ABCG2 and cancer: Besides, considering the multidrug resistance (MDR) that occurs in cancer cells is a major obstacle to efficient chemotherapy for tumors [30], the expression of certain ATP-binding cassette (ABC) transporters which are mainly influenced the MDR in chemotherapy included ABCB1, ABCC1 and ABCG2 were assessed in theses cell lines by qRT-PCR with the TMZ at 100 μM for 72 h.