Cell Viability Assay

Cell viability was assessed using an MTT assay, as previously described.³¹ Briefly, 8×10³ HCT116 cells/well were seeded into 96-well plates (Thermo Fisher Scientific, Inc.), allowed to attach overnight and then treated with 1.25, 2.5, 5, 7.5 or 10 μM tetrandrine for 24 h. Following the incubation, MTT (0.5 mg/mL) was added to each well and incubated for 3 h. The supernatant was subsequently discarded and DMSO was added to each well to dissolve the formazan crystals. The absorbance was measured at a wavelength of 570 nm using an ELISA reader; the absorbance of the control cells was set to 100% and each experimental group (six replicate wells/concentration) was normalized to the control group. At least four independent experiments were performed.