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.