Thy1-Targeted Microbubbles for Ultrasound Molecular Imaging of Pancreatic Ductal Adenocarcinoma

Purpose: To engineer a dual human and murine Thy1-binding single-chain-antibody ligand (Thy1-scFv) for contrast microbubble-enhanced ultrasound molecular imaging of pancreatic ductal adenocarcinoma (PDAC). Experimental Design: Thy1-scFv were engineered using yeast-surface-display techniques. Binding to soluble human and murine Thy1 and to Thy1-expressing cells was assessed by flow cytometry. Thy1-scFv was then attached to gas-filled microbubbles to create MB Thy1-scFv. Thy1 binding of MB Thy1-scFv to Thy1-expressing cells was evaluated under flow shear stress conditions in flow-chamber experiments. MB scFv-scrambled and MB Non-targeted were used as negative controls. All microbubble types were tested in both orthotopic human PDAC xenografts and transgenic PDAC mice in vivo. Results: Thy1-scFv had a K D of 3.4±0.36 nM for human and 9.2±1.7 nM for murine Thy1 and showed binding to both soluble and cellularly expressed Thy1. MB Thy1-scFv attached to Thy1 with high affinity compared to negative control microbubbles P