Title:PEGylated Peptide-Based Imaging Agents for Targeted Molecular Imaging
Volume: 17
Issue: 6
Author(s): Huizi Wu and Jiaguo Huang
Affiliation:
Keywords:
Molecular imaging, imaging agents, peptide, polyethylene glycol, tumor target, renal clearance.
Abstract: Molecular imaging is able to directly visualize targets and characterize cellular pathways
with a high signal/background ratio, which requires a sufficient amount of agents to uptake and accumulate
in the imaging area. The design and development of peptide based agents for imaging and diagnosis
as a hot and promising research topic that is booming in the field of molecular imaging. To
date, selected peptides have been increasingly developed as agents by coupling with different imaging moieties (such as
radiometals and fluorophore) with the help of sophisticated chemical techniques. Although a few successes have been
achieved, most of them have failed mainly caused by their fast renal clearance and therefore low tumor uptakes, which
may limit the effectively tumor retention effect. Besides, several peptide agents based on nanoparticles have also been developed
for medical diagnostics. However, a great majority of those agents shown long circulation times and accumulation
over time into the reticuloendothelial system (RES; including spleen, liver, lymph nodes and bone marrow) after systematic
administration, such long-term severe accumulation probably results in the possible likelihood of toxicity and potentially
induces health hazards. Recently reported design criteria have been proposed not only to enhance binding affinity
in tumor region with long retention, but also to improve clearance from the body in a reasonable amount of time. PEGylation
has been considered as one of the most successful modification methods to prolong tumor retention and improve the
pharmacokinetic and pharmacodynamic properties for peptide-based imaging agents. This review summarizes an overview
of PEGylated peptides imaging agents based on different imaging moieties including radioisotopes, fluorophores,
and nanoparticles. The unique concepts and applications of various PEGylated peptide-based imaging agents are introduced
for each of several imaging moieties. Effects of PEGylation on their target capability, clearance kinetics and metabolic
stability are depicted. Problems and issues relating to the pharmacokinetic and optimization design of peptide-based
imaging agents are also discussed.
