Dichotomous roles of claudins as tumor promoters or suppressors: lessons from knockout mice

Omics analysis revealed the intestinal toxicity induced by aflatoxin B1 and aflatoxin M1

Aflatoxin B1 (AFB1), a common mycotoxin, can occur in agricultural products. As a metabolite of AFB1, aflatoxin M1 (AFM1) mainly exist in dairy products. These two mycotoxins threaten human health, although it is unclear how they affect the function of the intestinal barrier. In this study, mice were exposed to AFB1 (0.3 mg/kg body b.w.) and AFM1(3.0 mg/kg b.w.) either individually or in combination for 28 days to explore the main differentially expressed proteins (DEPs) and the associated enriched pathways. These findings were preliminarily verified by the transcriptomic and proteomic analyses in differentiated Caco-2 cells. The results revealed that AFB1 and AFM1 exposure in mice disrupted the function of the intestinal barrier, and the combined toxicity was greater than that of each toxin alone. Further proteomic analysis in mice demonstrated that the mechanisms underlying these differences could be explained as follows: (i) lipid metabolism was enriched by AFB1-induced DEPs. (ii) protein export pathway was stimulated by AFM1-induced DEPs. (iii) cell metabolic ability was inhibited (as evidenced by changes in UDP-GT1, UDP-GT2, and Gatm6), apoptosis was induced (MAP4K3), and epithelial cell integrity was disrupted (Claudin7 and IQGAP2), resulting in more extensive intestinal damage after combined treatment. In conclusion, the hazardous impact of co-exposure to AFB1 and AFM1 from proteomic perspectives was demonstrated in the present study.

First-in-human CLDN18.2 functional diagnostic pet imaging of digestive system neoplasms enables whole-body target mapping and lesion detection

PURPOSE

Claudin 18.2 (CLDN18.2) is a reliable target for lesion detection and could have clinical implications for epithelial tumors, especially digestive system neoplasms. However, there is no predictive technology for accurate whole-body mapping of CLDN18.2 expression in patients. This study assessed the safety of the 124I-18B10(10L) tracer and the feasibility of mapping whole-body CLDN18.2 expression using PET functional imaging.

METHODS

The 124I-18B10(10L) probe was synthesized manually, and preclinical experiments including binding affinity and specific targeting ability were conducted after testing in vitro model cells. Patients with pathologically confirmed digestive system neoplasms were enrolled in an ongoing, open-label, single-arm, first-in-human (FiH) phase 0 trial (NCT04883970). 124I-18B10(10L) PET/CT or PET/MR and 18F-FDG PET were performed within one week.

RESULTS

124I-18B10(10L) was successfully constructed with an over 95% radiochemical yield. The results of preclinical experiments showed that it had high stability in saline and high affinity in CLDN18.2 overexpressing cells (Kd = 4.11 nM). Seventeen patients, including 12 with gastric cancers, 4 with pancreatic cancers, and 1 with cholangiocarcinoma were enrolled. 124I-18B10(10L) displayed high uptake in the spleen and liver, and slight uptake in the bone marrow, lung, stomach and pancreas. The tracer uptake SUVmax in tumor lesions ranged from 0.4 to 19.5. Compared with that in lesions that had been treated with CLDN18.2-targeted therapy, 124I-18B10(10L) uptake was significantly higher in lesions that had not. Regional 124I-18B10(10L) PET/MR in two patients showed high tracer uptake in metastatic lymph nodes.

CONCLUSIONS

124I-18B10(10L) was successfully prepared and exhibited a high binding affinity and CLDN18.2 specificity in preclinical studies. As an FiH CLDN18.2 PET tracer, 124I-18B10(10L) was shown to be safe with acceptable dosimetry and to clearly reveal most lesions overexpressing CLDN18.2.

TRIAL REGISTRATION

NCT04883970; URL: https://register.

CLINICALTRIALS

gov/ . Registered 07 May 2021.

Paradoxical Behavior of Oncogenes Undermines the Somatic Mutation Theory

The currently accepted theory on the influence of DNA mutations on carcinogenesis (the Somatic Mutation Theory, SMT) is facing an increasing number of controversial results that undermine the explanatory power of mutated genes considered as "causative" factors. Intriguing results have demonstrated that several critical genes may act differently, as oncogenes or tumor suppressors, while phenotypic reversion of cancerous cells/tissues can be achieved by modifying the microenvironment, the mutations they are carrying notwithstanding. Furthermore, a high burden of mutations has been identified in many non-cancerous tissues without any apparent pathological consequence. All things considered, a relevant body of unexplained inconsistencies calls for an in depth rewiring of our theoretical models. Ignoring these paradoxes is no longer sustainable. By avoiding these conundrums, the scientific community will deprive itself of the opportunity to achieve real progress in this important biomedical field. To remedy this situation, we need to embrace new theoretical perspectives, taking the cell-microenvironment interplay as the privileged pathogenetic level of observation, and by assuming new explanatory models based on truly different premises. New theoretical frameworks dawned in the last two decades principally focus on the complex interaction between cells and their microenvironment, which is thought to be the critical level from which carcinogenesis arises. Indeed, both molecular and biophysical components of the stroma can dramatically drive cell fate commitment and cell outcome in opposite directions, even in the presence of the same stimulus. Therefore, such a novel approach can help in solving apparently inextricable paradoxes that are increasingly observed in cancer biology.

Micronutrient Improvement of Epithelial Barrier Function in Various Disease States: A Case for Adjuvant Therapy

The published literature makes a very strong case that a wide range of disease morbidity associates with and may in part be due to epithelial barrier leak. An equally large body of published literature substantiates that a diverse group of micronutrients can reduce barrier leak across a wide array of epithelial tissue types, stemming from both cell culture as well as animal and human tissue models. Conversely, micronutrient deficiencies can exacerbate both barrier leak and morbidity. Focusing on zinc, Vitamin A and Vitamin D, this review shows that at concentrations above RDA levels but well below toxicity limits, these micronutrients can induce cell- and tissue-specific molecular-level changes in tight junctional complexes (and by other mechanisms) that reduce barrier leak. An opportunity now exists in critical care—but also medical prophylactic and therapeutic care in general—to consider implementation of select micronutrients at elevated dosages as adjuvant therapeutics in a variety of disease management. This consideration is particularly pointed amidst the COVID-19 pandemic.

The role of GTPase-activating protein ARHGAP26 in human cancers

Rho GTPases are molecular switches that play an important role in regulating the behavior of a variety of tumor cells. RhoA GTPase-activating protein 26 (ARHGAP26) is a GTPase-activating protein and inhibits the activity of Rho GTPases by promoting the hydrolytic ability of Rho GTPases. It also affects tumorigenesis and progression of various tumors through several methods, including formation of abnormal fusion genes and circular RNA. This review summarizes the biological functions and molecular mechanisms of ARHGAP26 in different tumors, proposes the potential clinical value of ARHGAP26 in cancer treatment, and discusses current issues that need to be addressed.

Impacts of Fructose on Intestinal Barrier Function, Inflammation and Microbiota in a Piglet Model

The metabolic disorder caused by excessive fructose intake was reported extensively and often accompanied by intestinal barrier dysfunction. And the rising dietary fructose was consumed at an early age of human. However, related researches were almost conducted in rodent models, while in the anatomy and physiology of gastrointestinal tract, pig is more similar to human beings than rodents. Hence, weaned piglets were chosen as the model animals in our study to investigate the fructose’s impacts on intestinal tight junction, inflammation response and microbiota structure of piglets. Herein, growth performance, inflammatory response, oxidation resistance and ileal and colonic microbiota of piglet were detected after 35-day fructose supplementation. Our results showed decreased tight junction gene expressions in piglets after fructose addition, with no obvious changes in the growth performance, antioxidant resistance and inflammatory response. Moreover, fructose supplementation differently modified the microbiota structures in ileum and colon. In ileum, the proportions of Streptococcus and Faecalibacterium were higher in Fru group (fructose supplementation). In colon, the proportions of Blautia and Clostridium sensu stricto 1 were higher in Fru group. All the results suggested that tight junction dysfunction might be an earlier fructose-induced event than inflammatory response and oxidant stress and that altered microbes in ileum and colon might be the potential candidates to alleviate fructose-induced intestinal permeability alteration.

Identification of Claudin-6 as a Molecular Biomarker in Pan-Cancer Through Multiple Omics Integrative Analysis

Claudin-6 (CLDN6) is one of the 27 family members of claudins and majorly involved in the tight junction and cell-to-cell adhesion of epithelial cell sheets, playing a significant role in cancer initiation and progression. To provide a more systematic and comprehensive dimension of identifying the diverse significance of CLDN6 in a variety of malignant tumors, we explored CLDN6 through multiple omics data integrative analysis, including gene expression level in pan-cancer and comparison of CLDN6 expression in different molecular subtypes and immune subtypes of pan-cancer, targeted protein, biological functions, molecular signatures, diagnostic value, and prognostic value in pan-cancer. Furthermore, we focused on uterine corpus endometrial carcinoma (UCEC) and further investigated CLDN6 from the perspective of the correlations with clinical characteristics, prognosis in different clinical subgroups, co-expression genes, and differentially expressed genes (DEGs), basing on discussing the validation of its established monoclonal antibody by immunohistochemical staining and semi-quantification reported in the previous study. As a result, CLDN6 expression differs significantly not only in most cancers but also in different molecular and immune subtypes of cancers. Besides, high accuracy in predicting cancers and notable correlations with prognosis of certain cancers suggest that CLDN6 might be a potential diagnostic and prognostic biomarker of cancers. Additionally, CLDN6 is identified to be significantly correlated with age, stage, weight, histological type, histologic grade, and menopause status in UCEC. Moreover, CLDN6 high expression can lead to a worse overall survival (OS), disease-specific survival (DSS), and progression-free interval (PFI) in UCEC, especially in different clinical subgroups of UCEC. Taken together, CLDN6 may be a remarkable molecular biomarker for diagnosis and prognosis in pan-cancer and an independent prognostic risk factor of UCEC, presenting to be a promising molecular target for cancer therapy.

Targeting claudins in cancer: diagnosis, prognosis and therapy

Increasing evidence has linked claudins to signal transduction and tumorigenesis. The expression of claudins is frequently dysregulated in the context of neoplastic transformation, suggesting their promise as biomarkers for diagnosis and prognosis or targets for treatment. Claudin binders (Clostridium perfringens enterotoxin and monoclonal antibody) have been tested in preclinical experiments, and some of them have progressed into clinical trials involving patients with certain cancers. However, the clinical development of many of these agents has not advanced to clinical applications. Herein, I review the current status of preclinical and clinical investigations of agents targeting claudins for diagnosis, prognosis and therapy. I also discuss the potential of combining claudin binders with other currently approved therapeutic agents.

[A review on the effect of Claudin-18 on bronchopulmonary dysplasia in preterm infants]

Bronchopulmonary dysplasia (BPD) has the main manifestations of pulmonary edema in the early stage and characteristic alveolar obstruction and microvascular dysplasia in the late stage, which may be caused by structural and functional destruction of the lung epithelial barrier. The Claudin family is the main component of tight junction and plays an important role in regulating the permeability of paracellular ions and solutes. Claudin-18 is the only known tight junction protein solely expressed in the lung. The lack of Claudin-18 can lead to barrier dysfunction and impaired alveolar development, and the knockout of Claudin-18 can cause characteristic histopathological changes of BPD. This article elaborates on the important role of Claudin-18 in the development and progression of BPD from the aspects of lung epithelial permeability, alveolar development, and progenitor cell homeostasis, so as to provide new ideas for the pathogenesis and clinical treatment of BPD.

Analysis of the expression and genetic alteration of CLDN18 in gastric cancer

Claudin 18 (CLDN18) is a transmembrane protein that localizes to apical regions to form tight junction complexes. Abnormal expression of CLDN18 has been reported in gastric cancer (GC). The expression, genetic alterations, and prognostic role of CLDN18 were analyzed using public data from The Cancer Genome Atlas (TCGA), Gene Expression Omnibus (GEO), and Human Protein Atlas (HPA) databases using multiple online tools. The biological network of CLDN18 was determined using GeneMANIA. Expression of CLDN18 was restricted to lung and stomach in normal tissues, was significantly downregulated in GC, but was ectopically overexpressed in some other cancer types. There was no correlation between mRNA expression of CLDN18 and the clinicopathology of GC, although expression was higher in the Epstein-Barr virus (EBV)-positive subgroup than other subgroups. Genetic alteration of CLDN18 was not a common event in GC; the main alteration was gene fusion with ARHGAP26. CLDN18 expression did not predict the overall survival (OS) of GC patients. This study summarizes the expression features of CLDN18 in GC and suggests it may serve as a biomarker and therapy target for GC.

Evaluation and reflection on claudin 18.2 targeting therapy in advanced gastric cancer

Claudin 18.2 (CLDN18.2) is a tight-junction protein. CLDN18.2-targeting strategy has cut a striking figure in CLDN18.2 positive patients with advanced gastric cancer. Zolbetuximab, the CLDN18.2 antibody, obtained a better clinical benefit in patients compared with the controlled. In phase II trials, combination treatment of epirubicin, oxaliplatin and capecitabine (EOX) + zolbetuximab achieved the optimal effects of overall survival which extended to 13.2 months with tolerable safety events, indicating its greater potential playing the second promising target in gastric cancer. This review will reveal the definitive clinical benefit CLDN18.2-targeting therapies have achieved and update the highlighting development (like chimeric antigen receptor T-cell immunotherapy) to CLDN18.2 positive patients. We then focus on 10 questions arisen from recent progress and anticipate to provide a future perspective for novel cancer treatment.

Role of Claudin Proteins in Regulating Cancer Stem Cells and Chemoresistance-Potential Implication in Disease Prognosis and Therapy

Claudins are cell–cell adhesion proteins, which are expressed in tight junctions (TJs), the most common apical cell-cell adhesion. Claudin proteins help to regulate defense and barrier functions, as well as differentiation and polarity in epithelial and endothelial cells. A series of studies have now reported dysregulation of claudin proteins in cancers. However, the precise mechanisms are still not well understood. Nonetheless, studies have clearly demonstrated a causal role of multiple claudins in the regulation of epithelial to mesenchymal transition (EMT), a key feature in the acquisition of a cancer stem cell phenotype in cancer cells. In addition, claudin proteins are known to modulate therapy resistance in cancer cells, a feature associated with cancer stem cells. In this review, we have focused primarily on highlighting the causal link between claudins, cancer stem cells, and therapy resistance. We have also contemplated the significance of claudins as novel targets in improving the efficacy of cancer therapy. Overall, this review provides a much-needed understanding of the emerging role of claudin proteins in cancer malignancy and therapeutic management.