Molecular ultrasound imaging is a promising strategy for non-invasive and precise cancer diagnosis. Previously reported ultrasound contrast agents (UCAs) are mostly microbubbles or nanobubbles (NBs) larger than 200 nm, leading to less efficient tumor delivery. Here we synthesized NBs with a small size (~49 nm) and modified the NB surface with alanine-alanine-asparagine (NB-A) or arginine-glycine-aspartic acid peptide (NB-R) for concurrent active targeting towards legumain in tumor cells and integrin in tumor neovasculature. In vitro, the NB-A and NB-R presented echogenicity comparable with SonoVue MBs and showed specific binding with tumors cells and endothelial cells, respectively. In vivo, the combined NB-A/NB-R accumulated in tumor tissues selectively and provided ultrasound signals with prolonged duration and that were significantly stronger than non-targeted NBs, single-targeted NBs and SonoVue MBs. Overall, the dual targeted NBs served as efficient UCAs for specific imaging of breast cancer, and hold great potential for general cancer diagnosis/monitoring in the future.
Keywords: EPR effect; Legumain; Molecular ultrasound imaging; Nanobubbles; RGD.
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