BCRP

Breast cancer resistance protein (BCRP/ABCG2/MXR/ABCP) is an ATP-dependent efflux transporter, which belongs to the large ATP-binding cassette (ABC) transporter family present on cell membranes, and it is classified into the G subfamily of these transporters. BCRP is expressed in a variety of normal cells and acts as a xenobiotic efflux transporter. BCRP is often associated with cancer chemotherapeutic resistance. BCRP confers multidrug resistance (MDR) to a series of antitumor agents such as Mitoxantrone, Daunorubicin, SN-38, and Topotecan, and often limits the efficacy of chemotherapy.

BCRP physiologically functions as a part of a self-defense mechanism for the organism. It enhances elimination of toxic xenobiotic substances and harmful agents in the gut and biliary tract, as well as through the blood-brain, placental, and possibly blood-testis barriers. BCRP recognizes and transports numerous anticancer drugs including conventional chemotherapeutic and targeted small therapeutic molecules relatively new in clinical use. Thus, BCRP expression in cancer cells directly causes MDR by active efflux of anticancer drugs. Because BCRP is also known to be a stem cell marker, its expression in cancer cells could be a manifestation of metabolic and signaling pathways that confer multiple mechanisms of drug resistance, self-renewal (stemness), and invasiveness (aggressiveness), and thereby impart a poor prognosis. Therefore, blocking BCRP-mediated active efflux may provide a therapeutic benefit for cancers.