Development of Cyclic Peptide‐Based Radiotracers for uPAR

Abstract The urokinase plasminogen activator (uPA) system has garnered attention as a promising biomarker, with the uPA receptor (uPAR) playing a central role in system regulation and demonstrating strong associations with tumorigenicity, invasion, and metastasis. Radioligands targeting uPAR have emerged as powerful tools for the early diagnosis and treatment of malignant tumors. In this study, we developed and evaluated three novel cyclic peptide‐based positron emission tomography (PET) radioligands, denoted as [⁶⁴Cu]CARP‐1, [⁶⁴Cu]CARP‐2, and [⁶⁴Cu]CARP‐3, for uPAR imaging. These radioligands differ in the chiral configuration of their disulfide bond crosslinkers, which influences their binding ability and pharmacokinetic profiles. Among the three, [⁶⁴Cu]CARP‐2 demonstrated optimal tumor radioactivity accumulation, specificity, and favorable pharmacokinetics in an MC38 tumor‐bearing mouse model. Compared to [⁶⁴Cu]DOTA‐AE105, a well‐characterized radiotracer currently under clinical investigation, [⁶⁴Cu]CARP‐2 exhibited reduced non‐specific uptake and rapid clearance from normal tissues. These attributes highlight its potential as a diagnostic tool with improved imaging accuracy. The promising preclinical performance of [⁶⁴Cu]CARP‐2 underscores its potential for further clinical investigation as a uPAR‐targeting radiotracer.