Design and synthesis of new theranostic agents for near-infrared imaging of β-amyloid plaques and inhibition of β-amyloid aggregation in Alzheimer's disease

Abstract

The presence of amyloid plaques predisposes clinical symptoms of cognitive impairment, which occurs much earlier than other clinical symptoms and plays a crucial role in the neuropathology of AD. Thus, developing probes for Aβ species imaging could be used for early diagnosis of AD, and blocking the initial steps of Aβ aggregation with small molecules has emerged as a valid disease-modifying therapy for Aβ. Herein, we report the design, synthesis and evaluation of a series of new theranostic agents, which can simultaneously perform near infra-red imaging of Aβ plaques, prevent self-aggregation of Aβ monomer, disaggregate preformed Aβ fibrils and play a protective effect on the toxicity of human neuroblastoma cells (SHSY5Y) induced by Aβ1–42. Most of these probes displayed maximum emission in PBS (>650 nm), which falls in the good range for NIRF probes. Importantly, these probes are found to have a high binding affinity toward Aβ aggregates, to exhibit a large fluorescence enhancement upon interaction with Aβ aggregates accompanied by a blueshift in the emission spectra of 20–40 nm and to show an excellent targeting ability for Aβ plaques in slices of brain and eye containing retina tissue from double transgenic mice. These molecules show a promising potential as theranostic agents for the diagnosis and therapy of AD.