title: Positron emission tomography imaging of CD105 expression with 89Zr-Df-TRC105.
abstract: OBJECTIVE
  High tumor microvessel density correlates with a poor prognosis in multiple solid tumor types. The clinical gold standard for assessing microvessel density is CD105 immunohistochemistry on paraffin-embedded tumor specimens. The goal of this study was to develop an (89)Zr-based PET tracer for noninvasive imaging of CD105 expression.
  
  
  METHODS
  TRC105, a chimeric anti-CD105 monoclonal antibody, was conjugated to p-isothiocyanatobenzyl-desferrioxamine (Df-Bz-NCS) and labeled with (89)Zr. FACS analysis and microscopy studies were performed to compare the CD105 binding affinity of TRC105 and Df-TRC105. PET imaging, biodistribution, blocking, and ex-vivo histology studies were performed on 4T1 murine breast tumor-bearing mice to evaluate the pharmacokinetics and tumor-targeting of (89)Zr-Df-TRC105. Another chimeric antibody, cetuximab, was used as an isotype-matched control.
  
  
  RESULTS
  FACS analysis of HUVECs revealed no difference in CD105 binding affinity between TRC105 and Df-TRC105, which was further validated by fluorescence microscopy. (89)Zr labeling was achieved with high yield and specific activity. Serial PET imaging revealed that the 4T1 tumor uptake of (89)Zr-Df-TRC105 was 6.1 ± 1.2, 14.3 ± 1.2, 12.4 ± 1.5, 7.1 ± 0.9, and 5.2 ± 0.3 %ID/g at 5, 24, 48, 72, and 96 h after injection, respectively (n = 4), higher than all organs starting from 24 h after injection, which provided excellent tumor contrast. Biodistribution data as measured by gamma counting were consistent with the PET findings. Blocking experiments, control studies with (89)Zr-Df-cetuximab, and ex-vivo histology all confirmed the in vivo target specificity of (89)Zr-Df-TRC105.
  
  
  CONCLUSIONS
  We report here the first successful PET imaging of CD105 expression with (89)Zr as the radiolabel. Rapid, persistent, CD105-specific uptake of (89)Zr-Df-TRC105 in the 4T1 tumor was observed.
authors: Department of Radiology, University of Wisconsin-Madison, Madison, WI 53705, USA.
authors: Hao
authors: H
authors: Hong
authors: Gregory W
authors: GW
authors: Severin
authors: Yunan
authors: Y
authors: Yang
authors: Jonathan W
authors: JW
authors: Engle
authors: Yin
authors: Y
authors: Zhang
authors: Todd E
authors: TE
authors: Barnhart
authors: Glenn
authors: G
authors: Liu
authors: Bryan R
authors: BR
authors: Leigh
authors: Robert J
authors: RJ
authors: Nickles
authors: Weibo
authors: W
authors: Cai
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000493:pharmacokinetics; D015703:Antigens, CD / Q000378:metabolism*; D045744:Cell Line, Tumor; D003676:Deferoxamine / Q000031:analogs & derivatives* / Q000737:chemistry; D000071063:Endoglin; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D017879:Isothiocyanates / Q000737:chemistry*; D051379:Mice; D049268:Positron-Emission Tomography / Q000379:methods*; D011868:Radioisotopes; D011956:Receptors, Cell Surface / Q000378:metabolism*; D015040:Zirconium
chemical_list: C549125:4-isothiocyanatobenzyl-desferrioxamine; D000911:Antibodies, Monoclonal; D015703:Antigens, CD; C064206:ENG protein, human; D000071063:Endoglin; D017879:Isothiocyanates; D011868:Radioisotopes; D011956:Receptors, Cell Surface; D015040:Zirconium; D003676:Deferoxamine