title: BCRP/ABCG2 levels account for the resistance to topoisomerase I inhibitors and reversal effects by gefitinib in non-small cell lung cancer.
abstract: OBJECTIVE
  Breast cancer resistance protein (BCRP) confers resistance against topoisomerase I inhibitors in cancer cells. Very recently, we reported that gefitinib reverses BCRP-mediated drug resistance by direct inhibition. However, it remains undetermined how much BCRP contributes to the resistance to topoisomerase I inhibitors in non-small cell lung cancer (NSCLC). The present study was designed to examine whether BCRP levels in NSCLC cells are correlated with the resistance to topoisomerase I inhibitors and the reversal effect by gefitinib.
  
  
  METHODS
  BCRP levels and its function were evaluated by Western blotting and flowcytometry, respectively. Gefitinib-insensitive NSCLC cells expressed various levels of BCRP, which were closely correlated not only with the IC50 values of SN-38 (r=0.874, P<0.05) and those of topotecan (r=0.968, P<0.001), but also with the reversal effects of 1 microM gefitinib on SN-38 resistance (r=0.956, P<0.001) and topotecan resistance (r=0.977, P=0.0001).
  
  
  RESULTS
  BCRP levels accounted for between 80 and 90% of the variation in the resistance to topoisomerase I inhibitors and the reversal effects by gefitinib. Also, gefitinib increased intracellular topotecan accumulation in proportion to the BCRP levels.
  
  
  CONCLUSIONS
  These findings suggest that BCRP is the most important molecule responsible for topoisomerase I inhibitor resistance, and that the development of BCRP inhibitors is an effective approach for overcoming this resistance. In addition, the examination of BCRP levels in NSCLC tissues may identify an optimal patient population for treatment with topoisomerase I inhibitors alone or in combination with BCRP inhibitors.
authors.affiliation: Second Department of Internal Medicine, Nagasaki University School of Medicine, Nagasaki, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Nagashima
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Soda
authors.forename: Mikio
authors.initials: M
authors.lastname: Oka
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kitazaki
authors.forename: Ken
authors.initials: K
authors.lastname: Shiozawa
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Masaaki
authors.initials: M
authors.lastname: Takemura
authors.forename: Hikaru
authors.initials: H
authors.lastname: Yabuuchi
authors.forename: Minoru
authors.initials: M
authors.lastname: Fukuda
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Tsukamoto
authors.forename: Shigeru
authors.initials: S
authors.lastname: Kohno
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology; D015153:Blotting, Western; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D005434:Flow Cytometry / Q000379:methods; D000077156:Gefitinib; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D000077146:Irinotecan; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011799:Quinazolines / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D013050:Spectrometry, Fluorescence / Q000379:methods; D059004:Topoisomerase I Inhibitors; D019772:Topotecan / Q000378:metabolism / Q000494:pharmacology*
chemical_list: C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000970:Antineoplastic Agents; D009363:Neoplasm Proteins; D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D012333:RNA, Messenger; D059004:Topoisomerase I Inhibitors; D000077146:Irinotecan; D019772:Topotecan; D066246:ErbB Receptors; D000251:Adenosine Triphosphatases; D000077156:Gefitinib; D002166:Camptothecin