title: Development of 124I immuno-PET targeting tumor vascular TEM1/endosialin.
abstract: Tumor endothelial marker 1 (TEM1/endosialin) is a tumor vascular marker highly overexpressed in multiple human cancers with minimal expression in normal adult tissue. In this study, we report the preparation and evaluation of (124)I-MORAb-004, a humanized monoclonal antibody targeting an extracellular epitope of human TEM1 (hTEM1), for its ability to specifically and sensitively detect vascular cells expressing hTEM1 in vivo.
  
  
  METHODS
  MORAb-004 was directly iodinated with (125)I and (124)I, and in vitro binding and internalization parameters were characterized. The in vivo behavior of radioiodinated MORAb-004 was characterized in mice bearing subcutaneous ID8 tumors enriched with mouse endothelial cells expressing hTEM1 and by biodistribution and small-animal immuno-PET studies.
  
  
  RESULTS
  MORAb-004 was radiolabeled with high efficiency and isolated in high purity. In vitro studies demonstrated specific and sensitive binding of MORAb-004 to MS1 mouse endothelial cells expressing hTEM1, with no binding to control MS1 cells. (125)I-MORAb-004 and (124)I-MORAb-004 both had an immunoreactivity of approximately 90%. In vivo biodistribution experiments revealed rapid, highly specific and sensitive uptake of MORAb-004 in MS1-TEM1 tumors at 4 h (153.2 ± 22.2 percentage injected dose per gram [%ID/g]), 24 h (127.1 ± 42.9 %ID/g), 48 h (130.3 ± 32.4 %ID/g), 72 h (160.9 ± 32.1 %ID/g), and 6 d (10.7 ± 1.8 %ID/g). Excellent image contrast was observed with (124)I-immuno-PET. MORAb-004 uptake was statistically higher in TEM1-positive tumors than in control tumors. Binding specificity was confirmed by blocking studies using excess nonlabeled MORAb-004.
  
  
  CONCLUSIONS
  In our preclinical model, with hTEM1 exclusively expressed on engineered murine endothelial cells that integrate into the tumor vasculature, (124)I-MORAb-004 displays high tumor-to-background tissue contrast for detection of hTEM1 in easily accessible tumor vascular compartments. These studies strongly suggest the clinical utility of (124)I-MORAb-004 immuno-PET in assessing TEM1 tumor-status.
authors: Nuclear Medicine & Clinical Molecular Imaging, Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.|Institute for Translational Medicine and Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors: Ann-Marie
authors: AM
authors: Chacko
authors: Ovarian Cancer Research Center, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors: Chunsheng
authors: C
authors: Li
authors: Nuclear Medicine & Clinical Molecular Imaging, Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors: Madhura
authors: M
authors: Nayak
authors: Nuclear Medicine & Clinical Molecular Imaging, Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors: John L
authors: JL
authors: Mikitsh
authors: Ovarian Cancer Research Center, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors: Jia
authors: J
authors: Hu
authors: Nuclear Medicine & Clinical Molecular Imaging, Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors: Catherine
authors: C
authors: Hou
authors: Morphotek, Inc., Exton, Pennsylvania.
authors: Luigi
authors: L
authors: Grasso
authors: Morphotek, Inc., Exton, Pennsylvania.
authors: Nicholas C
authors: NC
authors: Nicolaides
authors: Institute for Translational Medicine and Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors: Vladimir R
authors: VR
authors: Muzykantov
authors: Nuclear Medicine & Clinical Molecular Imaging, Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors: Chaitanya R
authors: CR
authors: Divgi
authors: Ovarian Cancer Research Center, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors: George
authors: G
authors: Coukos
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000493:pharmacokinetics; D015703:Antigens, CD / Q000276:immunology*; D001808:Blood Vessels / Q000378:metabolism*; D002460:Cell Line; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes; D007553:Isotope Labeling; D051379:Mice; D009363:Neoplasm Proteins / Q000276:immunology*; D009369:Neoplasms / Q000098:blood supply*; D049268:Positron-Emission Tomography / Q000379:methods*
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D007457:Iodine Radioisotopes; D009363:Neoplasm Proteins; C509258:tumor endothelial marker 1, mouse
keywords: MORAb-004; TEM1; endosialin; immuno-PET; monoclonal antibodies