ABCG2 and cancer: The overexpression of ABC transporters effectively improves efflux function and reduces intracellular accumulation of chemotherapeutic agents to mediate drug resistance[45].The induction of ABC transporters is recognized as an early event in the development of chemoresistance[46].In order to reverse tumor MDR mediated by ABC transporters, enormous research effort has been made to develop ABC transporter modulators that could suppress the drug efflux activity of MDR cancer cells.