A multidrug-resistant transporter, breast cancer resistance protein (BCRP), was identified in human breast cancer cells MCF-7/AdrVp, which exhibit resistance to anthracycline drugs like mitoxantrone, doxorubicin, and daunorubicin. This resistance is not due to overexpression of known transporters like P-glycoprotein or multidrug resistance protein (MRP). RNA fingerprinting identified a 2.4-kb mRNA overexpressed in MCF-7/AdrVp cells, which encodes BCRP, a member of the ATP-binding cassette (ABC) transporter family. BCRP is an ATP-dependent xenobiotic transporter that contributes significantly to the multidrug resistance phenotype of MCF-7/AdrVp cells. BCRP overexpression in MCF-7 cells conferred resistance to anthracycline drugs, reduced daunorubicin accumulation, and enhanced efflux of rhodamine 123. BCRP is expressed in various human tissues, with highest levels in placenta. BCRP overexpression in MCF-7 cells led to resistance to mitoxantrone, doxorubicin, and daunorubicin, but not to cis-platin, paclitaxel, or vincristine. BCRP function is ATP-dependent, and its overexpression in MCF-7 cells resulted in reduced daunorubicin retention and increased resistance to anthracycline drugs. BCRP is structurally similar to other ABC transporters but has a distinct arrangement of transmembrane domains. BCRP may function as part of a multiprotein complex, contributing to drug resistance. The study highlights the role of BCRP in multidrug resistance in breast cancer cells.A multidrug-resistant transporter, breast cancer resistance protein (BCRP), was identified in human breast cancer cells MCF-7/AdrVp, which exhibit resistance to anthracycline drugs like mitoxantrone, doxorubicin, and daunorubicin. This resistance is not due to overexpression of known transporters like P-glycoprotein or multidrug resistance protein (MRP). RNA fingerprinting identified a 2.4-kb mRNA overexpressed in MCF-7/AdrVp cells, which encodes BCRP, a member of the ATP-binding cassette (ABC) transporter family. BCRP is an ATP-dependent xenobiotic transporter that contributes significantly to the multidrug resistance phenotype of MCF-7/AdrVp cells. BCRP overexpression in MCF-7 cells conferred resistance to anthracycline drugs, reduced daunorubicin accumulation, and enhanced efflux of rhodamine 123. BCRP is expressed in various human tissues, with highest levels in placenta. BCRP overexpression in MCF-7 cells led to resistance to mitoxantrone, doxorubicin, and daunorubicin, but not to cis-platin, paclitaxel, or vincristine. BCRP function is ATP-dependent, and its overexpression in MCF-7 cells resulted in reduced daunorubicin retention and increased resistance to anthracycline drugs. BCRP is structurally similar to other ABC transporters but has a distinct arrangement of transmembrane domains. BCRP may function as part of a multiprotein complex, contributing to drug resistance. The study highlights the role of BCRP in multidrug resistance in breast cancer cells.