Claudin-18 Splice Variant 2 Is a Pan-Cancer Target Suitable for Therapeutic Antibody Development

Abstract

Purpose: Antibody-based cancer therapies have emerged as the most promising therapeutics in oncology. The purpose of this study was to discover novel targets for therapeutic antibodies in solid cancer. Experimental Design:We combined data mining and wet-bench experiments to identify strictly gastrocyte lineage^specific cell surface molecules and to validate them as therapeutic antibody targets. Results: We identified isoform 2 of the tight junction molecule claudin-18 (CLDN18.2) as a highly selective cell lineage marker. Its expression in normal tissues is strictly confined to differentiated epithelial cells of the gastric mucosa, but it is absent from the gastric stem cell zone. CLDN18.2 is retained on malignant transformation and is expressed in a significant proportion of primary gastric cancers and the metastases thereof. In addition to its orthotopic expression, we found frequent ectopic activation of CLDN18.2 in pancreatic, esophageal, ovarian, and lung tumors, correlating with distinct histologic subtypes. The activation of CLDN18.2 depends on the binding of the transcription factor cyclic AMP^responsive element binding protein to its unmethylated consensus site. Most importantly, we were able to raise monoclonal antibodies that bind to CLDN18.2 but not to its lung-specific splice variant and recognize the antigen on the surface of cancer cells. Conclusions: Its highly restricted expression pattern in normal tissues, its frequent ectopic activation in a diversity of human cancers, and the ability to specifically target this molecule at the cell surface of tumor cells qualify CLDN18.2 as a novel, highly attractive pan-cancer target for the antibody therapy of epithelial tumors.Gastroesophageal and pancreatic cancers are among the malignancies with the highest unmet medical needs (1). Gastric cancer is the second leading cause of cancer death worldwide. In 2002, f1.4 million people worldwide developed gastroesophageal cancers and 1.1 million died (2). Esophageal cancer incidence has increased in recent decades, coinciding with a shift in histologic type and primary tumor location. Adenocarcinoma of the esophagus is now more prevalent than squamous cell carcinoma in the United States and Western Europe, with most tumors located in the distal esophagus (3).The overall 5-year survival rates for gastroesophageal cancers are 20% to 25% despite the aggressiveness of established standard treatments associated with substantial side effects (4, 5). For pancreatic cancer, there is an even greater medical need. Due to the advanced state of the disease at the time of diagnosis, the prognosis is extremely poor, with median survival times of less than 6 months and a 5-year survival rate of <5.5%. The lack of a major benefit from the various newergeneration combination chemotherapy regimens for these cancers has stimulated research into the use of targeted agents, such as small molecule -based kinase inhibitors and monoclonal antibodies (mAb; ref. 6). However, mAbs, such as bevacizumab, cetuximab, and trastuzumab...

Highly Specific Auto-Antibodies against Claudin-18 Isoform 2 Induced by a Chimeric HBcAg Virus-Like Particle Vaccine Kill Tumor Cells and Inhibit the Growth of Lung Metastases

“…These specifications imposed several requirements on the epitope to be selected. First, crossreactivity of antibodies with the highly related splice variant 1 of CLDN18, which is expressed in healthy lung tissue, had to be prevented to avoid harm to this toxicity-relevant organ (17,25). Both splice variants of the tetraspanin CLDN18 vary in their first extracellular domain (8 amino acids of 51 differ between both isoforms; Fig.…”

“…As a model antigen, we chose isoform 2 of the tight junction molecule claudin-18 (CLDN18.2), which is associated with gastroesophageal, pancreatic, and other cancers (16,17). CLDN18.2 is a highly selective cell-lineage marker and confined to short-lived differentiated epithelia of the gastric mucosa; it is absent from the gastric stem cell zone and any other healthy tissue (17).…”

“…CLDN18.2 is a highly selective cell-lineage marker and confined to short-lived differentiated epithelia of the gastric mucosa; it is absent from the gastric stem cell zone and any other healthy tissue (17). A recombinant mAb against this target is currently in clinical Phase II trials, which makes the evaluation of CLDN18.2 as a target for active immunization therapy particularly interesting.…”

Claudin-18 Is an Early-Stage Marker of Pancreatic Carcinogenesis

“…Therefore, CLDN18 can serve as an exceptionally useful early-stage marker of pancreatic ductal neoplasms. Of the two CLDN18 isoform transcripts, CLDN18.2 is a more highly selective gastric lineage marker and determines the gastric phenotype in neoplastic conditions (Sahin et al 2008;Niimi et al 2001;Sentani et al 2008;Sanada et al 2006;Yasui et al 2009). Although the antibody used in the present immunohistochemical study does not discriminate between these two isoforms, the CLDN18 immunoreactivity in the IPMNs was correlated with the expression of known gastric markers (MUC5AC and MUC6) and was inversely correlated with the expression of the intestinal markers (MUC2 and CDX2).…”

Transcriptional Control of Tight Junction Proteins via a Protein Kinase C Signal Pathway in Human Telomerase Reverse Transcriptase-Transfected Human Pancreatic Duct Epithelial Cells

“…16 In pancreatic cancer, claudin-4 and -18 are highly expressed 17,18 and are diagnostic or therapeutic targets of monoclonal antibodies against their extracellular loops. 19,20 In addition, because claudin-4 is also a high-affinity receptor of CPE, 21 fulllength CPE with a direct cytotoxic effect or the C-terminal receptor binding domain of CPE without a cytotoxic effect are used for selective treatment or drug delivery against claudin-4-expressing tumors. 17,22,23 However, the regulatory mechanisms of claudin-based tight junctions remain unknown even in normal human pancreatic duct epithelial (HPDE) cells.…”