[113mIn]In-AMBA: A Novel Diagnostic Agent for SPECT Imaging of GRPR-Expressing Tumors.

Purpose: Gastrin-releasing peptide receptor (GRPR), a member of the bombesin G-protein-coupled receptor family, is introduced as the promising target for the diagnosis and therapy of various tumors. This study aimed to develop a novel diagnostic agent of [^113mIn]In-AMBA for single photon emission computed tomography (SPECT) imaging of GRPR expressing tumors.

Methods: ^113mIn was provided from an in-house made ¹¹³Sn/^113mIn generator in the chloride form. [^113mIn]In-AMBA was prepared in the optimal conditions and the stability was checked in PBS buffer and human serum, Then the binding affinity and internalization of the radiolabeled compound were investigated in PC3 cell lines at 120 min. the biodistribution of the radiolabeled peptide was studied in normal rats.

Results: [^113mIn]In-AMBA was prepared with radiochemical purity (RCP) > 98% under the optimal labeling conditions. The compound indicated significant stability in PBS buffer and human serum (> 95% at 180 min post preparation). High binding affinity (51% at 60 min) and internalization (64% at 120 min) of the radiolabeled compound towards PC3 cell lines were also observed. The major accumulation of the compound was seen in kidneys, and other GRPR-expressing tissues.

Conclusion: The biodistribution of the labeled compound in normal rats indicated rapid elimination of the complex from the blood, and considerable accumulation in the GRPR-expressing organ of pancreas, in complete agreement with similar labeled compounds. [^113mIn]In-AMBA can be a suitable candidate for SPECT imaging of GRPR-expressed tumors.