Abstract B098: RAS(ON) multi-selective inhibition remodels cancer-associated fibroblast subtypes and extracellular matrix in pancreatic cancer

Abstract The advent of RAS inhibitors in the clinic offers the possibility of revolutionized care for patients with pancreatic ductal adenocarcinoma (PDAC). While RAS (ON) multi-selective inhibitors like the investigational agent daraxonrasib (RMC-6236) and the related preclinical tool compound RMC-7977 are designed to target the KRAS-mutant malignant epithelium, their effects on the surrounding tumor stroma remain underexplored. Prior studies using genetically engineered mouse models (GEMMs) have shown that aberrant oncogenic KRAS signaling is critical for the establishment and maintenance of the tumor microenvironment. In recent years, multiple CAF subtypes have been identified based on gene expression profiles, spatial distribution, and cellular origin. Myofibroblastic CAFs (myCAFs), which are located near the malignant epithelium, are marked by active Sonic Hedgehog (SHH) signaling, while inflammatory CAFs (iCAFs) and antigen-presenting CAFs (apCAFs) reside more peripherally. Here, we investigate how pan-RAS-GTP inhibition by RMC-7977 reshapes the CAF landscape in PDAC and its impact on the extracellular matrix (ECM). We profiled CAF subtype prevalence and transcriptional programs using single-cell RNA sequencing (scRNA-seq) of GEMM-derived tumors treated in vivo with RMC-7977 across multiple timepoints. These findings were corroborated by immunostaining of murine and patient-derived tumor explants treated ex vivo for 2 to 4 days. Tumor stiffness following RMC-7977 treatment was assessed using nanoindentation, and mechanistic studies were performed in vitro using reporter fibroblasts. Preliminary data reveal that short-term RMC-7977 treatment reduces myCAF abundance and proliferation, while iCAF and apCAF populations expand. Notably, supplementation with exogenous SHH restores the original myCAF-rich phenotype even in the presence of RMC-7977. Pan-RAS-GTP inhibition also remodels the ECM, resulting in decreased tumor stiffness. These preclinical findings suggest that systemic pan-RAS-GTP inhibition alters not only the malignant epithelium but also the broader PDAC architecture through effects on stromal components. Understanding these stromal adaptations will enable improved assessment of tumor behavior and the development of more effective combination therapies. Citation Format: Allison C. Hess, Lorenzo Tomassoni, Kevin Muñoz Forti, Hun Jin Jeong, Deanna J. Besart, Tanner C. Dalton, Carmine F. Palermo, Stephen A. Sastra, Chang H. Lee, Andrea Califano, Simon Schwörer, Kenneth P. Olive, Marie C. Hasselluhn. RAS (ON) multi-selective inhibition remodels cancer-associated fibroblast subtypes and extracellular matrix in pancreatic cancer abstract. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research—Emerging Science Driving Transformative Solutions; Boston, MA; 2025 Sep 28-Oct 1; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2025;85 (18Suppl₃): Abstract nr B098.