Normal human fetal colonic mucosa cells (FHC) and CRC cells (SW620 and SW480) were bought from the American Type Culture Collection (ATCC, Manassas, VA, USA). 5-FU-resistant CRC cells (SW620/5-FU and SW480/5-FU) were generated by treating SW620 and SW480 cells with increasing doses of 5-FU (Solarbio, Beijing, China), as previously described.23 (link) All these cells were maintained in Dulbecco’s modified Eagle’s medium (DMEM; HyClone, South Logan, UT, USA) supplemented with 10% fetal bovine serum (FBS; HyClone) and 1% penicillin-streptomycin (HyClone) at an atmosphere of 5% CO2 and 37°C. To maintain the resistance of SW620/5-FU and SW480/5-FU cells, 15.0 μg/mL 5-FU (Solarbio) was additionally added into the medium.