Abstract 6155: S-Nitrosylated COX-2 is a microenvironment-regulated breast cancer biomarker of mesenchymal phenotypes

Abstract COX-2 is an inducible enzyme key to the production of inflammatory prostaglandins. COX-2 also has tumor intrinsic oncogenic activity in mouse models of breast cancer. Previously, we reported that increased expression of Cys-526-nitrosylated COX-2 (SNO-COX-2), but not non-nitrosylated COX-2, associated with progression of early-stage human breast cancer to invasive ductal carcinoma. Here, we used a 3D culture model of early-stage human breast cancer (MCF10DCIS cells) to investigate the relationship between SNO-COX-2 expression and mesenchymal/invasive tumor cell morphology. We find that SNO-COX-2, but not non-nitrosylated COX-2, closely associated with mesenchymal phenotypes induced by fibrillar type I collagen. Interestingly, invasive phenotypes did not associate with induction of classic epithelial-to-mesenchymal transition (EMT) markers including SNAIL, CDH2 (N-cadherin), and VIM (vimentin). By contrast TGFβ-1 strongly induced EMT-related transcripts, but not SNO-COX-2 protein expression nor mesenchymal phenotypes. These observations suggest that in MCF10DCIS cells, SNO-COX-2 associates with mesenchymal phenotypes more strongly than non-nitrosylated COX-2 protein or expression of classic EMT transcripts. Supporting these observations in vivo, a heterogeneous mouse breast tumor model (D2A1 cell injection) demonstrates that invasive mesenchymal tumor regions also have increased SNO-COX-2 expression compared to epithelial tumor regions. Further, using a microenvironment microarray to test MCF10DCIS.com cells 300 distinct tumor microenvironment conditions we find SNO-COX-2 protein expression is driven by inflammation, wound resolution, and cancer-associated factors. Standouts include TNC, SPP1, decorin, fibrillar type I and III collagens, INF-γ, and IL-4/13, with evidence for specific extracellular matrix-ligand interactions driving both high and low SNO-COX-2 expression. In sum, in MCF10DCIS cells, expression of SNO-COX-2 is highly microenvironment-dependent and strongly associated with invasive/mesenchymal growth, indicating potential for SNO-COX-2 as a biomarker to assess risk of early-stage breast cancer progression. Citation Format: Reuben J. Hoffmann, AeSoon Bensen, Mark Dane, Jane Arterberry, Rebecca Smith, James Korkola, Pepper Schedin. S-Nitrosylated COX-2 is a microenvironment-regulated breast cancer biomarker of mesenchymal phenotypes [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 6155.