ABCG2 and cancer: The activity on MRP1 and BCRP was evaluated on cancer cell lines overexpressing each transporter (MDCK-MRP1 and MDCK-BCRP cells), by measuring the inhibition of the efflux of the pro-fluorescent probe Calcein-AM in MDCK-MRP1 cells or the fluorescent probe Hoechst 33342 in MDCK-BCRP cells.