Screening approaches against claudin-4 focusing on therapeutics through molecular docking and the analysis of their relative dynamics: a theoretical approach.

Claudin-4 (CLDN4) is a class of transmembrane protein in the family of tight junction (TJ) proteins. Overexpression of CLDN4 is reported in the case of ovarian cancer and epithelial malignancies. The current study is focused on the identification of lead compounds for CLDN4 adopting the structure-based drug design method. The Schrodinger glide is used as a molecular docking tool for the initial docking of CLDN4 with Asinex Database by performing high throughput virtual screening, top hits were identified. Then, compounds BDF 33196188 and BDE 30874918 were identified by molecular docking based on binding energy in the active site of CLDN4. Subsequently, critical residues were identified such as Asp146 and Arg158 with the least binding energy from Extra Precision method. Further, molecular dynamics simulations of claudin-4 protein were used for the optimization of best ligands with claudin-4 in a dynamic system. Molecular docking and molecular dynamics simulations predicted critically important residues ASP146 and ARG158 involved in claudin-4 binding. The hits retrieved from screening were docked into protein by relevant procedures including HTVS, SP, and XP. Finally, two molecules were identified as potential claudin-4 inhibitors. The two ligands BDF 33196188 and BDE 30874918 are suggested as potential inhibitors for CLDN4. In summary, our computational strategy established novel leads against CLDN4 from Asinex Database and recommended as anti-cancer agents.

Targeting claudin-4 enhances chemosensitivity of pancreatic ductal carcinomas.

Claudin (CLDN) family comprises of protein that form a tight junction, and is involved in regulating polarity and differentiation of cells. Here, we aimed to investigate the effects of inhibiting CLDN4 in pancreatic ductal carcinomas (PDC). We first examined 91 cases of human PDC by immunohistochemistry and found that CLDN4 expression was correlated with tumor invasion, nodal metastasis, and distant metastasis. Anti-CLDN4 extracellular domain antibody, previously established by us (4D3), inhibited the proliferation of MIA-PaCa-2 PDC cells and increased intracellular 5-fluorouracil (5-FU) concentration with lowering transepithelial electrical resistance. Concurrent treatment of 5-FU and 4D3 resulted in synergistic inhibition of growth of MIA-PaCa-2 cells in nude mice. In addition, MIA-PaCa-2 cell tumors treated with full-dose folfirinox (FFX) decreased tumor diameters to 50%; however, 60% of mice were dead from adverse effects. In contrast, half-dose FFX concomitant with 4D3 treatment decreased tumors equivalent to full-dose FFX, but without the adverse effects. These findings suggest that targeting CLDN4 might increase the effectiveness and safety of anticancer drug therapy in PDC.

Synthesis, 18F-labelling and radiopharmacological characterisation of the C-terminal 30mer of Clostridium perfringens enterotoxin as a potential claudin-targeting peptide.

The cell surface receptor claudin-4 (Cld-4) is upregulated in various tumours and represents an important emerging target for both diagnosis and treatment of solid tumours of epithelial origin. The C-terminal fragment of the Clostridium perfringens enterotoxin cCPE290-319 appears as a suitable ligand for targeting Cld-4. The synthesis of this 30mer peptide was attempted via several approaches, which has revealed sequential SPPS using three pseudoproline dipeptide building blocks to be the most efficient one. Labelling with fluorine-18 was achieved on solid phase using N-succinimidyl 4-[18F]fluorobenzoate ([18F]SFB) and 4-[18F]fluorobenzoyl chloride as 18F-acylating agents, which was the most advantageous when [18F]SFB was reacted with the resin-bound 30mer containing an N-terminal 6-aminohexanoic spacer. Binding to Cld-4 was demonstrated via surface plasmon resonance using a protein construct containing both extracellular loops of Cld-4. In addition, cell binding experiments were performed for 18F-labelled cCPE290-319 with the Cld-4 expressing tumour cell lines HT-29 and A431 that were complemented by fluorescence microscopy studies using the corresponding fluorescein isothiocyanate-conjugated peptide. The 30mer peptide proved to be sufficiently stable in blood plasma. Studying the in vivo behaviour of 18F-labelled cCPE290-319 in healthy mice and rats by dynamic PET imaging and radiometabolite analyses has revealed that the peptide is subject to substantial liver uptake and rapid metabolic degradation in vivo, which limits its suitability as imaging probe for tumour-associated Cld-4.

Cytotoxicity of Clostridium perfringens enterotoxin depends on the conditions of claudin-4 in ovarian carcinoma cells.

Currently, Clostridium perfringens enterotoxin (CPE) is being investigated as an anti-cancer drug for tumors expressing the tight junction (TJ) transmembrane proteins claudin-3 and/or claudin-4. However, the optimal conditions for CPE cytotoxicity are still unclear. Our objectives were to determine the optimal conditions for CPE as an anti-cancer drug for treating ovarian cancer in vitro and in vivo. In our experiments, cells at low culture density showed higher sensitivity to CPE, suggesting that claudins at TJs were poorly accessible to CPE compared with those at the edge of cell colonies. Ovarian cancer cells cultured under calcium-depleted pretreatment conditions to disrupt TJs and to knock-down TJ proteins and E-cadherin production altered CPE cytotoxicity, which was mainly dependent on claudin-4 expression. These results suggest that the condition of claudin-4 at the cell surface is important for CPE cytotoxicity. Our in vivo experiments showed that a high dose of CPE is required for the effective treatment of peritoneal dissemination of ovarian cancer cells. Here, we suggest that the accessibility of CPE to claudins is important for its cytotoxicity and depends on the conditions of claudin-4 in vitro. In addition, E-cadherin expression in ovarian cancer cells affects the efficiency of CPE in vivo.

Claudin-4 knockout by TALEN-mediated gene targeting in MDCK cells: Claudin-4 is dispensable for the permeability properties of tight junctions in wild-type MDCK cells.

Epithelia act as a barrier between the internal and external environments, and the movement of substances via the paracellular pathway is regulated by tight junctions (TJs). Claudins are major determinants of TJ permeability. Claudin-4 was the first claudin whose involvement in the TJ permeability in cultured cells was directly demonstrated, but the permeability properties of individual claudins including claudin-4 are still incompletely clarified. In this study, we established claudin-4 knockout cells using transcription activator-like effector nucleases (TALENs), a recently developed method for genome editing, and investigated the permeability property of claudin-4 in MDCK II cells. We found that claudin-4 knockout has no apparent effect on the localization of other claudins and electrophysiological properties in MDCK II cells. Therefore we further established claudin-2 and claudin-4 double knockout clones and investigated the effects on TJs. Claudin-4 knockout in addition to claudin-2 knockout slightly increased the localization of other claudins at TJs but showed no obvious effects on the electrophysiological properties in MDCK II cells. These results indicate that claudin-4 is dispensable for the barrier property of TJs in wild-type as well as claudin-2 knockout MDCK II cells. Our results suggest the need for further knockout analysis to reveal the permeability properties of individual claudins.

Claudin-4 is required for vasculogenic mimicry formation in human breast cancer cells.

Vasculogenic mimicry (VM) refers to the unique capability of aggressive tumor cells to mimic the pattern of embryonic vasculogenic networks. Claudins are aberrantly expressed in aggressive breast cancer. However, the relationship between claudins and VM formation is not clear. We examined VM in two human breast cancer cell lines with different aggressive capabilities (MDA-MB-231 and MCF-7 cells) and one human umbilical vein endothelial cell line (HUVEC). Both HUVEC and MDA-MB-231 cells formed vascular channels in Matrigel cultures, while MCF-7 cells did not. Western blot analysis revealed a possible correlation between claudin-4 and -6 expression in breast cancer cell lines and tumor aggressiveness, with protein levels correlating with the ability to form vascular channels. Treatment of MDA-MB-231 and HUVEC cells with claudin-4 monoclonal antibodies completely inhibited the ability of cells to form vascular channels. Moreover, knockdown of claudin-4 by short hairpin RNA completely inhibited tubule formation in MDA-MB-231 cells. Overexpression of claudin-4 in MCF-7 cells induced formation of vascular channels. Immunocytochemistry revealed that membranous claudin-4 protein was significantly associated with vascular channel formation. Collectively, these results indicate that claudin-4 may play a critical role in VM in human breast cancer cells, opening new opportunities to improve aggressive breast cancer therapy.

Interleukin-18 enhances breast cancer cell migration via down-regulation of claudin-12 and induction of the p38 MAPK pathway.

Interleukin-18 (IL-18) was recently reported to have a pro-tumor effect in various cancers. Increased IL-18 levels in the serum of cancer patients correlated with malignancy, and IL-18 acts a crucial factor for cell migration in gastric cancer and melanoma. Claudins, which are the most important tight junction proteins, are also linked with cancer progression and metastasis. However, the relationship between claudins and IL-18 is not well-understood. Here, we show that the migratory ability of MCF-7 cells was reduced when endogenous IL-18 expression was inhibited with IL-18 siRNA. Moreover, exogenous IL-18 enhanced breast cancer cell migration and suppressed the expression of the tight junction proteins claudin-1, claudin-3, claudin-4, and claudin-12 in MCF-7 cells. Knockdown of claudin-3, claudin-4, and claudin-12, but not claudin-1, increased breast cancer migration with maximal effects observed in claudin-12 siRNA-transfected cells. To investigate whether the mitogen-activated protein kinase (MAPK) signaling pathway is involved in IL-18-induced cell migration and claudin-12 expression, cells were pretreated with SB203580 (an inhibitor of p38 MAPK) or PD98059 (an inhibitor of ERK1/2) prior to the addition of IL-18. Although pretreatment of MCF-7 cells with SB203580 blocked both the enhanced cell migration and the decreased claudin-12 expression, PD98059 only blocked cell migration and did not affect claudin-12 expression. In addition, exogenous IL-18 induced rapid phosphorylation of p38 MAPK. These results suggest that IL-18 is an important factor inducing breast cancer cell migration through down-regulation of claudin-12 and activation of the p38 MAPK pathway.

Genome-wide DNA methylation identifies trophoblast invasion-related genes: Claudin-4 and Fucosyltransferase IV control mobility via altering matrix metalloproteinase activity.

Previously we showed that extravillous cytotrophoblast (EVT) outgrowth and migration on a collagen gel explant model were affected by exposure to decidual natural killer cells (dNK). This study investigates the molecular causes behind this phenomenon. Genome wide DNA methylation of exposed and unexposed EVT was assessed using the Illumina Infinium HumanMethylation450 BeadChip array (450 K array). We identified 444 differentially methylated CpG loci in dNK-treated EVT compared with medium control (P < 0.05). The genes associated with these loci had critical biological roles in cellular development, cellular growth and proliferation, cell signaling, cellular assembly and organization by Ingenuity Pathway Analysis (IPA). Furthermore, 23 mobility-related genes were identified by IPA from dNK-treated EVT. Among these genes, CLDN4 (encoding claudin-4) and FUT4 (encoding fucosyltransferase IV) were chosen for follow-up studies because of their biological relevance from research on tumor cells. The results showed that the mRNA and protein expressions of both CLDN4 and FUT4 in dNK-treated EVT were significantly reduced compared with control (P < 0.01 for both CLDN4 and FUT4 mRNA expression; P < 0.001 for CLDN4 and P < 0.01 for FUT4 protein expression), and were inversely correlated with DNA methylation. Knocking down CLDN4 and FUT4 by small interfering RNA reduced trophoblast invasion, possibly through the altered matrix metalloproteinase (MMP)-2 and/or MMP-9 expression and activity. Taken together, dNK alter EVT mobility at least partially in association with an alteration of DNA methylation profile. Hypermethylation of CLDN4 and FUT4 reduces protein expression. CLDN4 and FUT4 are representative genes that participate in modulating trophoblast mobility.

Low expression of claudin-4: an indicator of recurrence in esophageal squamous cell carcinoma after Ivor Lewis esophagectomy?

The high recurrence rate after surgery is the main reason for the poor prognosis of esophageal squamous cell carcinoma (ESCC) patients. Finding indicators of recurrence and taking adjuvant therapy may be useful for patients in high risk of recurrence. claudin-4 (CLDN4) is the core protein to form the tight junction, which plays an important role in cell adhesion, and its aberrant expression were detected in various cancers while its expression and functions in ESCC still remained unclear. Here, we detected the expression of CLDN4 in 114 ESCC tissue samples by real-time RT-PCR and immunohistochemistry, and the result showed that the low expression of CLDN4 correlated with a higher T staging (P = 0.010), lymphatic metastasis (P < 0.001) and recurrence status (P = 0.002). And the Cox regression analysis showed that the T classification (P = 0.005), lymph node metastasis (P = 0.003) and low CLDN4 expression (P = 0.029) were independent risk factors of recurrence. Further, we proved the CLDN4 in inhibiting growth, colony formation and invasion in vitro by establishing two stable CLDN4-silencing ESCC cell lines. In conclusion, CLDN4 played an important role in preventing metastasis and could be an effective biomarker to predict the recurrence of ESCC.

Regulation of the Epithelial-Mesenchymal Transition by Claudin-3 and Claudin-4.

The mechanisms that control intracellular adhesion are central to the process of invasion and metastasis. Claudin-3 (CLDN3) and claudin-4 (CLDN4) are major structural molecules of the tight junctions that link epithelial cells. Our prior work has demonstrated that knockdown of the expression of either CLDN3 or CLDN4 produces marked changes in the phenotype of ovarian carcinoma cells including increases in growth rate in vivo, migration, invasion, metastasis, and drug resistance, similar to those produced by the epithelial-to-mesenchymal transition (EMT). We postulated that these changes may result from the ability of CLDN3 or CLDN4 to suppress EMT. In this study we found that knockdown of either CLDN3 or CLDN4 increased cell size and resulted in flattened morphology. While knockdown of CLDN3 or CLDN4 did not alter the expression of vimentin, it significantly down-regulated the level of E-cadherin and up-regulated N-cadherin expression. Conversely, over-expression of CLDN3 or CLDN4 in a cell line that does not express endogenous CLDN3 or CLDN4 decreased N-cadherin expression. Re-expression of E-cadherin in the CLDN3 or CLDN4 knockdown cells reduced migration, invasion and tumor growth in vivo. Loss of either CLDN3 or CLDN4 resulted in activation of the PI3K pathway as evidenced by increased Akt phosphorylation, elevated cellular PIP3 content and PI3K activity as well as up-regulation of the mRNA and protein levels of the transcription factor Twist. Taken together, these findings suggest that CLDN3 and CLDN4 function to sustain an epithelial phenotype and that their loss promotes EMT.

Claudins play a role in normal and tumor cell motility.

BACKGROUND: Claudins are key integral proteins of the tight junction. Although they play an essential role in controlling paracellular diffusion in epithelia, increasing evidence supports a role for these proteins in non-barrier forming activities. To elucidate a potential function for claudins outside of their traditional role in tight junctions, subcellular localization of claudin-4 was determined in normal mammary epithelial cells as well as breast and ovarian cancer cell lines and the effects of a claudin mimic peptide on cell motility were determined. RESULTS: Immunofluorescence revealed that claudin-4 was localized along cellular projections. Using a fluorescent peptide that mimics a conserved sequence in the second extracellular loop of a set of claudin subtypes, that includes claudin-4, exposure of this loop to the extracellular environment was confirmed in non-polarized cells. This peptide inhibited cell motility when normal mammary epithelial cells as well as breast and ovarian tumor cells were subjected to a wound healing assay. Knockdown of claudin-4 also inhibited cell motility and the mimic peptide had no effect on motility in the claudin-4 knockdown cells. This effect on motility was seen when cells were grown on collagen, but not when cells were grown on non-physiological cell adhesive or fibronectin. CONCLUSION: The second extracellular loop of claudins is able to interact with the extracellular environment to promote normal and tumor cell motility when it is not associated with tight junction structures.

Tight junction proteins claudin-3 and claudin-4 control tumor growth and metastases.

The extent of tight junction (TJ) formation is one of many factors that regulate motility, invasion, and metastasis. Claudins are required for the formation and maintenance of TJs. Claudin-3 (CLDN3) and claudin-4 (CLDN4) are highly expressed in the majority of ovarian cancers. We report here that CLDN3 and CLDN4 each serve to constrain the growth of human 2008 cancer xenografts and limit metastatic potential. Knockdown of CLDN3 increased in vivo growth rate by 2.3-fold and knockdown of CLDN4 by 3.7-fold in the absence of significant change in in vitro growth rate. Both types of tumors exhibited increase in birth rate as measured by Ki67 staining and decrease in death rate as reflected by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining. Knockdown of either claudin did not alter expression of other TJ protein but did reduce TJ formation as measured by transepithelial resistance and paracellular flux of dextran, enhance migration and invasion in in vitro assays, and increase lung colonization following intravenous injection. Knockdown of CLDN3 and CLDN4 increased total lung metastatic burden by 1.7-fold and 2.4-fold, respectively. Loss of either CLDN3 or CLDN4 resulted in down-regulation of E-cadherin mRNA and protein, increased inhibitory phosphorylation of glycogen synthase kinase-3ß (GSK-3ß), and activation of ß-catenin pathway signaling as evidenced by increases in nuclear ß-catenin, the dephosphorylated form of the protein, and transcriptional activity of ß-catenin/T-cell factor (TCF). We conclude that both CLDN3 and CLDN4 mediate interactions with other cells in vivo that restrain growth and metastatic potential by sustaining expression of E-cadherin and limiting ß-catenin signaling.

A simple reporter assay for screening claudin-4 modulators.

Claudin-4, a member of a tetra-transmembrane protein family that comprises 27 members, is a key functional and structural component of the tight junction-seal in mucosal epithelium. Modulation of the claudin-4-barrier for drug absorption is now of research interest. Disruption of the claudin-4-seal occurs during inflammation. Therefore, claudin-4 modulators (repressors and inducers) are promising candidates for drug development. However, claudin-4 modulators have never been fully developed. Here, we attempted to design a screening system for claudin-4 modulators by using a reporter assay. We prepared a plasmid vector coding a claudin-4 promoter-driven luciferase gene and established stable reporter gene-expressing cells. We identified thiabendazole, carotene and curcumin as claudin-4 inducers, and potassium carbonate as a claudin-4 repressor by using the reporter cells. They also increased or decreased, respectively, the integrity of the tight junction-seal in Caco-2 cells. This simple reporter system will be a powerful tool for the development of claudin-4 modulators.

Targeting claudin-4 in human pancreatic cancer.

INTRODUCTION: Pancreatic cancer is one of the most malignant human diseases and there is an urgent need to develop novel diagnostic and therapeutic strategies. Claudin-4, overexpressed in pancreatic cancer and its precursor lesions, is a receptor for Clostridium perfringens enterotoxin (CPE). The cytotoxic effects of CPE and monoclonal antibodies against claudin-4 are useful as novel therapeutic tools for pancreatic cancer. AREAS COVERED: This review describes and discusses the studies targeting claudin-4 in normal human pancreatic duct epithelial (HPDE) cells and cancer cells. EXPERT OPINION: Claudin-4 is in part regulated via a PKCα signal transduction pathway in pancreatic cancer cell lines. PKCα inhibitors may represent potential therapeutic agents against human pancreatic cancer cells by the use of CPE cytotoxicity via claudin-4. The COOH-terminal half fragment of CPE (C-CPE) enhances the effectiveness of clinically relevant chemotherapies and can be used as a carrier for drugs and other bacterial toxins to claudin-4-positive cancer cells. hTERT-HPDE cells, in which the human telomerase reverse transcriptase (hTERT) gene is introduced into normal HPDE cells, may be a useful model of normal HPDE cells not only for physiological regulation of claudin-4 expression but also for developing safer and more effective therapeutic methods targeting claudin-4 in pancreatic cancer.