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Imaging the inhibition by anti‐β1 integrin antibody of lung seeding of single osteosarcoma cells in live mice

Integrins play a role in tumor growth and metastasis. However, the effect of integrin inhibition has not been visualized on single cancer cells in vivo. In this study, we used a powerful subcellular in vivo imaging model to demonstrate how an anti‐integrin antibody affects seeding and growth of osteosarcoma cells on the lung. The 143B human osteosarcoma cell line, expressing red fluorescent protein (RFP) in the cytoplasm and green fluorescent protein (GFP) in the nucleus, was established. Such double‐labeled cells enable imaging of apoptosis and mitosis and other nuclear‐cytoplasmic dynamics. Using the double‐labeled osteosarcoma cells, single cancer‐cell seeding in the lung after i.v. injection of osteosarcoma cells was imaged. The anti‐β1 integrin monoclonal antibody, AIIB2, greatly inhibited the seeding of cancer cells on the lung (experimental metastasis) while a control antibody had no effect. To image the efficacy of the anti‐integrin antibody on spontaneous metastasis, mice with orthotopically‐growing 143B‐RFP cells in the tibia were also treated with AIIB2 or control anti‐rat IgG1 antibody. After 3 weeks treatment, mice were sacrificed and primary tumors and lung metastases were evaluated with fluorescence imaging. AIIB2 significantly inhibited spontaneous lung metastasis but not primary tumor growth, possibly due to inhibition of lung seeding of the cancer cells as imaged in the experimental metastasis study. AIIB2 treatment also increased survival of mice with orthotopically growing 143B‐RFP.