Toward Personalized Theranostics: A Modular PET Platform for Antibody‐Based Imaging and Therapy

ABSTRACT The expansion of personalized medicine is encouraging the development of platforms capable of supporting individualized imaging and therapeutic strategies. The combination of antibodies, with their intrinsic selectivity, and a modular molecular probe provides a strong foundation for such approaches. In this context, a versatile platform enabling positron emission tomography (PET) imaging followed by copper‐free click‐based functionalization is developed. A DFO–Lysine–DBCO probe is synthesized and site‐specifically coupled to trastuzumab, allowing the introduction of diverse payloads, including β‐ or α‐emitter chelators, a fluorophore, and a cytotoxic agent. Within this toolbox, the DFO/DOTAGA bischelate is selected for detailed evaluation. Radiolabeling confirms the selectivity of DFO and DOTAGA for 89 Zr and 177 Lu, respectively. PET imaging in mice bearing HCC1954 xenografts (HER2‐overexpressing, trastuzumab‐resistant) using [ 89 Zr]Zr‐ss‐Tzb‐DFO‐DOTAGA and [ 89 Zr]Zr‐ss‐Tzb‐DFO‐Lu(III)DOTAGA, in which DOTAGA is pre‐loaded with cold lutetium, enables clear tumor visualization and indicates that second‐chelator occupancy does not alter biodistribution. Despite unexpectedly lower internalization and tumor uptake, [ 177 Lu]Lu‐ss‐Tzb‐DFO‐DOTAGA demonstrates significant antitumor activity with good tolerability in a preliminary therapeutic study. This modular platform, enabling site‐specific conjugation, provides a broadly adaptable route to generate multifunctional antibody constructs, offering a versatile foundation for integrating imaging, therapy, and payload customization within a single molecular scaffold.