells were cultured with medium alone or 1 nM, 10 nM, 100 nM, or 1000 nM YM155 for 48 hours. The cells were then fixed and labeled with antibody to cleaved PARP.