Assessing Drug Sensitivity in Multidrug-Resistant Cell Lines

To determine the drug sensitivities of the previously described ABCB1-overexpressing KB-C2 cells, LLC-MDR1-WT cells, and ABCC10-overexpressing HEK293/ABCC10 cells, with KB-3-1, LLC-PK1, and HEK293/pcDNA3.1 cells as the respective controls [1 (link),16 (link)], a modified MTT assay was performed [1 (link),21 (link)]. Approximately 4,000 KB-3-1 cells, 7,000 KB-C2 cells, and 5,000 LLC-PK1, LLC-MDR1-WT, HEK293/pcDNA3.1, and HEK293/ABCC10 cells were seeded in 180 μL of medium in each well of 96-well plates. After incubating for 24 h at 37°C, 20 μL of paclitaxel or cabazitaxel (0.01 to 10 μmol/L) was added. Subsequently, cells treated with paclitaxel or cabazitaxel in DMEM supplemented with 10% FBS were incubated at 37°C for 72 h. After 72 h, 20 μL MTT (4 mg/mL) was added to each well. The cells were incubated at 37°C for another 4 h. The MTT with medium was removed, and 100 μL of DMSO was added to each well. The absorbance was measured at 570 nm by an Opsys microplate reader (Dynex Technologies, VA, USA). The degree of resistance was calculated by dividing the 50% inhibition concentration (IC₅₀) as calculated using the Bliss method for drug-resistant cells (KB-C2, LLC-MDR1-WT, and HEK293/ABCC10) by that of the parental drug-sensitive cells (KB-3-1, LLC-PK1, and HEK293/pcDNA3.1), respectively. Each MTT assay was run in triplicate.