18F-THK523: a novel in vivo tau imaging ligand for Alzheimer's disease

While considerable effort has focused on developing positron emission tomography beta-amyloid imaging radiotracers for the early diagnosis of Alzheimer's disease, no radiotracer is available for the non-invasive quantification of tau. In this study, we detail the characterization of F-18-THK523 as a novel tau imaging radiotracer. In vitro binding studies demonstrated that F-18-THK523 binds with higher affinity to a greater number of binding sites on recombinant tau (K18 delta 280K) compared with beta-amyloid(1-42) fibrils. Autoradiographic and histofluorescence analysis of human hippocampal serial sections with Alzheimer's disease exhibited positive THK523 binding that co-localized with immunoreactive tau pathology, but failed to highlight beta-amyloid plaques. Micro-positron emission tomography analysis demonstrated significantly higher retention of F-18-THK523 (48%; P < 0.007) in tau transgenic mice brains compared with their wild-type littermates or APP/PS1 mice. The preclinical examination of THK523 has demonstrated its high affinity and selectivity for tau pathology both in vitro and in vivo, indicating that F-18-THK523 fulfils ligand criteria for human imaging trials.