Lysosome-targeted near-infrared fluorescent probes for monitoring aβ plaques in vivo and aβ monomers dynamic degradation in vitro.

The aggregation of β-amyloid (Aβ) is a central pathological feature of Alzheimer's disease (AD), with its dynamic changes closely linked to disease progression. Lysosomes play a critical role in the clearance and degradation of Aβ, making them an important focus in AD research. In this study, a series of multifunctional lysosome-targeting near-infrared fluorescent probes based on a dicyanoisophorone scaffold were developed to enable simultaneous targeting of lysosomes and monitoring of Aβ aggregates. All probes effectively localized within cellular lysosomes, with NCM-4 demonstrating the most efficient lysosomal targeting, along with high selectivity, specificity, and strong binding affinity toward Aβ aggregates. Both in vivo imaging and ex vivo brain slice staining confirmed that the probe efficiently crossed the blood-brain barrier and selectively accumulated in the brains of APP/PS1 transgenic mice, allowing clear visualization of Aβ plaques. Furthermore, due to its lysosomal localization, NCM-4 enabled real-time tracking of the internalization of FITC-labeled Aβ monomers (FITC488Aβ) from the extracellular environment into lysosomes. This capability also allowed monitoring of how autophagy modulation, via chloroquine and rapamycin, influences Aβ clearance within lysosomes. Overall, these probes, particularly NCM-4, provide a valuable platform for AD diagnosis and offer powerful tools for studying lysosome-mediated Aβ clearance mechanisms and therapeutic interventions.