Project 2 of the proposed Center for Immunotherapeutic Transport Oncophysics (CITO) will focus on the determination of immune-related transport differentials in subtypes of pancreatic ductal adenocarcinoma (PDAC). PDAC is considered to be a non-T cell inflamed tumor, and current immunotherapy strategies have limited efficacy in treating PDAC. Biologically, the intense immune suppression of PDAC occurs due to the presence of myeloid-derived suppressor cells (MDSCs), regulatory T cells (Tregs), and M2 macrophages in the tumor microenvironment. While tremendous effort has focused on the biological pathways that regulate these immunosuppressive cells so that more effector T cells can infiltrate and kill cancer cells, an area that has not gained any significant attention is the contribution of multi-scale physical aberrations that are inherent in PDAC. We believe that immunotherapy response and resistance in primary and metastatic sites are dependent on both the molecular biology and heterogeneous multi-scale physical properties of a particular PDAC tumor. These issues will be examined with the support of the Transport Oncophysics Core (TOC). We hypothesize that the efficacy of immunotherapy is limited by the spatial distribution of nutrients in the tumor microenvironment, as its disorganization restricts access of effector T cells to the cancer cells. A common feature of PDAC is an acidic microenvironment that is rich in lactate, and extracellular lactate is known to inhibit T cells because they are dependent on glycolysis. Our group has shown that vascular, stromal and membrane transport processes work in concert to determine drug distribution in PDAC. We have now extended this concept to immune cell biodistribution, and our preliminary data support the hypothesis that conservation laws of mass transport can describe the spatial location of immune infiltrates in relation to cancer cells in human PDAC. We have also developed biomimetic probes to study these phenomena in more detail and to develop novel immune-based therapies. Moreover, we have identified biophysical subtypes of PDAC, which exhibit distinct physical and immune properties, suggesting they will have differential responses to immunotherapies. We will couple these preliminary data with a well-characterized immune checkpoint: phosphatidylserine (PS). PS functions upstream of other immune checkpoints such as PD1 and CTLA4. Cells in the tumor microenvironment express PS, which is recognized and bound by PS receptors on immune cells to induce and maintain immune suppression. PS- targeting agents induce immune activation of innate and adaptive anti-tumor activity. We hypothesize that PS contributes to PDAC immune evasion in concert with the aberrant physics of PDAC, and that PS inhibition will normalize the biological and physical immunosuppression of PDAC. Our ultimate objective is to develop new ways to non-invasively measure and modulate the immunosuppression of PDAC to improve outcomes for this deadly disease.
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