Ultrasound is among the world's most widely used biomedical imaging technologies due to its relative simplicity, low cost and ability to visualize deep tissues with high spatial and temporal resolution. However, ultrasound has historically had a small role in molecular and cellular imaging due to the lack of contrast agents connected to specific aspects of cellular function such as gene expression. To address this limitation, we are developing the first acoustic biomolecules ? proteins that can be imaged with ultrasound. These constructs are based on gas vesicles ? a unique class of gas-filled proteins from buoyant photosynthetic microbes, which we adapted as imaging agents for ultrasound in 2014. Since this key initial discovery, our laboratory has led the development of the emerging field of biomolecular ultrasound by engineering the physical, chemical and biological properties of gas vesicles to enable multiplexed imaging, cellular targeting and selective detection in vivo. In parallel, we have worked on transplanting the genetic program encoding gas vesicles into heterologous hosts, recently succeeding in doing so in commensal bacteria relevant to the mammalian microbiome, while in parallel making initial progress on expressing gas vesicles in mammalian cells. In addition, we discovered that gas vesicles can produce susceptibility-weighted MRI contrast erasable by ultrasound, providing an additional readout modality with unique advantages. Here we propose to build on these insights to advance gas vesicles as targeted nanoscale contrast agents, mammalian reporter genes and functional sensors for ultrasound. This work will focus on engineering gas vesicle properties for long-term circulation and extravascular targeting through the bloodstream, achieving robust expression of gas vesicles as reporter genes in mammalian cells, developing nonlinear ultrasound pulse sequences to maximize the sensitivity of gas vesicle imaging, and designing the first acoustic sensors of enzyme activity. The fundamental innovation contained in this research is that gas vesicle are the first biomolecular, genetically engineered and encoded contrast agent of any kind for ultrasound. As a result, they have the potential to transform this imaging modality analogously to the way fluorescent proteins transformed optical microscopy.

Public Health Relevance

Ultrasound is among the world's most widely used biomedical imaging technologies due to its relative simplicity, low cost and ability to visualize deep tissues with high resolution. However, ultrasound has relatively limited ability to visualize specific aspects of cellular function such as gene expression due to the lack of appropriate contrast agents. To address this limitation, we are developing acoustic biomolecules ? proteins that can be imaged with ultrasound, which we will engineer as targeted nanoscale contrast agents, reporter genes and functional molecular sensors for use in cancer and other areas of biology and medicine.

Agency
National Institute of Health (NIH)
Institute
National Institute of Biomedical Imaging and Bioengineering (NIBIB)
Type
Research Project (R01)
Project #
5R01EB018975-07
Application #
10070104
Study Section
Clinical Molecular Imaging and Probe Development (CMIP)
Program Officer
King, Randy Lee
Project Start
2019-03-01
Project End
2022-12-31
Budget Start
2021-01-01
Budget End
2021-12-31
Support Year
7
Fiscal Year
2021
Total Cost
Indirect Cost
Name
California Institute of Technology
Department
Type
Schools of Arts and Sciences
DUNS #
009584210
City
Pasadena
State
CA
Country
United States
Zip Code
91125
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