The stem-cell profile of ovarian surface epithelium is reproduced in the oviductal fimbriae, with increased stem-cell marker density in distal parts of the fimbriae

Walthard Cell Nests/Transitional Cell Metaplasia in Distal Fallopian Tubes and Pelvic Peritoneum Derived From Reserve Cells

Transitional cell metaplasia (TCM) resembling benign urothelium is commonly seen around the distal fallopian tube and/or neighboring mesothelial surface; however, its histogenesis remains largely unknown. We observed the emergence of a cytokeratin (CK) 17-positive reserve cell layer in early TCM foci beneath the tubal epithelium, leading us to hypothesize that TCM could be derived from reserve cells. To elucidate the histogenetic process of TCM, we analyzed the histomorphologic features and immunoprofiles for CK17, CK5/6, p63, GATA-3, estrogen receptor (ER), and androgen receptor (AR) in TCM foci arising in the tubal epithelium (31 foci) and pelvic mesothelium (35 foci). Overall, the histologic features and immunoprofiles of TCM in the tubal epithelium and pelvic mesothelium were similar, but distinct differences appeared during TCM development. A single-layered CK17-expressing reserve cells became apparent beneath the tubal epithelium, and the CK17 expression disappeared as these cells multiplied. In contrast, a short segment of normal mesothelium next to the tubo-peritoneal junction expressed CK17 even before the emergence of a single-layered reserve cells beneath the mesothelium, suggesting a potential reserve/stem cell function within the mesothelium itself. Then, the single-layered cells in both areas multiplied and differentiated to display urothelial characteristics, including nuclear grooves and clear cytoplasm. Strong CK5/6, p63, and GATA-3 expression appeared in the single-layered reserve cell stage and was maintained thereafter to the fully differentiated TCM. AR was expressed in both normal tubal epithelium and pelvic mesothelium, and the intensity of AR and ER were reciprocal during the entire histogenetic process of TCM in most reserve cell-derived populations (98.5%), AR expression being significantly stronger than ER. The histogenesis of TCM was initiated from the emergence of reserve cells beneath the tubal epithelium and pelvic mesothelium, which then multiplied and differentiated into urothelium. AR might have an important role during the histogenesis of TCM.

Identification and characterization of multipotential stem cells in immortalized normal ovarian surface epithelial cells

The ovarian surface epithelium (OSE) is a single layer of squamous-to-cuboidal epithelial cells that experience repetitive ovulatory rupture and subsequent repair. However, the characteristics of human immortalized ovarian surface epithelial cells (IOSE80) remain elusive. This study aims to determine whether IOSE80 cells have the characteristics of stem cell proliferation and multilineage differentiation and their application in regenerative medicine. IOSE80 cells are sequenced by high-throughput transcriptome analysis, and 5 sets of public data are used to compare the differences between IOSE80 cells and bone marrow mesenchymal stem cells, pluripotent stem cells, and oocytes in transcriptome profiling. The IOSE80 cells present a cobblestone-like monolayer and express the epithelial cell marker KRT18; the stem cell markers IFITM3, ALDH1A1, and VIM; lowly express stem cell marker LGR5 and germ cell markers DDX4 and DAZL. In addition, the GO terms "regulation of stem cell proliferation", "epithelial cell proliferation", etc., are significantly enriched ( P<0.05). IOSE80 cells have the potential to act as mesenchymal stem cells to differentiate into adipocytes with lipid droplets, osteoblasts, and chondroblasts in vitro. IOSE80 cells express pluripotent stem cell markers, including OCT4, SSEA4, TRA-1-60, and TRA-1-81, and they can be induced into three germ layers in vitro. IOSE80 cells also form oocyte-like cells in vitro and in vivo. In addition, IOSE80 cells exhibit robust proliferation, migration, and ovarian repair functions after in vivo transplantation. This study demonstrates that IOSE80 cells have the characteristics of pluripotent/multipotent stem cells, indicating their important role in tissue engineering and regenerative medicine.

The Challenges and Prospects of p53-Based Therapies in Ovarian Cancer

It has been well established that mutations in the tumor suppressor gene, p53, occur readily in a vast majority of cancer tumors, including ovarian cancer. Typically diagnosed in stages three or four, ovarian cancer is the fifth leading cause of death in women, despite accounting for only 2.5% of all female malignancies. The overall 5-year survival rate for ovarian cancer is around 47%; however, this drops to an abysmal 29% for the most common type of ovarian cancer, high-grade serous ovarian carcinoma (HGSOC). HGSOC has upwards of 96% of cases expressing mutations in p53. Therefore, wild-type (WT) p53 and p53-based therapies have been explored as treatment options via a plethora of drug delivery vehicles including nanoparticles, viruses, polymers, and liposomes. However, previous p53 therapeutics have faced many challenges, which have resulted in their limited translational success to date. This review highlights a selection of these historical p53-targeted therapeutics for ovarian cancer, why they failed, and what the future could hold for a new generation of this class of therapies.

The Role of Circulating Tumor Cells in Ovarian Cancer Dissemination

Metastatic ovarian cancer is the main reason for treatment failures and consequent deaths. Ovarian cancer is predisposed to intraperitoneal dissemination. In comparison to the transcoelomic route, distant metastasis via lymph vessels and blood is less common. The mechanisms related to these two modes of cancer spread are poorly understood. Nevertheless, the presence of tumor cells circulating in the blood of OC patients is a well-established phenomenon confirming the significant role of lymphatic and hematogenous metastasis. Thus, the detection of CTCs may provide a minimally invasive tool for the identification of ovarian cancer, monitoring disease progression, and treatment effectiveness. This review focuses on the biology of ovarian CTCs and the role they may play in cancer diagnosis and therapy.

Single-cell sequencing analysis reveals gastric cancer microenvironment cells respond vastly different to oxidative stress

Gastric cancer is a common type of gastrointestinal malignant tumor in China. The mechanism of the development and progression of gastric cancer remains the continuing research focus. The tumor microenvironment plays an important role in the development and progression of tumors. The present study used single-cell sequencing data to characterize the microenvironment of gastric cancer, investigate the effects of oxidative stress on gastric cancer microenvironmental cells through the comparison between cancer tissue and normal tissue, and identify the key genes associated with gastric cancer patients' survival. The results showed that compared with normal gastric tissue, gastric cancer tissue had a decreased oxidative stress response, weaker oxidative detoxification ability, and increased oxidative stress-induced cell death. In the different types of single cells of gastric cancer microenvironment, the oxidative stress response of T cell was increased, the ability of oxidative detoxification was enhanced, and the oxidative stress-induced cell death was exacerbate. Mucous cell showed the same trend as gastric cancer cells: decreased oxidative stress response, weak oxidative detoxification ability, and weakened oxidative stress-induced cell death. Moreover, TRIM62, MET, and HBA1, which were significantly associated with oxidative stress, may be biomarkers for the prognosis of gastric cancer. High expression of TRIM62 indicated a good prognosis, while MET and HBA1 indicated a poor prognosis, which will be confirmed by further clinical studies.

Cancer Stem Cells in Ovarian Cancer-A Source of Tumor Success and a Challenging Target for Novel Therapies

Ovarian cancer is the most lethal neoplasm of the female genital organs. Despite indisputable progress in the treatment of ovarian cancer, the problems of chemo-resistance and recurrent disease are the main obstacles for successful therapy. One of the main reasons for this is the presence of a specific cell population of cancer stem cells. The aim of this review is to show the most contemporary knowledge concerning the biology of ovarian cancer stem cells (OCSCs) and their impact on chemo-resistance and prognosis in ovarian cancer patients, as well as to present the treatment options targeted exclusively on the OCSCs. The review presents data concerning the role of cancer stem cells in general and then concentrates on OCSCs. The surface and intracellular OCSCs markers and their meaning both for cancer biology and clinical prognosis, signaling pathways specifically activated in OCSCs, the genetic and epigenetic regulation of OCSCs function including the recent studies on the non-coding RNA regulation, cooperation between OCSCs and the tumor microenvironment (ovarian cancer niche) including very specific environment such as ascites fluid, the role of shear stress, autophagy and metabolic changes for the function of OCSCs, and finally mechanisms of OCSCs escape from immune surveillance, are described and discussed extensively. The possibilities of anti-OCSCs therapy both in experimental settings and in clinical trials are presented, including the recent II phase clinical trials and immunotherapy. OCSCs are a unique population of cancer cells showing a great plasticity, self-renewal potential and resistance against anti-cancer treatment. They are responsible for the progression and recurrence of the tumor. Several completed and ongoing clinical trials have tested different anti-OCSCs drugs which, however, have shown unsatisfactory efficacy in most cases. We propose a novel approach to ovarian cancer diagnosis and therapy.

Functional expression of P2Y2 receptors in mouse ovarian surface epithelium (OSE)

Ovarian surface epithelium (OSE) is a cell monolayer surrounding the ovary; it is involved in the regulation of the ovulatory process and the genesis of ovarian carcinoma. However, intercellular messengers regulating signaling events, like proliferation in the OSE, have not been completely described. Purines have emerged as novel intercellular messengers in the ovary, in which expression of purinergic receptors has been reported in different cell types. In the present work, we described the functional expression of P2Y2 receptor (P2Y2R), a purinergic receptor widely associated with cell proliferation, in the OSE. The expression of P2Y2R by immunofluorescence and RT-PCR, and its functionality by Ca²⁺ recording was demonstrated in primary cultured OSE. Functional expression of P2Y2R was also exhibited in situ, by recording of intracellular Ca²⁺ release and detection of ERK phosphorylation after injection of a selective agonist into the ovarian bursa. Furthermore, P2Y2R activation with UTPγS, in situ, induced cell proliferation at 24 h, whereas continuous stimulation of P2Y2R during a complete estrous cycle significantly modified the size distribution of the follicular population. This is the first evidence of the functional expression of purinergic P2Y2R in the OSE and opens new perspectives on the roles played by purines in ovarian physiology.

Transcriptional heterogeneity of stemness phenotypes in the ovarian epithelium

The ovarian surface epithelium (OSE) is a monolayer of epithelial cells surrounding the ovary that ruptures during each ovulation to allow release of the oocyte. This wound is quickly repaired, but mechanisms promoting repair are poorly understood. The contribution of tissue-resident stem cells in the homeostasis of several epithelial tissues is widely accepted, but their involvement in OSE is unclear. We show that traits associated with stem cells can be increased following exposure to the cytokine TGFB1, overexpression of the transcription factor Snai1, or deletion of Brca1. We find that stemness is often linked to mesenchymal-associated gene expression and higher activation of ERK signalling, but is not consistently dependent on their activation. Expression profiles of these populations are extremely context specific, suggesting that stemness may not be associated with a single, distinct population, but rather is a heterogeneous cell state that may emerge from diverse environmental cues. These findings support that the OSE may not require distinct stem cells for long-term maintenance, and may instead achieve this through transient dedifferentiation into a stem-like state.

Using spheroids as a model, the authors report the molecular signatures of ovarian surface epithelial (OSE) cells exhibiting stemness phenotype under various conditions in vitro, and found that there is a large degree of heterogeneity in the transcriptional profiles of stem cells induced under different conditions. They suggest that maintenance of the OSE may not require a single stem cell population, but heterogeneous stem cells that can be induced transiently under diverse environmental cues.

Global miRNA/proteomic analyses identify miRNAs at 14q32 and 3p21, which contribute to features of chronic iron-exposed fallopian tube epithelial cells

Malignant transformation of fallopian tube secretory epithelial cells (FTSECs) is a key contributing event to the development of high-grade serous ovarian carcinoma (HGSOC). Our recent findings implicate oncogenic transformative events in chronic iron-exposed FTSECs, including increased expression of oncogenic mediators, increased telomerase transcripts, and increased growth/migratory potential. Herein, we extend these studies by implementing an integrated transcriptomic and mass spectrometry-based proteomics approach to identify global miRNA and protein alterations, for which we also investigate a subset of these targets to iron-induced functional alterations. Proteomic analysis identified > 4500 proteins, of which 243 targets were differentially expressed. Sixty-five differentially expressed miRNAs were identified, of which 35 were associated with the “top” proteomic molecules (> fourfold change) identified by Ingenuity Pathway Analysis. Twenty of these 35 miRNAs are at the 14q32 locus (encoding a cluster of 54 miRNAs) with potential to be regulated by DNA methylation and histone deacetylation. At 14q32, miR-432-5p and miR-127-3p were ~ 100-fold downregulated whereas miR-138-5p was 16-fold downregulated at 3p21 in chronic iron-exposed FTSECs. Combinatorial treatment with methyltransferase and deacetylation inhibitors reversed expression of these miRNAs, suggesting chronic iron exposure alters miRNA expression via epigenetic alterations. In addition, PAX8, an important target in HGSOC and a potential miRNA target (from IPA) was epigenetically deregulated in iron-exposed FTSECs. However, both PAX8 and ALDH1A2 (another IPA-predicted target) were experimentally identified to be independently regulated by these miRNAs although TERT RNA was partially regulated by miR-138-5p. Interestingly, overexpression of miR-432-5p diminished cell numbers induced by long-term iron exposure in FTSECs. Collectively, our global profiling approaches uncovered patterns of miRNA and proteomic alterations that may be regulated by genome-wide epigenetic alterations and contribute to functional alterations induced by chronic iron exposure in FTSECs. This study may provide a platform to identify future biomarkers for early ovarian cancer detection and new targets for therapy.

Comprehensive pathway-related genes signature for prognosis and recurrence of ovarian cancer

Background

Ovarian cancer (OC) is a highly malignant disease with a poor prognosis and high recurrence rate. At present, there is no accurate strategy to predict the prognosis and recurrence of OC. The aim of this study was to identify gene-based signatures to predict OC prognosis and recurrence.

Methods

mRNA expression profiles and corresponding clinical information regarding OC were collected from The Cancer Genome Atlas (TCGA) database. Gene set enrichment analysis (GSEA) and LASSO analysis were performed, and Kaplan–Meier curves, time-dependent ROC curves, and nomograms were constructed using R software and GraphPad Prism7.

Results

We first identified several key signalling pathways that affected ovarian tumorigenesis by GSEA. We then established a nine-gene-based signature for overall survival (OS) and a five-gene-based-signature for relapse-free survival (RFS) using LASSO Cox regression analysis of the TCGA dataset and validated the prognostic value of these signatures in independent GEO datasets. We also confirmed that these signatures were independent risk factors for OS and RFS by multivariate Cox analysis. Time-dependent ROC analysis showed that the AUC values for OS and RFS were 0.640, 0.663, 0.758, and 0.891, and 0.638, 0.722, 0.813, and 0.972 at 1, 3, 5, and 10 years, respectively. The results of the nomogram analysis demonstrated that combining two signatures with the TNM staging system and tumour status yielded better predictive ability.

Conclusion

In conclusion, the two-gene-based signatures established in this study may serve as novel and independent prognostic indicators for OS and RFS.

Morphological basics of ovarian tumor histogenesis

Researches about the origin of epithelial ovarian tumors (EOT) tell about its conception. In particular, the origin of cells from the secondary mullerian system. Also, in the article we examine a new hypothesis that the EOT originates in the epithelium of the fallopian tube (FT) – their contradictoriness and new conception of “precursor escape” which tries to explain the phenomenon of injuries absence of FT by high-grade serous ovarian carcinoma. Carcinogenesis from the FT represents great opportunities for reassessment of clinical data. Also, the article represents the role of stem cells of the surface epithelium of ovaries and FT in EOT carcinogenesis.

Ovarian Cancer, Cancer Stem Cells and Current Treatment Strategies: A Potential Role of Magmas in the Current Treatment Methods

Epithelial ovarian cancer (EOC) constitutes 90% of ovarian cancers (OC) and is the eighth most common cause of cancer-related death in women. The cancer histologically and genetically is very complex having a high degree of tumour heterogeneity. The pathogenic variability in OC causes significant impediments in effectively treating patients, resulting in a dismal prognosis. Disease progression is predominantly influenced by the peritoneal tumour microenvironment rather than properties of the tumor and is the major contributor to prognosis. Standard treatment of OC patients consists of debulking surgery, followed by chemotherapy, which in most cases end in recurrent chemoresistant disease. This review discusses the different origins of high-grade serous ovarian cancer (HGSOC), the major sub-type of EOC. Tumour heterogeneity, genetic/epigenetic changes, and cancer stem cells (CSC) in facilitating HGSOC progression and their contribution in the circumvention of therapy treatments are included. Several new treatment strategies are discussed including our preliminary proof of concept study describing the role of mitochondria-associated granulocyte macrophage colony-stimulating factor signaling protein (Magmas) in HGSOC and its unique potential role in chemotherapy-resistant disease.

PTTG1: a Unique Regulator of Stem/Cancer Stem Cells in the Ovary and Ovarian Cancer

Origin of cancer stem cells (CSCs) and mechanisms by which oncogene PTTG1 contributes to tumor progression via CSCs is not known. Ovarian CSCs exhibit characteristics of self-renewal, tumor-initiation, growth, differentiation, drug resistance, and tumor relapse. A common location of putative origin, namely the ovarian surface epithelium, is shared between the normal stem and CSC compartments. Existence of ovarian stem cells and their co-expression with CSC signatures suggests a strong correlation between origin of epithelial cancer and CSCs. We hereby explored a putative oncogene PTTG1 (Securin), reported to be overexpressed in various tumors, including ovarian. We report a previously overlooked role of PTTG1 as a marker of CSCs thereby modulating CSC, germline, and stemness-related genes. We further characterized PTTG1's ability to regulate (cancer) stem cell-associated self-renewal and epithelial-mesenchymal transition pathways. Collectively, the data sheds light on a potential target expressed during ovarian tumorigenesis and metastatically disseminated ascites CSCs in the peritoneal cavity. Present study highlights this unconventional, under-explored role of PTTG1 in regulation of stem and CSC compartments in ovary, ovarian cancer and ascites and highlights it as a potential candidate for developing CSC specific targeted therapeutics.

Procr-expressing progenitor cells are responsible for murine ovulatory rupture repair of ovarian surface epithelium

Ovarian surface epithelium (OSE) undergoes recurring ovulatory rupture and repair. The OSE replenishing mechanism post ovulation remains unclear. Here we report that the expression of Protein C Receptor (Procr) marks a progenitor population in adult mice that is responsible for OSE repair post ovulation. Procr+  cells are the major cell source for OSE repair. The mechanism facilitating the rapid re-epithelialization is through the immediate expansion of Procr+  cells upon OSE rupture. Targeted ablation of Procr+  cells impedes the repairing process. Moreover, Procr+  cells displayed robust colony-formation capacity in culture, which we harnessed and established a long-term culture and expansion system of OSE cells. Finally, we show that Procr+  cells and previously reported Lgr5+ cells have distinct lineage tracing behavior in OSE homeostasis. Our study suggests that Procr marks progenitor cells that are critical for OSE ovulatory rupture and homeostasis, providing insight into how adult stem cells respond upon injury.

The ovary is covered by a surface epithelium (OSE) and cells mediating its repair post ovulation are unclear. Here, the authors identify the Protein C Receptor (Procr) as marking progenitor cells, distinct from Lgr5+ stem cells, on the murine surface epithelium that repair the OSE post ovulation.

Ovarian Cancer Stem Cells: Role in Metastasis and Opportunity for Therapeutic Targeting

Ovarian cancer (OC) is a heterogeneous disease usually diagnosed at a late stage. Cancer stem cells (CSCs) that exist within the bulk tumor survive first-line chemotherapy and contribute to resistant disease with metastasis. Understanding the key features of CSC biology provides valuable opportunities to develop OCSC-directed therapeutics, which will eventually improve the clinical outcomes of patients. Although significant developments have occurred since OCSCs were first described, the involvement of CSCs in ovarian tumor metastasis is not fully understood. Here, we discuss putative CSC markers and the fundamental role of CSCs in facilitating tumor dissemination in OC. Additionally, we focus on promising CSC-targeting strategies in preclinical and clinical studies of OC and discuss potential challenges in CSC research.

IGF-axis confers transformation and regeneration of fallopian tube fimbria epithelium upon ovulation

Background

The fallopian tube fimbria is regarded as the main tissue of origin and incessant ovulation as the main risk factor of ovarian high-grade serous carcinoma. Previously, we discovered the tumorigenesis activity of human ovulatory follicular fluid (FF) upon injection to the mammary fat pad of Trp53-null mice. We also found a mutagenesis activity of FF-ROS and a apoptosis-rescuing activity of Hb from retrograde menstruation. However, neither of them can explain the tumorigenesis activities of FF.

Methods

From two cohorts of ovulatory FF retrieved from IVF patients, the main growth factor responsible for the transformation of human fimbrial epithelial cells was identified. Mechanism of activation, ways of signal transduction of the growth factor, as well as the cellular and genetic phenotypes of the malignant transformation was characterized.

Findings

In this study, we showed that insulin-like growth factor (IGF)-axis proteins, including IGFBP-bound IGF2 as well as the IGFBP-lytic enzyme PAPP-A, are abundantly present in FF. Upon engaging with glycosaminoglycans on the membrane of fimbrial epithelial cells, PAPP-A cleaves IGFBPs and releases IGF2 to bind with IGF-1R. Through the IGF-1R/AKT/mTOR and IGF-1R/AKT/NANOG pathways, FF-IGF leads to stemness and survival, and in the case of TP53/Rb or TP53/CCNE1 loss, to clonal expansion and malignant transformation of fimbrial epithelial cells. By depleting each IGF axis component from FF, we proved that IGF2, IGFBP2/6, and PAPP-A are all essential and confer the majority of the transformation and regeneration activities.

Interpretation

This study revealed that the FF–IGF axis functions to regenerate tissue damage after ovulation and promote the transformation of fimbrial epithelial cells that have been initiated by p53- and Rb-pathway disruptions.

Fund

The study was supported by grants of the Ministry of Science and Technology, Taiwan (MOST 106-2314-B-303-001-MY2; MOST 105-2314-B-303-017-MY2; MOST 107-2314-B-303-013-MY3), and Buddhist Tzu Chi General Hospital, Taiwan (TCMMP104-04-01).

High-Grade Serous Ovarian Cancer: Basic Sciences, Clinical and Therapeutic Standpoints

Among a litany of malignancies affecting the female reproductive tract, that of the ovary is the most frequently fatal. Moreover, while the steady pace of scientific discovery has fuelled recent ameliorations in the outcomes of many other cancers, the rates of mortality for ovarian cancer have been stagnant since around 1980. Yet despite the grim outlook, progress is being made towards better understanding the fundamental biology of this disease and how its biology in turn influences clinical behaviour. It has long been evident that ovarian cancer is not a unitary disease but rather a multiplicity of distinct malignancies that share a common anatomical site upon presentation. Of these, the high-grade serous subtype predominates in the clinical setting and is responsible for a disproportionate share of the fatalities from all forms of ovarian cancer. This review aims to provide a detailed overview of the clinical-pathological features of ovarian cancer with a particular focus on the high-grade serous subtype. Along with a description of the relevant clinical aspects of this disease, including novel trends in treatment strategies, this text will inform the reader of recent updates to the scientific literature regarding the origin, aetiology and molecular-genetic basis of high-grade serous ovarian cancer (HGSOC).

High-Grade Serous Ovarian Cancer: Basic Sciences, Clinical and Therapeutic Standpoints

Among a litany of malignancies affecting the female reproductive tract, that of the ovary is the most frequently fatal. Moreover, while the steady pace of scientific discovery has fuelled recent ameliorations in the outcomes of many other cancers, the rates of mortality for ovarian cancer have been stagnant since around 1980. Yet despite the grim outlook, progress is being made towards better understanding the fundamental biology of this disease and how its biology in turn influences clinical behaviour. It has long been evident that ovarian cancer is not a unitary disease but rather a multiplicity of distinct malignancies that share a common anatomical site upon presentation. Of these, the high-grade serous subtype predominates in the clinical setting and is responsible for a disproportionate share of the fatalities from all forms of ovarian cancer. This review aims to provide a detailed overview of the clinical-pathological features of ovarian cancer with a particular focus on the high-grade serous subtype. Along with a description of the relevant clinical aspects of this disease, including novel trends in treatment strategies, this text will inform the reader of recent updates to the scientific literature regarding the origin, aetiology and molecular-genetic basis of high-grade serous ovarian cancer (HGSOC).

High-Grade Serous Ovarian Cancer: Basic Sciences, Clinical and Therapeutic Standpoints

Among a litany of malignancies affecting the female reproductive tract, that of the ovary is the most frequently fatal. Moreover, while the steady pace of scientific discovery has fuelled recent ameliorations in the outcomes of many other cancers, the rates of mortality for ovarian cancer have been stagnant since around 1980. Yet despite the grim outlook, progress is being made towards better understanding the fundamental biology of this disease and how its biology in turn influences clinical behaviour. It has long been evident that ovarian cancer is not a unitary disease but rather a multiplicity of distinct malignancies that share a common anatomical site upon presentation. Of these, the high-grade serous subtype predominates in the clinical setting and is responsible for a disproportionate share of the fatalities from all forms of ovarian cancer. This review aims to provide a detailed overview of the clinical-pathological features of ovarian cancer with a particular focus on the high-grade serous subtype. Along with a description of the relevant clinical aspects of this disease, including novel trends in treatment strategies, this text will inform the reader of recent updates to the scientific literature regarding the origin, aetiology and molecular-genetic basis of high-grade serous ovarian cancer (HGSOC).

Does human endometrial LGR5 gene expression suggest the existence of another hormonally regulated epithelial stem cell niche?

STUDY QUESTION

Is human endometrial leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5) gene expression limited to the postulated epithelial stem cell niche, stratum basalis glands, and is it hormonally regulated?

SUMMARY ANSWER

LGR5 expressing cells are not limited to the postulated stem cell niche but LGR5 expression is hormonally regulated.

WHAT IS KNOWN ALREADY

The human endometrium is a highly regenerative tissue; however, endometrial epithelial stem cell markers are yet to be confirmed. LGR5 is a marker of stem cells in various epithelia.

STUDY DESIGN, SIZE, DURATION

The study was conducted at a University Research Institute. Endometrial samples from 50 healthy women undergoing benign gynaecological surgery with no endometrial pathology at the Liverpool Women's hospital were included and analysed in the following six sub-categories; proliferative, secretory phases of menstrual cycle, postmenopausal, those using oral and local progestagens and samples for in vitro explant culture.

PARTICIPANTS/MATERIALS, SETTING, METHODS

In this study, we used the gold standard method, in situ hybridisation (ISH) along with qPCR and a systems biology approach to study the location of LGR5 gene expression in full thickness human endometrium and Fallopian tubes. The progesterone regulation of endometrial LGR5 was examined in vivo and in short-term cultured endometrial tissue explants in vitro. LGR5 expression was correlated with epithelial proliferation (Ki67), and expression of previously reported epithelia progenitor markers (SOX9 and SSEA-1) immunohistochemistry (IHC).

MAIN RESULTS AND THE ROLE OF CHANCE

LGR5 gene expression was significantly higher in the endometrial luminal epithelium than in all other epithelial compartments in the healthy human endometrium, including the endometrial stratum basalis (P < 0.05). The strongest SSEA-1 and SOX9 staining was observed in the stratum basalis glands, but the general trend of SOX9 and SSEA-1 expression followed the same cyclical pattern of expression as LGR5. Stratum functionalis epithelial Ki67-LI and LGR5 expression levels correlated significantly (r = 0.74, P = 0.01), however, they did not correlate in luminal and stratum basalis epithelium (r = 0.5 and 0.13, respectively). Endometrial LGR5 demonstrates a dynamic spatiotemporal expression pattern, suggesting hormonal regulation. Oral and local progestogens significantly reduced endometrial LGR5 mRNA levels compared with women not on hormonal treatment (P < 0.01). Our data were in agreement with in silico analysis of published endometrial microarrays.

LARGE SCALE DATA

We did not generate our own large scale data but interrogated publically available large scale data sets.

LIMITATIONS, REASONS FOR CAUTION

In the absence of reliable antibodies for human LGR5 protein and validated lineage markers for the various epithelial populations that potentially exist within the endometrium, our study does not formally characterise or examine the functional ability of the resident LGR5+ cells as multipotent.

WIDER IMPLICATIONS OF THE FINDINGS

These data will facilitate future lineage tracing studies in the human endometrial epithelium; to identify the location of stem cells and further complement the in vitro functional studies, to confirm if the LGR5 expressing epithelial cells indeed represent the epithelial stem cell population.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by funding from the Wellbeing of Women project grant (RTF510) and Cancer Research UK (A14895). None of the authors have any conflicts of interest to disclose.

Role of tumor microenvironment in the pathobiology of ovarian cancer: Insights and therapeutic opportunities

Ovarian cancer is the fifth most common cancer affecting women and at present, stands as the most lethal gynecologic malignancy. The poor disease outcome is due to the nonspecific symptoms and the lack of effective treatment at advanced stages. Thus, it is of utmost importance to understand ovarian carcinoma through several lenses and to dissect the role that the unique peritoneal tumor microenvironment plays in ovarian cancer progression and metastasis. This review seeks to highlight several determinants of this unique tumor microenvironment, their influence on disease outcome and ongoing clinical trials targeting these determinants.

Characterization of stem cell and cancer stem cell populations in ovary and ovarian tumors

Background

Ovarian cancer is a complicated malady associated with cancer stem cells (CSCs) contributing to 238,700 estimated new cases and 151,900 deaths per year, worldwide. CSCs comprise a tiny fraction of tumor-bulk responsible for cancer recurrence and eventual mortality. CSCs or tumor initiating cells are responsible for self-renewal, differentiation and proliferative potential, tumor initiation capability, its progression, drug resistance and metastatic spread. Although several biomarkers are implicated in these processes, their distribution within the ovary and association with single cell type has neither been established nor demonstrated across ovarian tumor developmental stages. Therefore, precise identification, thorough characterization and effective targeted destruction of dormant and highly proliferating potent CSC populations is an immediate need.

Results

In view of this, distribution of various CSC (ALDH1/2, C-KIT, CD133, CD24 and CD44) and cell proliferation (KI67) specific markers in the ovarian surface epithelium (OSE) and cortex regions in normal ovary, and benign, borderline and high grade metastatic ovarian tumors by immuno-histochemistry and confocal microscopy was studied. We further confirmed their expression by RT-PCR analysis. Co-expression analysis of stem cell (OCT4, SSEA4) and CSC (ALDH1/2, CD44 and LGR5) markers with proliferation marker (KI67) in HG tumors revealed dual positive proliferating stem and CSCs, few non-proliferating stem/CSC (SSEA4⁺/KI67⁻ and ALDH1/2⁺/KI67⁻) and only KI67⁺ cells in cortex, signifying dynamic populations and interesting cellular hierarchy in cortex region. Smaller spherical (≤ 5 μm) and larger spindle/elliptical shaped (~ 10 μm) cell populations with high nucleo-cytoplasmic ratio were detected across all samples (including normal ovaries) but with variable distribution and characteristic stage-wise marker expression across different tumor stages.

Conclusions

Diverse stem and CSC populations expressing characteristic markers revealing distinct phenotypes (spherical ≤5 μm and spindle/elliptical ~ 10 μm) were distributed within different tumor stages studied signifying dynamic and probable functional hierarchy within these cell types. Involvement of extra-ovarian sites of origin of stem and CSCs requires rigorous evaluation. Quantitative analysis of potent CSC populations, their mechanisms and pathways for self-renewal, chemo-resistance, metastatic spread etc. with respect to various markers studied, will provide better insights and targets for developing effective therapeutics to prevent metastasis and eventually help improve patient mortality.

Electronic supplementary material

The online version of this article (10.1186/s13048-018-0439-3) contains supplementary material, which is available to authorized users.

Role of tumor microenvironment in ovarian cancer pathobiology

Ovarian cancer is the fifth most common cancer affecting the female population and at present, stands as the most lethal gynecologic malignancy. Poor prognosis and low five-year survival rate are attributed to nonspecific symptoms and below par diagnostic criteria at early phases along with a lack of effective treatment at advanced stages. It is thus of utmost importance to understand ovarian carcinoma through several lenses including its molecular pathogenesis, epidemiology, histological subtypes, hereditary factors, diagnostic approaches and methods of treatment. Above all, it is crucial to dissect the role that the unique peritoneal tumor microenvironment plays in ovarian cancer progression and metastasis. This review seeks to highlight several important aspects of ovarian cancer pathobiology as a means to provide the necessary background to approach ovarian malignancies in the future.

Molecular signatures of epithelial oviduct cells of a laying hen (Gallus gallus domesticus) and quail (Coturnix japonica)

Background

In this work we have determined molecular signatures of oviduct epithelial and progenitor cells. We have proposed a panel of selected marker genes, which correspond with the phenotype of oviduct cells of a laying hen (Gallus gallus domesticus) and quail (Coturnix japonica). We demonstrated differences in characteristics of those cells, in tissue and in vitro, with respect to different anatomical and functional parts of the oviduct (infundibulum (INF), distal magnum (DM, and proximal magnum (PM)). The following gene expression signatures were studied: (1) oviduct markers (estrogen receptor 1, ovalbumin, and SPINK7 - ovomucoid), (2) epithelial markers (keratin 5, keratin 14, and occludin) and (3) stem-like/progenitor markers (CD44 glycoprotein, LGR5, Musashi-1, and sex determining region Y-box 9, Nanog homebox, OCT4/cPOUV gene encoding transcription factor POU5F3).

Results

In chicken, the expression of oviduct markers increased toward the proximal oviduct. Epithelial markers keratin14 and occludin were high in distal oviduct and decreased toward the proximal magnum. In quail oviduct tissue, the gene expression pattern of oviduct/epithelial markers was similar to chicken. The markers of progenitors/stemness in hen oviduct (Musashi-1 and CD44 glycoprotein) had the highest relative expression in the infundibulum and decreased toward the proximal magnum. In quail, we found significant expression of four progenitor markers (LGR5 gene, SRY sex determining region Y-box 9, OCT4/cPOUV gene, and CD44 glycoprotein) that were largely present in the distal oviduct. After in vitro culture of oviduct cells, the gene expression pattern has changed. High secretive potential of magnum-derived cells diminished by using decreased abundance of mRNA. On the other hand, chicken oviduct cells originating from the infundibulum gained ability to express OVM and OVAL. Epithelial character of the cells was maintained in vitro. Among progenitor markers, both hen and quail cells expressed high level of SOX9, LGR5 and Musashi-1.

Conclusion

Analysis of tissue material revealed gradual increase/decrease pattern in majority of the oviduct markers in both species. This pattern changed after the oviductal cells have been cultured in vitro. The results can provide molecular tools to validate the phenotype of in vitro biological models from reproductive tissue.

Electronic supplementary material

The online version of this article (10.1186/s12861-018-0168-2) contains supplementary material, which is available to authorized users.

Further characterization of adult sheep ovarian stem cells and their involvement in neo-oogenesis and follicle assembly

BACKGROUND

Stem cells in the ovary comprise of two distinct populations including very small embryonic-like stem cells (VSELs) and slightly bigger progenitors termed ovarian stem cells (OSCs). They are lodged in ovary surface epithelium (OSE) and are expected to undergo neo-oogenesis and primordial follicle (PF) assembly in adult ovaries. The ovarian stem cells express follicle stimulating hormone (FSH) receptors and are directly activated by FSH resulting in formation of germ cell nests (GCN) in vitro. Present study was undertaken to further characterize adult sheep OSCs and to understand their role during neo-oogenesis and PF assembly.

METHODS

Stem cells were collected by gently scraping the OSE cells and were characterized by H&E staining, immuno-localization, immuno-phenotyping and RT-PCR studies. Expression of FSH receptors and markers specific for stem cells (OCT-4, SSEA-4) and proliferation (PCNA) were studied on stem/progenitor cells in OSE culture and on adult sheep ovarian cortical tissue sections. Effect of FSH on stem cells was also studied in vitro. Asymmetric cell division (ACD) was monitored by studying expression of OCT-4 and NUMB.

RESULTS

Additional evidence was generated on the presence of two populations of stem cells in the OSE including VSELs and OSCs. FSHR expression was observed on both VSELs and OSCs by immuno-localization and immuno-phenotyping studies. FSH treatment in vitro stimulated VSELs that underwent ACD to self-renew and give rise to OSCs which divided rapidly by symmetric cell divisions (SCD) and clonal expansion with incomplete cytokinesis to form GCN. ACD was further confirmed by differential expression of OCT-4 in VSELs and NUMB in the OSCs. Immuno-histochemical expression of OCT-4, PCNA and FSHR was noted on stem cells located in the OSE in sheep ovarian sections. GCN and cohort of PF were observed in the ovarian cortex and provided evidence in support of neo-oogenesis from the stem cells.

CONCLUSION

Results of present study provide further evidence in support of two stem cells populations in adult sheep ovary. Both VSELs, OSCs and GCN express FSH receptors and FSH possibly regulates their function to undergo neo-oogenesis and primordial follicle assembly.

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

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

Sequential molecular changes and dynamic oxidative stress in high-grade serous ovarian carcinogenesis

The mechanism of high-grade serous ovarian cancer (HGSC) development remains elusive. This review outlines recent advances in the understanding of sequential molecular changes associated with the development of HGSC, as well as describes oxidative stress-induced genomic instability and carcinogenesis. This article reviews the English language literature between 2005 and 2017. Clinicopathological features analysis provides a sequential progression of fallopian tubal epithelium to precursor lesions to type 2 HGSC. HGSC may develop over a long time after incessant ovulation and repeated retrograde menstruation via stepwise accumulation of genetic alterations, including PAX2, ALDH1A1, STMN1, EZH2 and CCNE1, which confer positive selection of cells with growth advantages through acquiring driver mutations such as BRCA1/2, p53 or PTEN/PIK3CA. Haemoglobin and iron-induced oxidative stress leads to the emergence of genetic alterations in fallopian tubal epithelium via increased DNA damage and impaired DNA repair. Serous tubal intraepithelial carcinoma (STIC), the likely precursor of HGSC, may be susceptible to DNA double-strand breaks, exhibit DNA replication stress and increase genomic instability. The induction of genomic instability is considered to be a driving mechanism of reactive oxygen species (ROS)-induced carcinogenesis. HGSC exemplifies the view of stepwise cancer development. We describe how genetic alterations emerge during HGSC carcinogenesis related to oxidative stress.

[Expansion of secretory cells in the fallopian tubal epithelium in the early stages of the pathogenesis of ovarian serous carcinomas]

AIM

to investigate the frequency of the types of fallopian tubal secretory cell expansion (SCE) in diseases of the reproductive organs and to determine the immunophenotype and biological role of the cells in the early stages of the pathogenesis of high-grade ovarian serous carcinomas (HGOSC).

SUBJECTS AND METHODS

The investigation enrolled 287 patients with extraovarian diseases and ovarian serous tumors varying in grade, whose fallopian tubes were morphologically and immunohistochemically examined using p53, Ki-67, PAX2, Bcl-2, beta-catenin, and ALDH1 markers. The material was statistically processed applying the Mann-Whitney test and χ2 test.

RESULTS

The rate of secretory cell proliferation (SCP) (more than 10 consecutive secretory cells) and that of secretory cell overgrowth (SCO) (more than 30 consecutive secretory cells) increase with age in all investigated reproductive system diseases. The rate of SCP in the corpus fimbriatum of the patients with HGOSC was 5.9 times higher than that in those with extraovarian disease (p<0.01); when comparing the same patient groups, that of SCO was 3.4 times higher (p<0.05). The immunohistochemical characteristics of the investigated lesions (in scores) were as follows: PAX2 was expressed in the intact epithelium (2.8), in SCP (1.3), in SCO (1.2), in serous tubal intraepithelial carcinoma (STIC) (1.0), and in HGOSC (0.9); Bcl-2 was in the intact epithelium (2.2), in SCP (2.1), STIC (0.9), and in HGOSC (0.6), β-catenin was in the intact epithelium (0.5), in SCP (2.85), in SCO (2.95), in STIC (0.6), and in HGOSC (0.5); ALDH1 was in the intact epithelium (0.5), in SCP (2.91), in SCO (2.92), in STIC (1.2), and in HGOSC (0.6). There were statistically significant differences with a 95% confidence interval (p<0.05) for: 1) PAX2 between the intact epithelium and pathology (fallopian tube lesions and HGOSC); 2) Bcl-2 between the intact epithelium and SCE (SCP and SCO) and between SCE and HGOSC; 3) beta-catenin between the intact epithelium and SCE (SCP and SCO) and between SCE and HGOSC; 4) ALDH1 between the intact epithelium and SCE, between and SCE and STIC, and between STIC and HGOSC.

CONCLUSION

SCE was shown to be an independent intraepithelial lesion. The incidence of this abnormality increased with age and significantly differed in the patients with fallopian tubal lesions in extraovarian diseases from that in those with malignant ovarian serous tumors (by 5.3 times), while these groups showed a three-fold difference in SCO. Thus, SCP may serve as a more sensitive marker for the early stages of the pathogenesis of ovarian serous carcinoma. The studied types of SCE demonstrated multiple molecular events (loss of PAX2 expression and increased Bcl-2, beta-catenin, and ALDH1 expressions), some of which underwent considerable changes, by increasing the severity of a pathological process (loss of ALDH1, and beta-catenin, and bcl-2 expressions). Thus, therapeutic exposure in the early stages of pathogenesis may have a few points of application and just several molecules can serve as independent markers for early pathological changes in the fallopian tubal epithelium.

The disparate origins of ovarian cancers: pathogenesis and prevention strategies

Ovarian cancer is the fifth cause of cancer-related death in women and comprises a histologically and genetically broad range of tumours, including those of epithelial, sex cord-stromal and germ cell origin. Recent evidence indicates that high-grade serous ovarian carcinoma, clear cell carcinoma and endometrioid carcinoma primarily arise from tissues that are not normally present in the ovary. These histogenetic pathways are informing risk-reduction strategies for the prevention of ovarian and ovary-associated cancers and have highlighted the importance of the seemingly unique ovarian microenvironment.

Small putative NANOG, SOX2, and SSEA-4-positive stem cells resembling very small embryonic-like stem cells in sections of ovarian tissue in patients with ovarian cancer

BACKGROUND

In previous studies it has been found that in cell cultures of human adult ovaries there is a population of small stem cells with diameters of 2-4 μm, which are present mainly in the ovarian surface epithelium and are comparable to very small embryonic-like stem cells (VSELs) from bone marrow. These cells are not observed by histopathologists in the ovarian tissue due to their small size and unknown clinical significance. Because these cells express a degree of pluripotency, they might be involved in the manifestation of ovarian cancer. Therefore we studied the ovarian tissue sections in women with borderline ovarian cancer and serous ovarian carcinoma to perhaps identify the small putative stem cells in situ.

METHODS

In 27 women with borderline ovarian cancer and 20 women with high-grade serous ovarian carcinoma the ovarian tissue sections were stained, per standard practice, with eosin and hematoxylin staining and on NANOG, SSEA-4 and SOX2 markers, related to pluripotency, using immunohistochemistry. We focused on the presence and localization of small putative stem cells with diameters of up to 5 μm and with the nuclei spread over nearly the full cell volume.

RESULTS

In ovarian sections of both borderline ovarian cancer and serous ovarian carcinoma patients we were able to identify the presence of small round cells complying with the above criteria. Some of these small cells were NANOG-positive, were located among epithelial cells in the ovarian surface epithelium and as a single cell or groups of cells/clusters in typical "chambers", were found only in the presence of ovarian cancer and not in healthy ovaries and are comparable to those in fetal ovaries. We envision that these small cells could be related to NANOG-positive tumor-like structures and oocyte-like cells in similar "chambers" found in sections of cancerous ovaries, which could support their stemness and pluripotency. Further immunohistochemistry revealed a similar population of SSEA-4 and SOX2-positive cells.

CONCLUSIONS

We may conclude that putative small stem cells expressing markers, related to pluripotency, are present in the ovarian tissue sections of women with borderline ovarian cancer and high-grade serous ovarian carcinoma thus indicating their potential involvement in ovarian cancer.

The role of reproductive hormones in epithelial ovarian carcinogenesis

Epithelial ovarian cancer comprises ∼85% of all ovarian cancer cases. Despite acceptance regarding the influence of reproductive hormones on ovarian cancer risk and considerable advances in the understanding of epithelial ovarian carcinogenesis on a molecular level, complete understanding of the biologic processes underlying malignant transformation of ovarian surface epithelium is lacking. Various hypotheses have been proposed over the past several decades to explain the etiology of the disease. The role of reproductive hormones in epithelial ovarian carcinogenesis remains a key topic of research. Primary questions in the field of ovarian cancer biology center on its developmental cell of origin, the positive and negative effects of each class of hormones on ovarian cancer initiation and progression, and the role of the immune system in the ovarian cancer microenvironment. The development of the female reproductive tract is dictated by the hormonal milieu during embryogenesis. Intensive research efforts have revealed that ovarian cancer is a heterogenous disease that may develop from multiple extra-ovarian tissues, including both Müllerian (fallopian tubes, endometrium) and non-Müllerian structures (gastrointestinal tissue), contributing to its heterogeneity and distinct histologic subtypes. The mechanism underlying ovarian localization, however, remains unclear. Here, we discuss the role of reproductive hormones in influencing the immune system and tipping the balance against or in favor of developing ovarian cancer. We comment on animal models that are critical for experimentally validating existing hypotheses in key areas of endocrine research and useful for preclinical drug development. Finally, we address emerging therapeutic trends directed against ovarian cancer.

Expression of Stem Cell Markers in Preinvasive Tubal Lesions of Ovarian Carcinoma

In order to better understand the ovarian serous carcinogenic process with tubal origin, we investigated the expression of stem cell markers in premalignant tubal lesions (serous tubal intraepithelial carcinoma or STIC). We found an increased stem cell marker density in the normal fallopian tube followed by a high CD117 and a low ALDH and CD44 expression in STICs raising the question of the role of the stem cell markers in the serous carcinogenic process.

Ovary and fimbrial stem cells: biology, niche and cancer origins

The mammalian ovary is covered by a single-layered epithelium that undergoes rupture and remodelling following each ovulation. Although resident stem cells are presumed to be crucial for this cyclic regeneration, their identity and mode of action have been elusive. Surrogate stemness assays and in vivo fate-mapping studies using recently discovered stem cell markers have identified stem cell pools in the ovary and fimbria that ensure epithelial homeostasis. Recent findings provide insights into intrinsic mechanisms and local extrinsic cues that govern the function of ovarian and fimbrial stem cells. These discoveries have advanced our understanding of stem cell biology in the ovary and fimbria, and lay the foundations for evaluating the contribution of resident stem cells to the initiation and progression of human epithelial ovarian cancer.

Discovery of microarray-identified genes associated with ovarian cancer progression

Ovarian cancer is the most lethal cancer of female reproductive system. There is a consistent and urgent need to better understand its mechanism. In this study, we retrieved 186 genes that were dysregulated by at least 4-fold in 594 ovarian serous cystadenocarcinomas in comparison with eight normal ovaries, according to The Cancer Genome Atlas Ovarian Statistics data deposited in Oncomine database. DAVID analysis of these genes enriched two biological processes indicating that the cell cycle and microtubules might play critical roles in ovarian cancer progression. Among these 186 genes, 46 were dysregulated by at least 10-fold and their expression was further confirmed by the Bonome Ovarian Statistics data deposited in Oncomine, which covered 185 cases of ovarian carcinomas and 10 cases of normal ovarian surface epithelium. Six genes, including aldehyde dehydrogenase 1 family, member A2 (ALDH1A2), alcohol dehydrogenase 1B (class I), β polypeptide (ADH1B), NEL-like 2 (chicken) (NELL2), hemoglobin, β (HBB), ATP-binding cassette, sub-family A (ABC1), member 8 (ABCA8) and hemoglobin, α1 (HBA1) were identified to be downregulated by at least 10-fold in 779 ovarian cancers compared with 18 normal controls. Using mRNA expression profiles retrieved from microarrays deposited in the Gene Expression Omnibus Profiles database, RT-qPCR measurement and bioinformatics analysis, we further indicated that high expression of HBB might predict a poorer 5-year survival, high expression of ALDH1A2 and ABCA8 might predict a poor outcome; while ALDH1A2, ADH1B, HBB and ABCA8, in particular the former two genes, might be associated with drug resistance, and ALDH1A2 and NELL2 might contribute to invasiveness and metastasis in ovarian cancer. This study thus contributes to our understanding of the mechanism of ovarian cancer progression and development, and the six identified genes may be potential therapeutic targets and biomarkers for diagnosis and prognosis.

[Importance of the tumor stem cell hypothesis for understanding ovarian cancer]

BACKGROUND

Despite complex surgical and systemic therapies epithelial ovarian cancer has a poor prognosis. A small quantity of tumorigenic cells termed cancer stem cells (CSC) are responsible for the development of chemoresistance and high rates of recurrence.

OBJECTIVES

This review presents the CSC hypothesis and describes methods of identification and enrichment of CSCs as well as approaches for the therapeutic use of these findings.

MATERIAL AND METHODS

A systematic literature review based on PubMed and Web of Science was carried out.

RESULTS

The CSC model is based on a hierarchical structure of tumors with few CSCs and variably differentiated tumor cells constituting the tumor bulk. Only the CSCs possess tumorigenic potential. Other essential functional characteristics of CSCs are their potential for self-renewal and their ability to differentiate into further cell types. The CSCs are structurally characterized by different surface markers and changes in certain signaling pathways. Currently there are phase I and II studies in progress investigating specific influences on CSCs.

CONCLUSION

Various clinical characteristics of the course of disease in ovarian cancer are aptly represented by the tumor stem cell model. In spite of precisely defined functional characteristics of CSCs, surface markers and signaling pathways show individual differences and vary between tumor entities. This complicates identification and enrichment. Current experimental findings in various approaches and even first clinical studies raise hopes for a personalized cancer therapy targeting CSCs.

Loss of ALDH1A1 expression is an early event in the pathogenesis of ovarian high-grade serous carcinoma

Tumor-initiating cells are thought to share features with normal somatic stem cells. In mice, stem cells at the ovarian hilum have been shown to express the stem cell marker, aldehyde dehydrogenase isoform 1A1 (ALDH1A1), and are prone to malignant transformation. The potential relevance of this finding to humans has not been established. In this study, we used immunohistochemistry to assess the distribution of ALDH1A1 staining in the epithelium of human fallopian tubes, with particular reference to the transition of tubal epithelium to mesothelium (ie, tubal-mesothelial junction), ovarian surface epithelium, as well as putative precursors of ovarian high-grade serous carcinoma, namely, serous tubal intraepithelial carcinoma and 'p53 signatures,' and overt serous carcinoma. Expression of ALDH1A1 was detected in both secretory and ciliated tubal epithelial cells, tubal-mesothelial junctions and ovarian surface epithelium, but was absent in serous tubal intraepithelial carcinoma and p53 signatures. Positive staining in high-grade serous carcinoma, when present, was typically limited to rare tumor cells. In silico analyses of the mRNA expression data set from The Cancer Genome Atlas revealed downregulation of ALDH1A1 transcripts in high-grade serous carcinoma relative to normal tubal epithelium, and no association between ALDH1A1 expression levels and overall survival. Our results do not support ALDH1A1 as a specific marker of stem cells in human fallopian tube and demonstrate that its loss of expression is an early event in the development of high-grade serous carcinoma.

Stem cells, progenitor cells, and lineage decisions in the ovary

Exploring stem cells in the mammalian ovary has unleashed a Pandora's box of new insights and questions. Recent evidence supports the existence of stem cells of a number of the different cell types within the ovary. The evidence for a stem cell model producing mural granulosa cells and cumulus cells is strong, despite a limited number of reports. The recent identification of a precursor granulosa cell, the gonadal ridge epithelial-like cell, is exciting and novel. The identification of female germline (oogonial) stem cells is still very new and is currently limited to just a few species. Their origins and physiological roles, if any, are unknown, and their potential to produce oocytes and contribute to follicle formation in vivo lacks robust evidence. The precursor of thecal cells remains elusive, and more compelling data are needed. Similarly, claims of very small embryonic-like cells are also preliminary. Surface epithelial cells originating from gonadal ridge epithelial-like cells and from the mesonephric epithelium at the hilum of the ovary have also been proposed. Another important issue is the role of the stroma in guiding the formation of the ovary, ovigerous cords, follicles, and surface epithelium. Immune cells may also play key roles in developmental patterning, given their critical roles in corpora lutea formation and regression. Thus, while the cellular biology of the ovary is extremely important for its major endocrine and fertility roles, there is much still to be discovered. This review draws together the current evidence and perspectives on this topic.

Morphological and immunohistochemical pattern of tubo-ovarian dysplasia and serous tubal intraepithelial carcinoma

OBJECTIVE

Histopathological examination of material from prophylactic salpingo-oophorectomies performed in patients at genetic risk of ovarian cancer can reveal abnormalities interpreted as possible pre-cancerous "ovarian dysplasia" and tubal precursors lesions. We sought to study the morphological features and immunohistochemical expression patterns of neoplasia-associated markers in prophylactically removed ovaries and fallopian tubes (pBSO) in comparison with a group of serous tubal intraepithelial carcinoma (STIC) and non-cancerous controls.

STUDY DESIGN

Morphological features and immunohistochemical expression patterns of Ki-67 (for proliferation biomarker), p53 (key pathway of mullerian serous tumorogenesis), Bcl2 (anti-apoptotic), γH2AX (a double-strand breaks marker) and ALDH1 (a stem cell marker significantly associated with early-stage ovarian cancer) were blindly evaluated by two pathologists in 111 pBSO, 12 STICs and 116 non-cancerous salpingo-oophorectomies (control group) (nBSO).

RESULTS

Morphological ovarian and tubal dysplasia scores were significantly higher in the pBSO than in controls (respectively, 8.8 vs 3.12, p<0.0001, for ovaries and 6.54 vs 1.58, p<0.0001 for tubes). Increased γH2AX expression was observed in the pBSO and STICs compared with the controls whereas expression patterns of Ki67, p53 and bcl2 were low to moderate in the pBSO group. STICs overexpressed Ki67 and p53 while bcl2 expression was low; Interestingly, ALDH1 expression was low in non dysplastic epithelium, high in dysplasia and constantly low in STICs.

CONCLUSION

The morphological and immunohistochemical profile of tubo-ovarian dysplasia and STICs might be consistent with progression toward neoplastic transformation in the Serous Carcinogenesis Sequence. These changes may be pre-malignant and could represent an important phase in early neoplasia. ALDH1 activation in pBSO samples and its extinction in STICs should be considered as a target for prevention.

Epithelial ovarian cancer stem cells: underlying complexity of a simple paradigm

The lack of significant progress in the treatment of epithelial ovarian cancer (EOC) underscores the need to gain a better understanding of the processes that lead to chemoresistance and recurrence. The cancer stem cell (CSC) hypothesis offers an attractive explanation of how a subpopulation of cells within a patient's tumour might remain refractory to treatment and subsequently form the basis of recurrent chemoresistant disease. This review examines the literature defining somatic stem cells of the ovary and fallopian tube, two tissues that give rise to EOC. In addition, considerable research has been reviewed, that has identified subpopulations of EOC cells, based on marker expression (CD133, CD44, CD117, CD24, epithelial cell adhesion molecule, LY6A, ALDH1 and side population (SP)), which are enriched for tumour initiating cells (TICs). While many studies identified either CD133 or CD44 as markers useful for enriching for TICs, there is little consensus. This suggests that EOC cells may have a phenotypic plasticity that may preclude the identification of universal markers defining a CSC. The assay that forms the basis of quantifying TICs is the xenograft assay. Considerable controversy surrounds the xenograft assay and it is essential that some of the potential limitations be examined in this review. Highlighting such limitations or weaknesses is required to properly evaluate data and broaden our interpretation of potential mechanisms that might be contributing to the pathogenesis of ovarian cancer.

FSH-FSHR3-stem cells in ovary surface epithelium: basis for adult ovarian biology, failure, aging, and cancer

Despite extensive research, genetic basis of premature ovarian failure (POF) and ovarian cancer still remains elusive. It is indeed paradoxical that scientists searched for mutations in FSH receptor (FSHR) expressed on granulosa cells, whereas more than 90% of cancers arise in ovary surface epithelium (OSE). Two distinct populations of stem cells including very small embryonic-like stem cells (VSELs) and ovarian stem cells (OSCs) exist in OSE, are responsible for neo-oogenesis and primordial follicle assembly in adult life, and are modulated by FSH via its alternatively spliced receptor variant FSHR3 (growth factor type 1 receptor acting via calcium signaling and the ERK/MAPK pathway). Any defect in FSH-FSHR3-stem cell interaction in OSE may affect folliculogenesis and thus result in POF. Ovarian aging is associated with a compromised microenvironment that does not support stem cell differentiation into oocytes and further folliculogenesis. FSH exerts a mitogenic effect on OSE and elevated FSH levels associated with advanced age may provide a continuous trigger for stem cells to proliferate resulting in cancer, thus supporting gonadotropin theory for ovarian cancer. Present review is an attempt to put adult ovarian biology, POF, aging, and cancer in the perspective of FSH-FSHR3-stem cell network that functions in OSE. This hypothesis is further supported by the recent understanding that: i) cancer is a stem cell disease and OSE is the niche for ovarian cancer stem cells; ii) ovarian OCT4-positive stem cells are regulated by FSH; and iii) OCT4 along with LIN28 and BMP4 are highly expressed in ovarian cancers.

Uncovering molecular events associated with the chemosuppressive effects of flaxseed: a microarray analysis of the laying hen model of ovarian cancer

Background

The laying hen model of spontaneous epithelial ovarian cancer (EOC) is unique in that it is the only model that enables observations of early events in disease progression and is therefore also uniquely suited for chemoprevention trials. Previous studies on the effect of dietary flaxseed in laying hens have revealed the potential for both amelioration and prevention of ovarian cancer. The objective of this study was to assess the effect of flaxseed on genes and pathways that are dysregulated in tumors. We have used a bioinformatics approach to identify these genes, followed by qPCR validation, immunohistochemical localization, and in situ hybridization to visualize expression in normal ovaries and tumors from animals fed a control diet or a diet containing 10% flaxseed.

Results

Bioinformatic analysis of ovarian tumors in hens led to the identification of a group of highly up-regulated genes that are involved in the embryonic process of branching morphogenesis. Expression of these genes coincides with expression of E-cadherin in the tumor epithelium. Levels of expression of these genes in tumors from flax-fed animals are reduced 40-60%. E-cadherin and miR200 are both up-regulated in tumors from control-fed hens, whereas their expression is decreased 60-75% in tumors from flax-fed hens. This does not appear to be due to an increase in ZEB1 as mRNA levels are increased five-fold in tumors, with no significant difference between control-fed and flax-fed hens.

Conclusions

We suggest that nutritional intervention with flaxseed targets the pathways regulating branching morphogenesis and thereby alters the progression of ovarian cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-709) contains supplementary material, which is available to authorized users.

Morphological and immunohistochemical study of ovarian and tubal dysplasia associated with tamoxifen

Ovarian epithelial dysplasia was initially described in material from prophylactic oophorectomies for BReast CAncer gene (BRCA) mutation. Similar histopathological abnormalities have been revealed after ovulation stimulation. Given that tamoxifen (TAM) has a clomid-like effect and is sometimes used to induce ovulation, we studied the morphological features and immunohistochemical expression patterns of neoplasia-associated markers in adnexectomies previously exposed to TAM for breast cancer. We blindly reviewed 173 histopathological slides of adnexectomies according to three groups – oophorectomies associated with TAM exposure (n=42), oophorectomies associated with clomiphene exposure (n=15) and a spontaneously fertile non cancerous control group (n=116). Morphological features (with an ovarian and tubal dysplasia scoring system) and immunohistochemical expression patterns of Ki-67, p53 and Aldehyde dehydrogenase 1 (ALDH1 is an enzyme significantly associated with earlystage ovarian cancer) were evaluated and correlated. Mean tubal dysplasia score was significantly higher in the TAM group and clomiphen group than in controls (respectively 7.8 vs 3.5, P<0.007 and 6.8 vs 3.5, P=0.008). There is no statistical difference for the ovarian score in TAM group in comparison with the control group whereas we found a significant score for clomiphen group (6.5, P=0.009). Increased ALDH1 expression was observed in the two exposed group whereas expression patterns of Ki67 and p53 were moderate. Interestingly, ALDH1 expression was low in non-dysplastic epithelium, high in dysplasia, and constantly low in the two carcinoma.

Furthemore, we confirm our previous results showing that ALDH1 may be a useful tissue biomarker in the subtle histopathological diagnosis of tubo-ovarian dysplasia.

Early preinvasive lesions in ovarian cancer

Faced with the catastrophic prognosis for ovarian cancer due to the fact that it is most often diagnosed late at the peritoneal carcinomatosis stage, screening and early detection could probably reduce the mortality rate. A better understanding of the molecular characteristics of the different ovarian cancer subtypes and their specific molecular signatures is indispensable prior to development of new screening strategies. We discuss here the early natural history of ovarian cancer and its origins.

A new spontaneously transformed syngeneic model of high-grade serous ovarian cancer with a tumor-initiating cell population

Improving screening and treatment options for patients with epithelial ovarian cancer has been a major challenge in cancer research. Development of novel diagnostic and therapeutic approaches, particularly for the most common subtype, high-grade serous ovarian cancer (HGSC), has been hampered by controversies over the origin of the disease and a lack of spontaneous HGSC models to resolve this controversy. Over long-term culture in our laboratory, an ovarian surface epithelial (OSE) cell line spontaneously transformed OSE (STOSE). The objective of this study was to determine if the STOSE cell line is a good model of HGSC. STOSE cells grow faster than early passage parental M0505 cells with a doubling time of 13 and 48 h, respectively. STOSE cells form colonies in soft agar, an activity for which M0505 cells have negligible capacity. Microarray analysis identified 1755 down-regulated genes and 1203 up-regulated genes in STOSE compared to M0505 cells, many associated with aberrant Wnt/β-catenin and Nf-κB signaling. Upregulation of Ccnd1 and loss of Cdkn2a in STOSE tumors is consistent with changes identified in human ovarian cancers by The Cancer Genome Atlas. Intraperitoneal injection of STOSE cells into severe combined immunodeficient and syngeneic FVB/N mice produced cytokeratin+, WT1+, inhibin-, and PAX8+ tumors, a histotype resembling human HGSC. Based on evidence that a SCA1+ stem cell-like population exists in M0505 cells, we examined a subpopulation of SCA1+ cells that is present in STOSE cells. Compared to SCA1- cells, SCA1+ STOSE cells have increased colony-forming capacity and form palpable tumors 8 days faster after intrabursal injection into FVB/N mice. This study has identified the STOSE cells as the first spontaneous murine model of HGSC and provides evidence for the OSE as a possible origin of HGSC. Furthermore, this model provides a novel opportunity to study how normal stem-like OSE cells may transform into tumor-initiating cells.

Ovarian cancer stem cells: are they real and why are they important?

The cancer stem cell hypothesis has been put forward as a paradigm to describe varying levels of aggressiveness in heterogeneous tumors. Specifically, many subpopulations have been clearly demonstrated to possess increased tumorigenicity in mice, broad differentiating capacity, and resistance to therapy. However, the extent to which these experimental findings are potentially clinically significant is still not clear. This review will describe the principles of this emerging hypothesis, ways in which it may be appropriate in ovarian cancer based on the clinical course of the disease, and how we might exploit it to improve outcomes in ovarian cancer patients.