title: Single-photon emission computed tomography of spontaneous liver metastasis from orthotopically implanted human colon cancer cell line stably expressing human sodium/iodide symporter reporter gene.
abstract: BACKGROUND
  We aimed to develop a mouse spontaneous liver metastasis model from an orthotopically implanted human colon cancer cell line stably expressing a human sodium/iodide symporter (NIS) reporter gene, which can be imaged with single-photon emission computed tomography (SPECT) using 99mTcO4-.
  
  
  METHODS
  A recombinant plasmid containing a constitutively driven NIS gene (pcDNA3-NIS) was transfected into the human colon cancer cell line HCT116, and stable cell lines were established. The stable cells were subcutaneously injected into the nude mice. When the diameter reached 10 mm, the xenografts were excised, cut into small fragments, and orthotopically implanted into the cecal walls of another nude mice. 99mTcO4- SPECT/CT imaging was initiated 8 weeks later and repeated every 1 to 2 weeks.
  
  
  RESULTS
  The production and function of NIS protein was confirmed in vitro by Western blotting and 99mTcO4- uptake assay. On SPECT/CT imaging, focal 99mTcO4- uptake was detected in the liver. Necropsy revealed local growth of the orthotopic colon xenografts with extensive invasion, microscopic serosal metastasis, and metastatic foci in the corresponding hepatic regions showing focal 99mTcO4- uptake. Immunohistochemistry revealed high levels of NIS expression in cells forming liver tumor, indicating that the liver tumor cells originated from the orthotopic colon xenografts.
  
  
  CONCLUSIONS
  The present proof-of-concept study provided a rationale for employing a radionuclide reporter gene for the specific visualization of spontaneous liver metastasis in living mice. This unique animal model of clinically relevant and externally detectable liver metastasis will be a powerful tool for investigating tumor biology and developing novel therapies for cancer metastasis.
authors.affiliation: Molecular Imaging Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba, 263-8555, Japan. inubushi@nirs.go.jp.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Inubushi
authors.forename: Yong-Nan
authors.initials: YN
authors.lastname: Jin
authors.forename: Chika
authors.initials: C
authors.lastname: Murai
authors.forename: Hironobu
authors.initials: H
authors.lastname: Hata
authors.forename: Yoshimasa
authors.initials: Y
authors.lastname: Kitagawa
authors.forename: Tsuneo
authors.initials: T
authors.lastname: Saga