Figure 3.

An overview of the leading compounds for GLP-1R-targeted probes. In the development of GLP-1R-targeted imaging probes, exendin-related peptides such as exendin-3, exendin-4, and exendin (9-39) have been investigated as promising compounds. These compounds have approximately 50% homology with human GLP-1 (hGLP-1) and show high stability in vivo and high affinity to GLP-1R, which qualifies their potential as tracers for in vivo β-cell imaging. Exendin-4 differs from exendin-3 by two amino acid substitutions (in orange). C-terminally modified derivatives tended to show superior specificity, whereas the modified derivatives on the residue Lys¹² of exendin-4 (in blue) demonstrated high affinity to GLP-1R and in vivo stability as in vivo imaging probes for β cells.