Synthesis and Application of a Long-Circulating Radiolabeled Peptide for Targeting of Osteosarcoma.

Purpose: The small peptide TMTP1 (NVVRQ) has been proved to target a series of highly metastatic tumor cells. The aim of this study was to develop a new agent based on TMTP1 conjugated with Evans blue (EB), to increase tumor uptake and modify the pharmacokinetic characteristics of the resulting radiolabeled agent.

Procedures: DOTA-EB-TMTP1 was prepared through conventional solid-phase peptide synthesis chemistry. Then, it was successfully labeled with Cu-64 to obtain [Cu]DOTA-EB-TMTP1. The tumor targeting properties were evaluated in vivo using 143B xenografts.

Results: DOTA-EB-TMTP1 was successfully labeled with Cu-64 in a yield of 87.3 ± 5.2 %. In a small animal positron emission tomography/X-ray computed tomography (PET/CT) study in osteosarcoma 143B xenograft mice, [Cu]DOTA-EB-TMTP1 was found to rapidly accumulate in the tumor tissue. The tumor uptake increased over time and reached a plateau of 6.50 ± 0.88 % ID/g 8 h after tail vein injection. The radioactivity remained in the tumor tissue 48 h postinjection with a negligible decrease.

Conclusions: Overall, the introduction of the EB motif to TMTP1 significantly changed its pharmacokinetics in vivo, and this strategy fulfills the purpose of prolonging the blood circulation and enhancing the tumor uptake. [Cu]DOTA-EB-TMTP1 is a promising agent for osteosarcoma targeting. Moreover, our study highlights that DOTA-EB-TMTP1 is a good candidate for labeling with different radionuclides for potential theranostic applications.