ABCB1 and cancer: Moreover, at a non-cytotoxic concentration of 1 μM, SGI-1776 resensitized ABCB1-overexpressing cancer cells to ABCB1 substrate drug daunorubicin with FR values of 2.9 and 4.0, whereas it resensitized ABCG2-overexpressing cancer cells to ABCG2 substrate drug mitoxantrone with FR values of 2.7 and 2.4 [41].