Bifunctional Hexadentate Pyclen–Based Chelating Agent for Mild Radiofluorination in Aqueous Solution at Room Temperature with a Ga‐18F Ternary Complex

• Published in: Chemistry : a European journal 2024-12, Vol.30 (68), p.e202403358-n/a
• Main Authors: Dioury, Fabienne, San, Carine, Gnanalingam, Gayathiri, Henoumont, Céline, Rousselin, Yoann, Haouz, Ahmed, Shepard, William, Hosten, Benoît, Vijayakumar, Kamsana, Laurent, Sophie, Port, Marc
• Format: Article
• Language: English
• Subjects: Aqueous solutions; Biomolecules; Bonding agents; Chelating agents; Chelation; Chemical bonds; Emissions; Fluorine; Fluorine isotopes; Fluorine-18; Gallium; Imaging agent for Positron Emission Tomography (PET); Macrocyclic N,O ligands; Positron emission; Positron emission tomography; Precision medicine; Probes; Radiochemistry; Room temperature; X-ray diffraction
• ISSN: 0947-6539; 1521-3765; 1521-3765
• DOI: 10.1002/chem.202403358

Positron Emission Tomography (PET) is used in oncology for tumor diagnosis, commonly relying on fluorine‐18 (18F) emission detection. The conventional method of 18F incorporation on to probes by covalent bonding is harsh for sensitive biomolecules, which are nonetheless compounds of choice for the development of targeted probes. This study explores gallium–18F (Ga18F) coordination, a milder alternative method occurring in aqueous media at the final stage of radiosyntheses. Pyclen‐based chelating agents were proposed to capture (GaF) species at room temperature and pH≥5 making the radiofluorination process compatible with heat‐ and acid‐sensitive biomolecules. Highly promising results were obtained with the PC2A–based chelating agent LH2 derived from the new bifunctional PC2A–OAE–NCS compound. The solid‐state structure of GaF(L) was elucidated by X‐ray diffraction and revealed an unconventional heptacoordination of Ga(III). A high radiochemical conversion (RCC) of 86 % was achieved at room temperature, in water at pH 5 within 20 minutes. Stability studies showed the robustness of the GaF(L) complex in aqueous media for at least one day and at least one hour for the radiolabeled analog Ga18F(L). These findings demonstrated that PC2A‐based compounds are chelating agents of choice for (Ga18F) species, suggesting a real technological breakthrough for PET imaging and precision medicine. Two pyclen‐based Ga3+ complexes resolved by X‐Ray crystallography showed a heptacoordination ability deviating from the recognized hexacoordination. This feature supports the suitability of these chelating agents for the Ga‐18F species. Radiolabeling by coordination of Ga‐18F was successfully achieved in water and at pH 5, at room temperature, with 86 % radioconversion in 20 minutes and a radiochelate stability demonstrated for at least one hour.