CtBP-a targetable dependency for tumor-initiating cell activity and metastasis in pancreatic adenocarcinoma

Identification and characterization of a new potent inhibitor targeting CtBP1/BARS in melanoma cells

BACKGROUND

The C-terminal-binding protein 1/brefeldin A ADP-ribosylation substrate (CtBP1/BARS) acts both as an oncogenic transcriptional co-repressor and as a fission inducing protein required for membrane trafficking and Golgi complex partitioning during mitosis, hence for mitotic entry. CtBP1/BARS overexpression, in multiple cancers, has pro-tumorigenic functions regulating gene networks associated with "cancer hallmarks" and malignant behavior including: increased cell survival, proliferation, migration/invasion, epithelial-mesenchymal transition (EMT). Structurally, CtBP1/BARS belongs to the hydroxyacid-dehydrogenase family and possesses a NAD(H)-binding Rossmann fold, which, depending on ligands bound, controls the oligomerization of CtBP1/BARS and, in turn, its cellular functions. Here, we proposed to target the CtBP1/BARS Rossmann fold with small molecules as selective inhibitors of mitotic entry and pro-tumoral transcriptional activities.

METHODS

Structured-based screening of drug databases at different development stages was applied to discover novel ligands targeting the Rossmann fold. Among these identified ligands, N-(3,4-dichlorophenyl)-4-{[(4-nitrophenyl)carbamoyl]amino}benzenesulfonamide, called Comp.11, was selected for further analysis. Fluorescence spectroscopy, isothermal calorimetry, computational modelling and site-directed mutagenesis were employed to define the binding of Comp.11 to the Rossmann fold. Effects of Comp.11 on the oligomerization state, protein partners binding and pro-tumoral activities were evaluated by size-exclusion chromatography, pull-down, membrane transport and mitotic entry assays, Flow cytometry, quantitative real-time PCR, motility/invasion, and colony assays in A375MM and B16F10 melanoma cell lines. Effects of Comp.11 on tumor growth in vivo were analyzed in mouse tumor model.

RESULTS

We identify Comp.11 as a new, potent and selective inhibitor of CtBP1/BARS (but not CtBP2). Comp.11 directly binds to the CtBP1/BARS Rossmann fold affecting the oligomerization state of the protein (unlike other known CtBPs inhibitors), which, in turn, hinders interactions with relevant partners, resulting in the inhibition of both CtBP1/BARS cellular functions: i) membrane fission, with block of mitotic entry and cellular secretion; and ii) transcriptional pro-tumoral effects with significantly hampered proliferation, EMT, migration/invasion, and colony-forming capabilities. The combination of these effects impairs melanoma tumor growth in mouse models.  CONCLUSIONS: This study identifies a potent and selective inhibitor of CtBP1/BARS active in cellular and melanoma animal models revealing new opportunities to study the role of CtBP1/BARS in tumor biology and to develop novel melanoma treatments.

E3 ubiquitin ligase FBXW11 as a novel inflammatory biomarker is associated with immune infiltration and NF-κB pathway activation in pancreatitis and pancreatic cancer

BACKGROUND

Pancreatic cancer (pancreatic ductal adenocarcinoma, PDAC) is an aggressive disease with an overall poor prognosis. Pancreatitis is a major risk factor for the development of PDAC. Due to the lack of reliable and accurate biomarkers, the diagnosis, treatment, and prognosis of PDAC face great challenges. It is of great significance to elucidate the pathogenesis of PDAC and explore novel inflammatory biomarkers.

METHODS

We identified E3 ubiquitin ligases associated with pancreatic inflammation by combining multiple GEO datasets and UbiNet 2.0, and integrating the WGCNA algorithm and Limma R package. A risk score model for PDAC patients was established by using LASSO regression. We investigated the correlation between FBXW11 and immune cell infiltration using CIBERSORT, mMCP-counter, ImmuCellAI-mouse, QUANTISEQ, and TIMER algorithms, based on GEO, ArrayExpress, and TCGA datasets. We used Ubibrowser 2.0 to predict potential substrates for FBXW11. WikiPathway, MSigDB Hallmark, and Elsevier pathway analysis of FBXW11 key substrates were also performed using the EnrichR database. We detected protein expression through IHC, immunofluorescence, and western blot in the cerulein-induced acute pancreatitis mouse model.

RESULTS

We first identified that FBXW11 exhibited a clear tendency to gradually increase in normal, pancreatitis, and PDAC patients. The validation analysis revealed that the FBXW11 protein exhibited significantly high expression in cerulein-induced acute pancreatitis mice, with its distribution primarily observed in the cytoplasm. Simultaneously, we developed a risk model utilizing the genes associated with FBXW11 to forecast the outcome of patients with PDAC and the likelihood of pancreatitis advancing to pancreatic cancer. Functional analysis showed that FBXW11, as a novel inflammatory biomarker, had a significant positive correlation with macrophage infiltration and the NF-κB signaling pathway. Finally, the western blot assay of the NF-κB signaling pathway in pancreatic tissues demonstrated that high activation of NF-κB was correlated with high expression of FBXW11.

CONCLUSIONS

Our research not only provides evidence for FBXW11 as a novel inflammatory biomarker but also provides new insights into the research and clinical treatment of pancreatic cancer.

Coordinate transcriptional regulation of ErbB2/3 by C-terminal binding protein 2 signals sensitivity to ErbB2 inhibition in pancreatic adenocarcinoma

There is a critical need to identify new therapeutic vulnerabilities in pancreatic ductal adenocarcinoma (PDAC). Transcriptional co-regulators C-terminal binding proteins (CtBP) 1 and 2 are highly overexpressed in human PDAC, and CRISPR-based homozygous deletion of Ctbp2 in a mouse PDAC cell line (CKP) dramatically decreased tumor growth, reduced metastasis, and prolonged survival in orthotopic mouse allografts. Transcriptomic profiling of tumors derived from CKP vs. Ctbp2-deleted CKP cells (CKP/KO) revealed significant downregulation of the EGFR-superfamily receptor Erbb3, the heterodimeric signaling partner for both EGFR and ErbB2. Compared with CKP cells, CKP/KO cells also demonstrated reduced Erbb2 expression and did not activate downstream Akt signaling after stimulation of Erbb3 by its ligand neuregulin-1. ErbB3 expression in human PDAC cell lines was similarly dependent on CtBP2 and depletion of ErbB3 in a human PDAC cell line severely attenuated growth, demonstrating the critical role of ErbB3 signaling in maintaining PDAC cell growth. Sensitivity to the ErbB2-targeted tyrosine kinase inhibitor lapatinib, but not the EGFR-targeted agent erlotinib, varied in proportion to the level of ErbB3 expression in mouse and human PDAC cells, suggesting that an ErBb2 inhibitor can effectively leverage CtBP2-driven transcriptional activation of physiologic ErbB2/3 expression and signaling in PDAC cells for therapeutic benefit.

Combined Targeting of NAD Biosynthesis and the NAD-dependent Transcription Factor C-terminal Binding Protein as a Promising Novel Therapy for Pancreatic Cancer

Cancer therapies targeting metabolic derangements unique to cancer cells are emerging as a key strategy to address refractory solid tumors such as pancreatic ductal adenocarcinomas (PDAC) that exhibit resistance to extreme nutrient deprivation in the tumor microenvironment. Nicotinamide adenine dinucleotide (NAD) participates in multiple metabolic pathways and nicotinamide phosphoribosyl transferase (NAMPT) is one of the key intracellular enzymes that facilitate the synthesis of NAD. C-terminal binding proteins 1 and 2 (CtBP) are paralogous NAD-dependent oncogenic transcription factors and dehydrogenases that nucleate an epigenetic complex regulating a cohort of genes responsible for cancer proliferation and metastasis. As adequate intracellular NAD is required for CtBP to oligomerize and execute its oncogenic transcriptional coregulatory activities, we hypothesized that NAD depletion would synergize with CtBP inhibition, improving cell inhibitory efficacy. Indeed, depletion of cellular NAD via the NAMPT inhibitor GMX1778 enhanced growth inhibition induced by either RNAi-mediated CtBP1/2 knockdown or the CtBP dehydrogenase inhibitor 4-chlorophenyl-2-hydroxyimino propanoic acid as much as 10-fold in PDAC cells, while untransformed pancreatic ductal cells were unaffected. The growth inhibitory effects of the NAMPT/CtBP inhibitor combination correlated pharmacodynamically with on-target disruption of CtBP1/2 dimerization, CtBP2 interaction with the CoREST epigenetic regulator, and transcriptional activation of the oncogenic target gene TIAM1. Moreover, this same therapeutic combination strongly attenuated growth of PDAC cell line xenografts in immunodeficient mice, with no observable toxicity. Collectively, our data demonstrate that targeting CtBP in combination with NAD depletion represents a promising therapeutic strategy for PDAC.

SIGNIFICANCE

Effective precision therapies are lacking in PDAC. We demonstrate that simultaneous inhibition of NAD metabolism and the oncoprotein CtBP is potently effective at blocking growth of both PDAC cells in culture and human PDAC-derived tumors in mice and should be explored further as a potential therapy for patients with PDAC.

Merging cultures and disciplines to create a drug discovery ecosystem at Virginia commonwealth university: Medicinal chemistry, structural biology, molecular and behavioral pharmacology and computational chemistry

The Department of Medicinal Chemistry, together with the Institute for Structural Biology, Drug Discovery and Development, at Virginia Commonwealth University (VCU) has evolved, organically with quite a bit of bootstrapping, into a unique drug discovery ecosystem in response to the environment and culture of the university and the wider research enterprise. Each faculty member that joined the department and/or institute added a layer of expertise, technology and most importantly, innovation, that fertilized numerous collaborations within the University and with outside partners. Despite moderate institutional support with respect to a typical drug discovery enterprise, the VCU drug discovery ecosystem has built and maintained an impressive array of facilities and instrumentation for drug synthesis, drug characterization, biomolecular structural analysis and biophysical analysis, and pharmacological studies. Altogether, this ecosystem has had major impacts on numerous therapeutic areas, such as neurology, psychiatry, drugs of abuse, cancer, sickle cell disease, coagulopathy, inflammation, aging disorders and others. Novel tools and strategies for drug discovery, design and development have been developed at VCU in the last five decades; e.g., fundamental rational structure-activity relationship (SAR)-based drug design, structure-based drug design, orthosteric and allosteric drug design, design of multi-functional agents towards polypharmacy outcomes, principles on designing glycosaminoglycans as drugs, and computational tools and algorithms for quantitative SAR (QSAR) and understanding the roles of water and the hydrophobic effect.

Metabolic modulation of CtBP dimeric status impacts the repression of DNA damage repair genes and the platinum sensitivity of ovarian cancer

Platinum drug-based chemotherapy plays a dominant role in OC (ovarian cancer) treatment. The expression of DNA damage repair (DDR) genes is critical in distinguishing drug-sensitive and drug-refractory patients, as well as in the development of drug resistance in long-term treated patients. CtBP is a highly expressed oncogene in OC and was found to repress DDR genes expression in our previous study. In the present study, the formation of CtBP dimers in live cells was studied, and the functional differences between monomeric and oligomeric CtBP were explored by CHIP-seq and RNA-seq. Besides, the dynamics of CtBP dimer formation in response to the metabolic modulation were investigated by the protein fragment complementation (PCA) assays. We show that dimerized CtBP, but not the dimerization-defective mutant, binds to and represses DDR gene expression in OC cells. Treatment of the mice tumors grown from engrafted OC cells by cisplatin disclosed that high-level CtBP expression promotes the CtBP dimerization and increases the therapeutic effect of cisplatin. Moreover, the CtBP dimerization is responsive to the intracellular metabolic status as represented by the free NADH abundance. Metformin was found to increase the dimerization of CtBP and potentiate the therapeutic effect of cisplatin in a CtBP dimerization-dependent manner. Our data suggest that the CtBP dimerization status is a potential biomarker to predict platinum drug sensitivity in patients with ovarian cancer and a target of metformin to improve the therapeutic effect of platinum drugs in OC treatment.

Molecular characterization of early breast cancer onset to understand disease phenotypes in African patients

Female breast cancer (BC) is the leading cause of cancer-related deaths worldwide with higher mortality rates and early onset in developing countries. The molecular basis of early disease onset is still elusive. We recruited 472 female breast cancer from two sub-Saharan African countries (Cameroon and Congo) between 2007 and 2018 and collected clinical data from these patients. To investigate the molecular drivers of early disease onset, we analyzed publicly available breast cancer molecular data from the cancer genome atlas (TCGA) and the gene expression omnibus (GEO) for copy number alteration, mutation and gene expression. Early BC onset (EOBRCA) (diagnosis before 45 years) was higher in African women compared with the TCGA cohort (51.7% vs 15.6%). The tumor grade, mitotic index, HER2 + phenotype, basal-like phenotype and ki67 were higher in EOBRCA for all cohorts. BC risk factors such as parity, breastfeeding early onset of menarche and use of hormonal contraceptives were significantly associated with EOBRCA (p < 0.05). EOBRCA was equally associated with copy number alterations in several oncogenes including CDH6 and FOXM1 and tumor suppressor including TGM3 and DMBT1 as well as higher TP53 mutation rates (OR: 2.93, p < 0.01). There was a significant enrichment of TGFß signaling in EOBRCA with TGM3 deletions, which was associated with high expression of all SMAD transcription factors as well as WNT ligands. The Frizzled receptors FZD1, FZD4 and FZD6 were significantly upregulated in EOBRCA, suggesting activation of non-canonical WNT signaling. Our data, suggest the implication of TGM3 deletion in early breast cancer onset. Further molecular investigations are warranted in African patients.

NADH/NAD+ binding and linked tetrameric assembly of the oncogenic transcription factors CtBP1 and CtBP2

The activation of oncogenic C-terminal binding Protein (CtBP) transcriptional activity is coupled with NAD(H) binding and homo-oligomeric assembly, although the level of CtBP assembly and nucleotide binding affinity continues to be debated. Here, we apply biophysical techniques to address these fundamental issues for CtBP1 and CtBP2. Our ultracentrifugation results unambiguously demonstrate that CtBP assembles into tetramers in the presence of saturating NAD⁺ or NADH with tetramer to dimer dissociation constants about 100 nm. Isothermal titration calorimetry measurements of NAD(H) binding to CtBP show dissociation constants between 30 and 500 nm, depending on the nucleotide and paralog. Given cellular levels of NAD⁺ , CtBP is likely to be fully saturated with NAD under physiological concentrations suggesting that CtBP is unable to act as a sensor for NADH levels.

The transrepression and transactivation roles of CtBPs in the pathogenesis of different diseases

Gene transcription is strictly controlled by transcriptional complexes, which are assemblies of transcription factors, transcriptional regulators, and co-regulators. Mammalian genomes encode two C-terminal-binding proteins (CtBPs), CtBP1 and CtBP2, which are both well-known transcriptional corepressors of oncogenic processes. Their overexpression in tumors is associated with malignant behavior, such as uncontrolled cell proliferation, migration, and invasion, as well as with an increase in the epithelial-mesenchymal transition. CtBPs coordinate with other transcriptional regulators, such as histone deacetylases (HDACs) and histone acetyltransferases (p300 and CBP [CREBP-binding protein]) that contain the PXDLS motif, and with transcription factors to assemble transcriptional complexes that dock onto the promoters of genes to initiate gene transcription. Emerging evidence suggests that CtBPs function as both corepressors and coactivators in different biological processes ranging from apoptosis to inflammation and osteogenesis. Therapeutic targeting of CtBPs or the interactions required to form transcriptional complexes has also shown promising effects in preventing disease progression. This review summarizes the most recent progress in the study of CtBP functions and therapeutic inhibitors in different biological processes. This knowledge may enable a better understanding of the complexity of the roles of CtBPs, while providing new insights into therapeutic strategies that target CtBPs.

Extraction of high-quality RNA from mouse pancreatic tumors

Extraction of high-quality RNA from pancreatic tumors for sequencing purposes is technically challenging, as the pancreas is an organ rich in ribonucleases. The majority of the established RNA isolation protocols for use with primary pancreatic tissue involve perfusion of RNA stabilizing reagent into the pancreatic tissue to protect RNA integrity before extraction. However, the additional time needed for this procedure can actually lead to further RNA degradation. We optimized a protocol suitable for high quality RNA isolation from mouse pancreatic tumors that is a simple, fast, and inexpensive modification of existing methods, combining the use of liquid nitrogen and guanidinium thiocyanate-chloroform extraction. Through this procedure, the mean RNA Integrity Number value obtained for RNA isolated from pancreatic tumors was 9.0, and was reproducibly suitable for RNAseq and qPCR.•

a protocol suitable for high quality RNA isolation from mouse pancreatic tumors as well as normal pancreas

•

combining the use of liquid nitrogen and guanidinium thiocyanate-chloroform extraction

NAD(H) phosphates mediate tetramer assembly of human C-terminal binding protein (CtBP)

C-terminal binding proteins (CtBPs) are cotranscriptional factors that play key roles in cell fate. We have previously shown that NAD(H) promotes the assembly of similar tetramers from either human CtBP1 and CtBP2 and that CtBP2 tetramer destabilizing mutants are defective for oncogenic activity. To assist structure-based design efforts for compounds that disrupt CtBP tetramerization, it is essential to understand how NAD(H) triggers tetramer assembly. Here, we investigate the moieties within NAD(H) that are responsible for triggering tetramer formation. Using multiangle light scattering (MALS), we show that ADP is able to promote tetramer formation of both CtBP1 and CtBP2, whereas AMP promotes tetramer assembly of CtBP1, but not CtBP2. Other NAD(H) moieties that lack the adenosine phosphate, including adenosine and those incorporating nicotinamide, all fail to promote tetramer assembly. Our crystal structures of CtBP1 with AMP reveal participation of the adenosine phosphate in the tetrameric interface, pinpointing its central role in NAD(H)-linked assembly. CtBP1 and CtBP2 have overlapping but unique roles, suggesting that a detailed understanding of their unique structural properties might have utility in the design of paralog-specific inhibitors. We investigated the different responses to AMP through a series of site-directed mutants at 13 positions. These mutations reveal a central role for a hinge segment, which we term the 120s hinge that connects the substrate with coenzyme-binding domains and influences nucleotide binding and tetramer assembly. Our results provide insight into suitable pockets to explore in structure-based drug design to interfere with cotranscriptional activity of CtBP in cancer.

Cryo-EM structure of CtBP2 confirms tetrameric architecture

C-terminal binding proteins 1 and 2 (CtBP1 and CtBP2) are transcriptional regulators that activate or repress many genes involved in cellular development, apoptosis, and metastasis. NADH-dependent CtBP activation has been implicated in multiple types of cancer and poor patient prognosis. Central to understanding activation of CtBP in oncogenesis is uncovering how NADH triggers protein assembly, what level of assembly occurs, and if oncogenic activity depends upon such assembly. Here, we present the cryoelectron microscopic structures of two different constructs of CtBP2 corroborating that the native state of CtBP2 in the presence of NADH is tetrameric. The physiological relevance of the observed tetramer was demonstrated in cell culture, showing that CtBP tetramer-destabilizing mutants are defective for cell migration, transcriptional repression of E-cadherin, and activation of TIAM1. Together with our cryoelectron microscopy studies, these results highlight the tetramer as the functional oligomeric form of CtBP2.

Low expression of CTBP2 and CASP8AP2 predicts risk of relapse in childhood B-cell precursor acute lymphoblastic leukemia: a retrospective cohort study

CtBP is a known corepressor abundantly expressed in cancer and regulates genes involved in cancer initiation, progression, and metastasis. This study aimed to investigate the prognostic significance of CTBP2 expression in a cohort of pediatric patients with B cell precursor acute lymphoblastic leukemia (BCP-ALL). It further evaluated the role of combined CTBP2 and CASP8AP2 expression in risk of relapse of BCP-ALL. The expression of CTBP2 mRNA was retrospectively detected by a qRT-PCR approach in bone marrow samples from 104 children with newly diagnosed BCP-ALL. CASP8AP2 was assessed simultaneously in the 100 patients included in this study. The receiver operating characteristic (ROC) curve analysis determined the cut off levels for CTBP2 and CASP8AP2 expression with good predictive significance for relapse of BCP-ALL. Patients with low CTBP2 expression had inferior relapse-free survival (RFS) and event-free survival (EFS) when compared to patients with high-CTBP2 expression. The expression level of CTBP2 was significantly associated with CASP8AP2 expression (r = 0.449, P < 0.001). Patients were stratified into three groups according to the combined evaluation of the two gene expression, and patients with simultaneous low-expression had the worst outcome (6-year RFS: 64.6%±12.8%, P < 0.001). Multivariate analysis demonstrated the expression of CTBP2 and CASP8AP2, minimal residual disease (MRD) at day 33 remained as independent prognostic factors for RFS. Based on the final Cox hazards model, we proposed an algorithm to calculate the risk index, which was more precise for predicting relapse. In conclusion, low expression of CTBP2 and CASP8AP2 correlated with poor outcome and predicted risk of relapse in pediatric BCP-ALL.

CtBP2 interacts with ZBTB18 to promote malignancy of glioblastoma

OBJECTIVE

To investigate how the interaction of CtBP2 with ZBTB18 affect glioblastoma (GBM).

METHODS

Western blotting was performed to detect CtBP2 and ZBTB18 expression in GBM and normal brain tissues (NBT). U-87 MG cells were transfected with ZBTB18 CRISPR activation plasmid, CtBP2 shRNA with/without ZBTB18 shRNA. The biological characteristics were detected by EdU assay, MTT, Wound-healing, Transwell, TUNEL staining, and Flow cytometry. Furthermore, U-87 MG cells transfected with CtBP2 shRNA and/or ZBTB18 shRNA were injected into the flank region of mice and the tumor volume was measured. The mRNA and protein expression was quantified by qRT-PCR or Western blotting.

RESULTS

GBM tissues exhibited increased CtBP2 expression and decreased ZBTB18 expression, which demonstrated a negative correlation in GBM tissues and showed the combined effect on prognosis. Based on immunoprecipitation and immunofluorescence, there was an interaction between CtBP2 and ZBTB18 in U-87 MG cells. CtBP2 shRNA counteracted the effect of ZBTB18 shRNA on inhibiting U-87 MG cell apoptosis, as well as promoting cell proliferation and viability with increased EMT, invasion and migration. Meanwhile, CtBP2 shRNA interact with ZBTB18 to block cells at phase G0/G1 and suppress SHH-GLI1 pathway. CtBP2 shRNA decreased tumor volume, increase ZBTB18 expression in tumor tissues, and inhibit SHH-GLI1 pathway in mice, which could be reversed by ZBTB18 shRNA.

CONCLUSION

CtBP2 elevation and ZBTB18 down-regulation were found in GBM, both of which were associated with prognosis of GBM patients. CtBP2 interacted with ZBTB18 to affect biological characteristics of GBM cells, and the tumor growth, which may be related to the SHH-GLI1 pathway.

Pancreatic Adenocarcinoma: Unconventional Approaches for an Unconventional Disease

This review highlights current treatments, limitations, and pitfalls in the management of pancreatic cancer and discusses current research in novel targets and drug development to overcome these clinical challenges. We begin with a review of the clinical landscape of pancreatic cancer, including genetic and environmental risk factors, as well as limitations in disease diagnosis and prevention. We next discuss current treatment paradigms for pancreatic cancer and the shortcomings of targeted therapy in this disease. Targeting major driver mutations in pancreatic cancer, such as dysregulation in the KRAS and TGFβ signaling pathways, have failed to improve survival outcomes compared with nontargeted chemotherapy; thus, we describe new advances in therapy such as Ras-binding pocket inhibitors. We then review next-generation approaches in nanomedicine and drug delivery, focusing on preclinical advancements in novel optical probes, antibodies, small-molecule agents, and nucleic acids to improve surgical outcomes in resectable disease, augment current therapies, expand druggable targets, and minimize morbidity. We conclude by summarizing progress in current research, identifying areas for future exploration in drug development and nanotechnology, and discussing future prospects for management of this disease.

CtBP determines ovarian cancer cell fate through repression of death receptors

C-terminal binding protein 2 (CtBP2) is elevated in epithelial ovarian cancer, especially in the aggressive and highly lethal subtype, high-grade serous ovarian cancer (HGSOC). However, whether HGSOC tumor progression is dependent on CtBP2 or its paralog CtBP1, is not well understood. Here we report that CtBP1/2 repress HGSOC cell apoptosis through silencing of death receptors (DRs) 4/5. CtBP1 or 2 knockdown upregulated DR4/5 expression, and triggered autonomous apoptosis via caspase 8 activation, but dependent on cell-type context. Activation of DR4/5 by CtBP1/2 loss also sensitized HGSOC cell susceptibility to the proapoptotic DR4/5 ligand TRAIL. Consistent with its function as transcription corepressor, CtBP1/2 bound to the promoter regions of DR4/5 and repressed DR4/5 expression, presumably through recruitment to a repressive transcription regulatory complex. We also found that CtBP1 and 2 were both required for repression of DR4/5. Collectively, this study identifies CtBP1 and 2 as potent repressors of DR4/5 expression and activity, and supports the targeting of CtBP as a promising therapeutic strategy for HGSOC.