A Novel Arene Trifluoromethyl-Based ¹⁸F-Labeling Strategy for Enhanced Biomolecular Tracer Development in PET Imaging

Biologically active molecules, such as carbohydrates, peptides, and proteins, are attractive candidates for positron emission tomography (PET) imaging because of their strong target affinity and biocompatibility. Among available radionuclides, fluorine-18 (¹⁸F) is widely used in clinical practice because of its moderate half-life and high-quality imaging properties. However, traditional ¹⁸F-labeling methods often require a laborious procedure and harsh conditions, which may compromise the structural integrity and biological functions. Developing mild and efficient ¹⁸F-labeling strategies is therefore critical for advancing biomolecular PET tracers. In this study, we developed a novel clickable ¹⁸F-labeled synthon, 1-ethynyl-3-([¹⁸F]trifluoromethyl)-5-(trifluoromethyl)benzene ([¹⁸F]1), prepared via an ¹⁸F/¹⁹F isotope exchange reaction (RCY = 17.2 ± 3.9%). [¹⁸F]1 exhibited excellent performance in copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) conjugation, enabling rapid and chemoselective labeling of azide-modified glucose derivatives, Arg-Gly-Asp (RGD) and cyclic RGD (cRGD) peptides, and phospholipids under mild conditions. PET imaging in U87 MG, 4T1, and BT474 xenograft models showed favorable tumor uptake for both [¹⁸F]5a and [¹⁸F]5b, peaking at 30 min postinjection. Tumor accumulation for [¹⁸F]5a reached 3.11 ± 0.21, 2.40 ± 0.17, and 1.95 ± 0.09% ID/g in U87 MG, 4T1, and BT474 models, respectively, while [¹⁸F]5b achieved higher values of 5.19 ± 0.42, 4.90 ± 0.97, and 2.05 ± 0.11% ID/g at the same time point─consistent with the superior binding affinity of cRGD. Tumor-to-muscle ratios were favorable, with[¹⁸F]5b reaching 4.32 ± 0.39 in the 4T1 model. Blocking studies in U87 tumors confirmed high binding specificity, with uptake reduced to approximately 1% ID/g. This isotope exchange-based CuAAC labeling strategy streamlines PET tracer synthesis, preserves biomolecule integrity, and offers a versatile platform for molecular imaging and pretargeting applications.