Preparation and evaluation of a new [sup.99m]Tc labeled bombesin derivative for tumor imaging

A variety of human tumors like prostate and breast cancer express bombesin receptors. Due to this a new bombesin analogue was labeled with [sup.99m]Tc via HYNIC and tricine as a coligand and investigated further. Peptide was synthesized on a solid phase using Fmoc strategy. Labeling with [sup.99m]Tc was performed at 100[degrees]C for 10 min and radiochemical analysis involved ITLC and HPLC methods. The stability of radiopeptide was checked in the presence of human serum at 37[degrees]C up to 24 h. Internalization was studied with the human GRP receptor cell line PC-3. The biodistribution was studied in mice. Labeling yield of >98% was obtained corresponding to a specific activity of ~80.9 GBq/[micro]mol. Radiopeptide internalization into PC-3 cells was moderate and specific (10.7 [+ or -] 1.2% at 4 h). A high and specific GRP receptor expressing mouse tumor and pancreas uptake (1.12 [+ or -] 0.08 and 1.04 [+ or -] 0.11% ID/g after 1 h respectively) was also determined. Keywords HYNIC * [sup.99m]Tc * Bombesin * Tumor * Labeling