Development of Cysteic Acid-Modified FAP Radioligands for Enhanced Renal Clearance: From Preclinical Optimization to First-in-Human Study

Fibroblast activation protein (FAP)-targeting radioligands hold promise for cancer theranostics. Cyclic peptide-based DOTA-FAP-2286 radioligands have demonstrated high kidney uptake and retention, raising concerns regarding potential nephrotoxicity. Hence, we aimed to design three cysteic acid-modified FAP-targeting cyclic peptide ligands (DOTA-C1/C2/C3-FAP-2286) for reducing renal retention and optimizing pharmacokinetic properties. Competitive binding assays revealed maintained potent affinity for FAP (IC₅₀ < 150 nM). Following systematic preclinical evaluation, [⁶⁸Ga]Ga-C1-FAP-2286 exhibited optimal biodistribution characteristics, reducing renal uptake by 50% (2.12 ± 0.19% ID/g, <i>P</i> < 0.05), while maintaining tumor accumulation (7.08 ± 0.35 vs 6.26 ± 0.82% ID/g for [⁶⁸Ga]Ga-FAP-2286), yielding a significantly improved tumor-to-kidney ratio (3.34 ± 0.15 vs 1.59 ± 0.53% ID/g). First-in-human PET/CT imaging in a metastatic gastric cancer patient demonstrated superior diagnostic performance compared to [¹⁸F]FDG, with intense uptake in primary lesions (SUV_max = 3.0), including [¹⁸F]FDG-negative and metastatic lesions. Thus, [⁶⁸Ga]Ga-C1-FAP-2286 is a clinically translatable tracer for imaging FAP-expressing malignancies.