Synthesis and evaluation of novel Tc‐99 m labeled NGR‐containing hexapeptides as tumor imaging agents

Asparagine‐glycine‐arginine (NGR)‐containing peptides targeting aminopeptidase N (APN)/CD13 can be an excellent candidate for targeting ligands in molecular tumor imaging. In this study, we developed two NGR‐containing hexapeptides, and evaluated the diagnostic performance of Tc‐99 m labeled hexapeptides as molecular imaging agents in an HT‐1080 fibrosarcoma‐bearing murine model. Peptides were synthesized using Fmoc solid‐phase peptide synthesis. Radiochemical purity of Tc‐99 m was evaluated using instant thin‐layer chromatography. The uptake of two NGR‐containing hexapeptides within HT‐1080 cells was evaluated in vitro . In HT‐1080 fibrosarcoma tumor‐bearing mice, gamma images were acquired. A biodistribution study was performed to calculate percentage of the injected dose per gram of tissue (%ID/g). Two hexapeptides, glutamic acid‐cysteine‐glycine (ECG)‐NGR and NGR‐ECG were successfully synthesized. After radiolabeling procedures with Tc‐99 m, the complexes Tc‐99 m hexapeptides were prepared in high yield. The uptake of Tc‐99 m ECG‐NGR within the tumor cells had been assured by in vitro studies. The gamma camera imaging in the murine model showed that Tc‐99 m ECG‐NGR was accumulated substantially in the subcutaneously engrafted tumor. However, Tc‐99 m NGR‐ECG was accumulated minimally in the tumor. Two NGR‐containing hexapeptides, ECG‐NGR and NGR‐ECG were developed as molecular imaging agents to target APN/CD13 in HT‐1080 fibrosarcoma. Tc‐99 m ECG‐NGR showed a significant uptake in the tumor, and it is a good candidate for tumor imaging.