Preclinical and first-in-human pilot evaluation of 177Lu-DOTA-7ND for fibroblast activation protein-α-targeted radionuclide imaging and therapy

Fibroblast activation protein-α (FAP) is an attractive cell surface target for radiopharmaceutical development due to its tumor-restricted expression. This study aimed to develop a novel dimeric FAP inhibitor (FAPI), DOTA-PEG 4 -CO- N -bis(PEG 4 -7N) (D7ND), and evaluate its potential as a therapeutic radiopharmaceutical in preclinical models and clinical studies. The precursor D7ND was synthesized and radiolabeled with 177 LuCl 3 . 177 Lu-D7ND was obtained with high radiochemical yield and purity (> 98%) and remained stable for up to 5 days. Competitive FAP binding and saturation binding assays demonstrated high binding affinity and selectivity for FAP. Preclinical biodistribution and imaging studies in U-87 MG and HT1080-hFAP xenograft models revealed high specific uptake in FAP-positive tumors. Considerable tumor washout occurred within 24 h, although residual tumor-associated activity remained detectable at 48 and 72 h. Rapid renal clearance and minimal accumulation in normal tissues were observed. Dose-dependent tumor growth inhibition was observed; notably, a 55.5-MBq dose achieved complete remission in a subset of HT1080-hFAP xenografts without significant weight loss or organ toxicity. In a first-in-human pilot study, five patients with FAP-positive breast or non-small cell lung cancer received therapeutic 177 Lu-D7ND. In these patients, 177 Lu-D7ND exhibited intense initial tumor uptake and measurable tumor retention on delayed imaging up to 7 days and no notable accumulation in critical organs. After one cycle, stable disease was achieved in three out of four evaluable patients, with minimal adverse effects. The dimeric radioligand 177 Lu-D7ND showed preclinical antitumor activity and provided preliminary data on its pharmacokinetics and short-term tolerability in a small pilot cohort. These findings support its further development as a potent FAP-targeted therapeutic agent.