Strain-promoted click chemistry boosts microbubbles for targeted ultrasound imaging and cancer chemotherapy

Targeted microbubbles (MBs) have emerged as pivotal dual-functional agents for molecular ultrasound (US) imaging and US-triggered targeted drug delivery. However, the efficacy of traditional ligand-directed MBs is often compromised by the inherent heterogeneity of tumor receptor expression and physiological barriers. Herein, we report a robust targeting platform based on dibenzocyclooctyne-functionalized MBs (MB-DBCO) that leverages metabolic glycoengineering and bioorthogonal strain-promoted azide-alkyne cycloaddition (SPAAC). This strategy decoupled targeting efficiency from genetic receptor expression by pre-installing azide chemical handles onto the tumor cell surface. Our results demonstrate that MB-DBCO provides a stable "chemical anchor" in both 4T1 tumor cells and vascular endothelial cells, significantly enhancing contrast-enhanced ultrasound (CEUS) sensitivity and tumor cell specificity. Crucially, the synergistic combination of SPAAC-mediated covalent tethering and US cavitation-induced sonoporation breaches the endothelial cell barrier and tumor stromal barriers, driving the deep penetration of the paclitaxel (PTX) payload. In vivo studies showed that the MB-DBCO + US treatment leads to profound tumor regression, extensive vascular depletion, and a significantly prolonged survival time in aggressive 4T1 tumor models. This study establishes a modular, chemically-defined, and scalable targeting platform that overcomes the critical biological barriers of solid tumors, offering a promising paradigm for CEUS imaging and US-triggered chemotherapy. STATEMENT OF SIGNIFICANCE: Contrast-enhanced ultrasound (CEUS) imaging and US-triggered targeted chemotherapy efficacy of dual functional microbubbles (MBs) is often compromised by heterogeneous receptor expression and the endothelial cell barrier of solid tumors. This study introduces a modular bioorthogonal platform that decouples tumor targeting from genetic markers by converting metabolic flux into a robust chemical interface for MBs anchoring. We demonstrate that this stable chemical-mechanical coupling enables localized cavitation to physically breach the tumor stroma, providing a scalable and universal framework for CEUS imaging and US-triggered targeted chemotherapy.