Project Summary: Early systemic dissemination, extraordinary local invasion, late diagnosis, and inadequate response to the existing chemotherapy contribute to poor prognosis for pancreatic ductal adenocarcinoma (PDAC) patients. While pancreatic tumors generally show a low intrinsic response to chemotherapies, most acquire resistance over the course of the treatment. Hence, there is an urgent need to understand the mechanisms contributing to acquired resistance to therapies and to identify novel therapies/therapeutic combinations that would significantly improve survival in patients. We have demonstrated that metabolic reprogramming presents a targetable vulnerability for abrogating acquired resistance and improving the therapy response in PDAC. The therapy resistance depends on both tumor cell-intrinsic mechanisms and a metabolic and signaling crosstalk between tumor cells and tumor microenvironment. Our unbiased preliminary data with multiple human PDAC patient-derived xenograft models identified peptidyl arginine deiminase 1 (PADI1) as the top upregulated gene that correlated significantly with poor patient prognosis. Citrullination or deimination of arginine residues produces a loss of a positive charge, increasing the mass and the acidity of the amino acid side chain, and the post-translational modification results in altered protein-protein interactions, signaling, and transcriptional responses. We noted robust expression of PADI1 in human PDAC tumors and cell lines and a correlation with patient survival. Inhibiting PADI activity or PADI1 knockdown significantly improved the responsiveness of PDAC cell lines and organoids to components of FOLFIRINOX therapy. PADI1 expressing PDAC tumors also demonstrated a significant correlation with the glycolytic phenotype and hypoxia gene signature, showing a reciprocal relationship with oxidative phosphorylation. We also performed an unbiased CRISPR screen and identified novel metabolic vulnerabilities that may be efficacious for co-targeting with agents inhibiting PADI1 downstream metabolic pathways. PADI expression also correlated with the reprogramming of immune and non-immune stroma in the microenvironment. Hence, the proposed project 1 will test the hypothesis if targeting PADI1 or downstream metabolic reprogramming will abrogate the development of resistance to FOLFIRINOX in PDAC. We will also investigate the mechanistic basis of stromal remodeling in PDAC tumors and the stromal reprogramming that contributes to acquired FOLFIRINOX resistance. We propose three specific aims to test the hypothesis. Aim 1 will investigate the efficacy of targeting PADI1 downstream pathways and associated mechanisms of stromal remodeling for abrogating resistance to FOLFIRINOX therapy. Aim 2 will determine the mechanism of tumor-cell intrinsic metabolic reprogramming that also feeds into stromal reprogramming by PADI1. Aim 3 will investigate the efficacy of targeting the pathways identified in Aims 1 and 2 in PDX m...