Gas-core nanoscale bubbles (or nanobubbles) have gained significant recent attention as promising
contrast agents for
cancer molecular imaging using medical ultrasound. Previous work has shown that active targeting of nanobubbles to
tumor biomarkers such as the prostate-specific membrane
antigen (PSMA) significantly prolongs ultrasound signal enhancement, which is a critical feature for successful
tumor diagnosis. However, the specific mechanism behind this effect is not well understood, and has not been previously studied in detail. Thus, in the current work, we investigated the process of
PMSA- targeted nanobubble transport in
tumors across different scales from in vivo whole
tumor imaging using high-frequency dynamic contrast-enhanced ultrasound to intracellular confocal imaging and, molecularly using headspace gas chromatography/mass spectrometry. Data demonstrated that, indeed, molecular targeting of nanobubbles to the PSMA
biomarker prolongs their
tumor uptake and retention across the entire
tumor volume, but with variability due to the expected
tumor heterogeneity. Importantly, in vitro, the active targeting of NBs results in internalization via receptor-mediated endocytosis into the target cells, and the co-localization with intracellular vesicles (late-stage endosomes/lysosomes) significantly prolongs
perfluorocarbon gas retention within the cells. This has not been directly observed previously. These results support the potential for nanobubbles to enable highly specific, background-free diagnostic imaging of the target cells/tissues using ultrasound.