MBL-II-141 is a potent ABCG2 inhibitor with an IC50 of 0.11 μM. It inhibits the transport function of ABCG2 in a non-competitive manner, preventing ABCG2 from expelling substrates (such as Irinotecan) out of cells, thereby increasing the intracellular accumulation of the drug. MBL-II-141 does not affect ABCB1 (P-gp) or ABCC1 (MRP1) and exhibits very low cytotoxicity (IG50 > 100 μM). This compound is useful for studying tumor multidrug resistance (MDR).