Distinct expression pattern of claudin-6, a primitive phenotypic tight junction molecule, in germ cell tumours and visceral carcinomas

Claudins: from gatekeepers of epithelial integrity to potential targets in hepato-pancreato-biliary cancers

Claudins, a family of tetraspan transmembrane proteins, are critical to the integrity of tight junctions in epithelia and endothelia, influencing cellular processes such as development, differentiation, and apoptosis. Abnormal claudin expression is associated with various malignancies, particularly affecting tissue architecture and potentially facilitating tumor invasion and metastasis. In this comprehensive review, we explore the multifaceted functions of claudins: their expression, specific roles in cancer with a focus on hepato-pancreato-biliary malignancies and highlight their potential as therapeutic targets. We discuss current claudin-targeted therapies, including monoclonal antibodies, antibody-drug conjugates, bispecific T-cell engager and chimeric antigen receptor T-cell therapies. These approaches show promise in pre-clinical and clinical studies, particularly in hepato-pancreato-biliary cancers with large unmet needs. Despite these early signs of efficacy, challenges remain in effectively targeting these proteins due to their structural resemblance and overlapping functions.

Preclinical efficacy and pharmacokinetics of an RNA-encoded T cell-engaging bispecific antibody targeting human claudin 6

We present the preclinical pharmacology of BNT142, a lipid nanoparticle (LNP)-formulated RNA (RNA-LNP) encoding a T cell-engaging bispecific antibody that monovalently binds the T cell marker CD3 and bivalently binds claudin 6 (CLDN6), an oncofetal antigen that is absent from normal adult tissue but expressed on various solid tumors. Upon BNT142 RNA-LNP delivery in cell culture, mice, and cynomolgus monkeys, RNA is translated, followed by self-assembly into and secretion of the functional bispecific antibody RiboMab02.1. In vitro, RiboMab02.1 mediated CLDN6 target cell-specific activation and proliferation of T cells, and potent target cell killing. In mice and cynomolgus monkeys, intravenously administered BNT142 RNA-LNP maintained therapeutic serum concentrations of the encoded antibody. Concentrations of RNA-encoded RiboMab02.1 were maintained longer in circulation in mice than concentrations of directly injected, sequence-identical protein. Weekly injections of mice with BNT142 RNA-LNP in the 0.1- to 1-μg dose range were sufficient to eliminate CLDN6-positive subcutaneous human xenograft tumors and increase survival over controls. Tumor regression was associated with an influx of T cells and depletion of CLDN6-positive cells. BNT142 induced only transient and low cytokine production in CLDN6-positive tumor-bearing mice humanized with peripheral blood mononuclear cells (PBMCs). No signs of adverse effects from BNT142 RNA-LNP administration were observed in mice or cynomolgus monkeys. On the basis of these and other findings, a phase 1/2 first-in-human clinical trial has been initiated to assess the safety and preliminary efficacy of BNT142 RNA-LNP in patients with CLDN6-positive advanced solid tumors (NCT05262530).

Claudins in Cancer: A Current and Future Therapeutic Target

Claudins are a family of 27 proteins that have an important role in the formation of tight junctions. They also have an important function in ion exchange, cell mobility, and the epithelial-to-mesenchymal transition, the latter being very important in cancer invasion and metastasis. Therapeutic targeting of claudins has been investigated to improve cancer outcomes. Recent evidence shows improved outcomes when combining monoclonal antibodies against claudin 18.2 with chemotherapy for patients with gastroesophageal junction cancer. Currently, chimeric antigen receptor T-cells targeting claudin 18 are under investigation. In this review, we will discuss the major functions of claudins, their distribution in the normal as well as cancerous tissues, and their effect in cancer metastasis, with a special focus on the therapeutic targeting of claudins to improve cancer outcomes.

Independent prognostic value of CLDN6 in bladder cancer based on M2 macrophages related signature

M2 macrophages are associated with the prognosis of bladder cancer. CLDN6 has been linked to immune infiltration and is crucial for predicting the prognosis in multi-tumor. The effect of CLDN6 on M2 macrophages in bladder cancer remains elusive. Here, we compared a total of 40 machine learning algorithms, then selected optimal algorithm to develop M2 macrophages-related signature (MMRS) based on the identified M2 macrophages related module. MMRS predicted the prognosis better than other models and associated to immunotherapy response. CLDN6, as an important variable in MMRS, was an independent factor for poor prognosis. We found that CLDN6 was highly expressed and affected immune infiltration, immunotherapy response, and M2 macrophages polarization. Meanwhile, CLDN6 promoted the growth of bladder cancer and enhanced the carcinogenic effect by inducing polarization of M2 macrophages. In total, CLDN6 is an independent risk factor in MMRS to predict the prognosis of bladder cancer.

CLDN6 inhibited cellular biological function of nonsmall cell lung cancer cells through suppressing aerobic glycolysis via the RIP1/ASK1/JNK axis

Claudin-6 (CLDN6) has been extensively studied in different tumors to date. However, in the case of nonsmall cell lung cancer (NSCLC), CLDN6 has a largely unknown role and molecular mechanism. We detected the expression of CLDN6 in NSCLC tissues and cells using reverse transcription-quantitative polymerase chain reaction (PCR) and western blot assays. A gain-of-function experiment was performed to evaluate the biological effects of CLDN6 on NSCLC cell behaviors. Methylation-specific PCR was utilized to detect the DNA methylation of CLDN6 gene promoter region. The interaction of CLDN6 and receptor interacting protein 1 (RIP1) was determined by coimmunoprecipitation assay. Furthermore, the modulation of CLDN6 on RIP1/apoptosis signal-regulating kinase 1 (ASK1)/c-Jun N-terminal kinase (JNK) axis was confirmed. The results showed that in NSCLC tissues and cells, CLDN6 expression level was declined, and was associated with a high level of DNA methylation. CLDN6 overexpression suppressed the viability, invasion, migration, and promoted cell apoptosis. Besides, the enhanced expression of CLDN6 reduced the glycolysis and the dysfunction of mitochondrial respiration of NSCLC cells. Mechanistic investigation confirmed that CLDN6 interacted with RIP1 and inhibited cellular biological function of NSCLC cells via RIP1/ASK1/JNK axis. Besides, CLDN6 overexpression inhibited tumor growth in vivo. In conclusion, CLDN6 inhibited NSCLC cell proliferation through inactivating aerobic glycolysis via the RIP1/ASK1/JNK axis.

Immuno-Oncology Advances in Genitourinary Cancers

Immuno-oncology (IO) has made monumental gains in the past decade in the genitourinary space. In this review, we highlight advances with IO in renal cell carcinoma where it now has become standard-of-care frontline therapy in the metastatic setting but also discuss challenges with the initial approach. In urothelial carcinoma, we discuss the growing use of IO including exciting recent updates with IO-based regimens that may soon become the new standard of care. We further discuss difficulties with IO in prostate cancer, germ cell tumors, and penile squamous cell carcinoma. Finally, we highlight advances in IO approaches beyond checkpoint inhibition including the role of the gut microbiome and T-cell redirecting therapies.

Chimeric Antigen Receptor T-Cell Therapy for Solid Tumors

We review chimeric antigen receptor (CAR) T-cell therapy for solid tumors. We discuss patient selection factors and aspects of clinical management. We describe challenges including physical and molecular barriers to trafficking CAR-Ts, an immunosuppressive tumor microenvironment, and difficulty finding cell surface target antigens. The application of new approaches in synthetic biology and cellular engineering toward solid tumor CAR-Ts is described. Finally, we summarize reported and ongoing clinical trials of CAR-T therapies for select disease sites such as head and neck (including thyroid cancer), lung, central nervous system (glioblastoma, neuroblastoma, glioma), sarcoma, genitourinary (prostate, renal, bladder, kidney), breast and ovarian cancer.

Expression patterns of claudins in cancer

Claudins are four-transmembrane proteins, which were found in tight junctions. They maintain cell barriers and regulate cell differentiation and proliferation. They are involved in maintaining cellular polarity and normal functions. Different claudins show different expression patterns. The expression level and localization of claudins are altered in various cancers. They promote or inhibit proliferation, invasion, and migration of cancer cells through multiple signaling pathways. Therefore, claudins may serve as diagnostic markers, novel therapeutic targets, and prognostic risk factors. The important roles of claudins in cancer aroused our great interest. In the present review, we provide a summary of insights into expression patterns of claudins in cancer, which is more comprehensive and provides new ideas for further research.

CLDN6-specific CAR-T cells plus amplifying RNA vaccine in relapsed or refractory solid tumors: the phase 1 BNT211-01 trial

The oncofetal antigen Claudin 6 (CLDN6) is highly and specifically expressed in many solid tumors, and could be a promising treatment target. We report dose escalation results from the ongoing phase 1/2 BNT211-01 trial evaluating the safety and feasibility of chimeric antigen receptor (CAR) T cells targeting the CLDN6 with or without a CAR-T cell-amplifying RNA vaccine (CARVac) at two dose levels (DLs) in relapsed/refractory CLDN6-positive solid tumors. The primary endpoints were safety and tolerability, maximum tolerated dose and recommended phase 2 dose (RP2D). Secondary endpoints included objective response rate (ORR) and disease control rate. We observed manageable toxicity, with 10 out of 22 patients (46%) experiencing cytokine release syndrome including one grade 3 event and 1 out of 22 (5%) with grade 1 immune effector cell-associated neurotoxicity syndrome. Dose-limiting toxicities occurred in two patients at the higher DL, resolving without sequelae. CAR-T cell engraftment was robust, and the addition of CARVac was well tolerated. The unconfirmed ORR in 21 evaluable patients was 33% (7 of 21), including one complete response. The disease control rate was 67% (14 of 21), with stable disease in seven patients. Patients with germ cell tumors treated at the higher DL exhibited the highest response rate (ORR 57% (4 of 7)). The maximum tolerated dose and RP2D were not established as the trial has been amended to utilize an automated manufacturing process. A repeat of the dose escalation is ongoing and will identify a RP2D for pivotal trials. ClinicalTrials.gov Identifier: NCT04503278 .

The tight junction protein claudin 6 is a potential target for patient-individualized treatment in esophageal and gastric adenocarcinoma and is associated with poor prognosis

BACKGROUND

The prognosis of esophageal adenocarcinoma (EAC) and gastric adenocarcinoma (GAC) remains poor, and new therapeutic approaches are urgently needed. Claudin 6 (CLDN6) is an oncofetal antigen that is largely absent in healthy tissues and upregulated in several cancers, making it a promising therapeutical target. In this study, the expression of CLDN6 was assessed in an large Caucasian EAC and GAC cohort.

METHODS

RNA-Seq data from 89 EACs and 371 GACs were obtained from The Cancer Genome Atlas project and EAC/GAC cases were stratified by CLDN6 mRNA expression based on a survival-associated cutoff. For groups with CLDN6 expression above or below this cutoff, differential gene expression analyses were performed using DESeq, and dysregulated biological pathways were identified using the Enrichr tool. Additionally, CLDN6 protein expression was assessed in more than 800 EACs and almost 600 GACs using a CLDN6-specific immunohistochemical antibody (clone 58-4B-2) that is currently used in Phase I/II trials to identify patients with CLDN6-positive tumors (NCT05262530; NCT04503278). The expression of CLDN6 was also correlated with histopathological parameters and overall survival (OS).

RESULTS

EACs and GACs with high CLDN6 mRNA levels displayed an overexpression of pathways regulating the cell cycle, DNA replication, and receptor / extracellular matrix interactions. CLDN6 protein expression was associated with shorter OS in EAC and GAC, both in treatment-naïve subgroups and cohorts receiving neoadjuvant therapy. In multivariate analysis, CLDN6 protein expression was an independent adverse prognostic factor in EAC associated with a shorter OS (HR: 1.75; p = 0.01) and GAC (HR: 2.74; p = 0.028).

CONCLUSIONS

High expression of CLDN6 mRNA is associated with the dysregulation of distinct biological pathways regulating cell growth, proliferation, and cell-matrix interactions. Clinically, the expression of CLDN6 protein is a valuable adverse prognostic marker in EAC and GAC.

[New forms of immunotherapy in uro-oncology : HLA-independent therapeutic approaches with bispecific antibodies and CAR T cells]

Immunotherapies using bispecific antibodies and chimeric antigen receptor (CAR) T cells do not depend on previous activation of T cells by the human leukocyte antigen (HLA) system. These HLA-independent approaches displayed groundbreaking clinical results in hematological malignancies-leading to drug approvals for diseases like acute lymphocytic leukemia (ALL), B-cell Non-Hodgkin's lymphoma and multiple myeloma. Currently, several phase I/II trials are investigating the transferability of these results to solid tumors-especially prostate cancer. Compared to established immune checkpoint blockade, bispecific antibodies and CAR T cells have novel and heterogenous side effects such as cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS). Treating these side effects and identifying suitable trial participants requires an interdisciplinary treatment approach.

Preclinical Efficacy of the Antibody-Drug Conjugate CLDN6-23-ADC for the Treatment of CLDN6-Positive Solid Tumors

PURPOSE

Claudin-6 (CLDN6) is expressed at elevated levels in multiple human cancers including ovarian and endometrial malignancies, with little or no detectable expression in normal adult tissue. This expression profile makes CLDN6 an ideal target for development of a potential therapeutic antibody-drug conjugate (ADC). This study describes the generation and preclinical characterization of CLDN6-23-ADC, an ADC consisting of a humanized anti-CLDN6 monoclonal antibody coupled to monomethyl auristatin E (MMAE) via a cleavable linker.

EXPERIMENTAL DESIGN

A fully humanized anti-CLDN6 antibody was conjugated to MMAE resulting in the potential therapeutic ADC, CLDN6-23-ADC. The antitumor efficacy of CLDN6-23-ADC was assessed for antitumor efficacy in CLDN6-positive (CLDN6+) and -negative (CLDN6-) xenografts and patient-derived xenograft (PDX) models of human cancers.

RESULTS

CLDN6-23-ADC selectively binds to CLDN6, versus other CLDN family members, inhibits the proliferation of CLDN6+ cancer cells in vitro, and is rapidly internalized in CLDN6+ cells. Robust tumor regressions were observed in multiple CLDN6+ xenograft models and tumor inhibition led to markedly enhanced survival of CLDN6+ PDX tumors following treatment with CLDN6-23-ADC. IHC assessment of cancer tissue microarrays demonstrate elevated levels of CLDN6 in 29% of ovarian epithelial carcinomas. Approximately 45% of high-grade serous ovarian carcinomas and 11% of endometrial carcinomas are positive for the target.

CONCLUSIONS

We report the development of a novel ADC, CLDN6-23-ADC, that selectively targets CLDN6, a potential onco-fetal-antigen which is highly expressed in ovarian and endometrial cancers. CLDN6-23-ADC exhibits robust tumor regressions in mouse models of human ovarian and endometrial cancers and is currently undergoing phase I study.

Claudin-6 enhances the malignant progression of gestational trophoblastic neoplasm by promoting proliferation and metastasis

PURPOSE

Choriocarcinoma (CC) is a rare and highly malignant epithelial tumour. However, the mechanism underlying its occurrence and development remains unknown. We aimed to reveal the biological significance and prognostic value of Claudin-6 (CLDN6) in gestational trophoblastic disease (GTD).

PATIENTS AND METHODS

We collected clinical GTD specimens from 2011 to 2019 and measured CLDN6 gene expression by immunohistochemistry (IHC). High-throughput mRNA sequencing (RNA-seq) revealed a GTD progression-associated gene. CCK-8, wound healing, and flow cytometry assays were used to assess the biological effects of CLDN6 overexpression and knockdown. The medical records of 118 GTD patients from 2011 to 2019 were retrospectively analysed to identify correlations between CLDN6 expression and GTD patient clinical-pathological parameters; these correlations were analysed using the chi-square test and one-way ANOVA. Univariate logistic regression was used to analyse various prognostic parameters of patients with post-molar GTN.

RESULTS

CLDN6 had the second highest fold change in gene expression between GTN and normal samples. CLDN6 was highly expressed in GTN tissues and CC cell lines, and silencing CLDN6 inhibited the proliferation and migration and promoted the apoptosis of CC cells. CLDN6 overexpression was significantly correlated with uterine size (p = 0.01) and ovarian cysts > 6 cm (p = 0.027), CLDN6 expression was significantly higher in HR-GTNs than in low-risk GTNs (LR-GTNs) (p = 0.008), and logistic regression analysis showed that CLDN6 expression in hydatidiform moles (HMs) was related to a high risk of developing post-molar GTN (OR = 2.393, p = 0.03).

CONCLUSION

We propose that CLDN6 participates in the development of GTD and may become a new therapeutic target for CC.

Targeting CLDN6 in germ cell tumors by an antibody-drug-conjugate and studying therapy resistance of yolk-sac tumors to identify and screen specific therapeutic options

BACKGROUND

Being the standard-of-care for four decades, cisplatin-based chemotherapy is highly efficient in treating germ cell tumors (GCT). However, often refractory patients present with a remaining (resistant) yolk-sac tumor (YST(-R)) component, resulting in poor prognosis due to lack of novel treatment options besides chemotherapy and surgery. The aim of this study was to identify novel targets for the treatment of YST by deciphering the molecular mechanisms of therapy resistance. Additionally, we screened the cytotoxic efficacy of a novel antibody-drug-conjugate targeting CLDN6 (CLDN6-ADC), as well as pharmacological inhibitors to target specifically YST.

METHODS

Protein and mRNA levels of putative targets were measured by flow cytometry, immunohistochemical stainings, mass spectrometry of formalin-fixed paraffin-embedded tissues, phospho-kinase arrays, or qRT-PCR. Cell viability, apoptosis and cell cycle assays of GCT and non-cancerous cells were performed using XTT cell viability assays or Annexin V / propidium iodide flow cytometry, respectively. Druggable genomic alterations of YST(-R) tissues were identified by the TrueSight Oncology 500 assay.

RESULTS

We demonstrated that treatment with a CLDN6-ADC enhanced apoptosis induction specifically in CLDN6+ GCT cells in comparison with non-cancerous controls. In a cell line-dependent manner, either an accumulation in the G2 / M cell cycle phase or a mitotic catastrophe was observed. Based on mutational and proteome profiling, this study identified drugs targeting the FGF, VGF, PDGF, mTOR, CHEK1, AURKA, or PARP signaling pathways as promising approaches to target YST. Further, we identified factors relevant for MAPK signaling, translational initiation and RNA binding, extracellular matrix-related processes as well as oxidative stress and immune response to be involved in therapy resistance.

CONCLUSIONS

In summary, this study offers a novel CLDN6-ADC to target GCT. Additionally, this study presents novel pharmacological inhibitors blocking FGF, VGF, PDGF, mTOR, CHEK1, AURKA, or PARP signaling for the treatment of (refractory) YST patients. Finally, this study shed light on the mechanisms of therapy resistance in YST.

A phase II study assessing the safety and efficacy of ASP1650 in male patients with relapsed refractory germ cell tumors

Claudin6(CLDN6) is a tight junction protein of claudin-tetraspanin family and is of the earliest molecules expressed in embryonic epithelium. CLDN6 is frequently aberrantly expressed in testicular germ-cell tumors(GCT). ASP1650 is a chimeric-mouse/human-IgG1 antibody directed against CLDN6. Two-part, open-label, phase-II trial investigating ASP1650 in patients with relapsed/refractory GCT and no curable options. Part1 was a safety lead-in to establish the recommended-phase-II-dose(RP2D). Part2 was a phase-II study designed to evaluate the antitumor effects of ASP1650. CLDN6 expression was centrally assessed on archival tumor tissue using immunohistochemistry. The primary objectives were to establish the RP2D(safety lead-in) and the antitumor activity(phase-II) of ASP1650. Nineteen male patients were enrolled: 6 patients in 1000 mg/m2 safety lead-in group, and 13 in 1500 mg/m2 group. Median age 37.2 years(range,20-58). Histology was non-seminoma in 17/19 patients. Median number of previous chemotherapy regimens was 3. Thirteen patients had prior high-dose chemotherapy. No dose-limiting toxicity events were reported at any study drug dose. A RP2D of 1500 mg/m2 every 2 weeks was established. No partial or complete responses were observed. The study was stopped at the end of Simon Stage-I due to lack of efficacy. 15/16 subjects with available tissue had CLDN6 positive staining. The mean percent membrane staining was 71.6% and the mean membrane H score was 152.6(SD 76). ASP1650 did not appear to have clinically meaningful single-agent activity in relapsed/refractory GCT. CLDN6 expression seems ubiquitous in all elements of GCT and is worthy of investigation as a diagnostic biomarker and therapeutic target. (Clinical trial information: NCT03760081).

Claudin-6 increases SNAI1, NANOG and SOX2 gene expression in human gastric adenocarcinoma AGS cells

BACKGROUND

Gastric cancer is a heterogeneous disease associated to deregulated gastric epithelia tight junction barrier function and di novo expression of claudin-6; these changes are associated with epithelial-mesenchymal transition, enhanced invasiveness, metastatic progression, resistance to chemotherapy, and poor prognosis. Gastric cancer stem cells represent a rare population of cells within the tumor implicated in tumor growth and higher tumorigenic capacity. The possible relation between claudin-6 expression and the expression of some markers associated to epithelial mesenchymal transition and cancer stem cells in gastric cancer cells have never been explored.

METHODS AND RESULTS

CD44, CD24, Twist, Villin, DCLK1, claudin-6, NANOG, E-Cadherin, SOX2, and SNAI1 expression was evaluated by immunofluorescence and cytofluorometry in wild type and Claudin-6 transfected AGS cells. Cell migration assays were also performed. Differentially expressed genes and biological processes analysis was performed to determine gene preponderance. The results showed that claudin-6 overexpression enriched the CD44 + /CD24- subpopulation with an overall increase in the expression and the number of CD44 + cells. A significant increase in NANOG, SOX2 and SNAI1 expression and enhanced cell migration was observed in claudin-6 transfected cells. Transcriptome analysis revealed 271 genes involved in enhanced biological processes with only 31 with a significantly p value; thirteen of those genes are closely associated to epithelial mesenchymal transition processes and folding and unfolding processes of proteins in the endoplasmic reticulum.

CONCLUSIONS

The pro-tumorigenic effect of claudin-6 in gastric cancer could be associated to dedifferentiation of epithelial cells and an increase in di novo cancer stem cell genesis.

EGF-Dependent Activation of ELK1 Contributes to the Induction of CLDND1 Expression Involved in Tight Junction Formation

Claudin proteins are intercellular adhesion molecules. Increased claudin domain-containing 1 (CLDND1) expression is associated with the malignant transformation of estrogen receptor-negative breast cancer cells with low sensitivity to hormone therapy. Abnormal CLDND1 expression is also implicated in vascular diseases. Previously, we investigated the regulatory mechanism underlying CLDND1 expression and identified a strong enhancer region near the promoter. In silico analysis of the sequence showed high homology to the ETS domain-containing protein-1 (ELK1)-binding sequence which is involved in cell growth, differentiation, angiogenesis, and cancer. Transcriptional ELK1 activation is associated with the mitogen-activated protein kinase (MAPK) signaling cascade originating from the epidermal growth factor receptor (EGFR). Here, we evaluated the effect of gefitinib, an EGFR tyrosine kinase inhibitor, on the suppression of CLDND1 expression using ELK1 overexpression in luciferase reporter and chromatin immunoprecipitation assays. ELK1 was found to be an activator of the enhancer region, and its transient expression increased that of CLDND1 at the mRNA and protein levels. CLDND1 expression was increased following EGF-induced ELK1 phosphorylation. Furthermore, this increase in CLDND1 was significantly suppressed by gefitinib. Therefore, EGF-dependent activation of ELK1 contributes to the induction of CLDND1 expression. These findings open avenues for the development of new anticancer agents targeting CLDND1.

The role of neoantigens in tumor immunotherapy

Tumor neoantigens are aberrant polypeptides produced by tumor cells as a result of genomic mutations. They are also tumor-specific antigens (TSA). Neoantigens are more immunogenic than tumor-related antigens and do not induce autoimmunity. Based on the rapid development of bioinformatics and the continuous update of sequencing technology, cancer immunotherapy with tumor neoantigens has made promising breakthroughs and progress. In this review, the generation, prediction, and identification of novel antigens, as well as the individualized treatments of neoantigens, were first introduced. Secondly, the mechanism of Chimeric Antigen Receptor T-Cell Immunotherapy (CAR-T) therapy and immune checkpoint blockade therapy in the treatment of tumors were outlined, and the three treatment methods were compared. Thirdly, the application of neoantigens in CAR-T therapy and PD-1/PD-L1 blockade therapy was briefly described. The benefits of the neoantigen vaccines over common vaccines were summarized as well. Finally, the prospect of neoantigen therapy was presented.

Research advance in lipid nanoparticle-mRNA delivery system and its application in CAR-T cell therapy

Chimeric antigen receptor (CAR) T cell therapy has shown significant efficacy for hematological malignancies, however, it needs to be further optimized. Recently, the lipid nanoparticle (LNP)-mRNA delivery system as a nonviral gene transfer vector has gained rapid progress in CAR-T cell therapy. The claudin-6 (CLDN6) mRNA is delivered to antigen presenting cells (APCs) through LNP system, thereby enhancing the function of CLDN6 CAR-T cells for the clearance of solid tumor cells. For treatment of acute cardiac injury, the fibroblast activation protein (FAP) CAR mRNA can be delivered to T cells through LNP system for the in vivo production of FAP CAR-T cells, thereby blocking the process of myocardial fibrosis. The LNP-mRNA delivery system has advantages including having no integration in host genome, inexpensiveness, low toxicity and modifiability; on the other hand, it has certain disadvantages such as limited cell persistence caused by transient protein expression and limitations in preparation techniques. This article reviews the research advance in LNP-mRNA in vivo delivery system and its application in CAR-T cell therapy.

Aberrant expression of claudin-6 contributes to malignant potentials and drug resistance of cervical adenocarcinoma

Recent studies have revealed that aberrant expression of tight junction (TJ) proteins is a hallmark of various solid tumors and it is recognized as a useful therapeutic target. Claudin‐6 (CLDN6), a member of the family of TJ transmembrane proteins, is an ideal therapeutic target because it is not expressed in human adult normal tissues. In this study, we found that CLDN6 is highly expressed in uterine cervical adenocarcinoma (ADC) and that high CLDN6 expression was correlated with lymph node metastasis and lymphovascular infiltration and was an independent prognostic factor. Shotgun proteome analysis revealed that cell‐cell adhesion‐related proteins and drug metabolism‐associated proteins (aldo‐keto reductase [AKR] family proteins) were significantly increased in CLDN6‐overexpressing cells. Furthermore, overexpression of CLDN6 enhanced cell‐cell adhesion properties and attenuated sensitivity to anticancer drugs including doxorubicin, daunorubicin, and cisplatin. Taken together, the results indicate that aberrant expression of CLDN6 enhances malignant potentials and drug resistance of cervical ADC, possibly due to increased cell‐cell adhesion properties and drug metabolism. Our findings provide an insight into a new therapeutic strategy, a CLDN6‐targeting therapy, against cervical ADC.

Identification of Claudin 6-specific HLA class I- and HLA class II-restricted T cell receptors for cellular immunotherapy in ovarian cancer

Adoptive cell therapy (ACT) is one of promising immunotherapies for cancer patients by providing a large amount of cancer antigen-specific effector T cells that can be manufactured rapidly by ex vivo gene engineering. To provide antigen-specificity to patients’ autologous T cells in a short-term culture, T-cell receptors (TCRs) or chimeric antigen receptors (CARs) are transduced to bulk T cells. Because of intra- and inter-tumoral heterogeneity in tumor antigen expression, a repertoire of TCR or CAR genes targeting a wide range of tumor antigens are required for a broad and effective treatment by ACT. Here, we characterized immunogenicity of claudin 6 (CLDN6) in ovarian cancer patients and identified specific TCR genes from CD8⁺ and CD4⁺ T cells. CLDN6 protein was frequently expressed on EpCAM⁺ ovarian cancer cells but not CD45⁺ lymphocytes in tumor ascites of ovarian cancer patients. Spontaneous CLDN6-specific CD4⁺ and CD8⁺ T-cell response was detected in peripheral blood mononuclear cells (PBMCs) from 1 out of 17 ovarian cancer patients. HLA-A*02:01 (A2) and DR*04:04 (DR4)-restricted TCR genes were isolated from CLDN6-specific CD8⁺ and CD4⁺ T cells, respectively. T cells that were engineered with A2-restricted TCR gene recognized and killed A2⁺CLDN6⁺ cancer cells. DR4-restricted TCR-transduced T cells directly recognized DR4⁺CLDN6⁺-overexpressed cancer cells. Our results demonstrate that these CLDN6-specific TCR genes are useful as therapeutic genes for ACT to patients with ovarian and other solid tumors expressing CLDN6.

Claudins and Gastric Cancer: An Overview

Simple Summary

Gastric cancer (GC) is one of the most common cancers and the third leading cause of cancer deaths worldwide, with a high frequency of recurrence and metastasis, and a poor prognosis. This review presents novel biological and clinical significance of claudin (CLDN) expression in GC, especially CLDN18, and clinical trials centered around CLDN18.2. It also presents new findings for other CLDNs.

Abstract

Despite recent improvements in diagnostic ability and treatment strategies, advanced gastric cancer (GC) has a high frequency of recurrence and metastasis, with poor prognosis. To improve the treatment results of GC, the search for new treatment targets from proteins related to epithelial–mesenchymal transition (EMT) and cell–cell adhesion is currently being conducted. EMT plays an important role in cancer metastasis and is initiated by the loss of cell–cell adhesion, such as tight junctions (TJs), adherens junctions, desmosomes, and gap junctions. Among these, claudins (CLDNs) are highly expressed in some cancers, including GC. Abnormal expression of CLDN1, CLDN2, CLDN3, CLDN4, CLDN6, CLDN7, CLDN10, CLDN11, CLDN14, CLDN17, CLDN18, and CLDN23 have been reported. Among these, CLDN18 is of particular interest. In The Cancer Genome Atlas, GC was classified into four new molecular subtypes, and CLDN18–ARHGAP fusion was observed in the genomically stable type. An anti-CLDN18.2 antibody drug was recently developed as a therapeutic drug for GC, and the results of clinical trials are highly predictable. Thus, CLDNs are highly expressed in GC as TJs and are expected targets for new antibody drugs. Herein, we review the literature on CLDNs, focusing on CLDN18 in GC.

CLDN6: From Traditional Barrier Function to Emerging Roles in Cancers

Claudins (CLDNs) are the most important tight junction proteins, which are mainly expressed in endothelial cells or epithelial cells in a tissue-specific manner. As a member of the CLDNs family, CLDN6 is highly expressed in fetal tissues such as the stomach, pancreas, lung, and kidney, but is not expressed in corresponding adult tissues. The expression of CLDN6 is regulated by a variety of factors, including but not limited to stimuli and transcription factors, DNA methylation, and post-translational modifications. CLDN6 has been found to have a key role in the formation of barriers, especially the lung epithelial barrier and the epidermal permeability barrier (EPB). Importantly, the roles of CLDN6 in cancers have gained focus and are being investigated in recent years. Strong evidence indicates that the altered expression of CLDN6 is linked to the development of various cancers. Malignant phenotypes of tumors affected by CLDN6 include proliferation and apoptosis, migration and invasion, and drug resistance, which are regulated by CLDN6-mediated key signaling pathways. Given the important role in tumors and its low or no expression in normal tissues, CLDN6 is an ideal target for tumor therapy. This review aims to provide an overview of the structure and regulation of CLDN6, and its traditional barrier function, with a special emphasis on its emerging roles in cancers, including its impact on the malignant phenotypes, signal-modulating effects, the prognosis of tumor patients, and clinical applications in cancers.

CRISPR/Cas9-mediated TGFβRII disruption enhances anti-tumor efficacy of human chimeric antigen receptor T cells in vitro

BACKGROUND

CAR T-cell therapy has been recently unveiled as one of the most promising cancer therapies in hematological malignancies. However, solid tumors mount a profound line of defense to escape immunosurveillance by CAR T-cells. Among them, cytokines with an inhibitory impact on the immune system such as IL-10 and TGFβ are of great importance: TGFβ is a pleiotropic cytokine, which potently suppresses the immune system and is secreted by a couple of TME resident and tumor cells.

METHODS

In this study, we hypothesized that knocking out the TGFβ receptor II gene, could improve CAR T-cell functions in vitro and in vivo. Hereby, we used the CRISPR/Cas9 system, to knockout the TGFβRII gene in T-cells and could monitor the efficient gene knock out by genome analysis techniques. Next, Mesothelin or Claudin 6 specific CAR constructs were overexpressed via IVT-RNA electroporation or retroviral transduction and the poly-functionality of these TGFβRII KO CAR T-cells in terms of proliferation, cytokine secretion and cytotoxicity were assessed and compared with parental CAR T-cells.

RESULTS

Our experiments demonstrated that TGFβRII KO CAR T-cells fully retained their capabilities in killing tumor antigen positive target cells and more intriguingly, could resist the anti-proliferative effect of exogenous TGFβ in vitro outperforming wild type CAR T-cells. Noteworthy, no antigen or growth factor-independent proliferation of these TGFβRII KO CAR T-cells has been recorded. TGFβRII KO CAR T-cells also resisted the suppressive effect of induced regulatory T-cells in vitro to a larger extent. Repetitive antigen stimulation demonstrated that these TGFβRII KO CAR T-cells will experience less activation induced exhaustion in comparison to the WT counterpart.

CONCLUSION

The TGFβRII KO approach may become an indispensable tool in immunotherapy of solid tumors, as it may surmount one of the key negative regulatory signaling pathways in T-cells.

Claudin 6: Therapeutic prospects for tumours, and mechanisms of expression and regulation (Review)

Tight junctions (TJs) are an important component of cell connectivity; they maintain cell polarity, permeability and adhesion, and participate in the regulation of cell proliferation and differentiation. The claudin (CLDN) family is integral to TJs, and CLDN6 is an important member of this family. Abnormal expression of CLDN6 can destroy the integrity of TJs through various mechanisms and can serve multiple roles in the occurrence and development of tumours. CLDN6 is widely expressed in various tumours but rarely expressed in healthy adult tissues. The aim of this review is to critically examine the recent literature on CLDN6, including its structure, expression in different tumours, regulatory mechanisms and therapeutic prospects. Although some conclusions are controversial, in certain tumours, such as liver, ovarian, endometrial and oesophageal cancer, and atypical teratoid/rhabdoid tumours, research consistently shows that CLDN6 is expressed in tumour tissues but is not expressed or is expressed at low levels in surrounding tissues. In these tumours, CLDN6 has potential as a carcinoembryonic antigen and a therapeutic target.

Aberrant Claudin-6-Adhesion Signaling Promotes Endometrial Cancer Progression via Estrogen Receptor α

Cell adhesion proteins not only maintain tissue integrity, but also possess signaling abilities to organize diverse cellular events in a variety of physiologic and pathologic processes; however, the underlying mechanism remains obscure. Among cell adhesion molecules, the claudin (CLDN) family is often aberrantly expressed in various cancers, but the biological relevance and molecular basis for this observation have not yet been established. Here, we show that high CLDN6 expression accelerates cellular proliferation and migration in two distinct human endometrial cancer cell lines in vitro. Using a xenograft model, we also revealed that aberrant CLDN6 expression promotes tumor growth and invasion in endometrial cancer tissues. The second extracellular domain and Y196/200 of CLDN6 were required to recruit and activate Src-family kinases (SFK) and to stimulate malignant phenotypes. Knockout and overexpression of ESR1 in endometrial carcinoma cells showed that the CLDN6-adhesion signal links to estrogen receptor α (ERα) to advance tumor progression. In particular, aberrant CLDN6-ERα signaling contributed to collective cell behaviors in the leading front of endometrial cancer cells. Importantly, we demonstrate that CLDN6/SFK/PI3K-dependent AKT and SGK (serum- and glucocorticoid-regulated kinase) signaling in endometrial cancer cells targets Ser518 in the human ERα to activate ERα transcriptional activity in a ligand-independent manner, thereby promoting tumor progression. Furthermore, CLDN6, at least in part, also regulated gene expression in an ERα-independent manner. IMPLICATIONS: The identification of this machinery highlights regulation of the transcription factors by cell adhesion to advance tumor progression.

Prognostic Significance of Aberrant Claudin-6 Expression in Endometrial Cancer

BACKGROUND

Among the claudin (CLDN) family, CLDN6 exhibits aberrant expression in various cancers, but its biological relevance has not yet been established. We generated a monoclonal antibody (mAb) against human CLDN6 and verified its specificity. By immunohistochemical staining and semi-quantification, we evaluated the relationship between CLDN6 expression and clinicopathological parameters in tissues from 173 cases of endometrial cancer.

RESULTS

The established mAb selectively recognized CLDN6 protein. Ten of the 173 cases (5.8%) showed high CLDN6 expression (score 3+), whereas 19 (11.0%), 18 (10.4%) and 126 (72.4%) cases revealed low CLDN6 expression (score 2+, 1+ and 0, respectively). In addition, intratumor heterogeneity of CLDN6 expression was observed even in the cases with high CLDN6 expression. The 5-year survival rates in the high and low CLDN6 groups was approximately 30% and 90%, respectively. Among the clinicopathological factors, the high CLDN6 expression was significantly associated with surgical stage III/IV, histological grade 3, lymphovascular space involvement, lymph node metastasis and distant metastasis. Furthermore, the high CLDN6 expression was an independent prognostic marker for overall survival of endometrial cancer patients (hazard ratio 3.50, p = 0.014).

CONCLUSIONS

It can be concluded that aberrant CLDN6 expression is useful to predict poor outcome for endometrial cancer and might be a promising therapeutic target.

Prevention of tumor risk associated with the reprogramming of human pluripotent stem cells

Human pluripotent embryonic stem cells have two special features: self-renewal and pluripotency. It is important to understand the properties of pluripotent stem cells and reprogrammed stem cells. One of the major problems is the risk of reprogrammed stem cells developing into tumors. To understand the process of differentiation through which stem cells develop into cancer cells, investigators have attempted to identify the key factors that generate tumors in humans. The most effective method for the prevention of tumorigenesis is the exclusion of cancer cells during cell reprogramming. The risk of cancer formation is dependent on mutations of oncogenes and tumor suppressor genes during the conversion of stem cells to cancer cells and on the environmental effects of pluripotent stem cells. Dissecting the processes of epigenetic regulation and chromatin regulation may be helpful for achieving correct cell reprogramming without inducing tumor formation and for developing new drugs for cancer treatment. This review focuses on the risk of tumor formation by human pluripotent stem cells, and on the possible treatment options if it occurs. Potential new techniques that target epigenetic processes and chromatin regulation provide opportunities for human cancer modeling and clinical applications of regenerative medicine.

Claudin-6 is a single prognostic marker and functions as a tumor-promoting gene in a subgroup of intestinal type gastric cancer

BACKGROUND

We aimed to identify novel tumor-promoting drivers highly expressed in gastric cancer (GC) that contribute to worsened prognosis in affected patients.

METHODS

Genes whose expression was increased and correlated with worse prognosis in GC were screened using datasets from the Cancer Genome Atlas and Gene Expression Omnibus. We examined Claudin-6 (CLDN6) immunoreactivity in GC tissues and the effect of CLDN6 on cellular functions in GC cell lines. The mechanisms underlying GC-promoting function of CLDN6 were also investigated.

RESULTS

CLDN6 was identified as a gene overexpressed in GC tumors as compared with adjacent non-tumorous tissues and whose increased expression was positively correlated with worse overall survival of GC patients, particularly those with Lauren's intestinal type GC, in data from multiple publicly available datasets. Additionally, membranous CLDN6 immunoreactivity detected in intestinal type GC tumors was correlated with worse overall survival. In CLDN6-expressing GC cells, silencing of CLDN6 inhibited cell proliferation and migration/invasion abilities, possibly via suppressing transcription of YAP1 and its downstream transcriptional targets at least in part.

CONCLUSIONS

This study identified CLDN6 as a GC-promoting gene, suggesting that CLDN6 to be a possible single prognostic marker and promising therapeutic target for a subset of GC patients.

An RNA vaccine drives expansion and efficacy of claudin-CAR-T cells against solid tumors

Chimeric antigen receptor (CAR)–T cells have shown efficacy in patients with B cell malignancies. Yet, their application for solid tumors has challenges that include limited cancer-specific targets and nonpersistence of adoptively transferred CAR-T cells. Here, we introduce the developmentally regulated tight junction protein claudin 6 (CLDN6) as a CAR target in solid tumors and a strategy to overcome inefficient CAR-T cell stimulation in vivo. We demonstrate that a nanoparticulate RNA vaccine, designed for body-wide delivery of the CAR antigen into lymphoid compartments, stimulates adoptively transferred CAR-T cells. Presentation of the natively folded target on resident antigen-presenting cells promotes cognate and selective expansion of CAR-T cells. Improved engraftment of CAR-T cells and regression of large tumors in difficult-to-treat mouse models was achieved at subtherapeutic CAR-T cell doses.

Antigen-specific oncolytic MV-based tumor vaccines through presentation of selected tumor-associated antigens on infected cells or virus-like particles

Recombinant vaccine strain-derived measles virus (MV) is clinically tested both as vaccine platform to protect against other pathogens and as oncolytic virus for tumor treatment. To investigate the potential synergism in anti-tumoral efficacy of oncolytic and vaccine properties, we chose Ovalbumin and an ideal tumor antigen, claudin-6, for pre-clinical proof of concept. To enhance immunogenicity, both antigens were presented by retroviral virus-like particle produced in situ during MV-infection. All recombinant MV revealed normal growths, genetic stability, and proper expression and presentation of both antigens. Potent antigen-specific humoral and cellular immunity were found in immunized MV-susceptible IFNAR^-/--CD46Ge mice. These immune responses significantly inhibited metastasis formation or increased therapeutic efficacy compared to control MV in respective novel in vivo tumor models using syngeneic B16-hCD46/mCLDN6 murine melanoma cells. These data indicate the potential of MV to trigger selected tumor antigen-specific immune responses on top of direct tumor lysis for enhanced efficacy.

Gastric Cancer With Primitive Enterocyte Phenotype: An Aggressive Subgroup of Intestinal-type Adenocarcinoma

A primitive cell-like gene expression signature is associated with aggressive phenotypes of various cancers. We assessed the expression of phenotypic markers characterizing primitive cells and its correlation with clinicopathologic and molecular characteristics in gastric cancer. Immunohistochemical analysis of a panel of primitive phenotypic markers, including embryonic stem cell markers (OCT4, NANOG, SALL4, CLDN6, and LIN28) and known oncofetal proteins (AFP and GPC3), was performed using tissue microarray on 386 gastric cancers. On the basis of the expression profiles, the 386 tumors were clustered into 3 groups: group 1 (primitive phenotype, n=93): AFP, CLDN6, GPC3, or diffuse SALL4 positive; group 2 (SALL4-focal, n=56): only focal SALL4 positive; and group 3 (negative, n=237): all markers negative. Groups 1 and 2 predominantly consisted of intestinal-type adenocarcinoma, including 13 fetal gut-like adenocarcinomas exclusively in group 1. Group 1 was significantly associated with higher T-stage, presence of vascular invasion and nodal metastasis when compared with groups 2 and 3. Group 1 was associated with patients' poor prognosis and was an independent risk factor for disease-free survival. Group 1 showed frequent TP53 overexpression and little association with Epstein-Barr virus or mismatch repair deficiency. Further analysis of the Cancer Genome Atlas data set validated our observations and revealed that tumors with primitive phenotypes were mostly classified as "chromosomal instability" in the Cancer Genome Atlas' molecular classification. We identified gastric cancer with primitive enterocyte phenotypes as an aggressive subgroup of intestinal-type/chromosomal instability gastric cancer. Therapeutic strategies targeting primitive markers, such as GPC3, CLDN6, and SALL4, are highly promising.

Claudin 6 expression is useful to distinguish myxofibrosarcomas from other myxoid soft tissue tumors

Myxofibrosarcoma (MFS) is characterized by abundant myxoid stroma, a wide spectrum of cytological atypia, and frequent local recurrence. Some soft tissue tumors with myxoid stroma can histologically mimic MFS, but have different biological behaviors. Here we sought to identify a useful diagnostic marker for MFS. After our analysis of the gene expression dataset from the Gene Expression Omnibus database, we focused on claudin 6 (CLDN 6). The status of CLDN 6 was assessed by immunohistochemistry in 61 samples of MFS and other (benign) myxoid soft tissue tumors (28 myxoma samples, 12 nodular fasciitis samples), 18 low-grade fibromyxoid sarcoma, 30 myxoid liposarcoma, 29 extraskeletal myxoid chondrosarcoma and 27 dedifferentiated liposarcoma with myxoid feature samples. The correlation between the expression of CLDN 6 and clinicopathological findings in MFS was also investigated. Immunohistochemically, high expression of CLDN 6 was observed in approx. 65% of the MFSs, whereas the benign soft tissue tumors did not show a high expression of CLDN 6. The expression of CLDN 6 in the MFS was significantly higher than those of other tumor specimens. Among the MFSs, the high expression of CLDN 6 was correlated with high FNCLCC grades and high AJCC stages. CLDN 6 may be useful for the differential diagnosis from benign myxoid tumor and for predicting the aggressive biological behavior of MFS.

Roles of the first-generation claudin binder, Clostridium perfringens enterotoxin, in the diagnosis and claudin-targeted treatment of epithelium-derived cancers

Given that most malignant tumors are derived from epithelium, developing a strategy for treatment of epithelium-derived cancers (i.e., carcinomas) is a pivotal issue in cancer therapy. Carcinomas, including ovarian, breast, prostate, and pancreatic cancers, are known to overexpress various claudins (CLDNs); in particular, CLDN-3 and -4 are frequently overexpressed in malignant case. The generation of CLDN binders is a key for expanding CLDN-targeted cancer therapy but has been delayed due to the small size of CLDN extracellular domains (approximately 50 amino acids for the first domain and 15 amino acids for the second) and their high homology among species. Interestingly, however, the receptors for Clostridium perfringens enterotoxin (CPE), a foodborne toxin in humans, happen to be identical to CLDN-3 and -4. Thus, the first CLDN binder, CPE, has provided us CLDN-targeted cancer therapy from a concept into a potential reality. In this review, we describe roles of CPE technology in cancer therapy and discuss future directions in the CLDN-targeting concept-to-therapy process.

Changes in the expression profiles of claudins during gonocyte differentiation and in seminomas

Testicular germ cell tumors (TGCTs) are the most common type of cancer in young men and their incidence has been steadily increasing for the past decades. TGCTs and their precursor carcinoma in situ (CIS) are thought to arise from the deficient differentiation of gonocytes, precursors of spermatogonial stem cells. However, the mechanisms relating failed gonocyte differentiation to CIS formation remain unknown. The goal of this study was to uncover genes regulated during gonocyte development that would show abnormal patterns of expression in testicular tumors, as prospective links between failed gonocyte development and TGCT. To identify common gene and protein signatures between gonocytes and seminomas, we first performed gene expression analyses of transitional rat gonocytes, spermatogonia, human normal testicular, and TGCT specimens. Gene expression arrays, pathway analysis, and quantitative real-time PCR analysis identified cell adhesion molecules as a functional gene category including genes downregulated during gonocyte differentiation and highly expressed in seminomas. In particular, the mRNA and protein expressions of claudins 6 and 7 were found to decrease during gonocyte transition to spermatogonia, and to be abnormally elevated in seminomas. The dynamic changes in these genes suggest that they may play important physiological roles during gonocyte development. Moreover, our findings support the idea that TGCTs arise from a disruption of gonocyte differentiation, and position claudins as interesting genes to further study in relation to testicular cancer.

Characterization of the first-in-class T-cell-engaging bispecific single-chain antibody for targeted immunotherapy of solid tumors expressing the oncofetal protein claudin 6

The fetal tight junction molecule claudin 6 (CLDN6) is virtually absent from any normal tissue, whereas it is aberrantly and frequently expressed in various cancers of high medical need. We engineered 6PHU3, a T-cell-engaging bispecific single chain molecule (bi-(scFv)₂) with anti-CD3/anti-CLDN6 specificities, and characterized its pharmacodynamic properties. Our data show that upon engagement by 6PHU3, T cells strongly upregulate cytotoxicity and activation markers, proliferate and acquire an effector phenotype. 6PHU3 exerts potent killing of cancer cells in vitro with EC₅₀ values in the pg/mL range. Subcutaneous xenograft tumors in NSG mice engrafted with human PBMCs are eradicated by 6PHU3 treatment and survival of mice is significantly prolonged. Tumors of 6PHU3-treated mice are strongly infiltrated with activated CD4⁺, CD8⁺ T cells and T_EM type cells but not T_regs and display a general activation of a mostly inflammatory phenotype. These effects are only observed upon bispecific but not monospecific engagement of 6PHU3. Together with the exceptionally cancer cell selective expression of the oncofetal tumor marker CLDN6, this provides a safeguard with regard to toxicity. In summary, our data shows that the concept of T-cell redirection combined with that of highly selective targeting of CLDN6-positive solid tumors is effective. Thus, exploring 6PHU3 for clinical therapy is warranted.

Low claudin-6 expression correlates with poor prognosis in patients with non-small cell lung cancer

Objective

Claudins are found in junctional complexes mediating cell adhesion and are involved in the attachment of tight junctions to the underlying cytoskeleton. Abnormal claudin-6 expression has been observed for a variety of malignant solid tumors, but the expression of claudin-6 in non-small cell lung cancer (NSCLC) has not yet been characterized.

Methods

Immunohistochemistry, reverse transcription-polymerase chain reaction (RT-PCR), and western blot analysis were used to quantify claudin-6 expression in 123 cases of NSCLC and non-cancerous adjacent tissue. We analyzed the relationship between claudin-6 expression and clinicopathological features of NSCLC. The Kaplan–Meier method was used to analyze postoperative survival rates, and the log-rank test was used to assess differences in survival rates. The Cox regression model was used to perform multivariate analysis.

Results

Claudin-6 expression was low for 61 of 123 (49.6%) NSCLC tissue samples and for 33 of 123 (26.8%) normal adjacent tissue samples. RT-PCR and western blot analyses confirmed the immunohistochemistry results. Claudin-6 expression was associated with lymph node metastasis (P<0.001) and TNM stage (P=0.007). Kaplan–Meier analysis indicated that patients with low claudin-6 expression had significantly lower survival rates than those with high claudin-6 expression. Multivariate analysis suggested that low claudin-6 expression was an independent indicator of prognosis in NSCLC patients.

Conclusion

Low claudin-6 expression is an independent prognostic biomarker that indicates a worse prognosis in patients with NSCLC.

Distinct claudin expression characterizes BRCA1-related breast cancer

AIMS

Members of the claudin family are involved in cancer progression and are differentially expressed in subtypes of breast cancer. Breast cancers in BRCA1 germ line mutation carriers have distinct clinicopathological characteristics. Biomarkers that discriminate between BRCA1-related and sporadic breast cancer cases are needed to improve early identification of mutation carriers. In this study we evaluated protein expression of five major claudins in BRCA1-related breast cancers in comparison with sporadic controls.

METHODS AND RESULTS

Forty breast cancers in BRCA1 mutation carriers and 40 age-matched sporadic breast cancers were immunohistochemically stained for claudins 1, 3, 4, 6 and 7. Total intratumoural expression levels were compared to those in the surrounding normal tissue. In addition, subcellular claudin expression was scored. Higher overexpression rates were observed for all five claudins in BRCA1-related breast cancers when compared to sporadic controls. In multivariate analysis, overexpression of claudin 3, 4, and 7 was mainly dependent on ER-status, whereas overexpression of claudin 6 and high membranous expression of claudin 1 were independent of other characteristics.

CONCLUSIONS

BRCA1-related breast cancers are characterized by frequent overexpression of claudins. Especially claudin 1 and 6 expression may help to discriminate mutation carriers from sporadic breast cancer cases.

Aberrantly activated claudin 6 and 18.2 as potential therapy targets in non-small-cell lung cancer

Claudins (CLDNs) are central components of tight junctions that regulate epithelial-cell barrier function and polarity. Altered CLDN expression patterns have been demonstrated in numerous cancer types and lineage-specific CLDNs have been proposed as therapy targets. The objective of this study was to assess which fraction of patients with non-small-cell lung cancer (NSCLC) express CLDN6 and CLDN18 isoform 2 (CLDN18.2). Protein expression of CLDN6 and CLDN18.2 was examined by immunohistochemistry on a tissue microarray (n = 355) and transcript levels were supportively determined based on gene expression microarray data from fresh-frozen NSCLC tissues (n = 196). Both were analyzed with regard to frequency, distribution and association with clinical parameters. Immunohistochemical analysis of tissue sections revealed distinct membranous positivity of CLDN6 (6.5%) and CLDN18.2 (3.7%) proteins in virtually non-overlapping subgroups of adenocarcinomas and large-cell carcinomas. Pneumocytes and bronchial epithelial cells were consistently negative. Corresponding to the protein expression, in subsets of non-squamous lung carcinoma high mRNA levels of CLDN6 (7-16%) and total CLDN18 (5-12%) were observed. Protein expression correlated well with total mRNA expression of the corresponding gene (rho = 0.4-0.8). CLDN18.2 positive tumors were enriched among slowly proliferating, thyroid transcription factor 1 (TTF-1)-negative adenocarcinomas, suggesting that isoform-specific CLDN expression may delineate a specific subtype. Noteworthy, high CLDN6 protein expression was associated with worse prognosis in lung adenocarcinoma in the univariate [hazard ratio (HR): 1.8; p = 0.03] and multivariate COX regression model (HR: 1.9; p = 0.02). These findings encourage further clinical exploration of targeting ectopically activated CLDN expression as a valuable treatment concept in NSCLC.