title: Evaluation of [(18)F]gefitinib as a molecular imaging probe for the assessment of the epidermal growth factor receptor status in malignant tumors.
abstract: OBJECTIVE
  Gefitinib, an inhibitor of the epidermal growth factor receptor-tyrosine kinase (EGFR-TK), has shown potent effects in a subset of patients carrying specific EGFR-TK mutations in advanced non-small-cell lung cancer. In this study, we asked whether PET with [(18)F]gefitinib may be used to study noninvasively the pharmacokinetics of gefitinib in vivo and to image the EGFR status of cancer cells.
  
  
  METHODS
  Synthesis of [(18)F]gefitinib has been previously described. The biodistribution and metabolic stability of [(18)F]gefitinib was assessed in mice and vervet monkeys for up to 2 h post injection by both micropositron emission tomography (PET)/computed tomography (CT) scans and postmortem ex vivo tissue harvesting. Uptake levels of radiolabeled gefitinib in EGFR-expressing human cancer cell lines with various levels of EGFR expression or mutation status were evaluated both in vivo and in vitro.
  
  
  RESULTS
  MicroPET/CT scans in two species demonstrated a rapid and predominantly hepatobiliary clearance of [(18)F]gefitinib in vivo. However, uptake levels of radiolabeled gefitinib, both in vivo and in vitro, did not correlate with EGFR expression levels or functional status. This unexpected observation was due to high nonspecific, nonsaturable cellular uptake of gefitinib.
  
  
  CONCLUSIONS
  The biodistribution of the drug analogue [(18)F]gefitinib suggests that it may be used to assess noninvasively the pharmacokinetics of gefitinib in patients by PET imaging. This is of clinical relevance, as insufficient intratumoral drug concentrations are considered to be a factor for resistance to gefitinib therapy. However, the highly nonspecific cellular binding of [(18)F]gefitinib may preclude the use of this imaging probe for noninvasive assessment of EGFR receptor status in patients.
authors.affiliation: Department of Molecular Medicine and Pharmacology, David Geffen School of Medicine, UCLA, Los Angeles, CA 90095, USA. helensu@mednet.ucla.edu
authors.forename: Helen
authors.initials: H
authors.lastname: Su
authors.forename: Yann
authors.initials: Y
authors.lastname: Seimbille
authors.forename: Gregory Z
authors.initials: GZ
authors.lastname: Ferl
authors.forename: Claudia
authors.initials: C
authors.lastname: Bodenstein
authors.forename: Barbara
authors.initials: B
authors.lastname: Fueger
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Kim
authors.forename: Yu-Tien
authors.initials: YT
authors.lastname: Hsu
authors.forename: Steven M
authors.initials: SM
authors.lastname: Dubinett
authors.forename: Michael E
authors.initials: ME
authors.lastname: Phelps
authors.forename: Johannes
authors.initials: J
authors.lastname: Czernin
authors.forename: Wolfgang A
authors.initials: WA
authors.lastname: Weber
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D066246:ErbB Receptors / Q000378:metabolism*; D005462:Fluorine Radioisotopes / Q000493:pharmacokinetics*; D000077156:Gefitinib; D008657:Metabolic Clearance Rate; D051379:Mice; D015336:Molecular Probe Techniques; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism*; D009928:Organ Specificity; D011799:Quinazolines / Q000493:pharmacokinetics*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D014018:Tissue Distribution
chemical_list: D005462:Fluorine Radioisotopes; D011799:Quinazolines; D019275:Radiopharmaceuticals; D066246:ErbB Receptors; D000077156:Gefitinib