Abstract PR05: Familial cancer patient specific iPSCs based study of a potential oncogenic factor, sFRP2, in osteosarcoma

Osteosarcoma (OS), despite being a serious pediatric cancer with the lowest survival rate, is not well studied due to its rare occurrence. For this reason, studying OS in a patient-specific manner is more challenging. In an attempt to establish a method to study OS in a patient-specific manner, we previously generated Li-Fraumeni syndrome (LFS---a germline P53 mutation disease) patient specific iPSCs, and demonstrated that the LFS-iPSC derived mesenchymal stem cells (MSCs) and osteoblasts (OBs) can recapitulate tumorigenic phenotypes in vitro and in vivo (Lee, Kim, et al., Cell 2015). Taking advantage of this new platform, we focused on finding potential therapeutic targets. We found SFRP2 (secreted frizzled related protein 2) to be highly expressed in LFS iPSC-derived MSCs and OBs by global RNA-seq gene expression analysis. Using global transcript profiling of ectopic overexpression (OE) of sFRP2 in wild-type MSCs, we discovered that sFRP2 regulates osteoblast differentiation, cell adhesion, cell proliferation, and apoptosis-related gene sets. Further functional assays revealed that sFRP2 OE contributes to the generation of abnormal osteoblast cells, which are the cause of OS, by suppressing osteogenic alkaline phosphatase activity, mineralization, and osteogenic BMP and WNT signaling. Furthermore, ectopic OE of sFRP2 is associated with LFS mediated tumorigenesis. sFRP2 OE in MSCs and OBs facilitates cell proliferation through cell cycle alteration and increases anchorage independency. In in ovo and in vivo xenograft assays (subcutaneous and intratibial injections), the tumor size is significantly increased in sFRP2 OE group and decreased in knockdown sFRP2 group. Interestingly, we also found that sFRP2 OE augments angiogenesis in vitro and in vivo, suggesting sFRP2 has a role as a paracrine factor. In the future, we will analyze sFRP2 expression levels in human OS tissue samples to determine whether sFRP2 OE has clinical relevance. Conclusively, this study demonstrates that P53 mutation-mediated osteosarcoma exerts oncogenicity through sFRP2 overexpression and that targeting of sFRP2 is a potential therapeutic strategy for OS treatment. This abstract is also being presented as Poster A22. Citation Format: Huen Suk Kim, Ye X. Yuan, Jeffrey M. Bernitz, Andreia Gomes, Christopher Schaniel, Dung-Fang Lee, Ihor R. Lemischka. Familial cancer patient specific iPSCs based study of a potential oncogenic factor, sFRP2, in osteosarcoma [abstract]. In: Proceedings of the AACR Conference on Advances in Sarcomas: From Basic Science to Clinical Translation; May 16-19, 2017; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(2_Suppl):Abstract nr PR05.