Development and biological analysis of peritoneal metastasis mouse models for human scirrhous stomach cancer

New insights into cancer pathology learned from the dynamics of cancer-associated fibroblasts

Paget's "Seed and Soil" theory, proposed in 1889, emphasizes the importance of the microenvironment where cancer cells grow in metastatic sites. Over a century later, this concept remains a cornerstone in comprehending cancer biology and devising treatment strategies. The "Seed and Soil" theory, which initially explained how cancer spreads to distant organs, now also applies to the tumor microenvironment (TME) within primary tumors. This theory emphasizes the critical interaction between cancer cells ("seeds") and their surrounding environment ("soil") and how this interaction affects both tumor progression within the primary site and at metastatic sites. An important point to note is that the characteristics of the TME are not static but dynamic, undergoing substantial changes during tumor progression and after treatment with therapeutic drugs. Cancer-associated fibroblasts (CAFs), recognized as the principal noncancerous cellular component within the TME, play multifaceted roles in tumor progression including promoting angiogenesis, remodeling the extracellular matrix, and regulating immune responses. In this comprehensive review, we focus on the findings regarding how the dynamics of CAFs contribute to cancer progression and drug sensitivity. Understanding the dynamics of CAFs could provide new insights into cancer pathology and lead to important advancements in cancer research and treatment.

Exosomes secreted by ST3GAL5high cancer cells promote peritoneal dissemination by establishing a premetastatic microenvironment

Peritoneal dissemination of cancer affects patient survival. The behavior of peritoneal mesothelial cells (PMCs) and immune cells influences the establishment of a microenvironment that promotes cancer cell metastasis in the peritoneum. Here, we investigated the roles of lactosylceramide alpha-2,3-sialyltransferase (ST3G5; also known as ST3GAL5 and GM3 synthase) in the exosome-mediated premetastatic niche in peritoneal milky spots (MSs). Exosomes secreted from ST3G5high cancer cells (ST3G5high -cExos) were found to contain high levels of hypoxia-inducible factor 1-alpha (HIF1α) and accumulated in MSs via uptake in macrophages (MΦs) owing to increased expression of sialic acid-binding Ig-like lectin 1 (CD169; also known as SIGLEC1). ST3G5high -cExos induced pro-inflammatory cytokines and glucose metabolic changes in MΦs, and the interaction of these MΦs with PMCs promoted mesothelial-mesenchymal transition (MMT) in PMCs, thereby generating αSMA+ myofibroblasts. ST3G5high -cExos also increased the expression of immune checkpoint molecules and T-cell exhaustion in MSs, which accelerated metastasis to the omentum. These events were prevented following ST3G5 depletion in cancer cells. Mechanistically, ST3G5high -cExos upregulated chemokines, including CC-chemokine ligand 5 (CCL5), in recipient MΦs and dendritic cells (DCs), which induced MMT and immunosuppression via activation of signal transducer and activator of transcription 3 (STAT3). Maraviroc, a C-C chemokine receptor type 5 (CCR5) antagonist, prevented ST3G5high -cExo-mediated MMT, T-cell suppression, and metastasis in MSs. Our results suggest ST3G5 as a suitable therapeutic target for preventing cExo-mediated peritoneal dissemination.

CCDC85A is regulated by miR-224-3p and augments cancer cell resistance to endoplasmic reticulum stress

MicroRNAs (miRNAs) play pivotal roles in the tumor microenvironment. Here, we analyzed miRNAs in tumor stromal fibroblasts. Expression of miR-224-3p in cancer-associated fibroblasts (CAF) from scirrhous gastric cancer patients was lower than in normal fibroblasts (NF). Introduction of a miR-224-3p mimic attenuated migration and invasion of CAF. Coiled-coil domain containing 85A (CCDC85A), whose function in tumors is not understood, was the target gene of miR-224-3p. Immunohistological analysis revealed that CCDC85A is expressed to varying degrees by cancer cells and CAFs in gastric and pancreatic carcinomas. Downregulation of CCDC85A in cancer cells revealed that these cells are vulnerable to endoplasmic reticulum (ER) stress induced by thapsigargin or tunicamycin, which were ameliorated after addback of CCDC85A. Injection of NF-derived exosomes containing miR-224-3p into the xenograft tumor increased tumor shrinkage by cisplatin treatment. Mechanistically, CCDC85A associated with the molecular chaperone GRP78 and GRP94, thereby inhibiting association of these negative regulators of the unfolded protein response (UPR), leading to sustained activation of PERK and downstream eIF2〈 and ATF4 upon ER stress. These data suggest a novel miR-224-3p-mediated function for CCDC85A: protection from ER stress and cisplatin resistance.

Towards an optimal model for gastric cancer peritoneal metastasis: current challenges and future directions

Peritoneal metastasis is a challenging aspect of clinical practice for gastric cancer. Animal models are crucial in understanding molecular mechanisms, assessing drug efficacy, and conducting clinical intervention studies, including those related to gastric cancer peritoneal metastasis. Unlike other xenograft models, peritoneal metastasis models should not only present tumor growth at the transplant site, but also recapitulate tumor cell metastasis in the abdominal cavity. Developing a reliable model of gastric cancer peritoneal metastasis involves several technical aspects, such as the selection of model animals, source of xenograft tumors, technology of transplantation, and dynamic monitoring of the tumor progression. To date, challenges remain in developing a reliable model that can completely recapitulate peritoneal metastasis. Thus, this review aims to summarize the techniques and strategies used to establish animal models of gastric cancer peritoneal metastasis, providing a reference for future model establishment.

Integration of pharmacoproteomic and computational approaches reveals the cellular signal transduction pathways affected by apatinib in gastric cancer cell lines

Apatinib is known to be a highly selective vascular endothelial growth factor receptor 2 (VEGFR2) inhibitor with anti-angiogenic and anti-tumor properties. In a phase III study, the objective response rate to apatinib was low. It remains unclear why the effectivity of apatinib varies among patients and what type of patients are candidates for the treatment. In this study, we investigated the anti-tumor efficacy of apatinib against 13 gastric cancer cell lines and found that it differed depending on the cell line. Using integrated wet and dry approaches, we showed that apatinib was a multi-kinase inhibitor of c-Kit, RAF1, VEGFR1, VEGFR2, and VEGFR3, predominantly inhibiting c-Kit. Notably, KATO-III, which was the most apatinib-sensitive among the gastric cancer cell lines investigated, was the only cell line expressing c-Kit, RAF1, VEGFR1, and VEGFR3 but not VEGFR2. Furthermore, we identified SNW1 as a molecule affected by apatinib that plays an important role in cell survival. Finally, we identified the molecular network related to SNW1 that was affected by treatment with apatinib. These results suggest that the mechanism of action of apatinib in KATO-III cells is independent of VEGFR2 and that the differential efficacy of apatinib was due to differences in expression patterns of receptor tyrosine kinases. Furthermore, our results suggest that the differential efficacy of apatinib in gastric cell lines may be attributed to SNW1 phosphorylation levels at a steady state. These findings contribute to a deeper understanding of the mechanism of action of apatinib in gastric cancer cells.

Tissue factor-induced fibrinogenesis mediates cancer cell clustering and multiclonal peritoneal metastasis

Peritoneal metastasis is one of the most frequent causes of death in several types of advanced cancers; however, the underlying molecular mechanisms remain largely unknown. In this study, we exploited multicolor fluorescent lineage tracking to investigate the clonality of peritoneal metastasis in mouse xenograft models. When peritoneal metastasis was induced by intraperitoneal or orthotopic injection of multicolored cancer cells, each peritoneally metastasized tumor displayed multicolor fluorescence regardless of metastasis sites, indicating that it consists of multiclonal cancer cell populations. Multicolored cancer cell clusters form within the peritoneal cavity and collectively attach to the peritoneum. In vitro, peritoneal lavage fluid or cleared ascitic fluid derived from cancer patients induces cancer cell clustering, which is inhibited by anticoagulants. Cancer cell clusters formed in vitro and in vivo are associated with fibrin formation. Furthermore, tissue factor knockout in cancer cells abrogates cell clustering, peritoneal attachment, and peritoneal metastasis. Thus, we propose that cancer cells activate the coagulation cascade via tissue factor to form fibrin-mediated cell clusters and promote peritoneal attachment; these factors lead to the development of multiclonal peritoneal metastasis and may be therapeutic targets.

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.

Transferrin receptor 1 promotes the fibroblast growth factor receptor-mediated oncogenic potential of diffused-type gastric cancer

Diffuse-type gastric cancer (DGC) is a highly invasive subtype of gastric adenocarcinoma that frequently exhibits scattered peritoneal metastasis. Previous studies have shown that the genes of receptor tyrosine kinases (RTKs), such as fibroblast growth factor receptor 2 (FGFR2) or Met, are amplified in some DGC cell lines, leading to the constitutive activation of corresponding RTKs. In these cell lines, the survival of cancer cells appears to be dependent on the activation of RTKs. To gain novel insights into the downstream signaling pathways of RTKs specific to DGC, phosphotyrosine-containing proteins associated with activated FGFR2 were purified through two sequential rounds of immunoprecipitation from the lysates of two DGC cell lines. As a result, transferrin receptor 1 (TfR1) was identified as the binding partner of FGFR2. Biochemical analysis confirmed that TfR1 protein binds to FGFR2 and is phosphorylated at tyrosine 20 (Tyr20) in an FGFR2 kinase activity-dependent manner. The knockdown of TfR1 and treatment with an inhibitor of FGFR2 caused significant impairment in iron uptake and suppression of cellular proliferation in vitro. Moreover, the suppression of expression levels of TfR1 in the DGC cells significantly reduced their tumorigenicity and potency of peritoneal dissemination. It was indicated that TfR1, when phosphorylated by the binding partner FGFR2 in DGC cells, promotes proliferation and tumorigenicity of these cancer cells. These results suggest that the control of TfR1 function may serve as a therapeutic target in DGC with activated FGFR2.

SHP2 as a Potential Therapeutic Target in Diffuse-Type Gastric Carcinoma Addicted to Receptor Tyrosine Kinase Signaling

Simple Summary

Diffuse-type gastric carcinoma (DGC) is characterized by rapid infiltrative growth associated with massive stroma and frequent peritoneal dissemination, which leads to poor patient outcomes. In this study, we found that the oncogenic tyrosine phosphatase SHP2 is tyrosine-phosphorylated downstream of the amplified receptor tyrosine kinases (RTKs) Met and fibroblast growth factor receptor 2 (FGFR2) in DGC cell lines. SHP2 knockdown or pharmacological inhibition selectively suppressed the growth of DGC addicted to amplified Met and FGFR2. Moreover, targeting SHP2 abrogated malignant phenotypes, including peritoneal dissemination, of Met-addicted DGC and could overcome acquired resistance to Met inhibitors. Our findings suggest that SHP2 is a potential target for the treatment of DGC addicted to amplified RTK signaling.

Abstract

Diffuse-type gastric carcinoma (DGC) exhibits aggressive progression associated with rapid infiltrative growth, massive fibrosis, and peritoneal dissemination. Gene amplification of Met and fibroblast growth factor receptor 2 (FGFR2) receptor tyrosine kinases (RTKs) has been observed in DGC. However, the signaling pathways that promote DGC progression downstream of these RTKs remain to be fully elucidated. We previously identified an oncogenic tyrosine phosphatase, SHP2, using phospho-proteomic analysis of DGC cells with Met gene amplification. In this study, we characterized SHP2 in the progression of DGC and assessed the therapeutic potential of targeting SHP2. Although SHP2 was expressed in all gastric carcinoma cell lines examined, its tyrosine phosphorylation preferentially occurred in several DGC cell lines with Met or FGFR2 gene amplification. Met or FGFR inhibitor treatment or knockdown markedly reduced SHP2 tyrosine phosphorylation. Knockdown or pharmacological inhibition of SHP2 selectively suppressed the growth of DGC cells addicted to Met or FGFR2, even when they acquired resistance to Met inhibitors. Moreover, SHP2 knockdown or pharmacological inhibition blocked the migration and invasion of Met-addicted DGC cells in vitro and their peritoneal dissemination in a mouse xenograft model. These results indicate that SHP2 is a critical regulator of the malignant progression of RTK-addicted DGC and may be a therapeutic target.

Cancer-associated fibroblasts educate normal fibroblasts to facilitate cancer cell spreading and T cell suppression

In some tumors, a small number of cancer cells are scattered in a large fibrotic stroma. Here, we demonstrate a novel mechanism for expansion of pro‐tumor fibroblasts via cancer‐associated fibroblast (CAF)‐mediated education of normal fibroblasts (NFs). When NFs were incubated with conditioned medium from CAFs, the resulting CAF‐educated fibroblasts (CEFs) generated reactive oxygen species, which induced NF‐κB‐mediated expression of inflammatory cytokines and the extracellular matrix protein asporin (ASPN), while expression of a common CAF marker gene, α‐SMA, was not increased. ASPN further increased CEF expression of downstream molecules, including indoleamine 2,3‐dioxygenase 1 (IDO‐1), kynureninase (KYNU), and pregnancy‐associated plasma protein‐A (PAPP‐A). These CEFs induce cytocidal effects against CD8⁺ T cells and IGF‐I activation in cancer cells. CEFs were generated without cancer cells by the direct mixture of NFs and CAFs in mouse xenografts, and once CEFs were generated, they sequentially educated NFs, leading to continuous generation of CEFs. In diffuse‐type gastric cancers, ASPN^high/IDO‐1^high/KYNU^high/α‐SMA⁻ CEFs were located at the distal invading front. These CEFs expanded in the fibrotic stroma and caused dissemination of cancer cells. ASPN may therefore be a key molecule in facilitating tumor spreading and T‐cell suppression.

Drug-exposed cancer-associated fibroblasts facilitate gastric cancer cell progression following chemotherapy

BACKGROUND

Cancer progression following chemotherapy is a significant barrier to effective cancer treatment. We aimed to evaluate the role of drug-exposed cancer-associated fibroblasts (CAFs) in the growth and progression of drug-exposed gastric cancer (GC) cells and to explore the underlying molecular mechanism.

METHODS

The human GC cell line 44As3 and CAFs were treated with 5-fluorouracil and oxaliplatin (5FU + OX). 5FU + OX-pretreated 44As3 cells were then cultured in a conditioned medium (CM) from 5FU + OX-pretreated CAFs, and the growth and migration/invasion ability of the cells were evaluated. We also compared the clinicopathological characteristics of the GC patients treated with S1 + OX in accordance with the properties of their resected specimens, focusing on the number of CAFs. Changes in gene expression in CAFs and 44As3 cells were comprehensively analyzed using RNA-seq analysis.

RESULTS

The CM from 5FU + OX-pretreated CAFs promoted the migration and invasion of 5FU + OX-pretreated 44As3 cells. Although the number of cases was relatively small (n = 21), the frequency of positive cases of lymphovascular invasion and the recurrence rate were significantly higher in those with more residual CAF. RNA-seq analysis revealed 5FU + OX-pretreated CAF-derived glycoprotein 130 (gp130) as a candidate factor contributing to the increased migration of 5FU + OX-pretreated 44As3 cells. Administration of the gp130 inhibitor SC144 prevented the increased migration ability of 5FU + OX-pretreated 44As3 cells owing to drug-treated CAFs.

CONCLUSIONS

Our findings provide evidence regarding the interactions between GC cells and CAFs in the tumor microenvironment following chemotherapy, suggesting that ligands for gp130 may be novel therapeutic targets for suppressing or preventing metastasis in GC.

Radioimmunotherapy with an 211 At-labeled anti-tissue factor antibody protected by sodium ascorbate

Tissue factor (TF), the trigger protein of the extrinsic blood coagulation cascade, is abundantly expressed in various cancers including gastric cancer. Anti-TF monoclonal antibodies (mAbs) capable of targeting cancers have been successfully applied to armed antibodies such as antibody-drug conjugates (ADCs) and molecular imaging probes. We prepared an anti-TF mAb, clone 1084, labeled with astatine-211 (²¹¹ At), as a promising alpha emitter for cancer treatment. Alpha particles are characterized by high linear energy transfer and a range of 50-100 µm in tissue. Therefore, selective and efficient tumor accumulation of alpha emitters results in potent antitumor activities against cancer cells with minor effects on normal cells adjacent to the tumor. Although the ²¹¹ At-conjugated clone 1084 (²¹¹ At-anti-TF mAb) was disrupted by an ²¹¹ At-induced radiochemical reaction, we demonstrated that astatinated anti-TF mAbs eluted in 0.6% or 1.2% sodium ascorbate (SA) solution were protected from antibody denaturation, which contributed to the maintenance of cellular binding activities and cytocidal effects of this immunoconjugate. Although body weight loss was observed in mice administered a 1.2% SA solution, the loss was transient and the radioprotectant seemed to be tolerable in vivo. In a high TF-expressing gastric cancer xenograft model, ²¹¹ At-anti-TF mAb in 1.2% SA exerted a significantly greater antitumor effect than nonprotected ²¹¹ At-anti-TF mAb. Moreover, the antitumor activities of the protected immunoconjugate in gastric cancer xenograft models were dependent on the level of TF in cancer cells. These findings suggest the clinical availability of the radioprotectant and applicability of clone 1084 to ²¹¹ At-radioimmunotherapy.

Mouse Models of Peritoneal Carcinomatosis to Develop Clinical Applications

Simple Summary

Peritoneal carcinomatosis mouse models as a platform to test, improve and/or predict the appropriate therapeutic interventions in patients are crucial to providing medical advances. Here, we overview reported mouse models to explore peritoneal carcinomatosis in translational biomedical research.

Abstract

Peritoneal carcinomatosis of primary tumors originating in gastrointestinal (e.g., colorectal cancer, gastric cancer) or gynecologic (e.g., ovarian cancer) malignancies is a widespread type of tumor dissemination in the peritoneal cavity for which few therapeutic options are available. Therefore, reliable preclinical models are crucial for research and development of efficacious treatments for this condition. To date, a number of animal models have attempted to reproduce as accurately as possible the complexity of the tumor microenvironment of human peritoneal carcinomatosis. These include: Syngeneic tumor cell lines, human xenografts, patient-derived xenografts, genetically induced tumors, and 3D scaffold biomimetics. Each experimental model has its own strengths and limitations, all of which can influence the subsequent translational results concerning anticancer and immunomodulatory drugs under exploration. This review highlights the current status of peritoneal carcinomatosis mouse models for preclinical development of anticancer drugs or immunotherapeutic agents.

Expression of asporin reprograms cancer cells to acquire resistance to oxidative stress

Asporin (ASPN), a small leucine‐rich proteoglycan expressed predominantly by cancer associated fibroblasts (CAFs), plays a pivotal role in tumor progression. ASPN is also expressed by some cancer cells, but its biological significance is unclear. Here, we investigated the effects of ASPN expression in gastric cancer cells. Overexpression of ASPN in 2 gastric cancer cell lines, HSC‐43 and 44As3, led to increased migration and invasion capacity, accompanied by induction of CD44 expression and activation of Rac1 and MMP9. ASPN expression increased resistance of HSC‐43 cells to oxidative stress by reducing the amount of mitochondrial reactive oxygen species. ASPN induced expression of the transcription factor HIF1α and upregulated lactate dehydrogenase A (LDHA) and PDH‐E1α, suggesting that ASPN reprograms HSC‐43 cells to undergo anaerobic glycolysis and suppresses ROS generation in mitochondria, which has been observed in another cell line HSC‐44PE. By contrast, 44As3 cells expressed high levels of HIF1α in response to oxidant stress and escaped apoptosis regardless of ASPN expression. Examination of xenografts in the gastric wall of ASPN^–/– mice revealed that growth of HSC‐43 tumors with increased micro blood vessel density was significantly accelerated by ASPN; however, ASPN increased the invasion depth of both HSC‐43 and 44As3 tumors. These results suggest that ASPN has 2 distinct effects on cancer cells: HIF1α‐mediated resistance to oxidative stress via reprogramming of glucose metabolism, and activation of CD44‐Rac1 and MMP9 to promote cell migration and invasion. Therefore, ASPN may be a new therapeutic target in tumor fibroblasts and cancer cells in some gastric carcinomas.

Potential association of LOXL1 with peritoneal dissemination in gastric cancer possibly via promotion of EMT

Background

Peritoneal dissemination (PD) frequently occurs in gastric cancer (GC) and is incurable. In this study, we aimed to identify novel PD-associated genes and clarify their clinical and biological significance in GC.

Materials and methods

We identified LOXL1 as a PD-associated candidate gene by in silico analysis of GC datasets (highly disseminated peritoneal GC cell line and two freely available GC datasets, GSE15459 and TCGA). Next, we evaluated the clinical significance of LOXL1 expression using RT-qPCR and immunohistochemistry staining (IHC) in a validation cohort (Kyushu cohort). Moreover, we performed gene expression analysis, including gene set enrichment analysis (GSEA) with GSE15459 and TCGA datasets. Finally, we performed a series of in vitro experiments using GC cells.

Results

In silico analysis showed that LOXL1 was overexpressed in tumor tissues of GC patients with PD and in highly disseminated peritoneal GC cells, relative to that in the control GC patients and cells, respectively. High expression of LOXL1 was a poor prognostic factor in the TCGA dataset. Next, IHC showed that LOXL1 was highly expressed in GC cells. High LOXL1 mRNA expression was associated with poorly differentiated histological type, lymph node metastasis, and was an independent poor prognostic factor in the Kyushu validation cohort. Moreover, LOXL1 expression was positively correlated with the EMT (epithelial-mesenchymal transition) gene set in GSEA. Finally, LOXL1-overexpressing GC cells changed their morphology to a spindle-like form. LOXL1 overexpression reduced CDH1 expression; increased the expression of VIM, CDH2, SNAI2, and PLS3; and promoted the migration capacity of GC cells.

Conclusions

LOXL1 is associated with PD in GC, possibly through the induction of EMT.

Long Noncoding RNA HOTAIR Promotes Epithelial-Mesenchymal Transition and Is a Suitable Target to Inhibit Peritoneal Dissemination in Human Scirrhous Gastric Cancers

OBJECTIVES

Scirrhous gastric cancer, which accounts for approximately 10% of all gastric cancers, often disseminates to the peritoneum, leading to intractable cases with poor prognosis. There is an urgent need for new treatment approaches for this difficult cancer.

METHODS

We previously established an original cell line, HSC-60, from a scirrhous gastric cancer patient and isolated a peritoneal-metastatic cell line, 60As6, in nude mice following orthotopic inoculations. In the present study, we focused on the expression of long noncoding ribonucleic acid (RNA) (lncRNA) in the cell lines and investigated the mechanism on peritoneal dissemination.

RESULTS

We demonstrated that an lncRNA, HOX transcript antisense RNA (HOTAIR), is expressed significantly more highly in 60As6 than HSC-60 cells. Then, using both HOTAIR knockdown and overexpression experiments, we showed that high-level expression of HOTAIR promotes epithelial-mesenchymal transition (EMT) in 60As6 cells. By luciferase assay, we found that HOTAIR directly targets and binds to miR-217, and that miR-217 directly binds to Zinc finger E-box-binding homeobox 1 (ZEB1). The knockdown of HOTAIR in 60As6 cells significantly reduced the invasion activity and peritoneal dissemination - and significantly prolonged the survival - in the orthotopic tumor mouse model.

CONCLUSION

An EMT-associated pathway (the HOTAIR-miR-217-ZEB1 axis) appears to inhibit peritoneal dissemination and could lead to a novel therapeutic strategy against scirrhous gastric cancer in humans.

Uc.63+ contributes to gastric cancer progression through regulation of NF-kB signaling

BACKGROUND

The transcribed ultraconserved regions (T-UCRs) are a novel class of long non-coding RNAs and are involved in the development of several types of cancer. Although several different papers have described the oncogenic role of Uc.63+, there are no reports mentioning its importance in gastric cancer (GC) biology.

METHODS

In this study, we evaluated Uc.63+ expression using clinical samples of GC by qRT-PCR, and also assessed the correlation between Uc.63+ expression and clinico-pathological factors.

RESULTS

The upregulation of Uc.63+ was significantly correlated with advanced clinico-pathological features. Knockdown of Uc.63+ significantly repressed GC cell growth and migration, whereas overexpression of Uc.63+ conversely promoted those of GC cells. In situ hybridization of Uc.63+ revealed its preferential expression in poorly differentiated adenocarcinoma. We further conducted a microarray analysis using MKN-1 cells overexpressing Uc.63- and found that NF-κB signaling was significantly upregulated in accordance with Uc.63+ expression.

CONCLUSION

Our results suggest that Uc.63+ could be involved in GC progression by regulating GC cell growth and migration via NF-κB signaling.

Peritoneal Metastatic Cancer Stem Cells of Gastric Cancer with Partial Mesenchymal-Epithelial Transition and Enhanced Invasiveness in an Intraperitoneal Transplantation Model

OBJECTIVES

This preliminary study is aimed at enriching and isolating peritoneal metastatic cancer stem cells (pMCSCs) of gastric cancer and assessing their epithelial-mesenchymal transition (EMT) phenotype and invasiveness.

METHODS

Cancer stem cells of human gastric cancer (CSC-hGC) were previously isolated and transfected with green fluorescent protein and luciferase genes to validate the mouse model of peritoneal metastasis established via transplantation. The first and second generations ([G1] and [G2], respectively) of pMCSCs were isolated from intraperitoneally transplanted CSC-hGC (pMCSC-tGC) by spherical culture. CSC and EMT-related markers and regulators in the two generations of intraperitoneally transplanted tumors were examined by immunohistochemistry, immunofluorescence staining, and quantitative PCR. Cell mobility was examined by a transwell assay.

RESULTS

The nude mouse model of intraperitoneally transplanted CSC-hGC was successful in establishing sequential formation of peritoneal tumors and enrichment of pMCSCs. CD44 and CD54 were consistently expressed in the two generations of transplanted tumors. In vitro cell (migration) assays and immunocytofluorescence assays showed that in pMCSC-tGC[G2], E-cad, Survivin, and Vimentin expression was stable; α-SMA expression was decreased; and OVOL2, GRHL2, and ZEB1 expression was increased. PCR analysis indicated that in pMCSC-tGC[G2], the mRNA expression of E-cad, α-SMA, MMP9, MMP2, and Vimentin was downregulated, while that of ZEB1, OVOL2, and GRHL2 was upregulated. In vivo tumor (homing) assays and immunohistochemical assays demonstrated that in pMCSC-tGC[G2], E-cad and Snail were upregulated, while α-SMA was downregulated. The numbers of migrated and invaded pMCSC-tGC[G1] and pMCSC-tGC[G2] were significantly higher than those of CSC-hGC in migration and invasion assays.

CONCLUSIONS

pMCSCs might be a specific subpopulation that can be sequentially enriched by intraperitoneal transplantation. pMCSCs exhibited a tendency towards partial mesenchymal-epithelial transition, enhancing their invasiveness during homing and the formation of peritoneal tumors. However, these preliminary findings require validation in further experiments.

Phosphatidylinositol 4,5-bisphosphate is localized in the plasma membrane outer leaflet and regulates cell adhesion and motility

Phospholipids are distributed asymmetrically in the plasma membrane (PM) of mammalian cells. Phosphatidylinositol (PI) and its phosphorylated forms are primarily located in the inner leaflet of the PM. Among them, phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂) is a well-known substrate for phospholipase C (PLC) or phosphoinositide-3 kinase, and is also a regulator for the actin cytoskeleton or ion channels. Although functions of PI(4,5)P₂ in the inner leaflet are well characterized, those in the outer leaflet are poorly understood. Here, PI(4,5)P₂ was detected in the cell surface of non-permeabilized cells by anti-PI(4,5)P₂ antibodies and the pleckstrin-homology (PH) domain of PLCδ1 that specifically binds PI(4,5)P₂. Cell surface PI(4,5)P₂ signal was universally detected in various cell lines and freshly isolated mouse bone marrow cells and showed a punctate pattern in a cholesterol, sphingomyelin, and actin polymerization-dependent manner. Furthermore, blocking cell surface PI(4,5)P₂ by the addition of anti-PI(4,5)P₂ antibody or the PH domain of PLCδ1 inhibited cell attachment, spreading, and migration. Taken together, these results indicate a unique localization of PI(4,5)P₂ in the outer leaflet that may have a crucial role in cell attachment, spreading, and migration.

Reinforcement of antitumor effect of micelles containing anticancer drugs by binding of an anti-tissue factor antibody without direct cytocidal effects

It has been preclinically and clinically proven that anticancer agent-incorporating (ACA-incorporating) polymeric micelles selectively accumulate in tumor via the enhanced permeability and retention (EPR) effect, yielding a wider therapeutic window and greater safety than conventional low-molecular weight ACAs. To increase the antitumor effect of these safer micelle formulations, epirubicin-incorporating polymer micelles (NC-6300) conjugated with monoclonal antibodies (mAbs) have been prepared. In this study, we used two types of mAb: an anti-tissue factor (TF) mAb that does not exert a direct cytocidal effect, and an anti-HER2 mAb that has a direct cytocidal effect. We compared the antitumor effects and pharmacological properties of the two types of antibody conjugated to NC-6300. Immunomicelles conjugated to anti-TF mAb exerted greater antitumor activity toward TF-positive stomach cancer than the combination of anti-TF mAb and NC-6300, and were distributed more uniformly throughout TF-positive tumor tissue than NC-6300. On the other hand, immunomicelles conjugated to anti-HER2 mAb did not exert significant antitumor activity toward HER2-positive stomach cancer relative to the combined use of anti-HER2 mAb and NC-6300. Thus, this immunomicelle-based strategy may be useful for antibodies that target cancer as pilot molecules even when the antibodies themselves do not have an antitumor effect.

In vivo effects of mutant RHOA on tumor formation in an orthotopic inoculation model

Ras homolog family member A (RHOA) mutations are driver genes in diffuse‑type gastric cancers (DGCs), and we previously revealed that RHOA mutations contribute to cancer cell survival and cell migration through their dominant negative effect on Rho‑associated kinase (ROCK) signaling in vitro. However, how RHOA mutations contribute to DGC development in vivo is poorly understood. In the present study, the contribution of RHOA mutations to tumor morphology was investigated using an orthotopic xenograft model using the gastric cancer cell line MKN74, in which wild‑type (WT) or mutated (Y42C and Y42S) RHOA had been introduced. When we conducted RNA sequencing to distinguish between the genes expressed in human tumor tissues from those in mouse stroma, the expression profiles of the tumors were clearly divided into a Y42C/Y42S group and a mock/WT group. Through gene set enrichment analysis, it was revealed that inflammation‑ and hypoxia‑related pathways were enriched in the mock/WT tumors; however, cell metabolism‑ and cell cycle‑related pathways such as Myc, E2F, oxidative phosphorylation and G2M checkpoint were enriched in the Y42C/Y42S tumors. In addition, the gene set related to ROCK signaling inhibition was enriched in the RHOA‑mutated group, which indicated that a series of events are related to ROCK inhibition induced by RHOA mutations. Histopathological analysis revealed that small tumor nests were more frequent in RHOA mutants than in the mock or WT group. In addition, increased blood vessel formation and infiltration of macrophages within the tumor mass were observed in the RHOA mutants. Furthermore, unlike mock/WT, the RHOA‑mutated tumor cells had little antitumor host reaction in the invasive front, which is similar to the pattern of mucosal invasion in clinical RHOA‑mutated DGC. These transcriptome and pathological analyses revealed that mutated RHOA functionally contributes to the acquisition of DGC features, which will accelerate our understanding of the contribution of RHOA mutations in DGC biology and the development of further therapeutic strategies.

High expression of DNA methyltransferase 1 in Kazakh esophageal epithelial cells may promote malignant transformation induced by N-methyl-N′-nitro-N-nitrosoguanidine

We examined the role of DNA methyltransferase 1 (DNMT1) in N-methyl- N′-nitro- N-nitrosoguanidine (MNNG)–induced malignant transformation of Kazakh esophageal epithelial (EE) cells to better understand the pathogenesis of esophageal cancer (EC). The 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di- phenytetrazoliumromide method and colony formation assays were performed to determine the MNNG dose for malignant transformation. Colony formation assays showed the effects of different frequencies of MNNG exposure and different cell passages on malignant transformation. A nude mouse tumor experiment indicated the malignancy of Kazakh EE cells expressing high DNMT1 levels and of transformed cells. The result shows that when the dose, frequency, and time of MNNG exposure increased, cell morphology became irregular, cell-contact suppression disappeared, and cell tolerance and growth rate increased. Colony formation occurred in the Kazakh-DNMT1 group after 14 transfections and 27 passages. Significant differences in DNMT1 mRNA and protein levels were observed in different types of cells and tumor tissues ( F = 140.644, p < 0.001; F = 105.545, p < 0.001). Our study demonstrated that DNMT1 could promote MNNG to induce malignant transformation of EE cells, and this study will help understand EC better in order to develop appropriate treatment strategies.

Metabolic Profiling of Tumors, Sera, and Skeletal Muscles from an Orthotopic Murine Model of Gastric Cancer Associated-Cachexia

Cachexia is a complex metabolic derangement syndrome that affects approximately 50-80% of cancer patients. So far, few works have been reported to provide a global overview of gastric cancer cachexia (GCC)-related metabolic changes. We established a GCC murine model by orthotopicly implanting BGC823 cell line and conducted NMR-based metabolomic analysis of gastric tissues, sera, and gastrocnemius. The model with typical cachexia symptoms, confirmed by significant weight loss and muscle atrophy, showed distinctly distinguished metabolic profiles of tumors, sera, and gastrocnemius from sham mice. We identified 20 differential metabolites in tumors, 13 in sera, and 14 in gastrocnemius. Tumor extracts displayed increased pyruvate and lactate, and decreased hypoxanthine, inosine, and inosinate, indicating significantly altered glucose and nucleic acid metabolisms. Cachectic mice exhibited up-regulated serum lactate and glycerol, and down-regulated glucose, which were closely related to hyperlipidemia and hypoglycemia. Furthermore, gastrocnemius transcriptomic and metabolomic data revealed that GCC induced perturbed pathways mainly concentrated on carbohydrate and amino acid metabolism. Specifically, cachectic gastrocnemius exhibited increased α-ketoglutarate and decreased glucose. In vitro study indicated that α-ketoglutarate could prompt myoblasts proliferation and reduce glucose deficiency-induced myotubes atrophy. Overall, this work provides a global metabolic overview to understand the metabolic alterations associated with GCC-induced muscle atrophy.

Development and Biological Analysis of a Novel Orthotopic Peritoneal Dissemination Mouse Model Generated Using a Pancreatic Ductal Adenocarcinoma Cell Line

OBJECTIVES

Peritoneal dissemination (PD) is an important cause of morbidity and mortality among patients with pancreatic ductal adenocarcinoma (PDAC). We sought to develop and characterized a novel PD mouse model by using a previously established PDAC cell line TCC-Pan2.

METHODS

TCC-Pan2 cell line was characterized for growth rate, tumor markers, histology, and somatic mutations. TCC-Pan2 cells were implanted orthotopically to produce PD. TCC-Pan2 cells from these metastatic foci were expanded in vitro and then implanted orthotopically in mice. This PD model was used for comparing the antitumor effect of paclitaxel and NK105.

RESULTS

Orthotopically implanted TCC-Pan2 cells caused tumor formation and PD with high frequency in mice. A potent metastatic subline-Pan2M-was obtained. NK105 exerted a stronger antitumor effect than paclitaxel against Pan2M cells harboring a luciferase gene (Pan2MmLuc). Notably, the survival rate on day 80 in the Pan2MmLuc mouse model was 100% for the NK105 group and 0% for the paclitaxel group.

CONCLUSION

TCC-Pan2 cell line and Pan2MmLuc PD model can serve as useful tools for monitoring the responses to antineoplastic agents and for studying PDAC biology.

Mieap-induced accumulation of lysosomes within mitochondria (MALM) regulates gastric cancer cell invasion under hypoxia by suppressing reactive oxygen species accumulation

Mitochondrial quality control (MQC) protects against potentially damaging events, such as excessive generation of mitochondrial reactive oxygen species (mtROS). We investigated the contribution of the two major MQC processes, namely, mitophagy and Mieap-induced accumulation of lysosomes within mitochondria (MALM), to the response to hypoxia of two human gastric cancer (GC) cell lines. We found that hypoxia increased mtROS generation and cell invasion in 58As9, but not in MKN45, although the transcription factor hypoxia-inducible factor 1α was induced in both cell lines. Colocalisation of lysosomes with mitochondria was found only in hypoxic MKN45 cells, suggesting that hypoxia-induced MQC functions normally in MKN45 but may be impaired in 58As9. Hypoxia did not lead to decreased mitochondrial mass or DNA or altered appearance of autophagosomes, as judged by electron microscopy, suggesting that mitophagy was not induced in either cell line. However, western blot analysis revealed the presence of the MALM-associated proteins Mieap, BNIP3 and BNIP3L, and the lysosomal protein cathepsin D in the mitochondrial fraction of MKN45 cells under hypoxia. Finally, Mieap knockdown in MKN45 cells resulted in increased mtROS accumulation and cell invasion under hypoxia. Our results suggest that hypoxia-induced MALM suppresses GC cell invasion by preventing mtROS generation.

A 3E8.scFv.Cys-IR800 Conjugate Targeting TAG-72 in an Orthotopic Colorectal Cancer Model

PURPOSE

Optical surgical navigation (OSN) will be a potent tool to help surgeons more accurately and efficiently remove tumors. The purpose of this study was to evaluate a novel humanized 3E8 antibody (3E8 MAb) fragment site-specifically conjugated with IR800, 3E8.scFv.Cys-IR800, as a potential OSN agent to target colorectal adenocarcinoma.

PROCEDURES

An engineered single-chain variable fragment of 3E8 MAb (targeted to TAG-72), appending a C-terminal cysteine residue (3E8.scFv.Cys), was created and reacted with IRDye800-maleimide. 3E8.scFv.Cys-IR800 identity and purity were verified by MALDI-TOF mass spectra and 800 nm detected size exclusion column HPLC. In vitro human colon adenocarcinoma LS-174 T cells binding and competition assay validated biological functionality. We further evaluated the imaging ability and receptor-specific binding of 3E8.scFv.Cys-IR800 in an orthotopic LS-174 T mouse model.

RESULTS

A 1:1 dye to protein conjugate was achieved at greater than 90 % HPLC purity. A 1 nmol dose of 3E8.scFv.Cys-IR800 via intraperitoneal injection administration was sufficient to produce high tumor to background fluorescence contrast. Blocking competition studies both in vitro and in vivo using a different blocking protein, 3E8ΔCH2, demonstrated 3E8.scFv.Cys-IR800 binding specificity for TAG-72 antigen.

CONCLUSIONS

3E8.scFv.Cys-IR800 shows properties useful in a clinically viable OSN agent for colorectal cancer.

Overexpression of FGFR1 Promotes Peritoneal Dissemination Via Epithelial-to-Mesenchymal Transition in Gastric Cancer

BACKGROUND

Peritoneal dissemination (PD) is one of the most common causes of cancer-related mortality in gastric cancer (GC). We aimed to identify PD-associated genes and investigate their role in GC.

MATERIALS AND METHODS

We identified FGFR1 as a putative PD-associated gene using a bioinformatics approach. The biological significance of FGFR1 in epithelial-to-mesenchymal transition (EMT) was evaluated according to the correlation with genes that participated in EMT and FGFR1 knockdown experiments. The associations between FGFR1 expression and the clinicopathological features were examined.

RESULTS

FGFR1 expression positively correlated with SNAI1, VIM and ZEB1 expression, and negatively correlated with CDH1 expression. Knockdown of FGFR1 suppressed the malignant phenotype of GC cells. High FGFR1 expression significantly correlated with the peritoneal lavage cytology and synchronous PD positivity as well as poor prognosis.

CONCLUSION

High FGFR1 expression was associated with PD via promotion of EMT and led to a poor prognosis of GC patients.

MicroRNAs Associated with Epithelial-Mesenchymal Transition Can Be Targeted to Inhibit Peritoneal Dissemination of Human Scirrhous Gastric Cancers

OBJECTIVES

Scirrhous gastric cancers grow rapidly, and frequently invade the peritoneum. Such peritoneal dissemination properties markedly reduce patient survival. Thus, an effective means for inhibiting peritoneal dissemination is urgently required.

METHODS

We previously established a cell line, HSC-58, from a scirrhous gastric cancer patient, and further successfully isolated a metastatic line, 58As9, in nude mice upon orthotopic inoculation. Using the lines, we examined the mechanism underlying peritoneal dissemination from the viewpoint of microRNA (miRNA) expression.

RESULTS

miRNA array and qRT-PCR analysis showed that the expressions of epithelial-mesenchymal transition (EMT)-associated miRNAs such as miR-200c and miR-141 were significantly low in 58As9. Using 58As9 with stably overexpressing miR-200c, miR-141, or both, together with a luciferase reporter assay, we found that miR-200c targeted zinc finger E-box-binding homeobox 1 (ZEB1) and miR-141 targeted ZEB2. The overexpressed lines reversed the EMT status from mesenchymal to epithelial in 58As9, and significantly reduced the invasion activity and peritoneal dissemination for a significant prolongation of survival in the orthotopic tumor models in nude mice.

CONCLUSIONS

EMT-associated miRNAs such as miR-200c and miR-141 and their target genes ZEB1/ZEB2 have good potential for antiperitoneal dissemination therapy in patients with scirrhous gastric cancers.

PLOD2 as a potential regulator of peritoneal dissemination in gastric cancer

Peritoneal dissemination is the most common metastatic pattern in advanced gastric cancer (GC) and has a very poor prognosis. However, its molecular mechanism has not been elucidated. Our study investigated genes associated with peritoneal dissemination of GC. We performed combined expression analysis of metastatic GC cell lines and identified Procollagen-lysine, 2-oxoglutarate 5-dioxygenase2 (PLOD2) as a potential regulator of peritoneal dissemination. PLOD2 is regulated by hypoxia-inducible factor-1 (HIF-1) and mediates extracellular matrix remodeling, alignment, and mechanical properties. We analyzed PLOD2 expression immunohistochemically in 179 clinical samples, and found high PLOD2 expression to be significantly associated with peritoneal dissemination, leading to poor prognosis. In an in vivo-collected metastatic cell line, downregulation of PLOD2 by siRNA reduced invasiveness and migration. Hypoxia upregulated PLOD2 mediated by HIF-1, and promoted invasiveness and migration. After exposure to hypoxia, a cell line transfected with siPLOD2 exhibited significantly suppressed invasiveness and migration, despite high HIF-1 expression. These findings indicate that PLOD2 is a regulator of, and candidate therapeutic target for peritoneal dissemination of GC. Although peritoneal dissemination of GC has a very poor prognosis, its molecular mechanism has not been elucidated. We identified PLOD2 regulated by HIF-1 as a potential regulator of peritoneal dissemination of GC. Finally, we showed that PLOD2 promotes cell invasiveness and migration in GC under hypoxia and lead to peritoneal dissemination of GC.

Identification of ARL4C as a Peritoneal Dissemination-Associated Gene and Its Clinical Significance in Gastric Cancer

BACKGROUND

In gastric cancer (GC), peritoneal dissemination (PD) occurs frequently and is incurable. In this study, we aimed to identify PD-associated genes in GC.

METHODS

We identified a PD-associated gene using three GC datasets: highly disseminated peritoneal GC cell lines, the Singapore dataset and The Cancer Genome Atlas (TCGA) dataset. We assessed the clinicopathological significance of the gene expression using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and performed immunohistochemical analysis for the gene in our patient cohort. We also performed survival analyses of the gene in our patient cohort, the Singapore dataset and the GSE62254 datasets. Moreover, gene set enrichment analysis (GSEA) was performed using the Singapore and TCGA datasets. Finally, in vitro experiments such as invasion/migration assays, immunofluorescence staining of actin filaments, epidermal growth factor (EGF) treatment analysis, and gene expression analysis were conducted using three gene-knockdown GC cell lines (AGS, 58As9, MKN45).

RESULTS

ADP-ribosylation factor-like 4c (ARL4C) was identified as a PD-associated gene, and immunohistochemical analysis showed that ARL4C was overexpressed in GC cells. High ARL4C expression was associated with the depth of invasion (p < 0.01) and PD (p < 0.05) and was a poor prognostic factor (p < 0.05) in our patient cohort, the Singapore dataset and the GSE62254 dataset. ARL4C expression positively correlated with the epithelial-mesenchymal transition (EMT) gene set in GSEA. Moreover, ARL4C knockdown reduced invasion/migration capacity, SLUG expression, and the formation of lamellipodia or filopodia in AGS and 58As9 cells. Finally, EGF treatment increased ARL4C expression in MKN45 cells.

CONCLUSIONS

ARL4C was associated with PD and was a poor prognostic factor in GC, possibly through promoting invasive capacity by activation of both EMT and motility.

Improvement of anti-cancer drug efficacy via thermosensitive hydrogel in peritoneal carcinomatosis in gastric cancer

Peritoneal carcinomatosis (PC) of gastric origin has a poor prognosis with short survival due to lack of effective therapeutic modalities. Here, we evaluated the therapeutic efficacy of an injectable thermosensitive poly (organophosphazene) (PPZ) hydrogel with docetaxel (DTX-gel) to develop an effective therapeutic agent for patient with PC. Three days after inoculation of highly metastatic 44As3Luc cells into peritoneal cavity, the mice were intravenously or intraperitoneally administered with docetaxel alone (DTX-sol IV or IP), and intraperitoneally injected with DTX-gel. The anti-tumor activity was monitored by bioluminescence live imaging system. Compared to DTX-sol IV or IP, the tumor growth was significantly reduced in the DTX-gel treated mice (p<0.0001, p=0.0001). Furthermore, the survival rate was significantly increased in the DTX-gel treated mice compared to DTX-sol IV or IP treated mice (p<0.0001, p=0.0068). Our results demonstrated that DTX-gel suppresses peritoneal metastasis by continuing release of chemotherapy agent, which leads to increase the survival rate in a PC model. Therefore, biodegradable thermosensitive hydrogel with docetaxel system can be a good anti-cancer agent for PC.

Low-dose YC-1 combined with glucose and insulin selectively induces apoptosis in hypoxic gastric carcinoma cells by inhibiting anaerobic glycolysis

This study aimed to establish a therapeutic strategy targeting hypoxic cancer cells in gastric carcinoma (GC). YC-1 is a HIF-1α inhibitor, and we revealed that low-dose YC-1 (10 µM) suppressed HIF-1α expression, and induced hypoxia-dependent apoptosis in the GC cell line 58As9. This hypoxia-specific apoptosis induction by YC-1 involved excessive reactive oxygen species (ROS) generation. The apoptotic effect of 10 µM YC-1 was enhanced by additional glucose (G) and insulin (I) treatments. RT-PCR demonstrated that 10 µM YC-1 reduced hypoxia-induced expression of HIF-1α targets involved in anaerobic glycolysis. Metabolic analysis showed that YC-1 shifted glucose metabolism in hypoxic cells from anaerobic glycolysis to oxidative phosphorylation (OXPHOS). Additional GI accelerated membranous GLUT1 translocation, elevating glucose uptake, and increased acetyl-CoA levels, leading to more ROS generation in hypoxic YC-1-treated cells. Finally, we evaluated the anti-cancer effect of low-dose YC-1 (1 mg/kg) + G (2 g/kg) and I (1 unit/3 g G) treatment in xenograft models. YC-1 + GI therapy strongly inhibited tumour growth. Immunohistochemical analysis demonstrated that YC-1 + GI reduced HIF-1α expression and pimonidazole accumulation in tumours. Conversely, YC-1 + GI increased intra-tumoral 8-OHdG and levels of apoptosis markers. Low-dose YC-1 + GI is a unique therapy targeting hypoxic GC cells that generates lethal ROS via forced activation of OXPHOS.

Hypoxia-induced ANGPTL4 sustains tumour growth and anoikis resistance through different mechanisms in scirrhous gastric cancer cell lines

Patients with scirrhous gastric cancer (SGC) frequently develop peritoneal dissemination, which leads to poor prognosis. The secreted protein angiopoietin-like-4 (ANGPTL4), which is induced by hypoxia, exerts diverse effects on cancer progression. Here, we aimed to determine the biological function of ANGPTL4 in SGC cells under hypoxia. ANGPTL4 levels were higher in SGC cells under hypoxia than in other types of gastric cancer cells. Hypoxia-induced ANGPTL4 mRNA expression was regulated by hypoxia-inducible factor-1α (HIF-1α). Under hypoxic conditions, monolayer cultures of ANGPTL4 knockdown (KD) 58As9 SGC (58As9-KD) cells were arrested in the G₁ phase of the cell cycle through downregulation of c-Myc and upregulation of p27, in contrast to control 58As9-SC cells. Moreover, the ability of 58As9-KD xenografts to form tumours in nude mice was strongly suppressed. When 58As9-KD cells were cultured in suspension, hypoxia strongly increased their susceptibility to anoikis through suppression of the FAK/Src/PI3K-Akt/ERK pro-survival pathway, followed by activation of the apoptotic factors caspases-3, -8 and -9. The development of peritoneal dissemination by 58As9-KD cells was completely inhibited compared with that by 58As9-SC cells. In conclusion, ANGPTL4 is uniquely induced by hypoxia in cultured SGC cells and is essential for tumour growth and resistance to anoikis through different mechanisms.

Novel small molecule inhibiting CDCP1-PKCδ pathway reduces tumor metastasis and proliferation

CUB domain‐containing protein‐1 (CDCP1) is a trans‐membrane protein predominantly expressed in various cancer cells and involved in tumor progression. CDCP1 is phosphorylated at tyrosine residues in the intracellular domain by Src family kinases and recruits PKCδ to the plasma membrane through tyrosine phosphorylation‐dependent association with the C2 domain of PKCδ, which in turn induces a survival signal in an anchorage‐independent condition. In this study, we used our cell‐free screening system to identify a small compound, glycoconjugated palladium complex (Pd‐Oqn), which significantly inhibited the interaction between the C2 domain of PKCδ and phosphorylated CDCP1. Immunoprecipitation assays demonstrated that Pd‐Oqn hindered the intercellular interaction of phosphorylated CDCP1 with PKCδ and also suppressed the phosphorylation of PKCδ but not that of ERK or AKT. In addition, Pd‐Oqn inhibited the colony formation of gastric adenocarcinoma 44As3 cells in soft agar as well as their invasion. In mouse models, Pd‐Oqn markedly reduced the peritoneal dissemination of gastric adenocarcinoma cells and the tumor growth of pancreatic cancer orthotopic xenografts. These results suggest that the novel compound Pd‐Oqn reduces tumor metastasis and growth by inhibiting the association between CDCP1 and PKCδ, thus potentially representing a promising candidate among therapeutic reagents targeting protein–protein interaction.

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

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

Transcription factor RUNX2 up-regulates chemokine receptor CXCR4 to promote invasive and metastatic potentials of human gastric cancer

Runt-related transcription factor 2 (RUNX2) is a regulator of embryogenesis and development, but has also been implicated in the progression of certain human cancer. This study aimed to elucidate the role of RUNX2 in the invasive and metastatic potentials of human gastric cancer (GC) and the underlying mechanisms. We found that the levels of RUNX2 expression in gastric cancer tissues were correlated with the differentiation degrees, invasion depth and lymph node metastasis. COX regression analysis indicated that RUNX2 was an independent prognostic indicator for GC patients. RUNX2 significantly increased the migration and invasion ability of GC cells in vitro and enhanced the invasion and metastatic potential of GC cells in an orthotopic GC model of nude mice. Mechanistically, RUNX2 directly bound to the promoter region of the gene coding for the chemokine receptor CXCR4 to enhance its transcription. CXCR4 knockdown or treatment with AMD3100, a CXCR4 inhibitor, attenuated RUNX2-promoted invasion and metastasis. These results demonstrate that RUNX2 promotes the invasion and metastasis of human GC by transcriptionally up-regulating the chemokine receptor CXCR4. Therefore, the RUNX2-CXCR4 axis is a potential therapeutic target for GC.

Integrated Molecular Profiling of Human Gastric Cancer Identifies DDR2 as a Potential Regulator of Peritoneal Dissemination

Peritoneal dissemination is the most frequent, incurable metastasis occurring in patients with advanced gastric cancer (GC). However, molecular mechanisms driving peritoneal dissemination still remain poorly understood. Here, we aimed to provide novel insights into the molecular mechanisms that drive the peritoneal dissemination of GC. We performed combined expression analysis with in vivo-selected metastatic cell lines and samples from 200 GC patients to identify driver genes of peritoneal dissemination. The driver-gene functions associated with GC dissemination were examined using a mouse xenograft model. We identified a peritoneal dissemination-associated expression signature, whose profile correlated with those of genes related to development, focal adhesion, and the extracellular matrix. Among the genes comprising the expression signature, we identified that discoidin-domain receptor 2 (DDR2) as a potential regulator of peritoneal dissemination. The DDR2 was upregulated by the loss of DNA methylation and that DDR2 knockdown reduced peritoneal metastasis in a xenograft model. Dasatinib, an inhibitor of the DDR2 signaling pathway, effectively suppressed peritoneal dissemination. DDR2 was identified as a driver gene for GC dissemination from the combined expression signature and can potentially serve as a novel therapeutic target for inhibiting GC peritoneal dissemination.

Loss of FOXO1 promotes gastric tumour growth and metastasis through upregulation of human epidermal growth factor receptor 2/neu expression

BACKGROUND

The biological significance of FOXO1, a member of the forkhead box O transcription factor family, in gastric cancer (GC) remains unclear. The present study provides direct evidence of the role of FOXO1 in tumour growth and metastasis of GC in relation to human epidermal growth factor receptor 2 (HER2).

METHODS

The expressions of FOXO1 and HER2 were modulated in GC cell lines (SNU-638, MKN45, SNU-216 and NCI-N87) by stable transfections. The effects of transfection on GC phenotypes were evaluated in vitro and in animal models. In addition, the relationship between FOXO1 and HER2 was analysed using GC clinical specimens, cell lines and xenografts.

RESULTS

FOXO1 silencing in GC cells increased colony formation and mesenchymal transition in vitro, as well as tumour growth and metastasis in nude mice, whereas HER2 silencing induced the opposite results.. Furthermore, an inverse relationship between FOXO1 and HER2 was found in clinical specimens of GC, GC cells and GC xenograft tumours. Although a negative crosstalk between these two molecules was shown, double knockdown of both FOXO1 and HER2 in GC cells revealed that HER2 silencing reversed the FOXO1 shRNA-induced migration and invasion even without the FOXO1 restoration.

CONCLUSIONS

Our results indicate that loss of FOXO1 promotes GC growth and metastasis by upregulating HER2 expression and that the HER2 expression is more critical to the induction of GC cell metastasis. The present study provides evidence that the FOXO1/HER2 pathway may regulate GC progression in a subgroup of GC patients.

The Apoptotic Effect of HIF-1α Inhibition Combined with Glucose plus Insulin Treatment on Gastric Cancer under Hypoxic Conditions

Gastric cancer grows under a hypoxic environment. HIF-1α is known to play an important role in controlling the production of reactive oxygen species (ROS) in the mitochondria under hypoxic conditions. We previously established HIF-1α knockdown (KD) cells and control (SC) cells in the 58As9 gastric cancer cell line. In this study, we revealed that KD cells, but not SC cells, induced apoptosis under conditions of hypoxia (1% O2) due to excessive production of ROS. A quantitative RT-PCR analysis demonstrated that the expressions of ten genes, which are involved in the control mechanisms of ROS (including the Warburg effect, mitophagy, electron transport chain [ETC] modification and ROS scavenging), were regulated by HIF-1α. Moreover, the promotion of glucose uptake by glucose plus insulin (GI) treatment enhanced the apoptotic effect, which was accompanied by further ROS production in hypoxic KD cells. A Western blot analysis showed that the membranous expression of GLUT1 in KD cells was elevated by glucose and/or insulin treatments, indicating that the GI-induced glucose uptake is mediated by the increased translocation of GLUT1 on the cell membrane. Finally, the anti-tumor effect of HIF-1α knockdown (KD) plus GI was evaluated using a tumor xenograft model, where a hypoxic environment naturally exists. As a result, the GI treatment strongly inhibited the growth of the KD tumors whereby cell apoptosis was highly induced in comparison to the control treatment. In contrast, the growth of the SC tumors expressing HIF-1α was not affected by the GI treatment. Taken together, the results suggest that HIF-1α inhibition plus GI may be an ideal therapy, because the apoptosis due to the destruction of ROS homeostasis is specifically induced in gastric cancer that grows under a hypoxic environment, but not in the normal tissue under the aerobic conditions.

Identification and Characterization of CXCR4-Positive Gastric Cancer Stem Cells

Diffuse-type solid tumors are often composed of a high proportion of rarely proliferating (i.e., dormant) cancer cells, strongly indicating the involvement of cancer stem cells (CSCs) Although diffuse-type gastric cancer (GC) patients have a poor prognosis due to high-frequent development of peritoneal dissemination (PD), it is limited knowledge that the PD-associated CSCs and efficacy of CSC-targeting therapy in diffuse-type GC. In this study, we established highly metastatic GC cell lines by in vivo selection designed for the enrichment of PD-associated GC cells. By microarray analysis, we found C-X-C chemokine receptor type 4 (CXCR4) can be a novel marker for highly metastatic CSCs, since CXCR4-positive cells can grow anchorage-independently, initiate tumors in mice, be resistant to cytotoxic drug, and produce differentiated daughter cells. In clinical samples, these CXCR4-positive cells were found from not only late metastasis stage (accumulated ascites) but also earlier stage (peritoneal washings). Moreover, treatment with transforming growth factor-β enhanced the anti-cancer effect of docetaxel via induction of cell differentiation/asymmetric cell division of the CXCR4-positive gastric CSCs even in a dormant state. Therefore, differentiation inducers hold promise for obtaining the maximum therapeutic outcome from currently available anti-cancer drugs through re-cycling of CSCs.

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.

ZnPPIX inhibits peritoneal metastasis of gastric cancer via its antiangiogenic activity

Our previous study suggests that heme oxygenase-1 (HO-1) may play an important role in the metastasis of gastric cancer. Zinc protoporphyrin IX (ZnPPIX) is a special HO-1 inhibitor that inhibits the angiogenesis of pancreatic and lung cancer. In this study, we employed ZnPPIX to investigate the role of HO-1 in peritoneal metastasis of gastric cancer (PMGC) and explored the potential mechanism. We established animal model of PMGC by orthotopic implantation into nude mice of human gastric cancer cell line GC9811-P with high peritoneal metastasis potential. The mice were injected intraperitoneally with saline, CTX or ZnPPIX. Tumor microvessel density (MVD) in peritoneal metastatic nodules was determined by immunohistochemistry, and vascular endothelial growth factor (VEGF) level was determined by ELISA. We found that the number, volume, weight of peritoneal metastatic nodules and volume of seroperitoneum in ZnPPIX (4 mg/kg) group decreased remarkably compared with control group. MVD value and VEGF level of peritoneal metastatic tumor in ZnPPIX (4 mg/kg) group also decreased significantly, while the survival rate and survival time of the mice were higher than control group. ZnPPIX dose-dependently suppressed VEGF and GC9811-P induced angiogenesis. Furthermore, ZnPPIX suppressed VEGF induced reactive oxygen species production and ERK phosphorylation in human umbilical vein endothelial cells. In conclusion, our results suggest that HO-1 plays an important role in PMGC and ZnPPIX is an effective antitumor and antiangiogenic agent for PMGC.

Stromal cells positively and negatively modulate the growth of cancer cells: stimulation via the PGE2-TNFα-IL-6 pathway and inhibition via secreted GAPDH-E-cadherin interaction

Fibroblast-like stromal cells modulate cancer cells through secreted factors and adhesion, but those factors are not fully understood. Here, we have identified critical stromal factors that modulate cancer growth positively and negatively. Using a cell co-culture system, we found that gastric stromal cells secreted IL-6 as a growth and survival factor for gastric cancer cells. Moreover, gastric cancer cells secreted PGE2 and TNFα that stimulated IL-6 secretion by the stromal cells. Furthermore, we found that stromal cells secreted glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Extracellular GAPDH, or its N-terminal domain, inhibited gastric cancer cell growth, a finding confirmed in other cell systems. GAPDH bound to E-cadherin and downregulated the mTOR-p70S6 kinase pathway. These results demonstrate that stromal cells could regulate cancer cell growth through the balance of these secreted factors. We propose that negative regulation of cancer growth using GAPDH could be a new anti-cancer strategy.

Agr2 mediates paracrine effects on stromal fibroblasts that promote invasion by gastric signet-ring carcinoma cells

Agr2 is a disulfide isomerase residing in the endoplasmic reticulum (ER), which physiologically regulates protein folding and mediates resistance to ER stress. Agr2 is overexpressed in adenocarcinomas of various organs, where it participates in neoplastic transformation and metastasis, therefore acts as a pro-oncogenic protein. Besides its normal localization in the ER, Agr2 is also found in the serum and urine of cancer patients, although the physiological significance of extracellular Agr2 is poorly understood. In this study, we demonstrated that extracellular Agr2 can activate stromal fibroblasts and promote fibroblast-associated cancer invasion in gastric signet-ring cell carcinoma (SRCC), where Agr2 is highly expressed. Agr2 secreted from SRCC cells was incorporated by the surrounding gastric fibroblasts and promoted invasion by these cells. In turn, activated fibroblasts coordinated the invasive behavior of fibroblasts and cancer cells. Our findings suggested that Agr2 drives progression of gastric SRCC by exerting paracrine effects on fibroblasts in the tumor microenvironment, acting also to increase the growth and resistance of SRCC cells to oxidative and hypoxic stress as cell autonomous effects.