Diagnostic Imaging Group, Molecular Imaging Center, National Institute of Radiological Sciences, Chiba 263-8555, Japan.
Nucl Med Biol. 2010 Feb;37(2):179-87. doi: 10.1016/j.nucmedbio.2009.10.008. Epub 2009 Nov 26.
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.
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.
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.
The anti-c-kit monoclonal antibody labeled with a metal radionuclide would be promising for c-kit-targeted imaging of GISTs.
胃肠道间质瘤（GIST）是最常见的源自胃肠道的间叶性肿瘤，高度表达突变型 c-kit。我们旨在开发一种使用放射性标记的抗 c-kit 单克隆抗体检测 GIST 的特异且敏感的方法。
通过将突变型 c-kit 基因表达载体转染到 HEK293 人胚肾细胞中，建立了一个表达突变型 c-kit 的细胞克隆。通过将表达 c-kit 的细胞接种到裸鼠中，发展了肿瘤。通过细胞结合、竞争抑制和细胞内化实验，以及在荷瘤小鼠中的生物分布和成像研究，评估了（125）I-和（111）In 标记的抗 c-kit 抗体（12A8 和 41A11）的体外和体内性能。
（125）I-和（111）In 标记的抗体均与高亲和力表达 c-kit 的细胞特异性结合（解离常数 = 2.2-7.1x10(9) M(-1)）。内化实验表明，（125）I 标记的抗体迅速内化并脱卤，导致细胞相关放射性随时间减少。相比之下，（111）In 标记的抗体被内化，但不会导致与肿瘤细胞相关的放射性减少。反映出这一现象，（125）I 标记抗体的体内肿瘤摄取在第 1 天较低，随时间进一步减少，而（111）In 标记抗体的肿瘤摄取在第 1 天较高，随时间进一步增加。注射（111）In 标记的抗体后，通过闪烁照相术可以清晰地显示异种移植肿瘤。
用金属放射性核素标记的抗 c-kit 单克隆抗体有望用于 GIST 的 c-kit 靶向成像。
