title: Differential effects of the breast cancer resistance protein on the cellular accumulation and cytotoxicity of 9-aminocamptothecin and 9-nitrocamptothecin.
abstract: Breast cancer resistance protein (BCRP)/MXR/ABCG2 is a new member of the family of ATP-dependent drug efflux proteins. Whereas overexpression of another member of this family, P-glycoprotein, minimally affects the cytotoxicity of camptothecins (CPTs), overexpression of wild-type as well as certain mutant BCRPs confers resistance to CPT analogues that are used clinically, including topotecan and irinotecan. Relatively little is known regarding the effects of BCRP on other CPT analogues. We now report studies of 9-aminocamptothecin (9-AC) and 9-nitrocamptothecin (9-NC) using mammalian cells stably transfected with constructs expressing a variety of efflux proteins, including wild-type BCRP and a mutant BCRP that contains a threonine rather than an arginine at position 482 (R482T). The results indicate that overexpression of either P-glycoprotein, multidrug resistance protein type 1, or multidrug resistance protein type 2 has little effect on the cytotoxicity of 9-NC or 9-AC. By contrast, overexpression of either wild-type or R482T BCRP confers resistance to 9-AC, but not to 9-NC. Furthermore, overexpression of wild-type or mutant BCRP is associated with reduced intracellular accumulation of 9-AC, but not 9-NC. In addition, immunoblotting studies indicate that whereas increased BCRP expression is evident in cells selected for resistance to irinotecan, BCRP expression is not detectable in two different cell lines selected for resistance to 9-NC. Taken together, these findings suggest that wild-type as well as R482T BCRP mediates cellular efflux of 9-AC but not 9-NC. Furthermore, the results suggest that polar groups at the 9 or 10 position of the CPT A ring facilitate interaction with BCRP and have implications for the clinical development of new CPT analogues.
authors.affiliation: Department of Pharmacology, Cancer Institute of New Jersey, Robert Wood Johnson-University of Medicine and Dentistry of New Jersey, New Brunswick, New Jersey 08901, USA.
authors.forename: Rajeev
authors.initials: R
authors.lastname: Rajendra
authors.forename: Murugesan K
authors.initials: MK
authors.lastname: Gounder
authors.forename: Ahamed
authors.initials: A
authors.lastname: Saleem
authors.forename: Jan H M
authors.initials: JH
authors.lastname: Schellens
authors.forename: Douglas D
authors.initials: DD
authors.lastname: Ross
authors.forename: Susan E
authors.initials: SE
authors.lastname: Bates
authors.forename: Patrick
authors.initials: P
authors.lastname: Sinko
authors.forename: Eric H
authors.initials: EH
authors.lastname: Rubin
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000502:physiology*; D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000378:metabolism*; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D004285:Dogs; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D006801:Humans; D026901:Membrane Transport Proteins; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000378:metabolism; D009363:Neoplasm Proteins / Q000235:genetics / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000502:physiology; D012641:Selection, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000972:Antineoplastic Agents, Phytogenic; D002166:Camptothecin; D026901:Membrane Transport Proteins; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009363:Neoplasm Proteins; D011993:Recombinant Fusion Proteins; C116614:ABCG2 protein, human; C080125:9-aminocamptothecin; C079905:rubitecan; C421109:multidrug resistance-associated protein 1