C-kit-targeted imaging of gastrointestinal stromal tumor using radiolabeled anti-c-kit monoclonal antibody in a mouse tumor model

Introduction: 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. 125I- and 111In-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 125I- and 111In-labeled antibodies showed specific binding with c-kit-expressing cells with high affinity (dissociation constants= 2.2-7.1x109 M-1). Internalization assay showed that 125I-labeled antibodies were rapidly internalized and dehalogenated, with the release of 125I from the cells, resulting in reduction of cell-associated radioactivity with time. In contrast, 111In-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 125I-labeled antibody was low on Day 1, further decreasing with time, while tumor uptake of 111In-labeled antibody was high on Day 1, further increasing with time. The xenografted tumor was clearly visualized by scintigraphy after injection of 111In-labeled antibody.Conclusion: The anti-c-kit monoclonal antibody labeled with a metal radionuclide would be promising for c-kit-targeted imaging of GISTs