title: A comparative PET imaging study with the reversible and irreversible EGFR tyrosine kinase inhibitors [(11)C]erlotinib and [(18)F]afatinib in lung cancer-bearing mice.
abstract: BACKGROUND
  Tyrosine kinase inhibitors (TKIs) have experienced a tremendous boost in the last decade, where more than 15 small molecule TKIs have been approved by the FDA. Unfortunately, despite their promising clinical successes, a large portion of patients remain unresponsive to these targeted drugs. For non-small cell lung cancer (NSCLC), the effectiveness of TKIs is dependent on the mutational status of epidermal growth factor receptor (EGFR). The exon 19 deletion as well as the L858R point mutation lead to excellent sensitivity to TKIs such as erlotinib and gefitinib; however, despite initial good response, most patients invariably develop resistance against these first-generation reversible TKIs, e.g., via T790M point mutation. Second-generation TKIs that irreversibly bind to EGFR wild-type and mutant isoforms have therefore been developed and one of these candidates, afatinib, has now reached the market. Whether irreversible TKIs differ from reversible TKIs in their in vivo tumor-targeting properties is, however, not known and is the subject of the present study.
  
  
  METHODS
  Erlotinib was labeled with carbon-11 and afatinib with fluorine-18 without modifying the structure of these compounds. A preclinical positron emission tomography (PET) study was performed in mice bearing NSCLC xenografts with a representative panel of mutations: an EGFR-WT xenograft cell line (A549), an acquired treatment-resistant L858R/T790M mutant (H1975), and a treatment-sensitive exon 19 deleted mutant (HCC827). PET imaging was performed in these xenografts with both tracers. Additionally, the effect of drug efflux transporter permeability glycoprotein (P-gp) on the tumor uptake of tracers was explored by therapeutic blocking with tariquidar.
  
  
  RESULTS
  Both tracers only demonstrated selective tumor uptake in the HCC827 xenograft line (tumor-to-background ratio, [(11)C]erlotinib 1.9 ± 0.5 and [(18)F]afatinib 2.3 ± 0.4), thereby showing the ability to distinguish sensitizing mutations in vivo. No major differences were observed in the kinetics of the reversible and the irreversible tracers in each of the xenograft models. Under P-gp blocking conditions, no significant changes in tumor-to-background ratio were observed; however, [(18)F]afatinib demonstrated better tumor retention in all xenograft models.
  
  
  CONCLUSIONS
  TKI-PET provides a method to image sensitizing mutations and can be a valuable tool to compare the distinguished targeting properties of TKIs in vivo.
authors: Department of Radiology and Nuclear Medicine, VU University Medical Center, De Boelelaan 1117, Amsterdam, 1081 HV The Netherlands ; Department of Otolaryngology/Head and Neck Surgery, VU University Medical Center, De Boelelaan 1117, Amsterdam, 1081 HV The Netherlands.
authors: Paul
authors: P
authors: Slobbe
authors: Department of Radiology and Nuclear Medicine, VU University Medical Center, De Boelelaan 1117, Amsterdam, 1081 HV The Netherlands.
authors: Albert D
authors: AD
authors: Windhorst
authors: Department of Otolaryngology/Head and Neck Surgery, VU University Medical Center, De Boelelaan 1117, Amsterdam, 1081 HV The Netherlands.
authors: Marijke
authors: M
authors: Stigter-van Walsum
authors: Department of Pulmonary Diseases, VU University Medical Center, De Boelelaan 1117, Amsterdam, 1081 HV The Netherlands.
authors: Egbert F
authors: EF
authors: Smit
authors: Department of Translational Medicine and Clinical Pharmacology, Boehringer Ingelheim Pharma GmbH and Co. KG, Birkendorfer Straße 65, 88397 Biberach an der Riss, Germany.
authors: Heiko G
authors: HG
authors: Niessen
authors: Department of Pharmacology and Translational Research, Boehringer Ingelheim GmbH and Co. KG, Doktor-Boehringer-Gasse 5-11, Vienna, A-1120 Austria.
authors: Flavio
authors: F
authors: Solca
authors: Therapeutic Area Oncology, Boehringer Ingelheim Pharma GmbH and Co. KG, Birkendorfer Straße 65, 88397 Biberach an der Riss, Germany.
authors: Gerd
authors: G
authors: Stehle
authors: Department of Radiology and Nuclear Medicine, VU University Medical Center, De Boelelaan 1117, Amsterdam, 1081 HV The Netherlands ; Department of Otolaryngology/Head and Neck Surgery, VU University Medical Center, De Boelelaan 1117, Amsterdam, 1081 HV The Netherlands.
authors: Guus A M S
authors: GA
authors: van Dongen
authors: Department of Radiology and Nuclear Medicine, VU University Medical Center, De Boelelaan 1117, Amsterdam, 1081 HV The Netherlands ; Department of Otolaryngology/Head and Neck Surgery, VU University Medical Center, De Boelelaan 1117, Amsterdam, 1081 HV The Netherlands.
authors: Alex J
authors: AJ
authors: Poot
keywords: Activated EGFR; Afatinib; Erlotinib; PET; Personalized medicine; Radiochemistry