An ultrasound-activated PROTAC prodrug with self-reporting fluorescence for targeted protein degradation

PROteolysis TArgeting Chimeras (PROTACs) have emerged as a pharmacological tool for selectively degrading disease-associated proteins of interest (POIs). However, PROTACs-mediated protein degradation often lacks precise spatiotemporal control, potentially disrupting protein homeostasis in normal tissues and causing physiological toxicity. To address these challenges, we developed an ultrasound-activated PROTAC prodrug platform (US-PROTAC) that enables spatiotemporally controlled PROTAC activation with non-invasive, in situ fluorescence-guided monitoring. This platform consists of three essential components: a near-infrared fluorescent reporter (methylene blue, MB) for bioimaging feedback, a PROTAC molecule selectively targeting POIs, and a self-immolative linker for ultrasound-triggered activation. The protein degradation activity of US-PROTAC is masked under physiological conditions. However, ultrasonic stimulation generates hydroxyl radicals (•OH) through cavitation dynamics, selectively cleaving urea bonds and restoring MB fluorescence. This process simultaneously triggers a self-immolative reaction that releases active PROTAC. Importantly, MB fluorescence recovery enables real-time visualization of ultrasound-triggered PROTAC release in vitro and in vivo. The combination of ultrasound-mediated activation and fluorescence imaging further enables modulation of therapeutic efficacy by adjusting ultrasound parameters, offering a practical tool for optimizing spatiotemporal control of targeted protein degradation.