Cancer-associated mesothelial cell-derived ANGPTL4 and STC1 promote the early steps of ovarian cancer metastasis

Ovarian cancer (OvCa) preferentially metastasizes in association with mesothelial cell-lined surfaces. We sought to determine if mesothelial cells are required for OvCa metastasis and detect alterations in mesothelial cell gene expression and cytokine secretion upon interaction with OvCa cells. Using omental samples from patients with high-grade serous OvCa and mouse models with Wt1-driven GFP-expressing mesothelial cells, we validated the intratumoral localization of mesothelial cells during human and mouse OvCa omental metastasis. Removing mesothelial cells ex vivo from human and mouse omenta or in vivo using diphtheria toxin-mediated ablation in Msln-Cre mice significantly inhibited OvCa cell adhesion and colonization. Human ascites induced angiopoietin-like 4 (ANGPTL4) and stanniocalcin 1 (STC1) expression and secretion by mesothelial cells. Inhibition of STC1 or ANGPTL4 via RNAi obstructed OvCa cell-induced mesothelial cell to mesenchymal transition while inhibition of ANGPTL4 alone obstructed OvCa cell-induced mesothelial cell migration and glycolysis. Inhibition of mesothelial cell ANGPTL4 secretion via RNAi prevented mesothelial cell-induced monocyte migration, endothelial cell vessel formation, and OvCa cell adhesion, migration, and proliferation. In contrast, inhibition of mesothelial cell STC1 secretion via RNAi prevented mesothelial cell-induced endothelial cell vessel formation and OvCa cell adhesion, migration, proliferation, and invasion. Additionally, blocking ANPTL4 function with Abs reduced the ex vivo colonization of 3 different OvCa cell lines on human omental tissue explants and in vivo colonization of ID8p53-/-Brca2-/- cells on mouse omenta. These findings indicate that mesothelial cells are important to the initial stages of OvCa metastasis and that the crosstalk between mesothelial cells and the tumor microenvironment promotes OvCa metastasis through the secretion of ANGPTL4.

The Natural Product β-Escin Targets Cancer and Stromal Cells of the Tumor Microenvironment to Inhibit Ovarian Cancer Metastasis

Simple Summary

β-escin, a component of horse chestnut seed extract, was first identified as an inhibitor of ovarian cancer (OvCa) adhesion/invasion in our high-throughput screening program using a three-dimensional organotypic model assembled from primary human cells and extracellular matrix. The goal of the study presented here is to determine if β-escin and structurally-similar compounds have a therapeutic potential against OvCa metastasis. β-escin and cardiac glycosides inhibit ovarian cancer adhesion/invasion to the omental microenvironment in vivo, and β-escin inhibits ovarian cancer metastasis in the prevention and intervention setting. Additionally, β-escin was found to decrease the stemness of ovarian cancer cells, inhibit extracellular matrix production in the tumor microenvironment, and inhibit HIF1α stability in ovarian cancer cells and the tumor microenvironment. This study reveals that the natural compound β-escin has therapeutic potential because of its ability to prevent OvCa dissemination by targeting both cancer and stromal cells in the OvCa tumor microenvironment.

Abstract

The high mortality of OvCa is caused by the wide dissemination of cancer within the abdominal cavity. OvCa cells metastasize to the peritoneum, which is covered by mesothelial cells, and invade into the underlying stroma, composed of extracellular matrices (ECM) and stromal cells. In a study using a three-dimensional quantitative high-throughput screening platform (3D-qHTS), we found that β-escin, a component of horse chestnut seed extract, inhibited OvCa adhesion/invasion. Here, we determine whether β-escin and structurally similar compounds have a therapeutic potential against OvCa metastasis. Different sources of β-escin and horse chestnut seed extract inhibited OvCa cell adhesion/invasion, both in vitro and in vivo. From a collection of 160 structurally similar compounds to β-escin, we found that cardiac glycosides inhibited OvCa cell adhesion/invasion and proliferation in vitro, and inhibited adhesion/invasion and metastasis in vivo. Mechanistically, β-escin and the cardiac glycosides inhibited ECM production in mesothelial cells and fibroblasts. The oral administration of β-escin inhibited metastasis in both OvCa prevention and intervention mouse models. Specifically, β-escin inhibited ECM production in the omental tumors. Additionally, the production of HIF1α-targeted proteins, lactate dehydrogenase A, and hexokinase 2 in omental tumors was blocked by β-escin. This study reveals that the natural compound β-escin has a therapeutic potential because of its ability to prevent OvCa dissemination by targeting both cancer and stromal cells in the OvCa tumor microenvironment.

Neutrophil elastase selectively kills cancer cells and attenuates tumorigenesis

Cancer cell genetic variability and similarity to host cells have stymied development of broad anti-cancer therapeutics. Our innate immune system evolved to clear genetically diverse pathogens and limit host toxicity; however, whether/how innate immunity can produce similar effects in cancer is unknown. Here, we show that human, but not murine, neutrophils release catalytically active neutrophil elastase (ELANE) to kill many cancer cell types while sparing non-cancer cells. ELANE proteolytically liberates the CD95 death domain, which interacts with histone H1 isoforms to selectively eradicate cancer cells. ELANE attenuates primary tumor growth and produces a CD8+T cell-mediated abscopal effect to attack distant metastases. Porcine pancreatic elastase (ELANE homolog) resists tumor-derived protease inhibitors and exhibits markedly improved therapeutic efficacy. Altogether, our studies suggest that ELANE kills genetically diverse cancer cells with minimal toxicity to non-cancer cells, raising the possibility of developing it as a broad anti-cancer therapy.

Mesothelial Cell HIF1α Expression Is Metabolically Downregulated by Metformin to Prevent Oncogenic Tumor-Stromal Crosstalk

The tumor microenvironment (TME) plays a pivotal role in cancer progression, and, in ovarian cancer (OvCa), the primary TME is the omentum. Here, we show that the diabetes drug metformin alters mesothelial cells in the omental microenvironment. Metformin interrupts bidirectional signaling between tumor and mesothelial cells by blocking OvCa cell TGF-β signaling and mesothelial cell production of CCL2 and IL-8. Inhibition of tumor-stromal crosstalk by metformin is caused by the reduced expression of the tricarboxylic acid (TCA) enzyme succinyl CoA ligase (SUCLG2). Through repressing this TCA enzyme and its metabolite, succinate, metformin activated prolyl hydroxylases (PHDs), resulting in the degradation of hypoxia-inducible factor 1α (HIF1α) in mesothelial cells. Disruption of HIF1α-driven IL-8 signaling in mesothelial cells by metformin results in reduced OvCa invasion in an organotypic 3D model. These findings indicate that tumor-promoting signaling between mesothelial and OvCa cells in the TME can be targeted using metformin.

Abstract NT-097: QUANTITATIVE HIGH-THROUGHPUT SCREENING USING AN ORGANOTYPIC MODEL IDENTIFIES TWO KINASE INHIBITORS THAT INHIBIT OVARIAN CANCER METASTASIS

The cancer cells, stromal cells and stroma in the tumor microenvironment contribute to cancer metastasis and drug resistance. Therefore we applied an organotypic, robust and reliable assay for quantitative high throughput screening (qHTS) in drug discovery. This 1536-well HTS culture contains primary human mesothelial cells, fibroblasts, fibronectin and collagen type I and reproduces the human ovarian cancer (OvCa) metastatic microenvironment. The qHTS assay identifies small molecule compounds that inhibit OvCa adhesion/migration/invasion to the organotypic metastatic microenvironment.

Over 44,000 small molecules were screened in the primary qHTS assay. A counter screen was performed to eliminate any compounds toxic to the mesothelial cells or fibroblasts within the metastatic microenvironment. The activity of hit compounds was confirmed using five OvCa cell lines, and validated in secondary in vitro and in vivo biological assays. The active compounds directly inhibit at least two of three OvCa functions: adhesion, invasion and growth. In vivo, these compounds prevent OvCa adhesion/invasion and metastasis, and improve survival in mouse models.

Collectively, these data indicate that the three compounds, two tyrosine kinase inhibitors and one novel compound, identified using an complex organtoypic culture of the tumor microenvironment for qHTS are potential therapeutics for OvCa metastasis.

Citation Format: Hilary A. Kenny, Madhu Lal, Min Shen, Dominik Nahotko, Sarah Fazal, Siquan Chen, Chun-Yi Chiang, Betul Kara, S. Diane Yamada, Kyle Brimacombe, Juan Marugan, Marc Ferrer and Ernst Lengyel. QUANTITATIVE HIGH-THROUGHPUT SCREENING USING AN ORGANOTYPIC MODEL IDENTIFIES TWO KINASE INHIBITORS THAT INHIBIT OVARIAN CANCER METASTASIS [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr NT-097.

Cancer-derived small extracellular vesicles promote angiogenesis by heparin-bound, bevacizumab-insensitive VEGF, independent of vesicle uptake

Cancer-derived small extracellular vesicles (sEVs) induce stromal cells to become permissive for tumor growth. However, it is unclear whether this induction solely occurs through transfer of vesicular cargo into recipient cells. Here we show that cancer-derived sEVs can stimulate endothelial cell migration and tube formation independently of uptake. These responses were mediated by the 189 amino acid isoform of vascular endothelial growth factor (VEGF) on the surface of sEVs. Unlike other common VEGF isoforms, VEGF189 preferentially localized to sEVs through its high affinity for heparin. Interaction of VEGF189 with the surface of sEVs profoundly increased ligand half-life and reduced its recognition by the therapeutic VEGF antibody bevacizumab. sEV-associated VEGF (sEV-VEGF) stimulated tumor xenograft growth but was not neutralized by bevacizumab. Furthermore, high levels of sEV-VEGF were associated with disease progression in bevacizumab-treated cancer patients, raising the possibility that resistance to bevacizumab might stem in part from elevated levels of sEV-VEGF.

Quantitative High-Throughput Screening Using an Organotypic Model Identifies Compounds that Inhibit Ovarian Cancer Metastasis

The tumor microenvironment (TME) is a key determinant of metastatic efficiency. We performed a quantitative high-throughput screen (qHTS) of diverse medicinal chemistry tractable scaffolds (44,420 compounds) and pharmacologically active small molecules (386 compounds) using a layered organotypic, robust assay representing the ovarian cancer metastatic TME. This 3D model contains primary human mesothelial cells, fibroblasts, and extracellular matrix, to which fluorescently labeled ovarian cancer cells are added. Initially, 100 compounds inhibiting ovarian cancer adhesion/invasion to the 3D model in a dose-dependent manner were identified. Of those, eight compounds were confirmed active in five high-grade serous ovarian cancer cell lines and were further validated in secondary in vitro and in vivo biological assays. Two tyrosine kinase inhibitors, PP-121 and milciclib, and a previously unreported compound, NCGC00117362, were selected because they had potency at 1 μmol/L in vitro Specifically, NCGC00117362 and PP-121 inhibited ovarian cancer adhesion, invasion, and proliferation, whereas milciclib inhibited ovarian cancer invasion and proliferation. Using in situ kinase profiling and immunoblotting, we found that milciclib targeted Cdk2 and Cdk6, and PP-121 targeted mTOR. In vivo, all three compounds prevented ovarian cancer adhesion/invasion and metastasis, prolonged survival, and reduced omental tumor growth in an intervention study. To evaluate the clinical potential of NCGC00117362, structure-activity relationship studies were performed. Four close analogues of NCGC00117362 efficiently inhibited cancer aggressiveness in vitro and metastasis in vivo Collectively, these data show that a complex 3D culture of the TME is effective in qHTS. The three compounds identified have promise as therapeutics for prevention and treatment of ovarian cancer metastasis.

Inhibition of fascin in cancer and stromal cells blocks ovarian cancer metastasis

OBJECTIVE

Ovarian cancer (OvCa) metastasis requires the coordinated motility of both cancer and stromal cells. Cellular movement is a dynamic process that involves the synchronized assembly of f-actin bundles into cytoskeletal protrusions by fascin. Fascin directly binds f-actin and is an integral component of filopodia, lamellapodia and stress fibers. Here, we examine the expression pattern and function of fascin in the cancer and stromal cells of OvCa tumors.

METHODS

Fascin expression was evaluated in human cells and tissues using immunohistochemistry and immunofluorescence. The functional role of fascin in cancer and stromal cells was assessed with in vitro functional assays, an ex vivo colonization assay and in vivo metastasis assays using siRNA/shRNA and an inhibitor. The effect of fascin inhibition on Cdc42 and Rac1 activity was evaluated using GTPase activity assays and immunofluorescence.

RESULTS

Fascin expression was found to be higher in the stromal cell, when compared to the cancer cell, compartment of ovarian tumors. The low expression of fascin in the cancer cells of the primary tumor indicated a favorable prognosis for non-serous OvCa patients. In vitro, both knockdown and pharmacologic inhibition of fascin decreased the migration of cancer and stromal cells. The inhibition of fascin impaired Cdc42 and Rac1 activity in cancer cells, and cytoskeletal reorganization in the cancer and stromal cells. Inhibition of fascin ex vivo blocked OvCa cell colonization of human omental tissue and in vivo prevented and reduced OvCa metastases in mice. Likewise, knockdown of fascin specifically in the OvCa cells using a fascin-specific lentiviral-shRNA also blocked metastasis in vivo.

CONCLUSION

This study reveals the therapeutic potential of pharmacologically inhibiting fascin in both cancer and stromal cells of the OvCa tumor microenvironment.

Fibroblasts Mobilize Tumor Cell Glycogen to Promote Proliferation and Metastasis

Successful metastasis requires the co-evolution of stromal and cancer cells. We used stable isotope labeling of amino acids in cell culture coupled with quantitative, label-free phosphoproteomics to study the bidirectional signaling in ovarian cancer cells and human-derived, cancer-associated fibroblasts (CAFs) after co-culture. In cancer cells, the interaction with CAFs supported glycogenolysis under normoxic conditions and induced phosphorylation and activation of phosphoglucomutase 1, an enzyme involved in glycogen metabolism. Glycogen was funneled into glycolysis, leading to increased proliferation, invasion, and metastasis of cancer cells co-cultured with human CAFs. Glycogen mobilization in cancer cells was dependent on p38α MAPK activation in CAFs. In vivo, deletion of p38α in CAFs and glycogen phosphorylase inhibition in cancer cells reduced metastasis, suggesting that glycogen is an energy source used by cancer cells to facilitate metastatic tumor growth.

Neutrophils facilitate ovarian cancer premetastatic niche formation in the omentum

Metastasis of ovarian cancer frequently involves the omentum and has been described as a passive process that is governed by peritoneal fluid dynamics. Lee et al. show that metastatic tropism of ovarian cancer is actively orchestrated through the induction, by early-stage tumors, of neutrophil influx and chromatin extrusion in the premetastatic omental niche.

Ovarian cancer preferentially metastasizes to the omentum, a fatty tissue characterized by immune structures called milky spots, but the cellular dynamics that direct this tropism are unknown. Here, we identified that neutrophil influx into the omentum is a prerequisite premetastatic step in orthotopic ovarian cancer models. Ovarian tumor–derived inflammatory factors stimulated neutrophils to mobilize and extrude chromatin webs called neutrophil extracellular traps (NETs). NETs were detected in the omentum of ovarian tumor–bearing mice before metastasis and of women with early-stage ovarian cancer. NETs, in turn, bound ovarian cancer cells and promoted metastasis. Omental metastasis was decreased in mice with neutrophil-specific deficiency of peptidylarginine deiminase 4 (PAD4), an enzyme that is essential for NET formation. Blockade of NET formation using a PAD4 pharmacologic inhibitor also decreased omental colonization. Our findings implicate NET formation in rendering the premetastatic omental niche conducive for implantation of ovarian cancer cells and raise the possibility that blockade of NET formation prevents omental metastasis.

Abstract A28: Beta-escin inhibits ovarian cancer metastasis by targeting the tumor microenvironment

The high mortality rate that results from ovarian cancer (OvCa) is caused by the wide dissemination of cancer cells within the abdominal cavity. OvCa cells metastasize to the peritoneum, which is covered by a single layer of mesothelial cells, and invade into the underlying stroma, composed of extracellular matrices including fibronectin (FN) and stromal cells such as fibroblasts. Using a three-dimensional organotypic quantitative high-throughput screening platform (3D-qHTS) modeling the peritoneum, we discovered that beta-escin inhibited OvCa adhesion and invasion to the peritoneum. Beta-escin is a natural triterpenoid saponin from Chinese horse chestnut seeds and has a variety of known pharmacologic effects. We hypothesize that beta-escin targets both the cancer cells and the stromal cells to inhibit the metastatic niche. The therapeutic effects of beta-escin and horse chestnut seed extract were tested in vivo using xenograft and syngeneic models of OvCa prevention and intervention. The mechanisms of beta-escin action in cancer cells and microenvironmental cells was explored in vitro using OvCa cell lines and primary human mesothelial cells and fibroblasts, and in vivo using different mouse models of metastasis. Moreover, a collection of 160 analogs of beta-escin were gathered and screened using our 3D-qHTS platform for inhibitory activity in OvCa cell adhesion/invasion. Our results reveal that beta-escin and horse chestnut extract taken orally inhibit metastasis in both OvCa prevention and intervention models. In addition, beta-escin mechanistically depresses the pluripotent stem cell population, inflammatory cytokine secretion, HIF-1alpha expression, and fibronectin production, while it increases autophagy in the tumor microenvironment. Furthermore, three distant analogs of beta-escin inhibited OvCa metastasis, and all three are cardiac glycosides. Taken together, we reveal a potential therapeutic value for beta-escin and/or analogs of beta-escin in preventing and treating OvCa dissemination.

Citation Format: Hilary A. Kenny, Madhu Lal, Min Shen, Betul Kara, Chun-Yi Chiang, Karen Watters, Peter Hart, Marc Ferrer, Ernst Lengyel. Beta-escin inhibits ovarian cancer metastasis by targeting the tumor microenvironment. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr A28.

Unsaturated Fatty Acids Maintain Cancer Cell Stemness

Investigation of the metabolic regulation of cancer stem cells is an emerging field that offers promising approaches for identifying and targeting recalcitrant stem cell populations. In this issue of Cell Stem Cell, Li et al. (2017) indicate that increased lipid desaturation is essential to stem-like characteristics in ovarian cancer cells.

A High-Throughput Screening Model of the Tumor Microenvironment for Ovarian Cancer Cell Growth

The tumor microenvironment plays an important role in the processes of tumor growth, metastasis, and drug resistance. We have used a multilayered 3D primary cell culture model that reproduces the human ovarian cancer metastatic microenvironment to study the effect of the microenvironment on the pharmacological responses of different classes of drugs on cancer cell proliferation. A collection of oncology drugs was screened to identify compounds that inhibited the proliferation of ovarian cancer cells growing as monolayers or forming spheroids, on plastic and on a 3D microenvironment culture model of the omentum metastatic site, and also cells already in preformed spheroids. Target-based analysis of the pharmacological responses revealed that several classes of targets were more efficacious in cancer cells growing in the absence of the metastatic microenvironment, and other target classes were less efficacious in cancer cells in preformed spheres compared to forming spheroid cultures. These findings show that both the cellular context of the tumor microenvironment and cell adhesion mode have an essential role in cancer cell drug resistance. Therefore, it is important to perform screens for new drugs using model systems that more faithfully recapitulate the tissue composition at the site of tumor growth and metastasis.

Reversal of Chemoresistance in Ovarian Cancer by Co-Delivery of a P-Glycoprotein Inhibitor and Paclitaxel in a Liposomal Platform

The overexpression of permeability-glycoprotein (P-gp), an ABC transporter involved in the cellular exclusion of chemotherapeutic drugs, is a major factor in paclitaxel-resistant ovarian cancer. However, in clinical trials, co-administration of P-gp inhibitors and anticancer drugs has not resulted in the efficient reversal of drug resistance. To improve administration, we encapsulated the third-generation P-gp inhibitor tariquidar (XR-9576, XR), alone or in combination with paclitaxel (PCT) in liposomes (LP). After optimization, the liposomes demonstrated favorable physicochemical properties and the ability to reverse chemoresistance in experiments using chemosensitive/chemoresistant ovarian cancer cell line pairs. Analyzing publicly available datasets, we found that overexpression of P-gp in ovarian cancer is associated with a shorter progression-free and overall survival. In vitro, LP(XR) significantly increased the cellular retention of rhodamine 123, a P-gp substrate. LP(XR,PCT) synergistically inhibited cell viability, blocked proliferation, and caused G₂-M arrest in paclitaxel-resistant SKOV3-TR and HeyA8-MDR cell lines overexpressing P-gp. Holographic imaging cytometry revealed that LP(XR,PCT) treatment of SKOV3-TR cells induced almost complete mitotic arrest, whereas laser scanning cytometry showed that the treatment induced apoptosis. In proof-of-concept preclinical studies, LP(XR,PCT), when compared with LP(PCT), significantly reduced tumor weight (43.2% vs. 16.9%, P = 0.0007) and number of metastases (44.4% vs. 2.8%, P = 0.012) in mice bearing orthotopic HeyA8-MDR ovarian tumors. In the xenografts, LP(XR,PCT) efficiently induced apoptosis and impaired proliferation. Our findings suggest that co-delivery of a P-gp inhibitor and paclitaxel using a liposomal platform can sensitize paclitaxel-resistant ovarian cancer cells to paclitaxel. LP(XR,PCT) should be considered for clinical testing in patients with P-gp-overexpressing tumors. Mol Cancer Ther; 15(10); 2282-93. ©2016 AACR.

Molecular pathways: trafficking of metabolic resources in the tumor microenvironment

A model of tumor metabolism is proposed that describes how the complementary metabolic functions of the local stroma and the tumor cells contribute to cancer progression. Cancer cells alter the metabolism of cancer-associated fibroblasts to obtain lactate and amino acids, which are utilized for energy production, rapid growth, and resistance to chemotherapy drugs. Cancer cells use glutamine supplied by cancer-associated fibroblasts to replenish tricarboxylic acid cycle intermediates and as a nitrogen source for nucleotide synthesis. Moreover, adipocytes in the microenvironment attract cancer cells through the secretion of inflammatory cytokines and proteases. The cancer cells then induce metabolic changes in the adipocytes to acquire free fatty acids that are oxidized by cancer cells to generate energy for proliferation. Increasing knowledge about the metabolic symbiosis within the tumor has led to novel therapeutic strategies designed to restrict metabolic adaptation, including inhibiting lactate transporters and repurposing antidiabetic drugs (thiazolidinediones, metformin).

Abstract POSTER-THER-1440: Targeted delivery of doxorubicin loaded nanobins to ovarian cancer cells through the urokinase plasminogen activator system

The therapeutic efficacy of antitumor drugs is often limited by non-specific, systematic delivery. Here we report a novel targeted delivery platform designed by coupling liposomal nanobins (NB) with the urokinase plasminogen activator receptor (u-PAR) antibody (ATN-658). The urokinase system is overexpressed in epithelial ovarian cancer (OvCa) cells and is expressed only at low levels in normal cells. Doxorubicin (Dox), a FDA approved antitumor drug, had been loaded into the nanobins as a payload. The size and surface charge of the nanobins were optimized to facilitate specific binding to u-PAR expressing OvCa cells. Confocal and transmission electron microscopy showed that ATN-658-NB(Dox) was internalized in OvCa cells in a receptor-dependent manner and was released from endosomes as a function of time. This uptake could be blocked by stably down-regulating u-PAR expression in the OvCa cells using shRNA. In an orthotopic ovarian cancer model, athymic mice treated with ATN-658-NB(Dox) had a significantly greater reduction in tumor burden (0.06±0.01g versus 0.1±0.01g; p<0.001) than mice treated with NB(Dox), which was corroborated by in vivo fluorescence imaging results. A survival study showed that targeted nanobins prolonged the survival of mice by 3 days (43 days versus 40 days, median survival) as compared to untargeted nanobins. Immunoblot analysis of tumor sections showed that targeted nanobins induced apoptosis (cleaved caspase 3) and inhibited proliferation (Ki-67) more efficiently when compared to untargeted nanobins. Furthermore, tumor-targeted delivery of ATN-658-ND(Dox) was confirmed by ex vivo fluorescence imaging, FACS analysis, and confocal microscopy. Taken together, our findings show that receptor-mediated delivery of targeted nanobins to cancer cells could serve as a novel approach to ovarian cancer treatment.

Citation Format: Yilin Zhang, Elden P. Swindell, Patrick L. Hankins, Hilary A. Kenny, Thomas V. O’Halloran, Andrew P. Mazar, Ernst Lengyel. Targeted delivery of doxorubicin loaded nanobins to ovarian cancer cells through the urokinase plasminogen activator system [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr POSTER-THER-1440.

Three-dimensional modeling of ovarian cancer

New models for epithelial ovarian cancer initiation and metastasis are required to obtain a mechanistic understanding of the disease and to develop new therapeutics. Modeling ovarian cancer however is challenging as a result of the genetic heterogeneity of the malignancy, the diverse pathology, the limited availability of human tissue for research, the atypical mechanisms of metastasis, and because the origin is unclear. Insights into the origin of high-grade serous ovarian carcinomas and mechanisms of metastasis have resulted in the generation of novel three-dimensional (3D) culture models that better approximate the behavior of the tumor cells in vivo than prior two-dimensional models. The 3D models aim to recapitulate the tumor microenvironment, which has a critical role in the pathogenesis of ovarian cancer. Ultimately, findings using models that accurately reflect human ovarian cancer biology are likely to translate into improved clinical outcomes. In this review we discuss the design of new 3D culture models of ovarian cancer primarily using human cells, key studies in which these models have been applied, current limitations, and future applications.

Mesothelial cells promote early ovarian cancer metastasis through fibronectin secretion

Ovarian cancer (OvCa) metastasizes to organs in the abdominal cavity, such as the omentum, which are covered by a single layer of mesothelial cells. Mesothelial cells are generally thought to be "bystanders" to the metastatic process and simply displaced by OvCa cells to access the submesothelial extracellular matrix. Here, using organotypic 3D cultures, we found that primary human mesothelial cells secrete fibronectin in the presence of OvCa cells. Moreover, we evaluated the tumor stroma of 108 human omental metastases and determined that fibronectin was consistently overexpressed in these patients. Blocking fibronectin production in primary mesothelial cells in vitro or in murine models, either genetically (fibronectin 1 floxed mouse model) or via siRNA, decreased adhesion, invasion, proliferation, and metastasis of OvCa cells. Using a coculture model, we determined that OvCa cells secrete TGF-β1, which in turn activates a TGF-β receptor/RAC1/SMAD-dependent signaling pathway in the mesothelial cells that promotes a mesenchymal phenotype and transcriptional upregulation of fibronectin. Additionally, blocking α5 or β1 integrin function with antibodies reduced metastasis in an orthotopic preclinical model of OvCa metastasis. These findings indicate that cancer-associated mesothelial cells promote colonization during the initial steps of OvCa metastasis and suggest that mesothelial cells actively contribute to metastasis.

Abstract PR11: Ovarian cancer cells activate the mesothelium in the peritoneal microenvironment promoting fibronectin production and the early steps of metastasis

The main site of ovarian cancer (OvCa) metastasis is the omentum, which is covered by a single layer of mesothelial cells overlaying an extracellular matrix interspersed with fibroblasts (mesothelium). A 3D model of the human peritoneal surface (in vitro), fragments of human omentum (ex vivo), and a mouse xenograft model (in vivo) of OvCa were used to investigate the early effects of cancer cells on the host stromal microenvironment. Our results reveal that fibronectin is overexpressed in the stroma of more than 93% of OvCa omental metastases. OvCa cells induce fibronectin matrix assembly in omental stromal cells, and stimulate fibronectin expression in mesothelial cells. The fibronectin produced by human mesothelial stromal cells promotes OvCa cell adhesion, invasion and proliferation. Inhibition of fibronectin production in mesothelial cells or omental surface cells using a fibronectin specific siRNA decreases OvCa cell adhesion, invasion and proliferation. Genetic knock-down of fibronectin in vitro and in vivo, using fibronectinfl/fl mice, also impaired OvCa cell adhesion/invasion and metastasis. Re-analysis of an Australian OvCa study gene array data set suggested that OvCa, which highly express fibronectin, show co-activation of TGFβ1/Rac1 dependent signaling pathways. Indeed, OvCa cells increase phosphorylation of Smad2/3 in mesothelial cells upon co-culture. Inhibition of TGFβ1 in OvCa cells or inhibition of Smad 3, as well as TGFβRI or TGFβRII, in mesothelial cells resulted in decreased fibronectin production. Moreover, Rac 1 activity was increased upon the co-culture of OvCa and mesothelial cells. Subsequent inhibition of Rac 1 in mesothelial cells led to a decrease in fibronectin secretion. Our data suggest that OvCa cells regulate fibronectin expression in mesothelial cells through a TGFβ1/Rac1 dependent pathway. In vitro and in vivo therapy with a fibronectin inhibitor, ATN161, a peptide derived from the synergy region of fibronectin, reduced OvCa invasion, proliferation and metastasis. In summary, we show that abdominally metastasizing cancer cells induce fibronectin production in the peritoneal and omental microenvironment and that inhibition of this fibronectin-response prevents the first steps of peritoneal metastasis. By understanding the mechanism of OvCa metastasis we will be better able to target cells in the tumor microenvironment (i.e. mesothelial cells, fibroblasts and macrophages) during early ovarian cancer metastasis.

This abstract is also presented as Poster A60.

Citation Format: Hilary A. Kenny, Chun-Yi Chiang, Andras Ladanyi, Joshy George, David D. Bowtell, Katja Gwin, Andrew Mazar, Ernst Lengyel. Ovarian cancer cells activate the mesothelium in the peritoneal microenvironment promoting fibronectin production and the early steps of metastasis. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr PR11.

Urokinase plasminogen activator system-targeted delivery of nanobins as a novel ovarian cancer therapy

The urokinase system is overexpressed in epithelial ovarian cancer cells and is expressed at low levels in normal cells. To develop a platform for intracellular and targeted delivery of therapeutics in ovarian cancer, we conjugated urokinase plasminogen activator (uPA) antibodies to liposomal nanobins. The arsenic trioxide-loaded nanobins had favorable physicochemical properties and the ability to bind specifically to uPA. Confocal microscopy showed that the uPA-targeted nanobins were internalized by ovarian cancer cells, whereas both inductively coupled plasma optical mass spectrometry (ICP-MS) and fluorescence-activated cell sorting (FACS) analyses confirmed more than four-fold higher uptake of targeted nanobins when compared with untargeted nanobins. In a coculture assay, the targeted nanobins showed efficient uptake in ovarian cancer cells but not in the normal primary omental mesothelial cells. Moreover, this uptake could be blocked by either downregulating uPA receptor expression in the ovarian cancer cells using short-hairpin RNA (shRNA) or by competition with free uPA or uPA antibody. In proof-of-concept experiments, mice bearing orthotopic ovarian tumors showed a greater reduction in tumor burden when treated with targeted nanobins than with untargeted nanobins (47% vs. 27%; P < 0.001). The targeted nanobins more effectively inhibited tumor cell growth both in vitro and in vivo compared with untargeted nanobins, inducing caspase-mediated apoptosis and impairing stem cell marker, aldehyde dehydrogenase-1A1 (ALDH1A1), expression. Ex vivo fluorescence imaging of tumors and organs corroborated these results, showing preferential localization of the targeted nanobins to the tumor. These findings suggest that uPA-targeted nanobins capable of specifically and efficiently delivering payloads to cancer cells could serve as the foundation for a new targeted cancer therapy using protease receptors.

Epithelial ovarian cancer experimental models

Epithelial ovarian cancer (OvCa) is associated with high mortality and, as the majority (>75%) of women with OvCa have metastatic disease at the time of diagnosis, rates of survival have not changed appreciably over 30 years. A mechanistic understanding of OvCa initiation and progression is hindered by the complexity of genetic and/or environmental initiating events and lack of clarity regarding the cell(s) or tissue(s) of origin. Metastasis of OvCa involves direct extension or exfoliation of cells and cellular aggregates into the peritoneal cavity, survival of matrix-detached cells in a complex ascites fluid phase and subsequent adhesion to the mesothelium lining covering abdominal organs to establish secondary lesions containing host stromal and inflammatory components. Development of experimental models to recapitulate this unique mechanism of metastasis presents a remarkable scientific challenge, and many approaches used to study other solid tumors (for example, lung, colon and breast) are not transferable to OvCa research given the distinct metastasis pattern and unique tumor microenvironment (TME). This review will discuss recent progress in the development and refinement of experimental models to study OvCa. Novel cellular, three-dimensional organotypic, and ex vivo models are considered and the current in vivo models summarized. The review critically evaluates currently available genetic mouse models of OvCa, the emergence of xenopatients and the utility of the hen model to study OvCa prevention, tumorigenesis, metastasis and chemoresistance. As these new approaches more accurately recapitulate the complex TME, it is predicted that new opportunities for enhanced understanding of disease progression, metastasis and therapeutic response will emerge.

The first line of intra-abdominal metastatic attack: breaching the mesothelial cell layer

Iwanicki and colleagues reveal that ovarian cancer spheroids clear mesothelial cells which cover the surface of the abdominal cavity using myosin-generated force.

Abstract 5185: Ovarian cancer cells induce fibronectin production in the peritoneal microenvironment through a TGFβRI-dependent mechanism which promotes the early steps of metastasis

The high mortality rate that results from ovarian cancer (OvCa) is caused by the wide dissemination of cancer cells within the abdominal cavity. OvCa cells metastasize to the peritoneum, which is covered by a single layer of mesothelial cells, and invade into the underlying stroma, composed of extracellular matrices (ECM) including fibronectin (FN) and stromal cells such as fibroblasts. We hypothesize that cancer cells stimulate stromal cells to produce and secrete FN, initiating the metastatic niche. A 3D model of the human peritoneal surface (in vitro), pieces of human omentum (ex vivo), and a mouse xenograft model (in vivo) of OvCa were used to investigate the early effects of cancer cells on the host microenvironment. FN expression was investigated in human normal and tumor tissues using tissue microarrays, reverse-phase protein arrays, and preserved tissues. The different model systems and tissues were examined utilizing a number of techniques including; immunohistochemistry, immunofluorescence, ECM extraction, real-time quantitative PCR, and immunoblotting. Our results reveal that FN is overexpressed in the stroma of more than 90% of OvCa metastatic tissues examined. Moreover, total FN expression levels are significantly greater in omental metastases as compared to patient-matched primary tumor tissues. Additionally, the EDA+ fragment of FN is upregulated in OvCa metastases when compared to normal omental tissue. Cancer cell adhesion and proliferation are increased on omental metastases-derived ECM as compared to normal omental-derived ECM, which are significantly inhibited when the interaction between FN and its receptor, integrin α5β1 is blocked. Using the in vitro 3D model, we found that mesothelial cells and fibroblasts are the source of FN, and multiple peritoneal cancer cells induce FN production. Knocking-down FN in mesothelial cells (in vitro), sections of human omentum (ex vivo), and mouse peritoneum (in vivo) perturbs OvCa cell adhesion, invasion, and proliferation. Likewise, treatment with ATN-161, which antagonizes the interaction between FN and its receptor, integrin α5β1, also reduces OvCa cell adhesion, invasion, and proliferation in the 3D omental model (in vitro), and OvCa metastasis in the xenograft model (in vivo). OvCa cells increase phosphorylation and nuclear localization of Smad2/3 in mesothelial cells upon co-culture, and inhibition of Smad 3 as well as TGFβRI in mesothelial cells resulted in decreased FN production. Moreover, Rac 1 activity is increased upon co-culture of OvCa and mesothelial cells, and subsequent inhibition of Rac 1 in mesothelial cells lead to a decrease in FN production. Taken together, we show that abdominally metastasizing cancer cells induce FN production in the microenvironment and inhibition of this response may prevent the first steps of peritoneal metastasis.

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 5185. doi:1538-7445.AM2012-5185

Abstract 2885: Urokinase plasminogen activator system targeted delivery of arsenic trioxide loaded nanobins as a novel ovarian cancer therapeutic

That the urokinase plasminogen activator receptor (uPAR) system is constitutively expressed in primary and metastatic ovarian cancer regardless of grade or stage, while it is only weakly expressed in normal tissues, identifies it as a possible therapeutic target. Taking advantage of the tumor-specific expression of uPAR, a nanoscale liposome (nanobin, NB) was coupled with an antibody (ATN 291) against the uPAR ligand, uPA, to facilitate receptor-mediated, targeted drug delivery. The nanobin was loaded with arsenic trioxide (As2O3, in short As), since our previous results had demonstrated effective tumor uptake and induction of tumor cell apoptosis using As loaded nanobins in an orthotropic model of human triple negative breast cancer. We hypothesized that the ATN 291-conjugated nanobin (NB-uPA Ab) would allow specific cellular internalization and increase the therapeutic index of As in ovarian cancer cells. Using flow cytometry and fluorescence microscopy, we measured the cellular uptake of NB(Calcein)-uPA antibody (Ab) in HeyA8, ovarian cancer cells. The data showed a dose-dependent pattern of internalization with maximum internalization at 24 hours. Furthermore, NB-uPA Ab showed elevated cellular uptake when compared to non-targeted NB. More importantly, delivery of the targeted nanobins is uPA/uPAR dependent. High doses of ATN-291 or scuPA inhibited the cellular binding of NB-uPA Ab to HeyA8 cells. Moreover, down-regulation of uPAR expression via RNA interference in ovarian cancer cells inhibited the cellular uptake of the NB-uPA Ab. The cell viability of HeyA8 cells was significantly reduced following treatment of both non-targeted NB(As) and NB(As)-uPA Ab when compared to empty NB treatment as determined by a cytotoxicity assay. However, the cytotoxicity of NB(As)-uPA Ab is 2.1-fold more potent than the non-targeted NB(As). Taken together, these data indicate that the uPA Ab conjugated nanobins improved drug delivery and enhanced the anti-cancer effects of As, demonstrating the utility of targeting the uPA/uPAR system in ovarian cancer chemotherapeutics.

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 2885. doi:1538-7445.AM2012-2885

Adipocytes promote ovarian cancer metastasis and provide energy for rapid tumor growth

Intra-abdominal tumors, such as ovarian cancer, have a clear predilection for metastasis to the omentum, an organ primarily composed of adipocytes. Currently, it is unclear why tumor cells preferentially home to and proliferate in the omentum, yet omental metastases typically represent the largest tumor in the abdominal cavities of women with ovarian cancer. We show here that primary human omental adipocytes promote homing, migration and invasion of ovarian cancer cells, and that adipokines including interleukin-8 (IL-8) mediate these activities. Adipocyte-ovarian cancer cell coculture led to the direct transfer of lipids from adipocytes to ovarian cancer cells and promoted in vitro and in vivo tumor growth. Furthermore, coculture induced lipolysis in adipocytes and β-oxidation in cancer cells, suggesting adipocytes act as an energy source for the cancer cells. A protein array identified upregulation of fatty acid-binding protein 4 (FABP4, also known as aP2) in omental metastases as compared to primary ovarian tumors, and FABP4 expression was detected in ovarian cancer cells at the adipocyte-tumor cell interface. FABP4 deficiency substantially impaired metastatic tumor growth in mice, indicating that FABP4 has a key role in ovarian cancer metastasis. These data indicate adipocytes provide fatty acids for rapid tumor growth, identifying lipid metabolism and transport as new targets for the treatment of cancers where adipocytes are a major component of the microenvironment.

Targeting the urokinase plasminogen activator receptor inhibits ovarian cancer metastasis

PURPOSE

To understand the functional and preclinical efficacy of targeting the urokinase plasminogen activator receptor (u-PAR) in ovarian cancer.

EXPERIMENTAL DESIGN

Expression of u-PAR was studied in 162 epithelial ovarian cancers, including 77 pairs of corresponding primary and metastatic tumors. The effect of an antibody against u-PAR (ATN-658) on proliferation, adhesion, invasion, apoptosis, and migration was assessed in 3 (SKOV3ip1, HeyA8, and CaOV3) ovarian cancer cell lines. The impact of the u-PAR antibody on tumor weight, number, and survival was examined in corresponding ovarian cancer xenograft models and the mechanism by which ATN-658 blocks metastasis was explored.

RESULTS

Only 8% of all ovarian tumors were negative for u-PAR expression. Treatment of SKOV3ip1, HeyA8, and CaOV3 ovarian cancer cell lines with the u-PAR antibody inhibited cell invasion, migration, and adhesion. In vivo, anti-u-PAR treatment reduced the number of tumors and tumor weight in CaOV3 and SKOV3ip1 xenografts and reduced tumor weight and increased survival in HeyA8 xenografts. Immunostaining of CaOV3 xenograft tumors and ovarian cancer cell lines showed an increase in active-caspase 3 and TUNEL staining. Treatment with u-PAR antibody inhibited α(5)-integrin and u-PAR colocalization on primary human omental extracellular matrix. Anti-u-PAR treatment also decreased the expression of urokinase, u-PAR, β(3)-integrin, and fibroblast growth factor receptor-1 both in vitro and in vivo.

CONCLUSIONS

This study shows that an antibody against u-PAR reduces metastasis, induces apoptosis, and reduces the interaction between u-PAR and α(5)-integrin. This provides a rationale for targeting the u-PAR pathway in patients with ovarian cancer and for further testing of ATN-658 in this indication.

Abstract 2331: One of the first steps of metastasis is remodeling of the extracellular matrix microenvironment

During metastasis tumor cells initiate processes that lead to the loss of normal tissue architecture and formation of the tumor microenvironment. The main site of metastasis in ovarian cancer (OvCa) is the omentum. Little is known about the initial changes in extra-cellular matrix (ECM) during early OvCa metastasis. A 3-dimensional (D) organotypic model of the omentum was used to investigate the remodeling of the ECMs during the initial steps of OvCa metastasis. Vitronectin and fibronectin increased when OvCa cells (SKOV3ip1 and Hey A8) were added to the 3D omental model, while collagen type I decreased. Vitronectin was produced by the cancer cells and stroma, while fibronectin was produced solely by cancer cells. Collagen type I decreases in stroma and increases in OvCa when co-cultured. Vitronectin, fibronectin and collagen type I are produced by primary human mesothelial cells and fibroblasts and are present in ascites. Two immunohistochemical studies with human tumors confirmed the above findings. First during early OvCa metastasis in humans, fibronectin is present in the stroma, while vitronectin and collagen type I are present in both cancer cells and the stroma. Second, ECM localization in 20 sets of primary and omental metastasis tumors from the same patients was performed. Fibronectin was absent in the primary tumor and present in the metastatic tumor stroma, while vitronectin was produced in cancer cells and stroma in primary and metastatic tumors. Additionally, a Reverse-Phase Protein Array was performed on primary versus omental metastasis tissue from 20 postmenopausal patients with FIGO Stage III/IV, high grade papillary-serous OvCa. Fibronectin was significantly increased, while vitronectin was significantly decreased in the omental metastasis vs. primary tumor, respectively. Additional experiments revealed changes in the tumor cell cytoskeleton in conjunction with increased expression of integrins (α5β1-and αvβ3-integrin) and proteases (uPA, uPAR, MMP-2 and MMP-9). Integrins and proteases were transiently knocked down using sequence-specific siRNA. Both α5β1-integrin and MMP-2, but not αvβ3-integrin and MMP-9, were found to be necessary for the remodeling of fibronectin. Taken together, these findings reveal the initial transformation of ECM in the normal omental architecture during early OvCa metastasis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2331.

{beta}3-integrin expression on tumor cells inhibits tumor progression, reduces metastasis, and is associated with a favorable prognosis in patients with ovarian cancer

The role of the vitronectin receptor (alpha(v)beta(3)-integrin) as a tumor promoter seems well established, and, consequently, therapies that block this integrin are currently in clinical testing. We undertook the current study to determine whether alpha(v)beta(3)-integrin is an appropriate target in ovarian cancer treatment. Expression of beta(3)-integrin in SKOV3ip1 ovarian cancer cells led to the overexpression of alpha(v)beta(3)-integrin on the cell surface and increased adhesion. However, alpha(v)beta(3)-integrin-overexpressing cells showed impaired invasion, protease expression, and colony formation. These results were recapitulated in xenograft studies: alpha(v)beta(3)-integrin-expressing cells showed increased adhesion to mouse peritoneum, but the overall number of metastatic nodules (105 versus 68 tumors) and tumor weight were significantly lower than those in the parental SKOV3ip1 cells. The alpha(v)beta(3)-integrin-overexpressing cells had a decreased proliferation rate mediated by inhibition of cyclin B1 and induction of phospho-Cdc2 and p53 expression, consistent with a G(2)M cell cycle arrest. Confirming the above results, inhibition of beta(3)-integrin in cultured or primary OvCa cells decreased adhesion but increased invasion and proliferation. Patients with tumors expressing high beta(3)-integrin had significantly better disease-free and overall survival (52 months versus 27 months, P < 0.05). This study shows that alpha(v)beta(3)-integrin expression on tumor cells actually slows tumor progression and acts as a tumor suppressor. Therefore, the vitronectin receptor might not be an appropriate therapeutic target in ovarian cancer.

MMP-2 functions as an early response protein in ovarian cancer metastasis

The most common site (80%) of ovarian cancer metastasis is the omentum, a large (15 x 10 x 2 cm) peritoneal fold covering the small bowel. Because of the absence of model systems that accurately reproduce the microenvironment of the human omentum, the biological mechanism of early ovarian cancer metastasis is poorly understood. Using a new organotypic 3D culture of the omentum, we show that when cancer cells adhere, matrix-metalloproteinase (MMP)-2 is upregulated and proteolytically activated in these cells. The activated MMP-2 cleaves the matrix proteins fibronectin, vitronectin and collagen I into smaller fragments. The cleaved extra-cellular matrix (ECM) fragments then facilitate and accelerate cancer cell adhesion and invasion by binding to their cognate integrin receptors. In vivo inhibition of MMP-2 before adhesion by using a siRNA or a blocking antibody significantly reduced the number of metastasis and tumor weight in a xenograft mouse model. After metastasis had been established, blocking MMP-2 produced less of an effect. Our data identify tumor-derived proteolytically active MMP-2 as an early regulator of ovarian cancer metastasis.

The initial steps of ovarian cancer cell metastasis are mediated by MMP-2 cleavage of vitronectin and fibronectin

Most patients (80%) with ovarian cancer (OvCa) present with metastatic disease. Attachment of OvCa cells to peritoneum and omentum represents the first rate-limiting step for metastatic spread. Therefore, identifying factors regulating cell attachment in the abdominal cavity is critical to the development of therapeutic agents. We show here that MMP-2 expression was upregulated in OvCa cells upon attachment to their microenvironment. Downregulation of MMP-2 mRNA or pharmacological inhibition of MMP-2 proteolytic function, in both human OvCa primary cells and cell lines, reduced attachment of OvCa cells to a 3D organotypic model of metastatic OvCa, full human omentum or peritoneum, and in vivo to mouse peritoneum and omentum. Absence of MMP-2 in the host did not alter OvCa adhesion, as determined utilizing mice harboring homozygous null mutations in either the Mmp2 or Mmp9 genes. Conversely, adhesion induced upregulation of MMP-2 mRNA in OvCa cells. MMP-2 inhibition in OvCa cells through pharmacological or antibody treatment prior to i.p. dissemination in nude mice significantly decreased tumor growth and metastasis and extended survival. MMP-2 enhanced peritoneal adhesion of OvCa cells through cleavage of ECM proteins fibronectin (FN) and vitronectin (Vn) into small fragments and increased binding of OvCa cells to these FN and Vn fragments and their receptors, alpha5beta1 and alphaVbeta3 integrin. These findings indicate that MMP-2 expressed by metastatic OvCa cells functionally regulates their attachment to peritoneal surfaces.

Loss of E-cadherin promotes ovarian cancer metastasis via alpha 5-integrin, which is a therapeutic target

E-cadherin loss is frequently associated with ovarian cancer metastasis. Given that adhesion to the abdominal peritoneum is the first step in ovarian cancer dissemination, we reasoned that down-regulation of E-cadherin would affect expression of cell matrix adhesion receptors. We show here that inhibition of E-cadherin in ovarian cancer cells causes up-regulation of alpha(5)-integrin protein expression and transcription. When E-cadherin was blocked, RMUG-S ovarian cancer cells were able to attach and invade more efficiently. This greater efficiency could, in turn, be inhibited both in vitro and in vivo with an alpha(5)beta(1)-integrin-blocking antibody. When E-cadherin is silenced, alpha(5)-integrin is up-regulated through activation of an epidermal growth factor receptor/FAK/Erk1-mitogen-activated protein kinase-dependent signaling pathway and not through the canonical E-cadherin/beta-catenin signaling pathway. In SKOV-3ip1 ovarian cancer xenografts, which express high levels of alpha(5)-integrin, i.p. treatment with an alpha(5)beta(1)-integrin antibody significantly reduced tumor burden, ascites, and number of metastasis and increased survival by an average of 12 days when compared with IgG treatment (P < 0.0005). alpha(5)-Integrin expression was detected by immunohistochemistry in 107 advanced stage ovarian cancers using a tissue microarray annotated with disease-specific patient follow-up. Ten of 107 tissues (9%) had alpha(5)-integrin overexpression, and 39% had some level of alpha(5)-integrin expression. The median survival for patients with high alpha(5)-integrin levels was 26 months versus 35 months for those with low integrin expression (P < 0.05). Taken together, we have identified alpha(5)-integrin up-regulation as a molecular mechanism by which E-cadherin loss promotes tumor progression, providing an explanation for how E-cadherin loss increases metastasis. Targeting this integrin could be a promising therapy for a subset of ovarian cancer patients.

Thrombin induces tumor invasion through the induction and association of matrix metalloproteinase-9 and beta1-integrin on the cell surface

The procoagulatory serine protease, thrombin, is known to induce invasion and metastasis in various cancers, but the mechanisms by which it promotes tumorigenesis are poorly understood. Because the 92-kDa gelatinase (MMP-9) is a known mediator of tumor cell invasion, we sought to determine whether and how thrombin regulates MMP-9. The thrombin receptor, PAR-1, and MMP-9 are expressed in osteosarcomas, as determined by immunohistochemistry. Stimulation of U2-OS osteosarcoma cells with thrombin and a thrombin receptor-activating peptide induced pro-MMP-9 secretion as well as cell surface-associated pro-MMP-9 expression and proteolytic activity. This was paralleled by an increase in MMP-9 mRNA and MMP-9 promoter activity. Thrombin-induced invasion of U2-OS cells through Matrigel was mediated by the phosphatidylinositol 3-kinase signaling pathway and could be inhibited with an MMP-9 antibody. The stimulation of MMP-9 by thrombin was paralleled by an increase in beta1-integrin mRNA and beta1-integrin expression on the cell surface, which was also mediated by phosphatidylinositol 3-kinase and was required for invasion. Thrombin activation induced and co-localized both beta1-integrin and pro-MMP-9 on the cell membrane, as evidenced by co-immunoprecipitation, confocal microscopy, and a protein binding assay. The thrombin-mediated association of these two proteins, as well as thrombin-mediated invasion of U2-OS cells, could be blocked with a cyclic peptide and with an antibody preventing binding of the MMP-9 hemopexin domain to beta1-integrin. These results suggest that thrombin induces expression and association of beta1-integrin with MMP-9 and that the cell surface localization of the protease by the integrin promotes tumor cell invasion.

Use of a novel 3D culture model to elucidate the role of mesothelial cells, fibroblasts and extra-cellular matrices on adhesion and invasion of ovarian cancer cells to the omentum

The omentum is a major site of ovarian cancer metastasis. Our goal was to establish a three-dimensional (3D) model of the key components of the omental microenvironment (mesothelial cells, fibroblasts and extracellular matrices) to study ovarian cancer cell adhesion and invasion. The 3D model comprised of primary human fibroblasts extracted from normal human omentum, mixed with ECM and covered by a layer of primary human mesothelial cells, also from normal human omentum. After addition of ovarian cancer cells, the histological appearance of the 3D culture mimicked microscopic metastases to the omentum from patients with ovarian cancer. When ovarian cancer cells, SKOV3ip.1 and HeyA8, were applied to the 3D omental culture, 60% and 68% of all cells attached, respectively, but only 18% and 25% were able to invade. Ovarian cancer cells preferentially adhered to and invaded collagen I, followed by binding to collagen IV, fibronectin, vitronectin, laminin 10 and 1. Omental mesothelial cells significantly inhibited ovarian cancer cell adhesion and invasion, while omental fibroblasts induced adhesion and invasion. This effect is clearly mediated by direct cell-cell contact, since conditioned medium from mesothelial cells or fibroblasts has a minimal, or no, effect on ovarian cancer cell adhesion and invasion. In summary, we have established a 3D model to study the early steps of ovarian cancer metastasis to the human omentum, and found that omental mesothelial cells inhibit, while omental fibroblasts and the ECM enhance, the attachment and invasion of ovarian cancer cells.

Follicle size class contributes to distinct secretion patterns of inhibin isoforms during the rat estrous cycle

The differential production of inhibins must be exquisitely controlled at the cellular level to ensure the secretion of the appropriate ligand at specific times during the reproductive cycle. The mechanisms underlying inhibin dimer assembly, processing and secretion are not well understood. Here we verify that the secretion of inhibin A and inhibin B from the granulosa cell is discordant during the estrous cycle: discordant production or secretion of the inhibins was not observed during the pregnant mare serum gonadotropin-induced cycle. We correlated the discordant production and secretion of inhibin A and inhibin B into the serum with distinct patterns of inhibin alpha- and beta-subunit colocalization during the cycle in granulosa cells. We determined that the discordant pattern of inhibin A and inhibin B during the rat estrous cycle is due to independent populations of antral follicles making inhibin B (small antral follicles) or inhibin A (large antral follicles).

Ovarian Follicle Development Requires Smad3

Smad3 is an important mediator of the TGFβ signaling pathway. Interestingly, Smad3-deficient (Smad3−/−) mice have reduced fertility compared with wild-type (WT) mice. To better understand the molecular mechanisms underlying the reduced fertility in Smad3−/− animals, this work tested the hypothesis that Smad3 deficiency interferes with three critical aspects of folliculogenesis: growth, atresia, and differentiation. Growth was assessed by comparing the size of follicles, expression of proliferating cell nuclear antigen, and expression of cell cycle genes in Smad3−/− and WT mice. Atresia was assessed by comparing the incidence of atresia and expression of bcl-2 genes involved in cell death and cell survival in Smad3−/− and WT mice. Differentiation was assessed by comparing the expression of FSH receptor (FSHR), estrogen receptor (ER) α, ERβ, and inhibin α-, βA-, and βB-subunits in Smad3−/− and WT mice. Because growth, atresia, and differentiation are regulated by hormones, estradiol, FSH, and LH levels were compared in Smad3−/− and WT mice. Moreover, because alterations in folliculogenesis can affect the ability of mice to ovulate, the number of corpora lutea and ovulated eggs in response to gonadotropin treatments were compared in Smad3−/− and WT animals. The results indicate that Smad3 deficiency slows follicle growth, which is characterized by small follicle diameters, low levels of proliferating cell nuclear antigen, and low expression of cell cycle genes (cyclin-dependent kinase 4 and cyclin D2). Smad3 deficiency also causes atretic follicles, degenerated oocytes, and low expression of bcl-2. Furthermore, Smad3 deficiency affects follicular differentiation as evidenced by decreased expression of ERβ, increased expression of ERα, and decreased expression of inhibin α-subunits. Smad3 deficiency causes low estradiol and high FSH levels. Finally, Smad3−/− ovaries have no corpora lutea, and they do not ovulate after ovulatory induction with exogenous gonadotropins. Collectively, these data provide the first evidence that reduced fertility in Smad3−/− mice is due to impaired folliculogenesis, associated with altered expression of genes that control cell cycle progression, cell survival, and cell differentiation. The findings that Smad3−/− follicles have impaired growth, increased atresia, and altered differentiation in the presence of high FSH levels, normal expression of FSHR, and lower expression of cyclin D2, suggest a possible interaction between Smad3 and FSH signaling downstream of FSHR in the mouse ovary.

Photoperiod-dependent regulation of inhibin in Siberian hamsters: I. Ovarian inhibin production and secretion

Follicle-stimulating hormone (FSH) stimulates ovarian follicle development and the production of protein hormones including inhibin A and inhibin B. The inhibins are dimeric proteins (alpha-beta(A) or alpha-beta(B)) secreted by growing follicles that suppress FSH in a classical endocrine negative feedback loop. Siberian hamsters, Phodopus sungorus, exhibit seasonal variation in FSH levels. Given the role of inhibin in FSH regulation, we hypothesized that ovarian inhibin expression differs between animals reared in long (16 h light:8 h darkness) and short (6 h light:18 h darkness) photoperiods. To examine inhibin expression in animals housed under long or short photoperiods, hamster inhibin alpha-, beta(A)-, and beta(B)-subunits were cloned and used to detect and localize inhibin subunit mRNA in developing follicles. Ovarian inhibin alpha-subunit mRNA levels were significantly higher in long day-exposed (LD) than in short day-exposed (SD) hamsters. In addition, dimeric inhibin, as well as inhibin alpha-, beta(A)-, and beta(B)-subunit protein levels were higher in the LD than in the SD hamster ovaries.

Photoperiod-dependent regulation of inhibin in Siberian hamsters: II. Regulation of inhibin production and secretion by pregnant mare serum gonadotropin

Inhibin production differs in ovaries of Siberian hamsters (Phodopus sungorus) exposed to long days (LD) or short days (SD). We believe that seasonal differences in serum follicle-stimulating hormone contribute to this difference. However, given the profound photoperiodic differences in follicle maturation, serum gonadotropins alone may not account for all of the observed differences in inhibin processing. To test this hypothesis, we challenged LD and SD female hamsters with exogenous gonadotropins. While both groups responded with increased inhibin expression, the effects were muted in ovaries of SD females and there was no evidence of ovulation in these animals. These data indicate that the ovaries of SD females are not immediately equipped to respond to gonadotropin stimulation. More generally, these data suggest that photoperiodic history affects ovarian inhibin production and secretion in response to gonadotropins.