Establishment and Validation of an Alternative Automated Synthesis of [68Ga]Ga-DOTA-Siglec-9 in an Independent Laboratory for Clinical Use

Background Siglec-9, a member of the Siglec family of receptors, plays a crucial role in modulating immune cell trafficking and inflammation, with significant clinical implications. It is predominantly expressed on immune cells such as neutrophils, monocytes, and dendritic cells –key components of both innate and adaptive immunity. Siglec-9 binds to sialic acid residues on glycoproteins, commonly found on endothelial cells, a mechanism central to immune regulation during inflammation and tissue injury. Notably, its interaction with vascular adhesion protein 1 (VAP-1), an endothelial adhesion molecule, is of particular interest for therapeutic development in chronic inflammatory diseases, autoimmune disorders, and cancer. Recent studies have demonstrated that a Siglec-9 motif-containing peptide conjugated with 1,4,7,10-tetraazacyclododecane-N,N′,N′′,N′′′-tetraacetic acid (DOTA) and radiolabelled with gallium-68 ([⁶⁸Ga]Ga-DOTA-Siglec-9) enables effective positron emission tomography (PET) imaging of these pathological conditions. This study aimed to develop a new automated radiolabelling protocol for the preparation of [⁶⁸Ga]Ga-DOTA-Siglec-9 for clinical use. The synthesis was carried out using a fully automated module with real-time monitoring of key parameters including time, temperature, and radioactivity. Results Following optimization of labelling conditions and assessment of peptide stability, [⁶⁸Ga]Ga-DOTA-Siglec-9 was successfully synthesized with a radiochemical yield (RY) of 55.04%, radiochemical purity (RCP) of 99.48%, and molar activity (Am) of 23.15 GBq/µmol at 65°C in 6 minutes. Process validation yielded consistent mean values of RY (56.16%), RCP (99.40%). and Am (20.26 GBq/µmol). Stability testing at room temperature over 3 hours demonstrated that [⁶⁸Ga]Ga-DOTA-Siglec-9 maintained acceptable RCP (mean99.29%), pH, appearance, and sterility. Conclusion The final product meets Ph. Eur. quality requirements and is suitable for clinical application.