Sequential FAP and Mitochondria-Targeting Radioconjugate with High Tumor Uptake Efficiency and Long Retention Time for Radiopharmaceutical Therapy

Fibroblast activation protein inhibitors (FAPIs) have transformed cancer imaging, yet their therapeutic potential remains limited by rapid tumor clearance. To overcome this barrier, we introduce a mitochondria-targeted FAPI derivative, FAPI-PEG3-K-TPP, designed for sequential targeting: initial FAP binding, followed by subcellular localization to mitochondria. Constructed by conjugating a triphenylphosphonium (TPP) moiety to FAPI-46 via a flexible PEG3-K linker, the agent was efficiently radiolabeled with 68Ga and 177Lu, exhibiting high radiochemical purity (>95%), yield (>95%), stability, and dual targeting specificity. In vivo SPECT studies revealed tumor retention exceeding 120 hdramatically longer than the <48 h observed with FAPI-46along with enhanced tumor uptake and potent suppression of tumor growth by the 177Lu-labeled complex. This work establishes mitochondrial sequestration as a powerful strategy to augment targeted radionuclide therapy and opens avenues for theranostic applications of organelle-targeted radiopharmaceuticals.