Preclinical Evaluation of a High-Affinity 18F-Trifluoroborate Octreotate Derivative for Somatostatin Receptor Imaging

Recent studies have highlighted the high sensitivity of PET imaging with 68Ga-labeled octreotide derivatives for the detection and staging of neuroendocrine tumors. A somatostatin receptor ligand that is easily radiolabeled with 18F-fluoride could improve the availability of PET imaging of neuroendocrine tumors. We report an alkyltrifluoroborate– octreotate conjugate that is radiolabeled in a 1-step 18F exchange reaction in high yield and with high specific activity. Methods: We conjugated a new alkyltrifluoroborate to octreotate to obtain AMBF3-TATE, which was stored in 50-nmol aliquots for radiolabeling. 18F labeling was performed by 18F-19F isotope exchange with 18F-fluoride, and the tracer was purified by C18 cartridge separation. The radio-chemical yield was 20%–25%. PET imaging and biodistribution were performed on mice bearing AR42J tumor xenografts.Results: AMBF3-TATE bound the somatostatin receptor subtype 2 with high affinity (inhibition constant, 0.13 ± 0.03 nM). Starting with 29.6–37 GB