Abstract 4873: Therapeutic targeting of LSD1 in Ewing sarcoma with SP-2509

Abstract

Abstract Objective: Multimodal regimes remain the cornerstone treatment for Ewing sarcoma (ES), the second most common solid bone malignancy diagnosed in pediatric and young adolescent populations. We have reached a therapeutic ceiling with conventional cytotoxic agents, highlighting the need to adopt novel approaches specifically targeting the drivers of ES oncogenesis. As LSD1 (Lysine Specific Demethylase 1) is highly expressed in ES tumors, with elevated expression levels associated with worse overall survival, this study examined biomarkers of sensitivity/mechanisms of cytotoxicity to targeted LSD1 inhibition using SP-2509 (reversible LSD1 inhibitor). Methods: The antiproliferative effects of SP-2509 were determined through Cell Titre Glo assays following 72hrs of treatment in a panel of 17 ES cell lines with varying STAG2/TP53 mutational status and basal LSD1 expression levels. RNA-seq analysis of six ES cell lines -/+ SP-2509 treatment (2μM) was also conducted. Results: Innate resistance to SP-2509 was not observed in our cell line cohort (72hr IC50:81nM-1593nM). In contrast, resistance to the clinical next-generation LSD1 irreversible inhibitor GSK-LSD1 was observed across multiple cell lines (144hr IC50>300μM). Although TP53/STAG2 mutational status and basal LSD1 mRNA/protein levels did not correlate with SP-2509 response, induction of LSD2 (homologue of LSD1) following SP-2509 treatment was strongly associated with SP-2509 hypersensitivity (R2=0.562). shRNA mediated knockdown of LSD2 significantly reduced the cytotoxic effects of SP-2509 (4.3 fold IC50 increase) only in hypersensitive cell lines. Mechanistically, RNA-seq analysis revealed that SP-2509 imparts apoptosis through engagement of the endoplasmic reticulum stress pathway, with hypersensitive cell lines sharing similar transcriptomic profiles. In addition, ETS1/HIST1H2BM were specifically induced/repressed, respectively, following SP-2509 treatment only in our hypersensitive cell lines. Finally, we demonstrate that the transcriptional profile driven by SP-2509 strongly mirrors LSD1 genetic depletion. Conclusion: Our findings provide key insights into the mechanisms of SP-2509 cytotoxicity as well as biomarkers that can be used to predict LSD1 inhibitor sensitivity in ES. Citation Format: Kathleen Pishas, Megann Boone, Sunil Sharma, Stephen Lessnick. Therapeutic targeting of LSD1 in Ewing sarcoma with SP-2509 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4873.