Catalytically distinct IDH1 mutants tune phenotype severity in tumor models

Mutations in isocitrate dehydrogenase 1 (IDH1) impart a neomorphic reaction that produces the oncometabolite D-2-hydroxyglutarate (D2HG), which can inhibit DNA and histone demethylases to drive tumorigenesis via epigenetic changes. Though heterozygous point mutations in patients primarily affect residue R132, there are myriad D2HG-producing mutants that display unique catalytic efficiency of D2HG production. Here, we show that catalytic efficiency of D2HG production is greater in IDH1 R132Q than R132H mutants, and expression of IDH1 R132Q in cellular and mouse xenograft models leads to higher D2HG concentrations in cells, tumors, and sera compared to R132H-expressing models. Reduced representation bisulfite sequencing (RRBS) analysis of xenograft tumors shows expression of IDH1 R132Q relative to R132H leads to hypermethylation patterns in pathways associated with DNA damage. Transcriptome analysis indicates that the IDH1 R132Q mutation has a more aggressive pro-tumor phenotype, with members of EGFR, Wnt, and PI3K signaling pathways differentially expressed, perhaps through non-epigenetic routes. Together, these data suggest that the catalytic efficiency of IDH1 mutants modulate D2HG levels in cellular and in vivo models, resulting in unique epigenetic and transcriptomic consequences where higher D2HG levels appear to be associated with more aggressive tumors.

Omental preadipocytes stimulate matrix remodeling and IGF signaling to support ovarian cancer metastasis

Ovarian cancer can metastasize to the omentum, which is associated with a complex tumor microenvironment. Omental stromal cells facilitate ovarian cancer colonization by secreting cytokines and growth factors. Improved understanding of the tumor supportive functions of specific cell populations in the omentum could identify strategies to prevent and treat ovarian cancer metastasis. Here, we showed that omental preadipocytes enhance the tumor initiation capacity of ovarian cancer cells. Secreted factors from preadipocytes supported cancer cell viability during nutrient and isolation stress and enabled prolonged proliferation. Co-culturing with pre-adipocytes led to upregulation of genes involved in extracellular matrix (ECM) organization, cellular response to stress, and regulation of insulin-like growth factor (IGF) signaling in ovarian cancer cells. IGF-1 induced ECM genes and increased alternative NF-κB signaling by activating RelB. Inhibiting the IGF-1 receptor (IGF1R) initially increased tumor omental adhesion but decreased growth of established preadipocyte-induced subcutaneous tumors as well as established intraperitoneal tumors. Together, this study shows that omental preadipocytes support ovarian cancer progression, which has implications for targeting metastasis.

Toward a Transportable Cell Culture Platform for Evaluating Radiotherapy Dose Modifying Factors

The current tools for validating dose delivery and optimizing new radiotherapy technologies in radiation therapy do not account for important dose modifying factors (DMFs), such as variations in cellular repair capability, tumor oxygenation, ultra-high dose rates and the type of ionizing radiation used. These factors play a crucial role in tumor control and normal tissue complications. To address this need, we explored the feasibility of developing a transportable cell culture platform (TCCP) to assess the relative biological effectiveness (RBE) of ionizing radiation. We measured cell recovery, clonogenic viability and metabolic viability of MDA-MB-231 cells over several days at room temperature in a range of concentrations of fetal bovine serum (FBS) in medium-supplemented gelatin, under both normoxic and hypoxic oxygen environments. Additionally, we measured the clonogenic viability of the cells to characterize how the duration of the TCCP at room temperature affected their radiosensitivity at doses up to 16 Gy. We found that (78±2)% of MDA-MB-231 cells were successfully recovered after being kept at room temperature for three days in 50% FBS in medium-supplemented gelatin at hypoxia (0.4±0.1)% pO2, while metabolic and clonogenic viabilities as measured by ATP luminescence and colony formation were found to be (58±5)% and (57±4)%, respectively. Additionally, irradiating a TCCP under normoxic and hypoxic conditions yielded a clonogenic oxygen enhancement ratio (OER) of 1.4±0.6 and a metabolic OER of 1.9±0.4. Our results demonstrate that the TCCP can be used to assess the RBE of a DMF and provides a feasible platform for assessing DMFs in radiation therapy applications.

UGDH promotes tumor-initiating cells and a fibroinflammatory tumor microenvironment in ovarian cancer

BACKGROUND

Epithelial ovarian cancer (EOC) is a global health burden, with the poorest five-year survival rate of the gynecological malignancies due to diagnosis at advanced stage and high recurrence rate. Recurrence in EOC is driven by the survival of chemoresistant, stem-like tumor-initiating cells (TICs) that are supported by a complex extracellular matrix and immunosuppressive microenvironment. To target TICs to prevent recurrence, we identified genes critical for TIC viability from a whole genome siRNA screen. A top hit was the cancer-associated, proteoglycan subunit synthesis enzyme UDP-glucose dehydrogenase (UGDH).

METHODS

Immunohistochemistry was used to characterize UGDH expression in histological and molecular subtypes of EOC. EOC cell lines were subtyped according to the molecular subtypes and the functional effects of modulating UGDH expression in vitro and in vivo in C1/Mesenchymal and C4/Differentiated subtype cell lines was examined.

RESULTS

High UGDH expression was observed in high-grade serous ovarian cancers and a distinctive survival prognostic for UGDH expression was revealed when serous cancers were stratified by molecular subtype. High UGDH was associated with a poor prognosis in the C1/Mesenchymal subtype and low UGDH was associated with poor prognosis in the C4/Differentiated subtype. Knockdown of UGDH in the C1/mesenchymal molecular subtype reduced spheroid formation and viability and reduced the CD133 + /ALDH high TIC population. Conversely, overexpression of UGDH in the C4/Differentiated subtype reduced the TIC population. In co-culture models, UGDH expression in spheroids affected the gene expression of mesothelial cells causing changes to matrix remodeling proteins, and fibroblast collagen production. Inflammatory cytokine expression of spheroids was altered by UGDH expression. The effect of UGDH knockdown or overexpression in the C1/ Mesenchymal and C4/Differentiated subtypes respectively was tested on mouse intrabursal xenografts and showed dynamic changes to the tumor stroma. Knockdown of UGDH improved survival and reduced tumor burden in C1/Mesenchymal compared to controls.

CONCLUSIONS

These data show that modulation of UGDH expression in ovarian cancer reveals distinct roles for UGDH in the C1/Mesenchymal and C4/Differentiated molecular subtypes of EOC, influencing the tumor microenvironmental composition. UGDH is a strong potential therapeutic target in TICs, for the treatment of EOC, particularly in patients with the mesenchymal molecular subtype.

NF-κB Signaling Modulates miR-452-5p and miR-335-5p Expression to Functionally Decrease Epithelial Ovarian Cancer Progression in Tumor-Initiating Cells

Epithelial ovarian cancer (EOC) remains the fifth leading cause of cancer-related death in women worldwide, partly due to the survival of chemoresistant, stem-like tumor-initiating cells (TICs) that promote disease relapse. We previously described a role for the NF-κB pathway in promoting TIC chemoresistance and survival through NF-κB transcription factors (TFs) RelA and RelB, which regulate genes important for the inflammatory response and those associated with cancer, including microRNAs (miRNAs). We hypothesized that NF-κB signaling differentially regulates miRNA expression through RelA and RelB to support TIC persistence. Inducible shRNA was stably expressed in OV90 cells to knockdown RELA or RELB; miR-seq analyses identified differentially expressed miRNAs hsa-miR-452-5p and hsa-miR-335-5p in cells grown in TIC versus adherent conditions. We validated the miR-seq findings via qPCR in TIC or adherent conditions with RELA or RELB knocked-down. We confirmed decreased expression of hsa-miR-452-5p when either RELA or RELB were depleted and increased expression of hsa-miR-335-5p when RELA was depleted. Either inhibiting miR-452-5p or mimicking miR-335-5p functionally decreased the stem-like potential of the TICs. These results highlight a novel role of NF-κB TFs in modulating miRNA expression in EOC cells, thus opening a better understanding toward preventing recurrence of EOC.

Abstract 3781: NF-κB classical and alternative signaling differentially regulate miRNA expression in ovarian cancer

The NF-κB signaling pathway has been shown to contribute to epithelial ovarian cancer (EOC) through its classical and alternative pathways, characterized by the RelA and RelB transcription factors respectively. Previous studies have highlighted the role of RelA in sustaining the proliferative cancer cell population, while RelB aids in promoting the survival of chemoresistant, stem-like tumor-initiating cells (TICs) that promote disease relapse. In further characterizing the downstream effects of NF-κB signaling on EOC, we hypothesize NF-κB signaling differentially regulates the expression of several microRNAs (miRNAs) to promote TIC survival and proliferation through its classical and alternative pathways. miRNAs comprise a subset of small, noncoding RNAs that regulate gene expression, making them amenable for therapeutic targeting. Inducible shRNA stably expressed in OV90 EOC cells to knockdown RelA or RelB were analyzed by miR-seq to identify the differential expression of miRNAs in cells grown in TIC vs adherent (adh) conditions. Several miRNAs were differentially expressed in these conditions with RelA or RelB knockdown; we identified and validated the expression of two candidate miRNAs: hsa-miR-452-5p and hsa-miR-335-5p. We observed the decreased expression of hsa-miR-452-5p when either RelA or RelB is knocked down, while also observing the increased expression of hsa-miR-335-5p when RelA is knocked down. By inhibiting miR-452-5p in conjunction with disrupting NF-κB activity, we found changes in cell viability, sphere formation, and expression of the stem cell marker ALDH. Understanding the role of miRNA signaling in the context of NF-κB will better define the transcriptional roles of RelA and RelB in EOC. Ongoing work will further characterize the downstream targets of these miRNAs as potential therapeutic targets.

Citation Format: Rahul D. Kamdar, Brittney S. Harrington, Soumya Korrapati, Emma Attar, Nathan Wong, Carrie D. House, Christina M. Annunziata. NF-κB classical and alternative signaling differentially regulate miRNA expression in ovarian cancer. [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 3781.

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

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

IMPLICATIONS

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

Insulin-like growth factor binding protein 5: Diverse roles in cancer

Insulin-like growth factor binding proteins (IGFBPs) and the associated signaling components in the insulin-like growth factor (IGF) pathway regulate cell differentiation, proliferation, apoptosis, and adhesion. Of the IGFBPs, insulin-like growth factor binding protein 5 (IGFBP5) is the most evolutionarily conserved with a dynamic range of IGF-dependent and -independent functions, and studies on the actions of IGFBP5 in cancer have been somewhat paradoxical. In cancer, the IGFBPs respond to external stimuli to modulate disease progression and therapeutic responsiveness in a context specific manner. This review discusses the different roles of IGF signaling and IGFBP5 in disease with an emphasis on discoveries within the last twenty years, which underscore a need to clarify the IGF-independent actions of IGFBP5, the impact of its subcellular localization, the differential activities of each of the subdomains, and the response to elements of the tumor microenvironment (TME). Additionally, recent advances addressing the role of IGFBP5 in resistance to cancer therapeutics will be discussed. A better understanding of the contexts in which IGFBP5 functions will facilitate the discovery of new mechanisms of cancer progression that may lead to novel therapeutic opportunities.

Abstract 3833: The role of chemotherapy-induced fibrosis in the maintenance of tumor initiating cells

Around 80 percent of high-grade serous ovarian cancer patients will relapse with chemotherapy resistant disease. Despite extensive research and developments in immunotherapy, there are limited improvements in overall survival for these patients. Recent research has found that the tumor microenvironment (TME) plays a crucial role in tumor initiation, therapy resistance, and tumor relapse. The TME, which consists of immune cells, blood vessels, and an extracellular matrix (ECM) built primarily by fibroblasts, may enhance the survival and growth of tumor-initiating cells (TICs), chemoresistant stem-like cells thought to be responsible for tumor relapse. Cytotoxic chemotherapies have been shown to modify the TME and this modulation may favor the survival of TICs. For example, carboplatin can activate stromal cells such as fibroblasts to secrete an altered ECM profile, including increases in collagen 1a1 and fibronectin production, which can bind specific integrins upregulated in TICs. Using ex-vivo decellularized peritoneum tissues from mice exposed to chemotherapy or vehicle treatment, we observed a 2-fold increase in growth in peritoneums pre-exposed to chemotherapy relative to those pre-exposed to vehicle. We hypothesize that alterations in the ECM following chemotherapy treatment permit TIC adhesion and growth. To investigate this, mouse embryonic fibroblasts (3T3s) were exposed to chemotherapy during ECM production, decellularized, and reseeded with a panel of ovarian cancer cell lines. Our results suggest a significant increase in cell survival in matrices pre-exposed to chemotherapy compared to control matrices pre-exposed to vehicle. Using this model, we are examining the features of cells that preferentially survive on these matrices. In addition to drug resistance, we are using flow cytometry to assess TIC markers, such as CD117, and CD133, and qRT-PCR to measure stemness genes such as SOX2, OCT4, and NANOG. These studies highlight the need for further investigation into the systemic effects of chemotherapies on the TME and how these changes may be fostering cancer cell adhesion, growth, and survival. Understanding these mechanisms will allow us to develop therapies to achieve better clinical outcomes.

Citation Format: Omar Lujano-Olazaba, Mikella Robinson, Samuel F. Gilbert, Emily Kogan, Carrie D. House. The role of chemotherapy-induced fibrosis in the maintenance of tumor initiating cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3833.

Abstract 3129: TWEAK cytokine supports ovarian cancer tumor-initiating cell (TIC) phenotypes important for relapse

Ovarian cancer is the deadliest gynecological cancer with over 13,000 deaths estimated in the United States this year. While there is an initial high response rate to cytotoxic chemotherapy, over 80% of advanced cases relapse within 24 months, presenting an urgent need to better understand the molecular mechanisms permitting relapse. Current research suggests that cancer recurrence can be attributed to a small subpopulation of cancer stem-like tumor-initiating cells (TICs) that possess the ability to both resist chemotherapy and initiate tumorigenesis. Our lab previously demonstrated an essential role for alternative NF-kB signaling in maintaining ovarian TICs, yet it is not fully understood how this pathway becomes activated in ovarian cancer. To begin to address this, we used an NF-kB reporter system to screen soluble factors known to be in the ovarian tumor microenvironment (TME) to identify the strongest inducers of NF-kB activation in ovarian cancer cells. We found that tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) is a strong inducer of alternative NF-kB signaling. In vitro experiments demonstrate enhanced expression of stemness genes including SOX2, OCT4 and NANOG and increased spheroid formation ability after stimulation with TWEAK. Moreover, flow cytometry analysis of several TIC markers shows a significant enrichment of TICs when chemotherapy was combined with TWEAK, relative to chemotherapy alone. Stimulation of CD117+ cells led to higher expression of stemness genes relative to stimulation of CD117- cells, suggesting TWEAK activity may be specific to TICs and enhances their stem-like phenotype. In support of this, we found that CD117+ cells have higher expression of the TWEAK receptor FN14. We investigated the role of TWEAK in aiding relapse in vivo using an intraperitoneal xenograft mouse model and found that administration of a small molecule inhibitor of TWEAK-FN14 signaling as a maintenance treatment following chemotherapy significantly prolonged survival. These findings highlight a potential mechanism of TIC enrichment in response to chemotherapy that contributes to relapse.

Citation Format: Denay N. Stevenson, Ryne M. Holmberg, Samuel F. Gilbert, Mikella Robinson, Carrie D. House. TWEAK cytokine supports ovarian cancer tumor-initiating cell (TIC) phenotypes important for relapse [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3129.

Abstract 901: Sox2 and Oct4 activity identify CSC populations in ovarian cancer

High Grade Serous Ovarian Cancer is the most lethal gynecological cancer, mainly due to late-stage diagnosis and prevalence of chemotherapy-resistant disease. Tumors are comprised of heterogenous cancer cells, which makes targeted therapies challenging. Studies have identified a subset of cancer stem-like cells (CSCs) that, unlike bulk tumor cells, can evade chemotherapy and induce relapse. Cell surface markers such as CD133, CD44, CD117, or ALDH enzyme activity are typically used to identify and isolate CSCs; however, these markers are inconsistent across cell lines and patient samples making them unreliable for isolating CSCs. Consistent indicators of CSCs may be activity of stem cell transcription factors, such as SOX2, OCT4, and NANOG, which are known to promote long-term self-renewal and asymmetric division, processes required for tumor repopulation. We hypothesize that a reporter responding to SOX2 and OCT4 activity will represent a functionally relevant and reliable marker for identifying CSCs capable of enabling relapse. We have stably transduced a reporter (termed SORE6), which detects SOX2 and OCT4 activity, into OV90 and ACI23 ovarian cancer cells. SORE6+ cells, isolated using fluorescence assisted cell sorting (FACS), have 2 to 15-fold increases in SOX2/OCT4/NANOG transcripts, relative to SORE6- cells. Comparison of CSC markers in chemotherapy versus vehicle conditions suggests that SORE6 more consistently identifies the CSC population. Specifically, flow cytometry analysis of ACI23 cells showed a 2-fold increase in SORE6+ cells, 7-fold increase in CD117+ cells, and a 1.2-fold increase in CD133 cells in carboplatin treated cells relative to vehicle. For OV90, SORE6+ increases again by 2-fold, while CD117+ increases by 5-fold and CD133 increases by 1.5-fold. SORE6+ cells also showed significantly enhanced spheroid formation efficiency in low serum conditions and resistance to carboplatin and paclitaxel chemotherapies, relative to SORE6- cells. Finally, in vivo limiting dilution studies in mice showed a significant difference in tumorigenicity of SORE6+ cells at low dilutions in ACI23 cells, but not for OV90 cells. Flow cytometry analysis of disassociated tumors showed that tumors created using pure SORE6- cells remained SORE6-, while tumors created using pure SORE6+ cells maintained only 10% SORE6+, indicating the ability of SORE6+ cells to asymmetrically divide to create a heterogeneous tumor. In conclusion, these data suggest that the SORE6 reporter identifies a CSC population within ovarian cancer cell lines and could be a useful tool for consistent isolation of CSCs. Use of this reporter will enhance our understanding of mechanisms, such as SOX2 and OCT4 activity, that support chemoresistance and tumor repopulation. More reliable identification of CSCs will enable the design of therapies to overcome chemotherapy resistance and disease recurrence.

Citation Format: Luisjesus S. Cruz, Mikella Robinson, Samuel F. Gilbert, Omar Lujano-Olazaba, Logan A. Alexander, Alex Horkowitz, Carrie D. House. Sox2 and Oct4 activity identify CSC populations in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 901.

Abstract 2535: Omental preadipocytes support ovarian cancer tumorigenesis by mediating genes important for extracellular matrix reorganization

Ovarian cancer is the most lethal gynecological malignancy in the United States, with a known predilection for metastasizing to the omentum, a sheet of fatty tissue that encloses the abdomen. While it has been shown that ovarian cancer cells invade towards mature adipocytes in vitro, the contribution of stromal cells that reside in the omentum is not well understood. We hypothesize that preadipocytes, the precursor cells that give rise to omental adipocytes, are important mediators of cancer progression in the omental tumor microenvironment as they have a pro-inflammatory secretome that is distinct from that of mature adipocytes. To evaluate this hypothesis, we tested whether preadipocyte secreted factors altered tumorgenicity of ovarian cancer cells using colony formation and cell viability in vitro and a limiting dilution in vivo in a subcutaneous mouse model. The mouse studies showed that low dilutions of cancer cells require preadipocytes for engraftment and tumor formation. A transplantation assay showed that cancer cells require the presence of preadipocytes for sustained tumor formation capacity. In vitro co-culture assays revealed that preadipocytes secrete factors that increase clonogenicity and extend cell viability in serum-free conditions. To identify signaling pathways induced by preadipocytes we co-cultured cancer cells with either primary human omental preadipocytes or differentiated mature adipocytes derived from the same female donor and performed RNA sequencing and gene set enrichment analysis (GSEA). We identified differentially expressed genes in cancer cells that were unique to preadipocyte co-culture, including DCN, MMP2, COL6A2 and COL12A1, genes involved in extracellular matrix organization. The most significantly upregulated gene was insulin-like growth factor binding protein 5 (IGFBP5), which has functions in insulin-like growth factor signaling and ECM interactions. Ongoing studies using CRISPR edited cancer cells suggest IGFBP5 mediates the enhanced tumorigenesis of cancer cells in the presence of preadipocytes. Our findings highlight the role of preadipocytes in the ovarian tumor microenvironment and implicate IGFBP5 as a preadipocyte-mediated gene. Future studies will determine if there is a link between the upregulation of IGFBP5 and modulation of extracellular matrix proteins that promote cancer progression. Understanding these processes will enable the design of more effective therapies for treating ovarian cancer.

Citation Format: Jennifer A. Waters, Mikella Robinson, Samuel F. Gilbert, Ixchel Urbano, Carrie D. House. Omental preadipocytes support ovarian cancer tumorigenesis by mediating genes important for extracellular matrix reorganization [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2535.

Abstract 5727: Using ChIP-seq to identify genes regulated by RelA or RelB that support ovarian cancer tumor-initiating cell (TIC) characteristics

Ovarian cancer is the most lethal gynecologic malignancy in the US. Although high-grade serous ovarian cancer (HGSOC) patients initially respond to chemotherapy, over 70% relapse in two years. This paradigm can be understood through ovarian cancer’s pronounced heterogeneity whereby a majority of cancer cells are highly proliferative and chemosensitive and a minority of cells, termed tumor-initiating cells (TICs), are relatively quiescent and chemoresistant stem-like cells. Both are presumed to be important for tumor repopulation. Our lab previously demonstrated that TICs exhibit an upregulation of stem cell genes and NF-κB signaling. RNA sequencing of cells grown in TIC enhancing, non-adherent conditions shows significantly increased expression of NF-kB genes NFKB2, RELA, and RELB, as well as stem cell genes SOX2 and ALDH1A2. In this study, we are investigating the mechanism through which the NF-κB transcription factors RelA and RelB support TICs to promote relapse in ovarian cancer. RNA sequencing of shRNA knockdowns of RELA or RELB from cells grown in TIC conditions shows that RELA knockdown impacts 1415 unique genes, RELB knockdown impacts 2016 unique genes, and RELA or RELB knockdown decreases expression of 1912 shared genes. Gene ontology analysis suggests RELA regulates genes in growth and differentiation pathways while RELB regulates genes in metabolic pathways. Specifically, RELA knockdown significantly decreased expression of NF-kB pathway genes (RELA, RELB, NFKB2) as well as stem cell genes CD117 and ALDH1A2. RELB knockdown significantly decreased expression of NF-kB pathway genes (RELA, RELB) as well as stem cell genes CD117, CD133, ALDH1A1, and ALDH1A2. To expand on these findings we performed ChIP-sequencing of RelA and RelB in OV90 cells cultured in TIC enhancing or adherent monolayer conditions. Our results show that both RelA and RelB bind at promoter sites for NFKBIA and NUAK1 in both conditions. In monolayer cultures RelA uniquely binds 14 different genes, including lncRNAs, miRNAs, and Cyclin L1, important in G0-G1 cell cycle progression. In TIC conditions, RelB uniquely binds 16 different genes, including lncRNAs, miRNAs, and WNT10A, important in stem cell self-renewal. Experiments are underway to validate our top hits in ovarian cancer, using siRNA knockdowns to corroborate the genes and pathways through which RelB supports self-renewal and RelA supports cell cycle progression. The ultimate goal of this project is to identify downstream pathways regulated by NF-kB that can be targeted to overcome relapse in HGSOC.

Citation Format: Emily M. Mu, Samuel F. Gilbert, Mikella Robinson, Jacqueline Lara, Omar Lujano-Olazaba, Christina M. Annunziata, Carrie D. House. Using ChIP-seq to identify genes regulated by RelA or RelB that support ovarian cancer tumor-initiating cell (TIC) characteristics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5727.

Abstract 3188: Modulating UGDH expression in ovarian cancer tumor-initiating cells alters the tumor microenvironment

Epithelial ovarian cancer (EOC) is a global health burden, with the poorest five-year survival rate of the gynecological malignancies due to diagnosis at advanced stage and high recurrence rate. Recurrence in EOC is driven by the survival of chemoresistant, stem-like tumor-initiating cells (TICs) that are supported by a complex extracellular matrix (ECM) and immunosuppressive microenvironment. To target TICs to prevent recurrence, we identified genes critical for TIC viability from a whole genome siRNA screen. A top hit was the cancer-associated, ECM synthesis enzyme UDP-glucose dehydrogenase (UGDH). Immunohistochemistry was used to delineate UGDH expression in histological and molecular subtypes of EOC. Clustering analysis was performed to characterize EOC cell lines to aligned to the molecular subtypes observed in tumors. UGDH expression was modulated in the cell lines using inducible shRNA, and the effects on TICs and on the cells in the supporting microenvironment were examined. High UGDH expression was observed in the majority of high-grade serous ovarian cancers and variable expression was observed in clear cell, mucinous and endometrioid histotypes. A distinctive survival prognostic for UGDH expression was revealed when serous cancers were stratified by molecular subtype, where high UGDH was associated with a poor prognosis in the mesenchymal subtype. Using OV90 as a representative cell line for the mesenchymal subtype, we examined the effect of UGDH knockdown on the tumor cells alone, and on mesothelial support cells in co-culture with the tumor cells. Knock down of UGDH in the OV90 cells reduced the viability, sphere-formation and colony formation capacity of TICs and reduced extracellular hyaluronan production. Knocking down UGDH in the tumors affected the mesothelial cells in co-culture by significantly reducing the expression of ECM signaling and remodeling proteins Versican, Vitronectin, Laminin and matrix metalloprotease 1. These data show that modulation of UGDH expression in tumors influences cells in the microenvironment and reveal a distinct role for UGDH in the mesenchymal molecular subtype of EOC. UGDH is a strong prospective therapeutic target in TICs, for the treatment of metastatic and recurrent EOC, particularly in patients with the mesenchymal molecular subtype.

Citation Format: Brittney S. Harrington, Rahul Kamdar, Nathan Wong, Carrie D. House, Christina M. Annunziata. Modulating UGDH expression in ovarian cancer tumor-initiating cells alters the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3188.

Abstract 5820: NF-κB signaling regulates miRNA expression in ovarian cancer

Epithelial ovarian cancer (EOC) remains the fifth leading cause of cancer related death in women worldwide, partly due to the survival of chemoresistant, stem-like tumor-initiating cells (TICs) that promote disease relapse. Previous studies described the role of the NF-kB pathway in promoting TIC chemoresistance and survival through the action of key transcription factors (TFs) like RelA and RelB. These TFs serve as key master regulators of genes important for the inflammatory response, which also overlap with the regulation of targets associated with cancer promotion. We previously showed that RelA and RelB exert different effects in ovarian cancer cells, with RelB relatively more important for tumor initiation. In this study, we hypothesize that NF-kB signaling regulates the expression of several microRNAs (miRNAs) differentially through RelA and RelB to promote TIC survival and proliferation. miRNAs comprise a subset of small, noncoding RNAs that regulate gene expression and present potential therapeutic targets for clinical use. Inducible shRNA stably was expressed in OV90 EOC cells to knockdown RelA or RelB; cells were subsequently analyzed by miR-seq to identify differentially expressed miRNAs in cells grown in TIC vs adherent (adh) conditions. To validate the miR-seq findings, we performed qPCR assays of the candidate miRNAs differentially expressed in TIC or adh conditions with RelA or RelB knocked down. We confirmed the decreased expression of oncogenic miRNAs hsa-miR-105-5p and hsa-miR-452-5p, while also confirming the increased expression of tumor suppressive miRNA hsa-miR-34a-5p observed in the miR-seq using OV90 cells. Ongoing work will validate these expression changes in additional cell lines and conduct functional assays to characterize the effect of mimicking or inhibiting these miRNAs of interest. The identification of miRNAs differentially expressed in TICs under the control of RelA or RelB will provide key insights in designing treatments against them to prevent disease relapse in patients with EOC.

Citation Format: Rahul D. Kamdar, Brittney S. Harrington, Soumya Korrapati, Nathan Wong, Carrie D. House, Christina M. Annunziata. NF-κB signaling regulates miRNA expression in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5820.

Characterization of SOX2, OCT4 and NANOG in Ovarian Cancer Tumor-Initiating Cells

The identification of tumor-initiating cells (TICs) has traditionally relied on surface markers including CD133, CD44, CD117, and the aldehyde dehydrogenase (ALDH) enzyme, which have diverse expression across samples. A more reliable indication of TICs may include the expression of embryonic transcription factors that support long-term self-renewal, multipotency, and quiescence. We hypothesize that SOX2, OCT4, and NANOG will be enriched in ovarian TICs and may indicate TICs with high relapse potential. We evaluated a panel of eight ovarian cancer cell lines grown in standard 2-D culture or in spheroid-enriching 3-D culture, and correlated expression with growth characteristics, TIC marker expression, and chemotherapy resistance. RNA-sequencing showed that cell cycle regulation pathways involving SOX2 were elevated in 3-D conditions. HGSOC lines had longer doubling-times, greater chemoresistance, and significantly increased expression of SOX2, OCT4, and NANOG in 3-D conditions. CD117+ or ALDH+/CD133+ cells had increased SOX2, OCT4, and NANOG expression. Limiting dilution in in vivo experiments implicated SOX2, but not OCT4 or NANOG, with early tumor-initiation. An analysis of patient data suggested a stronger role for SOX2, relative to OCT4 or NANOG, for tumor relapse potential. Overall, our findings suggest that SOX2 may be a more consistent indicator of ovarian TICs that contribute to tumor repopulation following chemotherapy. Future studies evaluating SOX2 in TIC biology will increase our understanding of the mechanisms that drive ovarian cancer relapse.

Abstract 4960: Sox2, Oct4, and Nanog expression for identification of ovarian cancer tumor initiating cells

High Grade Serous Ovarian Cancer (HGSOC) is the most lethal gynecological disease in women, with over 70% of advanced stage disease relapsing within 18 months. Recent studies suggest that tumor-initiating cells (TICs) support tumor heterogeneity, chemoresistance, and relapse in HGSOC. Identification of TICs has traditionally relied on expression of surface markers such as CD133, CD44, and CD117 and/or enzymes such as aldehyde dehydrogenase (ALDH). Unfortunately, these markers are often cell type specific and not reproducible across patient samples. More reliable markers of TICs may include stem cell transcription factors such as Sox2, Oct4, and Nanog that function to support long-term self-renewal, multipotency, and quiescence, although these factors have not been comprehensively evaluated in ovarian cancer. We have previously shown that ovarian cancer cells cultured in 3D spheroid-supporting conditions have enhanced expression of Sox2, Oct4, and Nanog and are more tumorigenic than cells cultured in 2D as a monolayer. We hypothesize that Sox2, Oct4, and Nanog support spheroid formation, chemotherapy resistance, and tumorigenicity more reliably than traditional TIC markers. To investigate this hypothesis we evaluated five HGSOC cell lines (CAOV3/CAOV4/OV90/OVCAR4/OVCAR8), two undefined serous lines (ACI23, OVCAR5) and one non-serous line (SKOV3) in 2D vs 3D conditions and quantitated Sox2, Oct4, and Nanog expression, spheroid formation, chemotherapy resistance and tumorigenicity. Our data show that OVCAR4, OVCAR5, and OVCAR8 had the highest expression of Sox2, Oct4, and Nanog in 3D conditions and at least half of the cell lines had enriched expression of all three factors after chemotherapy treatment. A correlation analysis of the traditional TIC markers shows that the surface marker CD133 positively correlated with expression of Sox2, Oct4, and Nanog. Analysis of TCGA data shows that Sox2, Oct4, and Nanog are prone to amplification or gain of function events in 21%, 4%, and 7% of patients, respectively, and these patients are significantly more likely to have recurrent disease. Overall our findings suggest that Sox2, Oct4, and Nanog correlate with TIC features and may be more reliable markers for the identification of cells with enhanced tumor-initiation capacity and drug resistance. Our data further clarify specific ovarian cancer cell lines that have greater dependence on these factors. More reliable and consistent identification of ovarian TICs will improve our understanding of TIC biology and enable the design of therapies to overcome chemotherapy resistance and disease relapse.

Citation Format: Mikella Robinson, Samuel F. Gilbert, Logan J. Alexander, Samuel E. Green, Omar Lujano-Olazaba, Omid Patrus, Jennifer A. Waters, Jacqueline M. Lara, Carrie D. House. Sox2, Oct4, and Nanog expression for identification of ovarian cancer tumor initiating 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 4960.

Abstract 4941: Identification and isolation of ovarian cancer stem cell populations using a novel functional reporter may provide new insights into ovarian cancer cell dynamics and drug resistance

Background: Ovarian cancer is the most lethal gynecologic malignancy mainly due to a high prevalence of chemotherapy-resistant recurrent disease. This mechanism is unknown but recent studies have pointed to a small population of chemoresistant cancer stem cells (CSC) as the driver of these recurrences. Traditional surface markers of cancer stem cells (CD44, ALDH, CD117, etc.) have shown mixed success in identifying this subpopulation, with different cell lines and patient samples exhibiting dissimilar profiles. These markers are often related to the cell of origin and are not necessarily specific to CSCs. As such, a reporter that responds to functional features of stem cells would be beneficial in identifying the CSC subpopulation regardless of cell line and patient sample. Here we demonstrate that using a reporter to detect SOX2 and OCT4 overexpression (called SORE6) can identify the CSC subpopulation within ovarian cancer cell lines.

Methods: The SORE6 reporter was stably transduced into OV90 and ACI23 ovarian cancer cell lines. The subpopulation of cells having high SOX2/OCT4 expression (SORE6+) were isolated using fluorescence assisted cell sorting (FACs) and evaluated for CSC characteristics relative to SORE6- cells. Gene expression, viability, spheroid formation capacity, and tumorigenicity was assessed for both SORE6+ and SORE6- cells. In vivo limiting dilution analyses were performed on athymic nude female mice using subcutaneous injection.

Results: Compared to the bulk population which has low levels of SOX2/OCT4 expression (SORE6-), SORE6+ cells showed a 1.5-fold increase in SOX2/OCT4/NANOG transcript levels in ACI23 cells and 2 to 15-fold increase in these transcript levels in the OV90 cells. SORE6+ cells showed enhanced chemoresistance when treated with conventional chemotherapies for ovarian cancer, carboplatin and paclitaxel, although this difference was more dramatic in the OV90 cells (four-fold) relative to ACI23 (two-fold). These findings indicate that SOX2/OCT4 expression could contribute to drug resistance and clinical recurrence. SORE6+ cells also showed an increased capacity to form spheroids in low-serum conditions and again this difference was more dramatic in the OV90 cells. In vivo limiting dilution studies are underway but appear to show significant differences in tumorigenicity at low dilutions of ≤5,000 cells/mouse.

Conclusion: The SORE6 reporter construct identifies CSC populations within ovarian cancer cell lines and may be a reliable tool for isolating CSCs that depend on SOX2 and OCT4 expression. Use of this reporter will enhance our understanding of mechanisms that support chemoresistance and enable the study of CSC dynamics within the tumor microenvironment, both of which have significant implications for ovarian cancer progression and treatment.

Citation Format: Samuel F. Gilbert, Mikella Robinson, Logan A. Alexander, Omar Lujano-Olazaba, Jacqueline M. Lara, Jennifer A. Waters, Omid Patrus, Alex Horkowitz, Carrie D. House. Identification and isolation of ovarian cancer stem cell populations using a novel functional reporter may provide new insights into ovarian cancer cell dynamics and drug resistance [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 4941.

Abstract 6116: Role of secretory factors from obese-derived omentum in supporting ovarian cancer progression

Ovarian cancer is the most lethal gynecological malignancy in the United States, with a known predilection for metastasizing to the omentum, a sheet of fatty peritoneal tissue that encloses the abdomen. This finding coincides with some evidence that ovarian cancer is more aggressive in the obese setting with worse overall survival. While it has been shown that ovarian cancer cells invade towards adipocytes in vitro, the mechanism by which they support formation of secondary tumors is not well understood. We hypothesize that soluble factors enriched in the obese setting are activating signaling pathways in tumor cells to drive migration and proliferation. To evaluate this hypothesis we co-cultured primary human omental adipocytes derived from obese female donors with ovarian cancer cell lines and profiled secretory factors (cytokines and adipokines) responsible for increasing tumor initiation in vivo and clonogenicity, proliferation, and drug resistance in vitro. Secretion of cytokines IL-6, IL-8, and CCL2 by adipocytes is enhanced when co-cultured with ovarian cancer cells. A subcutaneous tumor model showed that low dilutions of ovarian cancer cells require adipocytes for engraftment and tumor formation. A transplantation assay showed that ovarian cancer cells require the presence of adipocytes for sustained tumor-initiation capacity. Studies are underway to investigate adipocyte-secreted factors in this process. Our findings highlight the role of adipocytes in the ovarian tumor microenvironment and uncover signaling factors that may enhance ovarian cancer progression. Understanding these processes will enable the design of more effective therapies for treating ovarian cancer.

Citation Format: Jennifer Waters, Mikella Robinson, Samuel F. Gilbert, Logan J. Alexander, Carrie D. House. Role of secretory factors from obese-derived omentum in supporting ovarian cancer progression [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 6116.

Drugs Targeting Tumor-Initiating Cells Prolong Survival in a Post-Surgery, Post-Chemotherapy Ovarian Cancer Relapse Model

Disease recurrence is the major cause of morbidity and mortality of ovarian cancer (OC). In terms of maintenance therapies after platinum-based chemotherapy, PARP inhibitors significantly improve the overall survival of patients with BRCA mutations but is of little benefit to patients without homologous recombination deficiency (HRD). The stem-like tumor-initiating cell (TIC) population within OC tumors are thought to contribute to disease recurrence and chemoresistance. Therefore, there is a need to identify drugs that target TICs to prevent relapse in OC without HRD. RNA sequencing analysis of OC cells grown in TIC conditions revealed a strong enrichment of genes involved in drug metabolism, oxidative phosphorylation and reactive oxygen species (ROS) pathways. Concurrently, a high-throughput drug screen identified drugs that showed efficacy against OC cells grown as TICs compared to adherent cells. Four drugs were chosen that affected drug metabolism and ROS response: disulfiram, bardoxolone methyl, elesclomol and salinomycin. The drugs were tested in vitro for effects on viability, sphere formation and markers of stemness CD133 and ALDH in TICs compared to adherent cells. The compounds promoted ROS accumulation and oxidative stress and disulfiram, elesclomol and salinomycin increased cell death following carboplatin treatment compared to carboplatin alone. Disulfiram and salinomycin were effective in a post-surgery, post-chemotherapy OC relapse model in vivo, demonstrating that enhancing oxidative stress in TICs can prevent OC recurrence.

Abstract 5470: IKK-epsilon supports anchorage independent growth via alternative NF-kB signaling in triple-negative breast cancer

Metastatic breast cancer carries a poor prognosis despite the success of newly targeted therapies and treatment options remain especially limited for the subtype of triple negative breast cancer (TNBC). Several signaling pathways, including NF-κB, are altered in TNBC. Given that ΙΚΚε behaves as an oncogene in breast cancer we hypothesized that IKKε regulates classical or alternative NF-κB signaling to control diverse oncogenic functions in TNBC. Vector expression and RNA interference were used to investigate the functional role of IKKε in triple-negative breast cancer cells. Viability, protein expression, NF-κB binding activity, invasion, anoikis, and spheroid formation were examined in cells expressing high or low levels of IKKε in conjunction with alternative NF-κB p52 RNA interference or MEK inhibition. Our data show that p52 protein levels and binding activity are inversely proportional to ΙΚΚε. Moreover, knockdown of IKKε leads to increased expression of p52 and the p52-regulated gene CXCL1. This interaction was confirmed by CHiP-PCR experiments showing increased binding of p52 in the CXCL1 promoter of cells with IKKε knockdown relative to control. We further found that IKKε and MEK were required for growth in anchorage supportive conditions whereas p52 was required in anchorage resistant conditions. Western blots confirm diminished IKKε expression and enhanced p52 processing in anchorage resistant conditions relative to anchorage supportive conditions. In this model, IKKε and MEK cooperate to support growth of cancer cells in the attached, anchored environment, whereas p52 is required for growth in unattached 3-D environment. These studies reveal novel information about the role of IKKε in TNBC and highlight the adaptability of NF-κB signaling in maintaining cancer cell survival under different growth conditions. Current studies are underway to clarify the mechanism of IKKε regulation of p52. A better understanding of the diversity of NF-κB signaling may ultimately improve the development of novel therapeutic regimens for TNBC.

Citation Format: Carrie D. House, Valentina Grajales, Michelle Ozaki, Elizabeth Jordan, Helmae Wubneh, Danielle Kimble, Marianne Kim, Christina M. Annunziata. IKK-epsilon supports anchorage independent growth via alternative NF-kB signaling in triple-negative breast cancer [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 5470.

Abstract 167: Targeting the NF-kappaB pathway with bardoxolone methyl to inhibit ovarian cancer spheroid formation

Over 70% of patients with advanced stage ovarian cancer relapse within 2 years, with long term overall survival being only 25%. Tumor-initiating cells (TICs) are thought to contribute to this high rate of recurrence as they can resist killing by platinum-based chemotherapy. In this study we sought to identify pathways unique to TICs and to disrupt these pathways in order to more effectively target this population of cells. We conducted an siRNA screen which identified NF-kappaB signaling as an important pathway in the maintenance of ovarian cancer cells grown in non-adherent spheroid cultures that mimic TICs. Downregulation of several known NF-kappaB target genes, including NXF1, RAC2, CDC42, BCL2L1 and SERPINB3, significantly decreased growth of TIC cultures but not the corresponding adherent cultures, thereby indicating that expression of these genes is necessary for growth in TIC cultures. These findings are consistent with previous studies which showed that higher NF-kappaB activity is linked with drug resistance in patients. In parallel, we conducted a drug screen to identify compounds that target TICs. One clear candidate was bardoxolone methyl, which has been shown to inhibit IKK, an upstream NF-kappaB signaling protein. We confirmed the results of the drug screen in a panel of ovarian cancer cell lines, showing that bardoxolone methyl decreased known TIC markers CD133 and ALDH by flow cytometry, and decreased NF-kappaB proteins by western blot. To further elucidate the mechanism of bardoxolone methyl on TICs we conducted an RNAi screen +/- bardoxolone methyl. Interestingly, the knockdown of genes including BRAF, MAP3K8, LMNA and SMAD6 acted in a synthetically lethal manner with bardoxolone methyl in the TICs. To begin translating to a clinically relevant model, we proceeded to test whether bardoxolone methyl could eliminate TICs that remained after treatment with platinum-based chemotherapy. We confirmed in vitro that bardoxolone methyl in combination with chemotherapy reduced TIC populations. Our ongoing studies will address whether this drug is effective in preventing relapse in vivo after chemotherapy treatment of ovarian cancer in mouse models.

Citation Format: Michelle K. Ozaki, Carrie D. House, Krystyna Mazan-Mamczarz, Madhu Lal-Nag, Craig Thomas, Christina M. Annunziata. Targeting the NF-kappaB pathway with bardoxolone methyl to inhibit ovarian cancer spheroid formation [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 167.

IΚΚε cooperates with either MEK or non-canonical NF-kB driving growth of triple-negative breast cancer cells in different contexts

BACKGROUND

Metastatic breast cancer carries a poor prognosis despite the success of newly targeted therapies. Treatment options remain especially limited for the subtype of triple negative breast cancer (TNBC). Several signaling pathways, including NF-κB, are altered in TNBC, and the complexity of this disease implies multi-faceted pathway interactions. Given that IKKε behaves as an oncogene in breast cancer, we hypothesized that IKKε regulates NF-κB signaling to control diverse oncogenic functions in TNBC.

METHODS

Vector expression and RNA interference were used to investigate the functional role of IKKε in triple-negative breast cancer cells. Viability, protein expression, NF-κB binding activity, invasion, anoikis, and spheroid formation were examined in cells expressing high or low levels of IKKε, in conjunction with p52 RNA interference or MEK inhibition.

RESULTS

This study found that non-canonical NF-κB p52 levels are inversely proportional to ΙΚΚε, and growth of TNBC cells in anchorage supportive, high-attachment conditions requires IKKε and activated MEK. Growth of these cells in anchorage resistant conditions requires IKKε and activated MEK or p52. In this model, IKKε and MEK cooperate to support overall viability whereas the p52 transcription factor is only required for viability in low attachment conditions, underscoring the contrasting roles of these proteins.

CONCLUSIONS

This study illustrates the diverse functions of IKKε in TNBC and highlights the adaptability of NF-κB signaling in maintaining cancer cell survival under different growth conditions. A better understanding of the diversity of NF-κB signaling may ultimately improve the development of novel therapeutic regimens for TNBC.

NFκB Promotes Ovarian Tumorigenesis via Classical Pathways That Support Proliferative Cancer Cells and Alternative Pathways That Support ALDH+ Cancer Stem-like Cells

Understanding the mechanisms supporting tumor-initiating cells (TIC) is vital to combat advanced-stage recurrent cancers. Here, we show that in advanced ovarian cancers NFκB signaling via the RelB transcription factor supports TIC populations by directly regulating the cancer stem-like associated enzyme aldehyde dehydrogenase (ALDH). Loss of RelB significantly inhibited spheroid formation, ALDH expression and activity, chemoresistance, and tumorigenesis in subcutaneous and intrabursal mouse xenograft models of human ovarian cancer. RelB also affected expression of the ALDH gene ALDH1A2 Interestingly, classical NFκB signaling through the RelA transcription factor was equally important for tumorigenesis in the intrabursal model, but had no effect on ALDH. In this case, classical signaling via RelA was essential for proliferating cells, whereas the alternative signaling pathway was not. Our results show how NFκB sustains diverse cancer phenotypes via distinct classical and alternative signaling pathways, with implications for improved understanding of disease recurrence and therapeutic response. Cancer Res; 77(24); 6927-40. ©2017 AACR.

BRD4 facilitates DNA damage response and represses CBX5/Heterochromatin protein 1 (HP1)

Ovarian cancer (OC) is a heterogeneous disease characterized by defective DNA repair. Very few targets are universally expressed in the high grade serous (HGS) subtype. We previously identified that CHK1 was overexpressed in most of HGSOC. Here, we sought to understand the DNA damage response (DDR) to CHK1 inhibition and increase the anti-tumor activity of this pathway. We found BRD4 suppression either by siRNA or BRD4 inhibitor JQ1 enhanced the cytotoxicity of CHK1 inhibition. Interestingly, BRD4 was amplified and/or upregulated in a subset of HGSOC with statistical correlation to overall survival. BRD4 inhibition increased CBX5 (HP1α) level. CHK1 inhibitor induced DDR marker, γ-H2AX, but BRD4 suppression did not. Furthermore, nuclear localization of CBX5 and γ-H2AX was mutually exclusive in BRD4-and CHK1-inhibited cells, suggesting BRD4 facilitates DDR by repressing CBX5. Our results provide a strong rationale for clinical investigation of CHK1 and BRD4 co-inhibition, especially for HGSOC patients with BRD4 overexpression.

Abstract 112: Identifying drugs that target ovarian cancer tumor initiating cells

Ovarian cancer is the most lethal gynecological cancer, with overall five-year survival for women with advanced disease being at only 25%. The current standard of care is treatment with a platinum-based chemotherapy drug. Unfortunately, a subpopulation of tumor cells often persists, contributing to platinum-based chemotherapy resistance and disease recurrence. In this study we investigated drugs to target these putative tumor-initiating cells (TICs), and explored the pathways of these drugs in both adherent proliferative cell culture conditions and non-adherent TIC-enriched cultures. We conducted a drug screen under both growth conditions, in order to identify compounds that are able to inhibit growth of TICs. Of the drugs identified, we focused further efforts on those involved with inhibiting the NF-kappaB pathway because prior studies have linked NF-kappaB activity with drug resistance and poor survival. Cell viability assays done with the four drugs, bardoxolone methyl, salinomycin, disulfiram, and elesclomol, show these drugs inhibit the growth of ovarian cancer cell lines both as TICs and in corresponding adherent cultures. Disulfiram showed preferential killing of TICs in some of the cell lines tested. All drugs showed some evidence for inhibiting NF-kappaB on Western blot, and ability to decrease CD133/ALDH double-positive TICs on flow cytometry. Carboplatin is known to kill proliferative ovarian cancer cells, and increase the relative percentage of CD133/ALDH positive TICs. Our ongoing studies will address combination of each drug with carboplatin, with the hypothesis that these drugs will increase in vivo efficacy by suppressing TICs, and thereby decrease recurrence of platinum-resistant ovarian cancer.

Citation Format: Michelle K. Ozaki, Carrie D. House, Christina M. Annunziata. Identifying drugs that target ovarian cancer tumor initiating cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 112. doi:10.1158/1538-7445.AM2017-112

Abstract 1910: NF-kappaB classical versus alternative pathways support distinct populations of ovarian cancer tumor-initiating cells

Ovarian cancer is the most lethal gynecological malignancy in the United States with high morbidity and mortality due to recurrence and chemoresistance. Our data suggest tumor-initiating cells (TICs) play an important role in disease biology. We previously showed that a subset of ovarian cancer cells depends on NF-kappaB signaling, and that expression of NF-kappaB proteins is associated with poor survival. Given that NF-kappaB expression correlates with a poor outcome in ovarian cancer, and NF-kappaB activity supports drug resistance and tumorigenicity, we hypothesize that NF-kappaB supports a TIC program responsible for ovarian cancer relapse. To investigate this pathway in TICs, we designed a novel method to enrich for TICs from cell lines and patient samples by culturing non-adherent, floating cells in stem cell conditions defined by low attachment flasks and serum free media. Preliminary data confirm that these cells have higher stem cell marker expression, are chemoresistant, and are more tumorigenic in nude mice compared to their adherent counterparts. These TIC-enriched culture conditions enhance NF-kappaB expression and activity. More specifically, alternative NF-kappaB signaling through the RelB transcription factor supports TIC populations by regulating aldehyde dehydrogenase (ALDH), an enzyme with high activity in TICs. Using an inducible shRNA targeting RelB we show that spheroid formation, ALDH expression and activity, chemoresistance, and tumorigenesis in both subcutaneous and intrabursal xenograft models, significantly decreased in the absence of RelB. Interestingly, loss of classical NF-kappaB signaling, through an shRNA targeting the RelA transcription factor, was less effective in targeting TICs, but more effective at targeting a proliferative subpopulation with high Ki67 staining. We conclude that classical and alternative NF-kappaB signaling support ovarian tumor cells with distinct phenotypes and the collaboration of these pathways may be critical for supporting tumor repopulation following chemotherapy. Current studies will measure system level changes induced by these shRNAs, and identify a gene signature specific to each NF-kappaB pathway in ovarian TICs. Clarifying the nuances of NF-kappaB signaling in TICs will increase our understanding of ovarian cancer recurrence and further focus therapeutic strategies to prevent relapse.

Citation Format: Carrie D. House, Christina M. Annunziata. NF-kappaB classical versus alternative pathways support distinct populations of ovarian cancer tumor-initiating cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1910. doi:10.1158/1538-7445.AM2017-1910

Abstract AP13: NF-KAPPAB CLASSICAL VERSUS ALTERNATIVE PATHWAYS SUPPORT DISTINCT POPULATIONS OF OVARIAN CANCER TUMOR-INITIATING CELLS

Ovarian cancer is the most lethal gynecological malignancy in the United States with high morbidity and mortality due to recurrence and chemoresistance. Our data suggest tumor-initiating cells (TICs) play an important role in disease biology. We previously showed that a subset of ovarian cancer cells depends on NF-kappaB signaling, and that expression of NF-kappaB proteins is associated with poor survival. Given that NF-kappaB expression correlates with a poor outcome in ovarian cancer, and NF-kappaB activity supports drug resistance and tumorigenicity, we hypothesize that NF-kappaB supports a TIC program responsible for ovarian cancer relapse. To investigate this pathway in TICs, we designed a novel method to enrich for TICs from cell lines and patient samples by culturing non-adherent, floating cells in stem cell conditions defined by low attachment flasks and serum free media. Preliminary data confirm that these cells have higher stem cell marker expression, are chemoresistant, and are more tumorigenic in nude mice compared to their adherent counterparts. These TIC-enriched culture conditions enhance NF-kappaB expression and activity. More specifically, alternative NF-kappaB signaling through the RelB transcription factor supports TIC populations by regulating aldehyde dehydrogenase (ALDH), an enzyme with high activity in TICs. Using an inducible shRNA targeting RelB we show that spheroid formation, ALDH expression and activity, chemoresistance, and tumorigenesis in both subcutaneous and intrabursal xenograft models, significantly decreased in the absence of RelB. Interestingly, loss of classical NF-kappaB signaling, through an shRNA targeting the RelA transcription factor, was less effective in targeting TICs, but more effective at targeting a proliferative subpopulation with high Ki67 staining. We conclude that classical and alternative NF-kappaB signaling support ovarian tumor cells with distinct phenotypes and the collaboration of these pathways may be critical for supporting tumor repopulation following chemotherapy. Current studies will measure system level changes induced by these shRNAs, and identify a gene signature specific to each NF-kappaB pathway in ovarian TICs. Clarifying the nuances of NF-kappaB signaling in TICs will increase our understanding of ovarian cancer recurrence and further focus therapeutic strategies to prevent relapse.

Citation Format: Carrie D. House, Elizabeth A. Jordan, Christina M. Annunziata. NF-KAPPAB CLASSICAL VERSUS ALTERNATIVE PATHWAYS SUPPORT DISTINCT POPULATIONS OF OVARIAN CANCER TUMOR-INITIATING CELLS [abstract]. In: Proceedings of the 11th Biennial Ovarian Cancer Research Symposium; Sep 12-13, 2016; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(11 Suppl):Abstract nr AP13.

Characterization of ovarian cancer cell lines as in vivo models for preclinical studies

OBJECTIVE

The value of cell lines for pre-clinical work lies in choosing those with similar characteristics. Selection of cell lines is typically based on patient history, histological subtype at diagnosis, mutation patterns, or signaling pathways. Although recent studies established consensus regarding molecular characteristics of ovarian cancer cell lines, data on in vivo tumorigenicity remains only sporadically available, impeding translation of in vitro work to xenograft models.

METHODS

We introduced 18 ovarian cancer cell lines into athymic nude mice through subcutaneous, intraperitoneal, and ovary intrabursal routes, and observed tumor development over 6weeks. We also profiled cell line gene expression and identified differentially expressed gene sets based on their ability to form tumors in the subcutaneous or intraperitoneal locations. Representative cell lines were further subjected to proteomic analyses.

RESULTS

Ovarian cancer cell lines showed variable ability to grow in mice when implanted subcutaneous, intraperitoneal, or intrabursal. While some cell lines grew well in both SC and IP locations, others showed a strong propensity to grow in one location only. Gene expression profiles suggested that cell lines showing preference for IP growth had gene expression patterns more similar to primary tumors.

CONCLUSIONS

We report the tumorigenicity of 17 human ovarian cancer cell lines and one mouse cell line in three distinct anatomical locations, and associated gene networks. Growth patterns and histopathology, linked to molecular characteristics, provide a valuable resource to the research community, and better guide the choice of cell lines for in vitro studies to translate efficiently into xenograft testing.

Abstract A72: Dissecting the role of NF-kappaB signaling in ovarian cancer tumor-initiating cells

Ovarian cancer is the most lethal gynecological malignancy in the United States with high morbidity and mortality due to recurrence and chemoresistance. Our data suggest tumor-initiating cells (TICs) play an important role in disease biology. We previously showed that a subset of ovarian cancer cells depends on NF-kappaB signaling, and that expression of NF-kappaB proteins is associated with poor survival. To investigate this pathway in TICs, we designed a novel method to enrich for TICs from cell lines and patient samples by culturing non-adherent, floating cells in stem cell conditions. Preliminary data show these cells have higher stem cell marker expression, are chemoresistant, and are more tumorigenic in nude mice compared to their adherent counterparts. Given that NF-kappaB expression correlates with a poor outcome in ovarian cancer, and NF-kappaB activity supports drug resistance and tumorigenicity, we hypothesize that NF-kappaB supports a TIC program responsible for ovarian cancer relapse. Preliminary data show TIC-enriched culture conditions increased NF-kappaB expression and activity in TICs and stimulation of NF-kappaB signaling enhanced chemoresistance and stem cell marker expression. Current studies focus on dissecting the role of individual NF-kappaB proteins in TICs using inducible shRNAs to measure changes in spheroid formation, chemoresistance, tumorigenesis, and disease relapse following chemotherapy in a xenograft model. Future studies will measure system level changes induced by these shRNAs, and identify a gene signature specific to NF-kappaB in ovarian TICs. Clarifying the nuances of NF-kappaB signaling in TICs will increase our understanding of ovarian cancer recurrence and may lead to improved therapeutic strategies.

Citation Format: Carrie D. House, Christina M. Annunziata. Dissecting the role of NF-kappaB signaling in ovarian cancer tumor-initiating cells. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr A72.

In vitro enrichment of ovarian cancer tumor-initiating cells

Evidence suggests that small subpopulations of tumor cells maintain a unique self-renewing and differentiation capacity and may be responsible for tumor initiation and/or relapse. Clarifying the mechanisms by which these tumor-initiating cells (TICs) support tumor formation and progression could lead to the development of clinically favorable therapies. Ovarian cancer is a heterogeneous and highly recurrent disease. Recent studies suggest TICs may play an important role in disease biology. We have identified culture conditions that enrich for TICs from ovarian cancer cell lines. Growing either adherent cells or non-adherent ‘floater’ cells in a low attachment plate with serum free media in the presence of growth factors supports the propagation of ovarian cancer TICs with stem cell markers (CD133 and ALDH activity) and increased tumorigenicity without the need to physically separate the TICs from other cell types within the culture. Although the presence of floater cells is not common for all cell lines, this population of cells with innate low adherence may have high tumorigenic potential.Compared to adherent cells grown in the presence of serum, TICs readily form spheres, are significantly more tumorigenic in mice, and express putative stem cell markers. The conditions are easy to establish in a timely manner and can be used to study signaling pathways important for maintaining stem characteristics, and to identify drugs or combinations of drugs targeting TICs. The culture conditions described herein are applicable for a variety of ovarian cancer cells of epithelial origin and will be critical in providing new information about the role of TICs in tumor initiation, progression, and relapse.

Abstract 1923: NF-κB signaling supports a sub-population of ovarian cancer tumor-initiating cells

Although most patients respond favorably to first-line chemotherapy, ovarian cancer remains the most lethal gynecological cancer in the United States primarily because of a high incidence of disease recurrence. The inability of traditional chemotherapy to eradicate tumor-initiating cells (TICs) is a plausible explanation for tumor relapse and we have begun to characterize TIC populations in ovarian cancer cell lines. Importantly, we are investigating the role of the NF-κB pathway in regulating this system. We have identified conditions that sustain a highly tumorigenic TIC population. Preliminary data suggest that NF-κB promotes and sustains TICs in ovarian cancer and current efforts are underway to characterize the molecular mechanisms underlying this preference. We will correlate activity of this pathway with expression of ovarian TIC protein markers such as CD133, Sox2, Nanog, and Oct-4 in TIC cell cultures and xenografts. Moreover we will use TICs to investigate effects of inhibiting this pathway on marker expression, proliferation, resistance to chemotherapy, and the ability to form tumors in mice. Clarifying the specific role of the NF-κB network in TIC populations will further our understanding of ovarian cancer initiation, progression, and relapse and may lead to improved therapeutic strategies for women in first remission, to prevent subsequent relapse to incurable disease.

Citation Format: Carrie D. House, Christina M. Annunziata. NF-κB signaling supports a sub-population of ovarian cancer tumor-initiating cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1923. doi:10.1158/1538-7445.AM2014-1923

Abstract 927: The ligand-gated Cl- channel GABA inhibits colon cancer invasion following activation by pharmacological treatments

Gamma-aminobutyric acid (GABA) receptors are ligand-gated ion channels that are essential for neurotransmitter function and neuronal cell homeostasis. Activation of these channels triggers the opening of a chloride-sensitive pore, which causes a hyperpolarization via an influx of chloride ions into the cell. The presence of these channels was recently implicated in several cancers, and the neurotransmitter GABA has been cited as a tumor suppressor. We propose that commercially available pharmacological treatments that manipulate GABA receptor function could be repurposed to target cancer. We have identified functional GABA receptors in a spectrum of colon cancer cell lines and examined the effects of the channels on invasion of the metastatic cell line SW620. Electrophysiological techniques were used to confirm that these channels have functional expression. Treatment with propofol, an agonist which slows the channel closing time, and GABA led to a decrease in invasive potential. Conversely, treatment with the antagonist gabazine, which allosterically blocks GABA from binding in the channel, facilitated invasion by preventing chloride influx. Curiously, treating the cells with bicuculline, which blocks GABA's inhibitory action, led to a decrease in invasion. In some situations bicuculline can also act as a GABA agonist by causing spontaneous gating of homomeric β3 channels. The expression of the β3 subunit was also confirmed through immunocytochemistry. In addition to colon cancer cell lines, β3 expression was detected at higher quantities in colon cancer patient samples compared to matched controls. To further understand how GABA signaling is implicated in cancer, we have looked at the association of GABA with the EGF signaling pathway, which is commonly dysregulated in cancer. The EGF pathway has also been linked with a loss of the glucagon receptor in liver cancer, suggesting that a common pathway may exist between GABA and glutamate that can be exploited for treatment. Altogether, our data suggest that ligand-gated GABA channels inhibit the metastatic potential of cancer cells and can be targeted to treat colon cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 927. doi:1538-7445.AM2012-927

Abstract 1418: Voltage-gated Na+ channel activation leads to increased invasion potential through persistent MAPK signaling involving PKA, Src, and Rap1

An interesting new field in cancer research is the role of voltage-gated Na+ channels (VGSCs) in cancer cell invasion. Expression of these ion channels is normally restricted to excitable cells, such as neurons, however functional expression has been demonstrated in multiple cancer cell types where channel activity leads to changes in invasion potential in vitro. We have recently demonstrated functional expression of Nav1.5, a protein encoded by SCN5A, in a variety of colon cancer cell lines. We showed that pharmacological inhibition of channel activity leads to a decrease in invasion potential, whereas pharmacological activation of the channel leads to an increase in invasion potential. Moreover, upon examination of patient samples we found that protein expression is restricted to malignant tissue. What has remained largely uncharacterized is the mechanism by which these channels promote oncogenic behavior. We have recently established that VGSC isoform SCN5A participates in an invasion gene network for colon cancer, regulating expression of several genes important for invasion. Our current study focuses on determining what non-genomic signaling pathway(s) are activated in response to VGSC activity that might lead gene expression changes. The MAPK pathway is deregulated in many cancers and VGSC activation in neurons leads to MAPK activation during neurogenesis. Coincidentally, many genes regulated by SCN5A have binding sites for transcription factors phosphorylated by ERK1/2. We hypothesized that VGSC activation promotes MAPK activation in colon cancer cells to provide an oncogenic advantage. Using pharmacological inhibition of MAPK, we demonstrate the requirement of this molecule for colon cancer invasion in vitro. Furthermore, we show through Western blot analysis of phosphorylated ERK1/2, that MAPK activity is diminished when colon cancer cells are treated with VGSC inhibitor, lidocaine, and persistently enhanced for 24-48 hours in the presence of the VGSC activator, veratridine. This persistent activation and the increase in invasion potential are partially lost when veratridine is used in the presence of a PKA inhibitor. Similarly, veratridine treatment in the presence of a siRNA directed against Rap1 leads to a decrease in both invasion potential and MAPK activity compared to veratridine alone. Lastly, we demonstrate increased Src activity after treatment with veratridine. Taken together, our data suggest that VGSC activation leads to an increase in MAPK activity through activation of PKA, Rap1 and Src in colon cancer cells. We further show that Rap1 activation is biphasic with early persistent signaling likely through PKA and delayed persistent signaling through Src. The proposed signaling pathway illustrates for the first time a potential mechanism by which VGSC activity promotes oncogenesis in colon cancer cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1418. doi:10.1158/1538-7445.AM2011-1418

Voltage-gated Na+ channel SCN5A is a key regulator of a gene transcriptional network that controls colon cancer invasion

Voltage-gated Na(+) channels (VGSC) have been implicated in the metastatic potential of human breast, prostate, and lung cancer cells. Specifically, the SCN5A gene encoding the VGSC isotype Na(v)1.5 has been defined as a key driver of human cancer cell invasion. In this study, we examined the expression and function of VGSCs in a panel of colon cancer cell lines by electrophysiologic recordings. Na(+) channel activity and invasive potential were inhibited pharmacologically by tetrodotoxin or genetically by small interfering RNAs (siRNA) specifically targeting SCN5A. Clinical relevance was established by immunohistochemistry of patient biopsies, with strong Na(v)1.5 protein staining found in colon cancer specimens but little to no staining in matched-paired normal colon tissues. We explored the mechanism of VGSC-mediated invasive potential on the basis of reported links between VGSC activity and gene expression in excitable cells. Probabilistic modeling of loss-of-function screens and microarray data established an unequivocal role of VGSC SCN5A as a high level regulator of a colon cancer invasion network, involving genes that encompass Wnt signaling, cell migration, ectoderm development, response to biotic stimulus, steroid metabolic process, and cell cycle control. siRNA-mediated knockdown of predicted downstream network components caused a loss of invasive behavior, demonstrating network connectivity and its function in driving colon cancer invasion.

Cytoplasmic polyadenylation element binding protein is a conserved target of tumor suppressor HRPT2/CDC73

Parafibromin, a tumor suppressor protein encoded by HRPT2/CDC73 and implicated in parathyroid cancer and the hyperparathyroidism-jaw tumor (HPT-JT) familial cancer syndrome, is part of the PAF1 transcriptional regulatory complex. Parafibromin has been implicated in apoptosis and growth arrest, but the mechanism by which its loss of function promotes neoplasia is poorly understood. In this study we report that a hypomorphic allele of hyrax (hyx), the Drosophila homolog of HRPT2/CDC73, rescues the loss-of-ventral-eye phenotype of lobe (Akt1s1). Such rescue is consistent with previous reports that hyx/parafibromin is required for the nuclear transduction of Wingless (Wg)/Wnt signals and that Wg signaling antagonizes lobe function. A screen using double hyx/lobe heterozygotes identified an additional interaction with orb and orb2, the homologs of mammalian cytoplasmic polyadenylation element binding protein (CPEB), a translational regulatory protein. Hyx and orb2 heterozygotes lived longer and were more resistant to starvation than controls. In mammalian cells, knockdown of parafibromin expression reduced levels of CPEB1. Chromatin immunoprecipitation (ChIP) showed occupancy of CPEB1 by endogenous parafibromin. Bioinformatic analysis revealed a significant overlap between human transcripts potentially regulated by parafibromin and CPEB. These results show that parafibromin may exert both transcriptional and, through CPEB, translational control over a subset of target genes and that loss of parafibromin (and CPEB) function may promote tumorigenesis in part by conferring resistance to nutritional stress.