Breast Cancer Resistance Protein Exports Sulfated Estrogens but Not Free Estrogens

• Published in: Molecular pharmacology Vol. 64; no. 3; pp. 610 - 618
• Main Authors: Imai, Yasuo, Asada, Sakiyo, Tsukahara, Satomi, Ishikawa, Etsuko, Tsuruo, Takashi, Sugimoto, Yoshikazu
• Format: Journal Article
• Language: English
• Published: United States American Society for Pharmacology and Experimental Therapeutics 01.09.2003
• Subjects: Animals; ATP Binding Cassette Transporter, Sub-Family G, Member 2; ATP-Binding Cassette Transporters - metabolism; Biological Transport; Breast Neoplasms - metabolism; Cell Line; Dose-Response Relationship, Drug; Drug Resistance, Neoplasm; Estrogens - metabolism; Estrogens, Conjugated (USP) - metabolism; Estrone - analogs & derivatives; Estrone - metabolism; LLC-PK1 Cells; Models, Molecular; Neoplasm Proteins - metabolism; Sulfates - metabolism; Swine
• ISSN: 0026-895X; 1521-0111
• DOI: 10.1124/mol.64.3.610

Breast cancer resistance protein (BCRP), an ATP-binding cassette transporter, confers resistance to a series of anticancer reagents such as mitoxantrone, 7-ethyl-10-hydroxycamptothecin, and topotecan. We reported previously that estrone and 17β-estradiol reverse BCRP-mediated multidrug resistance. In the present study, we demonstrate that BCRP exports estrogen metabolites. First, we generated BCRP -transduced LLC-PK1 (LLC/BCRP) cells, in which exogenous BCRP is expressed in the apical membrane, and investigated transcellular transport of 3 H-labeled compounds using cells plated on microporous filter membranes. The basal-to-apical transport (excretion) of mitoxantrone, estrone, and 17β-estradiol was greater in LLC/BCRP cells than in LLC-PK1 cells. Thin-layer chromatography of transported steroids revealed that the transport of estrone and 17β-estradiol was independent of BCRP expression. Alternatively, increased excretion of estrone sulfate and 17β-estradiol sulfate was observed in LLC/BCRP cells. BCRP inhibitors completely inhibited the increased excretion of sulfated estrogens across the apical membrane. Conversion of estrogens into their sulfate conjugates was similar between LLC/BCRP and LLC-PK1 cells, suggesting that the increased excretion of estrogen sulfates was attributable to BCRP-mediated transport. Next, the uptake of 3 H-labeled compounds in membrane vesicles from BCRP -transduced K562 (K562/BCRP) cells was investigated. 3 H-labeled estrone sulfate, but not 3 H-labeled estrone or 17β-estradiol, was taken up by membrane vesicles from K562/BCRP cells, and this was ATP-dependent. Additionally, BCRP inhibitors suppressed the transport of estrone sulfate in membrane vesicles from K562/BCRP cells. These results suggest that BCRP does not transport either free estrone or 17β-estradiol but exports sulfate conjugates of these estrogens.