title: Proof of target for SU11654: inhibition of KIT phosphorylation in canine mast cell tumors.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the effect of the receptor tyrosine kinase inhibitor SU11654 on the activity of its molecular target KIT in canine mast cell tumors (MCT) and correlate target inhibition with mutational status of the c-kit juxtamembrane domain and SU11654 plasma concentration.
  
  
  METHODS
  Tumor biopsies were obtained from dogs with advanced MCTs before and 8 h after administration of a single oral dose of SU11654, previously shown to be active in dogs with MCTs. Blood samples were taken to determine the plasma concentration of SU11654. Levels of phosphorylated KIT and ERK1/2 were assessed in tumor biopsies by Western blot. Tumors were analyzed by PCR for the presence or absence of an internal tandem duplication (ITD) in the juxtamembrane domain of c-kit.
  
  
  RESULTS
  Fourteen dogs with advanced MCTs were enrolled in the study; 11 of these were evaluable for KIT target modulation (the remaining tumor specimens had inevaluable amounts of total KIT protein). Of these, eight MCTs showed reduced levels of phosphorylated KIT relative to total KIT after treatment with SU11654, compared with pretreatment biopsies. All four evaluable MCTs expressing ITD mutant c-kitshowed modulation of KIT phosphorylation, as did four of seven tumors expressing non-ITD c-kit. Phosphorylated ERK1/2 was modulated in seven tumors; this did not correlate with inhibition of KIT phosphorylation
  
  
  CONCLUSIONS
  SU11654 treatment at the efficacious dose results in inhibition of KIT phosphorylation in canine MCTs.
authors.affiliation: SUGEN, Inc., South San Francisco, California 94080, USA. npryer@ravenbio.com
authors.forename: Nancy K
authors.initials: NK
authors.lastname: Pryer
authors.forename: Leslie B
authors.initials: LB
authors.lastname: Lee
authors.forename: Regina
authors.initials: R
authors.lastname: Zadovaskaya
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Yu
authors.forename: Juthamas
authors.initials: J
authors.lastname: Sukbuntherng
authors.forename: Julie M
authors.initials: JM
authors.lastname: Cherrington
authors.forename: Cheryl A
authors.initials: CA
authors.lastname: London
mesh_terms: D000818:Animals; D004283:Dog Diseases / Q000188:drug therapy* / Q000473:pathology; D004285:Dogs; D004791:Enzyme Inhibitors / Q000097:blood / Q000493:pharmacokinetics / Q000627:therapeutic use*; D007211:Indoles / Q000097:blood / Q000493:pharmacokinetics / Q000627:therapeutic use*; D008407:Mast Cells; D012515:Mast-Cell Sarcoma / Q000188:drug therapy / Q000473:pathology / Q000662:veterinary*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009362:Neoplasm Metastasis; D010766:Phosphorylation; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism*; D011758:Pyrroles / Q000097:blood / Q000493:pharmacokinetics / Q000627:therapeutic use*; D012008:Recurrence
chemical_list: D004791:Enzyme Inhibitors; D007211:Indoles; D011758:Pyrroles; C464577:toceranib phosphate; D019009:Proto-Oncogene Proteins c-kit; D020928:Mitogen-Activated Protein Kinases