Mutations of the SWI/SNF chromatin remodeling complex occur in 20% of all human cancers, including ovarian cancer. Approximately half of ovarian clear cell carcinomas (OCCC) carry mutations in the SWI/SNF subunit ARID1A, while small cell carcinoma of the ovary hypercalcemic type (SCCOHT) presents with inactivating mutations of the SWI/SNF ATPase SMARCA4 alongside epigenetic silencing of the ATPase SMARCA2. Loss of these ATPases disrupts SWI/SNF chromatin remodeling activity and may also interfere with the function of other histone-modifying enzymes that associate with or are dependent on SWI/ SNF activity. One such enzyme is lysine-specific histone demethylase 1 (LSD1/KDM1A), which regulates the chromatin landscape and gene expression by demethylating proteins such as histone H3. Cross-cancer analysis of the TCGA database shows that LSD1 is highly expressed in SWI/SNF-mutated tumors. SCCOHT and OCCC cell lines have shown sensitivity to the reversible LSD1 inhibitor SP-2577 (Seclidemstat), suggesting that SWI/SNFdeficient ovarian cancers are dependent on LSD1 activity. Moreover, it has been shown that inhibition of LSD1 stimulates interferon (IFN)-dependent anti-tumor immunity through induction of endogenous retroviral elements and may thereby overcome resistance to checkpoint blockade. In this study, we investigated the ability of SP-2577 to promote anti-tumor immunity and T-cell infiltration in SCCOHT and OCCC cell lines. We found that SP-2577 stimulated IFN-dependent anti-tumor immunity in SCCOHT and promoted the expression of PD-L1 in both SCCOHT and OCCC. Together, these findings suggest that the combination therapy of SP-2577 with checkpoint inhibitors may induce or augment immunogenic responses of SWI/SNF-mutated ovarian cancers and warrants further investigation.

Chromatin remodeling SWItch/Sucrose-NonFermentable (SWI/SNF) complexes, initially identified in yeast 20 years ago, are evolutionarily conserved multi-subunit protein complexes that use the energy from hydrolysis of adenosine triphosphate (ATP) to remodel nucleosome structure and modulate transcription. Mutations in proteins of SWI/SNF complexes occur in 20% of human cancers including ovarian cancer (OC). Approximately 50% of ovarian clear cell carcinoma (OCCC) carries mutations in the SWI/SNF subunit ARID1A while small cell carcinoma of the ovary hypercalcemic type (SCCOHT) is driven primarily by genetic inactivation of the SWI/SNF ATPase SMARCA4 (BRG1) alongside epigenetic silencing of the homolog ATPase SMARCA2 (BRM). Dual loss of these ATPases disrupts SWI/SNF chromatin remodeling activity and may alsointerfere with the function of other histone-modifying enzymes that associate with or are dependent on SWI/SNF activity. One such enzyme is lysine-specific histone demethylase 1 (LSD1/KDM1A) which regulates the chromatin landscape and gene expression by demethylating proteins, including histone H3. LSD1 associates with epigenetic complexes such as the nucleosome remodeling deacetylase complex (NuRD) and SWI/SNF to inhibit the transcription of genes involved in tumor suppression and cell differentiation. TGCA analysis of human cancers shows that LSD1 is highly expressed in SWI/SNF-mutated tumors. Further, SCCOHT and OCCC cell lines show low nM IC 50 s for the reversible LSD1 inhibitor SP-2577 (Seclidemstat, currently in clinical phase I trials), supporting that these SWI/SNF-deficient ovarian cancers are dependent on LSD1 activity. Recently, it has been also shown that inhibition of LSD1 stimulates interferon (IFN)-dependent anti-tumor immunity through induction of Endogenous Retroviruses Elements (ERVs) and may thereby overcome resistance to checkpoint blockade. Additionally, SCCOHTs have been shown to exhibit an immune-active tumor microenvironment with PD-L1 expression in both tumor and stromal cells that strongly correlated with T cell infiltration. Thus, in this study we investigated the ability of SP-2577 to promote anti-tumor immunity and T cell infiltration in SWI/SNF-mutant SCCOHT and OCCC models. Our data shows that the reversible LSD1 inhibitor SP-2577 stimulates IFN-dependent anti-tumor immunity in SCCOHT cells in vitro in a 3D immuneorganoid platform. Additionally, SP-2577 promoted the expression of PD-L1 in both SCCOHT and OCCC models. Together our findings suggest that SP-2577 and checkpoint inhibitors as a therapeutic combination may induce or augment immunogenic responses in these tumors.

The central role of β-catenin in the Wnt pathway makes it an attractive therapeutic target for cancers driven by aberrant Wnt signaling. We recently developed a small molecule inhibitor, BC-2059, that promotes apoptosis by disrupting the β-catenin /transducin β-like 1 (TBL1) complex through an unknown mechanism of action. In this study, we show that BC-2059 directly interacts with high affinity for TBL1 when in complex with β-catenin. We identified two amino acids in a hydrophobic pocket of TBL1 that are required for binding with β-catenin, and computational modeling predicted that BC-2059 interacts at the same hydrophobic pocket.Although this pocket in TBL1 is involved in binding with NCoR/SMRT complex members GSP2 and SMRT and p65 NFkB subunit, BC-2059 failed to disrupt the interaction of TBL1 with either NCoR/SMRT or NFkB. Together, our results show that BC-2059 selectively targets TBL1/β-catenin protein complex, suggesting BC-2059 as a therapeutic for tumors with deregulated Wnt signaling pathway.