title: An engineered cysteine-modified diabody for imaging activated leukocyte cell adhesion molecule (ALCAM)-positive tumors.
abstract: OBJECTIVE
  The purpose of this study was to generate and evaluate a positron emission tomography (PET) radiotracer targeting activated leukocyte cell adhesion molecule (ALCAM).
  
  
  METHODS
  A human anti-ALCAM single chain variable fragment was reformatted to produce a covalent dimer, termed a cys-diabody (CysDb). Purified CysDb was characterized by gel electrophoresis and size exclusion chromatography, and immunoreactivity was assessed by flow cytometry and immunofluorescence. Targeting and imaging of ALCAM-positive tumors using (64)Cu-DOTA-CysDb were evaluated in mice bearing human pancreatic adenocarcinoma xenografts (HPAF-II or BxPC-3).
  
  
  RESULTS
  CysDb binds specifically to ALCAM-positive cells in vitro with an apparent affinity in the range of 1-3 nM. MicroPET images at 4 h showed specific targeting of positive tumors in vivo, a finding confirmed by biodistribution analysis, with positive/negative tumor ratios of 1.9 ± 0.6 and 2.4 ± 0.6, and positive tumor/blood ratios of 2.5 ± 0.9 and 2.9 ± 0.6 (HPAF-II and BxPC-3, respectively).
  
  
  CONCLUSIONS
  Successful imaging with (64)Cu-DOTA-CysDb in animal models suggests further investigation of ALCAM as an imaging biomarker is warranted.
authors.affiliation: Crump Institute for Molecular Imaging, Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at University of California, Los Angeles, Los Angeles, CA, USA. kmccabe@ucla.edu
authors.forename: Katelyn E
authors.initials: KE
authors.lastname: McCabe
authors.forename: Bin
authors.initials: B
authors.lastname: Liu
authors.forename: James D
authors.initials: JD
authors.lastname: Marks
authors.forename: James S
authors.initials: JS
authors.lastname: Tomlinson
authors.forename: Hong
authors.initials: H
authors.lastname: Wu
authors.forename: Anna M
authors.initials: AM
authors.lastname: Wu
mesh_terms: D020410:Activated-Leukocyte Cell Adhesion Molecule / Q000032:analysis / Q000378:metabolism*; D000818:Animals; D014408:Biomarkers, Tumor / Q000032:analysis / Q000378:metabolism*; D045744:Cell Line, Tumor; D003301:Copper Radioisotopes / Q000737:chemistry; D003545:Cysteine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005260:Female; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental / Q000737:chemistry / Q000378:metabolism; D009942:Organometallic Compounds / Q000737:chemistry; D010190:Pancreatic Neoplasms / Q000378:metabolism; D049268:Positron-Emission Tomography / Q000379:methods*; D015202:Protein Engineering / Q000379:methods*; D051381:Rats; D057127:Single-Chain Antibodies / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D020410:Activated-Leukocyte Cell Adhesion Molecule; D014408:Biomarkers, Tumor; D003301:Copper Radioisotopes; D009942:Organometallic Compounds; D057127:Single-Chain Antibodies; D003545:Cysteine