Abstract
Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor arising from the human gastrointestinal (GI) tract. Overexpression of c-kit, encoding type III receptor tyrosine kinase, and its functional mutation is present in most GIST. [F-18]-fluoro-deoxyglucose (FDG) has been reported to highly accumulate in GIST, and FDG positron emission tomography (PET) is very useful for clinical tumor staging and also for the assessment of early response to GIST treatments using Imatinib (Gleevec). However, FDG-PET, in some cases, fails to detect relapse of GIST at early time point, and these cases showed c-kit positivity determined by biopsy. If we could develop a specific method to detect c-kit expression, it will lead to detect the early response and relapse of GISTs. In this study, we labeled anti-c-kit antibodies with I-125, and assessed its in vitro characteristics.
We constructed an expressing vector of mutated c-kit and transfected it to HEK293 human embryonic kidney cells and isolated several stable clones. Immunofluorescence staining showed that c-kit is primarily localized to the cell membrane in c-kit stably expressing cells like the original GIST cell line. We radiolabeled anti-c-kit murine monoclonal antibodies with I-125 and performed cell binding, competition and internalization assays in vitro. These results showed that radiolabeled antibodies specifically bound to c-kit expressing cells and be internalized. Therefore, antibodies labeled with metal radionuclide such as In-111 seem suitable for in vivo application.
