ABCG2 and hepatocellular carcinoma: For further validation, we employed cultured cell lines that over-express a single transporter and are reported to exhibit multidrug resistance, HCT-15 ([colorectal adenocarcinoma, overexpression of MDR1 [22]), HepG2 (hepatocellular carcinoma, overexpression of MRP [23], [24]), and HL-60/MX1 cell line (acute promielocytic leukemia, presumed overexpression of BCRP since mitoxantrone resistance is usually attributed to BCRP overexpression [33]).