Tau imaging with [¹⁸F]THK-5351 in progressive supranuclear palsy

Background and purpose: Visualization of pathogenic protein aggregates is crucial to elucidate pathomechanisms and to make an accurate diagnosis in many neurodegenerative conditions. Aggregates of the microtubule-binding protein, tau, are one of the most important pathogenic molecules in neurodegenerative disorders. Progressive supranuclear palsy (PSP) is characterized by the deposition of tau proteins in some specific area such as the basal ganglia and brainstem. We tried to detect tau lesions in the brains of living patients with PSP with a novel positron emission tomography (PET) tracer, [¹⁸F]THK-5351, which we have recently developed. Methods: Paraffin-embedded brain sections of the patients with PSP were used for autoradiography with [³H]THK-5351 and immunohistochemistry. Nine healthy controls, 13 patients with Alzheimer's disease and three patients with PSP participated in this PET study with [¹⁸F]THK-5351. To detect amyloid-β deposition, PET imaging with Pittsburgh compound B was also performed. Results: Autoradiography in the brain sections of patients with PSP demonstrated [³H]THK-5351 binding to tau deposits with a high selectivity. Although patients with PSP exhibited no remarkable [¹⁸F]THK-5351 retention in the temporal cortex, significantly higher tracer retention was observed in the globus pallidus and midbrain. In contrast, amyloid imaging with Pittsburgh compound B showed no remarkable accumulation in the cerebral cortex of PSP. Conclusions: We conclude that [¹⁸F]THK-5351 PET can potentially be used to detect the regional brain distribution of tau lesions in PSP, thereby facilitating the differential diagnosis of neurodegenerative disorders associated with tau protein.