C-kit-targeted imaging of gastrointestinal stromal tumor using radiolabeled anti-c-kit monoclonal antibody in a mouse tumor model.
BACKGROUND
Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor arising from the gastrointestinal tract and highly expresses mutated c-kit. We aimed to develop a specific and sensitive method for detecting GISTs using radiolabeled anti-c-kit monoclonal antibody.


METHODS
A mutated c-kit-expressing cell clone was established by transfecting an expressing vector of mutated c-kit gene into HEK293 human embryonic kidney cells. The tumors were developed by inoculating c-kit-expressing cells into nude mice. (125)I- and (111)In-labeled anti-c-kit antibodies (12A8 and 41A11) were evaluated in vitro by cell binding, competitive inhibition and cellular internalization assays, and in vivo by biodistribution and imaging studies in tumor-bearing mice.


RESULTS
Both (125)I- and (111)In-labeled antibodies showed specific binding with c-kit-expressing cells with high affinity (dissociation constants = 2.2-7.1x10(9) M(-1)). Internalization assay showed that (125)I-labeled antibodies were rapidly internalized and dehalogenated, with the release of (125)I from the cells, resulting in reduction of cell-associated radioactivity with time. In contrast, (111)In-labeled antibody was internalized but did not result in the reduced radioactivity associated with tumor cells. Reflecting this phenomenon, the in vivo tumor uptake of (125)I-labeled antibody was low on Day 1, further decreasing with time, while tumor uptake of (111)In-labeled antibody was high on Day 1, further increasing with time. The xenografted tumor was clearly visualized by scintigraphy after injection of (111)In-labeled antibody.


CONCLUSIONS
The anti-c-kit monoclonal antibody labeled with a metal radionuclide would be promising for c-kit-targeted imaging of GISTs.
Diagnostic Imaging Group, Molecular Imaging Center, National Institute of Radiological Sciences, Chiba 263-8555, Japan.
Chizuru
C
Sogawa
Atsushi B
AB
Tsuji
Hitomi
H
Sudo
Aya
A
Sugyo
Chisato
C
Yoshida
Kenichi
K
Odaka
Tomoya
T
Uehara
Yasushi
Y
Arano
Mitsuru
M
Koizumi
Tsuneo
T
Saga
D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry* / Q000276:immunology* / Q000378:metabolism / Q000493:pharmacokinetics; D001667:Binding, Competitive; D001692:Biological Transport; D045744:Cell Line, Tumor; D004195:Disease Models, Animal; D046152:Gastrointestinal Stromal Tumors / Q000000981:diagnostic imaging / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007205:Indium Radioisotopes / Q000737:chemistry*; D007457:Iodine Radioisotopes / Q000737:chemistry; D008297:Male; D051379:Mice; D057054:Molecular Imaging / Q000379:methods*; D009154:Mutation; D019009:Proto-Oncogene Proteins c-kit / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*; D015899:Tomography, Emission-Computed, Single-Photon
D000911:Antibodies, Monoclonal; D007205:Indium Radioisotopes; D007457:Iodine Radioisotopes; D019009:Proto-Oncogene Proteins c-kit