New prospects for ⁸⁹Zr-immuno-PET in brain applications - Alpha-synucleinopathies

Area of Science:

• Neuroimaging
• Radiochemistry
• Molecular Biology
• Neurodegenerative Diseases

Background:

• Alpha-synuclein is a key biomarker in Parkinson's Disease and related disorders.
• 89Zr-immuno-PET offers potential for non-invasive imaging of alpha-synuclein pathology.
• Transferrin-mediated transcytosis facilitates blood-brain-barrier penetration for PET tracers.

Purpose of the Study:

• To compare the targeting potential of two 8D3-based constructs (HLu-3-scFab8D3 vs. HLu-3-(scFv8D3)2) for alpha-synuclein immuno-PET.
• To evaluate these constructs in alpha-synuclein pre-formed fibril (PFF) deposition and seeding models.
• To assess the feasibility of imaging intraneuronal alpha-synuclein aggregates.

Main Methods:

• Antibodies were conjugated with DFO* and radiolabeled with 89Zr.
• Binding affinity was assessed via ELISA and FACS.
• PET imaging, biodistribution, autoradiography, and immunofluorescence were performed in PFF deposition and seeding models.

Main Results:

• Both constructs showed specific binding to alpha-synuclein deposits in the PFF deposition model, with HLu-3-scFab8D3 demonstrating higher uptake.
• PET imaging in the deposition model yielded variable results due to small target volumes.
• In the seeding model, no significant difference in brain uptake was observed between PFF-injected and control mice, despite confirmed intraneuronal pathology.

Conclusions:

• While successful target engagement was shown in deposition models, PET imaging of alpha-synuclein PFFs was variable.
• HLu-3-scFab8D3 showed better performance in the deposition model but failed to detect intraneuronal pathology in the seeding model.
• Imaging intraneuronal alpha-synuclein inclusions via immuno-PET remains a significant challenge.