Efficacy of Affibody-Based Ultrasound Molecular Imaging of Vascular B7-H3 for Breast Cancer Detection
Rakesh Bam, Patrick S. Lown, Lawrence A. Stern, Karina Sharma, Katheryne E. Wilson, Gregory R. Bean, A.M. Lutz, Ramasamy Paulmurugan, Benjamin J. Hackel, Jeremy Dahl, Lotfi Abou‐Elkacem
Abstract
Abstract Purpose: Human B7-H3 (hB7-H3) is a promising molecular imaging target differentially expressed on the neovasculature of breast cancer and has been validated for preclinical ultrasound (US) imaging with anti–B7-H3-antibody-functionalized microbubbles (MB). However, smaller ligands such as affibodies (ABY) are more suitable for the design of clinical-grade targeted MB. Experimental Design: Binding of ABYB7-H3 was confirmed with soluble and cell-surface B7-H3 by flow cytometry. MB were functionalized with ABYB7-H3 or anti–B7-H3-antibody (AbB7-H3). Control and targeted MB were tested for binding to hB7-H3–expressing cells (MS1hB7-H3) under shear stress conditions. US imaging was performed with MBABY-B7-H3 in an orthotopic mouse model of human MDA-MB-231 coimplanted with MS1hB7-H3 or control MS1WT cells and a transgenic mouse model of breast cancer development. Results: ABYB7-H3 specifically binds to MS1hB7-H3 and murine-B7-H3–expressing monocytes. MBABY-B7-H3 (8.5 ± 1.4 MB/cell) and MBAb-B7-H3 (9.8 ± 1.3 MB/cell) showed significantly higher (P < 0.0001) binding to the MS1hB7-H3 cells compared with control MBNon-targeted (0.5 ± 0.1 MB/cell) under shear stress conditions. In vivo, MBABY-B7-H3 produced significantly higher (P < 0.04) imaging signal in orthotopic tumors coengrafted with MS1hB7-H3 (8.4 ± 3.3 a.u.) compared with tumors with MS1WT cells (1.4 ± 1.0 a.u.). In the transgenic mouse tumors, MBABY-B7-H3 (9.6 ± 2.0 a.u.) produced higher (P < 0.0002) imaging signal compared with MBNon-targeted (1.3 ± 0.3 a.u.), whereas MBABY-B7-H3 signal in normal mammary glands and tumors with B7-H3 blocking significantly reduced (P < 0.02) imaging signal. Conclusions: MBABY-B7-H3 enhances B7-H3 molecular signal in breast tumors, improving cancer detection, while offering the advantages of a small size ligand and easier production for clinical imaging.