An Improved HPLC Separation Method for TSPO Radioligand [11C]ER176 Clinical Production

Mitochondrial membrane translocator protein 18 kDa (TSPO) expression is increased in activated microglia, established as a plausible target of neuroinflammation imaging. [¹¹C]ER176, specifically binding to TSPO, has been developed as the third generation of radioligand for PET imaging of TSPO, which showed the potential in better quantifying neuroinflammation than its predecessors. In the current study, we developed an automated radiosynthesis with an improved HPLC purification method for [¹¹C]ER176 clinical production. The improved HPLC separation was integrated into the automated production of [¹¹C]ER176 using a reverse phase semi-preparative HPLC column with an isocratic pump and the mixture of methanol and 50 mM ammonium acetate as the mobile phase. The fraction corresponding to [¹¹C]ER176 was collected around 8.5–9.0 min without the risk of getting contaminations from nearby impurities. The automated production process took about 30 min after end of bombardment (EOB) and the quality of the final product [¹¹C]ER176 met all specifications for clinical use based on current US Pharmacopeia and FDA CGMP requirements.