MTT cell viability assay

A total of 1×10⁴ MUM-2B cells were seeded in a 96-well plate for 24 h, then treated with 0, 1, 2.5, 5 10 or 20 µM damnacanthal for 12, 24 or 48 h. A total of 20 µl MTT (5 mg/ml; Sigma-Aldrich; Merck KGaA, Darmstadt, Germany) was added to each well prior to incubation for another 4 h at 37°C. The supernatants were aspirated and 150 µl dimethylsulfoxide (Sigma-Aldrich; Merck KGaA) was added to each well to dissolve the formazan crystals for 20 min at 37°C. The optical density (OD) at 490 nm was determined using a microplate reader (Molecular Devices, Sunnyvale, CA, USA).