Development and evaluation of [¹⁸F]AlF-NOTA-RI^DGE11: A novel retro-inverso peptide PET probe for EGFR imaging

The overexpression of epidermal growth factor receptor (EGFR) in multiple cancers establishes it as a valuable biomarker for targeted therapies and non-invasive imaging. This study developed a novel peptide-based PET probe targeting EGFR, [¹⁸F]AlF-NOTA-RI^DGE11, by conjugating a NOTA chelator to the D-type retro-inverso isomer of ^LGE11 (RI^DGE11) to enhance metabolic stability. Molecular docking reveals comparable EGFR binding affinity (-7.1 kcal/mol) to that of the native ^LGE11 peptide (-6.9 kcal/mol). Efficient radiolabeling was achieved within 30 min using the one-step ¹⁸F‑aluminum fluoride method (radiochemical yield of 18.3-28.4 %; radiochemical purity >99 %). The probe demonstrated high hydrophilicity (logD = -3.90 ± 0.01) with excellent stability in both vitro and vivo conditions (> 95 % intact after 2 h in plasma). In EGFR-positive HCT116 cells, [¹⁸F]AlF-NOTA-RI^DGE11 exhibited specific and blockable uptake (60 min: 1.96 ± 0.11 % ID/1 million cells). Micro-PET imaging in HCT116 tumor xenografts revealed moderate tumor uptake (60 min: 1.49 ± 0.37 % ID/g) with rapid clearance from non-target organs, resulting in favorable tumor-to-background ratios (tumor/muscle: 9.24 ± 3.51; tumor/liver: 2.25 ± 0.11). Specificity was confirmed by a significant reduction in tumor uptake (1.32 ± 0.15 % ID/g vs. 0.30 ± 0.04 % ID/g at 60 min; p < 0.01) following co-injection with excess ^LGE11 peptide. Biodistribution analyses corroborated the imaging findings and indicated predominant renal excretion. Kinetic modeling identified a reversible two-tissue compartment model as optimal. While the high hydrophilicity contributes to rapid washout from tumors, [¹⁸F]AlF-NOTA-RI^DGE11 exhibits promising characteristics for in vivo stability and pharmacokinetic properties, demonstrating its potential as a targeted tracer for EGFR-positive tumor imaging. Future studies will focus on probe optimization to enhance tumor retention.