GV21 enables ultrasound molecular imaging of tumor cell-associated VEGFR2 for early therapy assessment

Vascular endothelial growth factor receptor 2 (VEGFR2) plays a crucial role in tumor growth through accelerating tumor angiogenesis. Recently, increasing evidence indicates that VEGFR2 is also overexpressed on tumor cells in multiple cancers, contributing to tumor progression and survival. BR55, a kind of VEGFR2-targeted microbubbles, has been developed and exhibited a promising potential for ultrasound molecular imaging (USMI) of early-stage tumors. However, it can only detect the VEGFR2 expressed on the tumor vascular endothelial cells but not on the tumor cells because it is strictly confined to the vasculature. Here, we developed VEGFR2-targeted gas vesicles (GV21) for USMI to enable detection of VEGFR2 in both vascular and extravascular interstitial regions. Unlike microscale BR55, GV21 has only 211.74 ± 1.05 nm particle size and can directly extravasate from tumor blood vessels to bind onto tumor cells, generating stronger and more persistent USMI signals in VEGFR2-expressing tumors. More importantly, the tumor-cell USMI signals can be specifically separated through subtracting the USMI signals of tumor blood vessels obtained from BR55-mimic microbubbles from the total USMI signals of tumor tissue from GV21 nanobubbles, allowing earlier and more comprehensive evaluation of therapeutic responses with the VEGFR2 tyrosine kinase inhibitor apatinib. These findings suggest that GV21 enables sensitive USMI of VEGFR2 expression and provides a promising approach for noninvasive evaluation of tumor molecular characteristics.