PROJECT SUMMARY / ABSTRACT Pancreatic Ductal Adenocarcinoma (PDAC) is an almost uniformly lethal disease, with an overall survival under 10%. Despite therapeutic advances in all arenas of cancer treatment, including immunotherapy, overall survival has not significantly improved in PDAC, representing a critical need for the development of novel therapeutic strategies for this disease. The tumor microenvironment (TME) in PDAC is characterized by an immunosuppressive infiltrate causing T-cell exclusion, and dense stromal desmoplasia. The complement cascade is activated in the PDAC TME and may promote this uniquely challenging TME by signaling to immune cells and fibroblasts expressing complement receptors. Complement activation has previously been demonstrated to promote infiltration of immune cells which contribute to T-cell exclusion in multiple tumor types in a context-dependent fashion. The long-term objectives of this project are to understand microenvironmental mechanisms by which complement promotes oncogenesis in PDAC, and to elucidate the interactions between radiotherapy (RT) and complement blockade in PDAC. A novel autochthonous mouse model of PDAC was generated and crossed with complement deficient C3 knockout (KO) mice to allow for studies which define the role of complement in PDAC. Tumor growth in complement-proficient wild type (WT) PDAC mice and C3 KO PDAC mice will be tracked using serial, PET/CT imaging. Tumors will be assessed histologically from 3-6 months after induction with tamoxifen to determine histologic grade, normal acinar area, and fibrotic area. Flow cytometry will be used to determine the impact of complement on infiltrating immune cells while single-cell RNA-sequencing will provide insight into the development and activation of cancer-associated fibroblasts. We will also assess the role of tumor cell vs. stromally derived C3 with shRNA depletion of C3 in YFP-expressing KPC cells (KPCY) in flank tumor growth studies in WT and C3 KO mice as a second model to confirm these results. To assess the impact of photon, proton, and carbon ion RT on complement activation and immune tolerance we will irradiate KPCY using each radiation modality. Complement deposition assays will be performed by culturing irradiated and non-treated tumor cells in the presence of serum as a complement source, before measuring activation by flow cytometry. Next, dendritic cells will be co-cultured with irradiated and non-irradiated KPCY cells with serum to determine if complement deposition on irradiated tumor cells reduces dendritic cell activation markers measured by flow cytometry. Translational studies will be performed using neutralizing antibodies and small molecule inhibitors to blockade complement signaling alone and with RT in an orthotopic KPCY model. Mice will be treated with neutralizing antibodies and inhibitors to blockade complement signaling and irradiated with an X- strahl Small Animal Radiation Research Platform or a Varian ProBeam proton therapy machine and growth will be tracked by IVIS. Complement activation will be assessed by western blot and immunofluorescence, and flow cytometry will assess differences in infiltrating immune cells post-irradiation.

PROJECT NARRATIVE Pancreatic ductal adenocarcinoma (PDAC) is expected to become the second leading cause of cancer death by 2030 due to a dearth of therapeutic options which could extend survival. Using novel mouse models, we aim to understand how complement activation in the tumor microenvironment promotes oncogenesis by signaling to immune cells and cancer-associated fibroblasts. We further aim to study translational therapeutics which blockade complement signaling, both alone and in combination with radiotherapy as an ablative and immunomodulatory therapy to demonstrate novel immunotherapeutic strategies for PDAC.