title: Specific inhibitors of the breast cancer resistance protein (BCRP).
abstract: A new class of specific breast cancer resistance protein (BCRP) inhibitors was identified, showing no inhibition of the ATP binding cassette (ABC) transporters P-gp and MRP1. Some of these modulators inhibit BCRP with high potency; they are only slightly less potent than Ko143 and could serve as promising lead structures for the design of novel effective BCRP inhibitors. These inhibitors are structurally related to tariquidar (XR9576) and belong to a library of multidrug-resistance modulators synthesized by our research group. The absence of the tetrahydroisoquinoline substructure appears to play a crucial role for specificity; we found that the presence of this substructure is not essential for interaction with BCRP. To determine the type of interaction between pheophorbide A and compounds with and without the tetrahydroisoquinoline substructure, various substrate pheophorbide A concentrations were used in enzyme kinetics assays. The resulting data show that these compounds share a noncompetitive-type interaction with pheophorbide A. Experiments with imatinib and pheophorbide A revealed a mixed-type interaction. The combination of imatinib and compounds with and without the tetrahydroisoquinoline substructure resulted in a positive cooperative effect, indicating that imatinib engages a binding site distinct from that of the new compounds on one side and distinct from that of pheophorbide A on the other side as well. The results of this study suggest that the category of BCRP-specific inhibitors, which includes only fumitremorgin C, Ko143 and analogues, and novobiocin needs to be extended by this new class of inhibitors, which possess three key characteristics: specificity, potency, and low toxicity.
authors.affiliation: Institute of Pharmacy, University of Bonn, An der Immenburg 4, 53121 Bonn, Germany.
authors.forename: Anne
authors.initials: A
authors.lastname: Pick
authors.forename: Werner
authors.initials: W
authors.lastname: Klinkhammer
authors.forename: Michael
authors.initials: M
authors.lastname: Wiese
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000241:Adenosine / Q000031:analogs & derivatives / Q000627:therapeutic use; D001549:Benzamides; D001665:Binding Sites; D001943:Breast Neoplasms / Q000188:drug therapy; D045744:Cell Line, Tumor; D002734:Chlorophyll / Q000031:analogs & derivatives* / Q000737:chemistry / Q000627:therapeutic use; D054659:Diketopiperazines; D018432:Drug Resistance, Multiple / Q000187:drug effects; D005260:Female; D006576:Heterocyclic Compounds, 4 or More Rings; D006801:Humans; D000068877:Imatinib Mesylate; D007211:Indoles / Q000627:therapeutic use; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009675:Novobiocin / Q000627:therapeutic use; D010879:Piperazines / Q000627:therapeutic use; D011743:Pyrimidines / Q000627:therapeutic use; D011804:Quinolines / Q000138:chemical synthesis / Q000737:chemistry* / Q000627:therapeutic use; D013329:Structure-Activity Relationship
chemical_list: C541506:3-(6-isobutyl-9-methoxy-1,4-dioxo-1,2,3,4,6,7,12,12a-octahydropyrazino(1',2'-1,6)pyrido(3,4-b)indol-3-yl)propionic acid tert-butyl ester; C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D001549:Benzamides; D054659:Diketopiperazines; D006576:Heterocyclic Compounds, 4 or More Rings; D007211:Indoles; D009363:Neoplasm Proteins; D010879:Piperazines; D011743:Pyrimidines; D011804:Quinolines; D002734:Chlorophyll; D009675:Novobiocin; D000068877:Imatinib Mesylate; C010522:tryptoquivaline; C032623:pheophorbide a; C402343:tariquidar; D000241:Adenosine