title: Molecular characterization of irinotecan (SN-38) resistant human breast cancer cell lines.
abstract: BACKGROUND
  Studies in taxane and/or anthracycline refractory metastatic breast cancer (mBC) patients have shown approximately 30% response rates to irinotecan. Hence, a significant number of patients will experience irinotecan-induced side effects without obtaining any benefit. The aim of this study was to lay the groundwork for development of predictive biomarkers for irinotecan treatment in BC.
  
  
  METHODS
  We established BC cell lines with acquired or de novo resistance to SN-38, by exposing the human BC cell lines MCF-7 and MDA-MB-231 to either stepwise increasing concentrations over 6 months or an initial high dose of SN-38 (the active metabolite of irinotecan), respectively. The resistant cell lines were analyzed for cross-resistance to other anti-cancer drugs, global gene expression, growth rates, TOP1 and TOP2A gene copy numbers and protein expression, and inhibition of the breast cancer resistance protein (ABCG2/BCRP) drug efflux pump.
  
  
  RESULTS
  We found that the resistant cell lines showed 7-100 fold increased resistance to SN-38 but remained sensitive to docetaxel and the non-camptothecin Top1 inhibitor LMP400. The resistant cell lines were characterized by Top1 down-regulation, changed isoelectric points of Top1 and reduced growth rates. The gene and protein expression of ABCG2/BCRP was up-regulated in the resistant sub-lines and functional assays revealed BCRP as a key mediator of SN-38 resistance.
  
  
  CONCLUSIONS
  Based on our preclinical results, we suggest analyzing the predictive value of the BCRP in breast cancer patients scheduled for irinotecan treatment. Moreover, LMP400 should be tested in a clinical setting in breast cancer patients with resistance to irinotecan.
authors.affiliation: Faculty of Health and Medical Sciences, Department of Veterinary Disease Biology, Section for Molecular Disease Biology and Sino-Danish Breast Cancer Research Centre, University of Copenhagen, Strandboulevarden 49, DK-2100, Copenhagen, Denmark. jxm436@alumni.ku.dk.
authors.forename: Haatisha
authors.initials: H
authors.lastname: Jandu
authors.affiliation: Faculty of Health and Medical Sciences, Department of Veterinary Disease Biology, Section for Molecular Disease Biology and Sino-Danish Breast Cancer Research Centre, University of Copenhagen, Strandboulevarden 49, DK-2100, Copenhagen, Denmark. ljg630@alumni.ku.dk.
authors.forename: Kristina
authors.initials: K
authors.lastname: Aluzaite
authors.affiliation: Faculty of Health and Medical Sciences, Department of Veterinary Disease Biology, Section for Molecular Disease Biology and Sino-Danish Breast Cancer Research Centre, University of Copenhagen, Strandboulevarden 49, DK-2100, Copenhagen, Denmark. louisefogh82@gmail.com.
authors.forename: Louise
authors.initials: L
authors.lastname: Fogh
authors.affiliation: Faculty of Health and Medical Sciences, Department of Veterinary Disease Biology, Section for Molecular Disease Biology and Sino-Danish Breast Cancer Research Centre, University of Copenhagen, Strandboulevarden 49, DK-2100, Copenhagen, Denmark. sebthr@gmail.com.
authors.forename: Sebastian Wingaard
authors.initials: SW
authors.lastname: Thrane
authors.affiliation: Faculty of Health and Medical Sciences, Department of Veterinary Disease Biology, Section for Molecular Disease Biology and Sino-Danish Breast Cancer Research Centre, University of Copenhagen, Strandboulevarden 49, DK-2100, Copenhagen, Denmark. julienoer@gmail.com.
authors.forename: Julie B
authors.initials: JB
authors.lastname: Noer
authors.affiliation: Department of Pathology, Aarhus University Hospital, Noerrebrogade 44, building 18B, 8000, Aarhus C, Denmark. joanna.proszek@gmail.com.
authors.forename: Joanna
authors.initials: J
authors.lastname: Proszek
authors.affiliation: DTU Multiassay Core (DMAC), Technical University of Denmark, Kemitorvet Building 208, DK-2800, Lyngby, Denmark. khoanguyendo@gmail.com.
authors.forename: Khoa Nguyen
authors.initials: KN
authors.lastname: Do
authors.affiliation: Faculty of Health and Medical Sciences, Department of Veterinary Disease Biology, Section for Molecular Disease Biology and Sino-Danish Breast Cancer Research Centre, University of Copenhagen, Strandboulevarden 49, DK-2100, Copenhagen, Denmark. stih@sund.ku.dk.
authors.forename: Stine Ninel
authors.initials: SN
authors.lastname: Hansen
authors.affiliation: Faculty of Health and Medical Sciences, Department of Veterinary Disease Biology, Section for Molecular Disease Biology and Sino-Danish Breast Cancer Research Centre, University of Copenhagen, Strandboulevarden 49, DK-2100, Copenhagen, Denmark. brittdamsgaard@hotmail.com.
authors.forename: Britt
authors.initials: B
authors.lastname: Damsgaard
authors.affiliation: Faculty of Health and Medical Sciences, Department of Veterinary Disease Biology, Section for Molecular Disease Biology and Sino-Danish Breast Cancer Research Centre, University of Copenhagen, Strandboulevarden 49, DK-2100, Copenhagen, Denmark. siln@sund.ku.dk.
authors.forename: Signe Lykke
authors.initials: SL
authors.lastname: Nielsen
authors.affiliation: Department of Pathology, Aarhus University Hospital, Noerrebrogade 44, building 18B, 8000, Aarhus C, Denmark. magnstou@rm.dk.
authors.forename: Magnus
authors.initials: M
authors.lastname: Stougaard
authors.affiliation: Department of Molecular Biology and Genetics, Aarhus University, C.F. Møllers Allé 3, 8000, Aarhus C, Denmark. brk@mb.au.dk.
authors.forename: Birgitta R
authors.initials: BR
authors.lastname: Knudsen
authors.affiliation: Faculty of Health and Medical Sciences, Department of Veterinary Disease Biology, Section for Molecular Disease Biology and Sino-Danish Breast Cancer Research Centre, University of Copenhagen, Strandboulevarden 49, DK-2100, Copenhagen, Denmark. jomo@sund.ku.dk.
authors.forename: José
authors.initials: J
authors.lastname: Moreira
authors.affiliation: Brain Tumor Biology, Danish Cancer Society Research Center, Strandboulevarden 49, DK-2100, Copenhagen, Denmark. pkn@CANCER.DK.
authors.forename: Petra
authors.initials: P
authors.lastname: Hamerlik
authors.affiliation: Brain Tumor Biology, Danish Cancer Society Research Center, Strandboulevarden 49, DK-2100, Copenhagen, Denmark. makiga@cancer.dk.
authors.forename: Madhavsai
authors.initials: M
authors.lastname: Gajjar
authors.affiliation: Erasmus MC Cancer Institute, Department of Medical Oncology and Cancer Genomics Netherlands, Erasmus MC, Rotterdam, The Netherlands. m.smid@erasmusmc.nl.
authors.forename: Marcel
authors.initials: M
authors.lastname: Smid
authors.affiliation: Erasmus MC Cancer Institute, Department of Medical Oncology and Cancer Genomics Netherlands, Erasmus MC, Rotterdam, The Netherlands. j.martens@erasmusmc.nl.
authors.forename: John
authors.initials: J
authors.lastname: Martens
authors.affiliation: Erasmus MC Cancer Institute, Department of Medical Oncology and Cancer Genomics Netherlands, Erasmus MC, Rotterdam, The Netherlands. j.foekens@erasmusmc.nl.
authors.forename: John
authors.initials: J
authors.lastname: Foekens
authors.affiliation: National Institutes of Health, National Cancer Institute, Center for Cancer Research, Developmental Therapeutics Branch and Laboratory of Molecular, Pharmacology, 37 Convent Drive, Building 37, Room 5068, Bethesda, MD, 20892-4255, USA. PommierY@mail.nih.gov.
authors.forename: Yves
authors.initials: Y
authors.lastname: Pommier
authors.affiliation: Faculty of Health and Medical Sciences, Department of Veterinary Disease Biology, Section for Molecular Disease Biology and Sino-Danish Breast Cancer Research Centre, University of Copenhagen, Strandboulevarden 49, DK-2100, Copenhagen, Denmark. nbr@sund.ku.dk.
authors.forename: Nils
authors.initials: N
authors.lastname: Brünner
authors.affiliation: Faculty of Health and Medical Sciences, Department of Veterinary Disease Biology, Section for Molecular Disease Biology and Sino-Danish Breast Cancer Research Centre, University of Copenhagen, Strandboulevarden 49, DK-2100, Copenhagen, Denmark. sofie.rasmussen@gmail.com.
authors.forename: Anne-Sofie
authors.initials: AS
authors.lastname: Schrohl
authors.affiliation: Faculty of Health and Medical Sciences, Department of Veterinary Disease Biology, Section for Molecular Disease Biology and Sino-Danish Breast Cancer Research Centre, University of Copenhagen, Strandboulevarden 49, DK-2100, Copenhagen, Denmark. stenvang@sund.ku.dk.
authors.forename: Jan
authors.initials: J
authors.lastname: Stenvang
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis / Q000235:genetics*; D000951:Antigens, Neoplasm / Q000235:genetics; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics* / Q000473:pathology; D002166:Camptothecin / Q000008:administration & dosage / Q000009:adverse effects / Q000031:analogs & derivatives*; D004264:DNA Topoisomerases, Type I / Q000096:biosynthesis / Q000235:genetics*; D004250:DNA Topoisomerases, Type II / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D000077143:Docetaxel; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005260:Female; D018628:Gene Dosage / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D000077146:Irinotecan; D061986:MCF-7 Cells; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics*; D000075223:Poly-ADP-Ribose Binding Proteins; D043823:Taxoids / Q000008:administration & dosage
chemical_list: C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000951:Antigens, Neoplasm; D004268:DNA-Binding Proteins; D009363:Neoplasm Proteins; D000075223:Poly-ADP-Ribose Binding Proteins; D043823:Taxoids; D000077143:Docetaxel; D000077146:Irinotecan; D004264:DNA Topoisomerases, Type I; C528909:TOP1 protein, human; D004250:DNA Topoisomerases, Type II; C000618811:TOP2A protein, human; D002166:Camptothecin