Background and purpose: Bombesin is a 14-amino acid peptide with high biological functions which has a high affinity to GRP )Gastrin releasing peptide( receptor. GRP receptors are overexpressed in many malignant tumors such as prostate and breast cancers. The purpose of this study was to prepare [HYNIC-(Gly)_3-D-Phe¹³]Bombesin(7-14) to label it easily by ^99mTc and to evaluate it as a potential agent for imaging the tumors that have GRP receptors.

Materials and methods: In this experimental study, the prepared derivative Bombesin was radiolabelled by ^99mTc at 100°C in 10 minutes using the exchange method and radiolabelling analysis was applied by TLC and HPLC. Specific absorption test and specific internalization using prostate cancer cells PC-3 was done by blocking and unblocking the receptors. Biodistribution were determined in normal mice.

Results: More than 95% radiolabelling was obtained. Specific absorption and internalization after 4 hours were 17.9% and 9.5%, respectively in PC-3 cancer cells. Biodistribution data showed rapid clearance from blood with major renal excretion and specific binding to tissues that have GRP receptors such as pancreas.

Conclusion: Conjugated peptide radiolabelled with ^99mTc has promising characteristics as potential agent for imaging the tumors that overexpress the GRP receptors.