High gastrin releasing peptide receptor (GRPR) expression is associated with numerous cancers including prostate and breast cancer.The aim of the current study was to develop a55Co-labeled PET agent based on GRPR antagonist RM26 for visualization of GRPR-expressing tumors. Labeling with57Co and55Co, stability, binding specificity, and in vitro and in vivo characteristics of57Co-NOTA-PEG2-RM26 were studied.NOTA-PEG2-RM26 was successfully radiolabeled with57Co and55Co with high yields and demonstrated high stability.The radiopeptide showed retained binding specificity to GRPR in vitro and in vivo.57Co-NOTA-PEG2- RM26 biodistribution in mice was characterized by rapid clearance of radioactivity from blood and normal non-GRPR-expressing organs and low hepatic uptake.The clearance was predominantly renal with a low degree of radioactivity reabsorption. Tumor-toblood ratios were approximately 200 (3 h pi) and 1000 (24 h pi).The favorable biodistribution of cobalt-labeled NOTA-PEG2-RM26 translated into high contrast preclinical PET/CT (using55Co) and SPECT/CT (using57Co) images of PC-3 xenografts.The initial biological results suggest that55Co-NOTA-PEG2-RM26 is a promising tracer for PET visualization of GRPR-expressing tumors.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging