Molecular imaging of gastrointestinal stromal tumor using anti-c-KIT antibody and its fragments

Gastrointestinal stromal tumors (GISTs) are malignant subepithelial tumors, known for their poor prognosis due to distant metastasis. Because GIST is covered by a normal mucosal layer, effective tissue biopsy under conventional endoscopy is difficult, thereby leading to delayed diagnosis and a dismal prognosis. We performed molecular imaging of GIST targeting c-KIT using fluorescence-labeled anti-c-KIT antibody/fragments and fluorescent endoscopy.

Mouse anti-human c-KIT monoclonal antibody, its F(ab')₂ and Fab fragments were labeled with AF680. Two GIST cell lines (GIST-T1, GIST-882M) were used for experiments. Antibodies were intravenously administered to mice xenografted with GIST-T1 or GIST-882M, and each tumor was observed using IVIS Spectrum and self-developed simple fluorescent endoscopy.

The GIST-T1 cell live imaging revealed strong signals on cell membranes after 1 min incubation, and thereafter, they aggregated and internalized inside the cells within 130 min in all antibody/fragment groups. In vivo mouse experiments, AF680-labeled IgG slowly accumulated in tumors peaking at 24 h after injection. However, AF680-labeled F(ab')₂ and Fab rapidly accumulated in tumors peaking at 1-2 h, and completely cleared from the body within 24 h. Fab showed the strongest fluorescence intensity in tumors. Fluorescence endoscopy could clearly detect GIST xenograft tumors 1-2 h after AF680-labeled F(ab')₂ and Fab injection.

AF680-labeled antibody/fragments showed clear and specific fluorescence signals in GIST xenografts in mice. Particularly, AF680-labeled Fab showed the strongest signal intensity at 1-2 h post-administration and rapid clearance, suggestive of the safety. This approach may enable molecular imaging diagnosis of GIST by endoscopy in outpatient settings in the future.