Abstract
Background/Aim: Claudin 18.2 (CLDN18.2) has emerged as a highly selective biomarker and its abnormal expression has been reported in various primary malignant tumors. Recently, CLDN18.2 has gained attention as both a prognostic biomarker and a potential therapeutic target in gastric and gastroesophageal junction cancer. The purpose of this study was to investigate CLDN18.2 expression in a large cohort of 168 prostate cancer (PC) tissues, assess its correlation with clinicopathological factors, and evaluate its potential as a therapeutic target for anti-CLDN18.2 therapy.
Materials and Methods: Immunohistochemical staining was conducted using an approved diagnostic CLDN18.2 immunohistochemistry protocol (Ventana, 43-14A clone). Interpretation was carried out following the general rules for staining evaluation.
Results: Non-neoplastic gastric mucosa, used as a positive control for CLDN18.2 immunostaining, exhibited strong membranous staining. In contrast, no CLDN18.2 expression was detected in normal ductal and acinar cells of prostate tissue, nor in any of the 168 variable PC tissues.
Conclusion: CLDN18.2 is not expressed in normal prostate tissue or PC, suggesting that it is unlikely to serve as a prognostic marker or a potential target for immunotherapy in PC.
Introduction
Prostate cancer (PC) is the second most frequent cancer diagnosis made in men and the fifth leading cause of death worldwide (1). The heterogeneous nature of PC complicates its diagnosis, prognosis, and treatment. Numerous biomarkers have been explored for predictive, diagnostic, prognostic, and risk assessment purposes through various population studies. However, to date, no promising biomarker has been universally approved or validated for PC (2). Prostate-specific antigen (PSA) remains the standard biomarker for PC detection and screening, but its limited specificity and sensitivity reduce its diagnostic accuracy (3). Moreover, despite advancements in treatment modalities for PC, more than 30% of patients may eventually have their PC progress and metastasize/relapse and ultimately leading to fatal outcomes (4).
Claudins are integral membrane proteins that form tight junctions between cells, playing a crucial role in regulating paracellular transport and maintaining epithelial integrity (5). Among them, Claudin 18.2 (CLDN18.2) has emerged as a highly selective biomarker with limited expression in normal tissues and is involved in the proliferation, differentiation, and migration of tumor cells (6). Abnormal expression of CLDN18.2 has been reported in various primary malignant tumors, including gastric/gastroesophageal junction, pancreatic, ovarian, and non-small-cell lung cancer (6-9). Recently, CLDN18.2 has garnered attention as a potential therapeutic target in gastric and gastroesophageal junction cancers, with promising results from clinical trials involving Zolbetuximab, an antibody targeting CLDN18.2 (10).
In this study, we aimed to investigate CLDN18.2 expression in a large cohort of 168 prostate cancer (PC) tissues, examine its correlation with clinicopathological factors, and assess its potential as a candidate for anti-CLDN18.2 immunotherapy.
Materials and Methods
Study samples. We selected 168 cases of PC, including 162 prostatic acinar adenocarcinomas, four ductal adenocarcinomas, and two mucinous adenocarcinomas. Clinical, pathological, and follow-up data were collected from the patients’ medical records.
Immunohistochemistry with tissue microarray block. Tissue microarrays were constructed from paraffin-embedded blocks of PC tissues. Two to four 1.5-mm tissue cores were selected per patient, including cores from the most dominant Gleason grade, secondary Gleason grade, and adjacent benign prostatic tissue. Immunohistochemical staining was performed using an approved diagnostic protocol (11). Sections (4 μm thick) were deparaffinized and re-hydrated through serial treatments with xylene and ethanol. Endogenous peroxidase was blocked by incubation in 3% H2O2 for 10 min, followed by heat-induced antigen retrieval. IHC staining was carried out using a CLDN18.2 antibody (clone 43-14A; Ventana Medical Systems, Tucson, AZ, USA) with an autostainer (Benchmark ULTRA, Ventana Medical Systems) and an OptiView DAB Detection Kit (Ventana Medical Systems), in accordance with the manufacturer’s instructions. Interpretation of the staining was conducted according to the general rules for CLDN18.2 Staining Evaluation (11).
Results
CLDN18.2 expression. We performed CLDN18.2 staining in gastric and gastroesophageal junction cancers and used it as both a positive and negative control in this study. Diffuse and strong membranous staining of CLDN18.2 was observed in non-neoplastic gastric epithelium, while no staining was detected in adjacent adenocarcinoma (Figure 1). In prostate tissue, CLDN18.2 expression was absent in normal prostate glands (Figure 2A), prostatic intra-epithelial neoplasia, and in all 168 prostate cancers (including prostatic acinar cell adenocarcinoma (Figure 2B), ductal adenocarcinoma (Figure 2C), and mucinous adenocarcinoma (Figure 2D).
Non-neoplastic gastric glands exhibit strong membranous expression of Claudin 18.2 in contrast to the absence of Claudin 18.2 expression in the adjacent adenocarcinoma.
Lack of Claudin 18.2 expression in both normal prostate tissue or prostate cancer. (A) Normal prostate glands, (B) acinar adenocarcinoma, (C) ductal adenocarcinoma, (D) mucinous adenocarcinoma.
Discussion
Early detection of PC in the localized stage is associated with a relatively favorable prognosis and long-term survival (12). However, even among patients with early-stage PC, some of them show dismal clinical outcomes with surgery or radiation therapy alone (13). Therefore, there is a need for development of new therapeutic targets to improve the survival and the identification of molecular markers that are associated with aggressiveness and metastasis is essential for predicting clinical outcomes of PC.
Aberrant CLDN18.2 expression has been reported in cancers, including gastric/gastroesophageal junction cancer, pancreatic cancer, lung adenocarcinoma, and ovarian cancer, although its expression varies across cancer types and subtypes within each organ. In advanced gastric and gastroesophageal junction adenocarcinomas, aberrant CLDN18.2 expression was significantly associated with factors such as age under 70 years, Epstein-Barr virus positivity, higher disease stage (stages III and IV) at diagnosis, peritoneal involvement, and lower incidence of liver metastases. However, it did not show significant associations with overall survival and molecular markers such as human epidermal growth factor receptor 2 (HER2) status, mismatch repair (MMR) status, or programmed death-ligand 1 (PD-L1) combined positive score (CPS) (8, 9, 11, 14-16). Zolbetuximab, a mouse chimeric monoclonal antibody with a human IgG1 constant region, specifically binds CLDN18.2 and mediates tumor cell death via antibody-dependent cellular cytotoxicity (17). Recent studies have demonstrated that zolbetuximab, in combination with chemotherapy demonstrated a survival benefit in patients with CLDN18.2-positive and HER-2-negative gastric or gastroesophageal junction cancers, as shown in the global phase III SPOTLIGHT and GLOW trials (18). In pancreatic cancer, increased CLDN18.2 expression was associated with aggressive clinical outcomes and showed high sensitivity and specificity for diagnosing biliary tract adenocarcinoma or intraepithelial neoplasia (5, 19). In lung tissue, CLDN18.2 expression was absent in normal lung tissue and bronchial mucosal epithelium. However, slowly proliferating TTF-1 negative adenocarcinomas and large-cell carcinomas exhibited CLDN18.2 expression, suggesting that CLDN 18.2 expression in lung carcinoma may be associated with specific subtypes (6, 20). In tubo-ovarian cancer, CLDN18.2 expression was restricted to the mucinous subtypes (21).
Rashad et al. previously reported that positive CLDN18 (but not CLDN18.2) expression was detected in 30% of PC cases and was correlated with lymph node metastasis, Gleason grade, and tumor stage (22). However, in this study, CLDN18.2 showed no expression in normal prostate glands, prostatic intraepithelial neoplasia, or any of the 168 PC cases (including prostatic acinar cell adenocarcinoma, ductal adenocarcinoma, and mucinous adenocarcinoma).
Conclusion
We investigated the expression of CLDN18.2 in normal prostate tissue and PCs. Despite our expectation of detecting aberrant CLDN18.2 expression in PC, no such expression was found in normal prostate glands, prostatic intraepithelial neoplasia, or any of the PC. These findings suggest that CLDN18.2 may not serve as a viable biomarker for PC.
Footnotes
Authors’ Contributions
MJG conceived and designed the manuscript. JAB and YRS conducted the literature review on CLDN18.2 and performed the analysis. MJG drafted the manuscript. JAB and YRS reviewed and revised it. All Authors have read and approved the final manuscript.
Conflicts of Interest
The Authors declare that they have no competing interests in relation to this study.
Funding
This study was supported by a Yeungnam University Research Grant (2023).
- Received December 24, 2024.
- Revision received January 7, 2025.
- Accepted January 8, 2025.
- Copyright © 2025 The Author(s). Published by the International Institute of Anticancer Research.
This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY-NC-ND) 4.0 international license (https://creativecommons.org/licenses/by-nc-nd/4.0).
