Effects of mcl-1 ASO alone and in combination with STI571 on growth and viability of K562 cells. (A) Serial dilution of mcl-1 ASO and its effect on MCL-1 protein expression determined by Western blotting. β-actin served as loading control. (B) Time-dependent effect of mcl-1 ASO (250 nM) and scramble control on expression of MCL-1 protein (determined by Western blotting, top) and on viability, that is, the percentage of apoptotic K562 cells (bottom). Results represent the mean ± SD from 3 independent experiments. (C) Effects of mcl-1 ASO or scramble control (each 200 nM) applied with (+STI571, 200 nM) or without STI571 (-STI571), on expression of MCL-1 (determined by Western blotting, top) and on cell viability, that is, percentage of apoptotic cells (bottom); results represent the mean ± SD from 3 independent experiments. (D) Using CalcuSyn software, analyses of dose-effect relationships of STI571- and mcl-1 ASO-induced apoptosis in K562 cells were calculated according to the median effect method of Chou and Talalay.³⁸  A combination index (CI) less than 1 indicates synergism. (E) Effects of various concentrations of STI571 on ³H-thymidine uptake by K562 cells transfected with scramble control (▪) or mcl-1 antisense, 250 nM (•). Results are expressed as percent of control (ie, scramble control without STI571) and represent the mean ± SD of 3 independent experiments. Neither the scramble control nor lipofectin (used for transfection) produced a substantial decrease in ³H-thymidine uptake compared to untransfected cells (ie, control; see insert). CPM indicates counts per minute.