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

ABSTRACT

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] NH[2] designed for the labeling with 99mTc using tricine and EDDA as coligand. 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 [99m]Tc 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. 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]. [[99m]Tc-HYNIC]-GABA-Bombesin [7-14] NH[2] 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