A Radiofluorinated Nanobody PET Tracer to Dynamically Visualize Differential Nectin4 Expression <i>In Vivo</i>

Nectin4 is a potential therapeutic target for multiple cancer types. To develop a diagnostic radiotracer for nectin4, a nanobody-based PET tracer was selected from several candidate sequences and prepared via [¹⁸F]AlF radiolabeling. The radiochemical quality was assessed, and tracer uptake was evaluated in cell lines and tumor models with varying nectin4 expression levels. <i>In vitro</i> and <i>in vivo</i> studies showed that the tracer exhibited a specific affinity for nectin4, with a binding affinity (<i>K</i>_D) of 6.77 nM in cell lines. The tracer enabled clear visualization of nectin4-expressing lesions, and its uptake profile and pharmacokinetic behavior were characterized using dynamic PET imaging and kinetic analysis. A correlation between PET signal intensity and histological nectin4 expression was also observed in tumor models. Thus, it may have the potential to become a nectin4 tracer for clinical applications.