title: Kitlow stem cells cause resistance to Kit/platelet-derived growth factor alpha inhibitors in murine gastrointestinal stromal tumors.
abstract: OBJECTIVE
  Gastrointestinal stromal tumors (GIST) are related to interstitial cells of Cajal (ICC) and often contain activating stem cell factor receptor (Kit) or platelet-derived growth factor receptor alpha (Pdgfra) mutations. Kit/Pdgfra inhibitors such as imatinib mesylate have increased progression-free survival in metastatic GIST but are not curative. In mouse models we investigated whether Kit(low) ICC progenitors could represent an inherently Kit/Pdgfra inhibitor-resistant reservoir for GIST.
  
  
  METHODS
  Isolated Kit(low)Cd44(+)Cd34(+) cells were characterized after serial cloning. The tumorigenic potential of spontaneously transformed cells was investigated in nude mice. The Kit(low)Cd44(+)Cd34(+) cells' responsiveness to Kit activation and blockade was studied by enumerating them in Kit(K641E) mice (a GIST model), in mice with defective Kit signaling, and pharmacologically.
  
  
  RESULTS
  Single isolated Kit(low)Cd44(+)Cd34(+) cells were clonogenic and capable of self-renewal and differentiation into ICC. In nude mice, spontaneously transformed cells formed malignant tumors expressing GIST markers. The Kit(low)Cd44(+)Cd34(+) cells were resistant to in vitro Kit blockade, including by imatinib, and occurred in normal numbers in mice with reduced Kit signaling. In Kit(K641E) mice, the mutant ICC stem cells were grossly hyperplastic but remained imatinib-resistant. In contrast, the cancer stem, cell-targeting drug salinomycin blocked the proliferation of Kit(low)Cd44(+)Cd34(+) cells and increased their sensitivity to imatinib.
  
  
  CONCLUSIONS
  Kit(low)Cd44(+)Cd34(+) progenitors are true stem cells for normal and hyperplastic ICC and give rise to GIST. Resistance to Kit/Pdgfra inhibitors is inherent in GIST and is caused by the native ICC stem cells' lack of dependence on Kit for survival, which is maintained after the acquisition of oncogenic Kit mutation. Cancer stem cell drugs may target these cells.
authors.affiliation: Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota 55905, USA.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Bardsley
authors.forename: Viktor J
authors.initials: VJ
authors.lastname: Horváth
authors.forename: David T
authors.initials: DT
authors.lastname: Asuzu
authors.forename: Andrea
authors.initials: A
authors.lastname: Lorincz
authors.forename: Doug
authors.initials: D
authors.lastname: Redelman
authors.forename: Yujiro
authors.initials: Y
authors.lastname: Hayashi
authors.forename: Laura N
authors.initials: LN
authors.lastname: Popko
authors.forename: David L
authors.initials: DL
authors.lastname: Young
authors.forename: Gwen A
authors.initials: GA
authors.lastname: Lomberk
authors.forename: Raul A
authors.initials: RA
authors.lastname: Urrutia
authors.forename: Gianrico
authors.initials: G
authors.lastname: Farrugia
authors.forename: Brian P
authors.initials: BP
authors.lastname: Rubin
authors.forename: Tamas
authors.initials: T
authors.lastname: Ordog
mesh_terms: D000818:Animals; D018952:Antigens, CD34 / Q000032:analysis; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001549:Benzamides; D014408:Biomarkers, Tumor / Q000378:metabolism; D002454:Cell Differentiation; D049109:Cell Proliferation; D002470:Cell Survival; D002478:Cells, Cultured; D002999:Clone Cells; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm; D046152:Gastrointestinal Stromal Tumors / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D018960:Hyaluronan Receptors / Q000032:analysis; D006965:Hyperplasia; D000068877:Imatinib Mesylate; D056885:Interstitial Cells of Cajal / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D016688:Mice, Inbred NOD; D008819:Mice, Nude; D009154:Mutation; D014411:Neoplastic Stem Cells / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D010879:Piperazines / Q000494:pharmacology; D019009:Proto-Oncogene Proteins c-kit / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D011714:Pyrans / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D020796:Receptor, Platelet-Derived Growth Factor alpha / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013997:Time Factors; D047368:Tumor Burden; D000095662:Polyether Polyketides
chemical_list: D018952:Antigens, CD34; D000970:Antineoplastic Agents; D001549:Benzamides; D014408:Biomarkers, Tumor; D018960:Hyaluronan Receptors; D000068877:Imatinib Mesylate; D010879:Piperazines; D019009:Proto-Oncogene Proteins c-kit; D011714:Pyrans; D011743:Pyrimidines; D020796:Receptor, Platelet-Derived Growth Factor alpha; C476399:Cd44 protein, mouse; C010327:salinomycin; D000095662:Polyether Polyketides