title: ⁹⁹mTc-labeled single-domain antibody EG2 in targeting epidermal growth factor receptor: an in-vitro and mouse model in-vivo study.
abstract: OBJECTIVE
  The aim of this study was to explore the targeting ability and metabolic characteristics of the technetium-99m-labeled single-domain antibody (⁹⁹mTc-sdAb) EG2 targeting epidermal growth factor receptor (EGFR) through an in-vitro and in-vivo study.
  
  
  METHODS
  The sdAb EG2 was radiolabeled with Tc using a tricarbonyl kit. The EGFR expression level of A431 and OCM-1 cells was confirmed using immunofluorescence staining. Cell binding, blocking, uptake, and efflux studies were performed to investigate the binding specificity of ⁹⁹mTc-sdAb EG2 in vitro. Single-photon emission computed tomography imaging and biodistribution studies were used to explore the targeting abilities and metabolic characteristics of Tc-sdAb EG2 in vivo.
  
  
  RESULTS
  ⁹⁹mTc-sdAb EG2 was successfully prepared with labeling yields of 60-71% and specific activity of 1.83±0.29 GBq/mg (n=3). Immunofluorescence staining revealed high and low EGFR expression on the surface of A431 and OCM-1 cells, respectively. The binding affinity of ⁹⁹mTc-sdAb EG2 to A431 cells was 43.53±1.89 nmol/l. ⁹⁹mTc-sdAb EG2 uptake in A431 cells in vitro could be blocked by ∼19, 40, and 66% in the presence of excess unlabeled sdAb EG2 at 100, 500, and 1000 nmol/l, respectively. Single-photon emission computed imaging indicated that A431 tumor images could be clearly displayed at early scan time points after ⁹⁹mTc-sdAb EG2 injection, even as early as 1 h. Biodistribution study showed that the A431 tumor uptake of ⁹⁹mTc-sdAb EG2 was blocked by about 51% at 3 h after coinjecting excess of sdAb EG2. However, there were almost no OCM-1 tumor images at the corresponding scan time points and the OCM-1 tumor uptake was only 0.40±0.13% injected dose per gram of tissue (n=5) at 3 h.
  
  
  CONCLUSIONS
  This study demonstrated that sdAb EG2 can effectively target EGFR in vitro and in vivo in tumors, suggesting that it could be used as a molecular probe for EGFR detection.
authors.affiliation: aDepartment of Nuclear Medicine, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Hubei Province Key Laboratory of Molecular Imaging bDepartment of Nuclear Medicine, Zhongnan Hospital of Wuhan University, Wuhan cCAS Key Laboratory of Pathogenic Microbiology and Immunology (CASPMI), Centre for Molecular Immunology dChina-Japan Joint Laboratory of Molecular Immunology and Microbiology, Institute of Microbiology, Chinese Academy of Sciences, Beijing eCollege of Life Sciences, University of Science and Technology of China, Hefei, People's Republic of China.
authors.forename: Chongjiao
authors.initials: C
authors.lastname: Li
authors.forename: Bing
authors.initials: B
authors.lastname: Wen
authors.forename: Lifei
authors.initials: L
authors.lastname: Wang
authors.forename: Hongyan
authors.initials: H
authors.lastname: Feng
authors.forename: Xiaotian
authors.initials: X
authors.lastname: Xia
authors.forename: Zhiling
authors.initials: Z
authors.lastname: Ding
authors.forename: Bin
authors.initials: B
authors.lastname: Gao
authors.forename: Yongxue
authors.initials: Y
authors.lastname: Zhang
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Lan
mesh_terms: D000818:Animals; D001692:Biological Transport; D045744:Cell Line, Tumor; D066246:ErbB Receptors / Q000276:immunology*; D006801:Humans; D007553:Isotope Labeling; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D011854:Radiochemistry; D061905:Single-Domain Antibodies / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D013667:Technetium; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D061905:Single-Domain Antibodies; D013667:Technetium; D066246:ErbB Receptors