Labeling bombesin-like peptide with 99mTc via hydrazinonicotinamide: description of optimized radiolabeling conditions

Bombesin (BNN)-like peptides have very high binding affinity for the gastrin-releasing peptide (GRP) receptor. The goal of the current study was to optimize the labeling conditions of a new ^99mTc-radiolabeled BNN-like peptide based on the bifunctional chelating ligand HYNIC using different co-ligands (EDDA and tricine). The radiolabeling conditions (pH, amount of co-ligand, amount of stannous chloride, temperature and reaction time) for newly-formed ^99mTc-tricine-HYNIC-Q-Litorin and ^99mTc-EDDA-HYNIC-Q-Litorin were optimized and evaluated by RHPLC and RTLC. Radiochemical yields for ^99mTc-tricine-HYNIC-Q-Litorin and ^99mTc-EDDA-HYNIC-Q-Litorin were 98.0 ± 1.7 and 97.5 ± 2.5%, respectively. When EDDA was used as co-ligand, the labeling of ^99mTc-EDDA-HYNIC-Q-Litorin was optimal in the following reaction mixture: HYNIC-peptide: EDDA: 10 μg/5 mg, pH 3, SnCl₂ concentration: 12 μg/0.1 mL, reaction temperature: 100 °C, reaction time: 15 min. Besides, the optimum conditions were HYNIC-peptide:tricine: 10 μg/50 mg, pH 5, SnCl₂ concentration: 12 μg/0.1 mL, reaction temperature: 100 °C, reaction time: 15 min for preparing ^99mTc-tricine-HYNIC-Q-Litorin. The manufactured ^99mTc-HYNIC-Q-Litorin conjugates may offer new possibilities for imaging cancer cells expressing bombesin receptors.