BPR0L075 is not a substrate for another ATP-binding cassette efflux transporter breast cancer resistance protein (BCRP), evidenced by the comparable cytotoxicity in human breast cancer MCF7 cells (IC50 = 3.5 nM) and mitoxantrone-resistant MCF7/MX cells (IC50 = 4.0 nM), MCF7/MX cells are known to overexpress BCRP [23], [24], [25]. This evidence concerns the gene ABCG2 and breast cancer.