Integrin alpha6beta4 as a suppressor and a predictive marker for peritoneal dissemination in human gastric cancer

Diffuse tumors: Molecular determinants shared by different cancer types

Most cancer types have both diffuse and non-diffuse subtypes, which have rather distinct morphologies, namely scattered tiny tumors vs. one solid tumor, and different levels of aggressiveness. However, the causes for forming such distinct subtypes remain largely unknown. Using the diffuse and non-diffuse gastric cancers (GCs) as the illustrative example, we present a computational study based on the transcriptomic data from the TCGA and GEO databases, to address the following questions: (i) What are the key molecular determinants that give rise to the distinct morphologies between diffuse and non-diffuse cancers? (ii) What are the main reasons for diffuse cancers to be generally more aggressive than non-diffuse ones of the same cancer type? (iii) What are the reasons for their distinct immunoactivities? And (iv) why do diffuse cancers on average tend to take place in younger patients? The study is conducted using the framework we have previously developed for elucidation of general drivers cancer formation and development. Our main discoveries are: (a) the level of (poly-) sialic acids deployed on the surface of cancer cells is a significant factor contributing to questions (i) and (ii); (b) poly-sialic acids synthesized by ST8SIA4 are the key to question (iii); and (c) the circulating growth factors specifically needed by the diffuse subtype dictate the answer to question (iv). All these predictions are substantiated by published experimental studies. Our further analyses on breast, prostate, lung, liver, and thyroid cancers reveal that these discoveries generally apply to the diffuse subtypes of these cancer types, hence indicating the generality of our discoveries.

Identification of a Favorable Prognostic Subgroup in Oral Squamous Cell Carcinoma: Characterization of ITGB4/PD-L1high with CD8/PD-1high

Integrin β4 (ITGB4) is a member of the integrin family, which plays a crucial role in mediating cell adhesion to the extracellular matrix. Recent studies have demonstrated that ITGB4 is involved in tumorigenesis and metastasis during the development of cancer. However, the role of ITGB4 in oral squamous cell carcinoma (OSCC) remains unclear. A Multiplex immunohistochemistry (OPAL™, mIHC) assay was employed to stain ITGB4, ALDH1, PD-L1, cytokeratin (CK), CD8 and PD-1 in a human OSCC tissue microarray, containing 26 normal oral epithelium samples, 21 oral epithelium dysplasia samples and 76 OSCC samples. The expression pattern and clinicopathological characteristics of ITGB4 were analyzed and compared with those of PD-1, PD-L1, ALDH1 and CD8. The correlation between subgroups of tumor cells, including ITGB4⁺PD-L1⁺ and ITGB4⁺ALDH1⁺, and subgroups of T cells, including CD8⁺ and CD8⁺PD-1⁺, was evaluated using two-tailed Pearson's statistics. A Kaplan-Meier curve was built, and a log-rank test was performed to analyze the survival rate of different subgroups. The mIHC staining results show that ITGB4 was mostly expressed in the tumor cells, with a significant increase in the OSCC specimens compared with normal oral epithelium and oral epithelium dysplasia. The paired analysis, conducted between the OSCC tumor tissue and normal paracancer mucosa, confirmed the results. The study further revealed that ITGB4⁺PD-L1⁺ cancer cells, but not ITGB4⁺ALDH1⁺ cancer cells, were significantly associated with the infiltration of CD8⁺ T cells (positivity p = 0.005, positive number p = 0.03). Additionally, ITGB4⁺PD-L1⁺ tumor cells were positively correlated with CD8⁺PD-1⁺ T cells (positivity p = 0.02, positive number p = 0.03). Most intriguingly, the subgroup of ITGB4/PD-L1^high with CD8/PD-1^high displayed the best prognosis compared with the other considered subgroups. The results show that the expression of ITGB4 was increased in OSCC compared with normal oral mucosa. Furthermore, a specific subgroup with high levels of expression of ITGB4/PD-L1 and CD8/PD-1 was found to have a relatively better prognosis compared with the other subgroups. Ultimately, this study sheds light on the potential role of ITGB4 in OSCC and provides a basis for further investigation.

HMMR promotes peritoneal implantation of gastric cancer by increasing cell-cell interactions

BACKGROUND

Distant metastasis is the prominent factor for cancer-induced death of gastric cancer in which peritoneum is one of the dominating targets of gastric cancer metastasis. However, there is still a lack of effective predictive indicators and treatment methods for gastric cancer patients with peritoneal metastasis.

METHODS

A clustering assay was used to investigate the cell aggregates formation ability. While the soft agar assay and anoikis assay were performed to detect the anchorage-independent growth and anoikis-resistant ability respectively. Luciferase activity assay, western blotting and immunofluorescence were used to explore the effect of HMMR on AKT signaling activity. The peritoneal implantation model was examined to explore the role of HMMR in vivo.

RESULTS

Silencing of HMMR expression markedly reduced the peritoneal metastasis of gastric cancer cells through reducing cell-cell interactions. Mechanistically, HA-HMMR could activate Akt signaling, thus succeeding in distant colonization and metastatic outgrowth. Importantly, inducible depletion of HMMR significantly abrogates peritoneal implantation of gastric cancer in vitro and in vivo.

CONCLUSION

Our study highlights that HMMR promotes peritoneal implantation of gastric cancer. A better understanding of HMMR's functions and mechanism might provide a novel therapeutic target and prognostic marker for metastatic gastric cancer.

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.

Systematic Review of Prognostic Gene Signature in Gastric Cancer Patients

Gastric cancer (GC) is the second leading cause of cancer mortality and remains the fourth common cancer worldwide. The effective and feasible methods for predicting the possible outcomes for GC patients are still lacking. While genetic profiling might be suitable in some way, the application of gene expression signatures has been show to be a robust tool. Here, by performing a comprehensive search in PubMed, we provided an up-to-date summary of 39 prognostic gene signatures for GC patients, and described the processing procedure of the selection, calculation and construction of gene signature. We also reviewed current web tools including PROGgene and SurvExpress that can be used to analyze the prognostic value of multiple genes for GC. This review will aid in comprehensive understanding of the current prognostic gene signatures to accurately predict the outcome of GC patients, and may guide the future clinical management when the reliability of these signatures is validated in clinics.

The Extracellular Matrix: An Accomplice in Gastric Cancer Development and Progression

The extracellular matrix (ECM) is a dynamic and highly organized tissue structure, providing support and maintaining normal epithelial architecture. In the last decade, increasing evidence has emerged demonstrating that alterations in ECM composition and assembly strongly affect cellular function and behavior. Even though the detailed mechanisms underlying cell-ECM crosstalk are yet to unravel, it is well established that ECM deregulation accompanies the development of many pathological conditions, such as gastric cancer. Notably, gastric cancer remains a worldwide concern, representing the third most frequent cause of cancer-associated deaths. Despite increased surveillance protocols, patients are usually diagnosed at advanced disease stages, urging the identification of novel diagnostic biomarkers and efficient therapeutic strategies. In this review, we provide a comprehensive overview regarding expression patterns of ECM components and cognate receptors described in normal gastric epithelium, pre-malignant lesions, and gastric carcinomas. Important insights are also discussed for the use of ECM-associated molecules as predictive biomarkers of the disease or as potential targets in gastric cancer.

Extramedullary leukemia behaving as solid cancer: clinical, histologic, and genetic clues to chemoresistance in organ sites

Recent studies of leukemic tumors in individual extramedullary sites showed they adopt the clinical and metastatic behavior of solid cancers originating in those sites. To elucidate features of leukemic tumors that render them resistant to agents effective against marrow leukemia, we analyzed a series of AML breast tumors by histology, immunohistochemistry, and RNA sequencing. Striking histologic similarities to solid cancers were found: a single-filing architectural pattern virtually identical to that of invasive lobular breast carcinoma and dense desmoplastic keloid-like fibrosis similar to colon, gallbladder, and pancreas carcinomas. Sequencing found 2157 genes significantly downregulated in AML breast tumors compared to normal breast. Comparison to triple-negative breast cancer found 859 genes similarly downregulated. At least 30 of these genes have been associated with poor prognosis in breast cancers. Five were reported in AML marrow studies to correlate with poor prognosis. The findings of this pilot study suggest the seed-and-soil interaction recognized in solid cancer growth may help explain how leukemic cells, in some patients, adopt solid tumor behavior in non-marrow sites. Transformed cells that metastasize from tumor to marrow can impart chemoresistance and be an unrecognized cause of treatment failure and death. Further studies comparing leukemic tumor to simultaneous marrow could potentially identify biomarkers that predict extramedullary resistance and lead to new therapeutic targets. Recognizing the potential for leukemia to adopt solid tumor phenotype, and implementation of body scanning and ablative tumor treatment, could decrease the persistently high rates of marrow resistance and treatment failure.

Identification of genes and long non-coding RNAs associated with the pathogenesis of gastric cancer

Gastric cancer is a lethal disease characterized by high diffusivity and mortality. To examine the mechanisms involved in gastric cancer, we analyzed the microarray of GSE41476. GSE41476 was downloaded from the Gene Expression Omnibus and included 3 primary cell culture samples from gastric cancer tissues, 3 gastric cancer cell lines and 2 normal tissue samples. Long non-coding RNAs (lncRNAs) and differentially expressed genes (DEGs) were screened by Cuffdiff software. Functions of the DEGs were predicted by functional and pathway enrichment analyses. The interaction relationships of the proteins encoded by DEGs that were obtained from the STRING database and protein‑protein interaction (PPI) network were visualized using Cytoscape. Modules analysis of PPI network was performed using CFinder. Moreover, lncRNA analysis was performed. A total of 86 lncRNAs, and 1,088 up- and 1,537 downregulated transcriptions were screened. For DEGs in module A of the PPI network for upregulated genes, the enriched pathways included ECM-receptor interaction and focal adhesion, both of which involved COL and ITG genes. The COL genes interacted with the ITG genes (e.g., COL1A1‑ITGA5 and COL1A2‑ITGB1). For DEGs in module B of the PPI network for downregulated genes, the enriched pathways for DEGs included the T‑cell receptor signaling pathway, which involved PIK3CG and PIK3R5. PIK3CG had an interaction relationship with PIK3R5. In addition, IL7 was co-expressed with TCONS-00068220. In summary, the results showed that COL and ITG genes, PIK3CG, PIK3R5, IL7 and lncRNA TCONS‑00068220 may play a role in gastric cancer.

Plasma membrane proteomic analysis of human Gastric Cancer tissues: revealing flotillin 1 as a marker for Gastric Cancer

Background

Gastric cancer remains the second leading cause of cancer-related deaths in the world. Successful early gastric cancer detection is hampered by lack of highly sensitive and specific biomarkers. Plasma membrane proteins participate and/or have a central role in the metastatic process of cancer cells and are potentially useful for cancer therapy due to easy accessibility of the targets.

Methods

In the present research, TMT method followed by mass spectrometry analysis was used to compare the relative expression levels of plasma membrane proteins between noncancer and gastric cancer tissues.

Results

Of a total data set that included 501 identified proteins, about 35% of the identified proteins were found to be plasma membrane and associated proteins. Among them, 82 proteins were at least 1.5-fold up- or down-regulated in gastric cancer compared with the adherent normal tissues.

Conclusions

A number of markers (e.g. annexin A6, caveolin 1, epidermal growth factor receptor, integrin beta 4) were previously reported as biomarkers of GC. Additionally, several potential biomarkers participated in endocytosis pathway and integrin signaling pathways were firstly identified as differentially expressed proteins in GC samples. Our findings also supported the notion that flotillin 1 is a potential biomarker that could be exploited for molecular imaging-based detection of gastric cancer. Together, the results show that subcellular proteomics of tumor tissue is a feasible and promising avenue for exploring oncogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1343-5) contains supplementary material, which is available to authorized users.

Integrin expression in esophageal squamous cell carcinoma: loss of the physiological integrin expression pattern correlates with disease progression

The integrins are a family of heterodimeric transmembrane signaling receptors that mediate the adhesive properties of epithelial cells affecting cell growth and differentiation. In many epithelial malignancies, altered integrin expression is associated with tumor progression and often correlates with unfavorable prognosis. However, only few studies have investigated the role of integrin expression in esophageal squamous cell carcinoma (ESCC). Using a novel quantifying immunofluorescence-staining assay, we investigated the expression of the integrins α2β1, α3β1, α6β1, and α6β4 in primary ESCC of 36 patients who underwent surgical resection. Magnitude and distribution of expression were analyzed in primary tumor samples and autologous esophageal squamous epithelium. The persistence of the physiologically polarized expression of the subunits α6, β1, and β4 in the tumor tissue was significantly associated with prolonged relapse-free survival (p = 0.028, p = 0.034, p = 0.006). In contrast, patients with reduced focal α6 expression at the tumor invasion front shared a significantly shortened relapse-free survival compared to patients with strong α6 expression at their stromal surfaces, as it was regularly observed in normal esophageal epithelium (p = 0.001). Multivariate regression analysis identified the maintenance of strong α6 immunoreactivity at the invasion front as an independent prognostic factor for increased relapse-free and disease-specific survival (p = 0.003; p = 0.003). Our findings suggest that alterations in both pattern and magnitude of integrin expression may play a major role in the disease progression of ESCC patients. Particularly, the distinct expression of the integrins α6β4 and α6β1 at the invasion front as well as the maintenance of a polarized integrin expression pattern in the tumor tissue may serve as valuable new markers to assess the aggressiveness of ESCC.

Role of integrins in invasion and metastasis of gastric cancer: potential therapeutic implications

Integrins are a large family of cell adhesion molecules that are involved in many important cellular and pathological functions including cell survival, growth, differentiation, migration, inflammatory responses, platelet aggregation, tissue repair and tumor invasion. Over the past two decades, several integrin-targeted drugs have made their way into clinical practice, many others are increasing each year in clinical trials and still more are showing promising potential for therapeutic development based on preclinical studies. Additionally, the role of integrins in pathological conditions combined with their druggability by means of cell surface accessibility makes them attractive pharmacological targets in cancer research. As such, the identification of key roles of integrins in gastric cancer has revealed their substantial potential as therapeutic targets. This review summarizes recent progress in the study of correlation between integrins and invasion and metastasis of gastric cancer and evaluates their values in developing molecularly targeted therapies for this disease.

Connective tissue growth factor acts as a therapeutic agent and predictor for peritoneal carcinomatosis of colorectal cancer

PURPOSE

Here, we aimed to investigate the role of connective tissue growth factor (CTGF) in peritoneal carcinomatosis (PC) associated with colorectal cancer (CRC) and to characterize the underlying mechanism of CTGF mediating adhesion.

EXPERIMENTAL DESIGN

A cohort of 136 CRC patient specimens was analyzed in this study. CRC cell lines were used for in vitro adhesion assay and in vivo peritoneal dissemination experiment. Recombinant CTGF protein treatment, transfection of CTGF expression plasmids, and knockdown of CTGF expression in CRC cells were utilized to evaluate the integrin α5, which served as a target of CTGF in inhibiting peritoneal seeding.

RESULTS

The analysis of CRC tissues revealed an inverse correlation between CTGF expression and prevalence of PC. Lower CTGF level in CRC patients was associated with higher peritoneal recurrence rate after surgery. Inducing CTGF expression in cancer cells resulted in decreased incidence of PC and increased rate of mice survival. The mice received intraperitoneal injection of recombinant CTGF protein simultaneously with cancer cells or following tumor formation; in both cases, peritoneal tumor dissemination was found to be effectively inhibited in the mouse model. Functional assay revealed that CTGF significantly decreased the CRC cell adhesion ability, and integrin α5 was confirmed by reverse transcriptase PCR and functional blocking assay as a downstream effector in the CTGF-mediated inhibition of CRC cell adhesion.

CONCLUSIONS

CTGF acts as a molecular predictor of PC and could be a potential therapeutic target for the chemoprevention and treatment of PC in CRC patients.

An orthotopic implantation mouse model of human malignant pleural mesothelioma for in vivo photon counting analysis and evaluation of the effect of S-1 therapy

Human malignant pleural mesothelioma (HMPM) is an aggressive neoplasm that is highly resistant to conventional therapies. We established 3 HMPM cell lines (TCC-MESO-1, TCC-MESO-2 and TCC-MESO-3) from Japanese patients; the first 2 from the primary and metastatic tumors of a patient with the epithelioid type of HMPM, and the third from a patient with biphasic characteristics of the tumor (epithelioid and sarcomatous phenotypes). The 3 cell lines resembled the original HMPMs in their morphological and biological features, including the genetic alterations such as lack of p16 expression and mutation of p53. Their tumorigenicity was determined in SCID mice by orthotopic implantation (20-46%). The tumorigenicity of the HMPM cell lines, which was relatively low, was enhanced by repeated subcultures and orthotopic implantations, and 3 competent tumorigenic sublines were produced (Me1Tu, Me2Tu and Me3Tu sublines from the TCC-MESO-1, TCC-MESO-2 and TCC-MESO-3 cell lines, respectively). The resultant HMPM sublines efficiently generated tumors in the SCID mice (100%) following orthotopic implantation. SCID mice implanted with the competent sublines, into one of which the luciferase gene was introduced, displayed quantitative fluctuation of the bioluminescence for the tumor volume in vivo. Oral administration of S-1, an anticancer agent, suppressed the proliferation of the luciferase gene-expressing Me1Tu subline in the mouse models in vivo, with a treated-to-control ratio of the mean tumor volume of 0.2. The orthotopic implantation mouse model proved to be useful for quantitative evaluation of the efficacy of novel anticancer drugs and also for studying the biology of HMPMs in vivo.

Potentiation of cell invasion and matrix metalloproteinase production by alpha3beta1 integrin-mediated adhesion of gastric carcinoma cells to laminin-5

We previously reported that the adhesion of gastric carcinoma cells to the peritoneum mediated by the alpha3beta1 integrin-laminin interaction is a key step in the initial process of peritoneal metastatic dissemination. Carcinoma cells subsequently invade through the intercellular gaps of mesothelial linings. In this study, we examined the role of the interaction of carcinoma cells with laminin-5, which is a major component of submesothelial basement membranes and serves as a high-affinity ligand for alpha3beta1 integrin, in carcinoma cell invasion. Human gastric carcinoma cell lines (MKN1, GT3TKB, and NUGC-4) adhered in an alpha3beta1 integrin-dependent manner to the extracellular matrix deposited by peritoneal mesothelial cells. An in vitro invasion assay using the Boyden chamber system revealed that MKN1 cell migration through the membranes increased when the membranes were coated with matrices produced by mesothelial cells or with laminin-5-containing Matrigel as compared to Matrigel alone. The cell migration promoted by laminin-5-containing Matrigel was inhibited by the presence of anti-alpha3 integrin antibody. When MKN1 cells were cultured in a laminin-5-coated plate, these cells were promoted to produce matrix metalloproteinase (MMP)-9, as assessed by gelatin zymography, enzyme-linked immunosorbent assay, and reverse transcription-polymerase chain reaction. These results suggest that the production of MMP-9 by MKN1 cells was potentiated by the alpha3beta1 integrin-laminin-5 interaction, which facilitated their invasion via degradation of the matrix.

Application of a novel method of double APAAP staining with subsequent quantitative image analysis to the examination of integrin expression in undifferentiated-type gastric carcinomas

In undifferentiated-type gastric carcinoma (UGC), recognition of cancer cells is not easy, which has hampered its precise phenotypic analysis. To examine alterations of the integrin phenotype during the progression of UGC, we used double alkaline phosphatase anti-alkaline phosphatase staining and computer-aided image analyses for the expression of alpha1, alpha2, alpha3, alpha5, alpha6, alphaV, beta1, and beta4 integrin subunits and alphaVbeta3, alphaVbeta5, and alphaVbeta6 integrins in cytokeratin-positive cells in the mucosal, the submucosal, and the deeper parts of 10 early and 17 advanced UGCs, their non-neoplastic counterparts, and 9 lymph node (LN) metastases. We revealed declining expression of epithelial integrin subunits (alpha2, alpha3, alpha6, beta4) and increasing expression of mesenchymal integrin subunits (alpha1, alpha5) as the tumor invaded deeper, reflecting gradual epithelial-to-mesenchymal transition of the integrin phenotype during tumor invasion. Enhanced expression of the alphaV integrin subunit and alphaVbeta3 and alphaVbeta5 integrins correlated with tumor invasion, and that of alphaVbeta6 integrins with LN metastasis. Our results have demonstrated that the method we introduced is suitable for analysis of dynamic alterations of the integrin repertoire in UGC progression.

CUB-domain-containing protein 1 regulates peritoneal dissemination of gastric scirrhous carcinoma

CUB-domain-containing protein 1 (CDCP1) is a type-I transmembrane protein that is highly expressed in colon, breast, and lung cancers. We recently revealed that CDCP1 is associated with and phosphorylated by Src family kinases and is involved in the regulation of anchorage independence of certain lung cancer cell lines. In this study, we examined whether CDCP1 is involved in the regulation of tumor progression of scirrhous gastric cancer, which is a diffusely infiltrative carcinoma with high invasion potential. Expression and phosphorylation levels of CDCP1 correlated with the invasive potential of scirrhous gastric cancers. Reduction of CDCP1 expression by siRNA suppressed migration, invasion, and anchorage independence without affecting the proliferation of highly invasive scirrhous gastric cancer cells. However, CDCP1 overexpression promoted gastric cancer cell migration with low potential of invasion. Loss of CDCP1 suppressed invasion and dissemination of cancer cells that were orthotopically implanted in the gastric wall of nude mice. Expression and phosphorylation of CDCP1 were also detected in cancer cells of surgically resected tissues of human scirrhous gastric cancer by immunohistochemical analysis. Our results suggest that CDCP1 promotes invasion and peritoneal dissemination of cancer cells through the regulation of cell migration and anchorage independence. Therefore, it is both a potential prognostic and therapeutic target in certain types of gastrointestinal cancers, and suppression of its phosphorylation might be a useful strategy for modulating cancer metastasis.

The Role of Integrins in Cancer and the Development of Anti-Integrin Therapeutic Agents for Cancer Therapy

Integrins have been reported to mediate cell survival, proliferation, differentiation, and migration programs. For this reason, the past few years have seen an increased interest in the implications of integrin receptors in cancer biology and tumor cell aggression. This review considers the potential role of integrins in cancer and also addresses why integrins are present attractive targets for drug design. It discusses of the several properties of the integrin-based chemotherapeutic agents currently under consideration clinically and provides an insight into cancer drug development using integrin as a target.

A photon counting technique for quantitatively evaluating progression of peritoneal tumor dissemination

We recently established a mouse model of peritoneal dissemination of human gastric carcinoma, including the formation of ascites, by orthotopic transplantation of cultured gastric carcinoma cells. To clarify the processes of expansion of the tumors in this model, nude mice were sacrificed and autopsied at different points of time after the orthotopic transplantation of the cancer cells for macroscopic and histopathologic examination of the tumors. The cancer cells grew actively in the gastric submucosa and invaded the deeper layers to reach the serosal plane. The tumor cells then underwent exfoliation and became free followed by the formation of metastatic lesions initially in the greater omentum and subsequent colonization and proliferation of the tumors on the peritoneum. Although this model allowed the detection of even minute metastases, it was not satisfactory from the viewpoint of quantitative and objective evaluation. To resolve these problems, we introduced a luciferase gene into this tumor cell line with a high metastasizing potential and carried out in vivo photon counting analysis. This photon counting technique was found to allow objective and quantitative evaluation of the progression of peritoneal dissemination on a real-time basis. This animal metastatic model is useful for monitoring the responses of tumors to anticancer agents.

PGP9.5 methylation in diffuse-type gastric cancer

Diffuse-type gastric cancer (DGC) is the most deadly form of gastric cancer and is frequently accompanied by peritoneal dissemination and metastasis. The specific molecular events involved in DGC pathogenesis remain elusive. Accumulating evidence of epigenetic inactivation in tumor suppressor genes led us to conduct a comprehensive screen to identify novel methylated genes in human cancers using pharmacologic unmasking and subsequent microarray analysis. We compared differential RNA expression profiles of DGC and intestinal-type gastric cancer (IGC) cell lines treated with 5-aza-2'-deoxycytidine using microarrays containing 22,284 genes. We identified 16 methylated genes, including many novel genes, in DGC cell lines and studied PGP9.5 with particular interest. In primary gastric cancers, PGP9.5 was found to be more frequently methylated in DGCs (78%) than in IGCs (36%; DGC versus IGC, P < 0.05). Furthermore, real-time methylation-specific PCR analysis of PGP9.5 showed relatively higher methylation levels in DGC than in IGC. Our data thus implicate a molecular event common in the DGC phenotype compared with IGC.

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

The number of published studies on peritoneal dissemination of scirrhous gastric carcinoma is very small as a result of the unavailability of highly reproducible animal models. Orthotopic implantation of HSC-44PE and HSC-58 (scirrhous gastric carcinoma-derived cell lines) cells into nude mice led to dissemination of the tumor cells to the greater omentum, mesenterium, peritoneum and so on, and caused ascites in a small number of animals. Cycles of isolation of the ascitic tumor cells and orthotopic inoculation of these cells were repeated in turn to animals. This was to isolate highly metastatic cell lines with a strong capability of inducing the formation of ascites (44As3 from HSC-44PE; 58As1 and 58As9 from HSC-58). All three cell lines induced tumor formation at the site of orthotopic injection, and caused fatal cancerous peritonitis and bloody ascites in 90-100% of the animals approximately 3-5 weeks after the inoculation. When the parent cells were implanted, the animals became moribund in approximately 12-18 weeks, however, none of the animals developed ascites. Complementary DNA microarray and immunohistochemical analyses revealed differences in the expression levels of genes coding for the matrix proteinase, cell adhesion, motility, angiogenesis and proliferation between the highly metastatic- and parent-cell lines. The usefulness of this model for the evaluation of drugs was assessed by analyzing the stability of the metastatic potential of the cells and the reproducibility. Animals intravenously treated with CPT-11 and GEM showed suppressed tumor growth and significantly prolonged survival. The metastatic cell lines and the in vivo model established in the present study are expected to serve as a model of cancerous peritonitis developing from primary lesions, and as a useful means of clarifying the pathophysiology of peritoneal dissemination of scirrhous gastric carcinoma and the development of drugs for its treatment.

Integrin alpha6beta4-erbB2 complex inhibits haptotaxis by up-regulating E-cadherin cell-cell junctions in keratinocytes

Keratinocyte integrins alpha6beta4 and alpha3beta1 bind laminin-5, a component of basement membranes. We previously demonstrated that in keratinocytes, haptotactic migration on laminin-5 was stimulated by anti-beta1 integrin-activating antibody TS2/16, whereas antibodies to alpha6 and beta4, respectively, blocked TS2/16-induced, alpha3beta1-dependent migration. Moreover, alpha6beta4-associated haptotaxis inhibition was linked to a phosphatidylinositol 3-kinase (PI3K) pathway and required erbB2 activation. erbB2, the ligand-less member of the epidermal growth factor receptor family, was shown to form a complex with the hemidesmosomal integrin alpha6beta4. Here, we demonstrate that alpha6beta4 inhibitory effects on haptotaxis are abolished by an anti-E-cadherin antibody, which interferes with cell-cell adhesion. Furthermore, antibodies to alpha6 and beta4 stimulated adhesion to an E-cadherin-Fc recombinant protein. In addition, anti-alpha6/beta4 antibodies increased colony size in plated cells, stimulated cell-cell aggregation, and up-regulated E-cadherin localization to cell-cell contacts. These effects were abolished when erbB2 or PI3K were blocked. These results indicate that stimulation of alpha6beta4 increases E-cadherin-mediated cell-cell adhesion and that this mechanism depends on erbB2 activation. The molecule that links alpha6beta4 with E-cadherin may be the small GTPase cdc42, an effector of PI3K, because dominant-negative cdc42 abolished the inhibitory effect of anti-alpha6/beta4 antibodies and increased basal migration, whereas constitutively active cdc42 prevented the TS2/16-induced increase in haptotaxis. These findings suggest a model whereby alpha6beta4 can augment cell-cell adhesion and slow down haptotaxis over laminin-5 and point to the alpha6beta4-erbB2 heterodimer as an important signaling complex for the formation of cohesive keratinocyte layers.

The role of glial cell line-derived neurotrophic factor (GDNF) and integrins for invasion and metastasis in human pancreatic cancer cells

BACKGROUND AND OBJECTIVES

It is generally accepted that the malignancy of pancreatic cancer is dependent upon the extent of invasion as well as metastasis. However, the factors and mechanisms are incompletely understood. We investigated whether glial cell lined-derived neurotrophic factor (GDNF) enhances the invasive and adhesive behaviors of pancreatic cancer cells by altering of the expression of integrins.

METHODS

The expression of the GDNF receptor in pancreatic cancer cell lines (SW1990 and Capan-2) was confirmed by RT-PCR. Then we determined the expression of integrin subunits and the alteration of their expression by GDNF using flow-cytometric analysis and a cellular enzyme-linked immunosorbent assay (CELISA). Adhesion and invasion assay were performed to investigate whether increased integrin expression affected the interaction between cancer cells and ECM proteins.

RESULTS

The GDNF receptor subunits were expressed in pancreatic cancer cells. GDNF enhanced the expression of some of the integrin subunits and increased their adhesive and invasive abilities. The enhanced expression and associated increase in adhesive and invasive abilities were inhibited by blocking the GDNF receptor or the integrin beta1 subunit.

CONCLUSION

The enhancement of integrin expression by GDNF signaling through the GDNF receptor strongly influences invasion and adhesion to ECM proteins by pancreatic cancer cells.

Adhesion of gastric carcinoma cells to peritoneum mediated by alpha3beta1 integrin (VLA-3)

The interaction between gastric carcinoma cells and the peritoneal lining is a key step in peritoneal dissemination. In this study, we examined the roles of the beta1 family of integrin receptors in the adhesion of such cells to the peritoneum. The adhesion of several gastric carcinoma cell lines to peritonea excised from mice was inhibited most by an anti-alpha3 integrin antibody and to a lesser extent by an anti-alpha2 integrin antibody. In the peritoneal implantation of NUGC-4 human gastric carcinoma cells in athymic mice, treatment of the cells with anti-alpha2 or anti-alpha3 integrin antibody reduced the number of disseminated nodules; suppression by the anti-alpha3 integrin antibody was stronger than that by the anti-alpha2 integrin antibody. The cDNAs to human alpha2 and alpha3 integrins were introduced into K562 leukemic cells, which were positive for the integrin beta1 subunit but negative for the alpha2 or alpha3 subunit. The alpha3 integrin-transfected cells adhered to excised peritoneum and to a monolayer of peritoneal mesothelial cells more firmly than did the alpha2 integrin-transfected cells or the mock transfectant. Reverse transcription-PCR was used to analyze the expression of laminin-5 and laminin-10/11, which have been reported to serve as high-affinity ligands for alpha3beta1 integrin. mRNA for these laminin isoforms was found in mesothelial cells from the diaphragm and parietal peritoneum. These results strongly suggest that alpha3beta1 integrin plays an essential role in mediating the initial attachment of cancer cells to the peritoneum, leading to the formation of peritoneal metastasis.

Establishment of two cell lines from human gastric scirrhous carcinoma that possess the potential to metastasize spontaneously in nude mice

Few experimental studies have been conducted to clarify the mechanism of development of metastasis in scirrhous carcinoma of the stomach. In the present study, we attempted to establish gastric carcinoma cell lines by incubation of cancer cells collected from the body fluids of patients with gastric cancer. At the same time, xenografting of these cells to nude mice was performed. It was found that, of the gastric carcinoma cell lines thus established, two cell lines, designated as HSC-44PE and HSC-58, formed s.c. tumors with a high infiltrative potential (often invading the lymphatics around the cancer tissue) when implanted. Metastasis to the lymph nodes and lungs was observed in 20-40% of all the animals, indicating that the two cell lines are also capable of metastasizing spontaneously. Through repeated selection, i.e., repeated cycles of removal, culture, and implantation of the HSC cancer cells from metastatic lesions, we obtained 5 subclones of HSC-44PE and HSC-58 (designated as m2509, m2615, m2792, m2917, and m2691), which, when implanted orthotopically, exhibited the following characteristics as compared to the parent cells: (1) a higher percentage take (survival), similar frequency of metastasis, shorter time to metastasis (less than 100 days), and consistent metastasizing potential; (2) a relatively high frequency of metastasis to lymph nodes, including distant metastasis to axillary lymph nodes; (3) the potential to cause occasional bloody ascites; (4) enhanced expression of dysadherin, CD44, and other molecules. This is the first report of cultured scirrhous gastric carcinoma cells showing the potential for spontaneous metastasis.

Highly specific marker genes for detecting minimal gastric cancer cells in cytology negative peritoneal washings

Peritoneal wash cytology plays a pivotal role in the decision for gastric cancer treatment because advanced gastric cancer often turns out incurable with peritoneal metastasis. Molecular detection of minimal cancer cells from peritoneal washings may overcome the sensitivity boundary of conventional cytology and contribute to the prediction of the disease outcome. To select marker candidates out of ten thousands of genes, we performed microarray analyses in 12 gastric cell lines and 8 peritoneal washings of early stage cases. With 40 candidates selected by the above expression profiling, RT-PCR in 16 representative peritoneal wash samples was performed to identify genes specific to cytology positive samples. The finally selected five genes, CK20, FABP1, MUC2, TFF1, and TFF2, were then evaluated for their utility as a marker for minimal residual disease in 99 peritoneal wash samples. Nested RT-PCR using the five genes showed positive results highly specific to incurable cases (91-100%). With a high specificity, the combination of these five genes succeeded in identifying 6 out of 20 (30%) additional patients with all types of early recurrence that could not be predicted by the conventional method. The six newly identified recurrences included four non-peritoneal ones, showing that RT-PCR using the five genes without a real-time quantitative PCR technique contributes to the detection of minimal residual disease.

Magnitude of serosal changes predicts peritoneal recurrence of gastric cancer

BACKGROUND

Peritoneal dissemination is the most frequent mode of recurrence in patients with gastric cancer. We tried to identify factors that predict peritoneal recurrence with high sensitivity.

STUDY DESIGN

Clinical and pathologic data from 587 consecutive patients with gastric cancer were reviewed retrospectively. The stepwise Cox proportional hazards regression model was used to assess the prognostic significance of the magnitude of serosal changes. Multiple stepwise logistic regression analysis was used to determine factors associated with peritoneal recurrence in 375 patients who underwent curative resection.

RESULTS

The 5-year survival rate of patients with S2 disease (greatest dimension of macroscopic serosal changes >/= 2.5 cm) was 18%, which was worse than S0 (no serosal changes) and S1 disease (macroscopic serosal changes < 2.5 cm)(p < 0.001). Patients with S0 tumors who underwent curative resection had the best 5-year survival rate. Multivariate analyses indicated that the magnitude of serosal changes was an independent prognostic factor for survival both overall and after curative resection. Logistic regression analysis showed that peritoneal recurrence was more than four times as likely with S2 than with S0 or S1 tumors. The sensitivity for predicting peritoneal recurrence was 79%; the sensitivity of cytologic examination was 38%.

CONCLUSIONS

Magnitude of serosal changes is easy to measure intraoperatively and predicts peritoneal recurrence of gastric cancer with greater sensitivity than conventional peritoneal lavage cytology.

Alteration of integrin expression by glial cell line-derived neurotrophic factor (GDNF) in human pancreatic cancer cells

INTRODUCTION

Pancreatic cancer cells express a number of functionally active integrins that are related to their adhesive and invasive abilities.

AIMS

To determine whether glial cell line-derived neurotrophic factor (GDNF) influences the expression of integrins in pancreatic cancer cell lines and to elucidate the mechanisms of adhesion and invasion to extracellular matrix (ECM) proteins.

METHODOLOGY

The expression of integrin subunits and the alteration of their expression by GDNF were examined by flow-cytometric analysis and cellular enzyme-linked immunosorbent assay in pancreatic cancer cell lines (MIA PaCa-2 and BxPC-3). Assays of adhesion and invasion of cancer cells to ECM proteins were conducted to investigate whether increased integrin expression affects the interaction between cancer cells and putative integrin ECM ligands.

RESULTS

Expression of some of the integrin subunits in pancreatic cancer cells was enhanced by GDNF. The enhancement and associated increase in adhesive and invasive ability by GDNF were inhibited by blocking the GDNF receptor or the integrin beta1 subunit.

CONCLUSIONS

In pancreatic cancer, the enhancement of integrin expression by GDNF signaling through the GDNF receptor strongly influences adhesion and invasion to ECM proteins.

Cell adhesion system and human cancer morphogenesis

Cell-cell adhesion determines the polarity of cells and participates in the maintenance of the cell societies called tissues. Cell-cell adhesiveness is generally reduced in human cancers. Reduced intercellular adhesiveness allows cancer cells to disobey the social order, resulting in destruction of histological structure, which is the morphological hallmark of malignant tumors. Reduced intercellular adhesiveness is also indispensable for cancer invasion and metastasis. A tumor-suppressor gene product, E-cadherin, and its undercoat proteins, catenins, which connect cadherins to actin filaments, are located at lateral borders, concentrating on adherens junctions, of epithelial cells and establish firm cell-cell adhesion. The E-cadherin cell adhesion system in cancer cells is inactivated by various mechanisms that reflect the morphological and biological characteristics of the tumor. Silencing of the E-cadherin gene by DNA hypermethylation around the promoter region occurs frequently, even in precancerous conditions. In diffuse infiltrating cancers, mutations are found in the genes for E-cadherin and alpha- and beta-catenins. At the invading front of cancers, the E-cadherin cell adhesion system is inactivated by tyrosine phosphorylation of beta-catenin; an oncogene product, c-erbB-2 protein, is found to associate directly with beta-catenin. The E-cadherin cell adhesion system cross-talks with the Wingless/Wnt signaling pathway through beta-catenin, and expression of genes, which participate in cancer morphogenesis, may be regulated in conjunction with the Wingless/Wnt signaling pathway. Dysadherin, a newly identified cancer-associated cell membrane glycoprotein, down-regulates E-cadherin and promotes cancer metastasis. In conclusion, inactivation of the E-cadherin cell adhesion system by both genetic and epigenetic mechanisms plays a significant role during multistage human carcinogenesis.

Differential gene expression profiles of gastric cancer cells established from primary tumour and malignant ascites

Advanced gastric cancer is often accompanied by metastasis to the peritoneum, resulting in a high mortality rate. Mechanisms involved in gastric cancer metastasis have not been fully clarified because metastasis involves multiple steps and requires a combination of altered expressions of many different genes. Thus, independent analysis of any single gene would be insufficient to understand all of the aspects of gastric cancer peritoneal dissemination. In this study, we performed a global analysis of the differential gene expression of a gastric cancer cell line established from a primary main tumour (SNU-1) and of other cell lines established from the metastasis to the peritoneal cavity (SNU-5, SNU-16, SNU-620, KATO-III and GT3TKB). The application of a high-density cDNA microarray method made it possible to analyse the expression of approximately 21 168 genes. Our examinations of SNU-5, SNU-16, SNU-620, KATO-III and GT3TKB showed that 24 genes were up-regulated and 17 genes down-regulated besides expression sequence tags. The analysis revealed the following altered expression such as: (a) up-regulation of CD44 (cell adhesion), keratins 7, 8, and 14 (epitherial marker), aldehyde dehydrogenase (drug metabolism), CD9 and IP3 receptor type3 (signal transduction); (b) down-regulation of IL2 receptor gamma, IL4-Stat (immune response), p27 (cell cycle) and integrin beta4 (adhesion) in gastric cancer cells from malignant ascites. We then analysed eight gastric cancer cell lines with Northern blot and observed preferential up-regulation and down-regulation of these selected genes in cells prone to peritoneal dissemination. Reverse transcriptase-polymerase chain reaction confirmed that several genes selected by DNA microarray were also overexpressed in clinical samples of malignant ascites. It is therefore considered that these genes may be related to the peritoneal dissemination of gastric cancers. The results of this global gene expression analysis of gastric cancer cells with peritoneal dissemination, promise to provide a new insight into the study of human gastric cancer peritoneal dissemination.

The Promise of Integrins as Effective Targets for Anticancer Agents

This review will briefly describe integrin function, address why integrins are attractive targets for chemotherapeutic drug design, and discuss some ongoing studies aimed at inhibiting integrin activity. Integrins are cell surface heterodimeric receptors. They modulate many cellular processes including: growth, death (apoptosis), adhesion, migration, and invasion by activating several signaling pathways. Many potential chemotherapeutic agents target integrins directly (eg, polypeptides, monoclonal antibodies, adenovirus vectors). These agents may be clinically useful in controlling the metastatic spread of cancer.