Abstract 198: Unveiling chromatin accessibility landscape and convergent oncogenic pathway in angiosarcoma models using induced pluripotent stem cells
Authors: Wenthe Sophia , Becklin Kelsie , Napiwocki Brett , Kozurek Emma , Moriarity Branden , Kim Jong Hyuk 
Published: June 2022

Abstract
Angiosarcoma is a rare soft tissue sarcoma that forms malignant vessels. Angiosarcomas are aggressive and highly metastatic, resulting in a poor prognosis. Recurrent somatic mutations in TP53 and genes involved in PI3K/AKT/mTOR pathway such as PIK3CA and PIK3R1 are identified in angiosarcomas. However, angiosarcomas are genomically complex, and the oncogenic mechanisms are virtually unknown. Due to its rarity, establishment of experimental tumor models is an unmet need for angiosarcoma research. In this study, we used human induced pluripotent stem cells (iPSCs) to develop a novel, reliable model for angiosarcoma recapitulating the genomic complexity and the tumor immune landscape. Specifically, we induced TP53 mutations in human iPSCs using CRISPR/Cas9 with validation of p53 deficiency by gene sequencing and Western blotting. We then established protocols to differentiate genetically engineered iPSCs to mesoderm and subsequently bi-potential hemangioblasts, which are considered the putative cell-of-origin of angiosarcoma. We found that isogenic wild-type (WT) and TP53 mutant iPSCs were capable of generating hemangioblasts, with no significant differences in morphology or growth patterns observed between WT and mutant cells. Putative iPSC-derived hemangioblasts were CD34+ by flow cytometry and contained primitive endothelial cells with the capacity to form tube-like structures in Matrigel. RNA-seq data libraries were generated to profile global gene expression in non-differentiated cells, mesodermal precursors, hemangioblasts, and endothelial cells derived from WT and p53 mutant iPSCs during differentiation over time (day 0, 2, 5, 8). Principal component analysis revealed that gene expression patterns were altered between WT and p53 mutant cells during differentiation, representing distinct gene signatures unique to each cell type. Intriguingly, transcriptomic alteration of p53 mutant iPSC-derived cells was more variable than that of WT. Our data also showed that p53 mutation induced dysregulation of genes associated with chromosome maintenance, extracellular matrix organization, hemostasis, and receptor tyrosine kinase signaling in iPSC-derived hemangioblasts when compared isogenic WT controls. Our data highlights the role that mutant p53 plays in the induction of genomic instability and transcriptional programs that regulate hemogenic and endothelial function during differentiation. Additionally, ATAC-seq data were generated from WT and p53 mutant iPSC-derived cells to determine chromatin accessibility dynamics and identify key transcription factors that activate convergent vascular tumorigenic pathways. We are currently generating iPSC harboring co-mutations in TP53 and PIK3CA in order to determine the phenotype and tumorigenic capacity of engineered iPSC-derived hemangioblasts in xenograft models.
Citation Format: Sophia Wenthe, Kelsie Becklin, Brett Napiwocki, Emma Kozurek, Branden Moriarity, Jong Hyuk Kim. Unveiling chromatin accessibility landscape and convergent oncogenic pathway in angiosarcoma models using induced pluripotent stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 198.