Radiation dosimetry of [(18)F]-PSS232—a PET radioligand for imaging mGlu5 receptors in humans

PURPOSE: (E)-3-(pyridin-2-ylethynyl)cyclohex-2-enone O-(3-(2-[(18)F]-fluoroethoxy)propyl) oxime ([(18)F]-PSS232) is a new PET tracer for imaging of metabotropic glutamate receptor subtype 5 (mGlu5), and has shown promising results in rodents and humans. The aim of this study was to estimate the radiation dosimetry and biodistribution in humans, to assess dose-limiting organs, and to demonstrate safety and tolerability of [(18)F]-PSS232 in healthy volunteers. METHODS: PET/CT scans of six healthy male volunteers (mean age 23.5 ± 1.7; 21–26 years) were obtained after intravenous administration of 243 ± 3 MBq of [(18)F]-PSS232. Serial whole-body (vertex to mid-thigh) PET scans were assessed at ten time points, up to 90 min after tracer injection. Calculation of tracer kinetics and cumulated organ activities were performed using PMOD 3.7 software. Dosimetry estimates were calculated using the OLINDA/EXM software. RESULTS: Injection of [(18)F]-PSS232 was safe and well tolerated. Organs with highest absorbed doses were the gallbladder wall (0.2295 mGy/MBq), liver (0.0547 mGy/MBq), and the small intestine (0.0643 mGy/MBq). Mean effective dose was 3.72 ± 0.12 mSv/volunteer (range 3.61–3.96 mSv; 0.0153 mSv/MBq). CONCLUSION: [(18)F]-PSS232, a novel [(18)F]-labeled mGlu5 tracer, showed favorable dosimetry values. Additionally, the tracer was safe and well tolerated.