A novel peptide targeting gastrin releasing peptide receptor for pancreatic neoplasm detection

Pancreatic cancer has a high mortality rate and efforts towards diagnosis and therapy at an early stage are particularly appealing. Recently, a small peptide, BBN7-14, has attracted much attention for its specific binding ability to gastrin releasing peptide receptor (GRPR), which is highly overexpressed in various types of cancer, including pancreatic cancer. However, its poor stability in vivo restricts its direct clinical application. Herein, by rational design and transformation of BBN7-14, a novel six-amino acid peptide, GB-6, which maintains a specific GRPR-binding feature and exhibits enhanced stability in vitro and in vivo, was designed. Competitive binding with BBN7-14 and cellular uptake related to GRPR expression levels verified the specific affinity of GB-6 to GRPR. Additionally, this novel peptide was conjugated with near-infrared dye and the radionuclide 99mTc for pancreatic cancer diagnosis in cells and in vivo. Surprisingly, despite having the same cellular affinity as BBN7-14, GB-6 showed much higher pancreatic cancer-targeting ability than BBN7-14 by both fluorescence imaging and radionuclide imaging. It was proven that this strange phenomenon was attributed to the distinct in vivo stability of GB-6 and its more favorable pharmacokinetic properties and metabolic stability relative to BBN7-14. Altogether, this novel peptide GB-6, with GRPR-targeting ability and enhanced stability, is a more promising candidate for the clinical diagnosis of pancreatic cancer.