To overcome the photoisomerization issue inherent with xanthene radiotracer [11C]TMSX, a potent, selective, and reversible nonxanthene A2AR antagonist SCH442416 was radiolabeled to produce [11C]SCH442416 and exhibited a good striatum/cerebellum uptake ratio with slow rate of metabolism in rat.124 In rhesus monkeys, [11C]SCH442416 was rapidly accumulated in the brain, with twice as much radioactivity concentration in the striatum than in the cerebellum, but it showed a high nonspecific binding activity in monkey brain.124 [11C]SCH442416 has been used to study receptor occupancy and involvement of striatal A2ARs in the brain of PD patients with dyskinesia.125,126 Both A2ARs antagonists [11C]TMSX and [11C]SCH442416 have already been used in multiple studies in human.122,124 Preladenant, a PD drug, was also radiolabeled with 11C to produce [11C]Preladenant.126-128 Studies of this PET tracer in the brain of monkey showed an uptake that is consistent with the distribution of A2ARs with highest uptake in the putamen and the caudate, respectively.128 The lowest uptake of [11C]Preladenant was observed in the cerebellum. Estimated binding potential values of [11C]Preladenant with different scan durations were similar (4.3-5.3 in A2AR-rich regions).128 Preinjection with nonradiolabeled
