To develop radiolabeled FGFR2-targeting probes for visualizing fibroblast growth factor receptor (FGFR) expression levels in the tumor microenvironment, four novel 99mTc-labeled FGFR2-targeting peptides ([99mTc]Tc-FGFR2-1, [99mTc]Tc-FGFR2-2, [99mTc]Tc-FGFR2-3, and [99mTc]Tc-FGFR2-4) with different amino acid linkers between the targeted peptide moiety and the 99mTc chelating group were designed and synthesized. The in vitro cellular inhibition, internalization, and efflux results demonstrated that the four 99mTc complexes exhibited FGFR2-specific binding and prolonged cellular retention in DU145 human prostate cancer cells, which indicated that modification from the glycine side (N-terminal) of CH02 was feasible. Among them, [99mTc]Tc-FGFR2-1 exhibited the highest in vitro cellular uptake and in vivo tumor uptake at 30 min postinjection, and tumor uptake could be significantly inhibited by the competitor CH02 (53% inhibited, p < 0.05), suggesting the tumor-specific targeting ability of [99mTc]Tc-FGFR2-1. The DU145-xenografted tumor lesions were clearly visualized by single photon emission computed tomography (SPECT)/CT at 30 min postinjection of [99mTc]Tc-FGFR2-1, highlighting its potential as a SPECT imaging probe for tumor FGFR2 detection.
Keywords: 99mTc; FGFR2; SPECT; [99mTc]Tc-FGFR2-1; fibroblast growth factor receptors; tumor.