Inhibition of SUMOylation Induces Adaptive Anti-Tumor Immunity Against Pancreatic Cancer through Multiple Effects on the Tumor Microenvironment

Improvement of pancreatic ductal adenocarcinoma (PDAC) patients’ outcomes require exploration of novel therapeutic mechanisms. Thus far, most studies of PDAC therapies, including those inhibiting small ubiquitin-like modifications (SUMOylation), have focused on PDAC epithelial cell biology. The mechanisms by which SUMOylation impacts PDAC in the context of its tumor microenvironment (TME) are poorly understood. We used clinically relevant orthotopic PDAC mouse models to investigate the effect of SUMOylation inhibition using a specific, clinical stage compound, TAK-981. TAK-981 monotherapy improved survival in immunocompetent mice. However, in contrast to its inhibition of PDAC cell proliferation in vitro, the survival benefit of TAK-981 in vivo is dependent on the presence of T cells. Induction of adaptive anti-tumor immunity is the dominant anti-tumor effect of SUMOylation inhibition in vivo. To elucidate the mechanism of adaptive immunity, we performed comparative single cell transcriptomics analyses of murine and human PDAC tumors, including cancer cells, T cells, tumor associated macrophages (TAM) and cancer associated fibroblasts (CAF), in combination with immunofluorescence, immunohistochemistry, western blots and qPCR. Mechanistically, SUMOylation regulates T cell activation and differentiation. In addition, TAK-981 changed gene expression in TAM, CAF and cancer cells that are likely to enhance the anti-tumor T cell response. These findings provide rationale for combination strategies to augment adaptive immune responses to PDAC that are necessary for durable disease control in PDAC patients.