Abstract LB387: A claudin-4/Rab7-mediated mechanism promotes immune evasion and enhances survival in ovarian cancer

Abstract Objectives: Therapy resistance in ovarian cancer is closely tied to genomic instability (GI), a cancer hallmark driving tumor heterogeneity and immune evasion (IE). Cancer cells regulate GI to promote growth while evading cytoplasmic DNA detection, which could activate immune responses. Claudin-4, overexpressed in most epithelial ovarian cancers (EOC), is linked to therapy resistance and poor outcomes. It enhances GI management by remodeling nuclear architecture and the cell cycle and is involved in autophagy activation in response to GI. Claudin-4’s disruption sensitizes tumors to therapies, yet its role in immune evasion remains unexplored. This study investigated the immune response triggered by targeting claudin-4 and its connection to cytoplasmic DNA detection mechanisms. Methods: We used authenticated, mycoplasma-free EOC cell lines (OVCAR3, OVCAR8) to assess the effects of claudin-4 elimination (via CRISPR) and overexpression. Claudin-4 was also targeted with a claudin mimic peptide (CMP) in in vitro and in vivo studies using PDX-humanized mice. The cells were engineered with an interferon-stimulated response element (ISRE) reporter to measure type I interferon (IFN) responses under various conditions, including Rab7 mutant forms (dominant positive and negative) and the autophagy inhibitor chloroquine. Immunofluorescence, confocal microscopy, and immunoblotting were used to analyze cGAS-STING pathway components and phosphorylation. Flow cytometry characterized immune responses under treatments, including niraparib (50 mg/kg, P.O), CMP (4 mg/kg, I.P), and their combination. Tumor growth was monitored via IVIS scan, with data analyzed using ImageJ and Prism software (unpaired t-test, one-way ANOVA; p < 0.05). Results: Claudin-4 colocalized with Rab7 and modulated its expression in ovarian cancer cells, confirming their functional interaction, as Rab7 is known to bind claudin-4. Disruption of claudin-4 altered the phosphorylation of STING, leading to modified activation of the type I IFN response. This underscores claudin-4's role in regulating this pathway, which was further inhibited by Rab7 overexpression, highlighting Rab7’s negative regulatory effect on STING activation via lysosomal degradation. Notably, claudin-4's involvement in modulating the type I IFN response was linked to a mechanism of tumor IE, as evidenced by reduced expression of the TCR-zeta chain in T lymphocytes. This suggests altered cytokine profiles and tumor immune microenvironment changes. Targeting claudin-4 enhanced CD8+ T cell infiltration, restored TCR-zeta chain expression, and inhibited tumor growth, positioning claudin-4 as a promising therapeutic target. Conclusions: Claudin-4 promotes tumor immune evasion and survival by modulating the type I IFN response, a mechanism potentially linked to its regulation of genomic instability. Citation Format: Fabian Romero Villagomez, Julie Lang, Daniel Nunez-Avellaneda, Kian Behbakht, Hannah L. Dimmick, Patricia Webb, Margaret Neville, Elizabeth R. Woodruff, Benjamin G. Bitler. A claudin-4/Rab7-mediated mechanism promotes immune evasion and enhances survival in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB387.