Abstract 5164: Mesenchymal differentiation potentials modify osteosarcoma stem cell activities
Authors: Shimizu Takatsune , Ishikawa Tomoki , Sugihara Eiji , Kuninaka Shinji , Miyamoto Takeshi , Ito Takaaki , Okada Seiji , Ikeda Yasuo , Suda Toshio , Saya Hideyuki 
Published: February 2011

Abstract
Cancer stem cells (CSCs) are a subset of tumor cells that are responsible for initiating and maintaining the disease. However, the genetic changes and cellular context determining those characteristics of CSCs remain unclear. In addition, what differentiation properties are suitable or refractory to the generation of CSCs is still unknown. To address these questions, we attempted to establish CSCs from normal tissues. As the target tissue of tumorigenesis, we chose mouse bone marrow stromal cells (BMSCs), which comprise of various mesenchymal lineages at different maturation stages derived from mesenchymal stem cells (MSCs). By overexpressing c-MYC in BMSCs derived from Ink4a/Arf (−/−) mice, we generated mouse osteosarcoma (OS) CSC in vitro. The inoculation of the established cells resulted in lethal OS in C57BL/6 syngeneic mice. To clarify the cells of origin of OS, we performed single cell cloning. According to differentiation potentials, those c-MYC expressing BMSCs were composed of two distinctly-different clones: bipotent (osteogenic and chondrogenic) cells designated AX cells and tripotent (adipogenic, osteogenic, and chondrogenic) cells termed AO cells. Their differentiation potentials and gene expression profiling suggested that AX cells were derived from osteo-chondro-committed progenitor cells, while AO cells were originated from MSCs. Bipotent AX cells were highly tumorigenic and possessed high propensity for distant metastasis that mimics human disease. In addition, they showed both terminal differentiation and self-renewal capacity in vivo, which are properties ascribed to CSC. Notably, tripotent AO cells also developed lethal OS in syngeneic mice more slowly and less frequently than AX cells. Moreover, during OS development tripotent AO cells lost their adipogenic potential and transformed into AX-like cells in vivo. Thus, the loss of adipogenic potential was suggested to be an essential event for OS development. To confirm this notion, we shifted the mesenchymal differentiation property by depletion and overexpression of PPARγ in tripotent AO and bipotent AX cells, respectively. The PPARγ knockdown afforded tripotent AO cells the advantage to OS formation in both differentiation and proliferation. In contrast, overexpression of PPARγ in bipotent AX cells attenuated their OS CSC activities. Therefore, our findings indicated that differentiation potentials played key roles on the tumor initiating activity and lineage commitment to osteocyte might be a critical factor for the induction of OS CSC. Our induced OS CSC mouse model was useful for both basic and clinical research to develop novel therapeutic approaches.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5164.