Quantitative evaluation of ABC transporter-mediated drug resistance based on the determination of the anticancer activity of camptothecin against breast cancer stem cells using TIRF

Elevated expression of drug efflux pumps such as multidrug resistant protein-1 (MDR1/ABCB1) and multidrug resistance associated protein-1 (MRP1/ABCC1) in cancer stem cells (CSCs) among a bulky tumor cell population was attributed to drug resistance. For the first time, we have quantitatively evaluated the cytotoxic profile of camptothecin (CPT) against the CSC. In the present study, a Qdot based total internal reflection fluorescence (TIRF) detection system effectively interpreted that drug resistance to CPT was reduced in the CSC under ABCB1 inhibited conditions. This study revealed that quantitative finding of the EC50 value for apoptosis and necrosis in correlation with the ABC inhibitor and CSC population using TIRF could provide more details of the anti-cancer efficacy of chemotherapeutic agents.