4.8. Cell viability assay

Cytotoxicity of methotrexate was determined in MRP1‐ or MRP7‐overexpressing cell lines using the MTT assay as described previously. ³⁵ Briefly, equal number of cells were seeded in 96‐well plates 24 h prior to drug treatment. After incubation in culturing environment for 68 h, MTT was added and incubated for extra 4 h. DMSO was added in each well to dissolve the purple formazan. Absorbance at 570 nm was measured and IC₅₀ values were calculated as previously described. ³⁵