Abstract Background: Inflammatory breast cancer (IBC) is a rare and aggressive subtype of breast cancer, accounting for 2-5% of all cases. It is characterized by rapid progression and a high propensity for distant metastasis, including to the brain. We showed that elevated serum levels of soluble E-cadherin (sEcad), an 80 kDa ectodomain fragment, are independently correlated with poor survival and increased incidence of brain metastasis in IBC patients. sEcad overexpression also promoted brain metastasis growth in IBC xenograft models. RNA-seq analyses revealed activation of STAT3 and NFκB signaling in sEcad-overexpressing cells. Given the interaction between sEcad and Protein Disulfide Isomerase A4 (PDIA4), we hypothesize that sEcad promotes metastasis in IBC through PDIA4-dependent activation of STAT3 and NF-κB signaling pathways. Methods: Using lentiviral transduction, we stably overexpressed sEcad in the IBC cell lines SUM149 and MDA-IBC3. Protein expression and phosphorylation states of STAT3 and NFκB were validated by immunoblotting. Functional assays, including colony formation, migration, and invasion, were conducted to assess the impact of sEcad overexpression and PDIA4 knockdown using shRNA constructs. Pharmacological inhibition studies with STAT3 and NFκB pathway inhibitors (WP1066 and ATL) were conducted to evaluate pathway dependencies. To test the in vivo efficacy of these inhibitors on brain metastasis, SUM149-sEcad cells were injected via the intracardiac route into SCID/Beige mice. Molecular docking simulations using the Glowworm Swarm Optimization algorithm for protein-protein interactions, as well as a deep learning model based on diffusion algorithms for protein-ligand interactions, were used to assess binding interactions among sEcad, PDIA4, STAT3, and the inhibitors. Results: Overexpression of sEcad in SUM149 and MDA-IBC3 cells significantly increased phosphorylation of STAT3 and NFκB, and enhanced proliferation, colony formation, migration, and invasion. Knockdown of PDIA4 in sEcad-overexpressing cells reversed these effects and reduced pSTAT3 and pNFκB levels, highlighting PDIA4’s critical role in mediating sEcad-driven signaling. Both STAT3 and NFκB pathway inhibitors, either alone or in combination, reduced cell proliferation and colony formation in sEcad-high cells in a dose- and time-dependent manner. Moreover, treatment with brain-permeable inhibitors of STAT3 and NFκB reduced metastatic burden in an IBC brain metastasis model (p=0.03). Finally, molecular docking studies confirmed energetically favorable interactions between sEcad and PDIA4 (swarm 110; score: 38.6), as well as effective binding of PDIA4 with ATL (RMSD: 1.8 Å) and WP1066 (RMSD: 1.3 Å). Conclusion: Our findings demonstrate that sEcad is a key driver of aggressive oncogenic features in IBC through PDIA4-dependent activation of STAT3 and NFκB pathways. Targeting the sEcad-STAT3/NFκB signaling axis represents a promising therapeutic strategy for IBC. Citation Format: K. H. Tesfamariam, X. Hu, I. Longa Rizzo, E. S Villodre, L. TH Phi, J. Song, S. Krishnamurthy, Y. Gong, W. Priebe, W. A. Woodward, B. G. Debeb. Soluble E-cadherin-STAT3/NFκB axis in inflammatory breast cancer progression abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-02-18.
Tesfamariam et al. (Tue,) studied this question.