Abstract 6042: Targeting GABA signaling in cancer associated fibroblasts to reduce immunosuppression in pancreatic cancer

Abstract Pancreatic ductal adenocarcinoma (PDAC) is a devasting disease with few therapeuticoptions. This is due, in large part, to the expansion of the non-tumor cellular compartmentknown as the stroma. Cancer-associated fibroblasts (CAFs) are one of the major celltypes that populate the stroma of PDAC tumors and are extremely immunosuppressivebecause they produce large amounts of cytokines, growth factors and metabolites. Thus,understanding how CAFs impart severe immunosuppression in the tumormicroenvironment is critical to make PDAC amenable to immunotherapies. Using a novel3D culturing method, our data support the notion that PDAC CAFs produce the glutamatemetabolite and inhibitory neurotransmitter gamma aminobutyric acid (GABA), de novo,and we detected GABA (∼27µM) in tumor interstitial fluid (TIF) isolated from patient tissue(10 patients). Surprisingly, CAFs lacked expression of glutamate decarboxylase, thecanonical enzyme responsible for converting glutamate into GABA, which led us toexplore alternative, non-canonical pathways for GABA synthesis. We found that CAFsderived from patient PDAC tumors expressed the enzymes of the non-canonicalsynthesis pathway (ODC1, DAO, ALDH1A1 and ALDH9A1), and to a greater degreewhen compared to normal fibroblasts. In parallel, we demonstrated that, by exploringparacrine signaling, GABA treatment of CAFs resulted in changes in expression of p-p70,p-JNK, p-MTOR and p-AKT proteins, key signaling hubs involved in overcomingmetabolic stress in PDAC. In addition, GABA treatment increased the production of pro-tumor cytokines, such as TGFβ, IL8, and IL6, by CAFs. In preclinical orthotopic murinetumor models of PDAC, inhibition of GABA synthesis through ALDH1A1, and GABAsignaling through GABAB receptor inhibitors, reduced tumor burden, increased influx ofanti-tumor T and NK cells, and blocked production of pro-tumor cytokines in tumorexplants. Translationally, we have acquired patient matched plasma, TIF, and tissue from10 patients, and will compare their metabolic, immune, and spatial transcriptomic profileswith well annotated clinical parameters, in order to develop improved diagnostic tests.Overall, we have uncovered a novel signaling circuit driven by GABA that plays a role incontrolling the extremely immunosuppressive PDAC microenvironment. Citation Format: Ariana Musa de Aquino, Myree Graves, Kyra Langley, Peter Sajjakulnukit, Ian Loveless, Nina Steele, Julie Clark, Alexander Muir, Costas Andreas Lyssiotis, Ralph Francescone, Débora B. Vendramini-Costa, Guilaume Cognet G, David Kwon. Targeting GABA signaling in cancer associated fibroblasts to reduce immunosuppression in pancreatic cancer 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 6042.