Abstract 3919: The emerging role of claudin 18.2 as a potential driver in gastric cancer progression.

Abstract Gastric cancer (GC) represents one of the most impactful cancers on human health. Because of its strong aggressiveness and lack of resolutive therapies, researches are focusing their efforts on identifying novel molecular targets and new therapeutic strategies. Claudin 18.2 is a tight-junction protein expressed by the normal gastric epithelium. During malignant transformation, it is exposed on the whole tumor cell surface, becoming an accessible and druggable target. However, its role in tumor progression and proliferation is poorly investigated, partly due to the paucity of commercially available CLDN18.2-expressing cell lines. Taking advantage of our precious and molecularly annotated GC Patient-Derived Xenograft (PDX) platform, which includes approximately 200 primary cell lines and organoids, we assessed the Claudin 18.2 expression through RNA-Seq analysis, using the median expression value as the threshold for classification. The RNA-seq results were validated on representative PDXs using Real-Time-qPCR and Immunohistochemistry. Further, CLDN18.2 expression was evaluated in GC primary cell lines derived from low-, median-, and high-expressing PDXs (Real-Time-qPCR, Western Blot, and Immunofluorescence). For our analysis, we focused on four low-expressing (GTR181, GTR031, GTR498, GTR233), three median-expressing (GTR571, GTR797, GTR435), and three high-expressing (GTR789, GTR568, GTR816) CLDN18.2 cell lines. To explore the potential cell-autonomous role of CLDN18.2 as a driver in gastric cancer, we silenced the CLDN18.2 gene in median- and high-expressing cell lines. In high-expressing cells, CLDN18.2 silencing reduced cell proliferation compared with their wild-type counterparts, whereas no significant difference was observed in median-expressing cells, suggesting that high-expressing models are addicted to CLDN18.2. To further support the role of CLDN18.2 as a potential driver in high-expressing GC primary cell lines, we evaluated the cancer cell-autonomous sensitivity to Zolbetuximab - an anti-CLDN18.2 monoclonal antibody capable of inducing, in vivo, Antibody-Dependent Cellular Cytotoxicity (ADCC) and Complement-Dependent Cytotoxicity (CDC) - of low-, median-, and high-expressing models. High-expressing cell lines were highly sensitive, whereas sensitivity progressively decreased in median-expressing and low-expressing cells. These results suggest a potential CLDN18.2 dependency in high expressing GC cell lines, supporting a role for CLDN18.2 as a driver in GC proliferation. From a translational point of view, our preliminary data suggest that the efficacy of the anti-CLDN18.2 monoclonal antibody Zolbetuximab in high CLDN18.2-expressing tumor cells may be enhanced by the cancer cell-autonomous response, in addition to its established ADCC and CDC. Citation Format: Lisa Negro, Elisabetta Puliga, Emanuela Boccuni, Simona Corso, Silvia Giordano. The emerging role of claudin 18.2 as a potential driver in gastric cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3919.