Search

Purpose: We recently reported that the transcription factor NFATC4, in response to chemotherapy, drives cellular quiescence to increase ovarian cancer chemoresistance. The goal of this work was to better understand the mechanisms of NFATC4-driven ovarian cancer chemoresistance. Experimental Design: We used RNA sequencing to identify NFATC4-mediated differential gene expression. CRISPR-Cas9 and FST (follistatin)-neutralizing antibodies were used to assess impact of loss of FST function on cell proliferation and chemoresistance. ELISA was used to quantify FST induction in patient samples and in vitro in response to chemotherapy. Results: We found that NFATC4 upregulates FST mRNA and protein expression predominantly in quiescent cells and FST is further upregulated following chemotherapy treatment. FST acts in at least a paracrine manner to induce a p-ATF2–dependent quiescent phenotype and chemoresistance in non-quiescent cells. Consistent with this, CRISPR knockout (KO) of FST in ovarian cancer cells or antibody-mediated neutralization of FST sensitizes ovarian cancer cells to chemotherapy treatment. Similarly, CRISPR KO of FST in tumors increased chemotherapy-mediated tumor eradication in an otherwise chemotherapy-resistant tumor model. Suggesting a role for FST in chemoresistance in patients, FST protein in the abdominal fluid of patients with ovarian cancer significantly increases within 24 hours of chemotherapy exposure. FST levels decline to baseline levels in patients no longer receiving chemotherapy with no evidence of disease. Furthermore, elevated FST expression in patient tumors is correlated with poor progression-free, post–progression-free, and overall survival. Conclusions: FST is a novel therapeutic target to improve ovarian cancer response to chemotherapy and potentially reduce recurrence rates.

Ovarian clear cell carcinoma (OCCC) is a deadly and treatment-resistant cancer, which arises within the unique microenvironment of endometriosis. In this study, we identified a subset of endometriosis-derived mesenchymal stem cells (enMSC) characterized by loss of CD10 expression that specifically support OCCC growth. RNA sequencing identified alterations in iron export in CD10-negative enMSCs and reciprocal changes in metal transport in cocultured OCCC cells. CD10-negative enMSCs exhibited elevated expression of iron export proteins hephaestin and ferroportin and donate iron to associated OCCCs, functionally increasing the levels of labile intracellular iron. Iron is necessary for OCCC growth, and CD10-negative enMSCs prevented the growth inhibitory effects of iron chelation. In addition, enMSC-mediated increases in OCCC iron resulted in a unique sensitivity to ferroptosis. In vitro and in vivo, treatment with the ferroptosis inducer erastin resulted in significant death of cancer cells grown with CD10-negative enMSCs. Collectively, this work describes a novel mechanism of stromal-mediated tumor support via iron donation. This work also defines an important role of endometriosis-associated MSCs in supporting OCCC growth and identifies a critical therapeutic vulnerability of OCCC to ferroptosis based on stromal phenotype. Significance: Endometriosis-derived mesenchymal stem cells support ovarian clear cell carcinoma via iron donation necessary for cancer growth, which also confers sensitivity to ferroptosis-inducing therapy.

Supplementary Figure 2. RNA-seq analysis. A. Schematic of the RNA-seq experimental design. B. Waterfall plot of RNA-seq data showing the 141 genes which were DE at all time points compared to luciferase control in HEY1 and SKOV3 cell lines. C. Unsupervised clustering analysis of the 141 DE genes. D. Box plots demonstrating MYC expression following NFATC4 activation. E. STRING analysis of the 141 DE genes.

Purpose:We recently reported that the transcription factor NFATC4, in response to chemotherapy, drives cellular quiescence to increase ovarian cancer chemoresistance. The goal of this work was to better understand the mechanisms of NFATC4-driven ovarian cancer chemoresistance.Experimental Design:We used RNA sequencing to identify NFATC4-mediated differential gene expression. CRISPR-Cas9 and FST (follistatin)-neutralizing antibodies were used to assess impact of loss of FST function on cell proliferation and chemoresistance. ELISA was used to quantify FST induction in patient samples and in vitro in response to chemotherapy.Results:We found that NFATC4 upregulates FST mRNA and protein expression predominantly in quiescent cells and FST is further upregulated following chemotherapy treatment. FST acts in at least a paracrine manner to induce a p-ATF2–dependent quiescent phenotype and chemoresistance in non-quiescent cells. Consistent with this, CRISPR knockout (KO) of FST in ovarian cancer cells or antibody-mediated neutralization of FST sensitizes ovarian cancer cells to chemotherapy treatment. Similarly, CRISPR KO of FST in tumors increased chemotherapy-mediated tumor eradication in an otherwise chemotherapy-resistant tumor model. Suggesting a role for FST in chemoresistance in patients, FST protein in the abdominal fluid of patients with ovarian cancer significantly increases within 24 hours of chemotherapy exposure. FST levels decline to baseline levels in patients no longer receiving chemotherapy with no evidence of disease. Furthermore, elevated FST expression in patient tumors is correlated with poor progression-free, post–progression-free, and overall survival.Conclusions:FST is a novel therapeutic target to improve ovarian cancer response to chemotherapy and potentially reduce recurrence rates.

Supplementary figures and table

Ovarian clear cell carcinoma (OCCC) is a deadly and treatment-resistant cancer, which arises within the unique microenvironment of endometriosis. In this study, we identified a subset of endometriosis-derived mesenchymal stem cells (enMSC) characterized by loss of CD10 expression that specifically support OCCC growth. RNA sequencing identified alterations in iron export in CD10-negative enMSCs and reciprocal changes in metal transport in cocultured OCCC cells. CD10-negative enMSCs exhibited elevated expression of iron export proteins hephaestin and ferroportin and donate iron to associated OCCCs, functionally increasing the levels of labile intracellular iron. Iron is necessary for OCCC growth, and CD10-negative enMSCs prevented the growth inhibitory effects of iron chelation. In addition, enMSC-mediated increases in OCCC iron resulted in a unique sensitivity to ferroptosis. In vitro and in vivo, treatment with the ferroptosis inducer erastin resulted in significant death of cancer cells grown with CD10-negative enMSCs. Collectively, this work describes a novel mechanism of stromal-mediated tumor support via iron donation. This work also defines an important role of endometriosis-associated MSCs in supporting OCCC growth and identifies a critical therapeutic vulnerability of OCCC to ferroptosis based on stromal phenotype.Significance:Endometriosis-derived mesenchymal stem cells support ovarian clear cell carcinoma via iron donation necessary for cancer growth, which also confers sensitivity to ferroptosis-inducing therapy.

Supplementary Table 1. Primers used in this study.

Rationale: Ovarian cancer (OC) is an aggressive disease with the 3rd highest mortality to incidence ratio of all cancers. Aldehyde dehydrogenase-1A enzymes play a key role in retinoic acid (RA) synthesis. RA regulates cell proliferation, differentiation, and survival by activating nuclear receptor transcription factors (RAR, RXR). In cancer cells, increased ALDH expression correlates with chemoresistance and poor prognosis. Our goal is to effectively utilize ALDH inhibitors (ALDHi) as novel therapeutics and identify their mechanism in cancer and immune cells. Based on RNAseq data, NR4A1 has emerged as a possible ALDHi target. After binding RXRγ, NR4A1 serves as a ‘molecular switch’ for cancer cell survival. Here, we explore the potential use of ALDHi as immune modulators in OC. Methods: T cells: The effect of several ALDHi on T cells following anti-CD3/CD28 polyclonal stimulation was tested via flow cytometry. Macrophages: Human OC ascites samples were cultured and treated for 72h with ALDHi or DMSO control. Flow cytometry was performed to identify ascites resident cell populations. Western blot to detect NR4A1 was conducted. Dendritic cells (DCs): Murine bone-marrow derived DCs were exposed to ALDHi or DMSO and expanded in culture; cells were counted via hematocytometer to assess myeloid cell expansion and DC differentiation. DC vaccine: ALDHi and DMSO were used with a DC vaccine and sonic hedgehog inhibitor in a study of ID8 tumor-bearing mice to assess effects on tumor progression and survival. Results: We identified several novel ALDHi that promote T cell proliferation and CD8 expansion in vitro. Exposure of 5 patient ascites samples to ALDHi showed a significant decrease in CD14+ and CD163+ cells, indicating a loss of M2 immune-suppressive macrophages vs DMSO. NR4A1 expression was decreased in ALDHi treated cells vs DMSO. In contrast, no deleterious effect was observed on ascites T cells. DC expansion: There was a 10-fold increase in DC proliferation when cells were exposed to ALDHi vs DMSO in culture. DC vaccine: In vivo, addition of ALDHi to a DC vaccine did not provide a survival significance. Discussion: In vitro, ALDHi have differential, complementary effects on tumor and immune cells in OC. In tumor cells, ALDHi lower chemoresistance and trigger necroptosis. ALDHi support the expansion of polyclonal CD8 T cells and type-1 DCs and inhibit T-regulatory cells. In contrast, ALDHi reduce M2 macrophages. Despite beneficial effects in vitro, suggesting anti-tumor competence, there was a modest effect on survival in tumor bearing mice. This may be explained by poor bioavailability of current ALDHi. Further analyses of cryopreserved murine tissues (tumor, lymph nodes, spleen) using flow and CHIP cytometry to assess surface markers, Western blot to test levels of NR4A1, and IHC to assess intratumoral immune cell invasion will continue to test target engagement. Alternative in vivo treatment regimens with other compounds are ongoing. Citation Format: Julia Knight, Bingsi Gao, Mainpal Rana, Ibrahim Uygun, Ronald Buckanovich, Anda Vlad. ALDH inhibition as modulator of ovarian tumor associated immune 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 1798.

Rationale: Most ovarian tumors show some level of infiltration by T lymphocytes, and increasing levels of tumor-infiltrating lymphocytes (TIL) correlate with improved outcomes. The field of cancer immunotherapy has rapidly evolved and made a significant impact on many tumor types, including gynecologic cancers. However, single agent immune therapies have not yet demonstrated significant clinical success in epithelial ovarian cancer (EOC). We hypothesize that a combination of intraperitoneal (IP) chemotherapy (cisplatin) with dual agent immunotherapy using intravenous (IV) pembrolizumab (anti-PD1) and IP rintatolimod (TLR-3 agonist) will help overcome immune suppressive mechanisms for improved tumor response by promoting increased T cell chemotaxis and cytolytic function. Methods: To test our hypothesis, we are running an investigator initiated, phase II, single arm, efficacy/safety trial (NCT03734692). Peritoneal fluid aspiration (IP wash) was performed in 13 patients at multiple time points during each cycle of treatment. Washes were collected on Days 1-3 of each cycle, before and after each treatment. Washes from cycle 1, 4 and 6, were included in this analysis. The MesoScale Delivery (MSD) platform was used to profile different biomarkers in the peritoneal samples throughout treatment. Results: In this ongoing Phase II study, a total of 17 patients were enrolled and 13 were evaluable for response. The observed clinical responses were: 2 complete responses (15.4%), 3 partial responses (23.1%), 3 stable disease (23.1%), 5 progressions (38.4%) for an clinical benefit rate (CR+PR+SD) of 61.6%. From 13 patients, 7 IP wash samples were collected at serial time points. MSD measurements in IP washes revealed an acute increase in granzyme B, perforin, TNF alpha, CXCL9, CXCL10, CXCL11 after treatment (p Discussion: This is a novel, triple drug combination for EOC that leads to a locoregional acute response with an increase in biomarkers associated with T cell chemotaxis and cytolytic function. Longitudinal comparison of these biomarkers showed a gradual, durable response over time in T lymphotactic CXCR3 ligands. While an acute response was also noted in CXCL12, a marker of secondary suppression, a progressive increase over time was not detected. While these are interim analyses and ongoing evaluation of additional samples from the trial are needed to confirm our findings, the preliminary results show promise for novel treatment regimen. Citation Format: Mackenzy Radolec, Brian Orr, Mary Strange, Lixin Zhang, Haider Mahdi, Sarah Taylor, Gregory Willis, Robert Edwards, Anda Vlad. Combined loco-regional and systemic, triple agent chemoimmunotherapy increases biomarkers of T cell chemotaxis 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 6134.

Myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs) are critical negative regulators of immunity in cancer. Understanding factors which regulate these cells could result in the identification of new approaches to enhance anti-tumor immunotherapy. One such factor is Epidermal growth factor-like 6 (EGFL6). EGFL6 is a secreted factor known to promote cancer stem like cell migration and regulate cancer cell differentiation. Similarly, EGFL6 promotes endothelial cell migration and proliferation. Indicating a potential role for EGFL6 as a myeloid cell regulatory factor, we found that mice which overexpress Egfl6 have an increased numbers of granulocytes and monocytes in both the bone marrow and spleen. In vitro and ex-vivo analysis indicated that EGFL6, via binding with beta integrins and activation of Syk/ERK signaling, (i) acts as a chemotactic factor for human myeloid cells migration and (ii) promotes their differentiation toward a suppressive state. Suggesting an important role in promoting an immunosuppressive tumor microenvironment (TME), using two syngeneic mouse models of ovarian cancer, we found that expression of Egfl6 in tumor cells resulted in increased accumulation of intra-tumoral MDSCs and TAMs and fewer cytotoxic CD8+ T cells. This was associated with increased tumor growth and shortened animal survival. Gene expression profiling and flow cytometry analysis of tumor infiltrating myeloid cells indicated that Egfl6 induced the expression of immunosuppressive factors, including CXCL2, IL-10 and PD-L1. Consistent with Egfl6 driving an immune suppressive TME, EGFL6 expression in an otherwise immune ‘hot’/anti-PD-L1 responsive tumor model completely inhibited response to anti-PD-L-1 therapy. We are currently evaluating the impact of Egfl6 neutralizing antibody on the efficacy of ICI therapy and anti-tumor immunity. Combined our data show that EGFL6 acts as a chemotactic factor to both recruit myeloid cells to the ovarian TME and subsequently promotes their differentiation to an immunosuppressive phenotype. This suggests EGFL6 is a potential novel therapeutic target to ovarian tumor mediated immunosuppression and enhance response to immune therapy in ovarian cancer patients. Citation Format: Sarah Sinno, Shoumei Bai, Claudia Coronnello, Anda Vlad, Ronald J. Buckanovich, Sandra Cascio. EGFL6 induces immunosuppressive functions of tumor-associated myeloid cells and mediates resistance to anti-PDL1 therapy [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 3146.

Myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs) are critical negative regulators of immunity in cancer. Understanding factors which regulate these cells could result in the identification of new approaches to enhance anti-tumor immunotherapy. One such factor is epidermal growth factor-like 6 (EGFL6), a secreted factor known to promote cancer stem like cell migration and regulate cancer cell differentiation. We found that mice which overexpress Egfl6 have an increased numbers of granulocytes and monocytes in both the bone marrow and spleen. In vitro and ex-vivo analysis indicated that EGFL6, via binding with beta integrins and activation of SYK and ERK signaling, (i) acts as a chemotactic factor for myeloid cells migration and (ii) promotes their differentiation toward a suppressive state. Suggesting an important role in promoting an immunosuppressive tumor microenvironment (TME), using two syngeneic mouse models of ovarian cancer, we found that expression of Egfl6 in tumor cells resulted in increased accumulation of intra-tumoral MDSCs and TAMs and fewer cytotoxic CD8+ T cells. This was associated with increased tumor growth and shortened animal survival. Gene expression profiling of tumor infiltrating myeloid cells indicated that Egfl6 induced the expression of immunosuppressive factors, including CXCL2, IL-10 and PD-L1. Moreover, in an immune ‘hot’ tumor model, EGFL6 completely inhibited response to a-PD-L-1 therapy. Combined our data show that EGFL6 induces the recruitment of myeloid cells into the ovarian TME and subsequently promotes their immunosuppressive functions. This suggest EGFL6 is a potential novel therapeutic target to enhance response to immune therapy in OvCa patients. Supported by Ovarian Cancer Research Alliance

The ATR-CHEK1 pathway is upregulated and overactivated in Ataxia Telangiectasia (AT) cells, which lack functional ATM protein. Loss of ATM in AT confers radiosensitivity, although ATR-CHEK1 pathway overactivation compensates, leads to prolonged G(2) arrest after treatment with ionizing radiation (IR), and partially reverses the radiosensitivity. We observed similar upregulation of the ATR-CHEK1 pathway in a subset of oral squamous cell carcinoma (OSCC) cell lines with ATM loss. In the present study, we report copy number gain, amplification, or translocation of the ATR gene in 8 of 20 OSCC cell lines by FISH; whereas the CHEK1 gene showed copy number loss in 12 of 20 cell lines by FISH. Quantitative PCR showed overexpression of both ATR and CHEK1 in 7 of 11 representative OSCC cell lines. Inhibition of ATR or CHEK1 with their respective siRNAs resulted in increased sensitivity of OSCC cell lines to IR by the colony survival assay. siRNA-mediated ATR or CHEK1 knockdown led to loss of G(2) cell cycle accumulation and an increased sub-G(0) apoptotic cell population by flow cytometric analysis. In conclusion, the ATR-CHEK1 pathway is upregulated in a subset of OSCC with distal 11q loss and loss of the G(1) phase cell cycle checkpoint. The upregulated ATR-CHEK1 pathway appears to protect OSCC cells from mitotic catastrophe by enhancing the G(2) checkpoint. Knockdown of ATR and/or CHEK1 increases the sensitivity of OSCC cells to IR. These findings suggest that inhibition of the upregulated ATR-CHEK1 pathway may enhance the efficacy of ionizing radiation treatment of OSCC.

Objective: We explored mechanisms of PD-L1 upregulation in ovarian cancer cells and tested in vivo the efficacy of intraperitoneal anti-PD-L1 therapy in two different ovarian cancer mouse models. Methods: We have derived several novel murine ovarian cancer cell lines from orthotopic ovarian tumors of triple transgenic mice. 129x SvJ and C57Bl/6 tumor-bearing mice were treated with 200 μg anti-PD-L1 antibody (or rat IgG as control) every two weeks for three doses. Immune gene profiling of splenocytes collected at necropsy was performed using 561 Nanostring probes. Results: Cell cycle analysis of in vitro cultured tumor cells demonstrates that PD-L1 expression increases preferentially on cells in G2/M cells. Exposure to cisplatin modifies PD-L1 levels, although the effect varies according to tumors’ baseline susceptibility. In vivo, we observed murine PD-L1 upregulation on ascites resident tumor cells, an effect reproduced ex vivo upon exposure of tumor cells to ascites fluid. PD-L1 blockade triggers increase in survival in both preclinical models with immune gene signatures pointing to cytotoxic anti-tumor immune response. Conclusion: PD-L1 expression increases in response to inflammatory stimuli from cell-free ascites and shows preference for dividing cells. PD-L1 upregulation varies according to tumor cells’ susceptibility to cisplatin. PD-L1 blockade increases systemic T cell responses and intratumoral T cell accumulation suggesting therapeutic potential in ovarian cancer.

MUC1 is a large cell surface glycoprotein overexpressed by almost all types of adenocarcinomas, including those originating in the ovaries. We recently generated a triple transgenic MKP mouse model that carry conditional Kras mutations, Pten deletion and express human MUC1 as self. Upon AdCre injection under the ovarian bursa, the MKP mice progress to endometrioid ovarian tumors. Using a freshly isolated, orthotopic ovarian tumor from a MKP mouse, we generated an ovarian cancer cell line MKP-T-2F8 (or simply 2F8) that triggers multiple MUC1 expressing intraperitoneal (IP) tumors. At baseline, the cells express low PD-L1 but expression increases after in vivo growth. Using the 2F8 transplantable tumor model, we tested in vivo the therapeutic effectiveness of anti-PD-L1 antibody (10F.9G2). MUC1.Tg or wild type mice were IP injected with 8x10E5 of 2F8 cells, followed by three doses of 200ug of anti-PD-L1 (or isotype control) antibody, administered IP every 2 weeks, starting 3 weeks post-tumor challenge. The anti-PD-L1 treated MUC1.Tg mice showed significantly increased survival (p= 0.02), with no evidence for peritoneal tumor. In contrast, wild type mice which grow 2F8 tumors and develop spontaneous anti-MUC1 antibodies in high titers, did not respond to anti-PD-L1 therapy. These results demonstrate that targeting PD-L1 is a viable therapeutic strategy in ovarian cancer; however, tumor-bearing hosts with Th2-driven immune imbalance may not benefit from PD-L1 blockade.

Endometriosis is a largely benign, chronic inflammatory disease that may predispose to some of the ovarian tumors histotypes, collectively called endometriosis-associated ovarian cancers (EAOC). Although it is widely accepted that chronic inflammation drives cancer, the immune deregulation in chronic precursors of ovarian cancer has not been systematically studied. We performed here the first comprehensive gene profile of the tissue immune microenvironment in normal endometrium, benign endometriosis and EAOC (n=133), using Nanostring and the nCounter® GX Human Immunology Kit comprising probes for 511 immune genes. We found that the complement pathway was most prominently upregulated, suggesting its involvement in the transition from chronic endometriosis to atypical (premalignant) endometriosis and to EAOC. Complement protein expression was confirmed via immunohistochemistry, which identified upregulation of complement in epithelial cells. To explore the roles of complement in early EAOC carcinogenesis, we derived several novel ovarian cell lines with conditional mutations that can be turned on and off, using the Cre-loxP system. Using this in vitro model we demonstrate that genetic instability triggers upregulation of complement genes in epithelial cells, but without an advantage on cell death. These findings reveal an early link between epithelium and innate immune environment and further support a paradigm shift on complement roles in supporting cancer growth.