Preparation and Optimization of Radiolabeling Conditions of Targeted Fibroblast Activating Protein and Integrin Receptor Probe ¹⁸FAlF-NOTA-FAPI-RGD

Based on the high expression of specific receptors on the surface of tumor cells and neovascularization, non-invasive molecular imaging can be combined with specific ligands labeled with short half-life isotopes ¹⁸FF⁻ to monitor the lesion, which has the clinical application prospects. Due to the heterogeneity of various tumor biomarkers and complex tumor-matrix interactions, current imaging tracers still need to be improved, to develop a highly sensitive and specific molecular probe which targeting biological markers that are overexpressed in tumors. Small molecule-based heterodimeric radiotracer is a promising direction for future development. In this paper a dual targeting radioactive probe, ¹⁸FAlF-NOTA-FAPI-RGD, was designed and synthesized based on fluoaluminum labeling technology, leveraging the high expression of tumor-specific receptors on cancer cell surfaces and neovasculature, which targeted fibroblast activation protein (FAP) and integrin α_Ⅴβ₃. To further investigate the procedural conditions for fluorine aluminum labeling, non-carrier-added ¹⁸FF⁻ was introduced into reaction vials containing the labeled precursor NOTA-FAPI-RGD, AlCl₃, organic solvents (ethanol, acetonitrile, DMSO), and an acetic acid-sodium acetate buffer solution. The mixture was homogenized by vigorous shaking and heated at 80 ℃ for 20 min. Subsequently, ¹⁸FAlF-NOTA-FAPI-RGD was obtained through purification using a Waters Oasis HLB column and sterile filtration through a 0.22 µm microporous membrane. During labeling process optimization, key reaction parameters were systematically investigated. Solvent screening reveals that acetonitrile is the optimal condition in facilitating Al-F bond formation, with its high polarity and low coordination capacity. pH optimization via orthogonal experiments identified an optimal range of 4.0-4.5 using an acetic acid-sodium acetate buffer, balancing aluminum ion stability and ligand structural integrity. In addition, precursor quantity and AlCl₃ quantity were explored through dose titration, that demonstrated 50 μg of NOTA-FAPI-RGD precursor and 20 nmol/L AlCl₃ promote the peak labeling efficiency. After radiolabeling, the non-decay-corrected yield of ¹⁸FAlF-NOTA-FAPI-RGD is determined to be 35.0%±5.0%, with a radiochemical purity exceeding 90% and exhibiting excellent stability. The radiochemical purity of pharmaceutic preparation is still retained 91.71% after place in 2-8 ℃ for 4 h. The above results indicate that the radioactive probe has the potential to be a novel and high stability tumor targeted imaging agent. This dual-targeting design could enhance tumor localization accuracy and diagnostic sensitivity, it holds significant promise for early diagnosis and treatment monitoring of tumors, offering a powerful tool for precision oncology and advancing molecular imaging capabilities.