title: Mechanisms of resistance to imatinib mesylate in gastrointestinal stromal tumors and activity of the PKC412 inhibitor against imatinib-resistant mutants.
abstract: OBJECTIVE
  Resistance is a major challenge in the treatment of patients with gastrointestinal stromal tumors (GISTs). We investigated the mechanisms of resistance in patients with progressive GISTs with primary KIT mutations and the efficacy of the kinase inhibitor PKC412 for the inhibition of imatinib-resistant mutants.
  
  
  METHODS
  We performed a cytogenetic analysis and screened for mutations of the KIT and PDGFRA kinase domains in 26 resistant GISTs. KIT autophosphorylation status was assessed by Western immunoblotting. Imatinib-resistant GIST cells and Ba/F3 cells expressing these mutant proteins were tested for sensitivity to imatinib and PKC412.
  
  
  RESULTS
  Six distinct secondary mutations in KIT were detected in 12 progressive tumors, with V654A and T670I found to be recurrent. One progressive tumor showed acquired PDGFRA -D842V mutation. Amplification of KIT or KIT / PDGFRA was found in 2 patients. Eight of 10 progressive tumors available for analysis showed phosphorylated KIT. Two remaining progressive tumors lost KIT protein expression. GIST cells carrying KIT -del557-558/T670I or KIT -InsAY502-503/V654A mutations were resistant to imatinib, while PKC412 significantly inhibited autophosporylation of these mutants. Resistance to imatinib and sensitivity to PKC412 of KIT -T670I and PDGFRA -D842V mutants was confirmed using Ba/F3 cells.
  
  
  CONCLUSIONS
  This study shows the high frequency of KIT/PDGFRA kinase domain mutations in patients with secondary resistance and defines genomic amplification of KIT / PDGFRA as an alternative cause of resistance to the drug. In a subset of patients, cancer cells lost their dependence on the targeted tyrosine kinase. Our findings show the sensitivity of the imatinib-resistant KIT -T670I and KIT -V654A and of PDGFRA -D842V mutants to PKC412.
authors.affiliation: Center for uman Genetics, Catholic University of Leuven, Leuven, Belgium.
authors.forename: Maria
authors.initials: M
authors.lastname: Debiec-Rychter
authors.forename: Jan
authors.initials: J
authors.lastname: Cools
authors.forename: Herlinde
authors.initials: H
authors.lastname: Dumez
authors.forename: Raf
authors.initials: R
authors.lastname: Sciot
authors.forename: Michel
authors.initials: M
authors.lastname: Stul
authors.forename: Nicole
authors.initials: N
authors.lastname: Mentens
authors.forename: Hilde
authors.initials: H
authors.lastname: Vranckx
authors.forename: Bartosz
authors.initials: B
authors.lastname: Wasag
authors.forename: Hans
authors.initials: H
authors.lastname: Prenen
authors.forename: Johannes
authors.initials: J
authors.lastname: Roesel
authors.forename: Anne
authors.initials: A
authors.lastname: Hagemeijer
authors.forename: Allan
authors.initials: A
authors.lastname: Van Oosterom
authors.forename: Peter
authors.initials: P
authors.lastname: Marynen
mesh_terms: D000328:Adult; D000368:Aged; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D001549:Benzamides; D019008:Drug Resistance, Neoplasm; D005091:Exons; D005260:Female; D046152:Gastrointestinal Stromal Tumors / Q000188:drug therapy* / Q000235:genetics; D006801:Humans; D000068877:Imatinib Mesylate; D008297:Male; D008875:Middle Aged; D009154:Mutation; D010879:Piperazines / Q000627:therapeutic use*; D019009:Proto-Oncogene Proteins c-kit / Q000235:genetics*; D011743:Pyrimidines / Q000627:therapeutic use*; D020796:Receptor, Platelet-Derived Growth Factor alpha / Q000235:genetics*; D019311:Staurosporine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors*
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D019009:Proto-Oncogene Proteins c-kit; D020796:Receptor, Platelet-Derived Growth Factor alpha; D019311:Staurosporine; C059539:midostaurin