new freeze-dried kit for diagnosis of bombesin receptor expressing tumors

introduction: it has been shown that some primary human tumors and their metastases, including prostate and breast tumors, over-express gastrin-releasing peptide (grp) receptors. bombesin is a neuropeptide with a high affinity for these grp receptors. the purpose of this study was to prepare and evaluate the characteristics of a new freeze-dried kit, [6-hydrazinopyridine-3-carboxylic acid (hynic)]-gaba-bombesin [7-14] nh2 designed for the labeling with 99mtc using tricine and edda as coligand. methods: synthesis was performed on a solid phase using a standard fmoc strategy and hynic precursor coupled at the n-terminus. purified peptide conjugate was labeled with 99mtc at 100°c for 10 min. radiochemical analysis involved itlc and high-performance liquid chromatography methods. peptide conjugate stability and affinity to human serum was challenged for 24 hours. the internalization rate was studied in grp receptor expressing pc-3 cells. biodistribution of radiopeptide was studied in rats. results: radiolabeling was performed at high specific activities, and radiochemical purity was >98%. the stability of radiolabeled peptide in human serum was excellent. in vitro studies showed >14% of activity was specific internalized into pc-3 cells up to 4 h. after injection into rat biodistribution data showed a rapid blood clearance, with renal excretion and specific binding towards grp receptor-positive tissues such as pancreas (1.15±0.19% id/g after 4 h). conclusion: [99mtc-hynic]-gaba-bombesin [7-14] nh2 showed favorable radiochemical and biological characteristics which make our new designed labeled peptide conjugate as a very suitable agent for diagnostic purposes in malignant tumors.