Title: [P4–506]: COMPARISON BETWEEN MONOAMINE OXIDASE B INHIBITION ON THE UPTAKE OF [<sup>18</sup>F]THK5351
Abstract: High uptake of [18F]THK5351, a tau imaging agent to brain regions with high concentrations of monoamine oxidase B (MAO-B) suggests off target binding to MAO-B sites. We recently demonstrated that [18F]THK5351 uptake is reduced following a single dose of 10 mg MAO-B inhibitor, selegiline1. Given a previously reported 10 day course of 1 mg rasagiline demonstrating in vivo full brain MAO-B occupancy2, we tested the effects of rasagiline on [18F]THK5351 uptake. 2 clinically diagnosed progressive supranuclear palsy (PSP) participants underwent a baseline [18F]THK5351 scan and a follow-up [18F]THK5351 scan 2 weeks later, following a 10 day course of 1 mg rasagiline. In a previous study, 8 participants (5 mild cognitive impairment (MCI), 2 Alzheimer's disease (AD) and 1 PSP) underwent a baseline [18F]THK5351 scan and a follow-up [18F]THK5351 scan 1 week later, 1 hour after 10 mg of selegiline. The primary outcome was the standardized uptake value (SUV), calculated using tissue radioactivity concentration 50 to 70 min after [18F]THK5351 injection, normalizing for body weight and injected radioactivity. The post intervention SUV percentage change was then reported. The regional SUVs decreased on average by 72.1% to 92.0% following a 10 day course of 1 mg rasagiline. On the other hand, the regional SUVs decreased on average by 36.7% to 51.8% following a dose of 10 mg selegiline. In the cerebellar cortex, the SUV reduced by 72.1% and 41.6% following rasagiline and selegine intervention respectively. Abbreviations: PS = post-selegiline; PR = post-rasagiline.