Structure-Guided Designed [¹⁸F]-labeled FAPI for Enhanced Hydrophilicity: From Preclinical to First-In-Human Study

Fibroblast activation protein (FAP) is highly expressed in cancer-associated fibroblasts and represents an attractive target for PET imaging. Here, we report [¹⁸F]AlF-NOTA-GL01, an improved FAPI-46 derivative bearing an N-methyl-benzenesulfonic acid side chain and labeled via an Al[¹⁸F]-NOTA platform. [¹⁸F]AlF-NOTA-GL01 was obtained with high radiochemical purity (>95%), high FAP binding affinity (IC₅₀ = 2.94 nM), and high hydrophilicity (LogD = -3.06). In A549-hFAP xenografts, PET imaging showed high tumor uptake (7.45 ± 2.34%ID/g at 60 min), rapid renal clearance, and low hepatobiliary background, with strong concordance between PET-derived uptake and ex vivo biodistribution. In a first-in-human study, physiologic uptake decreased over time, whereas tumor uptake persisted to 120 min. The effective dose was 0.03 ± 0.01 mSv/MBq. Malignant lesions exhibited higher target-to-background ratios on [¹⁸F]AlF-NOTA-GL01 PET/CT than on [¹⁸F]FDG and [¹⁸F]FAPI-42. Collectively, these findings support the clinical translation potential of [¹⁸F]AlF-NOTA-GL01, which combines high affinity with excellent imaging contrast.