99mTc-HYNIC-Bombesin (7-14)NH2:: Radiochemical evaluation with co-ligands EDDA (EDDA = ethylenediamine-N,N′-diacetic acid), tricine, and nicotinic acid

Bombesin (BBN) is a peptide exhibiting high affinity for the gastrin releasing peptide receptor (GRPr), which is overexpressed on a variety of human tumors including breast, prostate, lung and pancreatic cancers. The specific aim of this study was to identify a new Tc-99m-radiolabeled BBN analogue based upon the bifunctional chelating ligand HYNIC (2-hydrazinonicotinamide) that might be used as a noninvasive tool for diagnosis of GRP receptor-positive tumors. In this study, HYNIC-beta-Ala-BBN(7-14)NH2 and HYNIC-5-Ava-BBN(7-14)NH2 were synthesized using traditional solid phase peptide synthetic techniques. The newly-formed conjugates were radiolabeled using Tc-99m in the presence of different coligands including tricine, ethylenediamine diacetic acid (EDDA), tricine/EDDA, and tricine/nicotinic acid. Radiolabeling conditions i.e., pH, temperature, and reaction time) were optimized and evaluated by ITLC and reversed-phase HPLC.