Q5 - Molecular ultrasound contrast agents for targeting cancer biomarkers

Introduction: : Ultrasound imaging has been widely used for disease diagnosis in clinics. Contrast-enhanced ultrasound imaging (CEUI) and super-resolution ultrasound imaging have been developed to better delineate fine structure deep inside tissues with improved contrast. However, ultrasound imaging has been limited to provide anatomical information. To address this, we have developed molecular ultrasound imaging contrast agents and imaging approaches to precisely localize them to visualize key biomarkers for cancer diagnosis.

Materials and

Methods: : We conjugated monoclonal antibodies (mAb) and nanometer-sized ultrasound contrast agents, gas vesicles (GV), to label human epidermal growth factor receptor 2 (HER2) and programmed death ligand 1 (PD-L1) [1]. Because GVs are protein shells, isolated from bacteria and archaea, with a plethora of lysine residues on their surface, the conjugation between lysine residues and N-hydroxysuccinimide (NHS) was utilized. Conjugates (mAb-GV) were incubated with HER2 and PD-L1 expressing cell lines in a dish to optically and acoustically confirm the targeting efficiency of developed molecular ultrasound contrast agents. Eigen-based imaging approach was developed to precisely localize mAb-GV conjugates. Singular value decomposition (SVD) identified unique GV cavitations under plane wave transmission by linear array transducers in a hierarchical order. We used unique GV cavitation to reconstruct images for GV localization. Vantage 256 ultrasound research platform, interfaced with a linear array transducer with a center frequency of 15 MHz, were used to acquire in-phase quadrature (IQ) images for post-processing. [2].

Results, Conclusions, and Discussions:: HER2 and PD-L1 specific targeting by developed contrast agents was confirmed. We also confirmed ultrasound signal increase after targeting HER2 and PD-L1 expressing cell lines imaged by the ultrasound imaging system (Fig. 1).

Conclusions: Our approach for ultrasound molecular imaging to visualize key biomarkers have successfully visualized HER2 and PD-L1 in vitro. We will continuously develop this technique for in vivo and clinical applications in the future.

Acknowledgements and/or References (Optional)::

References:
[1] S. Kim et al., “Multiplexed ultrasound imaging using spectral analysis on gas vesicles," Advanced Healthcare Materials, vol. 11, no. 17, pp. 2200568, 2022.
[2] J. Kim et al., "Compressed Sensing-Based Super-Resolution Ultrasound Imaging for Faster Acquisition and High Quality Images," IEEE Trans. Biomed. Eng., vol. 68, no. 11, pp. 3317-3326, 2021.

Acknowledgements: This work is partially supported by the National Institute of Health (NIH) grant No. GM152704 and the National Science Foundation (NSF) grant No. CBET1943852.