The Mesothelial Origin of Carcinoma Associated-Fibroblasts in Peritoneal Metastasis

Cancer Associated Fibroblasts: Naughty Neighbors That Drive Ovarian Cancer Progression

Ovarian cancer is the most lethal gynecologic malignancy, and patient prognosis has not improved significantly over the last several decades. In order to improve therapeutic approaches and patient outcomes, there is a critical need for focused research towards better understanding of the disease. Recent findings have revealed that the tumor microenvironment plays an essential role in promoting cancer progression and metastasis. The tumor microenvironment consists of cancer cells and several different types of normal cells recruited and reprogrammed by the cancer cells to produce factors beneficial to tumor growth and spread. These normal cells present within the tumor, along with the various extracellular matrix proteins and secreted factors, constitute the tumor stroma and can compose 10–60% of the tumor volume. Cancer associated fibroblasts (CAFs) are a major constituent of the tumor microenvironment, and play a critical role in promoting many aspects of tumor function. This review will describe the various hypotheses about the origin of CAFs, their major functions in the tumor microenvironment in ovarian cancer, and will discuss the potential of targeting CAFs as a possible therapeutic approach.

PAI-1 secreted from metastatic ovarian cancer cells triggers the tumor-promoting role of the mesothelium in a feedback loop to accelerate peritoneal dissemination

The mesothelium, covered by a continuous monolayer of mesothelial cells, is the first protective barrier against metastatic ovarian cancer. However, mesothelial cells release tumor-promoting factors that accelerate the process of peritoneal metastasis. We identified cancer-associated mesothelial cells (CAMs) that had tumor-promoting potential. Here, we found that plasminogen activator inhibitor-1 (PAI-1) induced the formation of CAMs, after which CAMs increasingly secreted the oncogenic factors interleukin-8 (IL-8) and C-X-C motif chemokine ligand 5 (CXCL5), further promoting the metastasis of ovarian cancer cells in a feedback loop. After the formation of CAMs, PAI-1 activated the nuclear factor kappa B (NFκB) pathway in the CAMs, thus transcriptionally upregulating the expression of the downstream NFκB targets IL-8 and CXCL5. Moreover, PAI-1 correlated with peritoneal metastasis in ovarian cancer patients and indicated a poor prognosis. In both ex vivo and in vivo models, after PAI-1 expression was knocked down, the metastasis of ovarian cancer cells decreased significantly. Therefore, targeting PAI-1 may provide a potential target for future therapeutics to prevent the formation of CAMs and alleviate peritoneal metastasis in ovarian cancer patients.

Exosomal miR-21-5p derived from gastric cancer promotes peritoneal metastasis via mesothelial-to-mesenchymal transition

Peritoneal metastasis is a primary metastatic route for gastric cancers, and the mechanisms underlying this process are still unclear. Peritoneal mesothelial cells (PMCs) undergo mesothelial-to-mesenchymal transition (MMT) to provide a favorable environment for metastatic cancer cells. In this study, we investigated how the exosomal miR-21-5p induces MMT and promotes peritoneal metastasis. Gastric cancer (GC)-derived exosomes were identified by transmission electron microscopy and western blot analysis, then the uptake of exosomes was confirmed by PKH-67 staining. The expression of miR-21-5p and SMAD7 were measured by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot, and the interactions between miR-21-5p and its target genes SMAD7 were confirmed by Luciferase reporter assays. The MMT of PMCs was determined by invasion assays, adhesion assays, immunofluorescent assay, and western blot. Meanwhile, mouse model of tumor peritoneal dissemination model was performed to investigate the role of exosomal miR-21-5p in peritoneal metastasis in vivo. We found that PMCs could internalize GC-derived exosomal miR-21-5p and led to increased levels of miR-21-5p in PMCs. Through various types of in vitro and in vivo assays, we confirmed that exosomal miR-21-5p was able to induce MMT of PMCs and promote tumor peritoneal metastasis. Moreover, our study revealed that this process was promoted by exosomal miR-21-5p through activating TGF-β/Smad pathway via targeting SMAD7. Altogether, our data suggest that exosomal miR-21-5p induces MMT of PMCs and promote cancer peritoneal dissemination by targeting SMAD7. The exosomal miR-21-5p may be a novel therapeutic target for GC peritoneal metastasis.

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.

Procancerogenic activity of senescent cells: A case of the peritoneal mesothelium

Human peritoneal mesothelial cells belong to a narrow group of somatic cells in which both the triggers and the mechanisms of senescence have already been well defined. Importantly, senescent mesothelial cells have been found in the peritoneal cavity in vivo. From a clinical point of view, peritoneal mesothelial cells have been recognized as playing a critical role in the intraperitoneal development of tumor metastases. The pro-cancerogenic behavior of mesothelial cells is even more pronounced when the cells exhaust their proliferative capacity and become senescent. In this review, we summarize the current state of art regarding the contribution of peritoneal mesothelial cells in the progression of ovarian, colorectal, and pancreatic carcinomas, with particular attention paid to the cancer-promoting activity of their senescent counterparts. Moreover, we delineate the mechanisms, mediators, and signaling pathways that are engaged by the senescent mesothelial cells to support such vital elements of cancer progression as adhesion, proliferation, migration, invasion, epithelial-mesenchymal transition, and angiogenesis. Finally, we discuss the experimental evidence regarding both natural and synthetic compounds that may either prevent or restrict cancer development by delaying senescence of mesothelial cells.

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.

Hypoxia, cytokines and stromal recruitment: parallels between pathophysiology of encapsulating peritoneal sclerosis, endometriosis and peritoneal metastasis

Peritoneal response to various kinds of injury involves loss of peritoneal mesothelial cells (PMC), danger signalling, epithelial-mesenchymal transition and mesothelial-mesenchymal transition (MMT). Encapsulating peritoneal sclerosis (EPS), endometriosis (EM) and peritoneal metastasis (PM) are all characterized by hypoxia and formation of a vascularized connective tissue stroma mediated by vascular endothelial growth factor (VEGF). Transforming growth factor-β1 (TGF-β1) is constitutively expressed by the PMC and plays a major role in the maintenance of a transformed, inflammatory micro-environment in PM, but also in EPS and EM. Persistently high levels of TGF-β1 or stimulation by inflammatory cytokines (interleukin-6 (IL-6)) induce peritoneal MMT, adhesion formation and fibrosis. TGF-β1 enhances hypoxia inducible factor-1α expression, which drives cell growth, extracellular matrix production and cell migration. Disruption of the peritoneal glycocalyx and exposure of the basement membrane release low molecular weight hyaluronan, which initiates a cascade of pro-inflammatory mediators, including peritoneal cytokines (TNF-α, IL-1, IL-6, prostaglandins), growth factors (TGF-α, TGF-β, platelet-derived growth factor, VEGF, epidermal growth factor) and the fibrin/coagulation cascade (thrombin, Tissue factor, plasminogen activator inhibitor [PAI]-1/2). Chronic inflammation and cellular transformation are mediated by damage-associated molecular patterns, pattern recognition receptors, AGE-RAGE, extracellular lactate, pro-inflammatory cytokines, reactive oxygen species, increased glycolysis, metabolomic reprogramming and cancer-associated fibroblasts. The pathogenesis of EPS, EM and PM shows similarities to the cellular transformation and stromal recruitment of wound healing.

The peritoneal "soil" for a cancerous "seed": a comprehensive review of the pathogenesis of intraperitoneal cancer metastases

Various types of tumors, particularly those originating from the ovary and gastrointestinal tract, display a strong predilection for the peritoneal cavity as the site of metastasis. The intraperitoneal spread of a malignancy is orchestrated by a reciprocal interplay between invading cancer cells and resident normal peritoneal cells. In this review, we address the current state-of-art regarding colonization of the peritoneal cavity by ovarian, colorectal, pancreatic, and gastric tumors. Particular attention is paid to the pro-tumoral role of various kinds of peritoneal cells, including mesothelial cells, fibroblasts, adipocytes, macrophages, the vascular endothelium, and hospicells. Anatomo-histological considerations on the pro-metastatic environment of the peritoneal cavity are presented in the broader context of organ-specific development of distal metastases in accordance with Paget's "seed and soil" theory of tumorigenesis. The activity of normal peritoneal cells during pivotal elements of cancer progression, i.e., adhesion, migration, invasion, proliferation, EMT, and angiogenesis, is discussed from the perspective of well-defined general knowledge on a hospitable tumor microenvironment created by the cellular elements of reactive stroma, such as cancer-associated fibroblasts and macrophages. Finally, the paper addresses the unique features of the peritoneal cavity that predispose this body compartment to be a niche for cancer metastases, presents issues that are topics of an ongoing debate, and points to areas that still require further in-depth investigations.

Development of Peritoneal Carcinomatosis in Epithelial Ovarian Cancer: A Review

Epithelial ovarian cancer (EOC) metastasizes intra-abdominally with often numerous, superficial, small-sized lesions. This so-called peritoneal carcinomatosis is difficult to treat, and peritoneal recurrences are frequently observed, leading to a poor prognosis. Underlying mechanisms of interactions between EOC and peritoneal cells are incompletely understood. This review summarizes and discusses the development of peritoneal carcinomatosis from a cell-biological perspective, focusing on characteristics of EOC and peritoneal cells. We aim to provide insight into how peritoneum facilitates tumor adhesion but limits size of lesions and depth of invasion. The development of peritoneal carcinomatosis is a multistep process that requires adaptations of EOC and peritoneal cells. Mechanisms that enable tumor adhesion and growth involve cadherin restructuring on EOC cells, integrin-mediated adhesion, and mesothelial evasion by mechanical forces driven by integrin-ligand interactions. Clinical trials targeting these mechanisms, however, showed only limited effects. Other factors that inhibit tumor growth and deep invasion are virtually unknown. Future studies are needed to elucidate the exact mechanisms that underlie the development and limited growth of peritoneal carcinomatosis. This review on development of peritoneal carcinomatosis of EOC summarizes the current knowledge and its limitations. Clarification of the stepwise process may inspire future research to investigate new treatment approaches of peritoneal carcinomatosis.

Combination of platelet count and neutrophil-lymphocyte ratio as a prognostic marker to predict chemotherapeutic response and survival in metastatic advanced gastric cancer

AIM

The study evaluated the prognostic impact of combination of platelet count and neutrophil-lymphocyte ratio (COP-NLR) for first-line chemotherapeutic response and survival outcomes in metastatic advanced gastric cancer patients.

METHODS

Two hundred and seventy-three patients were categorized into three COP-NLR groups (COP-NLR 0, 1, 2) according to their platelet count and neutrophil-lymphocyte ratio.

RESULTS

The COP-NLR 0 had a significantly higher disease control rate (93%) than the other two groups (p = 0.011). A logistic regression model showed that COP-NLR was an independent risk factor for response to chemotherapy (odds ratio: 2.247; 95% CI: 1.303-3.874; p = 0.044). The median overall survival for COP-NLR 0, 1 and 2 was 14.8, 10.3 and 9.1 months, respectively (p = 0.001).

CONCLUSION

COP-NLR is a useful predictor of survival outcomes and chemotherapeutic response in patients with metastatic advanced gastric cancer.

Gastric cancer-derived exosomes promote peritoneal metastasis by destroying the mesothelial barrier

An intact mesothelium serves as a protective barrier to inhibit peritoneal carcinomatosis. Cancer-derived exosomes can mediate directional tumor metastasis; however, little is known about whether gastric cancer-derived exosomes will destroy the mesothelial barrier and promote peritoneal dissemination. Here, we demonstrate that gastric cancer-derived exosomes facilitate peritoneal metastasis by causing mesothelial barrier disruption and peritoneal fibrosis. Injury of peritoneal mesothelial cells elicited by gastric cancer-derived exosomes is through concurrent apoptosis and mesothelial-to-mesenchymal transition (MMT). Additionally, upregulation of p-ERK in peritoneal mesothelial cells is primarily responsible for the MMT while contributing little to apoptosis. Together, these data support the concept that exosomes play a crucial role in remodeling the premetastatic microenvironment and identify a novel mechanism for peritoneal metastasis of gastric carcinoma.

Mesothelial-to-mesenchymal transition as a possible therapeutic target in peritoneal metastasis of ovarian cancer

Peritoneal dissemination is the primary metastatic route of ovarian cancer (OvCa), and is often accompanied by the accumulation of ascitic fluid. The peritoneal cavity is lined by mesothelial cells (MCs), which can be converted into carcinoma‐associated fibroblasts (CAFs) through mesothelial‐to‐mesenchymal transition (MMT). Here, we demonstrate that MCs isolated from ascitic fluid (AFMCs) of OvCa patients with peritoneal implants also undergo MMT and promote subcutaneous tumour growth in mice. RNA sequencing of AFMCs revealed that MMT‐related pathways – including transforming growth factor (TGF)‐β signalling – are differentially regulated, and a gene signature was verified in peritoneal implants from OvCa patients. In a mouse model, pre‐induction of MMT resulted in increased peritoneal tumour growth, whereas interfering with the TGF‐β receptor reduced metastasis. MC‐derived CAFs showed activation of Smad‐dependent TGF‐β signalling, which was disrupted in OvCa cells, despite their elevated TGF‐β production. Accordingly, targeting Smad‐dependent signalling in the peritoneal pre‐metastatic niche in mice reduced tumour colonization, suggesting that Smad‐dependent MMT could be crucial in peritoneal carcinomatosis. Together, these results indicate that bidirectional communication between OvCa cells and MC‐derived CAFs, via TGF‐β‐mediated MMT, seems to be crucial to form a suitable metastatic niche. We suggest MMT as a possible target for therapeutic intervention and a potential source of biomarkers for improving OvCa diagnosis and/or prognosis. © 2017 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Heterogeneity in Cancer Metabolism: New Concepts in an Old Field

SIGNIFICANCE

In the last years, metabolic reprogramming, fluctuations in bioenergetic fuels, and modulation of oxidative stress became new key hallmarks of tumor development. In cancer, elevated glucose uptake and high glycolytic rate, as a source of adenosine triphosphate, constitute a growth advantage for tumors. This represents the universally known Warburg effect, which gave rise to one major clinical application for detecting cancer cells using glucose analogs: the positron emission tomography scan imaging. Recent Advances: Glucose utilization and carbon sources in tumors are much more heterogeneous than initially thought. Indeed, new studies emerged and revealed a dual capacity of tumor cells for glycolytic and oxidative phosphorylation (OXPHOS) metabolism. OXPHOS metabolism, which relies predominantly on mitochondrial respiration, exhibits fine-tuned regulation of respiratory chain complexes and enhanced antioxidant response or detoxification capacity.

CRITICAL ISSUES

OXPHOS-dependent cancer cells use alternative oxidizable substrates, such as glutamine and fatty acids. The diversity of carbon substrates fueling neoplastic cells is indicative of metabolic heterogeneity, even within tumors sharing the same clinical diagnosis. Metabolic switch supports cancer cell stemness and their bioenergy-consuming functions, such as proliferation, survival, migration, and invasion. Moreover, reactive oxygen species-induced mitochondrial metabolism and nutrient availability are important for interaction with tumor microenvironment components. Carcinoma-associated fibroblasts and immune cells participate in the metabolic interplay with neoplastic cells. They collectively adapt in a dynamic manner to the metabolic needs of cancer cells, thus participating in tumorigenesis and resistance to treatments.

FUTURE DIRECTIONS

Characterizing the reciprocal metabolic interplay between stromal, immune, and neoplastic cells will provide a better understanding of treatment resistance. Antioxid. Redox Signal. 26, 462-485.

Changes in the coelomic microclimate during carbon dioxide laparoscopy: morphological and functional implications

In this article the adverse effects of laparoscopic CO2 pneumoperitoneum and coelomic climate change, and their potential prevention by warmed, humidified carbon dioxide insufflation are reviewed. The use of pressurized cold, dry carbon dioxide (C02) pneumoperitoneum causes a number of local effects on the peritoneal mesothelium, as well as systemic effects. These can be observed at a macroscopic, microscopic, cellular and metabolic level. Local effects include evaporative cooling, oxidative stress, desiccation of mesothelium, disruption of mesothelial cell junctions and glycocalyx, diminished scavenging of reactive oxygen species, decreased peritoneal blood flow, peritoneal acidosis, peritoneal hypoxia or necrosis, exposure of the basal lamina and extracellular matrix, lymphocyte infiltration, and generation of peritoneal cytokines such as IL-1, IL-6, IL-8 and TNFα. Such damage is increased by high CO2 insufflation pressures and gas velocities and prolonged laparoscopic procedures. The resulting disruption of the glycocalyx, mesothelial cell barrier and exposure of the extracellular matrix creates a cascade of immunological and pro-inflammatory events and favours tumour cell implantation. Systemic effects include cardiopulmonary and respiratory changes, hypothermia and acidosis. Such coelomic climate change can be prevented by the use of lower insufflation pressures and preconditioned warm humidified CO2. By achieving a more physiological temperature, pressure and humidity, the coelomic microenvironment can be better preserved during pneumoperitoneum. This has the potential clinical benefits of maintaining isothermia and perfusion, reducing postoperative pain, preventing adhesions and inhibiting cancer cell implantation in laparoscopic surgery.

Mesothelial Cells Create a Novel Tissue Niche That Facilitates Gastric Cancer Invasion

Peritoneal mesothelial cells (PMC) cover organ surfaces in the abdominal cavity. In this study, lineage tracing revealed that the PMCs guide cancer cell invasion in the gastric wall and in peritoneal metastatic lesions. Serosal PMCs covering the stomach surface entered the gastric wall to create a novel niche that favored gastric cancer cell invasion. PMC infiltration was induced by incorporation of cancer cell-derived, Wnt3a-containing extracellular vesicles. Infiltrated PMCs in turn promoted subserosal invasion of cancer cells. Mutual attraction between cancer cells and PMCs accelerated tumor invasion in the gastric wall, and PMC-led cancer cell invasion in disseminated tumors within the abdominal wall and diaphragm. Addition of the carboxyl terminus of Dickkopf-1 attenuated directional invasion of PMCs toward cancer cells both in vitro and in the gastric wall in vivo PMCs were sensitive to the aldehyde dehydrogenase (ALDH) inhibitor disulfiram (DSF), as ALDH activity is elevated in PMCs. Wnt3a upregulated ALDH, and addition of DSF inhibited the invasive properties of PMCs, whereas DSF pretreatment suppressed gastric infiltration of PMCs and subserosal invasion by cancer cells. Our results suggest that stabilization of PMCs may become an effective therapy for the prevention of local invasion and metastasis of gastric cancer. Cancer Res; 77(3); 684-95. ©2016 AACR.