Alternative splice variants of the mitochondrial fission protein DNM1L/Drp1 regulate mitochondrial dynamics and tumor progression in ovarian cancer

Aberrant mitochondrial fission/fusion dynamics have been reported in cancer cells. While post translational modifications are known regulators of the mitochondrial fission/fusion machinery, we show that alternative splice variants of the fission protein Drp1 (DNM1L) have specific and unique roles in cancer, adding to the complexity of mitochondrial fission/fusion regulation in tumor cells. Ovarian cancer specimens express an alternative splice transcript variant of Drp1 lacking exon 16 of the variable domain, and high expression of this splice variant relative to other transcripts is associated with poor patient outcome. Unlike the full-length variant, expression of Drp1 lacking exon 16 leads to decreased association of Drp1 to mitochondrial fission sites, more fused mitochondrial networks, enhanced respiration, and TCA cycle metabolites, and is associated with a more metastatic phenotype in vitro and in vivo. These pro-tumorigenic effects can also be inhibited by specific siRNA-mediated inhibition of the endogenously expressed transcript lacking exon 16. Moreover, lack of exon 16 abrogates mitochondrial fission in response to pro-apoptotic stimuli and leads to decreased sensitivity to chemotherapeutics. These data emphasize the significance of the pathophysiological consequences of Drp1 alternative splicing and divergent functions of Drp1 splice variants, and strongly warrant consideration of Drp1 splicing in future studies.

Genetically Engineered Probiotic Limosilactobacillus reuteri Releasing IL-22 (LR-IL-22) Modifies the Tumor Microenvironment, Enabling Irradiation in Ovarian Cancer

Despite recent advances in cancer therapy, ovarian cancer remains the most lethal gynecological cancer worldwide, making it crucial and of the utmost importance to establish novel therapeutic strategies. Adjuvant radiotherapy has been assessed historically, but its use was limited by intestinal toxicity. We recently established the role of Limosilactobacillus reuteri in releasing IL-22 (LR-IL-22) as an effective radiation mitigator, and we have now assessed its effect in an ovarian cancer mouse model. We hypothesized that an LR-IL-22 gavage would enable intestinal radioprotection by modifying the tumor microenvironment and, subsequently, improving overall survival in female C57BL/6MUC-1 mice with widespread abdominal syngeneic 2F8cis ovarian cancer. Herein, we report that the LR-IL-22 gavage not only improved overall survival in mice when combined with a PD-L1 inhibitor by inducing differential gene expression in irradiated stem cells but also induced PD-L1 protein expression in ovarian cancer cells and mobilized CD8+ T cells in whole abdomen irradiated mice. The addition of LR-IL-22 to a combined treatment modality with fractionated whole abdomen radiation (WAI) and systemic chemotherapy and immunotherapy regimens can facilitate a safe and effective protocol to reduce tumor burden, increase survival, and improve the quality of life of a locally advanced ovarian cancer patient.

Abstract PR016: Carcinoma-associated mesenchymal stem cells promote ovarian cancer metastasis by increasing tumor heterogeneity through direct mitochondrial transfer

Ovarian cancer is characterized by early, diffuse metastatic spread with most women presenting with widespread abdominal metastasis at the time of diagnosis. Prior work demonstrates carcinoma-associated mesenchymal stem cells (CA-MSCs) enhance ovarian cancer metastasis through a process of direct cellular interaction and formation of heterocellular CA-MSC and tumor cell complexes. Here we demonstrate CA-MSCs enhance metastasis via increasing tumor cell heterogeneity through mitochondrial donation. CA-MSCs directly interact with ovarian cancer cells forming tunneling nanotubules (TNTs). CA-MSCs transfer live mitochondria via these TNTs to ovarian cancer cells. This mitochondrial donation preferentially occurs in ovarian cancer cells with the least endogenous mitochondria (‘mito poor’ cancer cells). Mito poor cancer cells demonstrate decreased proliferation, increased sensitivity to chemotherapy and decreased oxidative phosphorylation compared to ‘mito rich’ cancer cells. CA-MSCs rescue the phenotype of these mito poor cancer cells restoring their proliferative capacity, increasing chemotherapy resistance and increasing oxidative phosphorylation. We validated these findings in a fully autologous system using CA-MSCs and cancer cells derived from the same patient to prevent confounding effects of cellular response to foreign organelle/DNA. Using a knockdown of the mitochondrial motor protein, MIRO1, we demonstrate mitochondrial transfer is necessary for the CA-MSC-mediated rescue of mito poor cancer cells. We developed a haplotype-specific quantification of mitochondrial DNA to differentiate CA-MSC derived mitochondria from endogenous tumor cell mitochondria. We used this system to both quantify the amount of CA-MSC mitochondrial donation and to demonstrate CA-MSC donated mitochondria persist in tumor cells over at least 14 days. Importantly, CA-MSC mitochondrial donation occurs in vivo and is associated with decreased survival in an orthotopic ovarian cancer mouse model. A DNA barcoding system was used to quantify tumor cell clonal heterogeneity. Using this system, we demonstrate CA-MSCs significantly enhance tumor cell heterogeneity, particularly during metastasis. This increase in tumor cell heterogeneity is dependent on CA-MSC mitochondrial transfer. Collectively, we report CA-MSC mitochondrial transfer as a critical mediator of ovarian cancer survival, heterogeneity and metastasis representing a potentially powerful therapeutic target.

Citation Format: Leonard G. Frisbie, Catherine A. Pressimone, Huda I. Atiya, Alexander T. Pearson, Lan G. Coffman. Carcinoma-associated mesenchymal stem cells promote ovarian cancer metastasis by increasing tumor heterogeneity through direct mitochondrial transfer [abstract]. In: Proceedings of the AACR Special Conference: Cancer Metastasis; 2022 Nov 14-17; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_2):Abstract nr PR016.

Phase I trial of ribociclib with platinum chemotherapy in recurrent ovarian cancer

BACKGROUND

New therapeutic combinations to improve the outcome of ovarian cancer patients are clearly needed. Preclinical studies with ribociclib (LEE-011), a CDK4/6 cell cycle checkpoint inhibitor, demonstrate a synergistic effect with platinum chemotherapy and efficacy as a maintenance therapy after chemotherapy. We tested the safety and initial efficacy of ribociclib in combination with platinum-based chemotherapy in recurrent ovarian cancer.

METHODS

This phase I trial combined weekly carboplatin and paclitaxel chemotherapy with ribociclib followed by ribociclib maintenance in patients with recurrent platinum-sensitive ovarian cancer. Primary objectives were safety and maximum tolerated dose (MTD) of ribociclib when given with platinum and taxane chemotherapy. Secondary endpoints were response rate (RR) and progression-free survival (PFS).

RESULTS

Thirty-five patients were enrolled. Patients had a mean 2.5 prior lines of chemotherapy, and 51% received prior maintenance therapy with Poly (ADP-ribose) polymerase inhibitors (PARPi) and/or Bevacizumab. The MTD was 400mg. The most common AEs included anemia (82.9%), neutropenia (82.9%), fatigue (82.9%), and nausea (77.1%). Overall RR was 79.3% with a stable disease (SD) rate of 18% resulting in a clinical benefit rate of 96.6%. The PFS was 11.4 months. RR and PFS did not differ based on number of lines of prior chemotherapy or prior maintenance therapy.

CONCLUSIONS

This work demonstrates the combination of ribociclib with chemotherapy in ovarian cancer is feasible and safe. With a clinical benefit rate of 97%, this work provides encouraging evidence of clinical efficacy in patients with recurrent platinum-sensitive disease.

TRIAL REGISTRATION

CLINICALTRIALS

gov NCT03056833.

FUNDING

This investigator-initiated trial was supported by Novartis who provided drug and funds for trial execution.

Novel Therapies in Gynecologic Cancer

During the past decade, considerable strides have been made in the understanding and treatment of gynecologic cancers. The advent of PARP inhibitors, antiangiogenic therapies, immunotherapy combinations, and targeted agents have altered the standard of care in ovarian, endometrial, and cervical cancers. However, continued advancement in the treatment of gynecologic cancers is critical. Fortunately, exciting work defining new therapeutic targets and novel treatment strategies is on the horizon. Here, we discuss emerging treatments for gynecologic cancers, including endometrial, cervical, ovarian, and rare gynecologic cancers. We highlight research that has deepened our understanding of the unique biology and molecular underpinnings of these cancers and is being translated into powerful new treatment approaches. We particularly highlight the advent of immunotherapy in endometrial cancer; radiosensitizers in cervical, vaginal, and vulvar cancers; targeted therapies in ovarian cancer; and molecularly driven approaches to treat rare gynecologic cancers. Continued basic, translational, and clinical research holds the promise to change the landscape of gynecologic cancer and improve the lives of all women impacted by these diseases.

Cancer-associated MSC drive tumor immune exclusion and resistance to immunotherapy, which can be overcome by Hedgehog inhibition

We investigated the impact of cancer-associated mesenchymal stem cells (CA-MSCs) on ovarian tumor immunity. In patient samples, CA-MSC presence inversely correlates with the presence of intratumoral CD8+ T cells. Using an immune “hot” mouse ovarian cancer model, we found that CA-MSCs drive CD8+ T cell tumor immune exclusion and reduce response to anti–PD-L1 immune checkpoint inhibitor (ICI) via secretion of numerous chemokines (Ccl2, Cx3cl1, and Tgf-β1), which recruit immune-suppressive CD14+Ly6C+Cx3cr1+ monocytic cells and polarize macrophages to an immune suppressive Ccr2hiF4/80+Cx3cr1+CD206+ phenotype. Both monocytes and macrophages express high levels of transforming growth factor β–induced (Tgfbi) protein, which suppresses NK cell activity. Hedgehog inhibitor (HHi) therapy reversed CA-MSC effects, reducing myeloid cell presence and expression of Tgfbi, increasing intratumoral NK cell numbers, and restoring response to ICI therapy. Thus, CA-MSCs regulate antitumor immunity, and CA-MSC hedgehog signaling is an important target for cancer immunotherapy.

Cost-effectiveness analysis of tumor molecular classification in high-risk early-stage endometrial cancer

PURPOSE

Tumor molecular analyses in endometrial cancer (EC) includes 4 distinct subtypes: (1) POLE-mutated, (2) mismatch repair protein (MMR) deficient, (3) p53 mutant, and (4) no specific molecular profile. Recently, a sub-analysis of PORTEC-3 demonstrated notable differences in treatment response between molecular classification (MC) groups. Cost of testing is one barrier to widespread adoption of MC. Therefore, we sought to determine the cost-effectiveness of MC in patients with stage I and II high-risk EC.

METHODS

A Markov decision model was developed to compare tumor molecular classification (TMC) vs. no testing (NT). A healthcare payor's perspective and 5-year time horizon were used. Base case data were abstracted from PORTEC-3 and the molecular sub-analysis. Cost and utility data were derived from public databases, peer-reviewed literature, and expert input. Strategies were compared using the incremental cost-effectiveness ratio (ICER) with effectiveness in quality-adjusted life years (QALYs) and evaluated with a willingness-to-pay threshold of $100,000 per QALY gained. Sensitivity analyses were performed to test model robustness.

RESULTS

When compared to NT, TMC was cost effective with an ICER of $25,578 per QALY gained; incremental cost was $1780 and incremental effectiveness was 0.070 QALYs. In one-way sensitivity analyses, results were most sensitive to the cost of POLE testing, but TMC remained cost-effective over all parameter ranges.

CONCLUSIONS

TMC in early-stage high-risk EC is cost-effective, and the model results were robust over a range of parameters. Given that MC can be used to guide adjuvant treatment decisions, these findings support adoption of TMC into routine practice.

B cell signatures and tertiary lymphoid structures contribute to outcome in head and neck squamous cell carcinoma

Current immunotherapy paradigms aim to reinvigorate CD8+ T cells, but the contribution of humoral immunity to antitumor immunity remains understudied. Here, we demonstrate that in head and neck squamous cell carcinoma (HNSCC) caused by human papillomavirus infection (HPV+), patients have transcriptional signatures of germinal center (GC) tumor infiltrating B cells (TIL-Bs) and spatial organization of immune cells consistent with tertiary lymphoid structures (TLS) with GCs, both of which correlate with favorable outcome. GC TIL-Bs in HPV+ HNSCC are characterized by distinct waves of gene expression consistent with dark zone, light zone and a transitional state of GC B cells. Semaphorin 4a expression is enhanced on GC TIL-Bs present in TLS of HPV+ HNSCC and during the differentiation of TIL-Bs. Our study suggests that therapeutics to enhance TIL-B responses in HNSCC should be prioritized in future studies to determine if they can complement current T cell mediated immunotherapies.

An Orthotopic Mouse Model of Ovarian Cancer using Human Stroma to Promote Metastasis

Ovarian cancer is characterized by early, diffuse metastasis with 70% of women having metastatic disease at the time of diagnosis. While elegant transgenic mouse models of ovarian cancer exist, these mice are expensive and take a long time to develop tumors. Intraperitoneal injection xenograft models lack human stroma and do not accurately model ovarian cancer metastasis. Even patient derived xenografts (PDX) do not fully recapitulate the human stromal microenvironment as serial PDX passages demonstrate significant loss of human stroma. The ability to easily model human ovarian cancer within a physiologically relevant stromal microenvironment is an unmet need. Here, the protocol presents an orthotopic ovarian cancer mouse model using human ovarian cancer cells combined with patient-derived carcinoma-associated mesenchymal stem cells (CA-MSCs). CA-MSCs are stromal progenitor cells, which drive the formation of the stromal microenvironment and support ovarian cancer growth and metastasis. This model develops early and diffuses metastasis mimicking clinical presentation. In this model, luciferase expressing ovarian cancer cells are mixed in a 1:1 ratio with CA-MSCs and injected into the ovarian bursa of NSG mice. Tumor growth and metastasis are followed serially over time using bioluminescence imaging. The resulting tumors grow aggressively and form abdominal metastases by 14 days post injection. Mice experienced significant decreases in body weight as a marker of systemic illness and increased disease burden. By day 30 post injection, mice met endpoint criteria of >10% body weight loss and necropsy confirmed intra-abdominal metastasis in 100% of mice and 60%-80% lung and parenchymal liver metastasis. Collectively, orthotopic engraftment of ovarian cancer cells and stroma cells generates tumors that closely mimic the early and diffuse metastatic behavior of human ovarian cancer. Furthermore, this model provides a tool to study the role of ovarian cancer cell: stroma cell interactions in metastatic progression.

Abstract PO021: Carcinoma-associated mesenchymal stem/stromal cells enhance ovarian cancer metastasis and increase cancer cell clonal heterogeneity through direct mitochondrial transfer

Ovarian cancer is the most deadly gynecologic cancer largely due to early, diffuse metastatic spread. The ovarian cancer tumor microenvironment (TME) significantly impacts the metastatic capacity of ovarian cancer. We recently demonstrated that a critical stromal progenitor cell within the TME, termed carcinoma-associated mesenchymal stem/stromal cells (CA-MSCs), dramatically enhance the metastasis of ovarian cancer cells. CA-MSCs directly bind to cancer cells forming heterocellular units which co-metastasize. The goal of this work is to understand the mechanism driving CA-MSC-mediated ovarian cancer metastasis. We hypothesize that CA-MSCs increase the metastatic potential of ovarian cancer cells during the process of co-metastasis. Ovarian cancer uses both hematogenous and transcoelomic routes of metastasis therefore we used two ovarian cancer murine models to evaluate both modes of metastasis. We used a genomic barcode system to assess the clonal patterns of metastasis. Ovarian cancer cells with one unique barcode per cell were grown with or without CA-MSCs. Sites of metastasis were quantified and cancer cells were harvested from each site. Barcodes were sequenced to determined clonal representation at each metastatic site. We found CA-MSCs increased the number of metastatic sites in both the hematogenous and transcoelomic mouse models. Interestingly, CA-MSCs also increased the clonal heterogeneity at all metastatic sites (2.5 - 5 fold increase in blood, lung and liver). To investigate the mechanism enabling CA-MSC-mediated enhancement of clonal heterogeneity, we studied primary patient derived CA-MSCs and ovarian cancer cells. The process of metastasis poses unique metabolic stresses on cancer cells and normal mesenchymal stem cells are known to donate mitochondria to damaged epithelial cells. We therefore assessed if CA-MSCs use a similar mechanism to enhance survival of metastatic cancer cells. We stably labeled CA-MSC mitochondria with COX8-GFP via lentiviral transduction to enable the visualization and quantification of potential mitochondrial transfer. We demonstrate that CA-MSCs actively transfer mitochondria to cancer cells. This transfer is dependent on the physical interaction of CA-MSCs with cancer cells and is increased 2-4 fold when CA-MSCs and cancer cells form metastatic heterocellular units under non-adherent conditions. We tested the functional consequences of CA-MSC to cancer cell mitochondrial transfer and demonstrate cancer cells which receive mitochondria have increased chemotherapy resistance, increased sphere forming capacity and stem-like properties. Collectively, our results indicate CA-MSCs are a significant driver of ovarian cancer metastasis by forming heterocellular metastatic units which enable CA-MSC to cancer cell mitochondrial transfer. This leads to increased cancer cell survival and tumor initiation properties and represents a novel method of maintaining cancer cell heterogeneity during metastasis.

Citation Format: Catherine A. Pressimone, Leonard G. Frisbie, Alexander Pearson, Lan G. Coffman. Carcinoma-associated mesenchymal stem/stromal cells enhance ovarian cancer metastasis and increase cancer cell clonal heterogeneity through direct mitochondrial transfer [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr PO021.

Epigenomic Reprogramming toward Mesenchymal-Epithelial Transition in Ovarian-Cancer-Associated Mesenchymal Stem Cells Drives Metastasis

A role for cancer cell epithelial-to-mesenchymal transition (EMT) in cancer is well established. Here, we show that, in addition to cancer cell EMT, ovarian cancer cell metastasis relies on an epigenomic mesenchymal-to-epithelial transition (MET) in host mesenchymal stem cells (MSCs). These reprogrammed MSCs, termed carcinoma-associated MSCs (CA-MSCs), acquire pro-tumorigenic functions and directly bind cancer cells to serve as a metastatic driver/chaperone. Cancer cells induce this epigenomic MET characterized by enhancer-enriched DNA hypermethylation, altered chromatin accessibility, and differential histone modifications. This phenomenon appears clinically relevant, as CA-MSC MET is highly correlated with patient survival. Mechanistically, mirroring MET observed in development, MET in CA-MSCs is mediated by WT1 and EZH2. Importantly, EZH2 inhibitors, which are clinically available, significantly inhibited CA-MSC-mediated metastasis in mouse models of ovarian cancer.

Phase II clinical trial of metformin as a cancer stem cell-targeting agent in ovarian cancer

BACKGROUNDEpidemiologic studies suggest that metformin has antitumor effects. Laboratory studies indicate metformin impacts cancer stem-like cells (CSCs). As part of a phase II trial, we evaluated the impact of metformin on CSC number and on carcinoma-associated mesenchymal stem cells (CA-MSCs) and clinical outcomes in nondiabetic patients with advanced-stage epithelial ovarian cancer (EOC).METHODSThirty-eight patients with stage IIC (n = 1)/III (n = 25)/IV (n = 12) EOC were treated with either (a) neoadjuvant metformin, debulking surgery, and adjuvant chemotherapy plus metformin or (b) neoadjuvant chemotherapy and metformin, interval debulking surgery, and adjuvant chemotherapy plus metformin. Metformin-treated tumors, compared with historical controls, were evaluated for CSC number and chemotherapy response. Primary endpoints were (a) a 2-fold or greater reduction in aldehyde dehydrogenase-positive (ALDH+) CD133+ CSCs and (b) a relapse-free survival at 18 months of more than 50%.RESULTSMetformin was well tolerated. Median progression-free survival was 18.0 months (95% CI 14.0-21.6) with relapse-free survival at 18 months of 59.3% (95% CI 38.6-70.5). Median overall survival was 57.9 months (95% CI 28.0-not estimable). Tumors treated with metformin had a 2.4-fold decrease in ALDH+CD133+ CSCs and increased sensitivity to cisplatin ex vivo. Furthermore, metformin altered the methylation signature in CA-MSCs, which prevented CA-MSC-driven chemoresistance in vitro.CONCLUSIONTranslational studies confirm an impact of metformin on EOC CSCs and suggest epigenetic change in the tumor stroma may drive the platinum sensitivity ex vivo. Consistent with this, metformin therapy was associated with better-than-expected overall survival, supporting the use of metformin in phase III studies.TRIAL REGISTRATIONClinicalTrials.gov NCT01579812.

The double edge sword of fibrosis in cancer

Cancer-associated fibrosis is a critical component of the tumor microenvironment (TME) which significantly impacts cancer behavior. However, there is significant controversy regarding fibrosis as a predominantly tumor promoting or tumor suppressing factor. Cells essential to the generation of tissue fibrosis such as fibroblasts and mesenchymal stem cells (MSCs) have dual phenotypes dependent upon their independence or association with cancer cells. Cancer-associated fibroblasts and cancer-associated MSCs have unique molecular profiles which facilitate cancer cell cross talk, influence extracellular matrix deposition, and direct the immune system to generate a protumorigenic environment. In contrast, normal tissue fibroblasts and MSCs are important in restraining cancer initiation, influencing epithelial cell differentiation, and limiting cancer cell invasion. We propose this apparent dichotomy of function is due to (1) cancer mediated stromal reprogramming; (2) tissue stromal source; (3) unique subtypes of fibrosis; and (4) the impact of fibrosis on other TME elements. First, as cancer progresses, tumor cells influence their surrounding stroma to move from a cancer restraining phenotype into a cancer supportive role. Second, cancer has specific organ tropism, thus stroma derived from preferred metastatic organs support growth while less preferred metastatic tissues do not. Third, there are subtypes of fibrosis which have unique function to support or inhibit cancer growth. Fourth, depleting fibrosis influences other TME components which drive the cancer response. Collectively, this review highlights the complexity of cancer-associated fibrosis and supports a dual function of fibrosis which evolves during the continuum of cancer growth.

Ovarian Carcinoma-Associated Mesenchymal Stem Cells Arise from Tissue-Specific Normal Stroma

Carcinoma-associated mesenchymal stem cells (CA-MSCs) are critical stromal progenitor cells within the tumor microenvironment (TME). We previously demonstrated that CA-MSCs differentially express bone morphogenetic protein family members, promote tumor cell growth, increase cancer "stemness," and chemotherapy resistance. Here, we use RNA sequencing of normal omental MSCs and ovarian CA-MSCs to demonstrate global changes in CA-MSC gene expression. Using these expression profiles, we create a unique predictive algorithm to classify CA-MSCs. Our classifier accurately distinguishes normal omental, ovary, and bone marrow MSCs from ovarian cancer CA-MSCs. Suggesting broad applicability, the model correctly classifies pancreatic and endometrial cancer CA-MSCs and distinguishes cancer associated fibroblasts from CA-MSCs. Using this classifier, we definitively demonstrate ovarian CA-MSCs arise from tumor mediated reprograming of local tissue MSCs. Although cancer cells alone cannot induce a CA-MSC phenotype, the in vivo ovarian TME can reprogram omental or ovary MSCs to protumorigenic CA-MSCs (classifier score of >0.96). In vitro studies suggest that both tumor secreted factors and hypoxia are critical to induce the CA-MSC phenotype. Interestingly, although the breast cancer TME can reprogram bone marrow MSCs into CA-MSCs, the ovarian TME cannot, demonstrating for the first time that tumor mediated CA-MSC conversion is tissue and cancer type dependent. Together these findings (a) provide a critical tool to define CA-MSCs and (b) highlight cancer cell influence on distinct normal tissues providing powerful insights into the mechanisms underlying cancer specific metastatic niche formation. Stem Cells 2019;37:257-269.

Leukemia inhibitory factor functions in parallel with interleukin-6 to promote ovarian cancer growth

Ovarian carcinoma-associated mesenchymal stem cells (CA-MSC) produce not only high levels of IL6 but also the related cytokine leukemia inhibitory factor (LIF). Interleukin 6 (IL6) mediated activation of STAT3 is implicated as a critical therapeutic target for cancer therapy. Less is known about the role of LIF, which can similarly activate STAT3, in ovarian cancer. We therefore sought to evaluate the tumorigenic effects of CA-MSC paracrine LIF signaling and the redundancy of IL6 and LIF in activating ovarian cancer STAT3 mediated cancer growth. As expected, we found that both IL6 and LIF induce STAT3 phosphorylation in tumor cells. In addition, both IL6 and LIF increased the percentage of ALDH+ ovarian cancer stem-like cells (CSC). Supporting redundancy of function by the two cytokines, CA-MSC induced STAT3 phosphorylation and increased cancer cell ‘stemness’. This effect was not inhibited by LIF or IL6 blocking antibodies alone, but was prevented by dual IL6/LIF blockade or JAK2 inhibition. Similarly, small hairpin RNA (shRNA)-mediated reduction of IL6 or LIF in CA-MSC partially decreased but could not completely abrograte the ability of CA-MSC to induce STAT3 phosphorylation and stemness. Importantly, the in vivo pro-tumorigenic effect of CA-MSC is abrogated by dual blockade with the JAK2 inhibitor ruxolitinib to a much greater extent than treatment with anti-IL6 or anti-LIF antibody alone. Ruxolitinib treatment also improves survival in the immunocompetent ovarian cancer mouse model system with ID8 tumor cells plus MSC. Ruxolitinib-treated tumors in both the immunocompromised and immunocompetent animal models demonstrate decreased phospho-STAT3, indicating on-target activity. In conclusion, CA-MSC activate ovarian cancer cell STAT3 signaling via IL6 and LIF and increase tumorigenesis cancer stemness. This functional redundancy suggests that therapeutic targeting of a single cytokine may be less effective than strategies such as dual inhibitor therapy or targeting shared downstream factors of the JAK/STAT pathway.

Abstract TMEM-019: NEW OVARIAN CANCER METASTASIS MODELS DEMONSTRATE PREFERENTIAL HEMATOGENOUS SPREAD OF OVARIAN CANCER CELLS TO THE OVARY AND A REQUIREMENT FOR THE OVARY FOR ABDOMINAL DISSEMINATION

BACKGROUND: Mounting evidence suggests that many high grade serous ‘ovarian’ cancers (HGSOC) start in the fallopian tube. Cancer cells are then recruited to the ovary and subsequently spread diffusely through the abdomen. The mechanism of ovarian cancer spread has long been thought to be largely due to direct shedding of tumor cells into the peritoneal cavity with vascular spread being of limited importance. Recent work challenges this dogma, suggesting hematogenous spread of ovarian cancer may play a larger role in ovarian cancer cell metastasis than previously thought. One reason the role of vascular spread of ovarian cancer has not been fully elucidated is the lack of easily accessible models of vascular ovarian cancer metastasis.

METHODS: We developed three metastatic models of ovarian cancer which confirm the ability of ovarian cancer to hematogenously spread. A murine tail vein injection model using human ovarian cancer cell lines was used to observe the general pattern of hematogenous spread when cells are directly introduced into the vasculature. A subcutaneous murine ovarian tumor model was developed to investigate patterns of metastasis in the setting of a fully murine tumor microenvironment. Finally, a human subcutaneous xenograft model using primary patient derived ovarian cancer cells, human carcinoma-associated mesenchymal stem cells and human endothelial cells was developed to investigate patterns of metastasis in the setting of a humanized microenvironment.

RESULTS: In all three models, we demonstrate the formation of distant metastasis via vascular spread. Strikingly, we observe a high rate of metastasis to the ovary (40-100%) in all three models representing a disproportionately large fraction of total metastatic burden. Mice which developed ovarian metastatic disease also developed further intra-abdominal metastatic disease and ascites. Interestingly, in the tail vein injection model, oophorectomy prior to ovarian cancer cell injection resulted in a complete loss of peritoneal metastases, ascites and decreased burden of liver metastasis. This ovary tropism appears to be unique to ovarian cancer cells as intravenous tail vein injection of breast cancer and lung cancer cell lines, while resulting in typical sites of disease in the lung and bone, did not result in ovary involvement.

CONCLUSIONS: Taken together our data indicates that hematogenously disseminated high grade serous ovarian cancer cells have a unique tropism for the ovary and that hematogenous spread in ovarian cancer may be more common than previously appreciated. Furthermore our studies support a critical role for the ovary in promoting high grade serous ovarian cancer cell metastasis to the abdomen. The models developed here represent important new tools to evaluate both the mechanism of cancer cell recruitment to the ovary and to understand and target key steps in ovarian cancer metastasis.

Citation Format: Lan G Coffman, Daniela Burgos-Ojeda, Rong Wu, Kathleen Cho, Shoumei Bai, and Ronald J Buckanovich. NEW OVARIAN CANCER METASTASIS MODELS DEMONSTRATE PREFERENTIAL HEMATOGENOUS SPREAD OF OVARIAN CANCER CELLS TO THE OVARY AND A REQUIREMENT FOR THE OVARY FOR ABDOMINAL DISSEMINATION [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 TMEM-019.

Abstract AP17: OVARIAN TUMOR STIMULATION CONVERTS NORMAL OVARY AND OMENTAL MESENCHYMAL STEM CELLS INTO TUMOR–PROMOTING CARCINOMA–ASSOCIATED MESENCHYMAL STEM CELLS

BACKGROUND: Ovarian carcinoma-associated mesenchymal stem cells (CA-MSCs) are multipotent cells which influence the creation of the ovarian tumor microenvironment. CA-MSCs strongly promote ovarian cancer growth, cancer stem cell-like cells and chemotherapy resistance. CA-MSCs lack tumor associated somatic mutations, however compared to normal MSCs, CA-MSCs have a unique expression profile which mediates their pro-tumorigenic properties. The origin of CA-MSCs is unknown. We hypothesized that CA-MSCs are derived from local tissue MSCs reprogrammed by the ovarian tumor to become pro-tumorigenic CA-MSCs.

METHODS: We define a “CA-MSC-like expression profile” of 6 genes significantly and reproducibly differentially expressed between normal human MSCs (from bone marrow (BM), omentum (OM) or ovary (OV)) and patient-derived CA-MSCs. Three normal MSC populations were grown with human ovarian cancer cells and analyzed to determine if tumor stimulation can induce a CA-MSC-like expression profile. Tumor stimulated MSCs were functionally analyzed to determine if acquisition of a CA-MSC-like expression profile correlates with development of pro-tumorigenic functions. Methylation array analysis of normal MSCs versus CA-MSCs was performed to explore the role of epigenetic regulation in the formation a CA-MSC.

RESULTS: Tumor stimulation of normal OV and OM MSCs but not BM MSCs yield expression changes which approximate the CA-MSC-like expression profile. In vivo tumor stimulation of normal OM MSCs most effectively induces a CA-MSC-like expression profile. The development of a CA-MSC-like expression profile correlates with gain of pro-tumorigenic functions including induction of cancer cell chemotherapy resistance, enrichment of the ovarian cancer stem cell-like pool and enhancement of tumor growth. In contrast, tumor stimulated BM MSCs--which do not develop a CA-MSC-like expression profile--fail to gain pro-tumorigenic functions. Further, methylation array analysis demonstrates significant global differences in methylation patterns of CA-MSCs versus normal MSCs, indicating that epigenetic alterations may drive the development of the CA-MSC phenotype.

CONCLUSIONS: Collectively we demonstrate that normal OV and OM MSCs are capable of becoming CA-MSCs through in vivo tumor stimulation with development of a distinct CA-MSC-like expression profile with corresponding pro-tumorigenic functions. These findings highlight the critical influence of the tumor on the normal host environment, manipulating normal cells to become cancer-supporting cells. The differential capacity of OV and OM MSCs but not BM MSCs to become CA-MSCs also highlights the heterogeneity of MSCs and may factor into the intraperitoneal tropism of ovarian cancer spread. Ultimately, understanding how tumor stimulation drives the development of CA-MSCs may identify powerful targets to disrupt the formation and function of the ovarian tumor microenvironment.

Citation Format: Coffman, LG and Buckanovich, RJ. OVARIAN TUMOR STIMULATION CONVERTS NORMAL OVARY AND OMENTAL MESENCHYMAL STEM CELLS INTO TUMOR–PROMOTING CARCINOMA–ASSOCIATED MESENCHYMAL STEM 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 AP17.

New models of hematogenous ovarian cancer metastasis demonstrate preferential spread to the ovary and a requirement for the ovary for abdominal dissemination

Emerging evidence suggest that many high-grade serous "ovarian" cancers (HGSOC) start in the fallopian tube. Cancer cells are then recruited to the ovary and then spread diffusely through the abdomen. The mechanism of ovarian cancer spread was thought to be largely due to direct shedding of tumor cells into the peritoneal cavity with vascular spread being of limited importance. Recent work challenges this dogma, suggesting hematogenous spread of ovarian cancer may play a larger role in ovarian cancer cell metastasis than previously thought. One reason the role of vascular spread of ovarian cancer has not been fully elucidated is the lack of easily accessible models of vascular ovarian cancer metastasis. Here, we present 3 metastatic models of ovarian cancer which confirm the ability of ovarian cancer to hematogenously spread. Strikingly, we observe a high rate of metastasis to the ovary with the development of ascites in these models. Interestingly, oophorectomy resulted in a complete loss of peritoneal metastases and ascites. Taken together, our data indicate that hematogenously disseminated HGSOC cells have a unique tropism for the ovary and that hematogenous spread in ovarian cancer may be more common than appreciated. Furthermore, our studies support a critical role for the ovary in promoting HGSOC cell metastasis to the abdomen. The models developed here represent important new tools to evaluate both the mechanism of cancer cell recruitment to the ovary and understand and target key steps in ovarian cancer metastasis.

Abstract B60: Identification of an ovarian tumor:stromal HH:BMP4 signaling loop critical to ovarian cancer growth and chemotherapy resistance

The ovarian tumor microenvironment is critical to ovarian cancer growth, spread, and survival. We recently identified a novel host cell component of the tumor microenvironment, human ovarian carcinoma-associated mesenchymal stem cells (CA-MSCs). CA-MSCs are of particular interest as they are multi-potent and can differentiate to create many components of the tumor microenvironment including fibroblasts, myofibroblasts and adipocytes. CA-MSCs, compared to normal MSCs, express high levels of BMP proteins and promote tumor growth by increasing numbers of cancer stem-like cells (CSCs). We now define a CA-MSC BMP4: ovarian tumor cell Hedgehog (HH) positive feedback loop critical to the cancer promoting functions of CA-MSCs. We demonstrate that CA-MSC expression of BMP4 is induced by ovarian tumor cell-secreted Hedgehog (HH). Reciprocally, CA-MSC-derived BMP4 increases ovarian tumor cell HH expression creating a positive feedback loop. Interruption of this loop with either a HH pathway inhibitor (IPI-926 or LDE-225) or BMP4 blocking antibody decreases the induction of CA-MSC-derived BMP4 and tumor-derived HH. This signaling loop is critical to the pro-tumorigenic effects of CA-MSCs as HH inhibition blocked CA-MSC-mediated tumorigenesis and reduced the number of CSCs. Additionally, HH inhibition reversed CA-MSC -induced chemotherapy resistance leading to significant cisplatin response in established platinum-resistant tumors. Collectively, we define a critical positive feedback loop between CA-MSC-derived BMP4 and ovarian tumor cell-secreted HH providing further support for clinical targeting of the HH pathway, particularly in combination with platinum-based chemotherapy, in ovarian cancer.

Citation Format: Lan G. Coffman, Yunjung Choi, Karen Mclean, Marina Pasca di Magliano, Benjamin Allen, Ronald J. Buckanovich. Identification of an ovarian tumor:stromal HH:BMP4 signaling loop critical to ovarian cancer growth and chemotherapy resistance. [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 B60.

Abstract C64: Iron regulatory gene signature predicts outcome in breast cancer

Extensive experimental and clinical literature attests to the importance of iron in tumor cell growth. For example, high levels of dietary iron have been linked epidemiologically to the increased development of tumors in humans; in animal models, levels of dietary iron affect tumor growth. However, pathways that underlie the apparent demand for iron by tumors remain largely uncharacterized. We recently discovered that an iron efflux pathway plays a role in breast cancer growth and metastasis: expression of the iron efflux pump ferroportin and its regulator hepcidin were predictive of metastasis-free survival in multiple independent breast cancer cohorts. To determine the optimal “iron gene regulatory signature,” we used microarray datasets comprising 674 breast cancer cases to systematically investigate how expression of genes related to iron metabolism is linked to breast cancer prognosis. Of 61 genes involved in iron regulation, 49% were statistically significantly associated with distant metastasis-free survival (DMFS). Optimal risk stratification was achieved with a model comprising 16 genes, which we term the iron regulatory gene signature (IRGS). Multivariable analysis revealed that the IRGS contributes information not captured by conventional prognostic indicators (hazard ratio 1.61; 95% CI 1.16–2.24; p=0.004). The IRGS successfully stratified homogeneously treated patients, including ER+ patients treated with tamoxifen monotherapy, both with (p=0.006) and without (p=0.03) lymph node metastases. To test whether multiple pathways were embedded within the IRGS, we evaluated the performance of two gene dyads with known roles in iron biology in ER+ patients treated with tamoxifen monotherapy (n=371). For both dyads, gene combinations that minimized intracellular iron content (anti-import: TFRCLow/HFEHigh; or pro-export: FPHigh/HAMPLow) were associated with favorable prognosis (p<0.005). Although the clinical utility of the IRGS will require prospective evaluation, its ability to both identify high risk patients within traditionally low risk groups and low risk patients within high risk groups has the potential to affect therapeutic decision-making.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr C64.

An iron regulatory gene signature predicts outcome in breast cancer

Changes in iron regulation characterize the malignant state. However, the pathways that effect these changes and their specific impact on prognosis remain poorly understood. We capitalized on publicly available microarray datasets comprising 674 breast cancer cases to systematically investigate how expression of genes related to iron metabolism is linked to breast cancer prognosis. Of 61 genes involved in iron regulation, 49% were statistically significantly associated with distant metastasis-free survival. Cases were divided into test and training cohorts, and the supervised principal component method was used to stratify cases into risk groups. Optimal risk stratification was achieved with a model comprising 16 genes, which we term the iron regulatory gene signature (IRGS). Multivariable analysis revealed that the IRGS contributes information not captured by conventional prognostic indicators (HR = 1.61; 95% confidence interval: 1.16-2.24; P = 0.004). The IRGS successfully stratified homogeneously treated patients, including ER+ patients treated with tamoxifen monotherapy, both with (P = 0.006) and without (P = 0.03) lymph node metastases. To test whether multiple pathways were embedded within the IRGS, we evaluated the performance of two gene dyads with known roles in iron biology in ER+ patients treated with tamoxifen monotherapy (n = 371). For both dyads, gene combinations that minimized intracellular iron content [anti-import: TFRC(Low)/HFE(High); or pro-export: SLC40A1 (ferroportin)(High)/HAMP(Low)] were associated with favorable prognosis (P < 0.005). Although the clinical utility of the IRGS will require further evaluation, its ability to both identify high-risk patients within traditionally low-risk groups and low-risk patients within high-risk groups has the potential to affect therapeutic decision making.

Serum ferritin: Past, present and future

BACKGROUND

Serum ferritin was discovered in the 1930s, and was developed as a clinical test in the 1970s. Many diseases are associated with iron overload or iron deficiency. Serum ferritin is widely used in diagnosing and monitoring these diseases.

SCOPE OF REVIEW

In this chapter, we discuss the role of serum ferritin in physiological and pathological processes and its use as a clinical tool.

MAJOR CONCLUSIONS

Although many aspects of the fundamental biology of serum ferritin remain surprisingly unclear, a growing number of roles have been attributed to extracellular ferritin, including newly described roles in iron delivery, angiogenesis, inflammation, immunity, signaling and cancer.

GENERAL SIGNIFICANCE

Serum ferritin remains a clinically useful tool. Further studies on the biology of this protein may provide new biological insights.

Ferritin for the clinician

Ferritin, a major iron storage protein, is essential to iron homeostasis and is involved in a wide range of physiologic and pathologic processes. In clinical medicine, ferritin is predominantly utilized as a serum marker of total body iron stores. In cases of iron deficiency and overload, serum ferritin serves a critical role in both diagnosis and management. Elevated serum and tissue ferritin are linked to coronary artery disease, malignancy, and poor outcomes following stem cell transplantation. Ferritin is directly implicated in less common but potentially devastating human diseases including sideroblastic anemias, neurodegenerative disorders, and hemophagocytic syndrome. Additionally, recent research describes novel functions of ferritin independent of iron storage.

Cleavage of high-molecular-weight kininogen by elastase and tryptase is inhibited by ferritin

Ferritin is a protein principally known for its role in iron storage. We have previously shown that ferritin can bind high-molecular-weight kininogen (HK). Upon proteolytic cleavage by the protease kallikrein, HK releases the proinflammatory peptide bradykinin (BK) and other biologically active products, such as two-chain high-molecular-weight kininogen, HKa. At inflammatory sites, HK is oxidized, which renders it a poor substrate for kallikrein. However, oxidized HK remains a good substrate for elastase and tryptase, thereby providing an alternative cleavage mechanism for HK during inflammation. Here we report that ferritin can retard the cleavage of both native HK and oxidized HK by elastase and tryptase. Initial rates of cleavage were reduced 45-75% in the presence of ferritin. Ferritin is not a substrate for elastase or tryptase and does not interfere with the ability of either protease to digest a synthetic substrate, suggesting that ferritin may impede HK cleavage through direct interaction with HK. Immunoprecipitation and solid phase binding studies reveal that ferritin and HK bind directly with a Kd of 134 nM. To test whether ferritin regulates HK cleavage in vivo, we used THP-1 cells, a human monocyte/macrophage cell line that has been used to model pulmonary inflammatory cells. We observed that ferritin impedes the cleavage of HK by secretory proteases in stimulated macrophages. Furthermore, ferritin, HK, and elastase are all present in or on alveolar macrophages in a mouse model of pulmonary inflammation. Collectively, these results implicate ferritin in the modulation of HK cleavage at sites of inflammation.