In contrast, at a non-cytotoxic concentration of 500 nM, TP-3654 did not resensitize ABCB1-overexpressing cancer cells to ABCB1 substrate drugs, but significantly resensitized ABCG2-overexpressing cancer cells to ABCG2 substrate drugs topotecan, SN-38, and mitoxantrone, with FR values ranging from approximately 4 to 32 (Table 3). This evidence concerns the gene ABCB1 and cancer.