Claudin-1-Mediated Signaling and Therapy Resistance in Colorectal Cancer: From Mechanism to Translation

Colorectal cancer (CRC) remains a leading cause of cancer-related mortality, with metastatic cases showing poor response to chemotherapy due to both intrinsic and acquired therapy resistance. Claudin-1 (CLDN1), a tight junction protein, is overexpressed and mislocalized outside of tight junctions in CRC, where it contributes to an aggressive, metastatic phenotype. Although this causal relationship has been well established, the mechanisms by which CLDN1 promotes tumor progression were unclear due to its lack of intrinsic enzymatic activity. This dissertation investigates the molecular mechanisms through which CLDN1 drives oncogenic signaling, its role in therapy resistance, and its translational potential as both a biomarker and therapeutic target in CRC. Single-cell analysis of CRC patient tumors shows that CLDN1 is selectively overexpressed in stem-like tumor cells, with minimal expression in normal colon tissue. We demonstrate that CLDN1 directly interacts with Ephrin receptor A2 (EPHA2) via its C-terminal PDZ-binding motif, stabilizing EPHA2 by preventing its lysosomal degradation. This interaction activates non-canonical EPHA2 signaling through the AKT/mTOR pathway, enhancing stemness and chemoresistance. We further characterized the broader CLDN1 interactome and its associated gene expression programs in CRC. Notably, CLDN1 engages with multiple signaling molecules and drives transcriptional changes that confer resistance to oxaliplatin-based therapies, but not irinotecan. This selective resistance was confirmed in both mouse models and ex vivo patient-derived organoids, supporting the potential of CLDN1 as a predictive biomarker for guiding first-line treatment selection. To explore therapeutic applications, we evaluated the efficacy of a humanized monoclonal antibody (H3L3) targeting non-junctional CLDN1. H3L3 treatment inhibited AKT/mTOR signaling and significantly reduced tumor growth in xenograft and patient-derived organoid models. Lastly, we developed a near-infrared fluorophore-conjugated anti-CLDN1 antibody for in vivo imaging. This probe selectively labeled CLDN1-expressing CRCs, including distant metastases, in both xenograft and orthotopic models, demonstrating its potential utility for tumor detection and fluorescence-guided surgery. Together, these findings identify CLDN1 as a critical mediator of CRC progression and chemoresistance, with significant translational potential as a biomarker, therapeutic target, and imaging agent for CRC diagnosis and treatment.