title: Molecular mechanisms of secondary imatinib resistance in patients with gastrointestinal stromal tumors.
abstract: OBJECTIVE
  Most gastrointestinal stromal tumor (GIST) patients respond to KIT inhibition therapy of imatinib, but eventually become resistant with a median time to progression of 2 years. The mechanism of acquired resistance to imatinib and oncogenic KIT signal transduction in GISTs has not been well defined. We sought to investigate the spectrum of molecular and genomic changes in imatinib-resistant GIST patients.
  
  
  METHODS
  KIT and PDGFRA mutations were evaluated in 48 samples obtained from 32 GIST patients who underwent surgery after imatinib treatment. KIT downstream signaling profiles were also investigated in eight specimens of five patients who were clinically responsive or resistant to imatinib therapy. Biochemical inhibition of KIT, mitogen-activated protein kinase (MAPK), mammalian target of rapamycin (MTOR), AKT, proliferating cell nuclear antigen (PCNA) and BCL-2 were determined by western blotting for protein activation.
  
  
  RESULTS
  In all 32 GIST patients, activating mutations in the KIT gene were seen in 26 (81.3%) patients, PDGFRA gene mutations were seen in 2 (6.2%) patients and no primary mutations were found in 4 (12.5%) patients. Secondary KIT mutations were identified in 11/14 (78.6%) imatinib-acquired-resistance patients, with nine patients in KIT gene exon17, and the other two in exon 13. The expressions of p-KIT, p-AKT, PCNA and BCL-2 were higher in the samples of imatinib-resistant GISTs than those of imatinib-responsive ones. P-KIT, p-AKT expressions were higher in imatinib acquired-resistance GISTs with secondary KIT mutations than imatinib-responsive ones with primary mutation. Total KIT, MAPK, p-MAPK, p-MTOR expressions were comparable in all varied GISTs.
  
  
  CONCLUSIONS
  Novel additional mutations of KIT gene exon 13 or exon 17 indicate the likely mechanism of secondary resistance to imatinib. The PI3-K/AKT pathway might be more relevant than MEK/MAPK for therapeutic targeting in imatinib-resistant GIST patients with secondary mutation.
authors.affiliation: Abdominal Department, Cancer Hospital, Fudan University, 270 Dong'an Road, 200032 Shanghai, People's Republic of China. cmwang1975@163.com
authors.forename: Chun-Meng
authors.initials: CM
authors.lastname: Wang
authors.forename: Kai
authors.initials: K
authors.lastname: Huang
authors.forename: Ye
authors.initials: Y
authors.lastname: Zhou
authors.forename: Chun-Yan
authors.initials: CY
authors.lastname: Du
authors.forename: Yan-Wei
authors.initials: YW
authors.lastname: Ye
authors.forename: Hong
authors.initials: H
authors.lastname: Fu
authors.forename: Xiao-Yan
authors.initials: XY
authors.lastname: Zhou
authors.forename: Ying-Qiang
authors.initials: YQ
authors.lastname: Shi
mesh_terms: D000328:Adult; D000368:Aged; D001549:Benzamides; D018450:Disease Progression; D019008:Drug Resistance, Neoplasm; D005260:Female; D005500:Follow-Up Studies; D046152:Gastrointestinal Stromal Tumors / Q000175:diagnosis / Q000235:genetics* / Q000628:therapy*; D005838:Genotype; D006801:Humans; D000068877:Imatinib Mesylate; D008297:Male; D008875:Middle Aged; D009154:Mutation; D010879:Piperazines / Q000627:therapeutic use*; D019009:Proto-Oncogene Proteins c-kit / Q000037:antagonists & inhibitors / Q000235:genetics*; D011743:Pyrimidines / Q000627:therapeutic use*; D017479:Receptors, Platelet-Derived Growth Factor / Q000037:antagonists & inhibitors / Q000235:genetics*; D015398:Signal Transduction / Q000235:genetics
chemical_list: D001549:Benzamides; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D019009:Proto-Oncogene Proteins c-kit; D017479:Receptors, Platelet-Derived Growth Factor