title: Radionuclide imaging of drug delivery for patient selection in targeted therapy.
abstract: BACKGROUND
  During the last decade, numerous antibodies and tyrosine kinase inhibitors have been developed for cancer treatment. However, only a limited number of these agents have been shown to significantly improve survival of patients. Therefore, it is of crucial importance to identify the subset of patients who benefit from targeted therapy. Biomarkers can play an important role in selecting the right drug for the right patient.
  
  
  METHODS
  In this review, the potential role of molecular imaging of drug delivery for patient selection in targeted therapy will be discussed. The advantages and limitations of molecular imaging will be compared to those of conventional biomarkers. Moreover, we will address the factors that affect imaging of drug delivery, such as target expression, type of drug, in vivo accessibility of the receptor (e.g., vascular density, vascular permeability, interstitial pressure), enhanced permeability and retention (EPR) effect, receptor internalization, tracer protein dose and timing of imaging.
  
  
  CONCLUSIONS
  Molecular imaging of drug delivery clearly has potential for patient selection for targeted therapy. The main advantage of this technique is that not only can antigen expression be measured noninvasively but also target accessibility is taken into account. However, up to now, most of these studies have been performed in preclinical models. Therefore, future research should focus on bringing promising tracers to the clinic, preferable in an early stage of drug development in order to test their potential role as a biomarker.
authors.affiliation: Radboud University Medical Center, Department of Nuclear Medicine , (Internal Postal Code 756), P.O. Box 9101, 6500 HB Nijmegen , The Netherlands +31243619097 ; +31243618942 ; sandra.heskamp@radboudumc.nl.
authors.forename: Sandra
authors.initials: S
authors.lastname: Heskamp
authors.forename: Hanneke W M
authors.initials: HW
authors.lastname: van Laarhoven
authors.forename: Winette T A
authors.initials: WT
authors.lastname: van der Graaf
authors.forename: Wim J G
authors.initials: WJ
authors.lastname: Oyen
authors.forename: Otto C
authors.initials: OC
authors.lastname: Boerman
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use; D015415:Biomarkers; D016503:Drug Delivery Systems; D006801:Humans; D057054:Molecular Imaging; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000188:drug therapy; D018579:Patient Selection; D011877:Radionuclide Imaging
chemical_list: D000970:Antineoplastic Agents; D015415:Biomarkers