A Bioluminescent Orthotopic Mouse Model of Human Osteosarcoma that Allows Sensitive and Rapid Evaluation of New Therapeutic Agents In Vivo

Osteosarcoma (OSA) is the most common primary malignant bone tumor in children, 30% of whom develop lung metastases despite aggressive treatment. Our objective was to develop a mouse model of OSA for preclinical studies that (i) incorporates the natural history of OSA including tumor growth in bone and development of lung metastasis and (ii) is amenable to non-invasive detection methods. A human OSA cell line that expresses high levels of luciferase was created. Following subcutaneous injection, nine out of ten mice showed tumor growth. Eight out of ten mice showed tumor growth following orthotopic injection into the proximal tibia. Thirty percent of mice showed pulmonary metastasis by bioluminescent imaging eight to 10 weeks following orthotopic injection. Animals receiving cisplatin treatment showed reduced tumor volume compared to animals treated with vehicle alone. This model allows real-time detection of tumors and can be used to study mechanisms of OSA metastasis and test new therapeutic agents. Osteosarcoma (OSA) is the second leading cause of cancer- related death in children, affecting primarily adolescents. There are an estimated 1,500 cases per year occurring in the United States, accounting for about 3.5% of all cancer cases in those under 20 years of age (1, 2). OSA also occurs in older adults, although at a lower frequency. The age distribution of OSA shows the highest incidence at 10-19 years of age while a second but lower peak in incidence occurs in the 7th decade of life (2). The distal femur, proximal tibia and proximal humerus are the most common primary sites of occurrence in humans. Treatment of OSA remains difficult. Five-year survival has increased from approximately 15% in the 1950s with surgical management to approximately 60% in the 1980s from inclusion of adjuvant chemotherapy, notably doxorubicin, methotrexate and cisplatin, in the treatment but has not changed recently due to the slow development of improved chemotherapies (3-5). One-third of patients diagnosed with OSA will develop pulmonary metastases that lead to death. Five-year survival for those presenting with pulmonary metastasis at diagnosis is less than 20% (6). The low survival rate of patients with OSA metastasis indicates that there is much room for improvement in the treatment of advanced and relapsed OSA. Most likely, this will involve the development of new drug therapies and the improvement of diagnostic and prognostic tools by making use of preclinical models of OSA. Animal models of OSA are critical for preclinical evaluation of therapeutic agents as relatively small numbers of children develop OSA and thus make clinical trials challenging to perform. However, few OSA models currently exist for studying the pathobiology of OSA tumor progression, metastasis and identifying anti-OSA agents. For a model to have the best chance at being predictive of clinical outcome, it should demonstrate the characteristics of the cancer in a human patient including histologic type and tendency to spontaneously metastasize. In addition, confirmation of the model's response to therapeutic drugs effective in treating OSA is an important step to validate the model for use in preclinical studies. It has been proposed that the use of panels of xenograft models that both mimic the characteristics of primary tumor and reflect the inherent variability in these types of cancer might be of more predictive value when testing new therapeutic agents (7). Accordingly, we explored the potential to add to and improve upon the currently available preclinical models of OSA.