Crystal violet

Cells were seeded into 96-well plates at 1000 cells/well. Each group was seeded into 3 wells. During the last 2 hrs of incubation, each well was added 10 μL/well of CCK8. The absorbance at 450 nm was used to determine cell viability.
To evaluate colony formation ability, cells seeded on 6-well plates (400 cells/well), were cultured for 14 days. After fixation with methanol for 20 mins, the cells were stained with crystal violet (Nanjing Jiancheng Bioengineering Institute, Nanjing, People’s Republic of China), following which the number of colonies were counted.

Cells were seeded in triplicate into 6-well plates at a density of 3×10
² cells/well and cultured for approximately 2 weeks. Cells were fixed with 4% paraformaldehyde and then stained with 1% crystal violet (Jiancheng, Nanjing, China). Cell colony formation was detected with a CK-2 inverted microscope (Olympus, Tokyo, Japan), and the colony number was counted with ImageJ software (NIH, Bethesda, USA).

MKN-28 and MGC-803 cells were seeded into a 6-well plate at a density of 500 cells/well and transfected with siRNA-ID1 or siRNA-NC the following day, as described above. The cells were subsequently cultured in RPMI-1640 medium containing 10% FBS and re-transfected every 4 days for 2 weeks. In addition, certain cell groups were treated with 1 µg/ml DDP. Cell colonies were subsequently fixed with methanol and stained with crystal violet (Nanjing Jiancheng Bioengineering Institute, Nanjing, China). Visible colonies of >50 cells were counted by eye for each sample and colony formation rates were subsequently calculated as follows: Number of colonies/the number of cells seeded. Colony formation assays were performed in triplicate.