We thus used three established human MDR tumor cell lines overexpressing the dominant MDR efflux transporters P-gp, MRP1 and BCRP (i.e. KB-V1, 2008/MRP1 and A549/K1.5, respectively), their drug sensitive parental counterparts, as well as their specific MDR transport inhibitors TQD [47], MK571 [48] and Ko143 [49]. The gene discussed is ABCG2; the disease is neoplasm.