Abstract The efficacy of anti β1 integrin monoclonal antibody (clone AIIB2) to inhibit lung seeding and colony formation of human osteosarcoma cells was imaged in real time. To visualize cancer cell seeding and metastasis in the lung, human osteosarcoma cells were used in which green fluorescent protein (GFP) is expressed in the nucleus and RFP is expressed in the cytoplasm. 143B cells were preincubated with AIIB2 or control antibody, and then injected into the nude mice via tail vein. Twenty four hours later, the lungs were fluorescently-imaged in live mice with the lung exposed. 143B cells which arrested in the lung were counted. Two weeks after the first observation, the animals were sacrificed and the lungs were resected and fluorescently imaged to quantitate resulting lung metastatic colonies. AIIB2 significantly inhibited osteosarcoma cells seeding and colony formation in the lung. This result indicates that β1 integrin plays an important role for osteosarcoma cell adhesion to lung. To evaluate efficacy of the AIIB2 antibody on primary tumor growth and spontaneous metastases, 143B osteosarcoma cells were orthotopically transplanted in the tibia. Two weeks later, mice were treated with either 40 µg or 200 µg AIIB2, or control antibody biweekly. After three weeks treatment, primary tumors and lung metastases were evaluated. Neither 40 µg nor 200 µg of AIIB2 significantly inhibited primary tumor growth. In contrast, both doses of AIIB2 significantly inhibited spontaneous lung metastasis. AIIB2 appears to be a specific anti-metastatic agent since it inhibited lung metastasis while not inhibiting primary tumor growth. This is consistent with AIIB2 inhibition of adhesion of 143B cells to the lung. These results suggest that anti-β1 integrin antibody treatment has clinical potential as an anti-metastatic agent. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1632. doi:10.1158/1538-7445.AM2011-1632