Ovarian cancer think tank: An overview of the current status of ovarian cancer screening and recommendations for future directions

Early diagnosis and screening of ovarian cancer remain significant challenges to improving patient outcomes. There is an urgent need to implement both established and modern strategies to address the "early detection" conundrum, especially as new research continues to uncover the complexities of the disease. The discussion provided is the result of a unique research conference focused on reviewing early detection modalities and providing insight into future approaches.

Combining EHMT and PARP Inhibition: A Strategy to Diminish Therapy-Resistant Ovarian Cancer Tumor Growth while Stimulating Immune Activation

Despite the success of Poly-ADP-ribose polymerase inhibitors (PARPi) in the clinic, high rates of resistance to PARPi presents a challenge in the treatment of ovarian cancer, thus it is imperative to find therapeutic strategies to combat PARPi resistance. Here, we demonstrate that inhibition of epigenetic modifiers Euchromatic histone lysine methyltransferases 1/2 (EHMT1/2) reduces the growth of multiple PARPi-resistant ovarian cancer cell lines and tumor growth in a PARPi-resistant mouse model of ovarian cancer. We found that combinatory EHMT and PARP inhibition increases immunostimulatory dsRNA formation and elicits several immune signaling pathways in vitro. Using epigenomic profiling and transcriptomics, we found that EHMT2 is bound to transposable elements, and that EHMT inhibition leads to genome-wide epigenetic and transcriptional derepression of transposable elements. We validated EHMT-mediated activation of immune signaling and upregulation of transposable element transcripts in patient-derived, therapy-naïve, primary ovarian tumors, suggesting potential efficacy in PARPi-sensitive disease as well. Importantly, using multispectral immunohistochemistry, we discovered that combinatory therapy increased CD8 T cell activity in the tumor microenvironment of the same patient-derived tissues. In a PARPi-resistant syngeneic murine model, EHMT and PARP inhibition combination inhibited tumor progression and increased Granzyme B+ cells in the tumor. Together, our results provide evidence that combinatory EHMT and PARP inhibition stimulates a cell autologous immune response in vitro, is an effective therapy to reduce PARPi resistant ovarian tumor growth in vivo, and promotes anti-tumor immunity activity in the tumor microenvironment of patient-derived ex vivo tissues of ovarian cancer.

Folate receptor alpha protein expression in ovarian serous cystadenocarcinoma tumors of The Cancer Genome Atlas: exploration beyond single-agent therapy

Epithelial ovarian cancer (EOC) can be highly lethal, with limited therapeutic options for patients with non-homologous recombination deficient (HRD) disease. Folate receptor alpha (FOLR1/FRα)-targeting agents have shown promise both alone and in combination with available therapies, but the relationship of FRα to other treatment-driving biomarkers is unknown. The Cancer Genome Atlas (TCGA) was queried to assess protein and mRNA expression and mutational burden in patients with differential FRα protein-expressing ovarian tumors, and the results referenced against the standard 324 mutations currently tested through FoundationOne Companion Diagnostics to identify targets of interest. Of 585 samples within TCGA, 121 patients with serous ovarian tumors for whom FRα protein expression was quantified were identified. FRα protein expression significantly correlated with FOLR1 mRNA expression (p=7.19×1014). Progression free survival (PFS) for the FRα-high group (Q1) was 20.7 months, compared to 16.6 months for the FRα-low group (Q4, Logrank, p=0.886). Overall survival (OS) was 54.1 months versus 36.3 months, respectively; however, this result was not significant (Q1 vs. Q4, Logrank, p=0.200). Mutations more commonly encountered in patients with high FRα-expressing tumors included PIK3CA and FGF family proteins. Combinations of FRα-targeting agents with PI3K, mTOR, FGF(R) and VEGF inhibitors warrant investigation to evaluate their therapeutic potential.

VDX-111, a novel small molecule, induces necroptosis to inhibit ovarian cancer progression

Epithelial ovarian cancers that are nonhomologous recombination deficient, as well as those that are recurrent and in a platinum-resistant state, have limited therapeutic options. The objectives of this study were to characterize the mechanism of action and investigate the therapeutic potential of a small molecule, VDX-111, against ovarian cancer. We examined the ability of VDX-111 to inhibit the growth of a panel of ovarian cancer cell lines, focusing on BRCA wild-type lines. We found that VDX-111 causes a dose-dependent loss of cell viability across ovarian cancer cell lines. Reverse phase protein array (RPPA) analysis was used to identify changes in cell signaling in response to VDX-111 treatment. An RPPA analysis performed on cells treated with VDX-111 detected changes in cell signaling related to autophagy and necroptosis. Immunoblots of OVCAR3 and SNU8 cells confirmed a dose-dependent increase in LC3A/B and RIPK1. Incucyte live cell imaging was used to measure cell proliferation and death in response to VDX-111 alone and with inhibitors of apoptosis, necroptosis, and autophagy. Annexin/PI assays suggested predominantly nonapoptotic cell death, while real-time kinetic imaging of cell growth indicated the necroptosis inhibitor, necrostatin-1, attenuates VDX-111-induced loss of cell viability, suggesting a necroptosis-dependent mechanism. Furthermore, VDX-111 inhibited tumor growth in patient-derived xenograft and syngeneic murine models. In conclusion, the cytotoxic effects of VDX-111 seen in vitro and in vivo appear to occur in a necroptosis-dependent manner and may promote an antitumor immune response.

Targeting Tryptophan Catabolism in Ovarian Cancer to Attenuate Macrophage Infiltration and PD-L1 Expression

High-grade serous carcinoma (HGSC) of the fallopian tube, ovary, and peritoneum is the most common type of ovarian cancer and is predicted to be immunogenic because the presence of tumor-infiltrating lymphocytes conveys a better prognosis. However, the efficacy of immunotherapies has been limited because of the immune-suppressed tumor microenvironment (TME). Tumor metabolism and immune-suppressive metabolites directly affect immune cell function through the depletion of nutrients and activation of immune-suppressive transcriptional programs. Tryptophan (TRP) catabolism is a contributor to HGSC disease progression. Two structurally distinct rate-limiting TRP catabolizing enzymes, indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase 2 (TDO2), evolved separately to catabolize TRP. IDO1/TDO2 are aberrantly expressed in carcinomas and metabolize TRP into the immune-suppressive metabolite kynurenine (KYN), which can engage the aryl hydrocarbon receptor to drive immunosuppressive transcriptional programs. To date, IDO inhibitors tested in clinical trials have had limited efficacy, but those inhibitors did not target TDO2, and we find that HGSC cell lines and clinical outcomes are more dependent on TDO2 than IDO1. To identify inflammatory HGSC cancers with poor prognosis, we stratified patient ascites samples by IL6 status, which correlates with poor prognosis. Metabolomics revealed that IL6-high patient samples had enriched KYN. TDO2 knockdown significantly inhibited HGSC growth and TRP catabolism. The orally available dual IDO1/TDO2 inhibitor, AT-0174, significantly inhibited tumor progression, reduced tumor-associated macrophages, and reduced expression of immune-suppressive proteins on immune and tumor cells. These studies demonstrate the importance of TDO2 and the therapeutic potential of AT-0174 to overcome an immune-suppressed TME.

SIGNIFICANCE

Developing strategies to improve response to chemotherapy is essential to extending disease-free intervals for patients with HGSC of the fallopian tube, ovary, and peritoneum. In this article, we demonstrate that targeting TRP catabolism, particularly with dual inhibition of TDO2 and IDO1, attenuates the immune-suppressive microenvironment and, when combined with chemotherapy, extends survival compared with chemotherapy alone.

Early Ovarian Cancer Detection in the Age of Fallopian Tube Precursors: A Systematic Review

OBJECTIVE

To determine biomarkers other than CA 125 that could be used in identifying early-stage ovarian cancer.

DATA SOURCES

Ovid MEDLINE ALL, EMBASE, Web of Science Core Collection, ScienceDirect, Clinicaltrials.gov , and CAB Direct were searched for English-language studies between January 2008 and April 2023 for the concepts of high-grade serous ovarian cancer, testing, and prevention or early diagnosis.

METHODS OF STUDY SELECTION

The 5,523 related articles were uploaded to Covidence. Screening by two independent reviewers of the article abstracts led to the identification of 245 peer-reviewed primary research articles for full-text review. Full-text review by those reviewers led to the identification of 131 peer-reviewed primary research articles used for this review.

TABULATION, INTEGRATION, AND RESULTS

Of 131 studies, only 55 reported sensitivity, specificity, or area under the curve (AUC), with 36 of the studies reporting at least one biomarker with a specificity of 80% or greater specificity or 0.9 or greater AUC.

CONCLUSION

These findings suggest that although many types of biomarkers are being tested in ovarian cancer, most have similar or worse detection rates compared with CA 125 and have the same limitations of poor detection rates in early-stage disease. However, 27.5% of articles (36/131) reported biomarkers with better sensitivity and an AUC greater than 0.9 compared with CA 125 alone and deserve further exploration.

αKG-mediated carnitine synthesis promotes homologous recombination via histone acetylation

Homologous recombination (HR) deficiency enhances sensitivity to DNA damaging agents commonly used to treat cancer. In HR-proficient cancers, metabolic mechanisms driving response or resistance to DNA damaging agents remain unclear. Here we identified that depletion of alpha-ketoglutarate (αKG) sensitizes HR-proficient cells to DNA damaging agents by metabolic regulation of histone acetylation. αKG is required for the activity of αKG-dependent dioxygenases (αKGDDs), and prior work has shown that changes in αKGDD affect demethylases. Using a targeted CRISPR knockout library consisting of 64 αKGDDs, we discovered that Trimethyllysine Hydroxylase Epsilon (TMLHE), the first and rate-limiting enzyme in de novo carnitine synthesis, is necessary for proliferation of HR-proficient cells in the presence of DNA damaging agents. Unexpectedly, αKG-mediated TMLHE-dependent carnitine synthesis was required for histone acetylation, while histone methylation was affected but dispensable. The increase in histone acetylation via αKG-dependent carnitine synthesis promoted HR-mediated DNA repair through site- and substrate-specific histone acetylation. These data demonstrate for the first time that HR-proficiency is mediated through αKG directly influencing histone acetylation via carnitine synthesis and provide a metabolic avenue to induce HR-deficiency and sensitivity to DNA damaging agents.

CASC4/GOLM2 drives high grade serous carcinoma anoikis resistance through the recycling of EGFR

Ovarian cancer is the deadliest gynecological malignancy, and accounts for over 150,000 deaths per year worldwide. The high grade serous ovarian carcinoma (HGSC) subtype accounts for almost 70% of ovarian cancers and is the deadliest. HGSC originates in the fimbria of the fallopian tube and disseminates through the peritoneal cavity. HGSC survival in peritoneal fluid requires cells to resist anoikis (anchorage-independent apoptosis). Most anoikis resistant mechanisms are dependent on microenvironment interactions with cell surface-associated proteins, such as integrins and receptor tyrosine kinases (RTKs). We previously identified the gene CASC4 as a driver of anoikis resistance. CASC4 is predicted to be a Golgi-associated protein that may regulate protein trafficking to the plasma membrane, but CASC4 is largely uncharacterized in literature; thus, we sought to determine how CASC4 confers anoikis resistance to HGSC cells. Mining of publicly available ovarian cancer datasets (TCGA) showed that CASC4 is associated with worse overall survival and increased resistance to platinum-based chemotherapies. For experiments, we cultured three human HGSC cell lines (PEO1, CaOV3, OVCAR3), and a murine HGSC cell line, (ID8) with shRNA-mediated CASC4 knockdowns (CASC4 KD) in suspension, to recapitulate the peritoneal fluid environment in vitro. CASC4 KD significantly inhibited cell proliferation and colony formation ability, and increased apoptosis. A Reverse Phase Protein Assay (RPPA) showed that CASC4 KD resulted in a broad re-programming of membrane-associated proteins. Specifically, CASC4 KD led to decreased protein levels of the RTK Epidermal Growth Factor Receptor (EGFR), an initiator of several oncogenic signaling pathways, leading us to hypothesize that CASC4 drives HGSC survival through mediating recycling and trafficking of EGFR. Indeed, loss of CASC4 led to a decrease in both EGFR membrane localization, reduced turnover of EGFR, and increased EGFR ubiquitination. Moreover, a syngeneic ID8 murine model of ovarian cancer showed that knocking down CASC4 leads to decreased tumor burden and dissemination.

The spatial structure of the tumor immune microenvironment can explain and predict patient response in high-grade serous carcinoma

Despite ovarian cancer being the deadliest gynecological malignancy, there has been little change to therapeutic options and mortality rates over the last three decades. Recent studies indicate that the composition of the tumor immune microenvironment (TIME) influences patient outcomes but are limited by a lack of spatial understanding. We performed multiplexed ion beam imaging (MIBI) on 83 human high-grade serous carcinoma tumors - one of the largest protein-based, spatially-intact, single-cell resolution tumor datasets assembled - and used statistical and machine learning approaches to connect features of the TIME spatial organization to patient outcomes. Along with traditional clinical/immunohistochemical attributes and indicators of TIME composition, we found that several features of TIME spatial organization had significant univariate correlations and/or high relative importance in high-dimensional predictive models. The top performing predictive model for patient progression-free survival (PFS) used a combination of TIME composition and spatial features. Results demonstrate the importance of spatial structure in understanding how the TIME contributes to treatment outcomes. Furthermore, the present study provides a generalizable roadmap for spatial analyses of the TIME in ovarian cancer research.

Claudin-4 modulates autophagy via SLC1A5/LAT1 as a tolerance mechanism for genomic instability in ovarian cancer

Genome instability is key for tumor heterogeneity and derives from defects in cell division and DNA damage repair. Tumors show tolerance for this characteristic, but its accumulation is regulated somehow to avoid catastrophic chromosomal alterations and cell death. Claudin-4 is upregulated and closely associated with genome instability and worse patient outcome in ovarian cancer. This protein is commonly described as a junctional protein participating in processes such as cell proliferation and DNA repair. However, its biological association with genomic instability is still poorly-understood. Here, we used CRISPRi and a claudin mimic peptide (CMP) to modulate the cladudin-4 expression and its function, respectively in in-vitro (high-grade serous carcinoma cells) and in-vivo (patient-derived xenograft in a humanized-mice model) systems. We found that claudin-4 promotes a protective cellular-mechanism that links cell-cell junctions to genome integrity. Disruption of this axis leads to irregular cellular connections and cell cycle that results in chromosomal alterations, a phenomenon associated with a novel functional link between claudin-4 and SLC1A5/LAT1 in regulating autophagy. Consequently, claudin-4's disruption increased autophagy and associated with engulfment of cytoplasm-localized DNA. Furthermore, the claudin-4/SLC1A5/LAT1 biological axis correlates with decrease ovarian cancer patient survival and targeting claudin-4 in-vivo with CMP resulted in increased niraparib (PARPi) efficacy, correlating with increased tumoral infiltration of T CD8+ lymphocytes. Our results show that the upregulation of claudin-4 enables a mechanism that promotes tolerance to genomic instability and immune evasion in ovarian cancer; thus, suggesting the potential of claudin-4 as a translational target for enhancing ovarian cancer treatment.

WNT4 Regulates Cellular Metabolism via Intracellular Activity at the Mitochondria in Breast and Gynecologic Cancers

Wnt ligand WNT4 is critical in female reproductive tissue development, with WNT4 dysregulation linked to related pathologies including breast cancer (invasive lobular carcinoma, ILC) and gynecologic cancers. WNT4 signaling in these contexts is distinct from canonical Wnt signaling yet inadequately understood. We previously identified atypical intracellular activity of WNT4 (independent of Wnt secretion) regulating mitochondrial function, and herein examine intracellular functions of WNT4. We further examine how convergent mechanisms of WNT4 dysregulation impact cancer metabolism. In ILC, WNT4 is co-opted by estrogen receptor α (ER) via genomic binding in WNT4 intron 1, while in gynecologic cancers, a common genetic polymorphism (rs3820282) at this ER binding site alters WNT4 regulation. Using proximity biotinylation (BioID), we show canonical Wnt ligand WNT3A is trafficked for secretion, but WNT4 is localized to the cytosol and mitochondria. We identified DHRS2, mTOR, and STAT1 as putative WNT4 cytosolic/mitochondrial signaling partners. Whole metabolite profiling, and integrated transcriptomic data, support that WNT4 mediates metabolic reprogramming via fatty acid and amino acid metabolism. Furthermore, ovarian cancer cell lines with rs3820282 variant genotype are WNT4 dependent and have active WNT4 metabolic signaling. In protein array analyses of a cohort of 103 human gynecologic tumors enriched for patient diversity, germline rs3820282 genotype is associated with metabolic remodeling. Variant genotype tumors show increased AMPK activation and downstream signaling, with the highest AMPK signaling activity in variant genotype tumors from non-White patients. Taken together, atypical intracellular WNT4 signaling, in part via genetic dysregulation, regulates the distinct metabolic phenotypes of ILC and gynecologic cancers.

SIGNIFICANCE

WNT4 regulates breast and gynecologic cancer metabolism via a previously unappreciated intracellular signaling mechanism at the mitochondria, with WNT4 mediating metabolic remodeling. Understanding WNT4 dysregulation by estrogen and genetic polymorphism offers new opportunities for defining tumor biology, precision therapeutics, and personalized cancer risk assessment.

Mechanisms of Ovarian Cancer-Associated Cachexia

Cancer-associated cachexia occurs in 50% to 80% of cancer patients and is responsible for 20% to 30% of cancer-related deaths. Cachexia limits survival and treatment outcomes, and is a major contributor to morbidity and mortality during cancer. Ovarian cancer is one of the leading causes of cancer-related deaths in women, and recent studies have begun to highlight the prevalence and clinical impact of cachexia in this population. Here, we review the existing understanding of cachexia pathophysiology and summarize relevant studies assessing ovarian cancer-associated cachexia in clinical and preclinical studies. In clinical studies, there is increased evidence that reduced skeletal muscle mass and quality associate with worse outcomes in subjects with ovarian cancer. Mouse models of ovarian cancer display cachexia, often characterized by muscle and fat wasting alongside inflammation, although they remain underexplored relative to other cachexia-associated cancer types. Certain soluble factors have been identified and successfully targeted in these models, providing novel therapeutic targets for mitigating cachexia during ovarian cancer. However, given the relatively low number of studies, the translational relevance of these findings is yet to be determined and requires more research. Overall, our current understanding of ovarian cancer-associated cachexia is insufficient and this review highlights the need for future research specifically aimed at exploring mechanisms of ovarian cancer-associated cachexia by using unbiased approaches and animal models representative of the clinical landscape of ovarian cancer.

Targeting BRPF3 moderately reverses olaparib resistance in high grade serous ovarian carcinoma

PARP inhibitors (PARPi) kill cancer cells by stalling DNA replication and preventing DNA repair, resulting in a critical accumulation of DNA damage. Resistance to PARPi is a growing clinical problem in the treatment of high grade serous ovarian carcinoma (HGSOC). Acetylation of histone H3 lysine 14 (H3K14ac) and associated histone acetyltransferases (HATs) and epigenetic readers have known functions in DNA repair and replication. Our objectives are to examine their expression and activities in the context of PARPi-resistant HGSOC, and to determine if targeting H3K14ac or associated proteins has therapeutic potential. Using mass spectrometry profiling of histone modifications, we observed increased H3K14ac enrichment in PARPi-resistant HGSOC cells relative to isogenic PARPi-sensitive lines. By reverse-transcriptase quantitative PCR and RNA-seq, we also observed altered expression of numerous HATs in PARPi-resistant HGSOC cells and a PARPi-resistant PDX model. Knockdown of HATs only modestly altered PARPi response, although knockdown and inhibition of PCAF significantly increased resistance. Pharmacologic inhibition of HBO1 depleted H3K14ac but did not affect PARPi response. However, knockdown and inhibition of BRPF3, a bromodomain and PHD-finger containing protein that is known to interact in a complex with HBO1, did reduce PARPi resistance. This study demonstrates that depletion of H3K14ac does not affect PARPi response in HGSOC. Our data suggest that the bromodomain function of HAT proteins, such as PCAF, or accessory proteins, such as BRPF3, may play a more direct role compared to direct HATs function in PARPi response.

SMASH: Scalable Method for Analyzing Spatial Heterogeneity of genes in spatial transcriptomics data

In high-throughput spatial transcriptomics (ST) studies, it is of great interest to identify the genes whose level of expression in a tissue covaries with the spatial location of cells/spots. Such genes, also known as spatially variable genes (SVGs), can be crucial to the biological understanding of both structural and functional characteristics of complex tissues. Existing methods for detecting SVGs either suffer from huge computational demand or significantly lack statistical power. We propose a non-parametric method termed SMASH that achieves a balance between the above two problems. We compare SMASH with other existing methods in varying simulation scenarios demonstrating its superior statistical power and robustness. We apply the method to four ST datasets from different platforms uncovering interesting biological insights.

Regulation of human interferon signaling by transposon exonization

Innate immune signaling is essential for clearing pathogens and damaged cells, and must be tightly regulated to avoid excessive inflammation or autoimmunity. Here, we found that the alternative splicing of exons derived from transposable elements is a key mechanism controlling immune signaling in human cells. By analyzing long-read transcriptome datasets, we identified numerous transposon exonization events predicted to generate functional protein variants of immune genes, including the type I interferon receptor IFNAR2. We demonstrated that the transposon-derived isoform of IFNAR2 is more highly expressed than the canonical isoform in almost all tissues, and functions as a decoy receptor that potently inhibits interferon signaling including in cells infected with SARS-CoV-2. Our findings uncover a primate-specific axis controlling interferon signaling and show how a transposon exonization event can be co-opted for immune regulation.

A platform-independent framework for phenotyping of multiplex tissue imaging data

Multiplex imaging is a powerful tool to analyze the structural and functional states of cells in their morphological and pathological contexts. However, hypothesis testing with multiplex imaging data is a challenging task due to the extent and complexity of the information obtained. Various computational pipelines have been developed and validated to extract knowledge from specific imaging platforms. A common problem with customized pipelines is their reduced applicability across different imaging platforms: Every multiplex imaging technique exhibits platform-specific characteristics in terms of signal-to-noise ratio and acquisition artifacts that need to be accounted for to yield reliable and reproducible results. We propose a pixel classifier-based image preprocessing step that aims to minimize platform-dependency for all multiplex image analysis pipelines. Signal detection and noise reduction as well as artifact removal can be posed as a pixel classification problem in which all pixels in multiplex images can be assigned to two general classes of either I) signal of interest or II) artifacts and noise. The resulting feature representation maps contain pixel-scale representations of the input data, but exhibit significantly increased signal-to-noise ratios with normalized pixel values as output data. We demonstrate the validity of our proposed image preprocessing approach by comparing the results of two well-accepted and widely-used image analysis pipelines.

Novel chromobox 2 inhibitory peptide decreases tumor progression

BACKGROUND

The Polycomb Repressor Complex 1 (PRC1) is an epigenetic regulator of differentiation and development, consisting of multiple subunits including RING1, BMI1, and Chromobox. The composition of PRC1 dictates its function and aberrant expression of specific subunits contributes to several diseases including cancer. Specifically, the reader protein Chromobox2 (CBX2) recognizes the repressive modifications including histone H3 lysine 27 tri-methylation (H3K27me3) and H3 lysine 9 dimethylation (H3K9me2). CBX2 is overexpressed in several cancers compared to the non-transformed cell counterparts, it promotes both cancer progression and chemotherapy resistance. Thus, inhibiting the reader function of CBX2 is an attractive and unique anti-cancer approach.

RESEARCH DESIGN & METHODS

Compared with other CBX family members, CBX2 has a unique A/T-hook DNA binding domain that is juxtaposed to the chromodomain (CD). Using a computational approach, we constructed a homology model of CBX2 encompassing the CD and A/T hook domain. We used the model as a basis for peptide design and identified blocking peptides that are predicted to directly bind the CD and A/T-hook regions of CBX2. These peptides were tested in vitro and in vivo models.

CONCLUSION

The CBX2 blocking peptide significantly inhibited both 2D and 3D growth of ovarian cancer cells, downregulated a CBX2 target gene, and blunted tumor growth in vivo.

Combination CDC-like kinase inhibition (CLK)/Dual-specificity tyrosine-regulated kinase (DYRK) and taxane therapy in CTNNB1-mutated endometrial cancer

SM08502 (cirtuvivint) is a novel pan CDC-like kinase (CLK) and Dual specificity tyrosine kinase (DYRK) inhibitor that targets mRNA splicing and is optimized for Wnt pathway inhibition. Previous evaluation of single agent CLK/DYRK inhibition (SM04690) demonstrated inhibition of tumor progression and β-catenin/TCF transcriptional activity in CTNNB1-mutant endometrial cancer (EC). In-vitro analysis of SM08502 similarly decreases Wnt transcriptional activity and cellular proliferation while increasing cellular apoptosis. SM08502 is an active single-agent therapy with IC50's in the nanomolar range for all EC cell lines evaluated. Combination of SM08502 with paclitaxel has synergistic effect in vitro, as demonstrated by Combination Index <1, and inhibits tumor progression in four endometrial cancer models (HEC265, Ishikawa, Ishikawa-S33Y, and SNGM). In our in vivo mouse models, Ishikawa demonstrated significantly lower tumor volumes of combination vs SM08502 alone (Repeated Measures one-way ANOVA, p = 0.04), but not vs paclitaxel alone. HEC265, SNGM, and Ishikawa-S33Y tumors all had significantly lower tumor volumes with combination SM08502 and paclitaxel compared to single-agent paclitaxel (Repeated Measures one-way ANOVA, p = 0.01, 0.004, and 0.0008, respectively) or single-agent SM08502 (Repeated Measures one-way ANOVA, p = 0.002, 0.005, and 0.01, respectively) alone. Mechanistically, treatment with SM08502 increases alternative splicing (AS) events compared to treatment with paclitaxel. AS regulation is an important post-transcriptional mechanism associated with the oncogenic process in many cancers, including EC. Results from these studies have led to a Phase I evaluation of this combination in recurrent EC.

Abstract 2551: CASC4 drives anoikis resistance in high grade serous ovarian cancer through recycling of EGFR

Introduction: Ovarian cancer is the deadliest gynecological malignancy, and accounts for over 150,000 deaths per year worldwide. The high grade serous ovarian cancer (HGSOC) subtype accounts for almost 60% of ovarian cancers and is the deadliest. HGSOC originates in the fimbria of the fallopian tube and disseminates through the peritoneal cavity. Survival of tumor cells in the peritoneal fluid requires cells to resist anoikis (anchorage-independent apoptosis). CRISPR/Cas9 and transcriptomic screens identified the Golgi protein CASC4 (GOLM2, H63) as a “driver” of anoikis resistance. As CASC4 is highly uncharacterized in literature, we sought to determine how CASC4 confers anoikis resistance to HGSOC cells.

Methods: Mining of publicly available ovarian cancer datasets (TCGA) showed that CASC4 is associated with worse clinical outcomes, such as worse overall survival and increased resistance to platinum-based chemotherapies. For experiments, we used HGSOC cell lines PEO1, CaOV3, and OVCAR3 with shRNA-mediated CASC4 knockdowns (CASC4 KD), cultured in forced suspension.

Results: Culturing cells in suspension, to recapitulate the peritoneal fluid environment in vitro, showed that CASC4 KD hampers cell proliferation and colony formation ability, and increases apoptosis. Additionally, a Reverse Phase Protein Assay (RPPA) showed that CASC4 KD results in significant changes in proteins known to be localized to the cell surface or secreted, including decreased protein levels of the receptor tyrosine kinase (RTK) Epidermal Growth Factor Receptor (EGFR), an initiator of several oncogenic signaling pathways. A paralog of CASC4, GOLM1, is known to drive hepatocellular carcinoma through various mechanisms, such as the recycling of internalized RTKs, including EGFR. Indeed, our experiments showed that CASC4 KD in ovarian cancer cells leads to decreased EGFR levels and decreased EGFR recycling.

Conclusion: Knocking down CASC4 results in decreased survivability in suspension, decreased EGFR levels at the plasma membrane, and decreased recycling of EGFR. Further elucidating mechanisms of CASC4-dependent anoikis resistance could lead to the development of novel therapeutic approaches, such as inhibitory peptides, and may assist in developing newer biomarkers for predicting ovarian cancer malignancy.

Citation Format: Jaidev Bapat, Lindsay W. Brubaker, Zachary L. Watson, Tomomi M. Yamamoto, Benjamin G. Bitler. CASC4 drives anoikis resistance in high grade serous ovarian cancer through recycling of EGFR [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2551.

SMASH: Scalable Method for Analyzing Spatial Heterogeneity of genes in spatial transcriptomics data

In high-throughput spatial transcriptomics (ST) studies, it is of great interest to identify the genes whose level of expression in a tissue covaries with the spatial location of cells/spots. Such genes, also known as spatially variable genes (SVGs), can be crucial to the biological understanding of both structural and functional characteristics of complex tissues. Existing methods for detecting SVGs either suffer from huge computational demand or significantly lack statistical power. We propose a non-parametric method termed SMASH that achieves a balance between the above two problems. We compare SMASH with other existing methods in varying simulation scenarios demonstrating its superior statistical power and robustness. We apply the method to four ST datasets from different platforms revealing interesting biological insights.

Expression and T cell regulatory action of the PD-1 immune checkpoint in the ovary and fallopian tube

PROBLEM

Immune cell trafficking and surveillance within the ovary and fallopian tube are thought to impact fertility and also tumorigenesis in those organs. However, little is known of how native cells of the ovary and fallopian tube interact with resident immune cells. Interaction of the Programmed Cell Death Protein-1 (PD-1/PDCD-1/CD279) checkpoint with PD-L1 is associated with downregulated immune response. We have begun to address the question of whether PD-1 ligand or its receptors (PD-L1/-L2) can regulate immune cell function in these tissues of the female reproductive tract.

METHOD OF STUDY

PD-1 and ligand protein expression was evaluated in human ovary and fallopian tube specimens, the latter of which included stages of tubal cell transformation and early tumorigenesis. Ovarian expression analysis included the determination of the proteins in human follicular fluid (HFF) specimens collected during in vitro fertilization procedures. Finally, checkpoint bioactivity of HFF was determined by treatment of separately-isolated human T cells and the measurement of interferon gamma (IFNγ).

RESULTS

We show that membrane bound and soluble variants of PD-1 and ligands are expressed by permanent constituent cell types of the human ovary and fallopian tube, including granulosa cells and oocytes. PD-1 and soluble ligands were present in HFF at bioactive levels that control T cell PD-1 activation and IFNγ production; full-length checkpoint proteins were found to be highly enriched in HFF exosome fractions.

CONCLUSION

The detection of PD-1 checkpoint proteins in the human ovary and fallopian tube suggests that the pathway is involved in immunomodulation during folliculogenesis, the window of ovulation, and subsequent egg and embryo immune-privilege. Immunomodulatory action of receptor and ligands in HFF exosomes is suggestive of an acute checkpoint role during ovulation. This is the first study in the role of PD-1 checkpoint proteins in human tubo-ovarian specimens and the first examination of its potential regulatory action in the contexts of normal and assisted reproduction.

Combinatory EHMT and PARP inhibition induces an interferon response and a CD8 T cell-dependent tumor regression in PARP inhibitor-resistant models

Euchromatic histone lysine methyltransferases 1 and 2 (EHMT1/2), which catalyze demethylation of histone H3 lysine 9 (H3K9me2), contribute to tumorigenesis and therapy resistance through unknown mechanisms of action. In ovarian cancer, EHMT1/2 and H3K9me2 are directly linked to acquired resistance to poly-ADP-ribose polymerase (PARP) inhibitors and are correlated with poor clinical outcomes. Using a combination of experimental and bioinformatic analyses in several PARP inhibitor resistant ovarian cancer models, we demonstrate that combinatory inhibition of EHMT and PARP is effective in treating PARP inhibitor resistant ovarian cancers. Our in vitro studies show that combinatory therapy reactivates transposable elements, increases immunostimulatory dsRNA formation, and elicits several immune signaling pathways. Our in vivo studies show that both single inhibition of EHMT and combinatory inhibition of EHMT and PARP reduces tumor burden, and that this reduction is dependent on CD8 T cells. Together, our results uncover a direct mechanism by which EHMT inhibition helps to overcome PARP inhibitor resistance and shows how an epigenetic therapy can be used to enhance anti-tumor immunity and address therapy resistance.

TWEAK-Fn14-RelB Signaling Cascade Promotes Stem Cell-like Features that Contribute to Post-Chemotherapy Ovarian Cancer Relapse

Disease recurrence in high-grade serous ovarian cancer may be due to cancer stem-like cells (CSC) that are resistant to chemotherapy and capable of reestablishing heterogeneous tumors. The alternative NF-κB signaling pathway is implicated in this process; however, the mechanism is unknown. Here we show that TNF-like weak inducer of apoptosis (TWEAK) and its receptor, Fn14, are strong inducers of alternative NF-κB signaling and are enriched in ovarian tumors following chemotherapy treatment. We further show that TWEAK enhances spheroid formation ability, asymmetric division capacity, and expression of SOX2 and epithelial-to-mesenchymal transition genes VIM and ZEB1 in ovarian cancer cells, phenotypes that are enhanced when TWEAK is combined with carboplatin. Moreover, TWEAK in combination with chemotherapy induces expression of the CSC marker CD117 in CD117- cells. Blocking the TWEAK-Fn14-RelB signaling cascade with a small-molecule inhibitor of Fn14 prolongs survival following carboplatin chemotherapy in a mouse model of ovarian cancer. These data provide new insights into ovarian cancer CSC biology and highlight a signaling axis that should be explored for therapeutic development.

IMPLICATIONS

This study identifies a unique mechanism for the induction of ovarian cancer stem cells that may serve as a novel therapeutic target for preventing relapse.

ATF6-Mediated Signaling Contributes to PARP Inhibitor Resistance in Ovarian Cancer

High-grade serous ovarian cancer (HGSOC) is the deadliest ovarian cancer histotype due in-part to the lack of therapeutic options for chemotherapy-resistant disease. PARP inhibitors (PARPi) represent a targeted treatment. However, PARPi resistance is becoming a significant clinical challenge. There is an urgent need to overcome resistance mechanisms to extend disease-free intervals. We established isogeneic PARPi-sensitive and -resistant HGSOC cell lines. In three PARPi-resistant models, there is a significant increase in AP-1 transcriptional activity and DNA repair capacity. Using RNA-sequencing and an shRNA screen, we identified activating transcription factor 6 (ATF6) as a mediator of AP-1 activity, DNA damage response, and PARPi resistance. In publicly available datasets, ATF6 expression is elevated in HGSOC and portends a poorer recurrence-free survival. In a cohort of primary HGSOC tumors, higher ATF6 expression significantly correlated to PARPi resistance. In PARPi-resistant cell lines and a PDX model, inhibition of a known ATF6 regulator, p38, attenuated AP-1 activity and RAD51 foci formation, enhanced DNA damage, significantly inhibited tumor burden, and reduced accumulation of nuclear ATF6.

IMPLICATIONS

This study highlights that a novel p38-ATF6-mediated AP-1 signaling axis contributes to PARPi resistance and provides a clinical rationale for combining PARPi and AP-1 signaling inhibitors.

Clinicopathologic Evaluation of CTNNB1 Mutations in High-Intermediate Risk Endometrial Endometrioid Carcinoma

CTNNB1 mutations convey increased risk of recurrence in low-risk endometrial endometrioid carcinoma (EEC). Results from previous high-intermediate risk (HIR) cohorts are mixed. The aims of this study were to correlate CTNNB1 mutational status with clinical outcomes and to evaluate the relationship between CTNNB1 mutations and the 4 prognostic subgroups defined by The Cancer Genome Atlas in HIR EEC. CTNNB1 mutational status was determined by Sanger sequencing of exon 3 of the CTNNB1 gene. Mismatch repair, POLE , p53, and L1 cell-adhesion molecule (L1CAM) status were also evaluated. Descriptive statistics and survival analyses were performed. Eighty-eight cases of HIR EEC were identified, of which 22 (25%) were CTNNB1 mutant ( CTNNB1 -mut) and 66 (75%) were wild-type ( CTNNB1 -WT). Median follow-up was 60 mo. Recurrence occurred in 13/88 (15%) patients. Recurrence rates were not significantly different between patients with CTNNB1- mut and CTNNB1- WT tumors (14% vs. 15%, P =0.86). Recurrence-free survival and overall survival were not significantly different (recurrence-free survival hazard ratio: 0.97, 95% confidence interval: 0.27-3.52, P =0.96; overall survival hazard ratio: 0.23, 95% confidence interval: 0.03-1.71, P =0.15). Mismatch repair deficiency was more prevalent in CTNNB1 -WT compared with CTNNB1 -mut tumors (46% vs. 14%, P =0.01); prevalence of POLE mutations and aberrant p53 were not significantly different. In contrast to patients with low-risk EEC, no differences in recurrence or survival were found in patients with HIR EEC with CTNNB1- mut compared with CTNNB1 -WT tumors.

Distinct roles of treatment schemes and BRCA2 on the restoration of homologous recombination DNA repair and PARP inhibitor resistance in ovarian cancer

Poly (ADP-ribose) polymerase inhibitors (PARPis) represent a major advance in ovarian cancer, now as a treatment and as a maintenance therapy in the upfront and recurrent settings. However, patients often develop resistance to PARPis, underlining the importance of dissecting resistance mechanisms. Here, we report different dosing/timing schemes of PARPi treatment in BRCA2-mutant PEO1 cells, resulting in the simultaneous development of distinct resistance mechanisms. PARPi-resistant variants PEO1/OlaJR, established by higher initial doses and short-term PARPi treatment, develops PARPi resistance by rapidly restoring functional BRCA2 and promoting drug efflux activity. In contrast, PEO1/OlaR, developed by lower initial doses with long-term PARPi exposure, shows no regained BRCA2 function but a mesenchymal-like phenotype with greater invasion ability, and exhibits activated ATR/CHK1 and suppressed EZH2/MUS81 signaling cascades to regain HR repair and fork stabilization, respectively. Our study suggests that PARPi resistance mechanisms can be governed by treatment strategies and have a molecular basis on BRCA2 functionality. Further, we define different mechanisms that may serve as useful biomarkers to assess subsequent treatment strategies in PARPi-resistant ovarian cancer.

Claudin-4 localization in epithelial ovarian cancer

Claudin-4, a protein with the structure of classic claudins most often found in cell-cell junctions, is frequently overexpressed in epithelial cancers where its localization has not been studied. In this study we aimed to find out where this membrane protein is localized in an ovarian tumor model, OVCAR3 cells, that express high levels of the protein. Immunohistochemical studies showed claudin-4 staining in a perinuclear region, at most plasma membranes and in cytoplasmic puncta. Native claudin-4 did not overlap with phosphorylated claudin-4, which was partially located in focal adhesions. Using claudin-4 BioID technology we confirmed that large amounts of claudin-4 are localized to the Golgi compartment, including in dispersed Golgi in cells where claudin-4 is partially knocked down and in dividing cells. Claudin-4 appears to be present in the vicinity of several types of cell-cell junctions, but there is no evidence that it forms tight junctions in these tumor cells. Both claudin-4, the Golgi marker GM130, and the plasma membrane receptor Notch2 were found in dispersed Golgi in dividing cells. This definition of the cellular architecture of claudin-4 should provide a framework for better understanding of the function of claudin-4 in tumor cells and its molecular interactions.

KDM5A Inhibits Antitumor Immune Responses Through Downregulation of the Antigen-Presentation Pathway in Ovarian Cancer

The extent to which effector CD8+ T cells infiltrate into tumors is one of the major predictors of clinical outcome for patients with epithelial ovarian cancer (EOC). Immune cell infiltration into EOC is a complex process that could be affected by the epigenetic makeup of the tumor. Here, we have demonstrated that a lysine 4 histone H3 (H3K4) demethylase, (lysine-specific demethylase 5A; KDM5A) impairs EOC infiltration by immune cells and inhibits antitumor immune responses. Mechanistically, we found that KDM5A silenced genes involved in the antigen processing and presentation pathway. KDM5A inhibition restored the expression of genes involved in the antigen-presentation pathway in vitro and promoted antitumor immune responses mediated by CD8+ T cells in vivo in a syngeneic EOC mouse model. A negative correlation between expression of KDM5A and genes involved in the antigen processing and presentation pathway such as HLA-A and HLA-B was observed in the majority of cancer types. In summary, our results establish KDM5A as a regulator of CD8+ T-cell infiltration of tumors and demonstrate that KDM5A inhibition may provide a novel therapeutic strategy to boost antitumor immune responses.

Targeting DUSP Activity as a Treatment for High-Grade Serous Ovarian Carcinoma

Identifying novel, durable treatments for high-grade serous ovarian cancer (HGSOC) is paramount to extend both progression-free survival (PFS) and overall survival (OS) in patients afflicted with this disease. Dual-specificity phosphatase 1 (DUSP1) was identified as one of seven genes that may significantly affect prognosis in patients with HGSOC; however, the role of DUSP inhibition (DUSPi) in the treatment of HGSOC remains largely unknown. In this study, we show that DUSP1 is highly expressed in HGSOC and confers worse PFS and OS. Further, we corroborate data that show DUSP1 expression is directly associated with therapy resistance. Using a tissue microarray of 137 different serous ovarian carcinomas, we demonstrate the high expression of DUSP1 in primary and recurrent serous ovarian cancer. In both acquired and de novo therapy HGSOC-resistant models, DUSPi both inhibited cellular proliferation and promoted cell death. RPPA analysis of HGSOC cells revealed DUSPi led to the differential regulation of several pathways, including AMPK and mTORC. Further, in a patient-derived xenograft HGSOC model, DUSPi significantly inhibited tumor progression.

On clustering for cell-phenotyping in multiplex immunohistochemistry (mIHC) and multiplexed ion beam imaging (MIBI) data

OBJECTIVE

Multiplex immunohistochemistry (mIHC) and multiplexed ion beam imaging (MIBI) images are usually phenotyped using a manual thresholding process. The thresholding is prone to biases, especially when examining multiple images with high cellularity.

RESULTS

Unsupervised cell-phenotyping methods including PhenoGraph, flowMeans, and SamSPECTRAL, primarily used in flow cytometry data, often perform poorly or need elaborate tuning to perform well in the context of mIHC and MIBI data. We show that, instead, semi-supervised cell clustering using Random Forests, linear and quadratic discriminant analysis are superior. We test the performance of the methods on two mIHC datasets from the University of Colorado School of Medicine and a publicly available MIBI dataset. Each dataset contains a bunch of highly complex images.

Loss of Claudin-4 Reduces DNA Damage Repair and Increases Sensitivity to PARP Inhibitors

High-grade serous ovarian cancer is the deadliest gynecologic malignancy due to progression to resistant disease. Claudin-4 is classically defined as a tight junction protein and is often associated with epithelial cancers. Claudin-4 is aberrantly expressed in nearly 70% of all ovarian cancer tumors and conveys a worse overall prognosis. Elevated claudin-4 expression correlates to increased DNA repair activity and resistance to DNA damaging agents. PARP inhibitors are emerging as an effective therapeutic option for patients with ovarian cancer and function by promoting DNA damage. The study examines the relationship between claudin-4 expression and the response to PARP inhibitors using both genetic and pharmacologic inhibition of claudin-4 in in vitro and ex vivo models of ovarian cancer to examine DNA repair markers and functional activity. Genetic inhibition of claudin-4 results in the downregulation of several DNA damage repair effectors, including 53BP1 and XRCC1. Claudin-4 knockdown did not change homology-directed repair but inhibited nonhomologous end-joining and reduced 53BP1 foci formation. In 15 primary ovarian cancer tumors, higher claudin-4 expression significantly correlated to a dampened PARP inhibitor-mediated antiproliferation response. Further, claudin-4 inhibition in high claudin-4 tumors sensitized tumor sections to PARP inhibition. These data highlight that claudin-4 expression in ovarian cancer tumors could serve as both a marker of PARP inhibitor response and a therapeutic target to improve PARP inhibitor response.

The SETDB1-TRIM28 Complex Suppresses Antitumor Immunity

The tumor immune microenvironment is influenced by the epigenetic landscape of the tumor. Here, we have identified the SETDB1-TRIM28 complex as a critical suppressor of antitumor immunity. An epigenetic CRISPR-Cas9 screen of 1,218 chromatin regulators identified TRIM28 as a suppressor of PD-L1 expression. We then revealed that expression of the SETDB1-TRIM28 complex negatively correlated with infiltration of effector CD8⁺ T cells. Inhibition of SETDB1-TRIM28 simultaneously upregulated PD-L1 and activated the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) innate immune response pathway to increase infiltration of CD8⁺ T cells. Mechanistically, SETDB1-TRIM28 inhibition led to micronuclei formation in the cytoplasm, which is known to activate the cGAS-STING pathway. Thus, SETDB1-TRIM28 inhibition bridges innate and adaptive immunity. Indeed, SETDB1 knockout enhanced the antitumor effects of immune checkpoint blockade with anti-PD-L1 in a mouse model of ovarian cancer in a cGAS-dependent manner. Our findings establish the SETDB1-TRIM28 complex as a regulator of antitumor immunity and demonstrate that its loss activates cGAS-STING innate immunity to boost the antitumor effects of immune checkpoint blockade.

Abstract P068: Different treatment schemes cause distinct PARP inhibitor resistance mechanisms in BRCA2-mutant ovarian cancer cells

Poly (ADP-ribose) polymerase inhibitors (PARPis) represent a major advance in ovarian cancer management, now as treatment for recurrent ovarian cancer and as a maintenance therapy following platinum-based chemotherapy in the upfront and platinum-sensitive recurrent settings. Yet, a growing number of patients progress through PARPis, creating a need for further understanding on resistance mechanisms. We hypothesized that different treatment dosing/timing schemes would cause distinct mechanisms of acquired resistance to PARPis. To test this hypothesis, we exposed BRCA2-mutant PEO1 ovarian cancer cells to 0.5 μM olaparib, doubling its concentration up to 40 μM over 3–4 months (PEO1/OlaJR). The second PARPi-resistant PEO1 cell line (PEO1/OlaR) was developed using a relatively low initial dose of 5 nM olaparib, and gradually increasing its concentration up to 20 μM over 6 months. To confirm PARPi resistance, cell proliferation and viability were measured by MTT and colony formation assay, respectively. Both cell lines were resistant to two different PARPis beyond clinically achievable concentrations (olaparib IC50 141.7–372.8 μM and rucaparib IC50 37.1–51.2 μM) and demonstrated restored homologous recombination (HR) repair as evidenced by increased HR-reporter activity (1.32 to 1.45-fold compared to PEO1, p &lt; 0.05) and RAD51 foci formation (5.2 to 6.1-fold compared to PEO1, p &lt; 0.001). For PEO1/OlaJR, distinct resistance mechanisms to PARPi were noted: 1) promoting drug efflux confirmed by increased MDR efflux activity (1.92-fold compared to PEO1, p &lt; 0.001) and increased protein levels of an ABCB1 transporter (7.2-fold compared to PEO1); and 2) enhancing HR repair restoration, likely via reduced REV7 protein expression (0.43-fold compared to PEO1). On the other hand, PEO1/OlaR exhibited a mesenchymal cell phenotype with greater invasion ability as measured by transwell invasion assay (2.25-fold compared to PEO1, p &lt; 0.001) and restored HR repair with upregulation of TRIP13 protein (1.85-fold compared to PEO1). PEO1/OlaR also showed increased cell survival, possibly via activation of PI3K/AKT signaling, as evidenced by increased p-AKT (2.12-fold compared to PEO1). No loss of 53BP1 was observed in either PEO1/OlaJR or PEO1/OlaR based on whole exome sequencing and immunoblotting of 53BP1. BRCA2 reversion mutation status is currently under investigation. Altogether, our findings suggest that mechanisms of resistance to PARPis arise differently based on the duration and concentrations of drug treatment, highlighting the importance of appreciating interplay between specific treatment schemes and the downstream consequences. Thus, developing tailored therapeutic strategies should consider various mechanisms of PARPi resistance.

Citation Format: Tzu-Ting Huang, Jayakumar R. Nair, Nitasha Gupta, Tomomi M. Yamamoto, Benjamin G. Bitler, Jung-Min Lee. Different treatment schemes cause distinct PARP inhibitor resistance mechanisms in BRCA2-mutant ovarian cancer cells [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P068.

The Spatial Context of Tumor-Infiltrating Immune Cells Associates with Improved Ovarian Cancer Survival

Ovarian cancer is the deadliest gynecologic malignancy. Multi-omics techniques have provided a platform for improved predictive modeling of therapy response and patient outcomes. While high-grade serous carcinoma (HGSOC) tumors are immunogenic and numerous studies have defined positive correlation to immune cell infiltration, immunotherapies in clinical trials have exhibited low efficacy rates. There is a significant need to better comprehend the role and composition of immune cells in mediating ovarian cancer therapeutic response and progression. We performed multiplex IHC with an HGSOC tissue microarray (n = 127) to characterize the immune cell composition within tumors. After analyzing the composition and spatial context of T cells (CD4/CD8), macrophages (CD68), and B cells (CD19) within the tumor, we found that increased B-cell and CD4 T-cell presence correlated with overall survival. More importantly, we observed that the proximity between tumor-associated macrophages and B cells or CD4 T cells significantly correlated with overall survival. IMPLICATIONS: The results highlight the antitumor role of B cells and CD4 T cells, and that the spatial interactions between immune cell types are a novel predictor of therapeutic response and patient outcomes.

Assessing Genetic Variants in Matched Biocompartments From Patients With Serous Ovarian Cancer

The clinical use of molecular tumor profiling (MTP) is expanding and there is an increasing use of MTP data to manage patient care. At the University of Colorado, 18 patients were diagnosed with primary serous ovarian cancer between 9/2015 and 6/2019 and consented for banking and analysis of tumor, ascites and plasma. All 18 patients had tumor and plasma samples that were sent for MTP, and 13 of 18 patients additionally had ascites collected and sent for MTP. 50-gene panel testing and BRCA testing were performed on primary tumor. BRCA genetic variants were more likely to be identified in plasma as compared to ascites or tumor, though not statistically significant (P = 0.17). Co-occurring genetic variants between plasma and ascites were less common in comparison to co-occurring variants between tumor and plasma or tumor and ascites, though not statistically significant (P = 0.68). Variants in KDR (VEGFR2) and TP53 were most likely to be conserved across all 3 biocompartments. Mutant allele frequencies (MAF) of individual genetic variants varied across biocompartments, though tended to be highest in the tumor, followed by ascites.

Decoding the dynamic tumor microenvironment

An opportunity to improve cancer outcomes with machine learning.

Inhibiting Wnt/beta-catenin in CTNNB1-mutated endometrial cancer

The role of β-catenin/TCF transcriptional activity in endometrial cancer (EC) recurrence is not well understood. We assessed the impact of Wnt/β-catenin inhibition in EC models. In an analysis of the Cancer Genome Atlas, we confirmed that CTNNB1 mutations are enriched in recurrent low-risk EC and showed that aberrant Wnt/β-catenin pathway activation is associated with recurrence. We studied CTNNB1-wildtype (HEC1B, Ishikawa) and CTNNB1-mutant (HEC108, HEC265, HEC1B-S33Y, Ishikawa-S33Y) EC cell lines. Dose response curves were determined for 5 Wnt/β-catenin pathway inhibitors (Wnt-C59, XAV-939, PyrPam, PRI-724, SM04690). XAV939, Wnt-C59 and PyrPam inhibited function upstream of β-catenin transcriptional activity and were ineffective at inhibiting cell viability. In contrast, PRI724 and SM04690 indirectly inhibited β-catenin transcriptional activity and significantly reduced cell viability in CTNNB1-mutant cell lines. Treatment with SM04690 reduced cell viability (Licor Cell stain) in all EC cell lines, but viability was significantly lower in CTNNB1-mutant cell lines (p < 0.01). Mechanistically, SM04690 significantly inhibited proliferation measured via 5'-bromo-2'-deoxyuridine incorporation and reduced T cell factor (TCF) transcriptional activity. HEC1B, HEC1B-S33Y and HEC265 tumor-bearing mice were treated with vehicle or SM04690. Tumors treated with SM04690 had smaller mean volumes than those treated with vehicle (p < 0.001, p = 0.014, p = 0.06). In HEC1B-S33Y and HEC265 tumors, SM04690 treatment significantly reduced Ki67 H-scores compared to vehicle (p = 0.035, p = 0.024). Targeting the Wnt/β-catenin pathway in CTNNB1-mutant EC effectively inhibited proliferation and β-catenin/TCF transcriptional activity and blunted tumor progression in in vivo models. These studies suggest β-catenin transcriptional inhibitors are effective in EC and particularly in CTNNB1-mutant EC, highlighting a potential therapeutic vulnerability for treatment of CTNNB1-mutant EC.

Abstract PO043: Targeting beta-catenin and Wnt signaling in CTNNB1-mutated endometrial cancer

Background: CTNNB1 mutations convey increased rates of disease recurrence in early stage, low grade endometrial cancer (EC). The role of beta-catenin transcriptional activity in CTNNB1-mutated EC recurrence is not well understood. We aim to assess the impact of Wnt/beta-catenin inhibition in EC models.

Methods: Data mining The Cancer Genome Atlas (TCGA) of endometrial carcinoma (PanCancer Atlas), we evaluated CTNNB1-mutated vs -wildtype tumors in a low-risk population. We then studied EC cell lines that are CTNNB1-wildtype (HEC1B, Ishikawa) or CTNNB1-mutated (HEC108, HEC265, HEC1B-S33Y, Ishikawa-S33Y). CTNNB1-S33Y cell lines were created via retroviral transduction. Treatment dose curves were determined for 5 Wnt/beta-catenin pathway inhibitors (Wnt-C59, XAV-939, PyrPam, PRI-724, SM04690). Cell viability was assessed with Licor Cell Staining. TCF transcriptional activity was determined via TOP/FOP reporter assay. Apoptosis following treatment with SM04690 was evaluated via Annexin V/propidium iodide (PI). HEC1B, HEC1B-S33Y and HEC265 tumor-bearing athymic nude mice were treated with vehicle or SM04690 25mg/kg. Tumor size was measured using calipers. Tumor cell proliferation and apoptosis were evaluated with immunohistochemistry for Ki67 and Cleaved Caspase 3.

Results: TCGA database analysis parallels previous findings that CTNNB1 mutations are enriched in recurrent low-risk EC. XAV939, Wnt-C59 and PyrPam all inhibit function upstream of beta-catenin transcriptional activity and were ineffective at inhibiting EC cell viability. In contrast, PRI724 and SM04690 indirectly inhibit beta-catenin transcriptional activity and significantly reduce cell viability in CTNNB1-mutated EC cell lines. Treatment with SM04690 reduced cell viability in all EC cell lines, but was significantly lower in HEC108, HEC265 and HEC1B-S33Y compared to HEC1B (24.2%, 32.3%, 44.4%, 71.4%, p&lt;0.01). Compared to control, SM04690 significantly induced apoptosis in HEC265 cells (3.98% vs. 6.91% AnnexinV/PI+, p=0.0443) and reduced TCF transcriptional activity in HEC1B-S33Y (-84%, p=0.017) and HEC108 (-74%, p=0.002) cells. In the mouse model, HEC1B, HEC1B-S33Y and HEC265 tumors treated with SM04690 had smaller mean tumor volumes than those treated with vehicle (146.4 vs 335.4cm3, p&lt;0.001; 136.4 vs. 243.1cm3, p=0.014; 105.7 vs. 321.8cm3, p=0.06). In HEC1B-S33Y tumors, SM04690 treatment significantly reduced Ki67 H-scores compared to vehicle (129.8 vs. 146.7, p=0.0351).

Conclusions: Targeting the Wnt/beta-catenin pathway in CTNNB1-mutated EC effectively inhibited proliferation and beta-catenin/TCF transcriptional activity. Further, the inhibitor SM04690 blunted tumor progression in multiple in vivo models. These studies demonstrate beta-catenin transcriptional inhibitors are effective in CTNNB1-mutated EC and have a more significant effect in CTNNB1-mutated EC than CTNNB1-wildtype EC. These findings highlight a potential therapeutic vulnerability for treatment of CTNNB1-mutated EC.

Citation Format: Marisa R. Moroney, Elizabeth R. Woodruff, Lubna Qamar, Benjamin G. Bitler, Bradley R. Corr. Targeting beta-catenin and Wnt signaling in CTNNB1-mutated endometrial cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference: Endometrial Cancer: New Biology Driving Research and Treatment; 2020 Nov 9-10. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(3_Suppl):Abstract nr PO043.

The Capacity of the Ovarian Cancer Tumor Microenvironment to Integrate Inflammation Signaling Conveys a Shorter Disease-free Interval

PURPOSE

Ovarian cancer has one of the highest deaths to incidence ratios across all cancers. Initial chemotherapy is effective, but most patients develop chemoresistant disease. Mechanisms driving clinical chemo-response or -resistance are not well-understood. However, achieving optimal surgical cytoreduction improves survival, and cytoreduction is improved by neoadjuvant chemotherapy (NACT). NACT offers a window to profile pre- versus post-NACT tumors, which we used to identify chemotherapy-induced changes to the tumor microenvironment.

EXPERIMENTAL DESIGN

We obtained matched pre- and post-NACT archival tumor tissues from patients with high-grade serous ovarian cancer (patient, n = 6). We measured mRNA levels of 770 genes (756 genes/14 housekeeping genes, NanoString Technologies), and performed reverse phase protein array (RPPA) on a subset of matched tumors. We examined cytokine levels in pre-NACT ascites samples (n = 39) by ELISAs. A tissue microarray with 128 annotated ovarian tumors expanded the transcriptional, RPPA, and cytokine data by multispectral IHC.

RESULTS

The most upregulated gene post-NACT was IL6 (16.79-fold). RPPA data were concordant with mRNA, consistent with elevated immune infiltration. Elevated IL6 in pre-NACT ascites specimens correlated with a shorter time to recurrence. Integrating NanoString (n = 12), RPPA (n = 4), and cytokine (n = 39) studies identified an activated inflammatory signaling network and induced IL6 and IER3 (immediate early response 3) post-NACT, associated with poor chemo-response and time to recurrence.

CONCLUSIONS

Multiomics profiling of ovarian tumor samples pre- and post-NACT provides unique insight into chemo-induced changes to the tumor microenvironment. We identified a novel IL6/IER3 signaling axis that may drive chemoresistance and disease recurrence.

Abstract 5305: Characterization of the ovarian tumor transcriptome and microenvironment in pre and post-chemotherapy treated patients

Purpose: Ovarian cancer has one of the highest deaths to incidence ratios across all cancers. Initial chemotherapy is typically effective, but most patients will experience recurrence and enter a cycle of response and recurrence, ultimately developing resistant disease. Importantly, the understanding of mechanisms contributing to clinical chemoresistance in ovarian cancer is limited. Achieving optimal cytoreduction improves survival. Gynecologic oncologists therefore perform laparoscopy to evaluate resectability and collect tumor biopsies. Patients identified with un-resectable tumor receive three cycles of neoadjuvant platinum/taxane-based chemotherapy (NACT) to improve the likelihood of optimal cytoreductive surgery. NACT offers a previously unavailable window for identifying therapy-induced remodeling of the tumor, potentially providing insight into drivers of chemo-resistance.

Experimental Design: We accessed formalin fixed (FFPE) tumor tissue from high-grade serous ovarian cancer NACT patients (n=6) pre- and post-chemotherapy. RNA was extracted and the mRNA transcript levels were examined for 791 genes via the Immunoncology 360 NanoString panel. Further, using the pre-treated ascites fluid we examined the cytokine environment through MesoScale Discovery multiplex ELISA. Transcriptional and cytokine profiles were correlated to clinical outcomes, such as days to recurrence.

Results: Component analysis found that transcriptional profiles separated based on pre- and post-chemotherapy status. Comparing the pre- (n=6) and post-chemotherapy (n=6), the most upregulated gene following therapy was IL6 (4.1 log2 fold change, adj. p = 0.045) and the most downregulated gene was UBE2C (-3.9 log2 fold change, adj. p = 0.001). Elevated IL-6 within ascites correlated to a shorter time to recurrence. On the patient-by-patient basis we compared transcriptional changes between pre- and post therapy. We correlated these changes to IL6 expression and time to recurrence uncovered that an increase in Immediate Early Response 3 (IER3) is a poor prognostic indicator. IER3/IEX-1 is a NF-κB target gene involved in apoptosis and potentiates MAPK activation.

Conclusion: Using ovarian cancer tumors from NACT patients provides a unique insight into chemo-induced transcriptional changes. To-date little is known of IER3's function in ovarian cancer thus future work will focus on a potential novel IL-6/IER3 signaling axis that protects tumors from chemotherapy-induced apoptosis. Also, computer modeling and integration of transcriptional and cytokine date could also provide an approach to predict recurrence.

Citation Format: Kimberly R. Jordan, Jill Slansky, Angela Minic, Jennifer K. Richer, James C. Costello, Aaron J. Clauset, Rajendra T. Kumar, Kian Behbakht, Matthew J. Sikora, Benjamin G. Bitler. Characterization of the ovarian tumor transcriptome and microenvironment in pre and post-chemotherapy treated patients [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5305.

Abstract A51: The role of ATF6-mediate AP-1 signaling in promoting PARP inhibitor-resistant ovarian cancer

The purpose of this study is to define the role of AP-1 mediated DNA repair in PARP inhibitor (PARPi)-resistant high-grade serous ovarian cancer (HGSOC). AP-1 is a dimeric transcription factor comprising Jun, Fos, and/or ATF proteins and its signaling is known to regulate multiple DNA repair genes, including PARP1. Wnt activation can promote AP-1 signaling and upregulates expression of AP-1 subunits. We previously published that hyperactive Wnt signaling in PARPi-resistant HGSOC cells promotes DNA repair and attenuates PARPi response. We therefore hypothesized that Wnt signaling drives PARPi resistance thorough increased AP1-signaling and subsequent enhanced DNA repair. We performed transcription factor analysis of RNA sequencing data from TP53/BRCA2-mutated olaparib-sensitive (PEO1) and -resistant (PEO1-OR) HGSOC cells. We observed increased AP-1 target genes in resistant cells and confirmed elevated AP-1 activity with a reporter assay. Quantitative PCR (qPCR) demonstrated that a majority of AP-1 subunits were upregulated in olaparib-resistant cells, namely JUN, ATF5, and ATF6. An shRNA screen was performed to determine which AP-1 subunits are necessary to convey olaparib resistance. Four out of five shRNAs targeting ATF6 effectively resensitized PARPi-resistant cells to olaparib. We confirmed that ATF6 protein was elevated in PEO1-OR cells. To further explore the role of ATF6 in AP-1 mediated PARPi resistance, ATF6 was stably knocked down in PEO1-OR cells. Colony formation assays confirmed that loss of ATF6 resensitized cells to olaparib. Knockdown of ATF6 also resulted in decreased transcription of PARP1, as measured by qPCR, and higher baseline levels of DNA damage, as measured by phosphorylated histone gamma-H2AX. Future studies will evaluate ATF6-dependent DNA repair in in vitro and in vivo models of PARPi-resistant HGSOC. In summary, these data indicate activation of AP-1 signaling through increased expression of ATF6 is promoting enhanced DNA repair capacity, which could be contributing to PARPi resistance. Thus, pharmacologic inhibition of AP-1 or ATF6 could provide a targetable approach to overcome resistance and improve patient outcomes.

Citation Format: Alexandra N. McMellen, Benjamin G. Bitler. The role of ATF6-mediate AP-1 signaling in promoting PARP inhibitor-resistant ovarian cancer [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr A51.

Abstract A77: Histone methyltransferases EHMT1 and EHMT2 (GLP/G9A) maintain PARP inhibitor resistance in high-grade serous ovarian carcinoma

The purpose of this study is to examine the contribution of epigenetics to PARP inhibitor (PARPi) resistance in high-grade serous ovarian carcinoma (HGSOC). To identify epigenetic mechanisms of PARPi resistance in HGSOC we utilized unbiased exploratory techniques, including mass spectrometry profiling of histone modifications and RNA-sequencing. Our data show that, compared to sensitive cells and tumors, PARPi-resistant HGSOC cell lines and in vivo patient-derived ascites display a global increase of histone H3 lysine 9 dimethylation (H3K9me2) accompanied by overexpression of histone methyltransferases EHMT1 and EHMT2. EHMT1/2 catalyze H3K9me2 and have canonical roles in epigenetic silencing of gene expression. EHMT1/2 also have direct roles in DNA repair and have previously been implicated in erlotinib resistance in non-small cell lung cancer. The role of EHMT1/2 in PARPi response has not been evaluated in HGSOC. Using immunohistochemistry, we stained a tissue microarray of over 100 primary ovarian tumors for H3K9me2. High H3K9me2 correlates with significantly worse overall survival. We then used genetic and pharmacologic methods to disrupt EHMT1/2 and examined PARPi sensitivity, apoptosis, DNA repair, and cell cycle. EHMT1/2 disruption reduced H3K9me2 and sensitizes HGSOC cells to PARPi. EHMT1/2 disruption does not increase PARPi-induced apoptosis, suggesting a cytostatic effect, rather than cytotoxic. Functional assays of DNA repair show that disruption of EHMT1/2 ablates both homologous recombination and nonhomologous end joining. Consistently, immunofluorescent staining of phosphorylated histone gamma-H2AX shows increases in DNA damage following EHMT1/2 inhibition. Propidium iodide staining and flow cytometry analysis of cell cycle shows PARPi treatment increases the proportion of PARPi-resistant cells in S and G2 phases, while cells treated with an EHMT1/2 inhibitor remain in G1. Co-treatment with PARPi and EHMT1/2 inhibitor produces an intermediate phenotype. Immunoblot of cell cycle regulators shows that combined EHMT1/2 and PARP inhibition reduces expression of Cyclin A, Cyclin B1, and M-phase inducer CDC25C. We also observed reduced phosphorylation of CDC25C and mitotic markers MPM2 and histone H3 serine 28. These data suggest EHMT1/2 increases DNA damage repair and regulates cell cycle progression, both of which contribute to PARPi resistance. In summary, this study demonstrates that disrupting EHMT1/2 sensitizes HGSOC cells to PARPi and suggests a potential mechanism through DNA damage and cell cycle dysregulation. Identification of factors promoting PARPi resistance, such as EHMT1/2 and H3K9me2, will facilitate development of novel prognostic and therapeutic strategies to successfully treat resistant HGSOC.

Citation Format: Zachary L. Watson, Tomomi M. Yamamoto, Connor J. Hughes, Lindsay J. Wheeler, Miriam D. Post, Kian Behbakht, Benjamin G. Bitler. Histone methyltransferases EHMT1 and EHMT2 (GLP/G9A) maintain PARP inhibitor resistance in high-grade serous ovarian carcinoma [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr A77.

Abstract A30: Claudin-4-dependent mechanisms of high-grade serous ovarian cancer progression

In The Cancer Genome Atlas, Claudins-3, -4, and -7 are highly expressed in high-grade serous ovarian cancer (HGSOC). While claudins-3 and -7 are often expressed at tight junctions, claudin-4 (CLDN4) appears to be cytoplasmic, both in normal cells where it is expressed rarely and in a model of HGSOC, often used to study cellular interactions in this disease, OVCAR3 cells. CLDN4 expression reduces response to paclitaxel and conveys worse overall survival. We, therefore, wanted to further elucidate CLDN4-dependent mechanisms of cancer progression and therapeutic response. To address CLDN4 biology, we utilized immunohistochemical (IHC) analysis, loss-of-function studies, and several nonbiased approaches, including RNA-sequencing and proteomics. The IHC showed CLDN4 protein localized in the Golgi compartment with GM130 and around the cells at sites of cell-cell contact. Knocking down CLDN4 by 80% in OVCAR3 cells led them to undergo a transition from a more epithelial morphology to a mesenchymal phenotype (EMT). RNA-Seq analysis supports this morphologic interpretation by showing an increase in mRNA for genes coding for mesenchymal proteins such as fibronectin-1 (FN1), CD44, VIM, TNC, MMP2, and SNAI2 and a decrease in epithelial genes such as E-cadherin (CDH1), CD24, KRT18, and KRT19. RNA-Seq analysis of non-membrane protein kinases showed a 2-fold increase in PLAU, MSN, CAV1, CAV2, and EPHA2 and a 2-fold decrease in IGFBP2 and ERBB2, results that correlate well with the sensitivity of cancer cells to the BCR-ABL inhibitor, dasatinib. To determine the proteins that associate with CLDN4, we performed biotin ligase analysis (Bio-ID) fusing biotin protein ligase to CLDN4 and introducing the gene for the fusion protein into both OVCAR3 and OVCAR8 cells. Of the 36 proteins repeatedly more highly biotinylated in the presence of CLDN4-biotin ligase, 20 were identified as plasma membrane proteins and eight as Golgi localized by Gene Ontology analysis. Notably, we discovered a tyrosine protein kinase, YES1, to be biotinylated in both cell lines. YES1 is a poor prognostic indicator in HGSOC and promotes signal propagation following receptor tyrosine kinase activation, which contributes to a plethora of downstream outputs, including cell-cell adhesion and cell survival. These findings imply that CLDN4 expression is related to EMT and knockdown of CLDN4 could increase the sensitivity HGSOC to inhibitors such as dasatinib (BCR-ABL) or saracatinib (c-Yes).

Citation Format: Patricia Webb, Margaret C. Neville, Heidi Baumgartner-Wilson, Miriam D. Post, Andrew Goodspeed, Benjamin G. Bitler. Claudin-4-dependent mechanisms of high-grade serous ovarian cancer progression [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr A30.

Targeting Fatty Acid Oxidation to Promote Anoikis and Inhibit Ovarian Cancer Progression

Epithelial-derived high-grade serous ovarian cancer (HGSOC) is the deadliest gynecologic malignancy. Roughly 80% of patients are diagnosed with late-stage disease, which is defined by wide-spread cancer dissemination throughout the pelvic and peritoneal cavities. HGSOC dissemination is dependent on tumor cells acquiring the ability to resist anoikis (apoptosis triggered by cell detachment). Epithelial cell detachment from the underlying basement membrane or extracellular matrix leads to cellular stress, including nutrient deprivation. In this report, we examined the contribution of fatty acid oxidation (FAO) in supporting anoikis resistance. We examined expression Carnitine Palmitoyltransferase 1A (CPT1A) in a panel of HGSOC cell lines cultured in adherent and suspension conditions. With CPT1A knockdown cells, we evaluated anoikis by caspase 3/7 activity, cleaved caspase 3 immunofluorescence, flow cytometry, and colony formation. We assessed CPT1A-dependent mitochondrial activity and tested the effect of exogenous oleic acid on anoikis and mitochondrial activity. In a patient-derived xenograft model, we administered etomoxir, an FAO inhibitor, and/or platinum-based chemotherapy. CPT1A is overexpressed in HGSOC, correlates with poor overall survival, and is upregulated in HGSOC cells cultured in suspension. CPT1A knockdown promoted anoikis and reduced viability of cells cultured in suspension. HGSOC cells in suspension culture are dependent on CPT1A for mitochondrial activity. In a patient-derived xenograft model of HGSOC, etomoxir significantly inhibited tumor progression. IMPLICATIONS: Targeting FAO in HGSOC to promote anoikis and attenuate dissemination is a potential approach to promote a more durable antitumor response and improve patient outcomes.

Wnt family member 4 (WNT4) and WNT3A activate cell-autonomous Wnt signaling independent of porcupine O-acyltransferase or Wnt secretion

Porcupine O-acyltransferase (PORCN) is considered essential for Wnt secretion and signaling. However, we observed that PORCN inhibition does not phenocopy the effects of WNT4 knockdown in WNT4-dependent breast cancer cells. This suggests a unique relationship between PORCN and WNT4 signaling. To examine the role of PORCN in WNT4 signaling, here we overexpressed WNT4 or WNT3A in breast cancer, ovarian cancer, and fibrosarcoma cell lines. Conditioned media from these lines and co-culture systems were used to assess the dependence of Wnt secretion and activity on the critical Wnt secretion proteins PORCN and Wnt ligand secretion (WLS) mediator. We observed that WLS is universally required for Wnt secretion and paracrine signaling. In contrast, the dependence of WNT3A secretion and activity on PORCN varied across the cell lines, and WNT4 secretion was PORCN-independent in all models. Surprisingly, WNT4 did not exhibit paracrine activity in any tested context. Absent the expected paracrine activity of secreted WNT4, we identified cell-autonomous Wnt signaling activation by WNT4 and WNT3A, independent of PORCN or Wnt secretion. The PORCN-independent, cell-autonomous Wnt signaling demonstrated here may be critical in WNT4-driven cellular contexts or in those that are considered to have dysfunctional Wnt signaling.

Histone methyltransferases EHMT1 and EHMT2 (GLP/G9A) maintain PARP inhibitor resistance in high-grade serous ovarian carcinoma

BACKGROUND

Euchromatic histone-lysine-N-methyltransferases 1 and 2 (EHMT1/2, aka GLP/G9A) catalyze dimethylation of histone H3 lysine 9 (H3K9me2) and have roles in epigenetic silencing of gene expression. EHMT1/2 also have direct roles in DNA repair and are implicated in chemoresistance in several cancers. Resistance to chemotherapy and PARP inhibitors (PARPi) is a major cause of mortality in high-grade serous ovarian carcinoma (HGSOC), but the contribution of the epigenetic landscape is unknown.

RESULTS

To identify epigenetic mechanisms of PARPi resistance in HGSOC, we utilized unbiased exploratory techniques, including RNA-Seq and mass spectrometry profiling of histone modifications. Compared to sensitive cells, PARPi-resistant HGSOC cells display a global increase of H3K9me2 accompanied by overexpression of EHMT1/2. EHMT1/2 overexpression was also observed in a PARPi-resistant in vivo patient-derived xenograft (PDX) model. Genetic or pharmacologic disruption of EHMT1/2 sensitizes HGSOC cells to PARPi. Cell death assays demonstrate that EHMT1/2 disruption does not increase PARPi-induced apoptosis. Functional DNA repair assays show that disruption of EHMT1/2 ablates homologous recombination (HR) and non-homologous end joining (NHEJ), while immunofluorescent staining of phosphorylated histone H2AX shows large increases in DNA damage. Propidium iodide staining and flow cytometry analysis of cell cycle show that PARPi treatment increases the proportion of PARPi-resistant cells in S and G2 phases, while cells treated with an EHMT1/2 inhibitor remain in G1. Co-treatment with PARPi and EHMT1/2 inhibitor produces an intermediate phenotype. Immunoblot of cell cycle regulators shows that combined EHMT1/2 and PARP inhibition reduces expression of specific cyclins and phosphorylation of mitotic markers. These data suggest DNA damage and altered cell cycle regulation as mechanisms of sensitization. RNA-Seq of PARPi-resistant cells treated with EHMT1/2 inhibitor showed significant gene expression changes enriched in pro-survival pathways that remain unexplored in the context of PARPi resistance, including PI3K, AKT, and mTOR.

CONCLUSIONS

This study demonstrates that disrupting EHMT1/2 sensitizes HGSOC cells to PARPi, and suggests a potential mechanism through DNA damage and cell cycle dysregulation. RNA-Seq identifies several unexplored pathways that may alter PARPi resistance. Further study of EHMT1/2 and regulated genes will facilitate development of novel therapeutic strategies to successfully treat HGSOC.

Abstract GMM-058: CBX2 IDENTIFIED AS DRIVER OF ANOIKIS ESCAPE AND DISSEMINATION IN HIGH GRADE SEROUS OVARIAN CANCER

The vast majority of high grade serous ovarian carcinomas (HGSOC) are diagnosed at an advanced stage. Chromobox 2 (CBX2), a polycomb repressor complex subunit, plays an oncogenic role in a variety of cancers. In prostate cancer, CBX2 is a driver of metastatic progression. Little is known about the role of CBX2 in HGSOC. Our hypothesis is that CBX2 upregulation promotes advanced HGSOC by promoting a stem-like transcriptional profile and inhibiting anoikis. Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) were queried to establish the role of CBX2 in HGSOC. In vitro evaluation of CBX2 occurred in OVCAR4, PEO1, and OVCAR8 HGSOC cell lines. PolyHEMA-coated plates forced cells to grow in suspension and simulated anoikis-escape. Quantitative polymerase chain reaction and immunoblots evaluated CBX2 expression. Small hairpin RNAs (shRNAs) knocked CBX2 down for loss of function studies. To mimic HGSOC progression several culture conditions, including 2D, colony formation, and 3D, spheroid, were examined. Secreted Gaussia luciferase (gLuc) activity was utilized as an indicator of proliferation. Stemness was tested with the Aldefluor assay, measuring aldehyde dehydrogenase activity (ALDH). Using patient tumors derived from the Gynecology Tissue and Fluid Bank (GTFB) and a HGSOC tissue microarray (TMA) with matched primary, metastatic, and lymph nodes, a CBX2 expression profile was established. Student's t-test was used to define statistical significance, with a p value of &lt; 0.05. Analysis of GEO databases established CBX2 is upregulated in HGSOC tumors compared to benign tissues. Analysis of TCGA found CBX2 expression conveyed worse disease-free survival (11.7 vs 17.6 months, Log-rank test p-value &lt; 0.005) and overall survival (34 vs. 44.8 months, Log-rank test p-value &lt;0.005). Examination of primary HGSOC tumors confirmed CBX2 was upregulated at the protein level in HGSOC compared to benign tissue. In vitro, OVCAR4, PEO1, and OVCAR8 cells upregulate CBX2 when grown in suspension compared to adherent conditions. CBX2 knockdown led to a significant inhibition of proliferation in 2D, 3D, and in suspension. Forced suspension promoted increased ALDH3A1 expression and ALDH activity. CBX2 knockdown led to a decrease in both ALDH3A1 expression and ALDH activity. HGSOC cells grown in suspension were found to be more chemoresistant compared cells grown under adherent conditions. Similarly, knockdown of CBX2 sensitized HGSOC cells to cisplatin. Examination of primary tissue in a TMA of matched patient samples revealed CBX2 is expressed in primary and metastatic disease. We conclude that CBX2 directly impacts proliferation and is overexpressed in HGSOC. Our work indicates that CBX2 is an important regulator of stem-ness, which could play a role in anoikis escape, HGSOC dissemination, and chemoresistance, suggesting that CBX2 may be associated with more advanced disease. This exploration expands our understanding of molecular drivers of HGSOC progression and potentially identifies a novel therapeutic target.

Citation Format: Lindsay J. Wheeler, Zachary L. Watson, Lubna Qamar, Alexandra McMellen, Tomomi Yamamoto, Kian Behbakht, and Benjamin G. Bitler. CBX2 IDENTIFIED AS DRIVER OF ANOIKIS ESCAPE AND DISSEMINATION IN HIGH GRADE SEROUS OVARIAN CANCER [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr GMM-058.

Abstract NT-114: CATALYTIC SUBUNITS SWITCH DRIVES RESISTANCE TO EZH2 INHIBITORS IN ARID1A-MUTATED CELLS

The SWI/SNF chromatin remodeling complex is altered in ~20% of human cancers. ARID1A, a component of the SWI/SNF chromatin-remodeling complex, is the most frequently mutated epigenetic regulator in human cancers. Inactivation of the SWI/SNF complex is synthetically lethal with inhibition of EZH2 activity. EZH2 inhibitors are entering clinical trials for specific tumor types with SWI/SNF mutations. However, mechanisms of de novo or acquired resistance to EZH2 inhibitors in cancers with inactivating SWI/SNF mutations are unknown. Here we show that the switch of the SWI/SNF catalytic subunits from SMARCA4 to SMARCA2 drives resistance to EZH2 inhibitors in ARID1A-mutated ovarian cancer cells. SMARCA4 decease dominates over SMARCA2 increase in the switch. SMARCA4 loss leads to suppression of apoptotic pathways through upregulating anti-apoptotic genes such as BCL2 in the EZH2 inhibitor resistant cells. EZH2 inhibitor resistant ARID1A-mutated cells are hypersensitive to BCL2 inhibitors such as ABT263. ABT263 is sufficient to overcome resistance to EZH2 inhibitor and synergistic with EZH2 inhibitor in vivo in ARID1A-inactivted ovarian tumour mouse models. Together, these data establish that the switch of the SWI/SNF catalytic subunits from SMARCA4 to SMARCA2 underlies the acquired resistance to EZH2 inhibitors and BCL2 inhibition alone or in combination with EZH2 inhibition represents a novel strategy to overcome and/or prevent EZH2 inhibitor resistance in ARID1A-mutated cancers. Given that the SWI/SNF subunits are among the most frequently mutated genes in human cancers and EZH2 inhibitors are in the clinical trials for tumor with mutations in the SWI/SNF complex, we expect our findings to have far-reaching implications for developing cancer epigenetic therapeutics.

Citation Format: Shuai Wu, Nail Fatkhutdinov, Takeshi Fukumoto, Benjamin G. Bitler, Pyoung Hwa Park, Andrew V. Kossenkov, Marco Trizzino, Alessandro Gardini, David W. Speicher, Rugang Zhang,. CATALYTIC SUBUNITS SWITCH DRIVES RESISTANCE TO EZH2 INHIBITORS IN ARID1A-MUTATED CELLS [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr NT-114.

Abstract GMM-040: TARGETING WNT SIGNALING TO OVERCOME PARP INHIBITOR RESISTANCE

PURPOSE: Epithelial ovarian cancer (EOC) has one of the highest death to incidence ratios of any cancer. High grade serous ovarian cancer (HGSOC) is the most common EOC and over 85% of HGSOCs are diagnosed at a late stage (III/IV). While about 80% of all HGSOC patients will respond to first line treatments (debulking surgeries and platinum-based therapies), the majority of patients will relapse. Poly(ADP)-ribose polymerase inhibitors (PARPi) are a promising treatment for recurring chemosensitive HGSOC. However, recurrence with resistance to both chemotherapies and PARPi is common, revealing a clinical need to understand the mechanisms underlying PARPi resistance. Canonical Wnt signaling is known to play a role in the tumorigenesis and chemoresistance of many cancers, including ovarian. Non-canonical Wnt signaling is able to inhibit beta-catenin dependent TCF/LEF transcription and loss of non-canonical Wnt signaling conveys a poor prognosis in HGSOC. Therefore, we sought to determine if aberrant canonical Wnt signaling plays a role in PARPi response/resistance in HGSOC.

METHODS: RNA sequencing was performed on PEO1 cells sensitive and resistant to a PARPi, olaparib, to determine differential expression of signaling pathways and transcription factors. This was validated with TOP/FOP-FLASH reporter assays and qPCR of genes associated with canonical Wnt signaling. Colony formation assays were performed to determine the effects of overexpressing a canonical Wnt ligand, Wnt3a, in sensitive cells treated with olaparib and to determine cell response to a Wnt inhibitor (pyrvinium pamoate; Pyr. Pam.). Levels of apoptosis after treatments with PARPi and/or Pyr. Pam. was measured with Annexin V/PI assays. DNA damage repair was assessed utilizing γH2Ax resolution and two-plasmid functional DNA repair assays. The effects of olaparib, Pyr. Pam. and combination treatments were assessed in vivo with a xenograft mouse model (intraperitoneal injection of PEO1-Wnt3a cells) and on ex vivo cultures of primary chemonaive tumors.

RESULTS: PARPi resistant cells had a significant enrichment of Wnt signaling and the TCF3/LEF transcription factors as compared to the sensitive cell lines. This also correlated with an increase in mRNA of canonical Wnt signaling activators, including the ligand WNT3A, and a decrease of Wnt repressors (SFRP1, WNT5A) in the resistant cells. Sensitive cells with Wnt3a overexpressed developed an increased resistance to olaparib. Treating PARPi resistant cells with Pyr. Pam. significantly decreased cell viability, suggesting a dependence on Wnt signaling. Combination treatment of olaparib and Pyr. Pam. resulted in a synergistic increase in apoptosis when compared to either treatment alone. PARPi resistant cells had a significant increase in the rate of γH2Ax resolution and higher DNA repair activity compared to sensitive cells. Pyr. Pam. exposure attenuated the DNA damage repair activity. In a xenograft mouse model combination olaparib and Pyr. Pam. resulted in significantly decreased tumor growth, tumor weight, and tumor nodule number as compared to control. In a primary HGSOC tumor ex vivo model, Pyr. Pam. significantly inhibited proliferation compared to control treatment.

CONCLUSION: Our data demonstrate that HGSOC cells upregulate canonical Wnt signaling to promote resistance to PARPi. Wnt inhibitors are a promising therapeutic approach for patients who develop PARPi resistance.

Citation Format: Tomomi M. Yamamoto, Alexandra McMellen, Zachary L. Watson, Jennifer Aguilera, Matthew J. Sikora, Rebecca Ferguson, Elmar Numammadov, George-Lucian Moldovan, Tanay Thakar, Hyunmin Kim, Diana M. Cittelly, Heidi Wilson, Kian Behbakht, and Benjamin G. Bitler. TARGETING WNT SIGNALING TO OVERCOME PARP INHIBITOR RESISTANCE [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr GMM-040.

Repurposing Pan-HDAC Inhibitors for ARID1A-Mutated Ovarian Cancer

ARID1A , a subunit of the SWI/SNF complex, is among the most frequently mutated genes across cancer types. ARID1A is mutated in more than 50% of ovarian clear cell carcinomas (OCCCs), diseases that have no effective therapy. Here, we show that ARID1A mutation confers sensitivity to pan-HDAC inhibitors such as SAHA in ovarian cancers. This correlated with enhanced growth suppression induced by the inhibition of HDAC2 activity in ARID1A-mutated cells. HDAC2 interacts with EZH2 in an ARID1A status-dependent manner. HDAC2 functions as a co-repressor of EZH2 to suppress the expression of EZH2/ARID1A target tumor suppressor genes such as PIK3IP1 to inhibit proliferation and promote apoptosis. SAHA reduced the growth and ascites of the ARID1A-inactivated OCCCs in both orthotopic and genetic mouse models. This correlated with a significant improvement of survival of mice bearing ARID1A-mutated OCCCs. These findings provided preclinical rationales for repurposing FDA-approved pan-HDAC inhibitors for treating ARID1A-mutated cancers.