Nanotheranostics 2022; 6(3):270-285. doi:10.7150/ntno.64735 This issue

Research Paper

Intracellular vesicle entrapment of nanobubble ultrasound contrast agents targeted to PSMA promotes prolonged enhancement and stability in vivo and in vitro

Reshani H. Perera1, Eric Abenojar1, Pinunta Nittayacharn2, Xinning Wang2, Gopal Ramamurthy2, Pubudu Peiris2, Ilya Bederman3, James P. Basilion2, Agata A. Exner1✉

1. Department of Radiology Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA
2. Department of Biomedical Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA
3. Department of Genetics and Genome Sciences, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA

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Citation:
Perera RH, Abenojar E, Nittayacharn P, Wang X, Ramamurthy G, Peiris P, Bederman I, Basilion JP, Exner AA. Intracellular vesicle entrapment of nanobubble ultrasound contrast agents targeted to PSMA promotes prolonged enhancement and stability in vivo and in vitro. Nanotheranostics 2022; 6(3):270-285. doi:10.7150/ntno.64735. Available from https://www.ntno.org/v06p0270.htm

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Abstract

Graphic abstract

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.

Keywords: nanobubble ultrasound contrast agents, ultrasound molecular imaging, prostate cancer, prostate-specific membrane antigen (PSMA), cellular internalization