Novel Covalent FAP-Targeted Radiotherapy Drug Based on DOTA-FAP-2286 for Enhanced Tumor Uptake, Retention, and Therapeutic Efficacy.

Fibroblast activation protein (FAP)-targeted radioligand therapy is often limited by insufficient tumor uptake and retention. We designed and synthesized two novel aryl fluorosulfate-based covalent FAP-targeted radioligands, [177Lu]Lu-DOTA-mFS-FAP-2286 and [177Lu]Lu-DOTA-mFS-KERERG-FAP-2286, to enhance tumor retention and therapeutic efficacy. Two FAP-targeted radioligands were synthesized, radiolabeled with 177Lu, and evaluated for radiochemical stability. Cellular uptake and internalization were assessed in HEK293-huFAP cells. Biodistribution and serial SPECT imaging were performed in tumor-bearing mice to evaluate tumor targeting and retention. Therapeutic efficacy was investigated in murine xenograft models, and the toxicity of [177Lu]Lu-DOTA-mFS-KERERG-FAP-2286 was assessed. A pilot clinical study including three patients with solid tumors was conducted to preliminarily evaluate the therapeutic potential. All radioligands were successfully labeled with radiochemical purity >95% and showed favorable stability. Cellular assays confirmed the high target specificity. In tumor-bearing mice, [177Lu]Lu-DOTA-mFS-KERERG-FAP-2286 demonstrated significantly higher tumor uptake at 1 h after injection than [177Lu]Lu-DOTA-FAP-2286 and [177Lu]Lu-DOTA-mFS-FAP-2286 (p < 0.01). Treatment with [177Lu]Lu-DOTA-mFS-KERERG-FAP-2286 significantly inhibited tumor growth and showed superior therapeutic efficacy compared with [177Lu]Lu-DOTA-FAP-2286 (p < 0.05). No treatment-related adverse events were observed in the three patients. Primary tumors and metastatic lesions demonstrated high tracer uptake with prolonged retention up to day 10 after injection. [177Lu]Lu-DOTA-mFS-KERERG-FAP-2286 showed favorable tumor targeting, prolonged retention, and potent therapeutic efficacy, supporting its further clinical development for FAP-targeted radioligand therapy (RLT).