Colony formation assays

In brief, cells were seeded into 6-well plates, at 0.1×10⁴ cells per well, and maintained for two weeks in a medium containing 10% FBS. When the clones exceeded 50 cells, the cells were fixed with 4% paraformaldehyde and stained with 1% crystal violet. Finally, the colonies were imaged by scanner (Samsung, Gyeonggi-do, Korea) and counted by the counting tool of Photoshop 6.0 (Adobe Photoshop, San Jose, CA, USA). The experiment was conducted in triplicate.