Peritoneal mesothelium promotes the progression of ovarian cancer cells in vitro and in a mice xenograft model in vivo

Metastasis-associated fibroblasts in peritoneal surface malignancies

Over decades, peritoneal surface malignancies (PSMs) have been associated with limited treatment options and poor prognosis. However, advancements in perioperative systemic chemotherapy, cytoreductive surgery (CRS), and hyperthermic intraperitoneal chemotherapy (HIPEC) have significantly improved clinical outcomes. PSMs predominantly result from the spread of intra-abdominal neoplasia, which then form secondary peritoneal metastases. Colorectal, ovarian, and gastric cancers are the most common contributors. Despite diverse primary origins, the uniqueness of the peritoneum microenvironment shapes the common features of PSMs. Peritoneal metastization involves complex interactions between tumour cells and the peritoneal microenvironment. Fibroblasts play a crucial role, contributing to tumour development, progression, and therapy resistance. Peritoneal metastasis-associated fibroblasts (MAFs) in PSMs exhibit high heterogeneity. Single-cell RNA sequencing technology has revealed that immune-regulatory cancer-associated fibroblasts (iCAFs) seem to be the most prevalent subtype in PSMs. In addition, other major subtypes as myofibroblastic CAFs (myCAFs) and matrix CAFs (mCAFs) were frequently observed across PSMs studies. Peritoneal MAFs are suggested to originate from mesothelial cells, submesothelial fibroblasts, pericytes, endothelial cells, and omental-resident cells. This plasticity and heterogeneity of CAFs contribute to the complex microenvironment in PSMs, impacting treatment responses. Understanding these interactions is crucial for developing targeted and local therapies to improve PSMs patient outcomes.

Involvement in Tumorigenesis and Clinical Significance of CXCL1 in Reproductive Cancers: Breast Cancer, Cervical Cancer, Endometrial Cancer, Ovarian Cancer and Prostate Cancer

C-X-C motif chemokine ligand 1 (CXCL1) is a member of the CXC chemokine subfamily and a ligand for CXCR2. Its main function in the immune system is the chemoattraction of neutrophils. However, there is a lack of comprehensive reviews summarizing the significance of CXCL1 in cancer processes. To fill this gap, this work describes the clinical significance and participation of CXCL1 in cancer processes in the most important reproductive cancers: breast cancer, cervical cancer, endometrial cancer, ovarian cancer, and prostate cancer. The focus is on both clinical aspects and the significance of CXCL1 in molecular cancer processes. We describe the association of CXCL1 with clinical features of tumors, including prognosis, ER, PR and HER2 status, and TNM stage. We present the molecular contribution of CXCL1 to chemoresistance and radioresistance in selected tumors and its influence on the proliferation, migration, and invasion of tumor cells. Additionally, we present the impact of CXCL1 on the microenvironment of reproductive cancers, including its effect on angiogenesis, recruitment, and function of cancer-associated cells (macrophages, neutrophils, MDSC, and T_reg). The article concludes by summarizing the significance of introducing drugs targeting CXCL1. This paper also discusses the significance of ACKR1/DARC in reproductive cancers.

The functional multipotency of transforming growth factor β signaling at the intersection of senescence and cancer

The transforming growth factor β (TGF-β) family of cytokines comprises a group of proteins, their receptors, and effector molecules that, in a coordinated manner, modulate a plethora of physiological and pathophysiological processes. TGF-β1 is the best known and plausibly most active representative of this group. It acts as an immunosuppressant, contributes to extracellular matrix remodeling, and stimulates tissue fibrosis, differentiation, angiogenesis, and epithelial-mesenchymal transition. In recent years, this cytokine has been established as a vital regulator of organismal aging and cellular senescence. Finally, the role of TGF-β1 in cancer progression is no longer in question. Because this protein is involved in so many, often overlapping phenomena, the question arises whether it can be considered a molecular bridge linking some of these phenomena together and governing their reciprocal interactions. In this study, we reviewed the literature from the perspective of the role of various TGF-β family members as regulators of a complex mutual interplay between senescence and cancer. These aspects are then considered in a broader context of remaining TGF-β-related functions and coexisting processes. The main narrative axis in this work is centered around the interaction between the senescence of normal peritoneal cells and ovarian cancer cells. The discussion also includes examples of TGF-β activity at the interface of other normal and cancer cell types.

Amelioration of human peritoneal mesothelial cell co-culture-evoked malignant potential of ovarian cancer cells by acacetin involves LPA release-activated RAGE-PI3K/AKT signaling

Background

Ovarian cancer is a devastating gynecological malignancy and frequently presents as an advanced carcinoma with disseminated peritoneum metastasis. Acacetin exerts anti-cancerous effects in several carcinomas. Here, we sought to investigate acacetin function in ovarian cancer malignancy triggered by peritoneal mesothelial cells.

Methods

Peritoneal mesothelial cells were treated with acacetin, and then the conditioned medium was collected to treat ovarian cancer cells. Then, cell proliferation was analyzed by MTT assay. Transwell analysis was conducted to evaluate cell invasion. Protein expression was determined by western blotting. ELISA and qRT-PCR were applied to analyze inflammatory cytokine levels. The underlying mechanism was also explored.

Results

Acacetin suppressed cell proliferation and invasion, but enhanced cell apoptosis. Furthermore, mesothelial cell-evoked malignant characteristics were inhibited when mesothelial cells were pre-treated with acacetin via restraining cell proliferation and invasion, concomitant with decreases in proliferation-related PCNA, MMP-2 and MMP-9 levels. Simultaneously, acacetin reduced mesothelial cell-induced transcripts and production of pro-inflammatory cytokine IL-6 and IL-8 in ovarian cancer cells. Mechanically, acacetin decreased lysophosphatidic acid (LPA) release from mesothelial cells, and subsequent activation of receptor for advanced glycation end-products (RAGE)-PI3K/AKT signaling in ovarian cancer cells. Notably, exogenous LPA restored the above pathway, and offset the efficacy of acacetin against mesothelial cell-evoked malignancy in ovarian cancer cells, including cell proliferation, invasion and inflammatory cytokine production.

Conclusions

Acacetin may not only engender direct inhibition of ovarian cancer cell malignancy, but also antagonize mesothelial cell-evoked malignancy by blocking LPA release-activated RAGE-PI3K/AKT signaling. Thus, these findings provide supporting evidence for a promising therapeutic agent against ovarian cancer.

Graphical Abstract

Cancer-associated mesothelial cells promote ovarian cancer chemoresistance through paracrine osteopontin signaling

Ovarian cancer is the leading cause of gynecological malignancy-related deaths, due to its widespread intraperitoneal metastases and acquired chemoresistance. Mesothelial cells are an important cellular component of the ovarian cancer microenvironment that promote metastasis. However, their role in chemoresistance is unclear. Here, we investigated whether cancer-associated mesothelial cells promote ovarian cancer chemoresistance and stemness in vitro and in vivo. We found that osteopontin is a key secreted factor that drives mesothelial-mediated ovarian cancer chemoresistance and stemness. Osteopontin is a secreted glycoprotein that is clinically associated with poor prognosis and chemoresistance in ovarian cancer. Mechanistically, ovarian cancer cells induced osteopontin expression and secretion by mesothelial cells through TGF-β signaling. Osteopontin facilitated ovarian cancer cell chemoresistance via the activation of the CD44 receptor, PI3K/AKT signaling, and ABC drug efflux transporter activity. Importantly, therapeutic inhibition of osteopontin markedly improved the efficacy of cisplatin in both human and mouse ovarian tumor xenografts. Collectively, our results highlight mesothelial cells as a key driver of ovarian cancer chemoresistance and suggest that therapeutic targeting of osteopontin may be an effective strategy for enhancing platinum sensitivity in ovarian cancer.

Malignant Ascites Promote Adhesion of Ovarian Cancer Cells to Peritoneal Mesothelium and Fibroblasts

Although malignant ascites (MAs) are known to contribute to various aspects of ovarian cancer progression, knowledge regarding their role in the adhesion of cancer cells to normal peritoneal cells is incomplete. Here, we compared the effect of MAs and benign ascites (BAs) on the adhesion of A2780 and OVCAR-3 cancer cells to omentum-derived peritoneal mesothelial cells (PMCs) and peritoneal fibroblasts (PFBs). The results showed that MAs stimulated the adhesion of A2780 and OVCAR-3 cells to PMCs and PFBs more efficiently than did BAs, and the strongest binding occurred when both cancer and normal cells were exposed to the fluid. Intervention studies showed that MAs-driven adhesion of A2780 cells to PMCs/PFBs depends on the presence of TGF-β1 and HGF, whereas binding of OVCAR-3 cells was mediated by TGF-β1, GRO-1, and IGF-1. Moreover, MAs upregulated α5β1 integrin expression on PFBs but not on PMCs or cancer cells, vimentin expression in all cells tested, and ICAM-1 only in cancer cells. When integrin-linked kinase was neutralized in PMCs or PFBs, cancer cell adhesion to PMCs and PFBs decreased. Collectively, our report shows that MAs may contribute to the early stages of ovarian cancer metastasis by modulating the proadhesive interplay between normal and cancer cells.

Hypoxia-autophagy axis induces VEGFA by peritoneal mesothelial cells to promote gastric cancer peritoneal metastasis through an integrin α5-fibronectin pathway

BACKGROUND

Peritoneal metastasis (PM) is an important pathological process in the progression of gastric cancer (GC). The metastatic potential of tumor and stromal cells is governed by hypoxia, which is a key molecular feature of the tumor microenvironment. Mesothelial cells also participate in this complex and dynamic process. However, the molecular mechanisms underlying the hypoxia-driven mesothelial-tumor interactions that promote peritoneal metastasis of GC remain unclear.

METHODS

We determined the hypoxic microenvironment in PM of nude mice by immunohistochemical analysis and screened VEGFA by human growth factor array kit. The crosstalk mediated by VEGFA between peritoneal mesothelial cells (PMCs) and GC cells was determined in GC cells incubated with conditioned medium prepared from hypoxia-treated PMCs. The association between VEGFR1 and integrin α5 and fibronectin in GC cells was enriched using Gene Set Enrichment Analysis and KEGG pathway enrichment analysis. In vitro and xenograft mouse models were used to evaluate the impact of VEGFA/VEGFR1 on gastric cancer peritoneal metastasis. Confocal microscopy and immunoprecipitation were performed to determine the effect of hypoxia-induced autophagy.

RESULTS

Here we report that in the PMCs of the hypoxic microenvironment, SIRT1 is degraded via the autophagic lysosomal pathway, leading to increased acetylation of HIF-1α and secretion of VEGFA. Under hypoxic conditions, VEGFA derived from PMCs acts on VEGFR1 of GC cells, resulting in p-ERK/p-JNK pathway activation, increased integrin α5 and fibronectin expression, and promotion of PM.

CONCLUSIONS

Our findings have elucidated the mechanisms by which PMCs promote PM in GC in hypoxic environments. This study also provides a theoretical basis for considering autophagic pathways or VEGFA as potential therapeutic targets to treat PM in GC.

Current strategies for different paclitaxel-loaded Nano-delivery Systems towards therapeutic applications for ovarian carcinoma: A review article

Ovarian carcinoma (OC) is one of the leading causes of death among gynecologic malignancies all over the world. It is characterized by high mortality rate because of the lack of early diagnosis. The first-line chemotherapeutic regimen for late stage epithelial ovarian cancer is paclitaxel in combination to carboplatin. However, in most of cases, relapse occurs within six months despite the initial success of this chemotherapeutic combination. A lot of challenges have been encountered with the conventional delivery of paclitaxel in addition to the occurrence of severe off-target toxicity. One major problem is poor paclitaxel solubility which was improved by addition of Cremophor EL that unfortunately resulted in hypersensitivity side effects. Another obstacle is the multi drug resistance which is the main cause of OC recurrence. Accordingly, incorporation of paclitaxel, solely or in combination to other drugs, in nanocarrier systems has grabbed attention of many researchers to circumvent all these hurdles. The current review is the first article that provides a comprehensive overview on multi-faceted implementations of paclitaxel loaded nanoplatforms to solve delivery obstacles of paclitaxel in management of ovarian carcinoma. Moreover, challenges in physicochemical properties, biological activity and targeted delivery of PTX were depicted with corresponding solutions using nanotechnology. Different categories of nanocarriers employed were collected included lipid, protein, polymeric, solid nanoemulsion and hybrid systems. Future perspectives including imperative research considerations in ovarian cancer therapy were proposed as well.

Senescence-related deterioration of intercellular junctions in the peritoneal mesothelium promotes the transmesothelial invasion of ovarian cancer cells

Mechanisms of transmesothelial invasion of ovarian cancer are still poorly understood. Here we examined whether this phenomenon may be determined by an expression of intercellular junctions in peritoneal mesothelial cells (PMCs). Analysis of ovarian tumors showed that cancer cells are localized below an intact layer of PMCs. The PMCs located near the invaded cancer cells displayed low expression of connexin 43, E-cadherin, occludin, and desmoglein, as well as expressed SA-β-Gal, a marker of senescence. Experiments in vitro showed that senescent PMCs exhibited decreased levels of the four tested intercellular junctions, and that the invasion of ovarian cancer cells through the PMCs increased proportionally to the admixture of senescent cells. Intervention studies showed that the expression of connexin 43, E-cadherin, occludin, and desmoglein in senescent PMCs could be restored upon the blockade of p38 MAPK, NF-κB, AKT, JNK, HGF, and TGF-β1. When these molecules were neutralized, the efficiency of the transmesothelial cancer cell invasion was diminished. Collectively, our findings show that the integrity of the peritoneal mesothelium, which is determined by the expression of junctional proteins, is critical for the invasion of ovarian cancer. They also indicate a mechanism by which senescent PMCs may promote the invasive potential of cancer cells.

A Unique Pattern of Mesothelial-Mesenchymal Transition Induced in the Normal Peritoneal Mesothelium by High-Grade Serous Ovarian Cancer

The study was designed to establish whether high aggressiveness of high-grade serous ovarian cancer cells (HGSOCs), which display rapid growth, advanced stage at diagnosis and the highest mortality among all epithelial ovarian cancer histotypes, may be linked with a specific pattern of mesothelial-mesenchymal transition (MMT) elicited by these cells in normal peritoneal mesothelial cells (PMCs). Experiments were performed on primary PMCs, stable and primary ovarian cancer cells, tumors from patients with ovarian cancer, and laboratory animals. Results of in vitro and in vivo tests showed that MMT triggered by HGSOCs (primary cells and OVCAR-3 line) is far more pronounced than the process evoked by cells representing less aggressive ovarian cancer histotypes (A2780, SKOV-3). Mechanistically, HGSOCs induce MMT via Smad 2/3, ILK, TGF-β1, HGF, and IGF-1, whereas A2780 and SKOV-3 cells via exclusively Smad 2/3 and HGF. The conditioned medium from PMCs undergoing MMT promoted the progression of cancer cells and the effects exerted by the cells triggered to undergo MMT by the HGSOCs were significantly stronger than those related to the activity of their less aggressive counterparts. Our findings indicate that MMT in PMCs provoked by HGSOCs is stronger, proceeds via different mechanisms and has more procancerous characteristics than MMT provoked by less aggressive cancer histotypes, which may at least partly explain high aggressiveness of HGSOCs.

Metastasis Organotropism: Redefining the Congenial Soil

Metastasis is the most devastating stage of cancer progression and causes the majority of cancer-related deaths. Clinical observations suggest that most cancers metastasize to specific organs, a process known as "organotropism." Elucidating the underlying mechanisms may help identify targets and treatment strategies to benefit patients. This review summarizes recent findings on tumor-intrinsic properties and their interaction with unique features of host organs, which together determine organ-specific metastatic behaviors. Emerging insights related to the roles of metabolic changes, the immune landscapes of target organs, and variation in epithelial-mesenchymal transitions open avenues for future studies of metastasis organotropism.

Collagen Remodeling in the Hypoxic Tumor-Mesothelial Niche Promotes Ovarian Cancer Metastasis

Peritoneal metastases are the leading cause of morbidity and mortality in high-grade serous ovarian cancer (HGSOC). Accumulating evidence suggests that mesothelial cells are an important component of the metastatic microenvironment in HGSOC. However, the mechanisms by which mesothelial cells promote metastasis are unclear. Here, we report that the HGSOC tumor-mesothelial niche was hypoxic, and hypoxic signaling enhanced collagen I deposition by mesothelial cells. Specifically, hypoxic signaling increased expression of lysyl oxidase (LOX) in mesothelial and ovarian cancer cells to promote collagen crosslinking and tumor cell invasion. The mesothelial niche was enriched with fibrillar collagen in human and murine omental metastases. Pharmacologic inhibition of LOX reduced tumor burden and collagen remodeling in murine omental metastases. These findings highlight an important role for hypoxia and mesothelial cells in the modification of the extracellular matrix and tumor invasion in HGSOC. SIGNIFICANCE: This study identifies HIF/LOX signaling as a potential therapeutic target to inhibit collagen remodeling and tumor progression in HGSOC.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/9/2271/F1.large.jpg.

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.

A 3D tumor microenvironment regulates cell proliferation, peritoneal growth and expression patterns

Peritoneal invasion through the mesothelial cell layer is a hallmark of ovarian cancer metastasis. Using tissue engineering technologies, we recreated an ovarian tumor microenvironment replicating this aspect of disease progression. Ovarian cancer cell-laden hydrogels were combined with mesothelial cell-layered melt electrospun written scaffolds and characterized with proliferation and transcriptomic analyses and used as intraperitoneal xenografts. Here we show increased cancer cell proliferation in these 3D co-cultures, which we validated using patient-derived cells and linked to peritoneal tumor growth in vivo. Transcriptome-wide expression analysis identified IGFBP7, PTGS2, VEGFC and FGF2 as bidirectional factors deregulated in 3D co-cultures compared to 3D mono-cultures, which we confirmed by immunohistochemistry of xenograft and patient-derived tumor tissues and correlated with overall and progression-free survival. These factors were further increased upon expression of kallikrein-related proteases. This clinically predictive model allows us to mimic the complexity and processes of the metastatic disease that may lead to therapies that protect from peritoneal invasion or delay the development of metastasis.

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.

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.

EPR Oximetry Sensor-Developing a TAM Derivative for In Vivo Studies

Oxygenation is one of the most important physiological parameters of biological systems. Low oxygen concentration (hypoxia) is associated with various pathophysiological processes in different organs. Hypoxia is of special importance in tumor therapy, causing poor response to treatment. Triaryl methyl (TAM) derivative radicals are commonly used in electron paramagnetic resonance (EPR) as sensors for quantitative spatial tissue oxygen mapping. They are also known as magnetic resonance imaging (MRI) contrast agents and fluorescence imaging compounds. We report the properties of the TAM radical tris(2,3,5,6-tetrachloro-4-carboxy-phenyl)methyl, (PTMTC), a potential multimodal (EPR/fluorescence) marker. PTMTC was spectrally analyzed using EPR and characterized by estimation of its sensitivity to the oxygen in liquid environment suitable for intravenous injection (1 mM PBS, pH = 7.4). Further, fluorescent emission of the radical was measured using the same solvent and its quantum yield was estimated. An in vitro cytotoxicity examination was conducted in two cancer cell lines, HT-29 (colorectal adenocarcinoma) and FaDu (squamous cell carcinoma) and followed by uptake studies. The stability of the radical in different solutions (PBS pH = 7.4, cell media used for HT-29 and FaDu cells culturing and cytotoxicity procedure, full rat blood and blood plasma) was determined. Finally, a primary toxicity test of PTMTC was carried out in mice. Results of spectral studies confirmed the multimodal properties of PTMTC. PTMTC was demonstrated to be not absorbed by cancer cells and did not interfere with luciferin-luciferase based assays. Also in vitro and in vivo tests showed that it was non-toxic and can be freely administrated till doses of 250 mg/kg BW via both i.v. and i.p. injections. This work illustrated that PTMTC is a perfect candidate for multimodal (EPR/fluorescence) contrast agent in preclinical studies.

Oxidative stress contributes to hepatocyte growth factor-dependent pro-senescence activity of ovarian cancer cells

The cancer-promoting activity of senescent peritoneal mesothelial cells (HPMCs) has already been well evidenced both in vitro and in vivo. Here we sought to determine if ovarian cancer cells may activate senescence in HPMCs. The study showed that conditioned medium (CM) from ovarian cancer cells (OVCAR-3, SKOV-3, A2780) inhibited growth and promoted the development of senescence phenotype (increased SA-β-Gal, γ-H2A.X, 53BP1, and decreased Cx43) in HPMCs. An analysis of tumors isolated from the peritoneum of patients with ovarian cancer revealed an abundance of senescent HPMCs in proximity to cancerous tissue. The presence of senescent HPMCs was incidental when fragments of peritoneum free from cancer were evaluated. An analysis of the cells' secretome followed by intervention studies with exogenous proteins and neutralizing antibodies revealed hepatocyte growth factor (HGF) as the mediator of the pro-senescence impact of the cancer cells. The activity of cancerous CM and HGF was associated with an induction of mitochondrial oxidative stress. Signaling pathways involved in the senescence of HPMCs elicited by the cancer-derived CM and HGF included p38 MAPK, AKT and NF-κB. HPMCs that senesced prematurely in response to the cancer-derived CM promoted adhesion of ovarian cancer cells, however this effect was effectively prevented by the cell protection against oxidative stress. Collectively, our findings indicate that ovarian cancer cells can elicit HGF-dependent senescence in HPMCs, which may contribute to the formation of a metastatic niche for these cells within the peritoneal cavity.

The protective activity of mesothelial cells against peritoneal growth of gastrointestinal tumors: The role of soluble ICAM-1

In this project we examined how the presence of human peritoneal mesothelial cells (HPMCs) modifies (supports or inhibits) colorectal and pancreatic cancer cell progression in mice peritoneal cavity. Experiments were performed using primary, omentum-derived HPMCs, commercially available colorectal (SW-480) and pancreatic (PSN-1) cancer cells, and immunocompromised SCID mice. Tumor growth within the peritoneal cavity was monitored using bioluminescence. Adhesion of the cancer cells to HPMCs was examined using a fluorescence-based method, while the incidence of apoptosis was quantified using flow cytometry. Experiments showed that SW480 and PSN-1 cells formed tumors in vivo at higher efficiency when they were injected alone than in the presence of HPMCs. In vitro investigations confirmed that firm adhesion of SW480 and PSN-1 cells to HPMCs is mediated by interactions between ICAM-1 and CD43. They also revealed that IL-6 and TNFα up-regulate the expression of cell-bound ICAM-1 and the secretion of soluble ICAM-1 (sICAM-1). The basal release of sICAM-1 by HPMCs positively correlated with the expression of the cell-bound molecule. sICAM-1 inhibited dose-dependently the adhesion of SW480 and PSN-1 cells to HPMCs. Cancer cells that did not adhere to HPMCs displayed increased activity of caspase-3 and -9, increased incidence of apoptosis, and an inability to re-adhesion, as compared with their intact counterparts not exposed to sICAM-1. Our findings indicate that under certain conditions HPMCs are capable of inhibiting growth of gastrointestinal tumors in a mechanism involving the anti-adhesive capabilities of sICAM-1.

Cancer-associated peritoneal mesothelial cells lead the formation of pancreatic cancer peritoneal dissemination

The interaction between the cancer cells and the peritoneal mesothelial cells (PMCs) plays an important role in the peritoneal dissemination in several types of cancer. However, the role of PMCs in the peritoneal dissemination of pancreatic cancer remains unclear. In the present study, we investigated the interaction between the pancreatic cancer cells (PCCs) and the PMCs in the formation of peritoneal dissemination in vitro and in vivo. The tumor-stromal interaction of PCCs and PMCs significantly enhanced their mobility and invasiveness and enhanced the proliferation and anoikis resistance of PCCs. In a 3D organotypic culture model of peritoneal dissemination, co-culture of PCCs and PMCs significantly increased the cells invading into the collagen gel layer compared with mono-culture of PCCs. PMCs pre-invaded into the collagen gel, remodeled collagen fibers, and increased parallel fiber orientation along the direction of cell invasion. In the tissues of peritoneal dissemination of the KPC (LSL-KrasG12D/+; LSL-Trp53R172H/+;Pdx-1-Cre) transgenic mouse, the monolayer of PMCs was preserved in tumor-free areas, whereas PMCs around the invasive front of peritoneal dissemination proliferated and invaded into the muscle layer. In vivo, intraperitoneal injection of PCCs with PMCs significantly promoted peritoneal dissemination compared with PCCs alone. The present data suggest that the cancer-associated PMCs have important promoting roles in the peritoneal dissemination of PCCs. Therapy targeting cancer-associated PMCs may improve the prognosis of patients with pancreatic cancer.

Senescent peritoneal mesothelium creates a niche for ovarian cancer metastases

Although both incidence and aggressiveness of ovarian malignancy rise with age, the exact reason for this tendency, in particular the contribution of senescent cells, remains elusive. In this project we found that the patient's age determines the frequency of intraperitoneal metastases of ovarian cancer. Moreover, we documented that senescent human peritoneal mesothelial cells (HPMCs) stimulate proliferation, migration and invasion of ovarian cancer cells in vitro, and that this effect is related to both the activity of soluble agents released to the environment by these cells and direct cell-cell contact. The panel of mediators of the pro-cancerous activity of senescent HPMCs appeared to be cancer cell line-specific. The growth of tumors in a mouse peritoneal cavity was intensified when the cancer cells were co-injected together with senescent HPMCs. This effect was reversible when the senescence of HPMCs was slowed down by the neutralization of p38 MAPK. The analysis of lesions excised from the peritoneum of patients with ovarian cancer showed the abundance of senescent HPMCs in close proximity to the cancerous tissue. Collectively, our findings indicate that senescent HPMCs which accumulate in the peritoneum in vivo may create a metastatic niche facilitating intraperitoneal expansion of ovarian malignancy.

Ovarian cancer-derived ascitic fluids induce a senescence-dependent pro-cancerogenic phenotype in normal peritoneal mesothelial cells

PURPOSE

After the seeding ovarian cancer cells into the peritoneal cavity, ascitic fluid creates a microenvironment in which these cells can survive and disseminate. The exact nature of the interactions between malignant ascitic fluids and peritoneal mesothelial cells (HPMCs) in ovarian cancer progression has so far remained elusive. Here we assessed whether malignant ascitic fluids may promote the senescence of HPMCs and, by doing so, enhance the acquisition of their pro-cancerogenic phenotype.

METHODS

Primary omentum-derived HPMCs, ovarian cancer-derived cell lines (A2780, OVCAR-3, SKOV-3), malignant ascitic fluids and benign ascitic fluids from non-cancerous patients were used in this study. Ovarian cancer cell proliferation, as well as HPMC proliferation and senescence, were determined using flow cytometry and β-galactosidase assays, respectively. Ovarian cancer cell migration was quantified using a Transwell assay. The concentrations of soluble agents in ascitic fluids, conditioned media and cell lysates were measured using DuoSet® Immunoassay Development kits.

RESULTS

We found that HPMCs, when exposed to malignant ascitic fluids, exhibited decreased proliferation and increased senescence rates. The malignant ascitic fluids were found to contain elevated levels of HGF, TGF-β1 and GRO-1, of which HGF and GRO-1 were able to induce senescence in HPMCs. We also found that HPMCs subjected to malignant ascitic fluids or exogenously added HGF and GRO-1 stimulated ovarian cancer cell progression, which was manifested by an increased production of HA (adhesion), uPA (proliferation), IL-8 and MCP-1 (migration).

CONCLUSION

Our results indicate that malignant ascitic fluids may contribute to ovarian cancer progression by accelerating the senescence of HPMCs.

Senescent peritoneal mesothelium induces a pro-angiogenic phenotype in ovarian cancer cells in vitro and in a mouse xenograft model in vivo

It is believed that senescent cells contribute to the progression of primary and metastatic tumors, however, the exact mechanisms of this activity remain elusive. In this report we show that senescent human peritoneal mesothelial cells (HPMCs) alter the secretory profile of ovarian cancer cells (A2780, OVCAR-3, SKOV-3) by increasing the release of four angiogenic agents: CXCL1, CXCL8, HGF, and VEGF. Proliferation and migration of endothelial cells subjected to conditioned medium generated by: cancer cells modified by senescent HPMCs; cancer cells co-cultured with senescent HPMCs; and by early-passage HPMCs from aged donors, were markedly intensified. The same was the case for the vascularization, size and number of tumors that developed in the mouse peritoneum upon injection of ovarian cancer cells with senescent HPMCs. When the identified pro-angiogenic proteins were neutralized in conditioned medium from the cancer cells, both aspects of endothelial cell behavior intensified in vitro in response to senescent HPMCs were markedly reduced. The search for mediators of senescent HPMC activity using specific neutralizing antibodies and recombinant exogenous proteins showed that the intensified angiogenic potential of cancer cells was elicited by IL-6 and TGF-β1. At the transcriptional level, increased proliferation and migration of endothelial cells exposed to cancer cells modified by senescent HPMCs was regulated by HIF-1α, NF-κB/p50 and AP-1/c-Jun. Collectively, our findings indicate that senescent HPMCs may promote the progression of ovarian cancer cells by reprogramming their secretory phenotype towards increased production of pro-angiogenic agents and subsequent increase in the angiogenic capabilities of the vascular endothelium.

Visceral Adipose Tissue Mesothelial Cells: Living on the Edge or Just Taking Up Space?

Visceral adiposity and pathological adipose tissue remodeling, a result of overnutrition, are strong predictors of metabolic health in obesity. Factors intrinsic to visceral adipose depots are likely to play a causal role in eliciting the detrimental effects of this tissue on systemic nutrient homeostasis. The visceral adipose-associated mesothelium, a monolayer of epithelial cells of mesodermal origin that line the visceral serosa, has recently attracted attention for its role in metabolic dysfunction. Here we highlight and consolidate literature from various fields of study that points to the visceral adipose-associated mesothelium as a potential contributor to adipose development and remodeling. We propose a hypothesis in which adipose mesothelial cells represent a visceral depot-specific determinant of adipose tissue health in obesity.

The Mesothelial Origin of Carcinoma Associated-Fibroblasts in Peritoneal Metastasis

Solid tumors are complex and unstructured organs that, in addition to cancer cells, also contain other cell types. Carcinoma-associated fibroblasts (CAFs) represent an important population in the tumor microenviroment and participate in several stages of tumor progression, including cancer cell migration/invasion and metastasis. During peritoneal metastasis, cancer cells detach from the primary tumor, such as ovarian or gastrointestinal, disseminate through the peritoneal fluid and colonize the peritoneum. Tumor cells metastasize by attaching to and invading through the mesothelial cell (MC) monolayer that lines the peritoneal cavity, then colonizing the submesothelial compact zone where CAFs accumulate. CAFs may derive from different sources depending on the surrounding metastatic niche. In peritoneal metastasis, a sizeable subpopulation of CAFs originates from MCs through a mesothelial-to-mesenchymal transition (MMT), which promotes adhesion, invasion, vascularization and subsequent tumor growth. The bidirectional communication between cancer cells and MC-derived CAFs via secretion of a wide range of cytokines, growth factors and extracellular matrix components seems to be crucial for the establishment and progression of the metastasis in the peritoneum. This manuscript provides a comprehensive review of novel advances in understanding how peritoneal CAFs provide cancer cells with a supportive microenvironment, as well as the development of future therapeutic approaches by interfering with the MMT in the peritoneum.

Emerging and Evolving Ovarian Cancer Animal Models

Ovarian cancer (OC) is the leading cause of death from a gynecological malignancy in the United States. By the time a woman is diagnosed with OC, the tumor has usually metastasized. Mouse models that are used to recapitulate different aspects of human OC have been evolving for nearly 40 years. Xenograft studies in immunocompromised and immunocompetent mice have enhanced our knowledge of metastasis and immune cell involvement in cancer. Patient-derived xenografts (PDXs) can accurately reflect metastasis, response to therapy, and diverse genetics found in patients. Additionally, multiple genetically engineered mouse models have increased our understanding of possible tissues of origin for OC and what role individual mutations play in establishing ovarian tumors. Many of these models are used to test novel therapeutics. As no single model perfectly copies the human disease, we can use a variety of OC animal models in hypothesis testing that will lead to novel treatment options. The goal of this review is to provide an overview of the utility of different mouse models in the study of OC and their suitability for cancer research.