Synthesis, radiolabeling, and evaluation of gastrin releasing peptide receptor antagonist Ga-HBED-CC-RM26.

The acyclic chelator HBED-CC has attained huge clinical significance owing to high thermodynamic and kinetic stability of Ga-HBED-CC chelate. It provides an excellent platform for quick preparation of Ga-based radiotracers in high yield. Thus, the present study aimed at conjugation of gastrin releasing peptide receptor (GRPr) antagonist, RM26, with HBED-CC chelator for Ga-labeling. In vitro and vivo behavior of the peptide tracer, Ga-HBED-CC-PEG -RM26, was assessed and compared with Ga-NODAGA-PEG -RM26. The peptide tracers, Ga-HBED-CC-PEG -RM26 and Ga-NODAGA-PEG -RM26, prepared either by wet chemistry or formulated using freeze-dried kits exhibited excellent radiochemical yield and in vitro stability. The two peptide tracers cleared rapidly from the blood. Biodistribution studies in normal mice demonstrated slightly higher or comparable uptake of Ga-HBED-CC-PEG -RM26 in GRPr-expressing organs pancreas, stomach, and intestine. The preliminary studies suggest high potential of Ga-HBED-CC-PEG -RM26 for further investigation as a GRPr imaging agent and the wide scope of HBED-CC chelator in development of Ga-based peptide tracers.