Abstract 1196: The epigenetic impact and therapeutic opportunity of AR-directed therapy for DSRCT
Authors: Truong Danh , Lamhamedi-Cherradi Salah-Eddine , Maitituoheti Mayinuer , Beird Hannah C. , Arslan Emre , Wu Chia-Chin , Krishnan Sandhya , Ingram Davis , Futreal P Andrew , Titus Mark , Rai Kunal , Lazar Alexander , MacLeod A Robert , Ratan Ravin , Livingston John Andrew , Daw Najat , Hayes-Dixon Andrea , Ludwig Joseph 
Published: April 2023

Abstract
Desmoplastic small round cell tumor (DSRCT) is a rare, usually incurable, aggressive sarcoma subtype that occurs predominantly in adolescent and young adult (AYA) males. At diagnosis, most present with hundreds of intraabdominal nodules composed of malignant cells that harbor a EWSR1-WT1 chromosomal translocation and resultant fusion protein (FP). It was shown that subset of DSRCT cells (mostly of epithelial histotype) highly express the androgen receptor (AR), a key epigenetic driver of prostate cancer (PC). To assess the role of AR more comprehensively in DSRCT, we tested if AR antagonists curb cell proliferation and tumor growth. Both enzalutamide and AR-antisense therapy blocked DHT-induced cell proliferation and reduce xenograft tumor burden. Next, to mechanistically interrogate AR’s oncogenic effects, we performed single-nuclei RNA-seq (snRNA-eq) and chromatin immunoprecipitation sequencing (ChIP-seq) on frozen patient specimens. Those studies revealed a surprising epigenetic similarity between DSRCT to PC. Though overlap exists in the DNA binding MOTIFs of AR in DSRCT and PC, our ChIP-seq results, interestingly, revealed DSRCT-specific AR DNA binding sites adjacent to key oncogenic regulators, including FOXF1 and WT1 (the C-terminal partner of the pathognomonic FP). To our surprise, we identified a subset of DSRCT samples that underwent partial neuroendocrine (NE) epigenetic reprogramming, akin to what occurs in ~1/3 of castrate-resistant PC (CRPC). Since androgen deprivation therapy (ADT) isn’t yet a standard treatment yet for DSRCT, it remains an enigma why DSRCT would spontaneously undergo NE reprogramming or how this might affect ADT sensitivity. To address this, nine DSRCT patient samples were profiled using snRNA-seq. Sub-clustering revealed epithelial, mesenchymal, or NE signatures and marked inter-patient and intra-tumoral heterogeneity. Notably, five of nine patients exhibited NE markers (SYP, ENO2, CHG, FOXA2, ASCL1, and SOX2), while three expressed epithelial markers (MUC1, MUC6, KRT18, KRT23, CDH1). One patient exhibited a hybrid AR indifferent phenotype. While strikingly different from PC morphologically and phenotypically, our data suggest that DSRCT is a second androgen-stimulated malignancy. Shared dependence upon AR for tumor growth and survival provides an exciting opportunity to prospectively study AR signaling in a different cancer type and younger DSRCT-stricken patient population. Ongoing work will determine if DSRCT undergoes dedifferentiation towards a more stem-like cell as an intermediary step before undergoing neural lineage commitment or transdifferentiation directly from an epithelial cell type towards a neuroendocrine cell fate. We are also exploring whether the FP acts as a Pioneer factor to direct AR towards DSRCT-specific androgen response elements that explain this sarcoma subtype’s unique clinical presentation.
Citation Format: Danh Truong, Salah-Eddine Lamhamedi-Cherradi, Mayinuer Maitituoheti, Hannah C. Beird, Emre Arslan, Chia-Chin Wu, Sandhya Krishnan, Davis Ingram, P Andrew Futreal, Mark Titus, Kunal Rai, Alexander Lazar, A Robert MacLeod, Ravin Ratan, John Andrew Livingston, Najat Daw, Andrea Hayes-Dixon, Joseph Ludwig. The epigenetic impact and therapeutic opportunity of AR-directed therapy for DSRCT [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1196.