Characterization of 3 Novel Tau Radiopharmaceuticals, 11C-RO-963, 11C-RO-643, and 18F-RO-948, in Healthy Controls and in Alzheimer Subjects

11 C-RO-963, 11 C-RO-643, and 18 F-RO-948 (previously referred to as 11 C-RO6924963, 11 C-RO6931643, and 18 F-RO6958948, respectively) have been reported as promising PET tracers for tau imaging based on in vitro and preclinical PET data. Here we describe the first, to our knowledge, human evaluation of these novel radiotracers. Methods: Amyloid PET–positive Alzheimer disease (AD) subjects and younger controls each received 2 different tau tracers. Dynamic 90-min scans were obtained after bolus injection of 11 C-RO-963, 11 C-RO-643, or 18 F-RO-948. Arterial blood sampling was performed on 11 healthy controls and 11 AD subjects. Regions were defined on MR images, and PET data were quantified by plasma reference graphical analysis (for total distribution volume) and target cerebellum ratio (SUV ratios of 60- to 90-min frames). SUV ratio images were also analyzed voxelwise. Five older controls each underwent 2 scans with 18 F-RO-948 for evaluation of test–retest variability. Four AD subjects underwent a repeated 18 F-RO-948 scan 6–22 mo after the first scan. Six additional healthy controls (3 men and 3 women; age range, 41–67 y) each underwent 1 whole-body dosimetry scan with 18 F-RO-948. Results: In younger controls, SUV peak was observed in the temporal lobe with values of approximately 3.0 for 11 C-RO-963, 1.5 for 11 C-RO-643, and 3.5 for 18 F-RO-948. Over all brain regions and subjects, the trend was for 18 F-RO-948 to have the highest SUV peak , followed by 11 C-RO-963 and then 11 C-RO-643. Regional analysis of SUV ratio and total distribution volume for 11 C-RO-643 and 18 F-RO-948 clearly discriminated the AD group from the healthy control groups. Compartmental modeling confirmed that 11 C-RO-643 had lower brain entry than either 11 C-RO-963 or 18 F-RO-948 and that 18 F-RO-948 showed better contrast between (predicted) areas of high versus low tau accumulation. Thus, our subsequent analysis focused on 18 F-RO-948. Both voxelwise and region-based analysis of 18 F-RO-948 binding in healthy controls versus AD subjects revealed multiple areas where AD subjects significantly differed from healthy controls. Of 22 high-binding regions, 13 showed a significant group difference (after ANOVA, F (1,21) = 45, P < 10 −5 ). Voxelwise analysis also revealed a set of symmetric clusters where AD subjects had higher binding than healthy controls (threshold of P < 0.001, cluster size > 50). Conclusion: 18 F-RO-948 demonstrates characteristics superior to 11 C-RO-643 and 1