MTT assay

All different cell lines were seeded in 96-well plates at 1×10⁵ cells/well for 24 h followed by culture medium removal and subsequently addition of culture medium containing different amounts of the precursors. At designated time (24/48/72 h), we added 10 μL MTT solution (5 mg/mL) to each well and incubated at 37°C for another 4 h, and then 100 μL of SDS-HCl solution was added to stop the reduction reaction and to dissolve the purple formazan. The absorbance of each well at 595 nm was measured by a multimode microplate reader. The cytotoxicity assay was performed three times, and the average value of the three measurements was taken.