Abstract 2660: Targeting PI3K pathway to reprogram the tumor immune niche in angiosarcoma
Authors: Kozurek Emma , Liu Zhiyan Silvia , Nguyen Hai Dang , Kim Jong Hyuk 
Published: June 2022

Abstract
Angiosarcoma is an aggressive, albeit rare, cancer in humans. Angiosarcomas are vascular malignancies that can occur anywhere in the body, and their metastatic propensity is high. The vascular sarcomas consist of disorganized, malignant vessel-forming cells. Recurrent mutations in the PIK3CA gene have been identified in angiosarcomas, and activation of the PI3K pathway appears to establish angiogenic programs. Naturally occurring hemangiosarcoma in dogs shares clinical and pathological features with human angiosarcoma. Our previous work has revealed that canine hemangiosarcomas and human angiosarcomas share mutational and transcriptional signatures that activate convergent PI3K signaling pathways. Appropriately powered canine studies take a comparative genomics approach, informing our research into human angiosarcomas. The cause of most sporadic angiosarcomas is unknown. Moreover, no therapeutic targets have been identified to improve outcomes. This study hypothesizes that the activation of PIK3CA mutations contributes to the molecular programs that modulate the immune niche in angiosarcoma.
We first induced PIK3CA hotspot mutations (H1047R) in canine hemangiosarcoma cell line DHSA-1426 using CRISPR/Cas9. We found that PI3K-alpha selective inhibitor BYL719 at 10uM decreased cell proliferation of PIK3CA mutant cells by 40-50% compared with that of wild-type cells. In comparison, no significant difference was observed between mutant and wild-type cells treated with pan PI3K inhibitor, ZSTK474. Our western blot data showed an increase in γH2AX, a marker of DNA damage, in mutant cells when treated with BYL719 in a dose-dependent manner. BYL719 inhibited the phosphorylation of AKT and ERK in PIK3CA mutant tumor cells. Our RNA-seq transcriptomic data analysis revealed that PIK3CA mutations altered gene regulation programs associated with lipid biosynthesis, including phosphatidylinositol, DNA replication, angiogenic and vascular functions, and immune regulation. These data suggest that the activation of the PI3K pathway is essential for tumor cell growth and that PI3K-alpha selective inhibitor interferes with PIK3CA mutation-induced pathways, including AKT and ERK, through DNA damage-dependent mechanism in angiosarcoma.
Our ongoing work is to determine if PIK3CA mutant tumor cells have cell-autonomous capacity to govern hematopoietic progenitors and immune cells, potentially establishing the tumor immune niche. It also includes establishing single-cell gene expression profiles to identify distinct cell clusters between PIK3CA mutant and wild-type cells, along with chromatin accessibility landscape using ATAC-seq. Tumorigenic capacity and immune regulatory mechanisms of PIK3CA mutations will be determined in angiosarcoma xenograft models.
Citation Format: Emma Kozurek, Zhiyan Silvia Liu, Hai Dang Nguyen, Jong Hyuk Kim. Targeting PI3K pathway to reprogram the tumor immune niche in angiosarcoma [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 2660.