Comprehensive review on design perspective of PET ligands based on β-amyloids, tau and neuroinflammation for diagnostic intervention of Alzheimer’s disease

Abstract

Alzheimer’s disease (AD) is a progressive neurodegenerative pathological condition that resulted from the deterioration of cholinergic neurons over time. The pathological hallmark features of AD include extracellular β-amyloids plaques, hyperphosphorylated τ protein (tau), which is the main component of neurofibrillary tangles (NFT) and neuroinflammation. This article aims to provide a comprehensive review of PET tracers for Alzheimer’s disease, focusing on developments for targets (β-amyloids, hyperphosphorylated τ protein (tau), neuroinflammation and other related targets) available for clinical PET imaging. Studies involving the existing PET tracers used in the imaging of Aβ, tau, and neuroinflammation with essential features and limitations are discussed. Experimental studies with the design perspective of PET tracers, for biomarkers like Aβ, tau protein, and neuroinflammation, which are exploited clinically through PET Imaging have been described in detail. Comparative data have been generated based on the strength and weakness of PET radioligands for preclinical and clinical studies based on their binding affinity, selectivity and imaging. PET tracers for other targets like cannabinoid receptor type 2 (CB2), P2X7 receptor, cyclooxygenase-2, macrophage colony-stimulating factor 1 receptor (CSF1R), and monoamine oxidase (MAO) have also been included. We have summarized the ideal properties in terms of tracer s design for each target and based on their target selectivity and affinity, considering its potential strength and limitations. Where multiple tracers were present for a target, we provide a comparison of their properties. A critical assessment of both the preclinical and clinical PET tracers is carried out where sufficient data are available. This can help in designing better and highly selective PET tracers. Our comprehensive review will provide comparison and help in the design perspective of the futuristic PET tracers for Alzheimer s disease by improving their affinity towards biomarkers with higher selectivity Aβ/tau for delineation of AD at an early stage.