title: Differentiated human colorectal cancer cells protect tumor-initiating cells from irinotecan.
abstract: OBJECTIVE
  Stem cells of normal tissues have resistance mechanisms that allow them to survive genotoxic insults. The stem cell-like cells of tumors are defined by their tumor-initiating capacity and may have retained these resistance mechanisms, making them resistant to chemotherapy. We studied the relationship between resistance to the topoisomerase I inhibitor irinotecan and tumor-initiating potential in human colonosphere cultures and in mice with colorectal xenograft tumors.
  
  
  METHODS
  Colonosphere cultures were established from human colorectal tumor specimens obtained from patients who underwent colon or liver resection for primary or metastatic adenocarcinoma. Stem cell and differentiation markers were analyzed by immunoblotting and fluorescence-activated cell sorting. Clone- and tumor-initiating capacities were assessed by single-cell cloning and in immune-deficient mice. Sensitivity to irinotecan was assessed in vitro and in tumor-bearing mice. The relationship between drug resistance and tumor-initiating capacity was tested by fluorescence-activated cell sorting of colonosphere cells, based on expression of ABCB1 and aldehyde dehydrogenase (ALDH) activity.
  
  
  RESULTS
  Colonosphere cultures had a high capacity to initiate tumors in mice and were resistant to irinotecan. Inhibition of the drug-efflux pump ABCB1 by PSC-833 allowed irinotecan to eradicate tumor-initiating cells. However, ABCB1 was expressed only by a subpopulation of differentiated tumor cells that did not form clones or tumors. Conversely, tumor-initiating cells were ABCB1-negative and were identified by high ALDH activity. Tumorigenic ALDHhigh/ABCB1negative cells generated nontumorigenic ALDHlow/ABCB1positive daughter cells in vitro and in tumor xenografts. PSC-833 increased the antitumor efficacy of irinotecan in mice.
  
  
  CONCLUSIONS
  The resistance of colorectal tumors to irinotecan requires the cooperative action of tumor-initiating ALDHhigh/ABCB1negative cells and their differentiated, drug-expelling, ALDHlow/ABCB1positive daughter cells.
authors: Department of Surgery, University Medical Center Utrecht, Utrecht, The Netherlands.
authors: Benjamin L
authors: BL
authors: Emmink
authors: Winan J
authors: WJ
authors: Van Houdt
authors: Robert G
authors: RG
authors: Vries
authors: Frederik J H
authors: FJ
authors: Hoogwater
authors: Klaas M
authors: KM
authors: Govaert
authors: Andre
authors: A
authors: Verheem
authors: Maarten W
authors: MW
authors: Nijkamp
authors: Ernst J A
authors: EJ
authors: Steller
authors: Connie R
authors: CR
authors: Jimenez
authors: Hans
authors: H
authors: Clevers
authors: Inne H M
authors: IH
authors: Borel Rinkes
authors: Onno
authors: O
authors: Kranenburg
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D000230:Adenocarcinoma / Q000188:drug therapy* / Q000378:metabolism / Q000556:secondary; D000444:Aldehyde Dehydrogenase / Q000378:metabolism; D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000378:metabolism / Q000494:pharmacology*; D014408:Biomarkers, Tumor / Q000378:metabolism; D015153:Blotting, Western; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects*; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D003524:Cyclosporins / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D005434:Flow Cytometry / Q000379:methods; D006801:Humans; D000077146:Irinotecan; D008113:Liver Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000556:secondary; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D014411:Neoplastic Stem Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D018874:Spheroids, Cellular; D013997:Time Factors; D059004:Topoisomerase I Inhibitors / Q000378:metabolism / Q000494:pharmacology*; D047368:Tumor Burden / Q000187:drug effects; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
chemical_list: C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000972:Antineoplastic Agents, Phytogenic; D014408:Biomarkers, Tumor; D003524:Cyclosporins; D059004:Topoisomerase I Inhibitors; D000077146:Irinotecan; D000444:Aldehyde Dehydrogenase; C070272:valspodar; D002166:Camptothecin