Development of ultrasound molecular contrast agents by site-specific conjugation of gas vesicles to antibodies

Ultrasound technology is a powerful tool for medical imaging and diagnosis especially when used in conjunction with a contrast agent to target proteins of interest. However, current ultrasound contrast agents are lacking the combination of specificity, stability, and size optimization. In this study we introduce and confirm the feasibility of using nanometer sized gas vesicles (GV) chemically click conjugated to antibodies (mAb) to make the first site-specific mAb-GV conjugates as a durable cancer cell targeting ultrasound molecular contrast agents. Protein expression of human epidermal growth factor receptor 2 (HER2) and programmed death-ligand 1 (PD-L1) were tested along with the antibody targeting efficiency using cancer cell lines and primary cells isolated from tumor bearing mice. The mAb conjugation was optimized to a site-specific method using the mAb glycans and tested with the addition of a clinically used mAb to target trophoblast cell surface antigen 2 (Trop-2). The developed contrast agents utilize the stability of GVs and the specificity of antibodies to label cancer biomarkers in various types of tumors for ultrasound imaging.