Abstract 489: The origin of osteosarcoma
Authors: Yang Yi , Zhang Wendong , Li Nan , Piperdi Sajida , Park Amy , Tripathi Sandeep , Gorlick Richard 
Published: June 2012

Abstract
Introduction: Osteosarcoma is the most prevalent primary malignant bone tumour in children and young adults, with poor survival in 40% of patients. Theoretically, osteosarcoma could potentially be derived from a cell anywhere on the differentiation pathway between human mesenchymal stem cell (hMSC) and a mature osteoblast (OB). To identify the cell of origin and the genetic alterations involved in osteosarcomagenesis, hMSCs and the OBs derived from the same hMSCs were serially transformed with viral constructs containing oncogenes.
Methods: Bone-marrow-derived hMSCs were characterized through FACS analysis, and were induced to osteogenic differentiation for 4-6 weeks. OBs derived from hMSCs were identified with alkaline phosphatase activity and alizarin red staining. The hMSCs and the OBs were serially transformed with retrovirus containing human telomerase reverse transcriptase (hTERT), simian virus 40 large t antigen (SV40 TAg) and lentivirus containing oncogenic H-Ras. Genome-wide expression profiles, karyotype, and multilineage differentiation capacity were tested in all genetically transformed cell lines. Orthotopic tumorigenicity assays and soft agar assay were used to compare the biologic behavior between hMSC and the derivatives.
Results: OBs differentiated from hMSCs showed a diffused positive staining for alkaline phosphatase activity and alizarin red. Levels of osteocalcin secretion from differentiated OBs in osteogenic medium were significantly higher than hMSCs. All genetically transformed cell lines were identified by RT-PCR and Western-Blot. In tumorigenicity assays, tumors formed with sarcomatous cell lines derived from hMSC and osteoblasts in either subcutaneously injected or orthotopic-injected mice 4 weeks after the implantation. In osteoblasts group, tumor showed a typical osteosarcoma appearance. All transforming cell lines derived from osteoblasts lost the adipogenic differentiation capacity.
Conclusion: Our previous study showed that two sarcomatous cell lines were established by introducing genetic alterations serially to transform hMSC into a malignant phenotype, but there was no osteoid production or osteoblast-like features observed in the neoplastic cells. In this study, we have successfully developed a human osteosarcoma model by introducing the same genetic alterations into preosteoblasts derived from hMSC by osteogenic differentiation. The neoplastic cells transformed from preosteoblasts, which only have bilineage (osteogenic and chondrogenic) differentiation potential, were apparently different from the derivatives of hMSCs. The gene expression profiles revealed some significant pathways involved in osteosarcomagenesis, in which losing adipogenic differentiation capacity may be a crucial step.
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 489. doi:10.1158/1538-7445.AM2011-489