4.3. Colony Formation Assay

A total of 2000 cells were seeded into each well of a 6-well plate, and the cells were transfected with various concentrations of chemotherapeutic drugs or control in the 6-well plate. The cells were incubated at 37 °C for 10 days. Then, colonies were fixed with 4% formaldehyde for 2 min and stained with crystal violet solution (containing 0.5% crystal violet, 5% formaldehyde, 50% ethanol, and 0.85% sodium chloride) for 2 h. The wells were rinsed with H₂O after air drying. The crystal violet staining of the cells in each well was solubilized using 1 mL of 10% acetic acid per well, and the absorbance (optical density) of the solution was measured using a spectrophotometer at a wavelength of 595 nm.