Abstract 902: Identification, characterization, and targeting of desmoplastic small round cell tumor cancer stem cell-like cells

• Published in: Cancer research (Chicago, Ill.) Vol. 82; no. 12_Supplement; p. 902
• Main Authors: Magrath, Justin W., Hartono, Alifiani B., Lee, Sean B.
• Format: Journal Article
• Language: English
• Published: 15-06-2022
• ISSN: 1538-7445; 1538-7445
• DOI: 10.1158/1538-7445.AM2022-902

Desmoplastic Small Round Cell Tumor (DSRCT) is a rare and aggressive form of pediatric cancer caused by a translocation between chromosomes 11 and 22, creating the novel EWSR1-WT1 fusion gene. Current therapy including surgery and the P6 chemotherapy regimen is insufficient, leading to a 5-year survival rate of only 15-25%. One potential explanation for this poor prognosis is the existence of a cancer stem cell (CSC) population with the ability to resist chemotherapy and cause both tumor recurrence and metastasis. While a CSC population has been identified in the closely related Ewing Sarcoma, most commonly caused by the EWSR1-FLI1 fusion gene, no CSC population has yet been identified in DSRCT. In this study, novel culture conditions were developed that enabled the formation of tumorspheres in vitro in the two commonly available DSRCT cell lines: JN-DSRCT-1 and BER-DSRCT. These novel culture conditions led to upregulation of stemness genes at the RNA and protein level including NANOG and SOX2, two genes that are associated with poor survival outcomes in TCGA sarcomas data. CCK-8 assay demonstrated an increased chemoresistance for tumorspheres versus normal adherent culture especially for doxorubicin, which was confirmed by reduction in PARP cleavage. This chemoresistance may be partially explained by a more quiescent CSC state as shown by reduced cell proliferation and a lower percentage of cells in the S and G2/M phases. However, cells grown in tumorspheres still robustly formed tumors in vivo, thus demonstrating the two hallmark CSC traits of chemoresistance and tumor formation. RNA-seq was performed to elucidate key differences between the adherent and sphere culture conditions and identify potential targets for the therapeutically important CSC-like population. Overrepresentation analysis and gene set enrichment analysis both showed upregulation of pathways related to chromatin assembly and disassembly, suggesting epigenetic changes as DSRCT cells move to a more stem-like state. RNA-seq further revealed kinases upregulated in tumorspheres including B-lymphocyte kinase (BLK) which previous studies have demonstrated is oncogenic, regulated by EWSR1-WT1, and not necessary for normal survival. BLK knockdown reduced CSC-like properties including abrogation of tumorsphere formation and reduction in the levels of SOX2 and NANOG. Together, this work for the first time identifies a CSC-like population in DSRCT and BLK as a potential DSRCT CSC target.
Citation Format: Justin W. Magrath, Alifiani B. Hartono, Sean B. Lee. Identification, characterization, and targeting of desmoplastic small round cell tumor cancer stem cell-like 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 902.