Abstract A13: Establishment and characterization of patient-derived xenograft models of gastrointestinal stromal tumor resistant to standard tyrosine kinase inhibitors
Authors: Na Young-Soon , Ryu Min-Hee , Park Sook Ryun , Lee Ju-Kyung , Kim Hanui , Lee Chae-Won , Lee Sun Young , Shin Young-Kyoung , Ku Ja-Lok , Ahn Sung-Min , Kang Yoon-Koo 
Published: May 2016

Abstract
BACKGROUND: The prognosis of gastrointestinal stromal tumor (GIST) has been dramatically improved after introduction of imatinib which can inhibit the driver mutated oncoproteins,KIT or PDGFRa. However, most patients eventually develop resistance to the tyrosine kinase inhibitors (TKIs) targeting these oncoproteins including imatinib, sunitinib, or regorafenib. The paucity of TKIs-resistant commercially available GIST cell lines hampers development of effective therapy for drug-resistant GIST. Therefore, we established patient-derived xenograft (PDX) models that faithfully recapitulate the genetic and phenotypic features of drug-resistant GIST.
METHODS: PDXs have been established in NOD-SCID mice with tumor fragments of patients with metastatic and/or unresectable GIST after failure of at least imatinib and/or sunitinib. The histological and genomic similarities between all xenografts and the parental tumors have been confirmed using H&E and KIT staining, and short tandem repeat (STR) analysis, respectively. Mutation was detected by whole exome sequencing of patients' tumors on a HiSeq2000 and validated by Sanger sequencing of patients tumors and PDXs. After sequential passaging to BALB/c nude mouse, drug sensitivity assay (imatininb, sunitinib, and regorafenib) was conducted in established PDX models along with Western blotting regarding to KIT and FGFR signaling pathway. As an imatinib-sensitive control model, a xenograft established with GIST-T1 cell line was used.
RESULTS: Three GIST PDX models were established from an imatinib/sunitinib/sorafenib-resistant GIST harboring KIT exon 11 (p.Y570-L576del) and 17 (p.D816E) mutations (AMC-GX1), an imatinib-resistant GIST harboring KIT exon 11 (p.K550_K558del) and 14 (p.T670I) mutations (AMC-GX2), and an imatinib/sunitinib-resistant GIST harboring KIT exon 11 (p.565-577GNNYVVIDPTQLP&gt;Q) and 17 (p.D820Y) mutations (AMC-GX3). Histologic and genetic similarities were confirmed between primary patients' tumors and PDXs. The mutation status of GIST PDXs was consistent with primary tumors. The GIST PDX models showed TKI sensitivity profiles comparable to clinical responses in patients. At day 21 after treatmemt with imatinib, tumor growth was inhibited by 17.8, 53.9, and 12.6% in AMC-GX1, GX2, and GX3, respectively, while by 80.0% in GIST-T1 xenografts. Western blotting analysis showed that KIT phosphorylation was inhibited by imatinib treatment in AMC-GX1 similar to GIST-T1, but not in AMC-GX2 and AMC-GX3. In contrast to GIST-T1, PI3K downstream of KIT was not inhibited with imatinib in AMC-GX1, GX2, and GX3. In addition, TKIs-resistant PDX models showed FGFR1 activation at baseline which was not evident in GIST-T1 xenografts.
CONCLUSION: We have established 3 TKI-resistant GIST PDX models harboring variable KIT mutations which show different KIT and FGFR signaling features from imatinib-sensitive models. The established GIST PDX models will play a role for further studies on mechanisms of resistance to TKI and evaluation of novel targeted therapies in GIST.
Citation Format: Young-Soon Na, Min-Hee Ryu, Sook Ryun Park, Ju-Kyung Lee, Hanui Kim, Chae-Won Lee, Sun Young Lee, Young-Kyoung Shin, Ja-Lok Ku, Sung-Min Ahn, Yoon-Koo Kang. Establishment and characterization of patient-derived xenograft models of gastrointestinal stromal tumor resistant to standard tyrosine kinase inhibitors. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A13.