Therapeutic Potential of CLDN Family Proteins in Ovarian Cancer: Emerging Biomarkers and Targets
Background: Claudins (CLDNs), key components of tight junctions, are dysregulated in various cancers. However, the roles and therapeutic potential of specific CLDN family members-particularly CLDN6, CLDN9, and CLDN10-in ovarian cancer (OC) remain incompletely defined. To address this gap, we conducted a comprehensive analysis of the CLDN family to identify novel diagnostic and prognostic biomarkers as well as potential therapeutic targets for OC. Methods: Gene expression profiles and corresponding clinical data from The Cancer Genome Atlas ovarian cancer cohort (TCGA-OV) and two Gene Expression Omnibus (GEO) datasets (GSE18520, GSE26712) were analyzed. Differential expression of CLDN genes between OC and normal tissues was evaluated using R with appropriate bioinformatics packages (e.g., limma). Logistic regression models were employed to calculate odds ratios (ORs), and receiver operating characteristic (ROC) curves were generated across all datasets to identify consistently dysregulated CLDNs associated with OC. Prognostic hazard ratios (HRs) for these CLDNs were extracted from the Kaplan-Meier Plotter (KM Plotter) database and synthesized using a random-effects model to assess their associations with overall survival. Intersection analysis was performed to identify CLDNs exhibiting both significant differential expression and prognostic significance. Candidate targets underwent comprehensive validation, including single-cell RNA sequencing (scRNA-seq) to characterize cell-type-specific expression patterns. Notably, Key findings regarding CLDN6 were further validated by immunohistochemistry (IHC) on an independent tissue microarray (TMA), as well as functional assays in OC cell lines following siRNA-mediated knockdown. These included transwell invasion, wound healing (scratch) test, and measurements of mitochondrial depolarization, reactive oxygen species (ROS) accumulation, cell cycle arrest, and apoptosis. Results: CLDN6, CLDN9, and CLDN10 were consistently and significantly upregulated in OC compared to normal tissues across all datasets. Single-cell RNA sequencing revealed that CLDN6 and CLDN10 were predominantly expressed in malignant epithelial cell subsets, a pattern associated with aggressive tumor phenotypes. Meta-analysis of HRs showed that HR >1 in CLDN6 and HR <1 in CLDN10. Although CLDN10 is highly expressed in tumor cells, its hazard ratio (HR) is less than 1, and the underlying mechanism of this gene remains unclear. Experiments have confirmed that CLDN6 is closely associated with tumor invasion. Computational analysis, meta-analysis, and single-cell data collectively confirm that only CLDN6 is a clearly defined gene closely associated with tumor progression, a finding subsequently validated by experimental results. Notably, the combined signature comprising CLDN6, CLDN9, and CLDN10 exhibited superior diagnostic performance, with higher area under the curve (AUC) values in ROC analysis, compared to individual CLDNs or established OC biomarkers such as carbohydrate antigen 125 (CA125), human epididymis 4 (HE4), carcinoembryonic antigen (CEA), and alpha-fetoprotein (AFP). The signature also showed enhanced prognostic discrimination, as indicated by time-dependent ROC analysis. Protein overexpression of these targets was validated by IHC and Western blot. Functional assays further demonstrated that siRNA-mediated knockdown of CLDN6 significantly inhibited the proliferation of OC cells, promoted cell apoptosis, increased production of ROS, induced G1 phase arrest, inhibited cell invasion and migration in vitro. Furthermore, western blot analysis identified that knockdown of CLDN6 repressed the Wnt/β-catenin pathway. Nude mice experiments indicated that CLDN6 knockdown in OC cells dramatically suppresses the tumor growth and lung metastasis in vivo. Conclusions: CLDN6, CLDN9, and CLDN10 are critically involved in the pathogenesis and progression of OC. A biomarker panel combining these three claudins demonstrates superior diagnostic and prognostic performance compared to individual markers and established clinical biomarkers such as CA125 and HE4. Notably, functional evidence indicates that CLDN6 plays a pivotal role in regulating malignant phenotypes, highlighting its potential as a novel therapeutic target. These findings collectively support the clinical utility of the CLDN6/9/10 axis as both a non-invasive biomarker signature and a promising avenue for targeted intervention in ovarian cancer.
