PROJECT SUMMARY The project titled “Neoadjuvant Stroma Modification in Pancreatic Cancer” is seeking advancement in understanding of pancreatic ductal adenocarcinoma (PDAC) which is a deadly disease with high propensity for early metastatic dissemination. Hence, surgery alone is rarely curative, whereas preoperative chemo- and radiotherapy has a potential of increasing the possibility for long-term survival and ultimate cure. Extensive prior work by our group over the past two decades has established that the degree of tumor replacement with desmoplastic scar tissue is prognostic for survival. This specific morphological pattern has been recently characterized by the Cukierman lab to demonstrate expression of activated β5 integrins in cancer associated fibroblasts (CAFs) as a survival-predictive biomarker (eLife, 2017). Reciprocal interactions between PDAC cells and the surrounding stroma promote tumor growth and resist chemotherapy via epigenetic changes in gene expression. Therefore, effective PDAC therapy must include interventions aimed at stroma “normalization” (re- institution of physically and/or biochemically tumor-suppressive stroma), rather than stroma destruction. Herein, we propose to determine mechanisms of resistance arising in PDAC tumors exposed to neoadjuvant chemoradiotherapy and test strategies aimed to disrupt the PDAC-stroma interactions. In aim 1, we will conduct a phase I feasibility trial of 3 stroma-modifying drugs (PHL: a vitamin D analog paricalcitol, hydroxychloroquine, and losartan) deployed to inactivate the PDAC CAFs during the 4-6 weeks window period between completion of induction FOLFIRINOX chemoradiotherapy and surgery. In aim 2, we will determine if PHL therapy is sufficient to reduce the percentage of chemoresistant EMT PDAC cells and suppress activated CAFs. To determine these biological features, we will deploy single-cell RNA sequencing linked to orthogonal in situ biomarkers established in our hands for activated CAFs in PDAC. To conduct this work, we assembled a team of experts in clinical and basic science of pancreatic cancer with a strong track record of collaborations in innovative therapies for PDAC. Since we anticipate PHL to be well tolerated, our study will pave the way for larger phase II-III trials in order to evaluate the PHL for clinical endpoints of efficacy such as R0 resection rate, time to relapse, and overall survival.