MTT assay

HT29 cells (1×10⁵ cells/ml) were seeded onto 12-well plates and incubated for 24 h, then incubated with 20 µl of MTT solution (5 mg/ml in PBS) for another 1 h. Followed by the removal of culture medium, converted purple formazan dye from MTT was solubilized in dimethyl sulfoxide (DMSO; Sigma-Aldrich; Merck KGaA, Darmstadt, Germany). Finally, optical densities from all the samples were measured at 595 nm by a mocroplate reader (BioRad, Hercules, CA, USA).