Abstract 3583: Enzalutamide and flutamide induce cytotoxicity in desmoplastic small round cell tumor independent of the androgen receptor

Abstract Desmoplastic Small Round Cell Tumor (DSRCT) is a rare, pediatric cancer caused by the EWSR1: : WT1 fusion protein. DSRCT predominantly occurs in males, which comprise 80-90% of the patient population. While the reason for the male prevalence remains unknown, one hypothesis is that the androgen receptor (AR), when stimulated by testosterone in males, plays a critical role in DSRCT tumor growth. As a rare pediatric cancer, DSRCT model systems including cell lines and patient-derived xenografts are scarce. Further, DSRCT cell lines have been thought to seed xenograft tumors poorly, with studies commonly using 5-10 million cells for one xenograft. Using a recently established DSRCT cancer stem cell (CSC) model, we sought to establish DSRCT xenografts from fewer cells to enable large-scale xenograft feasibility and reliability. To our surprise, we were able to consistently seed tumors with as few as 100 cells, not only from CSC spheres but also from standard adherent cells. We hypothesized that mouse sex may explain our ability to seed xenografts with so few cells, as many previous studies have utilized female mice. This observation led us to comprehensively investigate the role of the AR in DSRCT. Here, we demonstrate that AR is highly expressed in DSRCT relative to other fusion-driven sarcomas and that the AR antagonists - enzalutamide and flutamide - reduce DSRCT growth. We further elucidate a novel interaction between AR and EWSR1: : WT1, which may explain their co-occupancy in a subset of regulatory genomic regions. However, despite these findings, which suggest an essential role for AR in DSRCT, we find that DSRCT cell lines can form xenografts in female mice at the same rate as male mice and AR depletion does not significantly alter DSRCT growth in vitro. Further, we demonstrate that AR antagonists remain effective in DSRCT cells depleted of AR, establishing an AR-independent mechanism of action. Intriguingly, high-dose enzalutamide treatment reduces EWSR1: : WT1 oncoprotein expression and could explain its toxicity. DSRCT cells express high levels of NR3 nuclear receptors, including the glucocorticoid receptor (GR). Enzalutamide was shown to act on GR in AR-negative prostate cancer cell lines, which could possibly explain its effect on DSRCT independent of AR. Further examination of this mechanism may provide promising therapeutic implications for DSRCT and other fusion proteins driven by the EWSR1 promoter. Citation Format: Justin W. Magrath, Ilon N. Goldberg, Danh D. Truong, Alifinai B. Hartono, Shruthi Sanjitha Sampath, Chandler E. Jackson, Anushka Ghosh, Derrick L. Cardin, Haitao Zhang, Joseph A. Ludiwg, Sean B. Lee. Enzalutamide and flutamide induce cytotoxicity in desmoplastic small round cell tumor independent of the androgen receptor abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 3583.