Macropinocytosis maintains CAF subtype identity under metabolic stress in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) tumors are glutamine deficient, and both tumor cells and cancer-associated fibroblasts (CAFs) rely on this amino acid to maintain fitness and induce macropinocytosis as an adaptive response. CAFs play a critical role in sculpting the tumor microenvironment, yet how adaptations to metabolic stress impact the stromal architecture remains elusive. In this study, we find that macropinocytosis sustains the myCAF phenotype under glutamine limitation by preventing inflammatory reprogramming. Our data demonstrate that metabolic stress induces an intrinsic inflammatory CAF (iCAF) program through MEK-ERK signaling. We find that blocking macropinocytosis in vivo promotes myCAF-to-iCAF transitions, remodeling the tumor stroma. Importantly, stromal remodeling driven by macropinocytosis inhibition-including iCAF enrichment, collagen reduction, immune cell infiltration, and vascular expansion-sensitizes PDAC tumors to immunotherapy and chemotherapy. Our findings reveal that inhibiting macropinocytosis promotes an inflammatory, less fibrotic tumor microenvironment that can be leveraged to improve therapeutic responses in PDAC.