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Ultra-high-frequency radio-frequency acoustic molecular imaging with saline nanodroplets in living subjects

Abstract

Molecular imaging is a crucial technique in clinical diagnostics but it relies on radioactive tracers or strong magnetic fields that are unsuitable for many patients, particularly infants and pregnant women. Ultra-high-frequency radio-frequency acoustic (UHF-RF-acoustic) imaging using non-ionizing RF pulses allows deep-tissue imaging with sub-millimetre spatial resolution. However, lack of biocompatible and targetable contrast agents has prevented the successful in vivo application of UHF-RF-acoustic imaging. Here we report our development of targetable nanodroplets for UHF-RF-acoustic molecular imaging of cancers. We synthesize all-liquid nanodroplets containing hypertonic saline that are stable for at least 2 weeks and can produce high-intensity UHF-RF-acoustic signals. Compared with concentration-matched iron oxide nanoparticles, our nanodroplets produce at least 1,600 times higher UHF-RF-acoustic signals at the same imaging depth. We demonstrate in vivo imaging using the targeted nanodroplets in a prostate cancer xenograft mouse model expressing gastrin release protein receptor (GRPR), and show that targeting specificity is increased by more than 2-fold compared with untargeted nanodroplets or prostate cancer cells not expressing this receptor.

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Fig. 1: Experimental concept.
Fig. 2: Preparation of UHF-RF-acoustic contrast agents with engineered saline nanodroplets.
Fig. 3: In vitro contrast-enhanced UHF-RF-acoustic imaging.
Fig. 4: GRPR-targeted nanodroplets showed specific targeting to prostate cancer cells and low toxicity in cell culture.
Fig. 5: In vivo UHF-RF-acoustic molecular imaging using targeted nanodroplets.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

This work was supported in part by grants from NCI CCNE-TD U54 CA199075-04 (S.S.G.), The Canary Foundation (S.S.G.), The Sir Peter Michael Foundation (S.S.G.), Stanford’s Catalyst for Collaborative Solutions (J.D. and S.S.G.), Google Faculty Research Award (Y.-S.C.), The Jump ARCHES endowment through the Health Care Engineering Systems Center (Y.-S.C.), and NIGMS 1R21GM139022-01 (Y.Z.). The authors acknowledge the Stanford Center for Innovation in In Vivo Imaging (SCI3) for assistance with animal imaging and C. Chan for providing insightful discussions. This paper is dedicated to the memory of Dr Sanjiv Sam Gambhir.

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Contributions

S.S.G. conceived the original idea. Y.-S.C. and S.S.G. designed the experiments. Y.-S.C. developed the contrast agents and performed the in vitro and in vivo imaging. C.B., A.Z. and F.A. assisted in the in vivo experiments. Y.-S.C., Y.Z. and H.W. performed the theoretical study. D.-H.C. contributed to cryo-electron microscopy. C.B., A.Z., E.-C.H., F.A., T.S. and J.D. contributed to the discussion of the data and experimental results. Y.-S.C. and S.S.G. drafted the manuscript and all authors contributed to the writing of the manuscript. S.S.G. supervised the entire study.

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Correspondence to Yun-Sheng Chen.

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Competing interests

S.S.G. declared competing financial interests with Endra Inc and Visualsonics Inc.

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Peer review information Nature Nanotechnology thanks F. Kiessling, N. van den Berg and M. Tang for their contribution to the peer review of this work.

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Supplementary discussions, methods, Figs. 1–16 and Tables 1 and 2.

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Chen, YS., Zhao, Y., Beinat, C. et al. Ultra-high-frequency radio-frequency acoustic molecular imaging with saline nanodroplets in living subjects. Nat. Nanotechnol. 16, 717–724 (2021). https://doi.org/10.1038/s41565-021-00869-5

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