title: Characterization and assessment of the sensitivity and resistance of a newly established human gastrointestinal stromal tumour xenograft model to treatment with tyrosine kinase inhibitors.
abstract: BACKGROUND
  Acquired resistance to tyrosine kinase inhibitors (TKIs) in gastrointestinal stromal tumours (GISTs) is most commonly caused by secondary KIT or PDGFRA mutations. In this study we characterize a newly established GIST xenograft model, UZLX-GIST9, and evaluate the in vivo response of the model to standard TKIs (imatinib, sunitinib, and regorafenib).
  
  
  METHODS
  Tumour fragments from a metastatic lesion of a GIST patient clinically progressing after treatment with imatinib, sunitinib and regorafenib were engrafted in a nude, immunodeficient mouse. Upon sequential passaging from mouse to mouse, tumour fragments were collected for histopathological and molecular characterization. The sensitivity of the model to treatment with TKIs was evaluated in 28 mice [passage 2 (n = 8), passage 4 (n = 20), 41 tumours]. Mice were grouped as follows: control (untreated), imatinib (50 mg/kg/BID), imatinib (100 mg/kg/BID), sunitinib (40 mg/kg/QD), and regorafenib (30 mg/kg/QD). After three weeks of oral treatment, tumours were collected for subsequent analysis. The efficacy of treatment was assessed by tumour volume, histopathology and Western immunoblotting.
  
  
  RESULTS
  UZLX-GIST9 maintains the same typical morphological features and immunohistochemical characteristics as the original patient biopsy and expresses CD117 and DOG1. The KIT mutational profile (p.P577del + W557LfsX5+ D820G) remains the same as the original tissue sample originating from an intraspinal metastatic site. Three week treatment with different TKIs showed that the model is resistant to imatinib. Sunitinib induces tumour growth delay and regorafenib reduces the tumour burden by 30% as compared to control animals. While none of the TKIs had a significant effect on cell proliferation or cell survival, a remarkable increase of necrosis and significant reduction of microvessel density was observed under sunitinib and regorafenib. Western immunoblotting showed a mild reduction in KIT and AKT activation only in regorafenib treated tumours.
  
  
  CONCLUSIONS
  We established a novel human GIST xenograft, UZLX-GIST9, harbouring KIT exon 11 and 17 mutations and maintaining the pheno-and genotype of the original tumour. UZLX-GIST9 shows different levels of response to standard TKIs. This model will help to study TKI resistance and to explore novel treatment approaches for patients with TKI-resistant GIST.
authors.affiliation: Laboratory of Experimental Oncology, Department of Oncology, KU Leuven, Herestraat 49, Leuven, Belgium.
authors.forename: Thomas
authors.initials: T
authors.lastname: Van Looy
authors.affiliation: Laboratory of Experimental Oncology, Department of Oncology, KU Leuven, Herestraat 49, Leuven, Belgium.
authors.forename: Yemarshet Kelemework
authors.initials: YK
authors.lastname: Gebreyohannes
authors.affiliation: Laboratory of Experimental Oncology, Department of Oncology, KU Leuven, Herestraat 49, Leuven, Belgium.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Wozniak
authors.affiliation: Laboratory of Experimental Oncology, Department of Oncology, KU Leuven, Herestraat 49, Leuven, Belgium ; Department of General Medical Oncology, Leuven Cancer Institute, University Hospitals Leuven, Herestraat 49, Leuven, Belgium.
authors.forename: Jasmien
authors.initials: J
authors.lastname: Cornillie
authors.affiliation: Laboratory of Experimental Oncology, Department of Oncology, KU Leuven, Herestraat 49, Leuven, Belgium.
authors.forename: Jasmien
authors.initials: J
authors.lastname: Wellens
authors.affiliation: Laboratory of Experimental Oncology, Department of Oncology, KU Leuven, Herestraat 49, Leuven, Belgium.
authors.forename: Haifu
authors.initials: H
authors.lastname: Li
authors.affiliation: Laboratory of Experimental Oncology, Department of Oncology, KU Leuven, Herestraat 49, Leuven, Belgium.
authors.forename: Ulla
authors.initials: U
authors.lastname: Vanleeuw
authors.affiliation: Department of Pathology, KU Leuven and University Hospitals Leuven, Herestraat 49, Leuven, Belgium.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Floris
authors.affiliation: Department of Human Genetics, KU Leuven and University Hospitals Leuven, Herestraat 49, Leuven, Belgium.
authors.forename: Maria
authors.initials: M
authors.lastname: Debiec-Rychter
authors.affiliation: Department of Pathology, KU Leuven and University Hospitals Leuven, Herestraat 49, Leuven, Belgium.
authors.forename: Raf
authors.initials: R
authors.lastname: Sciot
authors.affiliation: Laboratory of Experimental Oncology, Department of Oncology, KU Leuven, Herestraat 49, Leuven, Belgium ; Department of General Medical Oncology, Leuven Cancer Institute, University Hospitals Leuven, Herestraat 49, Leuven, Belgium.
authors.forename: Patrick
authors.initials: P
authors.lastname: Schöffski
keywords: Gastrointestinal stromal tumour; Imatinib; Regorafenib; Resistance; Sunitinib; Tyrosine kinase inhibitor; Xenograft