Non-invasive imaging of tau-targeted probe uptake by whole brain multi-spectral optoacoustic tomography

Aim Abnormal tau accumulation plays an important role in tauopathy diseases such as Alzheimer’s disease and Frontotemporal dementia. There is a need for high-resolution imaging of tau deposits at the whole brain scale in animal models. Here, we demonstrate non-invasive whole brain imaging of tau-targeted PBB5 probe in P301L model of 4-repeat tau at 130 μm resolution using volumetric multi-spectral optoacoustic tomography (vMSOT). Methods The binding properties of PBB5 to 4-repeat K18 tau and Aβ 42 fibrils were assessed by using Thioflavin T assay and surface plasmon resonance assay. We identified the probe PBB5 suitable for vMSOT tau imaging. The imaging performance was first evaluated using postmortem human brain tissues from patients with Alzheimer’s disease, corticobasal degeneration and progressive supranuclear palsy. Concurrent vMSOT and epi-fluorescence imaging of in vivo PBB5 targeting ( i . v .) was performed in P301L and wild-type mice. Ex vivo measurements on excised brains along with multiphoton microscopy and immunofluorescence staining of tissue sections were performed for validation. The spectrally-unmixed vMSOT data was registered with MRI atlas for volume-of-interest analysis. Results PBB5 showed specific binding to recombinant K18 tau fibrils, Alzheimer’s disease brain tissue homogenate by competitive binding against [ 11 C]PBB3 and to tau deposits (AT-8 positive) in post-mortem corticobasal degeneration and progressive supranuclear palsy brain. i . v . administration of PBB5 in P301L mice led to retention of the probe in tau-laden cortex and hippocampus in contrast to wild-type animals, as also confirmed by ex vivo vMSOT, epi-fluorescence and multiphoton microscopy results. Conclusion vMSOT with PBB5 facilitates novel 3D whole brain imaging of tau in P301L animal model with high-resolution for future mechanistic studies and monitoring of putative treatments targeting tau.