HSF1 Inhibits Antitumor Immune Activity in Breast Cancer by Suppressing CCL5 to Block CD8+ T-cell Recruitment

Heat shock factor 1 (HSF1) is a stress-responsive transcription factor that promotes cancer cell malignancy. To provide a better understanding of the biological processes regulated by HSF1, here we developed an HSF1 activity signature (HAS) and found that it was negatively associated with antitumor immune cells in breast tumors. Knockdown of HSF1 decreased breast tumor size and caused an influx of several antitumor immune cells, most notably CD8+ T cells. Depletion of CD8+ T cells rescued the reduction in growth of HSF1-deficient tumors, suggesting HSF1 prevents CD8+ T-cell influx to avoid immune-mediated tumor killing. HSF1 suppressed expression of CCL5, a chemokine for CD8+ T cells, and upregulation of CCL5 upon HSF1 loss significantly contributed to the recruitment of CD8+ T cells. These findings indicate that HSF1 suppresses antitumor immune activity by reducing CCL5 to limit CD8+ T-cell homing to breast tumors and prevent immune-mediated destruction, which has implications for the lack of success of immune modulatory therapies in breast cancer.

SIGNIFICANCE

The stress-responsive transcription factor HSF1 reduces CD8+ T-cell infiltration in breast tumors to prevent immune-mediated killing, indicating that cellular stress responses affect tumor-immune interactions and that targeting HSF1 could improve immunotherapies.

Cancer associated fibroblasts serve as an ovarian cancer stem cell niche through noncanonical Wnt5a signaling

Frequent relapse and chemoresistance cause poor outcome in ovarian cancer (OC) and cancer stem cells (CSCs) are important contributors. While most studies focus exclusively on CSCs, the role of the microenvironment in providing optimal conditions to maintain their tumor-initiating potential remains poorly understood. Cancer associated fibroblasts (CAFs) are a major constituent of the OC tumor microenvironment and we show that CAFs and CSCs are enriched following chemotherapy in patient tumors. CAFs significantly increase OC cell resistance to carboplatin. Using heterotypic CAF-OC cocultures and in vivo limiting dilution assay, we confirm that the CAFs act by enriching the CSC population. CAFs increase the symmetric division of CSCs as well as the dedifferentiation of bulk OC cells into CSCs. The effect of CAFs is limited to OC cells in their immediate neighborhood, which can be prevented by inhibiting Wnt. Analysis of single cell RNA-seq data from OC patients reveal Wnt5a as the highest expressed Wnt in CAFs and that certain subpopulations of CAFs express higher levels of Wnt5a. Our findings demonstrate that Wnt5a from CAFs activate a noncanonical Wnt signaling pathway involving the ROR2/PKC/CREB1 axis in the neighboring CSCs. While canonical Wnt signaling is found to be predominant in interactions between cancer cells in patients, non-canonical Wnt pathway is activated by the CAF-OC crosstalk. Treatment with a Wnt5a inhibitor sensitizes tumors to carboplatin in vivo. Together, our results demonstrate a novel mechanism of CSC maintenance by signals from the microenvironmental CAFs, which can be targeted to treat OC chemoresistance and relapse.

G-quadruplex is critical to epigenetic activation of the lncRNA HOTAIR in cancer cells

The cancer-promoting lncRNA HOTAIR has multiple isoforms. Which isoform of HOTAIR accounts for its expression and functions in cancer is unknown. Unlike HOTAIR's canonical intergenic isoform NR_003716 (HOTAIR-C), the novel isoform NR_047517 (HOTAIR-N) forms an overlapping antisense transcription locus with HOXC11. We identified HOTAIR-N as the dominant isoform that regulates the gene expression programs and networks for cell proliferation, survival, and death in cancer cells. The CpG island in the HOTAIR-N promoter was marked with epigenetic markers for active transcription. We identified a G-quadruplex (G4) motif rich region in the HOTAIR-N CpG island. Our findings indicate that G4s in HOTAIR-N CpG island is critical for expression of HOTAIR-N in cancer cells. Disruption of G4 may represent a novel therapeutic approach for cancer. The transcriptomes regulated by HOTAIR-N and Bloom in cancer cells as provided herein are important resources for the exploration of lncRNA, DNA helicases, and G4 in cancer.

Abstract 2440: HOTAIR functionality and regulation in ovarian cancer stem cells

Ovarian cancer (OC) is the fifth leading cause of cancer-related death among American women. Persistence of OC stem cells (OCSCs) is believed to contribute to resistance to platinum-based chemotherapy and disease relapse. We have previously shown that epigenetic changes in OCSCs play a role in post-therapy OCSC persistence and demonstrated the potential to target OCSC using epigenetic therapies. HOXC transcript antisense RNA (HOTAIR) has been shown to be associated with chemoresistance and overexpressed in high-grade serous OC (HGSOC). HOTAIR interacts with Polycomb Repressive Complex 2 (PRC2) and plays a key role in chromatin remodeling. Because HOTAIR is a known epigenetic regulator of differentiation and developmental genes in OC, we hypothesized that HOTAIR regulates OCSCs and epigenetic targeting HOTAIR will prevent tumor relapse. To produce loss-of-function phenotypes of HOTAIR and investigate the function of this gene, we utilized the paired CRISPR guide RNA design to delete the functional sites of HOTAIR in a panel high grade serous OC cell lines (Kuramochi, OVCAR3) without affecting nearby protein-coding gene. Knockout of HOTAIR re-sensitized OC cells to platinum treatment and significantly decreased (P<0.001) the OCSC population and stemness-related phenotypes, including inhibiting stemness-associated gene expression ALDH1A1, Notch3, Sox9, and PROM1 and in vitro spheroid forming ability under low attachment conditions. Integrated analysis of RNA-seq and ATAC-seq on control and HOTAIR knockout cells revealed HOTAIR altered global chromatin dynamics to change downstream gene expression, particularly, the NF-kB pathway. In xenograft assays using HGSOC cells, combining a HOTAIR inhibitor with an EZH2 inhibitor and chemotherapy significantly decreased in vivo tumor formation and increased mouse survival. In summary, depletion of HOTAIR functionally decreased OCSC phenotypes and malignant potential and reprogrammed HGSOC to a less stem-like phenotype. There is an urgent need to develop new therapeutic strategies to target OCSCs and overcome chemoresistant OC, and the results of this study suggest that targeting HOTAIR in combination with epigenetic therapies may represent a novel therapeutic strategy to prevent tumor relapse in OC.

Citation Format: Weini Wang, Yanchi Zhou, Ji Wang, Ali Ozes, Heather M. O’Hagan, Anirban Mitra, Kenneth P. Nephew. HOTAIR functionality and regulation in ovarian cancer stem cells [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 2440.

Glutamine metabolism in breast cancer and possible therapeutic targets

Cancer is characterized by metabolic reprogramming, which is a hot topic in tumor treatment research. Cancer cells alter metabolic pathways to promote their growth, and the common purpose of these altered metabolic pathways is to adapt the metabolic state to the uncontrolled proliferation of cancer cells. Most cancer cells in a state of nonhypoxia will increase the uptake of glucose and produce lactate, called the Warburg effect. Increased glucose consumption is used as a carbon source to support cell proliferation, including nucleotide, lipid and protein synthesis. In the Warburg effect, pyruvate dehydrogenase activity decreases, thereby disrupting the TCA cycle. In addition to glucose, glutamine is also an important nutrient for the growth and proliferation of cancer cells, an important carbon bank and nitrogen bank for the growth and proliferation of cancer cells, providing ribose, nonessential amino acids, citrate, and glycerin necessary for cancer cell growth and proliferation and compensating for the reduction in oxidative phosphorylation pathways in cancer cells caused by the Warburg effect. In human plasma, glutamine is the most abundant amino acid. Normal cells produce glutamine via glutamine synthase (GLS), but the glutamine synthesized by tumor cells is insufficient to meet their high growth needs, resulting in a "glutamine-dependent phenomenon." Most cancers have an increased glutamine demand, including breast cancer. Metabolic reprogramming not only enables tumor cells to maintain the reduction-oxidation (redox) balance and commit resources to biosynthesis but also establishes heterogeneous metabolic phenotypes of tumor cells that are distinct from those of nontumor cells. Thus, targeting the metabolic differences between tumor and nontumor cells may be a promising and novel anticancer strategy. Glutamine metabolic compartments have emerged as promising candidates, especially in TNBC and drug-resistant breast cancer. In this review, the latest discoveries of breast cancer and glutamine metabolism are discussed, novel treatment methods based on amino acid transporters and glutaminase are discussed, and the relationship between glutamine metabolism and breast cancer metastasis, drug resistance, tumor immunity and ferroptosis are explained, which provides new ideas for the clinical treatment of breast cancer.

Fear of recurrence, emotional well-being and quality of life among long-term advanced ovarian cancer survivors

OBJECTIVE

Although advanced stage epithelial ovarian cancer is widely considered life-threatening, 17% of women with advanced disease will survive long-term. Little is known about the health-related quality of life (QOL) of long-term ovarian cancer survivors, or how fear of recurrence might affect QOL.

METHODS

58 long-term survivors with advanced disease participated in the study. Participants completed standardized questionnaires to capture cancer history, QOL, and fear of recurrent disease (FOR). Statistical analyses included multivariable linear models.

RESULTS

Participants averaged 52.8 years at diagnosis and had survived >8 years (mean:13.5); 64% had recurrent disease. Mean FACT-G, FACT-O, and FACT-O-TOI (TOI) scores were 90.7 (SD:11.6), 128.6 (SD:14.8), and 85.9 (SD:10.2) respectively. Compared to the U.S. population using T-scores, QOL for participants exceeded that of healthy adults (T-score (FACT-G) = 55.9). Overall QOL was lower in women with recurrent vs. non-recurrent disease though differences did not reach statistical significance (FACT-O = 126.1 vs. 133.3, p = 0.082). Despite good QOL, high FOR was reported in 27%. FOR was inversely associated with emotional well-being (EWB) (p < 0.001), but not associated with other QOL subdomains. In multivariable analysis, FOR was a significant predictor of EWB after adjusting for QOL (TOI). A significant interaction was observed between recurrence and FOR (p = 0.034), supporting a larger impact of FOR in recurrent disease.

CONCLUSION

QOL in long-term ovarian cancer survivors was better than the average for healthy U.S. women. Despite good QOL, high FOR contributed significantly to increased emotional distress, most notably for those with recurrence. Attention to FOR may be warranted in this survivor population.

Cholesterol Biosynthesis Inhibitor RO 48-8071 Suppresses Growth of Epithelial Ovarian Cancer Cells in Vitro and In Vivo

Introduction

Epithelial Ovarian Cancer (EOC) cells express enzymes in the cholesterol biosynthetic pathway, making this pathway an attractive therapeutic target for controlling ovarian cancer. Potent small molecule inhibitors of one biosynthetic enzyme, Oxidosqualene Cyclase (OSC), have been identified, and RO 48-8071 (4'-[6-(allylmethylamino)hexyloxy]-4-bromo-2'-fluorobenzophenone fumarate) (RO), has emerged as a useful chemotherapeutic agent for breast and prostate cancer.

Methods

Cell viability assays were performed to determine effects of RO 48-8071 on growth of EOC cells. Aldehyde Dehydrogenase (ALDH) assay was conducted to determine the effects of drug on reducing stem cell like properties of EOC cells. Finally, xenograft studies were performed to assess the ability of RO 48-8071 to inhibit the growth of EOC cells in vivo.

Results

We found that short-term (24-48 h) administration of pharmacological doses of RO effectively reduced the viability of drug-resistant EOC cells (SK-OV-3 and OVCAR-3), as determined with sulforhodamine B colorimetric assays. In 7-day assays, nanomolar concentrations of RO effectively inhibited the growth of EOC cells. RO also suppressed ALDH activity, a marker of stem cells. Importantly, RO significantly suppressed growth of xenografts derived from EOC cells when given to mice intraperitoneally (20-40 mg kg-1 day-1) for 27 days once tumors reached 100 mm3 (controls: 336 + 60 mm3; treated: 171 + 20 mm3) with no toxicity to the experimental animals. Mechanistically, RO induced apoptosis in tumor cells in vivo as shown with immunohistochemistry.

Conclusion

Cholesterol biosynthesis inhibitor RO 48-8071 is thus a novel and potent inhibitor of human EOC, including EOC stem cells.

Unintended Consequences of Antibiotic Therapy on the Microbiome Delivers a Gut Punch in Ovarian Cancer

While the early use of antibiotics during chemotherapy may be lifesaving, antibiotic therapy is associated with worse outcomes in patients with ovarian cancer during platinum chemotherapy. The study by Chambers and colleagues in this issue of Cancer Research provides mechanistic insights into how disrupting the gut microbiome with broad-spectrum antibiotics negatively influences the survival of patients with ovarian cancer and highlights the impact of the gut microbiome on tumor progression and response to therapy. Treatment of ovarian cancer models with a broad-spectrum antibiotic cocktail (ABX, vancomycin, neomycin sulfate, metronidazole, ampicillin) changed the gut microbiome and increased tumor growth and development of cisplatin resistance. Stem cells, reported to drive resistance to chemotherapy and disease recurrence in ovarian cancer, were enriched as a surprising consequence of ABX-induced microbiome disruption. Immune-competent and immune-deficient mice revealed that ABX treatment enhanced the cisplatin-induced stemness and provided evidence for immune surveillance of ovarian cancer stem cells through the gut microbiome. Two gut-derived metabolites, indole-3-propionic acid and indoxyl sulfate, suppressed by ABX treatment and reestablished with cecal microbial transplantation colonization of ABX-treated mice, were identified as potential effectors connecting the gut microbiome to ovarian cancer growth. This clinically relevant study opens new therapeutic opportunities for patients-one aimed at interventions to increase platinum sensitivity and another aimed at preventing the potential adverse effects of broad-spectrum antibiotic treatment. Both represent paradigm changes to standard care. See related article by Chambers et al., p. 4654.

Single-cell analysis of a high-grade serous ovarian cancer cell line reveals transcriptomic changes and cell subpopulations sensitive to epigenetic combination treatment

Ovarian cancer (OC) is a lethal gynecological malignancy with a five-year survival rate of only 46%. Development of resistance to platinum-based chemotherapy is a common cause of high mortality rates among OC patients. Tumor and transcriptomic heterogeneity are drivers of platinum resistance in OC. Platinum-based chemotherapy enriches for ovarian cancer stem cells (OCSCs) that are chemoresistant and contribute to disease recurrence and relapse. Studies examining the effect of different treatments on subpopulations of HGSOC cell lines are limited. Having previously demonstrated that combined treatment with an enhancer of zeste homolog 2 inhibitor (EZH2i) and a RAC1 GTPase inhibitor (RAC1i) inhibited survival of OCSCs, we investigated EZH2i and RAC1i combination effects on HGSOC heterogeneity using single cell RNA sequencing. We demonstrated that RAC1i reduced expression of stemness and early secretory marker genes, increased expression of an intermediate secretory marker gene and induced inflammatory gene expression. Importantly, RAC1i alone and in combination with EZH2i significantly reduced oxidative phosphorylation and upregulated Sirtuin signaling pathways. Altogether, we demonstrated that combining a RAC1i with an EZH2i promoted differentiation of subpopulations of HGSOC cells, supporting the future development of epigenetic drug combinations as therapeutic approaches in OC.

A Novel ALDH1A1 Inhibitor Blocks Platinum-Induced Senescence and Stemness in Ovarian Cancer

Ovarian cancer is a deadly disease attributed to late-stage detection as well as recurrence and the development of chemoresistance. Ovarian cancer stem cells (OCSCs) are hypothesized to be largely responsible for the emergence of chemoresistant tumors. Although chemotherapy may initially succeed at decreasing the size and number of tumors, it leaves behind residual malignant OCSCs. In this study, we demonstrate that aldehyde dehydrogenase 1A1 (ALDH1A1) is essential for the survival of OCSCs. We identified a first-in-class ALDH1A1 inhibitor, compound 974, and used 974 as a tool to decipher the mechanism of stemness regulation by ALDH1A1. The treatment of OCSCs with 974 significantly inhibited ALDH activity, the expression of stemness genes, and spheroid and colony formation. An in vivo limiting dilution assay demonstrated that 974 significantly inhibited CSC frequency. A transcriptomic sequencing of cells treated with 974 revealed a significant downregulation of genes related to stemness and chemoresistance as well as senescence and the senescence-associated secretory phenotype (SASP). We confirmed that 974 inhibited the senescence and stemness induced by platinum-based chemotherapy in functional assays. Overall, these data establish that ALDH1A1 is essential for OCSC survival and that ALDH1A1 inhibition suppresses chemotherapy-induced senescence and stemness. Targeting ALDH1A1 using small-molecule inhibitors in combination with chemotherapy therefore presents a promising strategy to prevent ovarian cancer recurrence and has the potential for clinical translation.

Platinum-induced mitochondrial OXPHOS contributes to cancer stem cell enrichment in ovarian cancer

Background

Platinum based agents—cisplatin and carboplatin in combination with taxanes are used for the treatment of ovarian cancer (OC) patients. However, the majority of OC patients develop recurrent, platinum resistant disease that is uniformly fatal. Platinum treatment enriches for chemoresistant aldehyde dehydrogenase (ALDH) + ovarian cancer stem cells (OCSCs), which contribute to tumor recurrence and disease relapse. Acquired platinum resistance also includes metabolic reprograming and switching to oxidative phosphorylation (OXPHOS). Chemosensitive cells rely on glycolysis while chemoresistant cells have the ability to switch between glycolysis and OXPHOS, depending on which pathway drives a selective advantage for growth and chemoresistance. High expression of genes involved in OXPHOS and high production of mitochondrial ROS are characteristics of OCSCs, suggesting that OCSCs favor OXPHOS over glycolysis. Based on connections between OCSCs, chemoresistance and OXPHOS, we hypothesize that platinum treatment induces changes in metabolism that contribute to platinum-induced enrichment of OCSCs.

Methods

The effect of cisplatin on mitochondrial activity was assessed by JC1 staining and expression of OXPHOS genes by RT-qPCR. Cisplatin-induced changes in Sirtuin 1 (SIRT1) levels and activity were assessed by western blot. Small molecule inhibitors of mitochondrial complex I and SIRT1 were used to determine if their enzymatic activity contributes to the platinum-induced enrichment of OCSCs. The percentage of ALDH + OCSCs in OC cells and tumor tissue from xenograft models across different treatment conditions was analyzed using ALDEFLUOR assay and flow cytometry.

Results

We demonstrate that platinum treatment increases mitochondrial activity. Combined treatment of platinum agents and OXPHOS inhibitors blocks the platinum-induced enrichment of ALDH + OCSCs in vitro and in vivo. Furthermore, platinum treatment increases SIRT1 levels and subsequent deacetylase activity, which likely contributes to the increase in platinum-induced mitochondrial activity.

Conclusions

These findings on metabolic pathways altered by platinum-based chemotherapy have uncovered key targets that can be exploited therapeutically to block the platinum-induced enrichment of OCSCs, ultimately improving the survival of OC patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03447-y.

Aberrant epigenetic and transcriptional events associated with breast cancer risk

BACKGROUND

Genome-wide association studies have identified several breast cancer susceptibility loci. However, biomarkers for risk assessment are still missing. Here, we investigated cancer-related molecular changes detected in tissues from women at high risk for breast cancer prior to disease manifestation. Disease-free breast tissue cores donated by healthy women (N = 146, median age = 39 years) were processed for both methylome (MethylCap) and transcriptome (Illumina's HiSeq4000) sequencing. Analysis of tissue microarray and primary breast epithelial cells was used to confirm gene expression dysregulation.

RESULTS

Transcriptomic analysis identified 69 differentially expressed genes between women at high and those at average risk of breast cancer (Tyrer-Cuzick model) at FDR < 0.05 and fold change ≥ 2. Majority of the identified genes were involved in DNA damage checkpoint, cell cycle, and cell adhesion. Two genes, FAM83A and NEK2, were overexpressed in tissue sections (FDR < 0.01) and primary epithelial cells (p < 0.05) from high-risk breasts. Moreover, 1698 DNA methylation changes were identified in high-risk breast tissues (FDR < 0.05), partially overlapped with cancer-related signatures, and correlated with transcriptional changes (p < 0.05, r ≤ 0.5). Finally, among the participants, 35 women donated breast biopsies at two time points, and age-related molecular alterations enhanced in high-risk subjects were identified.

CONCLUSIONS

Normal breast tissue from women at high risk of breast cancer bears molecular aberrations that may contribute to breast cancer susceptibility. This study is the first molecular characterization of the true normal breast tissues, and provides an opportunity to investigate molecular markers of breast cancer risk, which may lead to new preventive approaches.

The Ratio of Toxic-to-Nontoxic miRNAs Predicts Platinum Sensitivity in Ovarian Cancer

Ovarian cancer remains one of the deadliest gynecologic malignancies affecting women, and development of resistance to platinum remains a major barrier to achieving a cure. Multiple mechanisms have been identified to confer platinum resistance. Numerous miRNAs have been linked to platinum sensitivity and resistance in ovarian cancer. miRNA activity occurs mainly when the guide strand of the miRNA, with its seed sequence at position 2-7/8, is loaded into the RNA-induced silencing complex (RISC) and targets complementary short seed matches in the 3' untranslated region of mRNAs. Toxic 6mer seeds, which target genes critical for cancer cell survival, have been found in tumor-suppressive miRNAs. Many siRNAs and short hairpin RNAs (shRNA) can also kill cancer cells via toxic seeds, the most toxic of which carry G-rich 6mer seed sequences. We showed here that treatment of ovarian cancer cells with platinum led to increased RISC-bound miRNAs carrying toxic 6mer seeds and decreased miRNAs with nontoxic seeds. Platinum-tolerant cells did not exhibit this toxicity shift but retained sensitivity to cell death mediated by siRNAs carrying toxic 6mer seeds. Analysis of RISC-bound miRNAs in tumors from patients with ovarian cancer revealed that the ratio between miRNAs with toxic versus nontoxic seeds was predictive of treatment outcome. Application of the 6mer seed toxicity concept to cancer relevant miRNAs provides a new framework for understanding and predicting cancer therapy responses. SIGNIFICANCE: These findings demonstrate that the balance of miRNAs that carry toxic and nontoxic 6mer seeds contributes to platinum resistance in ovarian cancer.

ZEB2 regulates endocrine therapy sensitivity and metastasis in luminal a breast cancer cells through a non-canonical mechanism

PURPOSE

The transcription factors ZEB1 and ZEB2 mediate epithelial-to-mesenchymal transition (EMT) and metastatic progression in numerous malignancies including breast cancer. ZEB1 and ZEB2 drive EMT through transcriptional repression of cell-cell junction proteins and members of the tumor suppressive miR200 family. However, in estrogen receptor positive (ER +) breast cancer, the role of ZEB2 as an independent driver of metastasis has not been fully investigated.

METHODS

In the current study, we induced exogenous expression of ZEB2 in ER + MCF-7 and ZR-75-1 breast cancer cell lines and examined EMT gene expression and metastasis using dose-response qRT-PCR, transwell migration assays, proliferation assays with immunofluorescence of Ki-67 staining. We used RNA sequencing to identify pathways and genes affected by ZEB2 overexpression. Finally, we treated ZEB2-overexpressing cells with 17β-estradiol (E2) or ICI 182,780 to evaluate how ZEB2 affects estrogen response.

RESULTS

Contrary to expectation, we found that ZEB2 did not increase canonical epithelial nor decrease mesenchymal gene expressions. Furthermore, ZEB2 overexpression did not promote a mesenchymal cell morphology. However, ZEB1 and ZEB2 protein expression induced significant migration of MCF-7 and ZR-75-1 breast cancer cells in vitro and MCF-7 xenograft metastasis in vivo. Transcriptomic (RNA sequencing) pathway analysis revealed alterations in estrogen signaling regulators and pathways, suggesting a role for ZEB2 in endocrine sensitivity in luminal A breast cancer. Expression of ZEB2 was negatively correlated with estrogen receptor complex genes in luminal A patient tumors. Furthermore, treatment with 17β-estradiol (E2) or the estrogen receptor antagonist ICI 182,780 had no effect on growth of ZEB2-overexpressing cells.

CONCLUSION

ZEB2 is a multi-functional regulator of drug sensitivity, cell migration, and metastasis in ER + breast cancer and functions through non-canonical mechanisms.

NEK5 activity regulates the mesenchymal and migratory phenotype in breast cancer cells

PURPOSE

Breast cancer remains a prominent global disease affecting women worldwide despite the emergence of novel therapeutic regimens. Metastasis is responsible for most cancer-related deaths, and acquisition of a mesenchymal and migratory cancer cell phenotypes contributes to this devastating disease. The utilization of kinase targets in drug discovery have revolutionized the field of cancer research but despite impressive advancements in kinase-targeting drugs, a large portion of the human kinome remains understudied in cancer. NEK5, a member of the Never-in-mitosis kinase family, is an example of such an understudied kinase. Here, we characterized the function of NEK5 in breast cancer.

METHODS

Stably overexpressing NEK5 cell lines (MCF7) and shRNA knockdown cell lines (MDA-MB-231, TU-BcX-4IC) were utilized. Cell morphology changes were evaluated using immunofluorescence and quantification of cytoskeletal components. Cell proliferation was assessed by Ki-67 staining and transwell migration assays tested cell migration capabilities. In vivo experiments with murine models were necessary to demonstrate NEK5 function in breast cancer tumor growth and metastasis.

RESULTS

NEK5 activation altered breast cancer cell morphology and promoted cell migration independent of effects on cell proliferation. NEK5 overexpression or knockdown does not alter tumor growth kinetics but promotes or suppresses metastatic potential in a cell type-specific manner, respectively.

CONCLUSION

While NEK5 activity modulated cytoskeletal changes and cell motility, NEK5 activity affected cell seeding capabilities but not metastatic colonization or proliferation in vivo. Here we characterized NEK5 function in breast cancer systems and we implicate NEK5 in regulating specific steps of metastatic progression.

Abstract 3095: Targeting ALDH1A1 and regulatory networks that support stemness in ovarian cancer cells

Epithelial ovarian cancer (OC) is the deadliest amongst gynecologic cancers with the majority of deaths caused by cancer recurrence. A new paradigm explaining tumor relapse involves the persistence of cancer stem cells after chemotherapy. OC stem cells (OCSCs) are hypothesized to be largely responsible for the emergence of chemoresistant tumors, and we have previously shown that OCSCs contribute to recurrent, drug resistant high-grade serous OC (HGSOC) using ALDH (aldehyde dehydrogenase) activity as a robust functional marker to identify OCSCs. Of the ALDH isoforms, ALDH1A1 is an intracellular enzyme that oxidizes toxic aldehydes to carboxylic acids and plays a role in controlling cell differentiation pathways. High levels of ALDH1A1 expression have been associated with poor outcome in OC patients. Our group and others have demonstrated that OCSCs with high expression of ALDH1A1 have a greater ability to initiate ovarian tumors in vivo. However, the mechanism by which ALDH1A1 maintains stemness phenotype remains poorly understood. In the current study, we hypothesized that ALDH1A1 upregulation in OCSCs was associated with genetic changes that mediate the cellular signals needed for survival. To test this hypothesis, we used a novel ALDH1A1-specific small molecule inhibitor named compound 974. Treatment of HGSOC cell lines with compound 974 reduced ALDH enzyme activity (p&lt;0.01) and inhibited stem-like properties including spheroid formation (p&lt;0.01) and clonogenic survival (p&lt;0.05). To further examine the effect of compound 974 to inhibit ALDH1A1 and consequently tumor initiation, mice were injected with 106, 105 and 104 OVCAR3 cells treated in vitro with compound 974 (5µM for 48h). Tumor initiation was delayed by 974 treatment compared to vehicle-treated group. Extreme limiting dilution analysis revealed that compound 974 reduced CSC frequency compared to control. Transcriptomic sequencing of ovarian cancer cells treated with compound 974 revealed significant inhibition of genes and pathways associated with stemness (NF-κB, KLF4, FZD7), chemoresistance (ABCB1) and senescence pathway genes (p15, p21). Furthermore, key genes associated with senescence associated secretory phenotype (SASP) such as IL6, IL8 and IL1α were significantly inhibited. Taken together, these data warrant further investigation into the mechanism of ALDH1A1 inhibition and loss of stemness in HGSOC.

Citation Format: Vaishnavi Muralikrishnan, Kenneth P. Nephew, Thomas D. Hurley. Targeting ALDH1A1 and regulatory networks that support stemness in ovarian cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3095.

Constitutive activation of MEK5 promotes a mesenchymal and migratory cell phenotype in triple negative breast cancer

Triple negative breast cancer (TNBC) is an aggressive subtype of breast cancer with limited targeted therapeutic options. A defining feature of TNBC is the propensity to metastasize and acquire resistance to cytotoxic agents. Mitogen activated protein kinase (MAPK) and extracellular regulated kinase (ERK) signaling pathways have integral roles in cancer development and progression. While MEK5/ERK5 signaling drives mesenchymal and migratory cell phenotypes in breast cancer, the specific mechanisms underlying these actions remain under-characterized. To elucidate the mechanisms through which MEK5 regulates the mesenchymal and migratory phenotype, we generated stably transfected constitutively active MEK5 (MEK5-ca) TNBC cells. Downstream signaling pathways and candidate targets of MEK5-ca cells were based on RNA sequencing and confirmed using qPCR and Western blot analyses. MEK5 activation drove a mesenchymal cell phenotype independent of cell proliferation effects. Transwell migration assays demonstrated MEK5 activation significantly increased breast cancer cell migration. In this study, we provide supporting evidence that MEK5 functions through FRA-1 to regulate the mesenchymal and migratory phenotype in TNBC.

How Epigenetic Therapy Beats Adverse Genetics in Monosomy Karyotype AML

The study by Greve and colleagues, in this issue of Cancer Research, provides new molecular insights into the intriguing clinical activity of DNA hypomethylating agents (HMA) in patients with acute myeloid leukemia (AML) with monosomal karyotypes. Patients with AML with adverse monosomal karyotypes are known to benefit from HMAs, but not cytarabine, a cytidine analog without HMA activity, but the specific molecular mechanisms remain poorly understood. The authors investigated the mechanistic effects of HMAs on gene reactivation in AML in the context of the most common monosomal karyotypes, genetic deletion of chromosome 7q and 5q. They identified genes with tumor-suppressive properties, an endogenous retrovirus cooperatively repressed by DNA hypermethylation, and increased genetic losses on hemizygous chromosomal regions versus normal biallelic regions in AML cell models. Treatment with HMAs preferentially induced expression of these hemizygous genes to levels similar to those of genes in a biallelic state. In addition to CpG hypomethylation, decitabine treatment resulted in histone acetylation and an open chromatin configuration specifically at hemizygous loci. By using primary blood blasts isolated from patients with AML receiving decitabine and AML patient-derived xenograft models established from patients with either monosomal karyotypes or normal cytogenetics, Greve and colleagues both validated their findings in primary patient samples and demonstrated superior antileukemic activity of decitabine compared with chemotherapy with cytarabine. These mechanistic insights into how epigenetic therapy beats adverse genetics in monosomy karyotype AML will open new therapeutic opportunities for a difficult-to-treat patient group.See related article by Greve et al., p. 834.

Dual inhibition of MEK1/2 and MEK5 suppresses the EMT/migration axis in triple-negative breast cancer through FRA-1 regulation

Triple-negative breast cancer (TNBC) presents a clinical challenge due to the aggressive nature of the disease and a lack of targeted therapies. Constitutive activation of the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway has been linked to chemoresistance and metastatic progression through distinct mechanisms, including activation of epithelial-to-mesenchymal transition (EMT) when cells adopt a motile and invasive phenotype through loss of epithelial markers (CDH1), and acquisition of mesenchymal markers (VIM, CDH2). Although MAPK/ERK1/2 kinase inhibitors (MEKi) are useful antitumor agents in a clinical setting, including the Food and Drug Administration (FDA)-approved MEK1,2 dual inhibitors cobimetinib and trametinib, there are limitations to their clinical utility, primarily adaptation of the BRAF pathway and ocular toxicities. The MEK5 (HGNC: MAP2K5) pathway has important roles in metastatic progression of various cancer types, including those of the prostate, colon, bone and breast, and elevated levels of ERK5 expression in breast carcinomas are linked to a worse prognoses in TNBC patients. The purpose of this study is to explore MEK5 regulation of the EMT axis and to evaluate a novel pan-MEK inhibitor on clinically aggressive TNBC cells. Our results show a distinction between the MEK1/2 and MEK5 cascades in maintenance of the mesenchymal phenotype, suggesting that the MEK5 pathway may be necessary and sufficient in EMT regulation while MEK1/2 signaling further sustains the mesenchymal state of TNBC cells. Furthermore, additive effects on MET induction are evident through the inhibition of both MEK1/2 and MEK5. Taken together, these data demonstrate the need for a better understanding of the individual roles of MEK1/2 and MEK5 signaling in breast cancer and provide a rationale for the combined targeting of these pathways to circumvent compensatory signaling and subsequent therapeutic resistance.

Targeting Ovarian Cancer Stem Cells by Dual Inhibition of HOTAIR and DNA Methylation

Ovarian cancer is a chemoresponsive tumor with very high initial response rates to standard therapy consisting of platinum/paclitaxel. However, most women eventually develop recurrence, which rapidly evolves into chemoresistant disease. Persistence of ovarian cancer stem cells (OCSCs) at the end of therapy has been shown to contribute to resistant tumors. In this study, we demonstrate that the long noncoding RNA HOTAIR is overexpressed in HGSOC cell lines. Furthermore, HOTAIR expression was upregulated in OCSCs compared with non-CSC, ectopic overexpression of HOTAIR enriched the ALDH⁺ cell population and HOTAIR overexpression increased spheroid formation and colony-forming ability. Targeting HOTAIR using peptide nucleic acid-PNA3, which acts by disrupting the interaction between HOTAIR and EZH2, in combination with a DNMT inhibitor inhibited OCSC spheroid formation and decreased the percentage of ALDH⁺ cells. Disrupting HOTAIR-EZH2 with PNA3 in combination with the DNMTi on the ability of OCSCs to initiate tumors in vivo as xenografts was examined. HGSOC OVCAR3 cells were treated with PNA3 in vitro and then implanted in nude mice. Tumor growth, initiation, and stem cell frequency were inhibited. Collectively, these results demonstrate that blocking HOTAIR-EZH2 interaction combined with inhibiting DNA methylation is a potential approach to eradicate OCSCs and block disease recurrence.

Quality of Life and Adverse Events: Prognostic Relationships in Long-Term Ovarian Cancer Survival

BACKGROUND

There is a critical need to identify patient characteristics associated with long-term ovarian cancer survival.

METHODS

Quality of life (QOL), measured by the Functional Assessment of Cancer Therapy-Ovarian-Trial Outcome Index (FACT-O-TOI), including physical, functional and ovarian-specific subscales, was compared between long-term (LTS) (8+ years) and short-term (STS) (<5 years) survivors of GOG 218 at baseline, before cycles 4, 7, 13, 21, and 6 months post-treatment using linear and longitudinal mixed models adjusted for covariates. Adverse events (AEs) were compared between survivor groups at each assessment using generalized linear models. All p-values are two-sided.

RESULTS

QOL differed statistically significantly between STS (N = 1115) and LTS (N = 260) (p < .001). Baseline FACT-O-TOI and FACT-O-TOI change were independently associated with long-term survival (OR = 1.05, 95% CI = 1.03-1.06 and OR = 1.06, 95% CI = 1.05-1.07, respectively). A 7-point increase in baseline QOL was associated with a 38.0% increase in probability of LTS, while a 9-point increase in QOL change was associated with a 67.0% increase in odds for LTS. QOL decreased statistically significantly with increasing AE quartiles (cycle 4 quartiles: 0-5 v. 6-8 v. 9-11 v. ≥12 AEs, p = .01; cycle 21 quartiles: 0-2 v. 3 v. 4-5 v. ≥6 AEs, p = .001). Further, LTS reported statistically significantly better QOL compared to STS (p = .03 and p = .01, cycles 4 and 21, respectively), with similar findings across higher AE grades.

CONCLUSION

Baseline and longitudinal QOL change scores distinguished long versus short-term survivors and are robust prognosticators for long term survival. Results have trial design and supportive care implications, providing meaningful prognostic value in this understudied population.

Abstract LT020: Cancer associated fibroblasts in the tumor microenvironment maintain ovarian cancer stem cells through non-canonical Wnt5a signaling

Frequent relapse and development of chemoresistance are major causes of poor survival in ovarian cancer. Cancer stem cells (CSCs) consist of a small subpopulation in the tumor that are capable of initiation and maintenance. CSCs are typically resistant to cytotoxic chemotherapy and are a potential cause of relapse and chemoresistance. Most studies on CSCs focus on cancer cells alone while CSCs exist in a complex microenvironment in tumors. This microenvironment or CSC niche provides optimal conditions to maintain their tumor initiating potential. Hence, understanding the crosstalk between CSCs and the tumor microenvironment can potentially provide effective therapeutic targets to prevent chemoresistance and relapse. Cancer associated fibroblasts (CAFs) are a major constituent of the ovarian cancer tumor microenvironment and are highly enriched in the residual tumors following chemotherapy. Therefore, we studied the role of CAFs in promoting ovarian cancer chemoresistance and disease relapse through providing an optimal microenvironment for CSCs. CAFs isolated from ovarian cancer patient tumors were used in heterotypic 3D or 2D coculture systems with high grade serous ovarian cancer cell lines or with patient-derived ovarian cancer cells to study their effect on CSCs and chemoresistance. Matched pre- and post-chemotherapy patient tumors were used to confirm our findings. CAFs significantly increased resistance to carboplatin and enriched CSCs by increasing their symmetric division as well as dedifferentiation of bulk ovarian cancer cells. Pre-coculture with CAFs increased in vivo tumor initiation capacity of the ovarian cancer cells 10-fold. The CSC-CAF crosstalk responsible for CSC induction was found to be mediated by Wnt signaling. Inhibition of Wnt secretion by CAFs could block their effect on CSCs. Wnt5a was the most highly expressed Wnt in CAFs, which was further induced by ovarian cancer cells. CRISPR knockdown of Wnt5a in CAFs or treatment with a specific Wnt5a inhibitor abrogated the induction of CSCs by CAFs. Wnt5a was found to signal through a non-canonical Wnt pathway in the CSCs involving the coreceptor ROR2, protein kinase C (PKC), and CAMP Responsive Element Binding Protein 1 (CREB1). Inhibition of each of them prevented CSC induction and functional rescue experiments confirmed the sequence of the Wnt5a-ROR2-PKC-CREB1 axis. Treatment of mouse xenografts established by co-injection of CAFs and ovarian cancer cells, with the Wnt5a inhibitor sensitized them to carboplatin, and eliminated the CSCs in the residual tumors. Our results indicate that CAF-derived Wnt5a is instrumental in ovarian cancer CSC growth and maintenance. In the long term, our studies will broaden the understanding of the mechanism of CSC maintenance by the tumor microenvironment and contribute towards the development of novel therapeutic approaches to prevent ovarian cancer chemoresistance and relapse.

Citation Format: Yiming Fang, Xue Xiao, Ji Wang, Subramanyam Dasari, Kenneth P. Nephew, Dmitriy Zamarin, Anirban K. Mitra. Cancer associated fibroblasts in the tumor microenvironment maintain ovarian cancer stem cells through non-canonical Wnt5a signaling [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr LT020.

Turning Up the Heat on the Pancreatic Tumor Microenvironment by Epigenetic Priming

The study by Gonda and colleagues, in this issue of Cancer Research, represents the first combinatorial approach based on epigenetic therapy priming to overcome resistance to immunotherapy in pancreatic cancer. The authors show that treatment with a DNA hypomethylating agent causes profound changes in the pancreatic cancer microenvironment, including increased numbers of tumor-infiltrating T cells, elevated IFN signaling, and immune checkpoint expression, as well as increased antigen presentation in tumor cells. Accordingly, they show that the combination of decitabine plus immune checkpoint blockade effectively restores antitumor immunity and results in a significant survival benefit in a widely accepted mouse model of pancreatic cancer. The study provides evidence for a new therapeutic approach for pancreatic cancer having antitumor efficacy through modulation of the immune suppressive microenvironment, leading to an increased response to immune checkpoint inhibitors. As the incidence of pancreatic cancer continues to increase, new treatment strategies for this devastating disease are urgently needed. Gonda and colleagues provide preclinical proof of concept for a new therapeutic strategy and address an unmet need for this difficult to treat disease.See related article by Gonda et al., p. 4754.

A phase 1 study of combined guadecitabine and cisplatin in platinum refractory germ cell cancer

Purpose

Germ cell tumors (GCTs) are cured with therapy based on cisplatin, although a clinically significant number of patients are refractory and die of progressive disease. Based on preclinical studies indicating that refractory testicular GCTs are hypersensitive to hypomethylating agents (HMAs), we conducted a phase I trial combining the next‐generation HMA guadecitabine (SGI‐110) with cisplatin in recurrent, cisplatin‐resistant GCT patients.

Methods

Patients with metastatic GCTs were treated for five consecutive days with guadecitabine followed by cisplatin on day 8, for a 28‐day cycle for up to six cycles. The primary endpoint was safety and toxicity including dose‐limiting toxicity (DLT) and maximum tolerated dose (MTD).

Results

The number of patients enrolled was 14. The majority of patients were heavily pretreated. MTD was determined to be 30 mg/m² guadecitabine followed by 100 mg/m² cisplatin. The major DLTs were neutropenia and thrombocytopenia. Three patients had partial responses by RECIST criteria, two of these patients, including one with primary mediastinal disease, completed the study and qualified as complete responses by serum tumor marker criteria with sustained remissions of 5 and 13 months and survival of 16 and 26 months, respectively. The overall response rate was 23%. Three patients also had stable disease indicating a clinical benefit rate of 46%.

Conclusions

The combination of guadecitabine and cisplatin was tolerable and demonstrated activity in patients with platinum refractory germ cell cancer.

Hypermethylation and global remodelling of DNA methylation is associated with acquired cisplatin resistance in testicular germ cell tumours

Testicular germ cell tumours (TGCTs) respond well to cisplatin-based therapy. However, cisplatin resistance and poor outcomes do occur. It has been suggested that a shift towards DNA hypermethylation mediates cisplatin resistance in TGCT cells, although there is little direct evidence to support this claim. Here we utilized a series of isogenic cisplatin-resistant cell models and observed a strong association between cisplatin resistance in TGCT cells and a net increase in global CpG and non-CpG DNA methylation spanning regulatory, intergenic, genic and repeat elements. Hypermethylated loci were significantly enriched for repressive DNA segments, CTCF and RAD21 sites and lamina associated domains, suggesting that global nuclear reorganization of chromatin structure occurred in resistant cells. Hypomethylated CpG loci were significantly enriched for EZH2 and SUZ12 binding and H3K27me3 sites. Integrative transcriptome and methylome analyses showed a strong negative correlation between gene promoter and CpG island methylation and gene expression in resistant cells and a weaker positive correlation between gene body methylation and gene expression. A bidirectional shift between gene promoter and gene body DNA methylation occurred within multiple genes that was associated with upregulation of polycomb targets and downregulation of tumour suppressor genes. These data support the hypothesis that global remodelling of DNA methylation is a key factor in mediating cisplatin hypersensitivity and chemoresistance of TGCTs and furthers the rationale for hypomethylation therapy for refractory TGCT patients.

Regulation of cellular sterol homeostasis by the oxygen responsive noncoding RNA lincNORS

We hereby provide the initial portrait of lincNORS, a spliced lincRNA generated by the MIR193BHG locus, entirely distinct from the previously described miR-193b-365a tandem. While inducible by low O₂ in a variety of cells and associated with hypoxia in vivo, our studies show that lincNORS is subject to multiple regulatory inputs, including estrogen signals. Biochemically, this lincRNA fine-tunes cellular sterol/steroid biosynthesis by repressing the expression of multiple pathway components. Mechanistically, the function of lincNORS requires the presence of RALY, an RNA-binding protein recently found to be implicated in cholesterol homeostasis. We also noticed the proximity between this locus and naturally occurring genetic variations highly significant for sterol/steroid-related phenotypes, in particular the age of sexual maturation. An integrative analysis of these variants provided a more formal link between these phenotypes and lincNORS, further strengthening the case for its biological relevance.

Epigenetic Attire in Ovarian Cancer: The Emperor's New Clothes

Ovarian cancer is an aggressive epithelial tumor that remains a major cause of cancer morbidity and mortality in women. Epigenetic alterations including DNA methylation and histone modifications are being characterized in ovarian cancer and have been functionally linked to processes involved in tumor initiation, chemotherapy resistance, cancer stem cell survival, and tumor metastasis. The epigenetic traits of cancer cells and of associated tumor microenvironment components have been shown to promote an immunosuppressive tumor milieu. However, DNA methylation and histone modifications are reversible, and therapies targeting the epigenome have been implicated in potential reinvigoration of the antitumor immunity. In this review, we provide an overview specifically of DNA methylation and histone modifications as "clothes of the ovarian cancer genome" in relationship to their functional effects and highlight recent developments in the field. We also address the clinical implications of therapeutic strategies to remove or alter specific articles of genomic "clothing" and restore normal cellular function. As the clothes of the genome continue to be deciphered, we envision that the epigenome will become an important therapeutic target for cancer.

EZH2-Mediated Downregulation of the Tumor Suppressor DAB2IP Maintains Ovarian Cancer Stem Cells

The majority of women diagnosed with epithelial ovarian cancer eventually develop recurrence, which rapidly evolves into chemoresistant disease. Persistence of ovarian cancer stem cells (OCSC) at the end of therapy may be responsible for emergence of resistant tumors. In this study, we demonstrate that in OCSC, the tumor suppressor disabled homolog 2-interacting protein (DAB2IP) is silenced by EZH2-mediated H3K27 trimethylation of the DAB2IP promoter. CRISPR/Cas9-mediated deletion of DAB2IP in epithelial ovarian cancer cell lines upregulated expression of stemness-related genes and induced conversion of non-CSC to CSC, while enforced expression of DAB2IP suppressed CSC properties. Transcriptomic analysis showed that overexpression of DAB2IP in ovarian cancer significantly altered stemness-associated genes and bioinformatic analysis revealed WNT signaling as a dominant pathway mediating the CSC inhibitory effect of DAB2IP. Specifically, DAB2IP inhibited WNT signaling via downregulation of WNT5B, an important stemness inducer. Reverse phase protein array further demonstrated activation of noncanonical WNT signaling via C-JUN as a downstream target of WNT5B, which was blocked by inhibiting RAC1, a prominent regulator of C-JUN activation. Coadministration of EZH2 inhibitor GSK126 and RAC1 inhibitor NSC23766 suppressed OCSC survival in vitro and inhibited tumor growth and increased platinum sensitivity in vivo. Overall, these data establish that DAB2IP suppresses the cancer stem cell phenotype via inhibition of WNT5B-induced activation of C-JUN and can be epigenetically silenced by EZH2 in OCSC. Targeting the EZH2/DAB2IP/C-JUN axis therefore presents a promising strategy to prevent ovarian cancer recurrence and has potential for clinical translation. SIGNIFICANCE: These findings show that combining an epigenetic therapy with a noncanonical WNT signaling pathway inhibitor has the potential to eradicate ovarian cancer stem cells and to prevent ovarian cancer recurrence.

Abstract 1403: HOTAIR functions through NF-κB pathway in regulating ovarian cancer stem cells

Ovarian cancer (OC) is the fifth leading cause of cancer-related death among American women. Persistence of OC stem cells (OCSCs) is believed to contribute to resistance to platinum-based chemotherapy and disease relapse. Long non-coding RNA HOXC transcript antisense RNA (HOTAIR) has been shown to be associated with chemoresistance and overexpressed in many types of cancers, including high-grade serous OC (HGSOC). Previously published work has demonstrated that NF-κB was activated by HOTAIR through I-κB inhibition via trimethylation of histone H3 lysine K27, which contributes to chemoresistance in HGSOC. NF-κB-medicated signaling pathways involved in maintaining characteristics of CSCs, such as targeting stem cell markers, CD44, CD133, and ALDH1 has been demonstrated but not well defined in OC. The goals of this study are to understand the mechanism of HOTAIR-mediated NF-κB signaling pathway in regulating OCSCs and develop novel strategies to target OCSCs and overcome OC recurrence and drug resistance. Quantitative RT-PCR analysis revealed that HOTAIR was overexpressed in OCSCs compared to non-OCSCs. In order to produce loss-of-function phenotypes of HOTAIR and investigate the function of this gene, we utilized the paired CRISPR guide RNA design to delete the functional sites of HOTAIR without affecting nearby protein-coding gene. Knockout of HOTAIR re-sensitized OC cells to platinum treatment and significantly decreased (P&lt;0.001) OCSC population and stemness-related phenotypes, including spheroid formation and colony formation ability. ALDH1A1 and expression of other stemness-related genes, including Notch3, PROM1 were significantly decreased by HOTAIR knockout. Overexpression of HOTAIR in OC cells significantly increased (P&lt;0.05) these stem-like characteristics. Furthermore, we showed NF-κB nuclear accumulation and activation in OCSCs compared to non-OCSCs. Knockout of HOTAIR decreased (P&lt;0.01) nuclear localization of NF-κB in OCSCs. Inhibiting NF-κB in using a commercially available pharmacological approach as well as NF-κB knockout both significantly decreased OCSC population and stemness-related phenotypes, as well as ALDH1 protein expression (P&lt; 0.01). However, inhibition of NF-κB has no effect on OCSC characteristics in HOTAIR knockout cells, indicating that HOTAIR may function through constitutively activated NF-κB in regulating OCSCs. We suggest a better understanding of HOTAIR- NF-κB axis in regulating OCSCs will facilitate identifying the key therapeutic target to eliminate residual tumor cells after conventional chemotherapy and prevent OC recurrence and drug resistance.

Citation Format: Weini Wang, Fang Fang, Ali R. Özeş, Kenneth P. Nephew. HOTAIR functions through NF-κB pathway in regulating ovarian cancer stem cells [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 1403.

Platinum-Induced Ubiquitination of Phosphorylated H2AX by RING1A Is Mediated by Replication Protein A in Ovarian Cancer

Platinum resistance is a common occurrence in high-grade serous ovarian cancer and a major cause of ovarian cancer deaths. Platinum agents form DNA cross-links, which activate nucleotide excision repair (NER), Fanconi anemia, and homologous recombination repair (HRR) pathways. Chromatin modifications occur in the vicinity of DNA damage and play an integral role in the DNA damage response (DDR). Chromatin modifiers, including polycomb repressive complex 1 (PRC1) members, and chromatin structure are frequently dysregulated in ovarian cancer and can potentially contribute to platinum resistance. However, the role of chromatin modifiers in the repair of platinum DNA damage in ovarian cancer is not well understood. We demonstrate that the PRC1 complex member RING1A mediates monoubiquitination of lysine 119 of phosphorylated H2AX (γH2AXub1) at sites of platinum DNA damage in ovarian cancer cells. After platinum treatment, our results reveal that NER and HRR both contribute to RING1A localization and γH2AX monoubiquitination. Importantly, replication protein A, involved in both NER and HRR, mediates RING1A localization to sites of damage. Furthermore, RING1A deficiency impairs the activation of the G₂-M DNA damage checkpoint, reduces the ability of ovarian cancer cells to repair platinum DNA damage, and increases sensitivity to platinum. IMPLICATIONS: Elucidating the role of RING1A in the DDR to platinum agents will allow for the identification of therapeutic targets to improve the response of ovarian cancer to standard chemotherapy regimens.

ERK5 Is Required for Tumor Growth and Maintenance Through Regulation of the Extracellular Matrix in Triple Negative Breast Cancer

Conventional mitogen-activated protein kinase (MAPK) family members regulate diverse cellular processes involved in tumor initiation and progression, yet the role of ERK5 in cancer biology is not fully understood. Triple-negative breast cancer (TNBC) presents a clinical challenge due to the aggressive nature of the disease and a lack of targeted therapies. ERK5 signaling contributes to drug resistance and metastatic progression through distinct mechanisms, including activation of epithelial-to-mesenchymal transition (EMT). More recently a role for ERK5 in regulation of the extracellular matrix (ECM) has been proposed, and here we investigated the necessity of ERK5 in TNBC tumor formation. Depletion of ERK5 expression using the CRISPR/Cas9 system in MDA-MB-231 and Hs-578T cells resulted in loss of mesenchymal features, as observed through gene expression profile and cell morphology, and suppressed TNBC cell migration. In vivo xenograft experiments revealed ERK5 knockout disrupted tumor growth kinetics, which was restored using high concentration Matrigel™ and ERK5-ko reduced expression of the angiogenesis marker CD31. These findings implicated a role for ERK5 in the extracellular matrix (ECM) and matrix integrity. RNA-sequencing analyses demonstrated downregulation of matrix-associated genes, integrins, and pro-angiogenic factors in ERK5-ko cells. Tissue decellularization combined with cryo-SEM and interrogation of biomechanical properties revealed that ERK5-ko resulted in loss of key ECM fiber alignment and mechanosensing capabilities in breast cancer xenografts compared to parental wild-type cells. In this study, we identified a novel role for ERK5 in tumor growth kinetics through modulation of the ECM and angiogenesis axis in breast cancer.

Abstract A81: Targeting EZH2/DAB2IP/Wnt axis in ovarian cancer stem cells

Ovarian cancer (OC) is the leading cause of death from gynecologic malignancies. Recent data have pointed to the persistence of quiescent ovarian cancer stem cells (OCSCs) not eliminated by chemotherapy and able to regenerate tumors as the main contributor to tumor relapse and metastasis. Downregulation of tumor suppressor DAB2IP significantly correlated with poor patient survival in OC. In the current study, we tested the hypothesis that DAB2IP is downregulated by EZH2 methylation in OC and targeting DAB2IP inhibits OCSCs, which would prevent disease recurrence. Subpopulations of CSC and non-CSC were isolated from OC cell lines by fluorescence-activated cell sorting (FACS) based on aldehyde dehydrogenase (ALDH) activity, a consistent CSC marker. Expression of DAB2IP in ALDH(+) cells was lower (P&lt;0.05) compared to non-CSC ALDH(-) cells, which can be restored by EZH2 inhibition. Chromatin immunoprecipitation (ChIP) analysis demonstrated enrichment (P&lt;0.05) of H3K27me3 at DAB2IP promoter loci in CSC compared to non-CSC. Furthermore, inhibiting EZH2 decreased H3K27me3 and increased (P&lt;0.05) DAB2IP expression in OC cells, demonstrating that DAB2IP downregulation in CSC was due to EZH2. Knocking out DAB2IP using CRISPR/Cas9 system in OC cell lines upregulated (P&lt;0.05) expression of stemness-related genes and increased (P&lt;0.05) the percentage of ALDH(+) cells. Enforced overexpression of DAB2IP decreased (P&lt;0.05) the number of ALDH(+) cells and inhibited (P&lt;0.05) both spheroid and colony formation. Furthermore, elevated DAB2IP expression decreased (P&lt;0.05) cisplatin IC50 of both OCSCs and OC cells and inhibited (P&lt;0.05) cell migration capacity, suggesting DAB2IP plays a role in regulating OCSC function. OVCAR3 cells and DAB2IP-overexpressing OVCAR3 cells were further analyzed by RNA-sequencing and bioinformatics. Transcriptome analysis revealed that DAB2IP overexpression significantly (FDR &lt; 0.05, fold change &gt; 2) altered expression of 449 genes, including downregulation of ALDH1A1, LGR5, PROM1, and TWIST1, markers strongly associated with CSC phenotypes. Ingenuity Pathway Analysis for upstream regulators of differentially expressed genes revealed Wnt-signaling as a dominant pathway mediating the anti-OCSC effects of DAB2IP. Based on RNA-seq analysis, WNT5B expression decreased (P&lt;0.05) by 3.83 fold, indicating that DAB2IP may negatively regulate Wnt signaling pathway by repressing WNT5B. Furthermore, WNT5B recombinant protein significantly increased (P&lt;0.05) the OCSC population, and reverse phase protein array analysis demonstrated activation of JNK/c-Jun as a possible downstream target of WNT5B. Collectively, our data reveal that DAB2IP, via noncanonical Wnt-mediated signaling pathway, plays a critical role in modulating OCSC properties. Based on these novel findings, we are testing novel combination treatment strategies targeting OCSCs and with the goal of inhibiting tumor relapse and overcoming chemoresistance.

Citation Format: Xingyue Zong, Ali Ozes, Weini Wang, Kenneth P. Nephew. Targeting EZH2/DAB2IP/Wnt axis in ovarian cancer stem cells [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 A81.

Abstract B63: Lysophosphatidic acid as a mediator of ovarian cancer cell stemness

Epithelial ovarian cancer (OC) is the deadliest gynecologic malignancy. Recurrence of advanced, multidrug-resistant metastatic disease after initially good response to standard lines of chemotherapy occurs in the majority of OC patients. Chemoresistant, recurrent OC is essentially fatal. Disease relapse is due to survival and expansion of a small pool of chemorefractory ovarian cancer stem cells (OCSCs). OC evolution to a platinum-resistant state is associated with aberrant epigenetic modifications, including altered DNA methylation and histone modifications. In addition, OC cells residing in the peritoneal cavity are exposed to a variety of external cues arising from the ascitic microenvironment, including the bioactive molecule lysophosphatidic acid (LPA), which potentially contribute to cell stemness and chemoresistance. LPA in the intraperitoneal fluid of OC patients has been strongly implicated in ovarian carcinogenesis and metastasis through a variety of mechanisms. However, regulation of OC cells by LPA is incompletely understood, and the role of LPA in OCSC acquisition/chemoresistance remains unclear. In the current study, we tested the hypothesis that LPA is a mediator of OCSC promotion and survival. Expression of aldehyde dehydrogenase (ALDH), an accepted functional marker of cancer stem cells, was assessed in a panel of high-grade serous ovarian cancer (HGSOC) cell lines (OVSAHO, OVCAR3, OVCAR5, PEO1, and Kuramochi) using an Aldefluor assay. Treatment of HGSOC cells with increasing (0-80uM, 72h) doses of LPA enriched the ALDH+ population in a cell line-specific dose-dependent manner. In PEO1 and Kuramochi cells, intermediate LPA doses (1-10uM) resulted in a 1.5-2.5-fold increase (P&lt;0.05) of ALDH+ cells (from ∼4% to ∼8% in PEO1 and from ∼4% up to ∼10% in Kuramochi, respectively). However, 80uM LPA treatment was necessary to increase (P&lt;0.05) the percentage ALDH+ cells in OVCAR3 (from ∼17% to 34%) and OVSAHO cells (from ∼10% up to 29%). In accordance with the results of the flow cytometry analysis, cancer stem cell properties after LPA treatment (0-80uM, every 72hr, up to 21 days) were enhanced (P&lt;0.05), based on clonogenic assay. In particular, moderate (10-20uM) LPA treatment increased (P&lt;0.05) cell clonogenic survival of PEO1 and Kuramochi, while a greater (80uM) LPA dose was needed for OVCAR3 and OVSAHO. Furthermore, LPA (0-80uM, 14 days) augmented spheroid formation ability in PEO1 cells (3-4-fold increase; P&lt;0.05). Global transcriptomic and epigenomic assessment of altered genes/pathways induced by LPA are currently being examined to assess stemness-promoting pathways and epigenetic changes, which we believe will identify new biologic insights and potential therapeutic targets to eradicate OCSC in patients.

Citation Format: Yuliya Klymenko, Kenneth P. Nephew. Lysophosphatidic acid as a mediator of ovarian cancer cell stemness [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 B63.

In vivo modeling of metastatic human high-grade serous ovarian cancer in mice

Metastasis is responsible for 90% of human cancer mortality, yet it remains a challenge to model human cancer metastasis in vivo. Here we describe mouse models of high-grade serous ovarian cancer, also known as high-grade serous carcinoma (HGSC), the most common and deadliest human ovarian cancer type. Mice genetically engineered to harbor Dicer1 and Pten inactivation and mutant p53 robustly replicate the peritoneal metastases of human HGSC with complete penetrance. Arising from the fallopian tube, tumors spread to the ovary and metastasize throughout the pelvic and peritoneal cavities, invariably inducing hemorrhagic ascites. Widespread and abundant peritoneal metastases ultimately cause mouse deaths (100%). Besides the phenotypic and histopathological similarities, mouse HGSCs also display marked chromosomal instability, impaired DNA repair, and chemosensitivity. Faithfully recapitulating the clinical metastases as well as molecular and genomic features of human HGSC, this murine model will be valuable for elucidating the mechanisms underlying the development and progression of metastatic ovarian cancer and also for evaluating potential therapies.

Rarely does an experimental model fully replicate the clinical metastases of a human malignancy. Faithfully representing the clinical metastases of human high-grade serous ovarian cancer with complete penetrance, coupled with histopathological, molecular, and genomic similarities, these mouse models, particularly one harboring mutant p53, will be vital to elucidating the underlying pathogenesis of human ovarian cancer. In-depth understanding of the development and progression of ovarian cancer is crucial to medical advances in the early detection, effective treatment, and prevention of ovarian cancer. Also, these robust mouse models, as well as cell lines established from the mouse primary and metastatic tumors, will serve as useful preclinical tools to evaluate therapeutic target genes and new therapies in ovarian cancer.

Abstract P2-06-01: Intrinsic transcriptomic differences of luminal progenitors and mature luminal cells of the normal breast

Epithelial cells in the normal breast are organized hierarchically into stem, luminal progenitor (LP) and mature luminal cells (LC) with distinct gene expression patterns. However, whether these gene expression differences are cell-intrinsic, driven through LP-LC cell interactions or due to stromal-luminal cell interactions in the breasts of healthy women is incompletely understood. Furthermore, prior studies on these cell populations did not take genetic ancestry into consideration despite widely reported genetic ancestry-dependent differences in the normal breast biology and breast cancer susceptibility/outcome. We isolated LP and LC breast epithelial cells from core breast biopsies of healthy women representing European, African American and Latino ancestry (five each). After a brief propagation (five passages) under epithelial reprogramming assay conditions, transcriptomes and DNA methylomes were examined using RNA- and Methylcapture-sequencing. Differences in gene expression (FDR&lt;0.05, fold change &gt;2) in LC cells compared to LP cells were observed, with 1581 and 609 genes up- and down-regulated, respectively. These data were enriched for signaling networks associated with cell cycle control of chromosomal replication, mitotic roles of polo-like kinase (down-regulated genes), granulocyte adhesion and diapedesis and LXR/RXR signaling (up-regulated genes). Despite marked gene expression differences between LC and LP cells, only 14 upregulated genes and four down-regulated genes showed DNA hypo- and hyper-methylation, respectively, in LC cells compared to LP cells, suggesting a minimal role for DNA methylation in differential gene expression between the two cell types. Furthermore, of the 2190 differentially expressed genes, 7% (158 genes) were regulated by estrogen, suggesting that differences in hormone responsiveness contribute to differential gene expression in LP and LC cells. To determine relationships between genes differentially methylated and expressed in LC and LP cells and breast cancer, we used publicly available databases, including TCGA. Interestingly, all genes hypermethylated and expressed at lower levels in LC cells were similarly hypermethylated and expressed at lower levels in breast cancers compared to normal breast, suggesting that these genes are minimally altered in breast cancer. Furthermore, in LC compared to LP cells, of thegenes hypomethylated and expressed at higher levels, only four genes (AIM1L, PRSS27, PTK6 and UNC13D) showed a similar pattern in breast tumors compared to normal breast. Of these, PTK6 is significantly overexpressed in luminal and HER2+ breast cancers compared to basal-like breast cancers, suggesting that PTK6+ cells are the preferred cell-of origin of luminal breast cancers. Taken together, this is the first study to demonstrate that transcriptomic data of normal breast cells from healthy women can be used to further define cell-of-origin of tumors and identify cancer-specific gene expression changes in breast cancer.

Citation Format: Fang Fang, Poornima Bhat-Nakshatri, Manjushree Anjanappa, Dough Rusch, Aaron Buechlein, Dave Miller, Kenneth P Nephew, Harikrishna Nakshatri. Intrinsic transcriptomic differences of luminal progenitors and mature luminal cells of the normal breast [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-06-01.

A Randomized Phase II Trial of Epigenetic Priming with Guadecitabine and Carboplatin in Platinum-resistant, Recurrent Ovarian Cancer

PURPOSE

Platinum resistance in ovarian cancer is associated with epigenetic modifications. Hypomethylating agents (HMA) have been studied as carboplatin resensitizing agents in ovarian cancer. This randomized phase II trial compared guadecitabine, a second-generation HMA, and carboplatin (G+C) against second-line chemotherapy in women with measurable or detectable platinum-resistant ovarian cancer.

PATIENTS AND METHODS

Patients received either G+C (guadecitabine 30 mg/m² s.c. once-daily for 5 days and carboplatin) or treatment of choice (TC; topotecan, pegylated liposomal doxorubicin, paclitaxel, or gemcitabine) in 28-day cycles until progression or unacceptable toxicity. The primary endpoint was progression-free survival (PFS); secondary endpoints were RECIST v1.1 and CA-125 response rate, 6-month PFS, and overall survival (OS).

RESULTS

Of 100 patients treated, 51 received G+C and 49 received TC, of which 27 crossed over to G+C. The study did not meet its primary endpoint as the median PFS was not statistically different between arms (16.3 weeks vs. 9.1 weeks in the G+C and TC groups, respectively; P = 0.07). However, the 6-month PFS rate was significantly higher in the G+C group (37% vs. 11% in TC group; P = 0.003). The incidence of grade 3 or higher toxicity was similar in G+C and TC groups (51% and 49%, respectively), with neutropenia and leukopenia being more frequent in the G+C group.

CONCLUSIONS

Although this trial did not show superiority for PFS of G+C versus TC, the 6-month PFS increased in G+C treated patients. Further refinement of this strategy should focus on identification of predictive markers for patient selection.

Interferon-γ signaling is associated with BRCA1 loss-of-function mutations in high grade serous ovarian cancer

Loss-of-function mutations of the breast cancer type 1 susceptibility protein (BRCA1) are associated with breast (BC) and ovarian cancer (OC). To identify gene signatures regulated by epigenetic mechanisms in OC cells carrying BRCA1 mutations, we assessed cellular responses to epigenome modifiers and performed genome-wide RNA- and chromatin immunoprecipitation-sequencing in isogenic OC cells UWB1.289 (carrying a BRCA1 mutation, BRCA1-null) and UWB1.289 transduced with wild-type BRCA1 (BRCA1+). Increased sensitivity to histone deacetylase inhibitors (HDACi) was observed in BRCA1-null vs. BRCA1+ cells. Gene expression profiles of BRCA1-null vs. BRCA1+ cells and treated with HDACi were integrated with chromatin mapping of histone H3 lysine 9 or 27 acetylation. Gene networks activated in BRCA1-null vs. BRCA1 + OC cells related to cellular movement, cellular development, cellular growth and proliferation, and activated upstream regulators included TGFβ1, TNF, and IFN-γ. The IFN-γ pathway was altered by HDACi in BRCA1+ vs. BRCA1-null cells, and in BRCA1-mutated/or low vs. BRCA1-normal OC tumors profiled in the TCGA. Key IFN-γ-induced genes upregulated at baseline in BRCA1-null vs. BRCA1+OC and BC cells included CXCL10, CXCL11, and IFI16. Increased localization of STAT1 in the promoters of these genes occurred in BRCA1-null OC cells, resulting in diminished responses to IFN-γ or to STAT1 knockdown. The IFN-γ signature was associated with improved survival among OC patients profiled in the TCGA. In all, our results support that changes affecting IFN-γ responses are associated with inactivating BRCA1 mutations in OC. This signature may contribute to altered responses to anti-tumor immunity in BRCA1-mutated cells or tumors.

Abstract GMM-062: TARGETING OVARIAN CANCER STEM CELLS THROUGH THE TUMOR SUPPRESSOR DAB2IP-MEDIATED WNT SIGNALING PATHWAY

Ovarian cancer (OC) recurrence after tumor eradication by chemotherapy invariably heralds poor outcome. Recent data point to persistence of quiescent cancer stem cells (CSCs) not eliminated by chemotherapy and able to regenerate tumors as the main contributor to tumor relapse. Downregulation of tumor suppressor gene (TSG) DAB2IP, a member of the Ras GTPase-activating protein family, significantly correlated with poor patient survival in high-grade serous (HGS) OC. Furthermore, loss of DAB2IP in prostate and colon cancer enriched CSC population, suggesting a key role for DAB2IP in modulating cancer stemness. In the current study, we tested the hypothesis that targeting DAB2IP would inhibit CSCs in OC and prevent disease recurrence. Subpopulations of CSC and non-CSC were isolated from Kuramochi, OVCAR3 and COV362 HGSOC cell lines by fluorescence-activated cell sorting (FACS) based on aldehyde dehydrogenase (ALDH) activity, a consistent CSC marker. It was previously demonstrated by us and others that ALDH(+) cells share characteristics of normal stem cells such as the ability to form anchorage-independent multicellular aggregates (spheroids), undergo membrane efflux, express stem cell restricted transcription factors, and generate tumors in vivo. DAB2IP was examined in the FACS-sorted cells using qPCR and western blot. Expression of DAB2IP in ALDH(+) cells was lower (P&lt;0.05) compared to non-CSC ALDH(-) cells. Chromatin immunoprecipitation (ChIP) analysis revealed greater (P&lt;0.05) enrichment of H3K27me3 at DAB2IP promoter loci in CSC than non-CSC, suggesting that DAB2IP downregulation in CSC is caused by EZH2 methylation. Enforced overexpression of DAB2IP decreased (P&lt;0.05) the number of ALDH(+) cells, inhibited (P&lt;0.05) the ability of these cells to form spheroids (14-day incubation under stem cell conditions) and decreased (P&lt;0.05) colony formation. Furthermore, elevated DAB2IP expression decreased (P&lt;0.05) cisplatin IC50 of both OCSCs and HGSOC cells and inhibited (P&lt;0.05) cell migration capacity (Bowden chamber transwell assay), suggesting DAB2IP plays a role in regulating OCSC function. Mechanistically, decreased expression of stemness-related genes in DAB2IP-overexpressing OCSCs was also observed, indicating potential key effectors downstream of DAB2IP. Moreover, dual luciferase reporter assay showed that ALDH1A1 transcription level was significantly repressed (P&lt;0.05) in DAB2IP-overexpressing cells. OVCAR3 cells and DAB2IP-overexpressing OVCAR3 cells were further analyzed by RNA-sequencing and bioinformatics. This transcriptome analysis revealed that DAB2IP overexpression resulted in significantly (FDR &lt; 0.05, fold change &gt; 2) altered expression of 449 genes, including markers strongly associated with CSC phenotypes, including down-regulation of ALDH1A1, LGR5, PROM1, TWIST1 and ATP-binding cassette transporters. Differentially expressed genes were subjected to Ingenuity Pathway Analysis (IPA) for upstream regulators. IPA identified Wnt-signaling pathways as top upstream regulators of these differentially expressed genes, suggesting that Wnt-signaling is a dominant pathway mediating the anti-OCSC effects of DAB2IP. In addition, treating cells with Wnt inhibitor decreased (P&lt;0.05) the CSC population, colony formation ability and ALDH1 expression. Collectively, our data reveals that DAB2IP plays a critical role in modulating CSC properties via Wnt-mediated signaling pathway, suggesting novel combination treatment strategy targeting OCSCs and thus impacting tumor relapse and chemoresistance in OC.

Citation Format: Xingyue Zong, Ali R Ozes, Kenneth P Nephew. TARGETING OVARIAN CANCER STEM CELLS THROUGH THE TUMOR SUPPRESSOR DAB2IP-MEDIATED WNT SIGNALING PATHWAY [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-062.

Incorporating DNA Methyltransferase Inhibitors (DNMTis) in the Treatment of Genitourinary Malignancies: A Systematic Review

Inhibition of DNA methyltransferases (DNMTs) has emerged as a novel treatment strategy in solid tumors. Aberrant hypermethylation in promoters of critical tumor suppressor genes is the basis for the idea that treatment with hypomethylating agents may lead to the restoration of a "normal" epigenome and produce clinically meaningful therapeutic outcomes. The aim of this review article is to summarize the current state of knowledge of DNMT inhibitors in the treatment of genitourinary malignancies. The efficacy of these agents in genitourinary malignancies was reported in a number of studies and suggests a role of induced DNA hypomethylation in overcoming resistance to conventional cytotoxic treatments. The clinical significance of these findings should be further investigated.

Glutamine Metabolism Drives Growth in Advanced Hormone Receptor Positive Breast Cancer

Dependence on the glutamine pathway is increased in advanced breast cancer cell models and tumors regardless of hormone receptor status or function. While 70% of breast cancers are estrogen receptor positive (ER+) and depend on estrogen signaling for growth, advanced ER+ breast cancers grow independent of estrogen. Cellular changes in amino acids such as glutamine are sensed by the mammalian target of rapamycin (mTOR) complex, mTORC1, which is often deregulated in ER+ advanced breast cancer. Inhibitor of mTOR, such as everolimus, has shown modest clinical activity in ER+ breast cancers when given with an antiestrogen. Here we show that breast cancer cell models that are estrogen independent and antiestrogen resistant are more dependent on glutamine for growth compared with their sensitive parental cell lines. Co-treatment of CB-839, an inhibitor of GLS, an enzyme that converts glutamine to glutamate, and everolimus interrupts the growth of these endocrine resistant xenografts. Using human tumor microarrays, we show that GLS is significantly higher in human breast cancer tumors with increased tumor grade, stage, ER-negative and progesterone receptor (PR) negative status. Moreover, GLS levels were significantly higher in breast tumors from African-American women compared with Caucasian women regardless of ER or PR status. Among patients treated with endocrine therapy, high GLS expression was associated with decreased disease free survival (DFS) from a multivariable model with GLS expression treated as dichotomous. Collectively, these findings suggest a complex biology for glutamine metabolism in driving breast cancer growth. Moreover, targeting GLS and mTOR in advanced breast cancer may be a novel therapeutic approach in advanced ER+ breast cancer.

Abstract 3685: HOTAIR regulation and functionality in ovarian cancer stem cells

Ovarian cancer (OC) is the fifth leading cause of cancer-related death among American women. Persistence of OC stem cells (OCSCs) is believed to contribute to resistance to platinum-based chemotherapy and disease relapse. We have previously shown that epigenetic changes in OCSCs play a role in post-therapy OCSC persistence and demonstrated that is it possible to target OCSC using epigenetic therapies. HOXC transcript antisense RNA (HOTAIR) has been shown to be associated with chemoresistance and to be overexpressed in many types of cancers, including high-grade serous OC (HGSOC). HOTAIR interacts with Polycomb Repressive Complex 2 (PRC2) and due to its histone methyltransferases activity plays a key role in chromatin remodeling. Because HOTAIR is a known epigenetic regulator of differentiation and developmental genes in OC and other cancers, we hypothesize that HOTAIR is a key epigenetic regulator in OCSCs and therapeutically targeting HOTAIR in OCSCs will prevent tumor relapse. The goal of this study is to understand the role of HOTAIR in regulating OCSCs and further dissect the mechanism of action of HOTAIR in OCSCs. Aldehyde dehydrogenase (ALDH) activity and FACS was used to separate OCSCs from non-OCSCs in a panel of HGSOC cell lines (OVCAR3, CAOV3, OVCAR5, Kuramochi, COV362). Quantitative RT-PCR analysis revealed that HOTAIR was overexpressed in OCSC cells compared to non-OCSC cells. Knockout of HOTAIR using CRISPR-Cas9 system significantly decreased OCSC population and stemness-related phenotypes, including spheroid formation and colony formation ability. Overexpression of HOTAIR in HGSOC cells significantly increased these stem-like characteristics. Furthermore, targeting HOTAIR using peptide nucleic acid (PNA), which blocks interaction with Enhancer of Zeste Homologue 2 (EZH2), significantly decreased the OCSC population, indicating HOTAIR functions through EZH2 in regulating OCSCs. Combining the HOTAIR-targeting PNA with other epigenetic inhibitors, including the hypomethylating agent guadecitabine and the EZH2 inhibitor GSK503, significantly decreased proliferation and colony formation ability of HGSOC cells. We suggest that a better understanding of HOTAIR will facilitate identifying epigenomic alterations and chromatin landscape that contributes to OCSC phenotypes. Targeting HOTAIR in combination with epigenetic therapies may represent a therapeutic strategy to prevent tumor relapse.

Citation Format: Weini Wang, Fang Fang, Ali Ozes, Kenneth P. Nephew. HOTAIR regulation and functionality in ovarian cancer stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3685.

IL-6 mediates platinum-induced enrichment of ovarian cancer stem cells

In high-grade serous ovarian cancer (OC), chemotherapy eliminates the majority of tumor cells, leaving behind residual tumors enriched in OC stem cells (OCSC). OCSC, defined as aldehyde dehydrogenase-positive (ALDH+), persist and contribute to tumor relapse. Inflammatory cytokine IL-6 is elevated in residual tumors after platinum treatment, and we hypothesized that IL-6 plays a critical role in platinum-induced OCSC enrichment. We demonstrate that IL-6 regulates stemness features of OCSC driven by ALDH1A1 expression and activity. We show that platinum induces IL-6 secretion by cancer-associated fibroblasts in the tumor microenvironment, promoting OCSC enrichment in residual tumors after chemotherapy. By activating STAT3 and upregulating ALDH1A1 expression, IL-6 treatment converted non-OCSC to OCSC. Having previously shown altered DNA methylation in OCSC, we show here that IL-6 induces DNA methyltransferase 1 (DNMT1) expression and the hypomethylating agent (HMA) guadecitabine induced differentiation of OCSC and reduced - but did not completely eradicate - OCSC. IL-6 neutralizing antibody (IL-6-Nab) combined with HMA fully eradicated OCSC, and the combination blocked IL-6/IL6-R/pSTAT3-mediated ALDH1A1 expression and eliminated OCSC in residual tumors that persisted in vivo after chemotherapy. We conclude that IL-6 signaling blockade combined with an HMA can eliminate OCSC after platinum treatment, supporting this strategy to prevent tumor recurrence after standard chemotherapy.

Epigenetic Crosstalk between the Tumor Microenvironment and Ovarian Cancer Cells: A Therapeutic Road Less Traveled

Metastatic dissemination of epithelial ovarian cancer (EOC) predominantly occurs through direct cell shedding from the primary tumor into the intra-abdominal cavity that is filled with malignant ascitic effusions. Facilitated by the fluid flow, cells distribute throughout the cavity, broadly seed and invade through peritoneal lining, and resume secondary tumor growth in abdominal and pelvic organs. At all steps of this unique metastatic process, cancer cells exist within a multidimensional tumor microenvironment consisting of intraperitoneally residing cancer-reprogramed fibroblasts, adipose, immune, mesenchymal stem, mesothelial, and vascular cells that exert miscellaneous bioactive molecules into malignant ascites and contribute to EOC progression and metastasis via distinct molecular mechanisms and epigenetic dysregulation. This review outlines basic epigenetic mechanisms, including DNA methylation, histone modifications, chromatin remodeling, and non-coding RNA regulators, and summarizes current knowledge on reciprocal interactions between each participant of the EOC cellular milieu and tumor cells in the context of aberrant epigenetic crosstalk. Promising research directions and potential therapeutic strategies that may encompass epigenetic tailoring as a component of complex EOC treatment are discussed.

Abstract B07: Targeting DAB2IP in ovarian cancer stem cells

Ovarian cancer is the leading cause of death from gynecologic malignancies. Failure to eliminate ovarian cancer stem cells (OCSCs) by the end of conventional chemotherapy contributes to tumor relapse and metastasis. Understanding the molecular features of OCSCs may allow for effective targeting and eradicating these cells and tumor remission. We reported tumor-initiation and expansion capacity by ALDH+ OCSCs after platinum-based treatment of ovarian cancer xenografts. In addition, loss of DAB2IP in prostate and colon cancer promoted CSC-like features, suggesting a critical role in modulating CSC maintenance. DAB2IP, a novel member of Ras GTPase-activating (GAP) protein family, was identified as a potent tumor suppressor that interfered with many aspects of cancer progression and was frequently downregulated in tumors. In the current study, we aimed to elucidate the tumor-suppressor role of DAB2IP in ovarian cancer in the context of OCSCs and explore epigenetic approaches to upregulate its expression. OCSCs and non-CSCs subpopulations were isolated from multiple high-grade serous ovarian cancer cell lines (Kuramochi, OVCAR3, and COV362). Reduced (p&lt;0.05) DAB2IP expression in OCSCs compared to non-CSC counterparts was observed, suggesting that DAB2IP suppresses OCSC maintenance. Overexpression of DAB2IP in OCSCs derived from Kuramochi decreased (p&lt;0.05) OCSC population, and DAB2IP overexpression inhibited stemness-related phenotypes, including reduced (P&lt;0.05) spheroid formation ability after 14-day incubation under stem cell conditions and decreased (P&lt;0.05) colony formation. Decreased expression of stem cell markers (Oct4, Nanog, and Twist) in DAB2IP-overexpressing cells was also observed, indicating potential key effectors downstream of DAB2IP. Furthermore, elevated DAB2IP expression in OCSCs decreased (p&lt;0.05) cisplatin IC50 and cell migration capacity in transwell assay, suggesting DAB2IP plays a role in OCSC function. Aberrant DNA promoter methylation and histone modifications were previously shown to be two major mechanisms of DAB2IP inactivation in cancer. We treated OCSCs with next-generation DNMT inhibitor guadecitabine and EZH2 inhibitor GSK-126, either alone or in combination. Single-agent guadecitabine or GSK-126 decreased ALDH expression with greater (p&lt;0.05) effect in combination. Single GSK-126 was sufficient to increase DAB2IP expression (p&lt;0.05) with additional increase when combined with guadecitabine, correlating with decreased ALDH expression. Collectively, our data suggested a possible combination epigenetic therapy to eliminate OCSCs, potentially through targeting DAB2IP, an important OCSC regulator.

Citation Format: Xingyue Zong, Ali R. Ozes, Kenneth P. Nephew. Targeting DAB2IP in ovarian cancer stem cells. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr B07.

Epigenetic Targeting of Adipocytes Inhibits High-Grade Serous Ovarian Cancer Cell Migration and Invasion

Ovarian cancer (OC) cells frequently metastasize to the omentum, and adipocytes play a significant role in ovarian tumor progression. Therapeutic interventions targeting aberrant DNA methylation in ovarian tumors have shown promise in the clinic, but the effects of epigenetic therapy on the tumor microenvironment are understudied. Here, we examined the effect of adipocytes on OC cell behavior in culture and impact of targeting DNA methylation in adipocytes on OC metastasis. The presence of adipocytes increased OC cell migration and invasion, and proximal and direct coculture of adipocytes increased OC proliferation alone or after treatment with carboplatin. Treatment of adipocytes with hypomethylating agent guadecitabine decreased migration and invasion of OC cells toward adipocytes. Subcellular protein fractionation of adipocytes treated with guadecitabine revealed decreased DNA methyltransferase 1 (DNMT1) levels even in the presence of DNA synthesis inhibitor, aphidicolin. Methyl-Capture- and RNA-sequencing analysis of guadecitabine-treated adipocytes revealed derepression of tumor-suppressor genes and epithelial-mesenchymal transition inhibitors. SUSD2, a secreted tumor suppressor downregulated by promoter CpG island methylation in adipocytes, was upregulated after guadecitabine treatment, and recombinant SUSD2 decreased OC cell migration and invasion. Integrated analysis of the methylomic and transcriptomic data identified pathways associated with inhibition of matrix metalloproteases and fatty acid α-oxidation, suggesting a possible mechanism of how epigenetic therapy of adipocytes decreases metastasis. In conclusion, the effect of DNMT inhibitor on fully differentiated adipocytes suggests that hypomethylating agents may affect the tumor microenvironment to decrease cancer cell metastasis.Implications: Epigenetic targeting of tumor microenvironment can affect metastatic behavior of ovarian cancer cells. Mol Cancer Res; 16(8); 1226-40. ©2018 AACR.

Abstract 4319: Epigenetic reprogramming associated with BRCA1 loss of function in ovarian cancer induces enhanced interferon gamma signaling

Inactivating mutations of the breast cancer type 1 susceptibility protein (BRCA1) have been implicated in breast and ovarian cancer (OC) initiation. Having observed differential response of OC cells to histone deacetylase inhibitors (HDACi) dependent on the presence of a functional BRCA1, we mapped promoters marked by acetylation of lysine 9 or lysine 27 of histone H3 (H3K9ac, H3K27ac) by ChIP-sequencing, and measured gene expression by RNA-sequencing in the isogenic OC cell lines UWB1.289 carrying an inactivating mutation of BRCA1 (BRCA1-null) and UWB1.289 cells with restored BRCA1 gene (BRCA1+). Significant differences in promoter levels of H3K9 and H3K27 acetylation were associated with marked alteration of gene expression levels between BRCA-null and BRCA1+ cells and in response to the HDACi, entinostat. Pathway analyses revealed cellular movement, cellular development, cellular growth and proliferation, TGFβ1, TNF, and INF-γ among the top cellular/molecular functions and upstream regulators enriched by the absence of BRCA1 among H3K9ac differentially marked and differentially expressed genes. Importantly, the same pathways and regulators were enriched in response to entinostat in BRCA1+ cells, indicating that changes in gene expression affecting these functions and regulators in BRCA1-null cells depend on promoter-associated histone acetylation. Integrated analyses revealed that TGFβ1 and IFN-γ were also activated in BRCA1-null/or low vs. BRCA1-normal ovarian tumors in the TCGA database. IFN-γ target genes were upregulated at baseline and responded less to IFN-γ stimulation in BRCA1-null vs. BRCA1+ cells. Binding of HDAC1 to promoters of IFN-γ target genes was increased in BRCA1-null cells. Similarly, the BRCA1-null breast cancer cell line HCC1937 responded less to IFN-γ stimulation compared with HCC1937 cells in which BRCA1 was restored. The knockdown of STAT1, the main IFN-γ signaling transduction molecule, inhibited BRCA1+ cell proliferation, but did not affect BRCA1-null cells. We conclude that the transcriptome of BRCA1-null cells and tumors is altered through changes in histone acetylation affecting cancer-related pathways, including IFN-γ cellular responses. These changes could alter tumor progression in BRCA-null OC and impact response to immunotherapy.

Citation Format: Horacio Cardenas, Jessica Thomes Pepin, Guanglong Jiang, Salvatore Condello, Kenneth P. Nephew, Yunlong Liu, Daniela Matei. Epigenetic reprogramming associated with BRCA1 loss of function in ovarian cancer induces enhanced interferon gamma signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4319.

An Effective Epigenetic-PARP Inhibitor Combination Therapy for Breast and Ovarian Cancers Independent of BRCA Mutations

Purpose: PARP inhibitors (PARPi) are primarily effective against BRCA1/2-mutated breast and ovarian cancers, but resistance due to reversion of mutated BRCA1/2 and other mechanisms is common. Based on previous reports demonstrating a functional role for DNMT1 in DNA repair and our previous studies demonstrating an ability of DNA methyltransferase inhibitor (DNMTi) to resensitize tumors to primary therapies, we hypothesized that combining a DNMTi with PARPi would sensitize PARPi-resistant breast and ovarian cancers to PARPi therapy, independent of BRCA status.Experimental Design: Breast and ovarian cancer cell lines (BRCA-wild-type/mutant) were treated with PARPi talazoparib and DNMTi guadecitabine. Effects on cell survival, ROS accumulation, and cAMP levels were examined. In vivo, mice bearing either BRCA-proficient breast or ovarian cancer cells were treated with talazoparib and guadecitabine, alone or in combination. Tumor progression, gene expression, and overall survival were analyzed.Results: Combination of guadecitabine and talazoparib synergized to enhance PARPi efficacy, irrespective of BRCA mutation status. Coadministration of guadecitabine with talazoparib increased accumulation of ROS, promoted PARP activation, and further sensitized, in a cAMP/PKA-dependent manner, breast and ovarian cancer cells to PARPi. In addition, DNMTi enhanced PARP "trapping" by talazoparib. Guadecitabine plus talazoparib decreased xenograft tumor growth and increased overall survival in BRCA-proficient high-grade serous ovarian and triple-negative breast cancer models.Conclusions: The novel combination of the next-generation DNMTi guadecitabine and the first-in-class PARPi talazoparib inhibited breast and ovarian cancers harboring either wild-type- or mutant-BRCA, supporting further clinical exploration of this drug combination in PARPi-resistant cancers. Clin Cancer Res; 24(13); 3163-75. ©2018 AACR.