shRNA knockdown of RUNX1 in Meg-01 cells resulted in increased sensitivity to ara-C. (A-B) Meg-01 cells were infected by RUNX1 shRNA lentivirus clones. After selection with puromycin, infected Meg-01 cells were plated in soft agar. Colonies were isolated, expanded, and tested for RUNX1 expression by real-time RT-PCR (A) and Western blotting (B). Two colonies (designated RUNX1 1-1 and RUNX1 1-2) with decreased RUNX1 gene expression were selected as candidates for further study. A pool of cells from the negative control transduction was used as the control (designated negative). (C) The RUNX1 1-1, RUNX1 1-2, and negative cells were cultured in complete medium with dialyzed FBS in 96-well plates at a density of 4 × 10⁴ cells/mL. Cells were cultured continuously with a range of concentrations of ara-C at 37°C, and cell numbers were determined with the Cell Titer–blue reagent and a fluorescence microplate reader. The data represent mean values ± SEs from at least 3 independent experiments.