Establishment of Transplantable Murine Osteosarcoma Cell Line with Endochondral Ossification

Osteosarcoma is defined as a malignant mesenchymal tumor in which tumor cells produce bone matrix. Osteosarcoma cell line (Nishi-Hirosaki osteosarcoma, NHOS) from a spontaneous soft tissue tumor in an athymic mouse was established. The cultured NHOS cells formed a monolayer consisting of spindle to polygonal cells without extracellular matrix formation or mineralization. Incontrast,thetransplantedNHOStumorin immunodeficient mice consisted of short spindle and pleomorphiccells,associatedwithnetworksofcalcifiedbone and osteoid matrices, as well as small foci of chondroid matrix. Pulmonary metastasis was detected in 22 (42.3%) out of the 52 tumor-bearing mice when NHOS cells were transplanted into the murine flanks. Pulmonary metastasis was detected in all mice (6/6) at post-injection days 21-49 when the cells were injected into the murine tail veins. The NHOS transplantable osteosarcoma cell line with ossifying ability would be useful to clarify the mechanisms of aggressive metastatic potential, as well as for studying the ossification process involved in cell-to-matrix interactions. Osteosarcoma is defined as a malignant mesenchymal tumor in which the tumor cells produce bone matrix. It is the most common primary malignant tumor of bone (approximately 20% of primary bone cancers), exclusive of myeloma and malignant lymphoma. Osteosarcoma is one of the most aggressive tumors spreading through the bloodstream and approximately 10% to 20% of patients show pulmonary metastasis at the time of diagnosis. In these patients who die of the neoplasm, 90% have metastasis to the lungs, bones, brain and elsewhere. Recent advances in treatment have improved the prognosis of osteosarcoma. Long-term survival rates are now 60% to 70% , compared to previous rates of 25% (1). However, the inhibition of osteosarcoma metastasis, as well as the suppression of tumor growth, is still one of the most urgent issues in orthopedic oncology. Recent advances in molecular biological techniques have provided insight into carcinogenesis, neoplastic growth and differentiation in cell culture systems. However, in vivo molecular biological analyses have been restricted due to the limited amounts of tumor samples available for study, especially in primary neoplasms. An in vivo transplantable tumor system provides sufficient amounts of tumor tissue which retains the original biological characteristics of the tumor. Transplantable osteosarcoma cell lines with ossifying ability would be useful to clarify the mechanisms of aggressive metastatic potential, as well as for studying the ossification process involved in cell-to-matrix interactions (2). There are several human and rat osteosarcoma cell lines with bone formation (3-6), but they are only transplantable into athymic mice. Only a few murine cell lines have been reported (7-11). Therefore, too few transplantable osteosarcoma cell lines with bone formation and frequent metastasis have been established. An osteosarcoma cell line (Nishi-Hirosaki Osteosarcoma, NHOS) has recently been established from a spontaneous soft tissue tumor in an athymic mouse in our laboratory. In this study, we investigated whether this cell line has ossifying ability when transplantedinvivo , and characterized the tumor growth and metastatic potential of the cell line.