Abstract 781: Acidic microenvironment as a driver of cancer-stroma coevolution: Integrating experimental and mathematical models of fibroblast adaptation and metabolic remodeling.

Abstract The acidic microenvironment (AME) is a defining metabolic hallmark of solid tumors and a key driver of coevolution between cancer cells and the surrounding stroma. AME arises primarily from hypoxia in avascular tumor regions and from the Warburg effect in normoxic habitats, resulting in sustained extracellular acidosis that imposes strong selection pressure on all cellular populations within the tumor ecosystem. Cells adapt to this stress either through Darwinian selection of pre-existing variants or through non-Darwinian phenotypic plasticity, leading to metabolic and transcriptional heterogeneity that supports tumor progression. The AME profoundly influences multiple stromal components - including collagen, fibronectin, fibroblasts, macrophages, and immune cells - thereby remodeling the tumor habitat and promoting invasion and metastasis. To investigate the mechanisms of stromal adaptation, we performed single-cell MALDI imaging to profile metabolic and lipidomic heterogeneity in fibroblasts exposed to acidic conditions for short and long durations, representing stages of acclimation and adaptation. Acid-exposed fibroblasts displayed altered sphingolipid and ceramide metabolism, suggesting metabolic plasticity as a key mechanism of survival under low pH.We then co-cultured acid-adapted fibroblasts with cancer cells in 3D spheroids and analyzed them using spatial metabolomics and lipidomics. Acid-adapted fibroblasts induced distinct metabolic niches that enhanced cancer cell invasiveness and ecosystem-level cooperation. To extend our findings to patient samples, we used MACSima cyclic immunofluorescence and MALDI imaging on DCIS tissues to spatially correlate metabolic changes with stromal reprogramming. Acid-exposed regions exhibited fibroblast activation markers (α-SMA, FAP, vimentin) and histone variant enrichment, linking metabolic stress to epigenetic remodeling. Finally, we developed a mathematical model integrated with experimental data as a tool to test hypotheses of DCIS progression based on stromal adaptation and metabolic remodeling. The model incorporated tumor tissue histology images to simulate spatial metabolic interactions and fibroblast-cancer coevolution under acid stress, and predicted that fibroblast plasticity accelerates tumor expansion. Together, our findings reveal that acidosis-induced metabolic and epigenetic reprogramming of fibroblasts drives stromal activation, niche remodeling, and DCIS progression, providing an evolutionary framework to target tumor acidity and its adaptive consequences. Citation Format: Emma R. Downey, Ana M. Forero Pinto, Katarzyna A. Rejniak, Mehdi Damaghi. Acidic microenvironment as a driver of cancer-stroma coevolution: Integrating experimental and mathematical models of fibroblast adaptation and metabolic remodeling 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 781.