The imaging features and clinical associations of a novel tau PET tracer - 18F-APN1607(18F-PM-PBB3) in Alzheimer’s disease

Background: In vivo tau positron emission tomography (PET) imaging could help clarify the spatial distribution of tau deposition in Alzheimer’s disease (AD) and aid in the differential diagnosis of tauopathies. To date, there have been no in vivo 18 F-APN1607 tau PET studies in patients with AD.Methods: We applied tau tracer in twelve normal controls (NCs) and ten patients in the mild to moderate stage of probable AD. Detailed clinical information, cognitive measurements and disease severity were documented. Regional standardized uptake value ratios (SUVRs) from 18 F-AV-45 (florbetapir), 18 F-APN1607 PET images and regional gray matter (GM) atrophic ratios were calculated for further analysis.Results: Quantitative analyses showed significantly elevated SUVRs in the frontal, temporal, parietal, occipital lobes, anterior and posterior cingulate gyri, precuneus, and parahippocampal region (all ps < 0.01) with medium to large effect sizes (0.44 - 0.75). The SUVRs from 18 F-APN1607 PET imaging showed significant correlations with the ADAS-cog scores (all ps < 0.01) and strong correlation coefficients (R squared ranged from 0.54 to 0.68), even adjusted for age and gender effects. Finally, the SUVRs from 18 F-APN1607 PET imaging of the parahippocampal region showed rapid saturation as the ADAS-cog scores increased, and the SUVRs of the posterior cingulate gyrus and the temporal, frontal, parietal and occipital regions slowly increased. The combined SUVRs from 18 F-AV-45 PET, 18 F-APN1607 PET and regional GM atrophic ratio showed that uptake associated with the amyloid burden rapidly increased and reach a plateau, whereas uptake associated with tau depositions increased slowly and finally followed by regional GM atrophic ratios in most regions as the ADAS-cog scores increased. However, different regions exhibited various combinations of these patterns.Conclusions: Our findings suggest that the 18 F-APN1607 tau tracer showed a clear background without significant uptake in the basal ganglia or midbrain. Uptake of this tracer correlated well with cognitive changes and demonstrated the spatial pattern of amyloid, tau deposition and GM atrophy in the progression of AD. Thus, the regional base of dynamic biomarker changes was observed in the current study.Trial registration: registration number (NCT03625128), date of registration( August 10, 2018), retrospectively registered.