Automated Production of [¹⁸F]FEPPA as a Neuroinflammation Imaging Agent

Objectives Neuroinflammation plays an important role in many neurodegenerative diseases, including amyotrophic lateral sclerosis, Parkinson’s disease, multiple sclerosis and Alzheimer’s disease (1). Several PET tracers have been developed to monitor progression of neuroinflammation or measure therapeutic efficacy (2). Among those, [¹⁸F]FEPPA (2) has been found to be one of the potent neuroinflammation imaging agents (3). In order to fulfill the demand of this tracer for pre-clinical and clinical studies, we have developed an automated synthesis and simplified the purification procedure of 2. We report herein the automated synthesis of 2 and its application in neuroinflammation imaging.

Methods 2 was synthesized manually and purified with 50:50 MeOH:H₂O+0.5% formic acid as HPLC mobile phase previously (4). We have synthesized this tracer with TRACERlab FX_FN module and purified with 40% EtOH as HPLC mobile phase. Briefly, fluorination of the tosylate precursor (1) with K[¹⁸F]/K_2.2.2in anhydrous MeCN at 70 ⁰C for 20 min gave the crude product. After dilution with H₂O, the crude product was purified with a semi-preparative HPLC (Waters Xterra RP-18, 10⊆250mm, 40% EtOH, 4 mL/min). The fraction containing 2 was collected, diluted with H₂O and passed through a 0.22μm sterilizing filter into a sterile vial (Scheme 1). The neuroinflammation animal model was induced in male C57BL/6 mice. Mice (20-25 g, n=6) were intraperitoneally injected with a single dose of LPS (E. Coli 011:B4, 5 mg/kg). Twenty-four hours after LPS injection, mice were injected (i.v) with ~ 250 μCi of 2 and imaged with Argus PET/CT scanner. Dynamic sinograms were produced with 12 x10 sec, 3 x60 sec, 3 x 300 sec, 4 x 6000 sec, 2 x 900 sec frames. Averaged microPET images of the whole scan (90 min) were acquired using eXplore Vista PET-CT MMWKS software.

Results The radiochemical yield of 2 synthesized by this method was 13±8 % (EOS, n=5) in a synthesis time of ~59 min from EOB. Radiochemical purity was >95 % with a specific activity of 34±17 GBq/μmol (EOS, n=5). The EtOH content in 2 was < 10%. MicroPET images showed that LPS administration significantly increased mice brains uptake of 2 compared to normal mice (Fig. 1).

Conclusions With this improved synthesis method, 2 has been produced in high quantities with good quality, and is ready for using in various clinical or pre-clinical studies. REFERENCES: 1. Heneka MT, Golenbock DT, Latz E. Innate immunity in Alzheimer's disease. Nat Immunol. 2015;16(3):229-236. 2. Ory D, Celen S, Verbruggen A, Bormans G, PET radioligands for in vivo visualization of neuroinflammation. Current Pharmaceutical Design, 2014, 20, 5897-913. 3. Wilson AA, Garcia A, Parkes J, et al. Radiosynthesis and initial evaluation of [¹⁸F]FEPPA for PET imaging of peripheral benzodiazepine receptors. Nucl Med Biol. 2008;35(3):305-314. 4. Suridjan I, Pollock B, Verhoeff N, et al. In-vivo imaging of grey and white matter neuroinflammation in Alzheimer's disease: a positron emission tomography study with a novel radioligand, [¹⁸F]FEPPA. Mol Psychiatry. 2015;20(12):1579-1587. $$graphic_5EC71BED-4590-485B-99EC-502829DBC4BC$$ $$graphic_75B56F70-F579-492E-AF7F-DA331164CDC0$$