Project 3 - Abstract/Summary The desmoplastic stroma, consisting of fibroblasts, extracellular matrix (ECM) and immune cells, is a defining feature of human pancreatic ductal adenocarcinoma (PDAC), however its precise contribution to cancer progression is still evolving. Type I collagen (Col1), a dominant component of PDAC desmoplasia, is uniquely regulated in PDAC. Our preliminary studies uncovered that cancer cells produce a novel Col1 variant consisting of alpha 1 chain (Col1a1) homotrimers. Genetic deletion of the oncogenic Col1 in cancer cells extends the overall lifespan of PDAC genetically engineered mice (GEMs). Oncogenic Kras (Kras*), a central driver for PDAC, plays a key role in determining the host response, including tumor immunity and metabolic adaptation. We discovered that Kras* drives cancer cells’ production of oncogenic Col1 via epigenetic silencing of Col1a2. In contrast with the classical Col1 heterotrimer produced by fibroblasts, oncogenic Col1 uniquely promotes PDAC initiation and progression by influencing tumor metabolism and immunity. Col1 homotrimers bind to a3b1 integrin on PDAC cancer cells, a collagen receptor distinctly upregulated in mouse and human PDAC. This induces a sustained activation of FAK, Akt and Erk1/2 when compared with Col1 heterotrimers, promoting cancer cells growth and survival. Oncogenic Col1 also suppresses intratumoral T cells, and oncogenic Col1 deletion synergizes with anti- PD-1 immune checkpoint blockade to suppress tumor growth and increase overall survival of PDAC GEMs. Cancer cell-directed oncogenic Col1 homotrimer signaling also enhances glycolysis and mTOR signaling, supporting the metabolic reprogramming driven by Kras*. In Project 3, in close collaboration with Projects 1 and 2, we will define the role and regulation of Kras*-induced oncogenic Col1 signaling in impacting tumor immunity and metabolism. The proposed aims investigate Col1 homotrimers- a3b1 integrin targeting, immunotherapy, and anti-metabolism strategies, as an informed combination treatment modality. Our preliminary data support the feasibility and significance of this novel approach, and exploit a new vulnerability in PDAC signaling, with a translational potential to inform new therapies for PDAC.