ABCG2 and cancer: In the present study, we have used several models of MDR cancer cell lines including ATP-binding cassette (ABC)-transporter-overexpressing MDR-mediating P-glycoprotein (P-gp; ABCB1/MDR1) or breast cancer resistance protein (ABCG2/BCRP), a p53 knockout cell line, and a mutation-activated EGFR gene (ΔEGFR) cell line.