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 ABY B7-H3 was confirmed with soluble and cell-surface B7-H3 by flow cytometry. MB were functionalized with ABY B7-H3 or anti-B7-H3-antibody (Ab B7-H3). Control and targeted MB were tested for binding to hB7-H3-expressing cells (MS1 hB7-H3) under shear stress conditions. US imaging was performed with MB ABY-B7-H3 in an orthotopic mouse model of human MDA-MB-231 coimplanted with MS1 hB7-H3 or control MS1 WT cells and a transgenic mouse model of breast cancer development.
RESULTS: ABY B7-H3 specifically binds to MS1 hB7-H3 and murine-B7-H3-expressing monocytes. MB ABY-B7-H3 (8.5 ± 1.4 MB/cell) and MB Ab-B7-H3 (9.8 ± 1.3 MB/cell) showed significantly higher ( P < 0.0001) binding to the MS1 hB7-H3 cells compared with control MB Non-targeted (0.5 ± 0.1 MB/cell) under shear stress conditions. In vivo, MB ABY-B7-H3 produced significantly higher ( P < 0.04) imaging signal in orthotopic tumors coengrafted with MS1 hB7-H3 (8.4 ± 3.3 a.u.) compared with tumors with MS1 WT cells (1.4 ± 1.0 a.u.). In the transgenic mouse tumors, MB ABY-B7-H3 (9.6 ± 2.0 a.u.) produced higher ( P < 0.0002) imaging signal compared with MB Non-targeted (1.3 ± 0.3 a.u.), whereas MB ABY-B7-H3 signal in normal mammary glands and tumors with B7-H3 blocking significantly reduced ( P < 0.02) imaging signal.
CONCLUSIONS: MB ABY-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.
Bibliographical noteFunding Information:
We acknowledge the guidance and mentorship of the late Dr. Juergen K Willmann. We thank the Preclinical Imaging Core Facility and Proteomics Resource Facility at the Canary Center for Cancer Early Detection, Stanford University. IHC staining of human breast cancer specimens was performed at Human Pathology/Histology Service Center, Stanford University. This study was funded by the NCI under grant number R41-CA213544 and a Stanford Women's Cancer Center Innovation Award from the Stanford Cancer Institute, a NCI-designated Comprehensive Cancer Center.
PubMed: MeSH publication types
- Research Support, Non-U.S. Gov't
- Journal Article
- Research Support, N.I.H., Extramural