Synthesis and Preclinical Evaluation of Novel 68Ga-Labeled Bispecific SSTR/GLP-1R Targeting Probes for Neuroendocrine Neoplasms Imaging

Abstract

Purpose The neuroendocrine neoplasms (NENs) have a poor early diagnostic rate. To increase the detection rate of NENs, this project aims to build a PET probe, DOTA-exendin-4-TOC, that targets both SSTR and GLP-1R. Procedures The novel dual-target molecular probe DOTA-exendin-4-TOC was constructed, and radiolabeled with gallium-68 to target both SSTR and GLP-1R. In vivo and in vitro stability tests, cellular uptake tests, biodistribution, and microPET/CT studies were used to examine the PET probe properties in the tumor models including RIN-M5F, INS-1, and AR42J. Results The synthesis of [⁶⁸Ga]Ga-DOTA-exendin-4-TOC had a radiochemical purity of more than 95%. The radiolabel demonstrated better stability both in vivo (in mouse serum) and in vitro (in PBS), and it is eliminated by the urine system. RIN-M5F cells, INS-1 cells, and AR42J cells were found to have an uptake effect on [⁶⁸Ga]Ga-DOTA-exendin-4-TOC in vitro cell uptake experiments. The tumor models containing RIN-M5F, INS-1, and AR42J demonstrated uptake of [⁶⁸Ga]Ga-DOTA-exendin-4-TOC at 60 and 120 minutes, according to microPET/CT imaging. Higher values of tumor uptake were noted for AR42J at 1.50 ± 0.10 (120 min), INS-1 at 1.57 ± 0.12 (60 min), and RIN-M5F at 0.87 ± 0.11 (60 min). All three tumor models exhibited tumor tissues' uptake of [⁶⁸Ga]Ga-DOTA-exendin-4-TOC, according to in vivo metabolism studies. Furthermore, the kidneys had the highest distribution of radioactivity. Conclusions In this work, a new molecular probe that targets SSTR and GLP-1R was successfully constructed and radiolabeled with [⁶⁸Ga]Ga, called [⁶⁸Ga]Ga-DOTA-exendin-4-TOC. This novel dual-target probe could be applied as a valuable tool for improving the detection rate in patients in the future.