Near-Infrared Fluorescent PROTAC Enables Theranostic Imaging and Selective Tau Degradation in Alzheimer's Disease

The hyperphosphorylated Tau (p-Tau) protein plays a central role in the pathogenesis of Alzheimer's disease (AD) by driving neurofibrillary tangle formation and neuronal dysfunction. While proteolysis targeting chimeras (PROTACs) offer a promising approach for directly eliminating pathogenic proteins, their real-time visualization in living systems remains challenging. Here, we report the rational design and synthesis of a series of near-infrared (NIR) fluorescent Tau-targeting degraders that integrate theranostic imaging with targeted protein degradation. Among them, compound D9 emerges as a dual-functional degrader capable of both high-contrast fluorescence tracking and potent Tau clearance at 10 nM. Mechanistic investigations indicate that D9 induces Tau degradation through activation of the ubiquitin-proteasome system (UPS), as confirmed by inhibitor assays. Beyond Tau degradation, D9 also downregulates amyloid precursor protein (APP) and β-amyloid (Aβ) expression, suggesting broader neuroprotective effects. In in vivo studies, D9 significantly promotes p-Tau clearance and alleviates cognitive deficits in 3 ×Tg-AD mice. These findings demonstrate that D9 represents a first-in-class NIR fluorescent PROTAC for theranostic imaging and targeted degradation of Tau, providing a powerful platform for visualizing degradation dynamics and developing next-generation AD therapeutics.