*3.2. Cell Culture*

Human colorectal cancer cells (HCT116), gastric cancer cells (SNU638), breast cancer cells (MDA-MB-231), and liver cancer cells (SK-HEP-1) were purchased from American Type Culture Collection (Manassas, VA, USA). HCT116 and SNU638 cells were maintained in RPMI1640 medium, while MDA-MB-231 and SK-HEP-1 cells were cultured in DMEM medium that was supplemented with 10% heat-inactivated fetal bovine serum (FBS), 100 units/mL penicillin, 100 μg/mL streptomycin, and 250 ng/mL amphotericin B, respectively. Cells were maintained at 37 ◦C in a humidified atmosphere with 5% CO2.
