Growth factors in human ovarian cancer

Basics of immunotherapy for epithelial ovarian cancer

Epithelial ovarian cancer (EOC) is the most lethal of all gynecological cancers. Despite excellent responses to standard treatment in approximately 70% of patients, most of them will relapse within 5 years of initial treatment and many of them will develop chemotherapy-resistant disease. It is then important to find other means of treatment for these patients such as immunotherapy or targeted therapy. To understand immunotherapy, it is important to explain the dynamic interplay between cancer and the immune system. Compared to traditional tumor therapies, immunotherapy acts primarily on the immune system or the tumor microenvironment but not directly on the tumor cells, and it may also promote synergistic anti-tumor actions as part of a combined treatment. The aim of this narrative review is to provide a basic understanding of immunotherapy the interest of this treatment in EOC, and to present the main ongoing studies that could change patient management in the future.

A Novel ZIP4-HDAC4-VEGFA Axis in High-Grade Serous Ovarian Cancer

Simple Summary

Despite tremendous research efforts, epithelial ovarian cancer (EOC) remains one of the most difficult cancers to detect early and treat successfully for >5-year survival. We have recently shown that ZIP4, a zinc transporter, is a novel cancer stem cell (CSC) marker and a therapeutic target for EOC. The current work focuses on developing new strategies to target ZIP4 and inhibit its CSC activities in EOC. We found that cells expressing high levels of ZIP4 were supersensitive to a group of inhibitors called HDACis. One of the major targets of these inhibitors is a protein called HDAC4. We revealed the new molecular bases for the ZIP4-HDAC4 axis and tested the efficacies of targeting this axis in the lab and in mouse models. Our study provides a new mechanistic-based targeting strategy for EOC.

Abstract

We have recently identified ZIP4 as a novel cancer stem cell (CSC) marker in high-grade serous ovarian cancer (HGSOC). While it converts drug-resistance to cisplatin (CDDP), we unexpectedly found that ZIP4 induced sensitization of HGSOC cells to histone deacetylase inhibitors (HDACis). Mechanistically, ZIP4 selectively upregulated HDAC IIa HDACs, with little or no effect on HDACs in other classes. HDAC4 knockdown (KD) and LMK-235 inhibited spheroid formation in vitro and tumorigenesis in vivo, with hypoxia inducible factor-1 alpha (HIF1α) and endothelial growth factor A (VEGFA) as functional downstream mediators of HDAC4. Moreover, we found that ZIP4, HDAC4, and HIF1α were involved in regulating secreted VEGFA in HGSOC cells. Furthermore, we tested our hypothesis that co-targeting CSC via the ZIP4-HDAC4 axis and non-CSC using CDDP is necessary and highly effective by comparing the effects of ZIP4-knockout/KD, HDAC4-KD, and HDACis, in the presence or absence of CDDP on tumorigenesis in mouse models. Our results showed that the co-targeting strategy was highly effective. Finally, data from human HGSOC tissues showed that ZIP4 and HDAC4 were upregulated in a subset of recurrent tumors, justifying the clinical relevance of the study. In summary, our study provides a new mechanistic-based targeting strategy for HGSOC.

Lysophospholipid Signaling in the Epithelial Ovarian Cancer Tumor Microenvironment

As one of the important cancer hallmarks, metabolism reprogramming, including lipid metabolism alterations, occurs in tumor cells and the tumor microenvironment (TME). It plays an important role in tumorigenesis, progression, and metastasis. Lipids, and several lysophospholipids in particular, are elevated in the blood, ascites, and/or epithelial ovarian cancer (EOC) tissues, making them not only useful biomarkers, but also potential therapeutic targets. While the roles and signaling of these lipids in tumor cells are extensively studied, there is a significant gap in our understanding of their regulations and functions in the context of the microenvironment. This review focuses on the recent study development in several oncolipids, including lysophosphatidic acid and sphingosine-1-phosphate, with emphasis on TME in ovarian cancer.

Natural Killer Cell-Based Immunotherapy in Gynecologic Malignancy: A Review

Harnessing the immune system has proven an effective therapy in treating malignancies. Since the discovery of natural killer (NK) cells, strategies aimed to manipulate and augment their effector function against cancer have been the subject of intense research. Recent progress in the immunobiology of NK cells has led to the development of promising therapeutic approaches. In this review, we will focus on the recent advances in NK cell immunobiology and the clinical application of NK cell immunotherapy in ovarian, cervical, and uterine cancer.

Stromal cell-derived factor-1 (SDF-1)/CXCR4 axis enhances cellular invasion in ovarian carcinoma cells via integrin β1 and β3 expressions

Accumulating evidence has showed that stromal cell-derived factor-1 (SDF-1/CXCR4 axis played important roles in cancer metastases, but the detailed function in ovarian cancer is still largely unknown. In the present study, we determined the location of CXCR4 and lipid rafts, a specialized structure on cell membrane, in ovarian cancer tissues and ovarian cancer cell line SKOV3 cells by immunofluorescence. To analyze the role of SDF-1/CXCR4 and lipid rafts in tumor cell migration and invasion, Transwell assay and wound healing assay were also performed. Cytoflowmetry was carried out to determine the participation of integrins. Our data showed that CXCR4 and GM1 (marker of lipid rafts) were expressed in both ovarian cancer tissue and SKOV3 cells, and SDF-1 promoted the invasion and migration of SKOV3 cells, which was mediated by complete lipid rafts. Further studies uncovered that SDF-1 upregulated the expression of integrin β1 and β3, two molecules closely related with cancer metastasis. These results indicated that SDF-1 might promote the invasion and metastasis of ovarian cancer by regulating these two integrin molecules.

The Potential of the Tumor Microenvironment to Influence Apo2L/TRAIL Induced Apoptosis

Apo2L/TRAIL ligation of specific cell surface receptors (DR4 and DR5) induces apoptosis of many malignant cells with little effect on normal cells. This anti-tumor capability has been demonstrated using cell lines of many tumor types, both in vitro and in vivo when the cells are grown as xenografts. We have extended these studies to investigate the efficacy of Apo2L/TRAIL against patient tumor xenografts in SCID mice and found that the growth of many tumors, both of primary and metastatic origin, can be inhibited by Apo2L/TRAIL. The basis of resistance to Apo2L/TRAIL induced apoptosis in malignant cells and normal cells is not completely understood, but it is known that a variety of factors including hypoxia, MMPs and cytokines present in the tumor microenvironment can influence the response of malignant cells to Apo2L/TRAIL. Currently, the clinical potential of several molecules targeting the Apo2L/TRAIL receptors DR4 and DR5 is being investigated. Our goal in this review is to provide a brief overview of a number of factors that have potential to influence the response of patient tumors to Apo2L/TRAIL.

ERK activation and nuclear signaling induced by the loss of cell/matrix adhesion stimulates anchorage-independent growth of ovarian cancer cells

Ovarian cancer metastasis involves the sloughing of epithelial cells from the ovary into the peritoneal cavity, where the cells can survive and proliferate in peritoneal ascites under anchorage-independent conditions. For normal epithelial cells and fibroblasts, cell adhesion to the extracellular matrix is required to prevent apoptosis and for proper activation and nuclear signaling of the ERK MAP kinase. The mechanisms of ERK regulation by adhesion have been determined by our lab and others. In this report, we elucidate a novel means of ERK regulation by cellular adhesion in ovarian cancer cells. We demonstrate that ERK and its activator MEK are robustly stimulated after cell detachment from a substratum in several ovarian cancer cell lines, but not a benign ovarian cell line, independent of serum and FAK or PAK activity. MEK and ERK activation was sustained for 48 h after detachment, while activation by serum or growth factors in adherent cells was transient. Re-attachment of suspended ovarian cells to fibronectin restored basal levels of MEK and ERK activity. ERK activity in suspended cells was dynamically controlled through an autocrine stimulatory pathway and prevalent phosphatase activity. Suspended cells demonstrated higher levels of ERK nuclear signaling to Elk1 compared to adherent cells. Inhibition of ERK activation with the MEK inhibitor U0126 had minor effects on adherent cell growth, but greatly decreased growth in soft agar. These data demonstrate a unique regulation of ERK by cellular adhesion and suggest a mechanism by which ERK may regulate anchorage-independent growth of metastatic ovarian cancer cells.

Characterization of ovarian cancer ascites on cell invasion, proliferation, spheroid formation, and gene expression in an in vitro model of epithelial ovarian cancer

At least one third of all cases of epithelial ovarian cancer are associated with the production of ascites, although its effect on tumor cell microenvironment remains poorly understood. This study addresses the effect of the heterologous acellular fraction of ovarian cancer-derived ascites on a cell line (OV-90) derived from the chemotherapy-naïve ovarian cancer patient. Ascites were assayed for their effect on cell invasion, growth, and spheroid formation. When compared to either no serum or 5% serum, ascites fell into one of two categories: stimulatory or inhibitory. RNA from OV-90 cells exposed to selected ascites were arrayed on an Affymetrix HG-U133A GeneChip. A supervised analysis identified a number of differentially expressed genes and quantitative polymerase chain reaction validation based on OV-90 cells exposed to 54 independent ascites demonstrated that stimulatory ascites affected the expression of ISGF3G, TRIB1, MKP1, RGS4, PLEC1, and MOSPD1 genes. In addition, TRIB1 expression was shown to independently correlate with prognosis when its expression was ascertained in an independent set of primary cultures established from ovarian ascites. The data support the validity of the strategy to uncover molecular events that are associated with tumor cell behavior and highlight the impact of ascites on the cellular and molecular parameters of ovarian cancer.

A proteome resource of ovarian cancer ascites: integrated proteomic and bioinformatic analyses to identify putative biomarkers

Epithelial ovarian cancer is the most lethal gynecological malignancy, and disease-specific biomarkers are urgently needed to improve diagnosis, prognosis, and to predict and monitor treatment efficiency. We present an in-depth proteomic analysis of selected biochemical fractions of human ovarian cancer ascites, resulting in the stringent and confident identification of over 2500 proteins. Rigorous filter schemes were applied to objectively minimize the number of false-positive identifications, and we only report proteins with substantial peptide evidence. Integrated computational analysis of the ascites proteome combined with several recently published proteomic data sets of human plasma, urine, 59 ovarian cancer related microarray data sets, and protein-protein interactions from the Interologous Interaction Database I (2)D ( http://ophid.utoronto.ca/i2d) resulted in a short-list of 80 putative biomarkers. The presented proteomics analysis provides a significant resource for ovarian cancer research, and a framework for biomarker discovery.

SPARC inhibits LPA-mediated mesothelial-ovarian cancer cell crosstalk

The interplay between peritoneal mesothelial cells and ovarian cancer cells is critical for the initiation and peritoneal dissemination of, and ascites formation in, ovarian cancer. The production of lysophosphatidic acid (LPA) by both peritoneal mesothelial cells and ovarian cancer cells has been shown to promote metastatic phenotype in ovarian cancer. Herein, we report that exogenous addition or ectopic overexpression of the matricellular protein SPARC (secreted protein acidic and rich in cysteine) significantly attenuated LPA-induced proliferation, chemotaxis, and invasion in both highly metastatic SKOV3 and less metastatic OVCAR3 ovarian cancer cell lines. SPARC appears to modulate these functions, at least in part, through the regulation of LPA receptor levels and the attenuation of extracellular signal-regulated kinase (ERK) 1/2 and protein kinase B/AKT signaling. Moreover, our results show that SPARC not only significantly inhibited both basal and LPA-induced interleukin (IL) 6 production in both cell lines but also attenuated IL-6-induced mitogenic, chemotactic, and proinvasive effects, in part, through significant suppression of ERK1/2 and, to a lesser extent, of signal transducers and activators of transcription 3 signaling pathways. Our results strongly suggest that SPARC exerts a dual inhibitory effect on LPA-induced mesothelial-ovarian cancer cell crosstalk through the regulation of both LPA-induced IL-6 production and function. Taken together, our findings underscore the use of SPARC as a potential therapeutic candidate in peritoneal ovarian carcinomatosis.

Disaggregation and invasion of ovarian carcinoma ascites spheroids

BACKGROUND

Malignant ascites often develops in advanced stages of ovarian carcinoma, consisting of single and aggregated tumor cells, or spheroids. Spheroids have commonly been used as tumor models to study drug efficacy, and have shown resistance to some chemotherapies and radiation. However, little is known about the adhesive or invasive capabilities of spheroids, and whether this particular cellular component of the ascites can contribute to dissemination of ovarian cancer. Here, we examined the invasive ability of ascites spheroids recovered from seven ovarian carcinoma patients and one primary peritoneal carcinoma (PPC) patient.

METHODS

Ascites spheroids were isolated from patients, purified, and immunohistochemical analyses were performed by a pathologist to confirm diagnosis. In vitro assays were designed to quantify spheroid disaggregation on a variety of extracellular matrices and dissemination on and invasion into normal human mesothelial cell monolayers. Cell proliferation and viability were determined in each assay, and statistical significance demonstrated by the student's t-test.

RESULTS

Spheroids from all of the patients' ascites samples disaggregated on extracellular matrix components, with the PPC spheroids capable of complete disaggregation on type I collagen. Additionally, all of the ascites spheroid samples adhered to and disaggregated on live human mesothelial cell monolayers, typically without invading them. However, the PPC ascites spheroids and one ovarian carcinoma ascites spheroid sample occasionally formed invasive foci in the mesothelial cell monolayers, suggestive of a more invasive phenotype.

CONCLUSION

We present here in vitro assays using ascites spheroids that imitate the spread of ovarian cancer in vivo. Our results suggest that systematic studies of the ascites cellular content are necessary to understand the biology of ovarian carcinoma.

Stromal cell-derived factor-1alpha (SDF-1alpha/CXCL12) stimulates ovarian cancer cell growth through the EGF receptor transactivation

Ovarian cancer (OC) is the leading cause of death in gynecologic diseases in which there is evidence for a complex chemokine network. Chemokines are a family of proteins that play an important role in tumor progression influencing cell proliferation, angiogenic/angiostatic processes, cell migration and metastasis, and, finally, regulating the immune cells recruitment into the tumor mass. We previously demonstrated that astrocytes and glioblastoma cells express both the chemokine receptor CXCR4 and its ligand stromal cell-derived factor-1 (SDF-1), and that SDF-1alpha treatment induced cell proliferation, supporting the hypothesis that chemokines may play an important role in tumor cells' growth in vitro. In the present study, we report that CXCR4 and SDF-1 are expressed in OC cell lines. We demonstrate that SDF-1alpha induces a dose-dependent proliferation in OC cells, by the specific interaction with CXCR4 and a biphasic activation of ERK1/2 and Akt kinases. Our results further indicate that CXCR4 activation induces EGF receptor (EGFR) phosphorylation that in turn was linked to the downstream intracellular kinases activation, ERK1/2 and Akt. In addition, we provide evidence for cytoplasmic tyrosine kinase (c-Src) involvement in the SDF-1/CXCR4-EGFR transactivation. These results suggest a possible important "cross-talk" between SDF-1/CXCR4 and EGFR intracellular pathways that may link signals of cell proliferation in ovarian cancer.

Expression of the endothelial cell differentiation gene 7 (EDG-7), a lysophosphatidic acid receptor, in ovarian tumor

AIM

Lysophosphatidic acid (LPA) has received attention as a mitogen because the physiologically active lipid stimulates ovarian cancer cell growth by interacting with specific receptors, the endothelial cell differentiation gene (EDG) family. In the present study, we have investigated the expression of EDG-7 mRNA, part of the EDG family, in both human ovarian cancers and established human ovarian cancer cell lines.

METHODS

RNA was extracted from six ovarian cancer cell lines and multiple cancerous and normal ovarian tissues. The expression of EDG-7 mRNA was measured using reverse transcription-polymerase chain reaction and northern blotting, using reduced glyceraldehyde-phosphate dehydrogenase and S26 as internal controls.

RESULTS

Of the cell lines tested, EDG-7 mRNA was expressed most intensely in CRL-11731 and CRL-1572 and at a lesser but still substantial level in CRL-11732. The expression of EDG-7 mRNA was limited in MCAS, CRL-11730 and TYKnu. In the ovarian cancer tissues, EDG-7 mRNA was expressed most highly in endometrioid adenocarcinoma and serous cystadenocarcinoma. The expression of EDG-7 mRNA was limited in clear cell adenocarcinoma and undetectable in mucinous cystadenocarcinoma.

CONCLUSIONS

The intense EDG-7 expression in ovarian cancers suggests that the relation between LPA and EDG-7 (an LPA receptor) is involved in cancer cell growth and proliferation in some histologic subtypes of ovarian cancer.

Ovarian carcinoma spheroids disaggregate on type I collagen and invade live human mesothelial cell monolayers

Ovarian carcinoma patients frequently develop malignant ascites containing single and aggregated tumor cells, or spheroids. Spheroids have been shown to be resistant to many therapies, but their contribution to ovarian cancer dissemination remains undetermined. We have previously shown that ascites spheroids adhere to extracellular matrix (ECM) proteins and live human mesothelial cells via beta1 integrin subunits. Here, we assessed the ability of spheroids that were generated from the human ovarian carcinoma cell line NIH:OVCAR5 to disseminate and invade in vitro. Spheroids were seeded on ECM proteins for 24 h. While laminin and type IV collagen stimulated some cell migration, spheroids completely disaggregated on type I collagen substrates. A monoclonal antibody against the beta1 integrin subunit significantly inhibited disaggregation on all proteins tested. To test their invasive ability, spheroids were added to monolayers of live human LP9 mesothelial cells. Within 24 h, the spheroids adhered and disaggregated on top of the monolayers, and within a week had established foci of invasion encompassing a 200-fold larger surface area. Addition of a monoclonal antibody against the beta1 integrin subunit drastically reduced spheroid invasion into the mesothelial cell monolayers. GM 6001, a broad-scale matrix metalloproteinase inhibitor, also significantly blocked spheroid invasion into the mesothelial cell monolayers. Epsilon-amino-N-caproic acid, a serine protease inhibitor, partially inhibited spheroid invasion. Based on their ability to attach to, disaggregate on, and invade into live human mesothelial cell monolayers, spheroids should thus be regarded as potential contributors to the dissemination of ovarian cancer.

Clinical significance of heparin-binding epidermal growth factor-like growth factor in peritoneal fluid of ovarian cancer

Epidermal growth factor receptor (EGFR) has been implicated in tumour growth and extension of ovarian cancer. Peritoneal fluid in ovarian cancer patients contains various growth factors that can promote tumour growth and extension. In order to investigate the clinical significance of EGFR ligands as activating factors of ovarian cancer, we examined the cell proliferation-promoting activity and the level of EGFR ligands in peritoneal fluid obtained from 99 patients. Proliferation-promoting activity in peritoneal fluid from 63 ovarian cancer patients (OVCA) was much higher than peritoneal fluid from 18 ovarian cyst patients (OVC) and 18 normal ovary patients (NO), and the activity was suppressed only by antibodies against EGFR or heparin-binding epidermal growth factor (HB-EGF). A large difference was observed in the level of EGFR ligands between HB-EGF and TGF-α or amphiregulin. The concentration of HB-EGF in OVCA significantly increased compared to that in OVC or NO (P<0.01). No significant difference in the concentration of TGF-α and amphiregulin was found between the OVCA and NO or OVC groups. In peritoneal fluid, HB-EGF is sufficiently elevated to activate cancer cells even at an early stage of OVCA. These results suggested that HB-EGF in peritoneal fluid might play a key role in cell survival and in the proliferation of OVCA.

Translocation of lysophosphatidic acid phosphatase in response to gonadotropin-releasing hormone to the plasma membrane in ovarian cancer cell

OBJECTIVE

Lysophosphatidic acid mediates proliferative and/or morphologic effects on multiple cell lineages, which include ovarian cancer cells. Lysophosphatidic acid hydrolysis limits the duration of lysophosphatidic acid's action. We examined hormonal translocation of lipid phosphate phosphatase type 3 to the plasma membrane in gonadotropin-releasing hormone-responsive ovarian cancers.

STUDY DESIGN

Ovarian cancers that were removed surgically and the ovarian cancer cell lines Caov-3 and SK-OV-3 were examined. Lipid phosphate phosphatase type 3 protein and activity in plasma membranes were assessed by immunohistochemical staining with lipid phosphate phosphatase type 3-specific antibodies and by the measurement of the conversion of exogenous [(3)H-oleoyl]lysophosphatidic acid to mono[(3)H-oleoyl]glycerol, respectively.

RESULTS

In ovarian cancers that were removed surgically, the cell surface staining and activity measurements indicated that a portion of the enzyme was localized to the plasma membrane. In Caov-3 cells and SK-OV-3 cells, lipid phosphate phosphatase type 3 protein was present both in the cytoplasm and at the plasma membrane. Treatment of the cells with a gonadotropin-releasing hormone agonist buserelin produced a rapid and progressive translocation of lipid phosphate phosphatase type 3 protein to the plasma membrane, with a concomitant loss of cytoplasmic staining. The enzyme activity in plasma membrane was also increased when the cell lines were exposed to the gonadotropin-releasing hormone agonist in intact cells before the assay of the cell membranes.

CONCLUSION

These findings support the presence of lipid phosphate phosphatase type 3 in plasma membrane of ovarian cancers and provide for the ability of agonists (such as gonadotropin-releasing hormone) to induce the translocation of lipid phosphate phosphatase type 3 to plasma membrane in ovarian cancer cells.

Ovarian carcinoma ascites spheroids adhere to extracellular matrix components and mesothelial cell monolayers

OBJECTIVES

Ovarian carcinoma cells form multicellular aggregates, or spheroids, in the peritoneal cavity of patients with advanced disease. The current paradigm that ascites spheroids are non-adhesive leaves their contribution to ovarian carcinoma dissemination undefined. Here, spheroids obtained from ovarian carcinoma patients' ascites were characterized for their ability to adhere to molecules encountered in the peritoneal cavity, with the goal of establishing their potential to contribute to ovarian cancer spread.

METHODS

Spheroids were recovered from the ascites fluid of 11 patients with stage III or stage IV ovarian carcinoma. Adhesion assays to extracellular matrix (ECM) proteins and human mesothelial cell monolayers were performed for each of the ascites spheroid samples. Subsequently, inhibition assays were performed to identify the cell receptors involved.

RESULTS

Most ascites samples adhered moderately to fibronectin and type I collagen, with reduced adhesion to type IV collagen and laminin. Monoclonal antibodies against the beta1 integrin subunit partially inhibited this adhesion. Ascites spheroids also adhered to hyaluronan. Additionally, spheroids adhered to live, but not fixed, human mesothelial cell monolayers, and this adhesion was partially mediated by beta1 integrins.

CONCLUSIONS

The cellular content of the ascites fluid has often been considered non-adhesive, but our findings are the first to suggest that patient-derived ascites spheroids can adhere to mesothelial extracellular matrix via beta1 integrins, indicating that spheroids should not be ignored in the dissemination of ovarian cancer.

Differential expression of interleukins IL-13 and IL-15 in normal ovarian tissue and ovarian carcinomas

OBJECTIVE

To determine the temporal and spatial expression of interleukins (IL)-13 and IL-15 in ovarian carcinoma compared to normal ovarian tissue.

METHODS

Quantitative RT-PCR, ELISA and immunohistochemistry.

RESULTS

Q-RT-PCR, ELISA and immunohistochemical analysis indicates that IL-13 and IL-15 mRNA and protein are expressed in normal ovary at various phases of the menstrual cycle with immunoreactive proteins detected in granulosa/theca and luteal cells and to a lesser extent in stromal cells and surface epithelial cells. Compared to normal ovary, ovarian carcinoma expresses elevated levels of IL-13 and IL-15 mRNA, with higher IL-13 expression in primary vs. metastatic tumors. IL-13 and IL-15 protein expression was also higher in the tumor tissues compared to ascites. In normal ovary, ovarian tumors and ascites, the ratio of IL-13/IL-15 favored IL-13. Immunoreactive IL-13 and IL-15 proteins were localized primarily in the tumor cells and infiltrated inflammatory cells with increased intensity with disease stage.

CONCLUSION

Normal ovary and ovarian tumors express IL-13 and IL-15 and pattern of their expression in carcinomas suggests that these cytokines may function in various ovarian cellular activities including inflammatory/immune responses that are integrated cellular events taking place in normal ovary and ovarian tumors.

Evidence for tight coupling of Gi protein-mediated lysophosphatidic acid receptor to stimulated cytokine production in ovarian cancer cell

OBJECTIVE

Lysophosphatidic acid stimulates the proliferation of ovarian cancer cell through specific members of the guanosine triphosphate-binding protein-coupled receptor family. We attempted to identify the guanosine triphosphate-binding protein subtypes that are linked to lysophosphatidic acid receptor-stimulated production of cytokine, which are involved potentially in ovarian cancer development.

STUDY DESIGN

Cytokine assay kits were used to determine interleukin-6, interleukin-8, and tumor necrotic factor-alpha that were produced from Caov-3 and SK-OV3 ovarian cancer cell lines. Thealpha-subunit of Gi was detected by pertussis toxin-catalyzed adenosine diphosphate ribosylation from nicotinamide adenine dinucleotide in isolated plasma membrane.

RESULTS

Pertussis toxin, but not cholera toxin, brought about adenosine diphosphate ribosylation of Galphai of 41 kd in the plasma membrane. Incubation with lysophosphatidic acid and nonhydrolyzable guanosine triphosphate analog decreased the adenosine diphosphate-ribosylation activity in a dose-dependent manner; a one half-maximal effect occurred with 10 micromol/L lysophosphatidic acid. The apparent inhibition by lysophosphatidic acid of the adenosine diphosphate ribosylation demonstrated that lysophosphatidic acid resolved the alpha-subunit of the Gi to guanosine triphosphate-bound form in the membranes. Pretreatment of the ovarian cancer cells with the pertussis toxin completely inhibited lysophosphatidic acid-stimulated production of interleukin-6, interleukin-8 and tumor necrosis factor-alpha. The lysophosphatidic acid-stimulated cytokine production was dose-dependent with a one half-maximal effect at 10 micromol/L. Phosphatidic acid and ceramide 1-phosphate had no effect on the lysophosphatidic acid action on cytokine expression.

CONCLUSION

These data demonstrate the coupling of lysophosphatidic acid receptor to Gi protein subfamily in ovarian cancer cell. The Gi that couples lysophosphatidic acid receptor to the effector may define the differences in the signaling pathways of lysophosphatidic acid-activated cytokine expression and proliferation.

Potential for TRAIL as a Therapeutic Agent in Ovarian Cancer

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is known to induce apoptosis, otherwise known as programmed cell death, in many malignant cells without any known detrimental effects to normal cells. These aspects of TRAIL indicate the potential of TRAIL as a therapeutic agent in cancer. Ovarian cancer remains the deadliest gynecologic malignancy and is the fourth leading cause of death due to cancer in women. However, it has been shown in studies that ovarian cancer cells are sensitive to TRAIL-induced cell death when treated with TRAIL alone or in combination with chemotherapeutic agents. TRAIL signals through two death receptors, TRAIL-R1 and TRAIL-R2, to induce apoptosis. TRAIL also binds to two other cell surface receptors, TRAIL-R3 and TRAIL-R4, which do not have intracellular death domains and therefore do not transmit the apoptotic signal upon ligation with TRAIL. It has been shown that a chemokine, interleukin-8 (IL-8), may play a role in ovarian tumor progression due to its elevated presence in the fluid surrounding ovarian cancer tissues. Possible roles for IL-8 in ovarian tumorigenesis include angiogenesis and metastasis. Because the mechanism of regulation for TRAIL-induced apoptosis needs to be clarified, the role of IL-8 in TRAIL-induced apoptosis of ovarian cancer cells was studied. Results showed that the presence of IL-8 regulates cell-surface expression of TRAIL receptors in ovarian cancer cell lines in vitro. There may be a role for the p38 mitogen-activated protein kinase (MAPK) pathway in TRAIL-induced apoptosis of ovarian cancer cell.

Induction of FGF receptor 2-IIIb expression and response to its ligands in epithelial ovarian cancer

Epithelial ovarian cancers (EOCs) arise in the Ovarian Surface Epithelium (OSE). This tissue is a simple, poorly committed mesothelium which exhibits characteristics of epithelial and mesenchymal cells when grown in culture. In contrast, EOCs frequently exhibit properties of complex epithelial tissues of the female reproductive tract, such as oviductal, endometrial and cervical epithelia, and show induction of expression of epithelial markers such as E-cadherin. Fibroblast Growth Factor Receptor 2 isoform IIIb (FGF receptor 2-IIIb) is a spliced variant of FGF receptor 2 that binds the ligands FGF-1 and FGF-7 with high affinity, and is expressed exclusively by epithelial cells. We have studied the expression of FGF receptor 2-IIIb and its ligands in primary cultures of normal human OSE, EOC cell lines and snap frozen tissue from EOCs. Expression of FGF receptor 2-IIIb mRNA is undetectable in normal OSE, but is expressed in 16/20 (80%) of EOCs. FGFs 1 and 7 mRNAs are expressed in normal OSE, whilst only 4/20 (20%) and 12/20 (60%) of EOCs demonstrated expression for these ligands respectively. However, FGF-7 protein was detected in 70% (mean level=0.7 ng/ml) of ascitic fluids obtained from patients with EOC. FGFs 1 and 7 stimulate DNA synthesis in EOC cell lines that express FGF receptor 2-IIIb. Moreover, DNA synthesis in these cell lines can be partially blocked by blocking antisera to FGFs 1 and 7. It is suggested that induction of expression of FGF receptor 2-IIIb may play a role in the development of EOCs by rendering the OSE susceptible to paracrine and/or autocrine stimulation by its requisite FGF ligands.

Lysophospholipids increase interleukin-8 expression in ovarian cancer cells

OBJECTIVES

We have previously described that bioactive lysophospholipids-lysophosphatidic acid (LPA), sphingosine 1-phosphate (S1P), and sphingosylphosphorylcholine (SPC)-are present in ascitic fluids from patients with ovarian cancer. To understand the role of these lipids in ovarian cancer, we investigated the effects of these lipids on interleukin-8 (IL-8) production in ovarian cancer cells. IL-8 is a proinflammatory and proangiogenic factor, which is potentially involved in ovarian cancer development.

METHODS

The Clontech PCR-Select cDNA subtraction method (Clontech Laboratories, Inc., Palo Alto, CA) was used to identify genes potentially regulated by LPA in HEY and OCC1 ovarian cancer cell lines. Northern blot analysis was used to confirm and examine IL-8 mRNA regulation by lysolipids. Enzyme-linked immunosorbent assay (ELISA) was used for detecting secreted IL-8.

RESULTS

We describe here that LPA, S1P, and SPC increased mRNA levels (2- to 7-fold) and protein secretion (2- to 12-fold) of IL-8 from ovarian cancer cells (HEY, OCC1, and SKOV3) in vitro. These regulations were both dose- and time-dependent. All three lipids increased the stability IL-8 mRNA in HEY cells. In contrast to malignant ovarian cancer cells, immortalized human ovarian epithelial cells did not respond to any of these lipids to increase the secretion of IL-8, although these cells secreted similar basal levels of IL-8 (310 pg/ml/10,000 cells). Two breast cancer cell lines (MCF7 and T47D) secreted lower basal levels of IL-8 (48-80 pg/ml/10,000 cells), compared with ovarian cancer cells (200-500 pg/ml/10,000 cells). MCF7 cells responded to LPA, but not S1P and SPC, by increasing the secretion of IL-8. T47D and MCF10A, an immortalized breast cell line, did not respond to LPA, S1P, or SPC to increase IL-8 secretion.

CONCLUSIONS

LPA, S1P, and SPC regulate the mRNA and protein levels of the proinflammatory and proangiogenic factor IL-8 in ovarian cancer cells. The pathological significance of these regulations in ovarian cancer remains to be further investigated.

Electrospray ionization mass spectrometry analysis of lysophospholipids in human ascitic fluids: comparison of the lysophospholipid contents in malignant vs nonmalignant ascitic fluids

Lysophospholipids (lyso-PLs), including various glycerol-based and sphingosine-based lysophospholipids, play important roles in many biochemical, physiological, and pathological processes. The classical methods to analyze these lipids involve gas chromatography and/or high-performance liquid chromatography, which are time-consuming, cumbersome, and sometimes inaccurate due to the incomplete separation of closely related lipid species. We now describe the quantitative analysis of lyso-PLs in ascites samples from patients with ovarian cancer using electrospray ionization spectrometry. Three new classes of lyso-PL molecules are detected: alkyl-LPA, alkenyl-LPA, and methylated lysophosphatidylethanolamine. Importantly, the following lysophospholipid species are significantly increased in ascites from patients with ovarian cancer, compared to patients with nonmalignant diseases (e.g., liver failure): LPA (including acyl-, alkyl-, and alkenyl-LPA species), lysophosphatidylinositol, and sphingosylphosphorylcholine. Lysophosphorylcholine contents are also significantly different among ascitic fluids from the two groups of patients. However, the total phosphate content in ascites samples from patients with ovarian cancer is not significantly different compared to that from patients with nonmalignant disease.

A gonadotropin-releasing hormone-responsive phosphatase hydrolyses lysophosphatidic acid within the plasma membrane of ovarian cancer cells

Lysophosphatidic acid (LPA) mediates pleomorphic effects on multiple cell lineages, including an increased proliferative response of ovarian cancer cells both in vitro and in vivo, at least in part through the novel expression of LPA receptors. Thus, LPA hydrolysis is necessary to limit the duration of LPA's action on multiple cell types, including ovarian cancer cells. We determined the principal mechanism of LPA hydrolysis by ovarian cancer cells and its regulation by GnRH, which is known to have antiproliferative actions on ovarian carcinomas. LPA-hydrolyzing activity in cell membranes of ovarian cancer specimens was assessed by measuring the conversion of exogenous [3H-oleoyl]LPA to [3H]oleic acid or mono[3H-oleoyl]glycerol. Approximately 98% of LPA hydrolysis could be accounted for by the dephosphorylation of LPA to yield monoglyceride, with the deacylation reaction accounting for less than 1% of LPA hydrolysis. The phosphatase activity in the plasma membrane ovarian cancer cells was approximately 2.5- and 8-fold higher than those in microsome and homogenate fractions, respectively. The membrane phosphatase was Mg2+ independent and insensitive to inhibition by N-ethylmaleimide, characteristics suggestive of phosphatidic acid phosphatase activity. Incubation of membranes from GnRH receptor-positive ovarian cancer specimens with the GnRH agonist, buserelin, induced a dose-dependent increase in LPA phosphatase activity, with a half-maximal effect occurring with 30 nmol/L buserelin. The stimulatory action of buserelin could be neutralized by displacement of GnRH from its receptor by the GnRH antagonist, antide. The plasma membranes from GnRH receptor-negative ovarian cancer specimens did not respond to GnRH stimulation. LPA phosphatase activity was also increased when the ovarian cancer cell line Caov-3 was exposed to GnRH agonist in intact cells before assay of cell membranes. These data demonstrate that LPA is hydrolyzed in the plasma membrane of ovarian cancer cells by the action of LPA phosphatase and provide initial evidence for functional coupling of LPA phosphatase to GnRH receptor occupancy.

Chemokine receptors CXCR-1/2 activate mitogen-activated protein kinase via the epidermal growth factor receptor in ovarian cancer cells

Ovarian cancer typically disseminates widely in the abdomen, a characteristic that limits curative therapy. The mechanisms that promote ovarian cancer cell migration are incompletely understood. We studied model SK-OV-3 ovarian cancer cells and observed robust expression of the alpha chemokine receptors CXCR-1 and CXCR-2. Interleukin-8 (IL-8) treatment caused shape changes in the cells, with membrane ruffling and formation/retraction of thin actin-like projections, as detected by time-lapse microscopy. Stimulation of the CXCR-1/2 receptors by human interleukin 8 (IL-8) rapidly activated the p44/42 mitogen-activated protein (extracellular signal-regulated kinase (Erk1/2)) kinase pathway. Treatment of SK-OV-3 cells with the inhibitors genestein and herbimycin A indicated that tyrosine kinases were involved in the IL-8 activation of Erk1 and Erk2. Of note, IL-8 induced transient phosphorylation of the epidermal growth factor (EGF) receptor and its association with the adaptor molecules Shc and Grb2. This transactivation of the EGF receptor was dependent on intracellular Ca(2+) mobilization. Furthermore AG1478, a specific inhibitor of the EGF receptor kinase, blocked Erk1 and Erk2 activation. c-Src kinase was not involved in the IL-8-mediated phosphorylation of the EGF receptor, but was critical for Shc phosphorylation and downstream Erk1/2 kinase activation. These results suggest important "cross-talk" between chemokine and growth factor pathways that may link signals of cell migration and proliferation in ovarian cancer.

Expression and function of EGF-related peptides and their receptors in gynecological cancer--from basic science to therapy

EGF-related peptides and their receptors play an important, but not fully understood role, both, in epithelial physiology and pathophysiology but also in human tumor carcinogenesis and tumor behavior, respectively. Overexpression of EGF-related growth factors from normal epithelium to carcinomas has been demonstrated for several human tissues such as breast, endometrium, cervix and ovary. Additionally, the differential overexpression of EGFR or erb B-2 in various malignancies has already proven to be efficacious in stratifying patients with respect to a poor prognosis. These data suggest that EGF-related growth factors, erb B receptors or signaling proteins that function either upstream or downstream from these receptors may represent novel targets for selective tumor therapy. In the future, conventional chemotherapy regimes will ultimately be wedded to more biologically-oriented therapies. One important target for these novel therapeutic approaches in solid tumors will be the EGF-related growth factors and their receptors.

Malignant effusions contain lysophosphatidic acid (LPA)-like activity

BACKGROUND

Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are bioactive phospholipids with mitogenic and growth factor-like activities that act via specific cell-surface receptors present in many normal and transformed cell types. LPA has recently been implicated as a growth factor present in ascites of ovarian cancer patients. The presence of LPA-like activity and the hypothesis that levels of this bioactivity in effusions of ovarian cancer patients are higher than those in effusions of other cancer patients was studied.

MATERIALS AND METHODS

A neurite retraction bioassay in a neuroblastoma cell line previously developed for in vitro detection of LPA activity on cell lines was employed and bioactivity was expressed in virtual LPA-equivalent levels. LPA-equivalent levels were tested in effusions of 62 patients with a range of malignancies, including 13 ovarian cancer patients. Biochemical and clinical parameters were evaluated for correlations with LPA-equivalent levels.

RESULTS

Average LPA-equivalent levels were 50.2 microns (range 5.4-200) for all patients, and 94.5 microns (range 15-200) for ovarian cancer patients (P = 0.004). There were no additional independent significant correlations between LPA-equivalent levels in effusions and a range of other biochemical and clinical characteristics.

CONCLUSION

These data suggest a role for LPA-like lipids in the peritoneal spread of ovarian cancer and possibly that of other predominantly intraperitoneal malignancies.