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

Abstract

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-PEG4-CO-N-bis(PEG4-7N) (D7ND), and evaluate its potential as a therapeutic radiopharmaceutical in preclinical models and clinical studies. The precursor D7ND was synthesized and radiolabeled with 177LuCl3. 177Lu-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 177Lu-D7ND. In these patients, 177Lu-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 177Lu-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.