title: Overexpression of the ATP-binding cassette half-transporter, ABCG2 (Mxr/BCrp/ABCP1), in flavopiridol-resistant human breast cancer cells.
abstract: We sought to characterize the interactions of flavopiridol with members of the ATP-binding cassette (ABC) transporter family. Cells overexpressing multidrug resistance-1 (MDR-1) and multidrug resistance-associated protein (MRP) did not exhibit appreciable flavopiridol resistance, whereas cell lines overexpressing the ABC half-transporter, ABCG2 (MXR/BCRP/ABCP1), were found to be resistant to flavopiridol. Flavopiridol at a concentration of 10 microM was able to prevent MRP-mediated calcein efflux, whereas Pgp-mediated transport of rhodamine 123 was unaffected at flavopiridol concentrations of up to 100 microM. To determine putative mechanisms of resistance to flavopiridol, we exposed the human breast cancer cell line MCF-7 to incrementally increasing concentrations of flavopiridol. The resulting resistant subline, MCF-7 FLV1000, is maintained in 1,000 nM flavopiridol and was found to be 24-fold resistant to flavopiridol, as well as highly cross-resistant to mitoxantrone (675-fold), topotecan (423-fold), and SN-38 (950-fold), the active metabolite of irinotecan. Because this cross-resistance pattern is consistent with that reported for ABCG2-overexpressing cells, cytotoxicity studies were repeated in the presence of 5 microM of the ABCG2 inhibitor fumitremorgin C (FTC), and sensitivity of MCF-7 FLV1000 cells to flavopiridol, mitoxantrone, SN-38, and topotecan was restored. Mitoxantrone efflux studies were performed, and high levels of FTC-reversible mitoxantrone efflux were found. Northern blot and PCR analysis revealed overexpression of the ABCG2 gene. Western blot confirmed overexpression of ABCG2; neither P-glycoprotein nor MRP overexpression was detected. These results suggest that ABCG2 plays a role in resistance to flavopiridol.
authors.affiliation: Developmental Therapeutics Department, Medicine Branch, National Cancer Institute, NIH, Bethesda, Maryland 20892, USA.
authors.forename: R W
authors.initials: RW
authors.lastname: Robey
authors.forename: W Y
authors.initials: WY
authors.lastname: Medina-Pérez
authors.forename: K
authors.initials: K
authors.lastname: Nishiyama
authors.forename: T
authors.initials: T
authors.lastname: Lahusen
authors.forename: K
authors.initials: K
authors.lastname: Miyake
authors.forename: T
authors.initials: T
authors.lastname: Litman
authors.forename: A M
authors.initials: AM
authors.lastname: Senderowicz
authors.forename: D D
authors.initials: DD
authors.lastname: Ross
authors.forename: S E
authors.initials: SE
authors.lastname: Bates
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000037:antagonists & inhibitors / Q000378:metabolism; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D000970:Antineoplastic Agents / Q000378:metabolism / Q000494:pharmacology*; D015152:Blotting, Northern; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D002455:Cell Division / Q000187:drug effects; D017931:DNA Primers / Q000737:chemistry; D019008:Drug Resistance, Neoplasm; D005419:Flavonoids / Q000494:pharmacology*; D005455:Fluorescent Antibody Technique; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D008942:Mitoxantrone / Q000494:pharmacology; D009183:Mycotoxins / Q000494:pharmacology; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D010880:Piperidines / Q000494:pharmacology*; D016133:Polymerase Chain Reaction; D019275:Radiopharmaceuticals / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology
chemical_list: C116614:ABCG2 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000970:Antineoplastic Agents; D017931:DNA Primers; D005419:Flavonoids; D007211:Indoles; D009183:Mycotoxins; D009363:Neoplasm Proteins; D010880:Piperidines; D019275:Radiopharmaceuticals; C077990:alvocidib; D008942:Mitoxantrone; C010522:tryptoquivaline