title: In vivo imaging of radiation-induced tissue apoptosis by (99m)Tc(I)-his          (6)-annexin A5.
abstract: OBJECTIVE
  A recombinant annexin A5 with the N-terminal extension of six histidine residues was labeled with (99m)Tc(I)-tricarbonyl ion to produce the (99m)Tc-labeled annexin A5, referred to (99m)Tc(I)-his(6)-annexin A5. We have explored the agent as an effective imaging probe for in vivo detecting the apoptosis of internal tissue subjected with high radiation doses in a γ-irradiated mouse model.
  
  
  METHODS
  [(99m)Tc(CO)(3)(OH(2))(3)](+) was prepared and taken to directly label his(6)-annexin A5. The radiochemical purity of (99m)Tc(I)-his(6)-annexin A5 after size-exclusion separation was measured by HPLC. The binding affinity of (99m)Tc(I)-his(6)-annexin A5 to apoptotic cells was assessed using 20 Gy-irradiated Jurkat T cells. The effectiveness of (99m)Tc(I)-his(6)-annexin A5 as an imaging probe to detect the internal tissue apoptosis was assessed by biodistribution study and nanoSPECT/CT using the animal model of C57BL/6J mice conducted with 10 Gy γ irradiation.
  
  
  RESULTS
  The radiochemical purity of (99m)Tc(I)-his(6)-annexin A5 could attain ≥95%. The binding affinity of (99m)Tc(I)-his(6)-annexin A5 to the 20 Gy-irradiated Jurkat cells was found to be ca. 20-fold higher than that to the sham-irradiated cells. In the animal imaging study, the splenic uptake of (99m)Tc(I)-his(6)-annexin A5 for the 10 Gy-irradiated mice showed from ca. 3-fold to 5-fold higher than those of the sham-irradiated mice from 45 to 165 min postinjection. The corresponding intestinal uptake showed from ca. 2-fold to 3-fold higher during the same period of time postinjection. The biodistribution study demonstrated the organ uptakes comparable with the imaging results. The apoptotic extents of the spleen and the intestine from the SPECT/CT imaging were correlated with an immunohistochemical staining assay for caspase 3 active form fragment.
  
  
  CONCLUSIONS
  This work is the first study to demonstrate that (99m)Tc(I)-his(6)-annexin A5 is a potential clinical imaging agent for detecting radiation-induced tissue apoptosis in an animal model.
authors.affiliation: Molecular Imaging Center and Department of Nuclear Medicine, Chang Gung Memorial Hospital, Taoyuan, Taiwan.
authors.forename: Kun-Ju
authors.initials: KJ
authors.lastname: Lin
authors.forename: Chun-Chung
authors.initials: CC
authors.lastname: Wu
authors.forename: Yi-Hsin
authors.initials: YH
authors.lastname: Pan
authors.forename: Fang-Hsing
authors.initials: FH
authors.lastname: Chen
authors.forename: Sheng-Yung
authors.initials: SY
authors.lastname: Fu
authors.forename: Chi-Shiun
authors.initials: CS
authors.lastname: Chiang
authors.forename: Ji-Hong
authors.initials: JH
authors.lastname: Hong
authors.forename: Jem-Mau
authors.initials: JM
authors.lastname: Lo
mesh_terms: D000818:Animals; D017304:Annexin A5 / Q000493:pharmacokinetics; D017209:Apoptosis / Q000528:radiation effects*; D006801:Humans; D007422:Intestines / Q000000981:diagnostic imaging / Q000528:radiation effects; D019169:Jurkat Cells; D051379:Mice; D008810:Mice, Inbred C57BL; D064847:Multimodal Imaging / Q000379:methods*; D015609:Organotechnetium Compounds / Q000493:pharmacokinetics; D049268:Positron-Emission Tomography; D011833:Radiation Injuries, Experimental / Q000000981:diagnostic imaging / Q000473:pathology; D013154:Spleen / Q000000981:diagnostic imaging / Q000528:radiation effects; D014057:Tomography, X-Ray Computed
chemical_list: C568748:(99)mTc-(CO)(3) His-annexin A5; D017304:Annexin A5; D015609:Organotechnetium Compounds