Rask, G. C. | Search bioRxiv

bioRxiv2025

N'-(1-phenylethylidene)-benzohydrazide cytotoxicity is LSD1 independent and linked to Fe-S cluster disruption in Ewing sarcoma

The noncompetitive LSD1 inhibitors SP-2509 and SP-2577 are N-(1-phenylethylidene)-benzohydrazides that display potent activity in Ewing sarcoma. They block transcriptional regulation of the causative oncogenic fusion protein, EWSR1::FLI1, and cause cell death. However, SP-2509 and SP-2577 are the only LSD1 inhibitors active in Ewing sarcoma; other LSD1 inhibitors have little effect. Studies from our group and others suggest SP-2509 activity may result from off-target activity affecting the mitochondria. Here we identified potential off-target mechanisms of N-(1-phenylethylidene)-benzohydrazides using an unbiased approach, cellular thermal shift assay coupled to mass spectrometry (CETSA-MS). Interestingly, this revealed significant destabilization of the electron transport chain complex III protein ubiquinol-cytochrome c reductase (UQCRFS1). We find that UQCRFS1 destabilization is likely linked to impaired iron-sulfur (Fe-S) cofactor binding, and that SP-2509 broadly destabilizes cellular Fe-S proteins. Using both chemical and genetic tools, we show that SP-2509 mediated cell death is LSD1 independent and instead requires a N-(2-hydroxybenzylidene)hydrazide. Our studies suggest this core moiety alters iron metabolism in the cell. Importantly, we also find that the reversal of EWSR1::FLI1 transcriptional regulation by SP-2509 is independent from LSD1 inhibition. This unique activity is instead associated with the N-(2-hydroxybenzylidene)-hydrazide core and destabilization of Fe-S proteins. These findings reveal a novel mechanism of action for this class of compounds and raise additional questions regarding how EWSR1::FLI1 transcriptional regulation is linked to Fe-S biogenesis, the precise mechanisms of cell death, the biological features of susceptible cancer cells, and strategies for clinical translation.

pharmacology and toxicology↗

bioRxiv2024

Seclidemstat blocks the transcriptional function of multiple FET-fusion oncoproteins

Genes encoding the RNA-binding proteins FUS, EWSR1, and TAF15 (FET proteins) are involved in chromosomal translocations in rare sarcomas. FET-rearranged sarcomas are often aggressive malignancies affecting patients of all ages. New therapies are needed. These translocations fuse the 5 portion of the FET gene with a 3 partner gene encoding a transcription factor (TF). The resulting fusion proteins are oncogenic TFs with a FET protein low complexity domain (LCD) and a DNA binding domain. FET fusion proteins have proven stubbornly difficult to target directly and promising strategies target critical co-regulators. One candidate is lysine specific demethylase 1 (LSD1). LSD1 is recruited by multiple FET fusions, including EWSR1::FLI1. LSD1 promotes EWSR1::FLI1 activity and treatment with the noncompetitive inhibitor SP-2509 blocks EWSR1::FLI1 transcriptional function. A similar molecule, seclidemstat (SP-2577), is currently in clinical trials for FET-rearranged sarcomas (NCT03600649). However, whether seclidemstat has pharmacological activity against FET fusions has not been demonstrated. Here, we evaluate the in vitro potency of seclidemstat against multiple FET-rearranged sarcoma cell lines, including Ewing sarcoma, desmoplastic small round cell tumor, clear cell sarcoma, and myxoid liposarcoma. We also define the transcriptomic effects of seclidemstat treatment and evaluated the activity of seclidemstat against FET fusion transcriptional regulation. Seclidemstat showed potent activity in cell viability assays across FET-rearranged sarcomas and disrupted the transcriptional function of all tested fusions. Though epigenetic and targeted inhibitors are unlikely to be effective as a single agents in the clinic, these data suggest seclidemstat remains a promising new treatment strategy for patients with FET-rearranged sarcomas. SIGNIFICANCEHere, we show the noncompetitive inhibitor, seclidemstat, has in vitro activity against multiple FET fusion proteins that cause a number of rare and aggressive sarcomas. These data represent one of the largest analyses of FET fusion activity across multiple malignancies and are a valuable resource for those studying FET-rearranged sarcomas.

cancer biology↗