title: Three-dimensional histologic validation of high-resolution SPECT of antibody distributions within xenografts.
abstract: Longitudinal imaging of intratumoral distributions of antibodies in vivo in mouse cancer models is of great importance for developing cancer therapies. In this study, multipinhole SPECT with sub-half-millimeter resolution was tested for exploring intratumoral distributions of radiolabeled antibodies directed toward the epidermal growth factor receptor (EGFr) and compared with full 3-dimensional target expression assessed by immunohistochemistry.
  
  
  METHODS
  (111)In-labeled zalutumumab, a human monoclonal human EGFr-targeting antibody, was administered at a nonsaturating dose to 3 mice with xenografted A431 tumors exhibiting high EGFr expression. Total-body and focused in vivo tumor SPECT was performed at 0 and 48 h after injection and compared both visually and quantitatively with full 3-dimensional immunohistochemical staining for EGFr target expression.
  
  
  RESULTS
  SPECT at 48 h after injection showed that activity was predominantly concentrated in the tumor (10.5% ± 1.3% of the total-body activity; average concentration, 30.1% ± 4.6% of the injected dose per cubic centimeter). (111)In-labeled EGFr-targeting antibodies were distributed heterogeneously throughout the tumor. Some hot spots were observed near the tumor rim. Immunohistochemistry indicated that the antibody distributions obtained by SPECT were morphologically similar to those obtained for ex vivo EGFr target expression. Regions showing low SPECT activity were necrotic or virtually negative for EGFr target expression. A good correlation (r = 0.86, P < 0.0001) was found between the percentage of regions showing low activity on SPECT and the percentage of necrotic tissue on immunohistochemistry.
  
  
  CONCLUSIONS
  Multipinhole SPECT enables high-resolution visualization and quantification of the heterogeneity of (111)In-zalutumumab concentrations in vivo.
authors.affiliation: Image Sciences Institute, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Woutjan
authors.initials: W
authors.lastname: Branderhorst
authors.forename: Erwin L A
authors.initials: EL
authors.lastname: Blezer
authors.forename: Mischa
authors.initials: M
authors.lastname: Houtkamp
authors.forename: Ruud M
authors.initials: RM
authors.lastname: Ramakers
authors.forename: Jeroen H
authors.initials: JH
authors.lastname: van den Brakel
authors.forename: Henry
authors.initials: H
authors.lastname: Witteveen
authors.forename: Frans
authors.initials: F
authors.lastname: van der Have
authors.forename: Hugo A
authors.initials: HA
authors.lastname: Gratama van Andel
authors.forename: Brendan
authors.initials: B
authors.lastname: Vastenhouw
authors.forename: Chao
authors.initials: C
authors.lastname: Wu
authors.forename: Marijke Stigter-van
authors.initials: MS
authors.lastname: Walsum
authors.forename: Guus A M S
authors.initials: GA
authors.lastname: van Dongen
authors.forename: Max A
authors.initials: MA
authors.lastname: Viergever
authors.forename: Wim K
authors.initials: WK
authors.lastname: Bleeker
authors.forename: Freek J
authors.initials: FJ
authors.lastname: Beekman
mesh_terms: D000818:Animals; D000906:Antibodies / Q000737:chemistry*; D000911:Antibodies, Monoclonal / Q000737:chemistry; D061067:Antibodies, Monoclonal, Humanized; D045744:Cell Line, Tumor; D066246:ErbB Receptors / Q000378:metabolism*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D018796:Immunoconjugates / Q000737:chemistry; D007150:Immunohistochemistry; D007205:Indium Radioisotopes / Q000737:chemistry; D051379:Mice; D016513:Mice, SCID; D009368:Neoplasm Transplantation; D015203:Reproducibility of Results; D015899:Tomography, Emission-Computed, Single-Photon; D014057:Tomography, X-Ray Computed
chemical_list: D000906:Antibodies; D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D018796:Immunoconjugates; D007205:Indium Radioisotopes; C546618:zalutumumab; D066246:ErbB Receptors
keywords: EGFr; antibody; histology; micro-SPECT; zalutumumab