The role of human peritoneal mesothelial cells in the fibrosis and progression of gastric cancer

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.

Investigating the mechanisms of peritoneal metastasis in gastric adenocarcinoma using a novel ex vivo peritoneal explant model

Gastric adenocarcinoma, commonly known as stomach cancer, has a predilection for metastasis to the peritoneum, which portends limited survival. The peritoneal metastatic cascade remains poorly understood, and existing models fail to recapitulate key elements of the interaction between cancer cells and the peritoneal layer. To explore the underlying cellular and molecular mechanisms of peritoneal metastasis, we developed an ex vivo human peritoneal explant model. Fresh peritoneal tissue samples were suspended, mesothelial layer down but without direct contact, above a monolayer of red-fluorescent dye stained AGS human gastric adenocarcinoma cells for 24 h, then washed thoroughly. Implantation of AGS cells within the explanted peritoneum and invasion beyond the mesothelial layer were examined serially using real-time confocal fluorescence microscopy. Histoarchitecture of the explanted peritoneum was preserved over 5 days ex vivo. Both implantation and invasion were suppressed by restoration of functional E-cadherin through stable transfection of AGS cells, demonstrating sensitivity of the model to molecular manipulation. Thus, our ex vivo human peritoneal explant model permits meaningful investigation of the pathways and mechanism that contribute to peritoneal metastasis. The model will facilitate screening of new therapies that target peritoneal dissemination of gastric, ovarian and colorectal cancer.

Adipocytes contribute to tumor progression and invasion of peritoneal metastasis by interacting with gastric cancer cells as cancer associated fibroblasts

BACKGROUND

Peritoneal metastasis (PM) is one of the most common causes of noncurative surgery and the most frequent recurrence pattern in gastric cancer (GC). During the process of PM, GC cells detached from primary tumor interact with human peritoneal mesothelial cells (HPMC) overlapped with adipose tissues such as the omentum or mesentery. Although the interaction with HPMC promotes the malignancy of GC, the role of adipose tissues remains unclear.

AIMS

We aimed to clarify how adipose tissue are affected by adjacent primary tumors during the expression of adipokines and to elucidate whether GC cells transform adipocytes into CAFs in vitro. In addition, we investigated whether GC cells are affected by adipocytes in their ability to infiltrate.

METHODS

We investigated the phenotypic conversion of adipocytes during the malignant process of GC cells in vivo and in vitro. We evaluated the expression levels of adiponectin in the omental adipose tissue of gastric cancer patients by western blotting. Following adipocytes/gastric cancer cells coculture, adipocyte markers, adiponectin receptors, and inflammatory cytokine markers were detected by real-time PCR and/or western blotting in the single-cultured and co-cultured adipocytes; cancer-associated fibroblast (CAF) markers were detected by immunofluorescence and western blotting in the single-cultured and co-cultured adipocytes; invasion assays were performed in single cultured and co-cultured MKN45 and OCUM.

RESULTS

In omental adipose tissues that are situated close to the primary tumors, the expression of adiponectin tended to decrease in patients with subserosal or serosal invasion. By co-culturing with GC cells, adipocytes were dedifferentiated and the expression levels of CAF marker FSP1 and inflammatory cytokines, PAI-1 and IL-6, significantly increased (p < 0.05). Furthermore, GC cells co-cultured with adipocytes showed enhanced invasion ability.

CONCLUSION

Our findings suggest that the phenotypic conversion of adipocytes may promote the malignancy of GC in the construction of the cancer microenvironment of PM.

Molecular Mechanisms and Potential Rationale of Immunotherapy in Peritoneal Metastasis of Advanced Gastric Cancer

Peritoneal metastasis (PM) is one of the most frequent metastasis patterns of gastric cancer (GC), and the prognosis of patients with PM is very dismal. According to Paget’s theory, disseminated free cancer cells are seeded and survive in the abdominal cavity, adhere to the peritoneum, invade the subperitoneal tissue, and proliferate through angiogenesis. In these sequential processes, several key molecules are involved. From a therapeutic point of view, immunotherapy with chemotherapy combination has become the standard of care for advanced GC. Several clinical trials of newer immunotherapy agents are ongoing. Understanding of the molecular process of PM and the potential rationale of immunotherapy for PM treatment is necessary. Beyond understanding of the molecular aspect of PM, many studies have been conducted on the modality of treatment of PM. Notably, intraperitoneal approaches, including chemotherapy or immunotherapy, have been conducted, because systemic treatment of PM has limitations. In this study, we reviewed the molecular mechanisms and immunologic aspects of PM, and intraperitoneal approaches under investigation for treating PM.

Role of Peritoneal Mesothelial Cells in the Progression of Peritoneal Metastases

Peritoneal metastatic cancer comprises a heterogeneous group of primary tumors that originate in the peritoneal cavity or metastasize into the peritoneal cavity from a different origin. Metastasis is a characteristic of end-stage disease, often indicative of a poor prognosis with limited treatment options. Peritoneal mesothelial cells (PMCs) are a thin layer of cells present on the surface of the peritoneum. They display differentiated characteristics in embryonic development and adults, representing the first cell layer encountering peritoneal tumors to affect their progression. PMCs have been traditionally considered a barrier to the intraperitoneal implantation and metastasis of tumors; however, recent studies indicate that PMCs can either inhibit or actively promote tumor progression through distinct mechanisms. This article presents a review of the role of PMCs in the progression of peritoneum implanted tumors, offering new ideas for therapeutic targets and related research.

PDCD4 regulates apoptosis in human peritoneal mesothelial cells and promotes gastric cancer peritoneal metastasis

OBJECTIVE

Programmed cell death 4 (PDCD4) is a tumor suppressor gene, however, the function and regulatory mechanism remain to be discovered. The connection between tumorigenesis and apoptosis is one of the most important foci of cancer research. Our study aimed to explore the connections between PDCD4-mediated apoptosis of human peritoneal mesothelial cells (HPMC) and peritoneal metastasis in gastric cancer.

METHODS

The PDCD4 expression in 31 pairs of HPMC and tumor tissues was assessed by immunohistochemistry and RT-PCR. In cell experiments, we monitored gastric cancer cell migration with a Transwell chamber assay when PDCD4 was silenced in HPMC. Subsequently, apoptosis of HPMC was detected by a flow cytometric assay and western blotting. After analyzing cytokines in culture supernatants from gastric cancer with enzyme-linked immunosorbent assays (ELISAs), transforming growth factor-beta 1 (TGF-β1) was abundant in the culture supernatants of gastric cancer. Then, PDCD4 expression in HMrSV5 cells was analyzed by western blotting after retreatment with different concentrations of TGF-β1. Moreover, apoptosis of peritoneal mesothelial cells treated with TGF-β1 was detected according to the above methods.

RESULTS

In human metastatic peritoneal tissues, the expression of PDCD4 was significantly lower than that in normal tissues. At the same time, decreased expression of PDCD4 in HPMC was associated with increased migration capacity of gastric cancer cells. Moreover, suppressing the expression of PDCD4 promoted apoptosis in mesothelial cells which may be regulated by TGF-β secreted from gastric cancer cells.

CONCLUSIONS

These data suggested that decreased expression of PDCD4 significantly promoted apoptosis in human peritoneal mesothelial cells, thus inducing peritoneal metastasis, and that TGF-β1 secreted from gastric cancer cells may have played a crucial role.

Interleukin-17A derived from mast cells contributes to fibrosis in gastric cancer with peritoneal dissemination

OBJECTIVES

Interleukin-17A (IL-17A) is pro-inflammatory cytokine and acts as profibrotic factor in the fibrosis of various organs. Fibrosis tumor-like peritoneal dissemination of gastric cancer interferes with drug delivery and immune cell infiltration because of its high internal pressure. In this study, we examined the relationship between IL-17A and tissue fibrosis in peritoneal dissemination and elucidated the mechanism of fibrosis induced by IL-17A using human peritoneal mesothelial cells (HPMCs) and a mouse xenograft model.

METHODS

Seventy gastric cancer patients with peritoneal dissemination were evaluated. The correlation between IL-17A and fibrosis was examined by immunofluorescence and immunohistochemistry. A fibrosis tumor model was developed based on subcutaneous transplantation of co-cultured cells (HPMCs and human gastric cancer cell line MKN-45) into the dorsal side of nude mice. Mice were subsequently treated with or without IL-17A. We also examined the effect of IL-17A on HPMCs in vitro.

RESULTS

There was a significant correlation between IL-17A expression, the number of mast cell tryptase (MCT)-positive cells, and the degree of fibrosis (r = 0.417, P < 0.01). In the mouse model, IL-17A enhanced tumor progression and fibrosis. HPMCs treated with IL-17A revealed changes to a spindle-like morphology, decreased E-cadherin expression, and increased α-SMA expression through STAT3 phosphorylation. Moreover, HPMCs treated with IL-17A showed increased migration.

CONCLUSIONS

IL-17A derived from mast cells contributes to tumor fibrosis in peritoneal dissemination of gastric cancer. Inhibiting degranulation of mast cells might be a promising treatment strategy to control organ fibrosis.

Biomimetic construction of peritoneum to imitate peritoneal metastasis using digital micromirror device-based optical projection lithography

Currently, the mechanisms underlying the peritoneal metastasis of gastric cancer cells and the function of mesothelial cells during this process are unclear, primarily due to the absence of an effective in vitro peritoneal model. In this study, we constructed a biomimetic peritoneal model using a digital micromirror device-based optical projection lithography system. This model enabled the simulation of a damaged peritoneum, which allowed for a comparison of the characteristics of an undamaged peritoneum, such as porosity, mechanical properties, and surface morphology, with those of a damaged peritoneum. Biological inertness and removability of the polyethylene glycol dimethacrylate hydrogel were exploited to fabricate an arrayed heterogeneous interface that imitated a damaged human peritoneum. The porous structure of the peritoneum was achieved by adjusting the ratio of collagen I to gelatin methacryloyl; this structure of the peritoneum might contribute to its shock absorption property. Atomic force microscopy characterization showed that the outermost layers of the model peritoneum and real peritoneum were similar in surface morphology and mechanical properties. Furthermore, we reproduced the process of peritoneal metastasis in vitro. The numbers of gastric cancer cells that adhered to the heterogeneous interface were different, and mesothelial cells played an essential role in peritoneal metastasis. Our findings indicate that this model can be utilized in preclinical drug screening and personalized therapy.

Extravasated platelet aggregation contributes to tumor progression via the accumulation of myeloid-derived suppressor cells in gastric cancer with peritoneal metastasis

Extravasated platelet aggregation (EPA) serves an important role in the cancer microenvironment during cancer progression, and has been demonstrated to interact with tumor cells in several types of cancer. EPA induces epithelial-mesenchymal transition (EMT) via transforming growth factor-β, and also recruits immunosuppressive cells, including regulatory T (Treg) cells and myeloid-derived suppressor cells (MDSCs). However, the role of EPA in gastric cancer with peritoneal metastasis remains unknown. The present study analyzed the association between EPA and prognosis in patients with gastric cancer with peritoneal metastasis. The present study evaluated 62 patients diagnosed with advanced gastric cancer with peritoneal metastasis between 2001 and 2016. EPA, EMT, Treg cells and MDSCs in peritoneal metastatic lesions were detected by immunohistochemical evaluation of CD42b, SNAIL, FOXP3 and CD33, respectively. CD42b expression was observed in 56.5% (35/62) of peritoneal metastatic lesions. CD42b expression in peritoneal metastatic lesions was associated with poor overall survival compared with lower frequencies (hazard ratio, 2.03; 95% confidence interval, 1.12–3.69; P=0.018). SNAIL, FOXP3 and CD33 expression were not associated with overall survival, but CD33 expression was markedly higher in CD42b-positive patients (P=0.022). These results indicated that EPA affects immunosuppression by recruiting MDSCs in the tumor microenvironment via the secretion of soluble factors, resulting in tumor progression. EPA may be a novel therapeutic target for gastric cancer with peritoneal metastasis.

Mechanisms of the Epithelial-Mesenchymal Transition and Tumor Microenvironment in Helicobacter pylori-Induced Gastric Cancer

Helicobacter pylori (H. pylori) is one of the most common human pathogens, affecting half of the world’s population. Approximately 20% of the infected patients develop gastric ulcers or neoplastic changes in the gastric stroma. An infection also leads to the progression of epithelial–mesenchymal transition within gastric tissue, increasing the probability of gastric cancer development. This paper aims to review the role of H. pylori and its virulence factors in epithelial–mesenchymal transition associated with malignant transformation within the gastric stroma. The reviewed factors included: CagA (cytotoxin-associated gene A) along with induction of cancer stem-cell properties and interaction with YAP (Yes-associated protein pathway), tumor necrosis factor α-inducing protein, Lpp20 lipoprotein, Afadin protein, penicillin-binding protein 1A, microRNA-29a-3p, programmed cell death protein 4, lysosomal-associated protein transmembrane 4β, cancer-associated fibroblasts, heparin-binding epidermal growth factor (HB-EGF), matrix metalloproteinase-7 (MMP-7), and cancer stem cells (CSCs). The review summarizes the most recent findings, providing insight into potential molecular targets and new treatment strategies for gastric cancer.

The role of the peritoneal microenvironment in the pathogenesis of colorectal peritoneal carcinomatosis

Recent insights have implicated mesothelial-to-mesenchymal transition (MMT) as a mechanism by which mesothelial cells can transdifferentiate into cancer-associated fibroblasts (CAFs) in several cancers metastasizing to the peritoneum. However, this was not evaluated extensively in colorectal cancer. We examined the presumed mesothelial origin of CAFs in three types of colorectal carcinoma: conventional type adenocarcinoma, mucinous carcinoma and signet ring cell carcinoma. We evaluated the expression of mesothelial, mesenchymal, angiogenesis and colorectal cancer-related markers in peritoneal samples of twelve colorectal cancer patients with peritoneal carcinomatosis and four control patients by immunohistochemistry. We observed morphological and immunohistochemical changes in the vicinity of tumor implants in all studied colorectal cancer types. Mesothelial cells acquired a spindle-shaped myofibroblast-like morphology, lost expression of mesothelial markers, and gained expression of mesenchymal markers. Analysis of consecutive tissue sections and double staining for mesothelial and mesenchymal markers revealed overlap in expression of mesothelial and CAF markers. These findings are highly suggestive of a mesothelial origin of CAFs in peritoneal carcinomatosis in colorectal cancer. Interfering with the process of MMT might be a valuable approach in treating and preventing peritoneal carcinomatosis. Differences observed between colorectal cancer types suggest that one single strategy might not be applicable.

Exosomes and cancer: From oncogenic roles to therapeutic applications

Exosomes belong to extracellular vehicles that were produced and secreted from most eukaryotic cells and are involved in cell-to-cell communications. They are an effective delivery system for biological compounds such as mRNAs, microRNAs (miRNAs), proteins, lipids, saccharides, and other physiological compounds to target cells. In this way, they could influence on cellular pathways and mediate their physiological behaviors including cell proliferation, tumorigenesis, differentiation, and so on. Many research studies focused on their role in cancers and also on potentially therapeutic and biomarker applications. In the current study, we reviewed the exosomes' effects on cancer progression based on their cargoes including miRNAs, long noncoding RNAs, circular RNAs, DNAs, mRNAs, proteins, and lipids. Moreover, their therapeutic roles in cancer were considered. In this regard, we have given a brief overview of challenges and obstacles in using exosomes as therapeutic agents.

Comprehensive review on how platinum- and taxane-based chemotherapy of ovarian cancer affects biology of normal cells

One of the most neglected aspects of chemotherapy are changes, and possible consequences of these changes, that occur in normal somatic cells. In this review, we summarize effects of selected drugs used to treat ovarian cancer (platin derivatives-cisplatin and carboplatin; and taxanes-paclitaxel and docetaxel) on cellular metabolism, acquisition of reactive stroma features, cellular senescence, inflammatory reactions, apoptosis, autophagy, mitophagy, oxidative stress, DNA damage, and angiogenesis in various types of normal cells, including fibroblasts, epithelial cells, endothelial cells, and neurons. The activity of these drugs against the normal cells is presented from a broader perspective of their desirable anti-tumoral effects.

Low-dose eribulin mesylate exerts antitumor effects in gastric cancer by inhibiting fibrosis via the suppression of epithelial-mesenchymal transition and acts synergistically with 5-fluorouracil

Background

Characterized by aggressive proliferation, extensive stromal fibrosis, and resulting drug resistance, peritoneal dissemination in gastric cancer remains associated with poor prognosis. Interaction between cancer and stromal cells accelerates tumor progression via epithelial–mesenchymal transition (EMT), which is one of the major causes of tissue fibrosis, and human peritoneal mesothelial cells (HPMCs) play important roles as cancer stroma in peritoneal dissemination. Transforming growth factor-β (TGF-β) has a pivotal function in the progression of EMT, and Smad proteins play an important role in the TGF-β signaling pathway. Eribulin mesylate (eribulin), a nontaxane microtubule dynamics inhibitor used for the treatment of advanced breast cancer, inhibits EMT changes in triple-negative breast cancer cells. We examined its ability to inhibit tumor progression and EMT changes resulting from the interaction between gastric cancer cells and HPMCs and to act synergistically with 5-fluorouracil (5-FU), a key drug for gastric cancer.

Materials and methods

Proliferation of gastric cancer cells and HPMCs isolated from healthy omentum was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Following gastric cancer cell/HPMC coculture, EMT markers were detected by immunofluorescence, immunohistochemistry, and Western blotting; invasion assays were performed; and TGF-β and Smad phosphorylation were assessed by Western blotting and enzyme-linked immunosorbent assay. A mouse fibrotic tumor xenograft model was established using gastric cancer cell/HPMC cocultures. The effect of eribulin and/or 5-FU was tested in each case.

Results

Eribulin significantly suppressed gastric cancer cell proliferation and EMT changes in MKN-45 gastric cancer cells and HPMCs induced by their interaction in vitro. Eribulin inhibited EMT at much lower concentrations (≥0.5 nM for MKN-45 and ≥0.1 nM for HPMCs) than its half maximal inhibitory concentrations (2.2 nM for MKN-45 and 8.1 nM for HPMCs), and this resulted, at least partly, from the downregulation of TGF-β/Smad signaling. Eribulin administration of ≥0.1 mg/kg suppressed tumor progression (0.1 mg/kg, p=0.02), and fibrosis was inhibited by lower dose (0.05 mg/kg, p=0.008) in the xenograft model. Furthermore, 0.05 mg/kg administration with 5-FU brought about synergistic antitumor effects (p=0.006).

Conclusion

Low-dose eribulin combined with 5-FU might be a promising therapy for peritoneal dissemination in gastric cancer.

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.

Importance of human peritoneal mesothelial cells in the progression, fibrosis, and control of gastric cancer: inhibition of growth and fibrosis by tranilast

BACKGROUND

Scirrhous gastric cancer is an intractable disease with a high incidence of peritoneal dissemination and obstructive symptoms (e.g., ileus, jaundice, and hydronephrosis) arising from accompanying marked fibrosis. Microenvironmental interactions between cancer cells and cancer-associated fibroblasts are the suggested cause of the disease. We elucidated the mechanisms of tumor growth and fibrosis using human peritoneal mesothelial cells (HPMCs) and investigated the effects of tranilast treatment on cells and a xenograft mouse model of fibrosis.

METHODS

HPMCs were isolated from surgically excised omentum and their interaction with MKN-45 gastric cancer cells was investigated using co-culture. Furthermore, a fibrosis tumor model was developed based on subcutaneous transplantation of co-cultured cells into the dorsal side of nude mice to form large fibrotic tumors. Mice were subsequently treated with or without tranilast.

RESULTS

The morphology of HPMCs treated with transforming growth factor (TGF)-β1 changed from cobblestone to spindle-type. Moreover, E-cadherin was weakly expressed whereas high levels of α-smooth muscle actin expression were observed. TGF-β-mediated epithelial-mesenchymal transition-like changes in HPMCs were inhibited in a dose-dependent manner following tranilast treatment through inhibition of Smad2 phosphorylation. In the mouse model, tumor size decreased significantly and fibrosis was inhibited in the tranilast treatment group compared with that in the control group.

CONCLUSIONS

Tranilast acts on the TGF-β/Smad pathway to inhibit interactions between cancer cells and cancer-associated fibroblasts, thereby inhibiting tumor growth and fibrosis. This study supports the hypothesis that tranilast represents a novel strategy to prevent fibrous tumor establishment represented by peritoneal dissemination.

Cancer-associated fibroblasts regulate the biological behavior of cancer cells and stroma in gastric cancer

Gastric cancer (GC) is a frequently diagnosed type of cancer in China, and is associated with a high mortality rate. The biological behavior of GC requires investigation in order to provide an evidence base for the development of strategies to prevent and treat GC. For this purpose, the present review outlines the process of tumor microenvironment (TME) evolution, including the dynamic biological behavior of different types of cancer cell and stroma. Cancer-associated fibroblasts (CAFs) serve as prominent stromal cellular components in the GC TME, and exhibit an essential function in GC progression. In the present study, the function of CAFs in cancer cell proliferation, cell migration, invasion, extracellular matrix remodeling, pathological angiogenesis and immune cell infiltration were investigated. The studies discussed in the present review demonstrate that the cross-talk between CAF, cancer cells and tumor stroma promotes GC progression.

Mechanisms of peritoneal dissemination in gastric cancer

Peritoneal dissemination is the most frequent metastatic pattern of gastric cancer, but the mechanisms underlying peritoneal dissemination are yet to be elucidated. Paget's 'seed and soil' hypothesis is recognized as the fundamental theory of metastasis. The 'seeding' theory proposes that the formation of peritoneal dissemination is a multistep process, including detachment from the primary tumour, transmigration and attachment to the distant peritoneum, invasion into subperitoneal tissue and proliferation with blood vascular neogenesis. In the present review, the progress of each step is discussed. Milky spots, as a lymphatic apparatus, are indicative of lymphatic orifices on the surface of the peritoneum. These stomata are open gates for peritoneal-free cancer cells to migrate into the submesothelial space. Therefore, milky spots provide suitable 'soil' for cancer cells to implant. Other theories have also been proposed to clarify the peritoneal dissemination process, including the transvessel metastasis theory, which suggests that the peritoneal metastasis of gastric cancer develops via a vascular network mediated by hypoxia inducible factor-1α.

Blocking TGF-β1 by P17 peptides attenuates gastric cancer cell induced peritoneal fibrosis and prevents peritoneal dissemination in vitro and in vivo

Our previous study demonstrated that the peritoneal stroma environment favors proliferation of tumor cells by serving as a rich source of growth factors and chemokines known to be involved in tumor metastasis. In this study, we investigated the interaction between gastric cancer cells and peritoneal mesothelial cells, and determined the effects of TGF-β1 in this processing. Human peritoneal tissues and peritoneal wash fluid were obtained, which examined by hematoxylin and eosin staining or ELISA for measurements of TGF-β1 levels. The peritoneal mesothelial cells were co-incubated with the supernatants of gastric cancer, the expression of TGF-β1, collagen and fibronectin was observed by ELISA and western blot. We then investigated the effects of serum-free conditioned media from HSC-39 gastric cancer cells on the peritoneum of nude mice, and the effects of peritoneal fibrosis on the development of peritoneal metastasis in vivo. The peritoneum from gastric patients were thickened and contained extensive fibrosis. After co-culture both gastric tumor cells and mesothelial cells, we found that TGF-β1 expression was greatly increased in the co-culture system compared to individual culture condition. Serum-free Conditioned Media from HSC-39 was able to induce extracellular matrix expression in vitro and in vivo, and tumorigenicity in mice with peritoneal fibrosis was greater than in mice with normal peritoneum, while blocking TGF-β1 by peptide P17 can partially inhibit these effects. In conclusion, these results indicated that the interaction of gastric cancer with peritoneal fibrosis and determined that TGF-β1 plays a key role in induction of peritoneal fibrosis, which in turn affected dissemination of gastric cancer.

Establishing a xenograft mouse model of peritoneal dissemination of gastric cancer with organ invasion and fibrosis

Background

The clinical prognosis of gastric cancer with peritoneal dissemination is poor because of its chemoresistance and rich fibrosis. While several gastric cancer cell lines have been used to establish models of peritoneal dissemination by intraperitoneal injection, most peritoneal tumors that form adopt a medullary pattern in microscopic appearance. This histological finding for the model differs from that in the clinical situation. This study was performed to demonstrate the contribution of human peritoneal mesothelial cells (HPMCs) to fibrotic tumor formation and to establish a new xenograft model with high potential for peritoneal dissemination with organ invasion and extensive fibrosis.

Methods

We established four types of xenograft model: i) intraperitoneal injection of MKN45-P cells alone (control group), ii) injection of MKN45-P cells co-cultured with HPMCs (co-cultured group), iii) scratching the parietal peritoneum (parietal group), and iv) scratching the visceral peritoneum (visceral group) with a cotton swab before injection of co-cultured cells. Fibrosis, α-smooth muscle actin expression, and organ invasion by tumor cells were all assessed by immunohistochemical examination.

Results

All mice developed abdominal swelling with peritoneal tumors and bloody ascites. Tumors of the control and co-cultured groups were not invasive or fibrotic. Contrastingly, tumors of the scratch groups exhibited rich stromal fibrosis and possessed increased α-smooth muscle actin (α-SMA) expression. In particular, the visceral group showed edematous and spreading tumors invading the intestinal wall.

Conclusion

We established a model of peritoneal dissemination with organ invasion and stromal fibrosis. Formation of peritoneal dissemination required a favorable environment for cell adhesion, invasion, and growth. This model may be useful for analyzing the pathogenesis and treatment of peritoneal dissemination of gastric cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2991-9) contains supplementary material, which is available to authorized users.

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.

Mesothelial cells interact with tumor cells for the formation of ovarian cancer multicellular spheroids in peritoneal effusions

Epithelial ovarian cancer (EOC) dissemination is primarily mediated by the shedding of tumor cells from the primary site into ascites where they form multicellular spheroids that rapidly lead to peritoneal carcinomatosis. While the clinical importance and fundamental role of multicellular spheroids in EOC is increasingly appreciated, the mechanisms that regulate their formation and dictate their cellular composition remain poorly characterized. To investigate these important questions, we characterized spheroids isolated from ascites of women with EOC. We found that in these spheroids, a core of mesothelial cells was encased in a shell of tumor cells. Analysis further revealed that EOC spheroids are dynamic structures of proliferating, non-proliferating and hypoxic regions. To recapitulate these in vivo findings, we developed a three-dimensional co-culture model of primary EOC and mesothelial cells. Our analysis indicated that, compared to the OVCAR3 cell line, primary EOC cells isolated from ascites as well as mesothelial cells formed compact spheroids. Analysis of heterotypic spheroid microarchitecture revealed a structure that grossly resembles the structure of spheroids isolated from ascites. Cells that formed compact spheroids had elevated expression of β1 integrin and low expression of E-cadherin. Addition of β1 integrin blocking antibody or siRNA-mediated downregulation of β1 integrin resulted in reduced tightness of the spheroids. Interestingly, the loss of MUC16 and E-cadherin expression resulted in the formation of more compact spheroids. Therefore, our findings support the heterotypic nature of spheroids from malignant EOC ascites. In addition, our data describe an unusual link between E-cadherin expression and less compact spheroids. Our data also emphasize the role of MUC16 and β1 integrin in EOC spheroid formation.

Milky spots: omental functional units and hotbeds for peritoneal cancer metastasis

As the most common metastatic disease of abdomen pelvic cavity cancer, peritoneal carcinomatosis (PC) renders significant negative impact on patient survival and quality of life. Invasive peritoneal exfoliated cancer cells (PECCs) preferentially select the omentum as a predominant target site for cancer cell colonization and proliferation compared with other tissues in the abdominal cavity. The precise pathogenic mechanism remains to be determined. As omental milky spots (MSs) are the major implantation site for malignant cells in peritoneal dissemination, researches on mechanisms of PC have been mainly focused on MS, primitive lymphoid tissues with unique structural features, and functional characteristics. To date, extensive biophysical and biochemical methods have been manipulated to investigate the MS exact function in the peritoneal cavity. This review summarized MS as hotbeds for PECC. The anatomical distribution was briefly described first. Then, MS histology was systematically reviewed, including morphological features, cellular constituents, and histological staining methods. At last, the roles of MS in PC pathological process were summarized with special emphasis on the distinct roles of macrophages.

Endoglin overexpression mediates gastric cancer peritoneal dissemination by inducing mesothelial cell senescence

Peritoneal dissemination (PD), which is highly frequent in gastric cancer (GC) patients, is the main cause of death in advanced GC. Senescence of human peritoneal mesothelial cells (HPMC) may contribute to GC peritoneal dissemination (GCPD). In this study of 126 patients, we investigated the association between Endoglin expression in GC peritoneum and the clinicopathological features. The prognosis of patients was evaluated according to Endoglin and ID1 expression. In vitro, GC cell (GCC)-HPMC coculture was established. Endoglin and ID1 expression was evaluated by Western blot. Cell cycle and HPMC senescence were analyzed after harvesting HPMC from the coculture. GCC adhesion and invasion to HPMC were also assayed. Our results showed that positive staining of Endoglin (38%) was associated with a higher TNM stage and higher incidence of GCPD (both P < .05). Kaplan-Meier analysis showed that the patients who were Endoglin positive had a shorter survival time compared with Endoglin-negative patients (P = .02). Using the HPMC and GCC adherence and invasion assay, we demonstrated that transforming growth factor beta 1 (TGF-β)1-induced HPMC senescence was attenuated by silencing the Endoglin expression, which also prevented GCC attachment and invasion. Our study indicated a positive correlation between Endoglin overexpression and GCPD. Up-regulated Endoglin expression induced HPMC senescence via TGF-β1 pathway. The findings suggest that Endoglin-induced HPMC senescence may contribute to peritoneal dissemination of GCCs.

Tumor-associated macrophages of the M2 phenotype contribute to progression in gastric cancer with peritoneal dissemination

BACKGROUND

Tumor-associated macrophages (TAMs) of the M2 phenotype are known to promote tumor proliferation and to be associated with a poor prognosis in numerous cancers. Here, we investigated whether M2 macrophages participate in the development of peritoneal dissemination in gastric cancer.

METHODS

The characteristics of peritoneal macrophages in gastric cancer patients with or without peritoneal dissemination were examined by flow cytometry and the real-time quantitative polymerase chain reaction. The effects of M2 macrophages on phenotypic changes of the gastric cancer cell line MKN45 were assessed with a direct or indirect co-culture system in vitro and an in vivo mouse xenograft model.

RESULTS

The number of peritoneal macrophages with the M2 phenotype (CD68(+)CD163(+) or CD68(+)CD204(+)) was significantly higher in gastric cancer patients with peritoneal dissemination than in those without peritoneal dissemination. Higher expression of the M2-related messenger RNAs (IL-10, vascular endothelial growth factor A, vascular endothelial growth factor C, matrix metalloproteinase 1, and amphiregulin) and lower expression of M1-related messenger RNAs (TNF-α, CD80, CD86, and IL-12p40) were also confirmed in the TAMs. Macrophage co-culture with gastric cancer cells converted M1 phenotype into M2 phenotype. Moreover, the coexistence of MKN45 cells with M2 macrophages resulted in cancer cell proliferation and an acceleration of tumor growth in the xenograft model.

CONCLUSIONS

Intraperitoneal TAMs in gastric cancer patients with peritoneal dissemination were polarized to the M2 phenotype, and could contribute to tumor proliferation and progression. Therefore, intraperitoneal TAMs are expected to be a promising target in the treatment of peritoneal dissemination in gastric cancer.

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.

Peripheral opioid antagonist enhances the effect of anti-tumor drug by blocking a cell growth-suppressive pathway in vivo

The dormancy of tumor cells is a major problem in chemotherapy, since it limits the therapeutic efficacy of anti-tumor drugs that only target dividing cells. One potential way to overcome chemo-resistance is to “wake up” these dormant cells. Here we show that the opioid antagonist methylnaltrexone (MNTX) enhances the effect of docetaxel (Doc) by blocking a cell growth-suppressive pathway. We found that PENK, which encodes opioid growth factor (OGF) and suppresses cell growth, is predominantly expressed in diffuse-type gastric cancers (GCs). The blockade of OGF signaling by MNTX releases cells from their arrest and boosts the effect of Doc. In comparison with the use of Doc alone, the combined use of Doc and MNTX significantly prolongs survival, alleviates abdominal pain, and diminishes Doc-resistant spheroids on the peritoneal membrane in model mice. These results suggest that blockade of the pathways that suppress cell growth may enhance the effects of anti-tumor drugs.

Bone marrow derived "fibrocytes" contribute to tumor proliferation and fibrosis in gastric cancer

BACKGROUND

Cancer-associated fibroblasts (CAFs) in the stroma are considered to play important roles for gastric cancer proliferation, invasion, and fibrosis, but the source of CAFs and their interaction with cancer cells in the microenvironment have not been fully determined. Here we elucidated the role of bone marrow-derived cells, fibrocytes, in development of gastric cancers, as represented by scirrhous gastric cancer.

MATERIALS AND METHODS

In co-culturing MKN45 gastric cancer cells and purified fibrocytes from healthy volunteers, migration and endothelial mesenchymal transition associated gene expression were evaluated using western blot analysis. Also, mouse xenograft models of MKN45 with or without fibrocytes were conducted to investigate their tumorigenicity and immunohistological differences of tumors.

RESULTS

Co-culture of fibrocytes with MKN45 resulted in morphological changes from cobblestone-shape to spindle-shape and enhanced expression of α-SMA and collagen type I in fibrocytes, suggesting that co-culture with gastric cancer cells may have induced the differentiation of fibrocytes to myofibroblasts. Furthermore, enhanced expression of SDF-1 in MKN45 and CXCR4 in fibrocytes were also determined. Mouse xenograft models inoculated with MKN45 and fibrocytes revealed significantly larger tumors than those inoculated with MKN45 cells alone, and the stroma in co-inoculated tumors consisted of myofibroblasts and fibrosis. Mouse-derived cells expressing both CD45 and type I collagen were also observed in co-inoculated tumors.

CONCLUSION

Fibrocytes derived from bone marrow may migrate into the microenvironment of gastric cancer by SDF-1/CXCR4 system, and enhance the tumor proliferation and fibrosis as CAFs.

Protein-bound polysaccharide K suppresses tumor fibrosis in gastric cancer by inhibiting the TGF-β signaling pathway

Peritoneal carcinomatosis (PC) is the most frequent metastatic pattern of gastric cancer and its prognosis is extremely poor. PC is characterized by rich fibrosis and the development of obstructive disorders such as ileus, jaundice and hydronephrosis. Epithelial-mesenchymal transition (EMT) is one of the major causes of tissue fibrosis and transforming growth factor β (TGF-β) has a pivotal function in the progression of EMT. Protein-bound polysaccharide K (PSK) is a biological response modifier that can modulate the TGF-β/Smad signaling pathway in vitro. In the present study, we established a fibrotic tumor model using human peritoneal mesothelial cells (HPMCs) and a human gastric cancer cell line to evaluate whether PSK attenuates tumor fibrosis. HPMCs exposed to PSK did not undergo the morphological change from a cobblestone-like pattern to a spindle-shape pattern normally induced by treatment with TGF-β. Immunofluorescence further demonstrated that PSK suppressed TGF-β-induced overexpression of α-SMA in the HPMCs. We further showed that HPMCs contributed to the proliferation of tumor fibrosis by using a mouse xenograft model. Additionally, PSK treatment of these mice significantly reduced the area of observable tumor fibrosis. These results suggest that seeded cancer cells transformed HPMCs into myofibroblast-like cells through their release of TGF-β in the microenvironment, facilitating the development of fibrous tumors in organs covered with HPMCs. Therefore, our study indicates that PSK has potential utility as an anti-fibrotic agent in the treatment of gastric cancer patients with PC.

The Jak2 small molecule inhibitor, G6, reduces the tumorigenic potential of T98G glioblastoma cells in vitro and in vivo

Glioblastoma multiforme (GBM) is the most common and the most aggressive form of primary brain tumor. Jak2 is a non-receptor tyrosine kinase that is involved in proliferative signaling through its association with various cell surface receptors. Hyperactive Jak2 signaling has been implicated in numerous hematological disorders as well as in various solid tumors including GBM. Our lab has developed a Jak2 small molecule inhibitor known as G6. It exhibits potent efficacy in vitro and in several in vivo models of Jak2-mediated hematological disease. Here, we hypothesized that G6 would inhibit the pathogenic growth of GBM cells expressing hyperactive Jak2. To test this, we screened several GBM cell lines and found that T98G cells express readily detectable levels of active Jak2. We found that G6 treatment of these cells reduced the phosphorylation of Jak2 and STAT3, in a dose-dependent manner. In addition, G6 treatment reduced the migratory potential, invasive potential, clonogenic growth potential, and overall viability of these cells. The effect of G6 was due to its direct suppression of Jak2 function and not via off-target kinases, as these effects were recapitulated in T98G cells that received Jak2 specific shRNA. G6 also significantly increased the levels of caspase-dependent apoptosis in T98G cells, when compared to cells that were treated with vehicle control. Lastly, when T98G cells were injected into nude mice, G6 treatment significantly reduced tumor volume and this was concomitant with significantly decreased levels of phospho-Jak2 and phospho-STAT3 within the tumors themselves. Furthermore, tumors harvested from mice that received G6 had significantly less vimentin protein levels when compared to tumors from mice that received vehicle control solution. Overall, these combined in vitro and in vivo results indicate that G6 may be a viable therapeutic option against GBM exhibiting hyperactivation of Jak2.

Tks5 activation in mesothelial cells creates invasion front of peritoneal carcinomatosis

Scirrhous gastric cancer is frequently associated with peritoneal dissemination, and the interaction of cancer cells with peritoneal mesothelial cells (PMCs) is crucial for the establishment of the metastasis in the peritoneum. Although cells derived from PMCs are detected within tumors of peritoneal carcinomatosis, how PMCs are incorporated into tumor architecture is not understood. The present study shows that PMCs create the invasion front of peritoneal carcinomatosis, which depends on activation of Tks5 in PMCs. In peritoneal tumor implants, PMCs represent majority of cells located at the invasive edge of the cancer tissue. Exogenously implanted PMCs and host PMCs aggressively invade into abdominal wall upon the peritoneal inoculation of cancer cells, and PMCs locate ahead of cancer cells in the direction of invasion. Tks5, a substrate of Src kinase, is predominantly expressed in the PMCs of cancer tissue, and promotes the invasion of PMCs and cancer cells. Expression and activation of Tks5 was induced in PMCs following their exposure to gastric cancer cells, and increased Tks5 expression was detected in PMCs located at the invasion front. Reduced Tks5 expression in PMCs blocked PMC invasion, which in turn prevents cancer cell invasion both in vitro and in vivo. The peritoneal dissemination of gastric cancer was significantly increased by mixing cancer cells and PMCs, and was suppressed by knockdown of Tks5 in PMCs. These results suggest that cancer-activated PMCs create invasion front by guiding cancer cells. Signaling leading to Tks5 activation in PMCs may be a suitable therapeutic target for prevention of peritoneal carcinomatosis.

Peritoneal myofibroblasts at metastatic foci promote dissemination of pancreatic cancer

Myofibroblasts in the stroma of pancreatic cancers promote tumor proliferation, invasion and metastasis by increasing extracellular matrix and secretion of several growth factors. In contrast, the role of myofibroblasts at peritoneally disseminated sites of pancreatic cancer has not yet been determined. This study was designed to assess the role of myofibroblasts at peritoneally disseminated sites of pancreatic cancer. Three primary cultures of human peritoneal myofibroblasts (hPMFs) were established from disseminated sites of pancreatic cancer and their interactions with the SUIT-2 and CAPAN-1 human pancreatic cancer cell lines were analyzed in vitro. Using a model in BALB/c nu/nu mice, we compared the dissemination ability of intraperitoneally implanted pancreatic cancer cells, with and without hPMFs, and examined the presence of green fluorescent protein (GFP)-labeled hPMFs at peritoneally disseminated sites in mice. hPMFs significantly promoted the migration and invasion of pancreatic cancer cells (P<0.05), while the cancer cells significantly promoted the migration and invasion of hPMFs (P<0.05). In vivo, the number of peritoneally disseminated nodules, more than 3 mm in size, was significantly greater in mice implanted with cancer cells plus hPMFs compared to mice implanted with cancer cells alone, with GFP-labeled hPMFs surviving in the peritoneal cavity of the former. hPMFs promote the peritoneal dissemination of pancreatic cancer. The cancer-stromal cell interaction in the peritoneal cavity may be a new therapeutic target to prevent the dissemination of pancreatic cancer.

Tumor-associated mesothelial cells are negative prognostic factors in gastric cancer and promote peritoneal dissemination of adherent gastric cancer cells by chemotaxis

Peritoneal dissemination is highly frequent in gastric cancer. Damage to human peritoneal mesothelial cell (HPMC) barriers provokes gastric cancer peritoneal dissemination (GCPD), the key events during GCPD, is characterized by fibroblastic development. In this study, we have studied the association between fibroblast activation protein (FAP) expression in peritoneum and the pathological features of the primary tumor. The clinical prognosis of gastric cancer patients was evaluated according to FAP expression. In a gastric cancer cell-HPMC co-culture system, expression of E-cadherin, α-smooth muscle actin, and FAP were evaluated by Western blotting. Gastric cancer cell migration and adhesion to HPMC were also assayed. Our results showed positive peritoneal staining of FAP in 36/86 cases (41.9 %), which was associated with a higher TNM stage in primary gastric cancer and higher incidence of GCPD (both p<0.05). Survival analysis showed FAP expression was an independent prognostic factor of poor survival (p=0.02). Peritoneum of FAP-positive expression exhibited a distinct fibrotic development and expressed higher level of the mesenchymal marker α-SMA, which was confirmed by the in vitro Western blot assay. In HPMC and gastric cancer cell adherence assay, SGC-7901 cells preferentially adhered to TA-HPMC at different cell densities (both p<0.05). Additionally, SGC-7901 cells were more prone to chemotaxis by FAP-expressed tumor-associated-human peritoneal mesothelial cells (TA-HPMC) compared with HPMC co-cultured with normal gastric glandular epithelial cells in a time-dependent manner (both p<0.05). Our study indicated a positive correlation between peritoneum FAP expression and GCPD. FAP-expressed TA-HPMC might be an important cellular component and instigator of GCPD.

CD90+ mesothelial-like cells in peritoneal fluid promote peritoneal metastasis by forming a tumor permissive microenvironment

The peritoneal cavity is a common target of metastatic gastrointestinal and ovarian cancer cells, but the mechanisms leading to peritoneal metastasis have not been fully elucidated. In this study, we examined the roles of cells in peritoneal fluids on the development of peritoneal metastasis. We found that a minor subset of human intraperitoneal cells with CD90(+)/CD45(−) phenotype vigorously grew in culture with mesothelial-like appearance. The mesothelial-like cells (MLC) displayed the characteristics of mesenchymal stem cell, such as differentiating into adipocytes, osteocytes, and chondrocytes, and suppressing T cell proliferation. These cells highly expressed type I collagen, vimentin, α-smooth muscle actin and fibroblast activated protein-α by the stimulation with TGF-β, which is characteristic of activated myofibroblasts. Intraperitoneal co-injection of MLCs with the human gastric cancer cell line, MKN45, significantly enhanced the rate of metastatic formation in the peritoneum of nude mice. Histological examination revealed that many MLCs were engrafted in metastatic nodules and were mainly located at the fibrous area. Dasatinib, a potent tyrosine kinase inhibitor, strongly inhibited the proliferation of MLCs but not MKN45 in vitro. Nevertheless, oral administration of Dasatinib significantly inhibited the development of peritoneal metastasis of MKN45, and resulted in reduced fibrillar formation of metastatic nodules. These results suggest floating MLCs in the peritoneal fluids support the development of peritoneal metastasis possibly through the production of the permissive microenvironment, and thus the functional blockade of MLCs is a reasonable strategy to treat recurrent abdominal malignancies.

Transforming growth factor-beta1 signaling blockade attenuates gastric cancer cell-induced peritoneal mesothelial cell fibrosis and alleviates peritoneal dissemination both in vitro and in vivo

Peritoneal dissemination is the most frequent metastatic pattern of advanced gastric cancer and the main cause of death in gastric cancer patients. Transforming growth factor-beta1 (TGF- ß1), one of the most potent fibrotic stimuli for human peritoneal mesothelial cells, has been shown to play an important role in this process. In this study, we investigated the effect of TGF- ß1 signaling blockade in gastric cancer cell (GCC)-induced human peritoneal mesothelial cell (HPMC) fibrosis. HPMCs were cocultured with the high TGF- ß1 expressing GCC line SGC-7901 and various TGF- ß1 signaling inhibitors or SGC-7901 transfected with TGF-ß1-specific siRNA. HPMC fibrosis was monitored on the basis of morphology. Expression of the epithelial cell marker, E-cadherin, and the mesenchymal marker, α-smooth muscle actin (α-SMA), was evaluated by Western blotting and immunofluorescence confocal imaging. GCC adhesion to HPMC was also assayed. In nude mouse tumor model, the peritoneal fibrotic status was monitored by immunofluorescent confocal imaging and Masson's trichrome staining; formation of metastatic nodular and ascites fluid was also evaluated. Our study demonstrated that GCC expressing high levels of TGF-ß1 induced HMPC fibrosis, which is characterized by both upregulation of E-cadherin and downregulation of α-SMA. Furthermore, HPMC monolayers fibrosis was reversed by TGF- ß1 signaling blockade. In vivo, the TGF- ß1 receptor inhibitor SB-431542 partially attenuated early-stage gastric cancer peritoneal dissemination (GCPD). In conclusion, our study confirms the significance of TGFß1 signaling blockade in attenuating GCPD and may provide a therapeutic target for clinical therapy.

Milky spot macrophages remodeled by gastric cancer cells promote peritoneal mesothelial cell injury

Peritoneal dissemination (PD) is the most frequent metastatic pattern of advanced gastric cancer (GC) and the main cause of death in GC patients. Human peritoneal mesothelial cell (HPMC) injury induced by gastric cancer cells (GCCs) and GCC outgrowths supported by peritoneal milky spot macrophages (PMSMs) are the key events during gastric cancer peritoneal dissemination (GCPD). In this study, we investigated whether PMSMs remodeled by GCC can induce HPMC injury and create a favorable microenvironment for GCPD. We established a tumor-associated macrophage (TAM) model using in vitro cell coculture. Normal macrophages cocultured with GCCs down-regulated expression of antigen-presenting surface molecules CD80, CD86, and MHC-II, but, notably, they up-regulated expression of phagocytic scavenger receptor CD206, which is similar to the M2 macrophage phenotype. In further experiments, various experimental methods were applied to detect the injurious effect of TAMs on HPMCs in another TAM-HPMC coculture. Our results showed that GCCs can induce HPMC apoptosis by unregulated apoptosis associated with cleaved caspase3, cleaved caspase9, and p21 proteins. HPMC growth ceased, and both early- and late-stage apoptosis were observed. Additionally, GCCs can induce HPMC fibrosis via increased expression of epithelial cell marker E-cadherin and decreased expression of mesenchymal cell marker α-SMA. Our results demonstrate that, in the GCPD process, PMSMs were remodeled by GCCs, resulting in phenotypic and functional transformation. In turn, this transformation induced HPMC injury and provided a favorable microenvironment for GCC anchorage and growth. These results may provide new insight into the mechanisms of GCPD.

Low-dose paclitaxel modulates tumour fibrosis in gastric cancer

Various treatments have been used for peritoneal dissemination, which is the most common mode of metastasis in gastric cancer, but sufficiently good clinical outcomes have not yet been obtained because of the presence of rich fibrous components and acquired drug resistance. Epithelialmesenchymal transition (EMT) is one of the major causes of tissue fibrosis and transforming growth factor-β (TGF-β) has a pivotal function in the progression of EMT. Smad proteins play an important role in the TGF-β signalling pathway. The TGF-β/Smad signalling pathway can be modulated by stabilising microtubules with paclitaxel (PTX). Here, we investigated whether paclitaxel can modulate TGF-β/Smad signalling in human peritoneal methothelial cells (HPMCs). To determine the cytostatic concentrations of antineoplastic agents in HPMCs, a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was performed using PTX, 5-fluorouracil and cisplatin. The minimum concentration that caused significant inhibition of TGF-β1-induced morphological changes in human peritoneal methothelial cells on pre-treatment with PTX was 5 nM at 48 h (cell viability: 87.1±1.5%, P<0.01). The TGF-β signalling cascade and the status of various fibrous components were evaluated by immunofluorescence staining, real-time quantitative PCR and western blotting. TGF-β signalling induced morphological changes, α-SMA expression and collagen I synthesis in HPMCs and PTX treatment suppressed these EMT-like changes. Moreover, PTX treatment markedly suppressed Smad2 phosphorylation. These data suggest that at a low-dose, PTX can significantly suppress the TGF-β/Smad signalling pathway by inhibiting Smad2 phosphorylation in the human peritoneum and that this can reduce stromal fibrosis.