A FAP‐Targeted SMDC Platform Enables Synergistic Radionuclide–Chemotherapy with PET‐Guided Evaluation

ABSTRACT Fibroblast activation protein (FAP) is an attractive stromal target for cancer theranostics; however, developing agents that enable non‐invasive pharmacokinetic visualization while achieving effective combined radio‐chemotherapy remains challenging. Here we report an imaging‐enabled FAP‐targeted small molecule–drug conjugate (SMDC) platform that supports PET‐based pharmacokinetic visualization and synergistic radionuclide–chemotherapy using matched radiolabeled constructs. In this system, ⁶⁸ Ga‐labeled SMDCs enable positron emission tomography (PET) imaging to visualize in vivo biodistribution, whereas the corresponding ¹⁷⁷ Lu‐labeled analogues deliver combined radionuclide and cytotoxic therapy. By systematically comparing VC and GP cleavable linkers in DOTA‐containing MMAE conjugates, we establish a linker‐dependent structure–stability–efficacy relationship. FAPI‐46–based constructs retained nanomolar FAP affinity and enabled efficient enzyme‐triggered payload release while maintaining selective tumor accumulation in vivo as visualized by ⁶⁸ Ga‐PET. Therapeutic studies using ¹⁷⁷ Lu‐labeled conjugates produced pronounced tumor suppression (92–93% inhibition), outperforming either modality alone. Notably, the VC‐linked construct showed improved tolerability relative to the GP analogue. These findings establish an imaging‐guided strategy for optimizing FAP‐targeted radiochemotherapeutics and identify FAP‐O‐VC‐MMAE as a promising candidate for further translational development.