2.5. Colony formation assay

About 500 cells were plated into six-well plates for 24 h. Subsequently, cells were treated with 80 nM of digoxin, 40 µM of gemcitabine or in combination for 24 h. Drug-free growth medium was added and cells were further incubated for 14 days before fixation with 4% formaldehyde and staining with 0.5% crystal violet. The number of colonies were then counted microscopically.