Abstract B038: Tumor Derived Parathyroid Hormone Related Protein is an Orchestrator of Immunosuppression in Pancreatic Cancer

Abstract Pancreatic ductal adenocarcinoma (PDAC) has the lowest 5-year survival of common cancers, owing to a lack of early detection and ineffective therapies. Immune checkpoint inhibitors hold promise for PDAC patients, and while they represent the most ongoing clinical trials, they have had little success. Parathyroid Hormone Related Protein (PTHrP; encoded by PTHLH) defines the most aggressive squamous/basal/quasi-mesenchymal PDAC subtype. Our previous work revealed autocrine PTHrP signaling mediates tumor growth, epithelial-to-mesenchymal transition (EMT), and metastasis. However, PTHrP’s relationship with immune cells of the tumor microenvironment (TME) remains unknown. Investigation of tumors from KrasG12D; p53R172H; Pdx1-Cre; YFP (KPCY) and KPCY-Pthlh loxP/WT (KPCY-Pthlhhet) mice revealed less tumor associated neutrophils (TANs) and greater cytotoxic T cell infiltration, demonstrating the necessity of PTHrP for immune exclusion. Orthotopic implantation of Pthlh overexpressing KPCY cells (KPCY-PthlhOE) revealed a greater proportion of TANs than the control. A concomitant decrease in the number of effector T and natural killer cells in the KPCY-PthlhOE tumors was observed, showing PTHrP is sufficient to organize an immunosuppressive TME. Interestingly, recombinant human PTHrP was sufficient to induce TANs mobilization in vivo. To interrogate the mechanism of neutrophil trafficking into the TME, cytokine production was quantified in vitro. KPCY-PthlhOE exhibited a pronounced increase of Cxcl1 expression, a strong neutrophil chemokine, leading us to believe neutrophils migrate to the TME using a Cxcl1 gradient. Therefore, we hypothesized that PTHrP-mobilized neutrophils express the receptor for CXCL1; CXCR2. Indeed, recombinant PTHrP was sufficient to mobilize Cxcr2+ neutrophils in vivo. Furthermore, recombinant PTHrP was able to induce Cxcl1 production by KPCY tumor cells in vitro in a cAMP response element-binding protein(CREB)-dependent manner. These data describe a novel mechanism for the mobilization and infiltration of immune suppressive TANs into the TME, initiated by PTHrP. The PTHrP-dependent immunosuppressive TME excludes and inhibits effector immune cells. Further interrogation of PTHrP signaling during the genesis of the immune suppressive TME in PDAC may lead to the development of therapeutics to meet this unmet clinical need. Citation Format: Calvin Johnson, Jason Pitarresi. Tumor Derived Parathyroid Hormone Related Protein is an Orchestrator of Immunosuppression in Pancreatic Cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B038.