Abstract B033: Tumor cell-intrinsic mPGES-1-PGE2-EP4 signaling is a major immunosuppressive pathway in pancreatic cancer

Abstract

Abstract Pancreatic adenocarcinoma (PDA) is the 4th leading cause of cancer-related deaths in the US partly because of its resistance to conventional chemotherapies. Immunotherapies that improve survival in many cancers, almost universally fail in PDA. The resistance to immune checkpoint blockade is at least partially explained by the lack of T cells in the tumor microenvironment (TME) in PDA. As demonstrated previously, tumor cell-derived prostaglandin E2 (PGE2) is one of the tumor intrinsic factors that creates/supports immunosuppressive TME in PDA. The current study investigates how depleting tumor cell-derived PGE2 or disrupting its autocrine signaling through the cognate EP4 receptors on tumor cells reverses the T cell low, myeloid cell rich PDA TME and suppresses the tumor growth. Pharmacological blockade of EP4 receptors combined with anti-PD-1 and agonistic CD40 antibodies induced complete tumor regressions with a lasting vaccine effect. Knockout (KO) of Ptges, the gene encoding PGE2 synthesis enzyme mPGES-1, or EP4 receptor gene, Ptger4, in KrasG12D/P53R172H/Yfp/PdxCre (KPCY) pancreatic tumor cells was sufficient to abolish the growth of implanted tumors (p<0.0001 both). The rejection of the primary KO and rechallenge control tumors was T cell-dependent as it did not happen in hosts depleted of CD4+ and CD8+ T cells. Both KO tumor cells were more susceptible to TNF-a killing while their TMEs were enriched with central memory T cells and phagocytic macrophages and depleted of granulocytic myeloid-derived suppressor cells (gMDSC). Further analysis of Ptger4 tumors revealed changes in CCL2, CXCL9, and GM-CSF production probably causing the changes in TME. In addition, in both Ptges and Ptger4 KO tumors, the adenosine synthesis pathway was significantly downregulated probably due to decreased TGF-b signaling in tumor cells. When cultured ex vivo in hypoxic conditions, Ptger4 KO tumors made significantly less immunosuppressive adenosine (p<0.001). Consequently, 57% of Ptger4 KO tumors in adenosine deaminase inhibitor treated hosts accumulated enough adenosine to suppress the anti-tumor immune response and grow out. The study demonstrates a primary role for the tumor cell-intrinsic mPGES1-PGE2-EP4 signaling in creating immune-suppressive TME in PDA, suggesting EP4 blockade as a novel approach in the treatment of pancreatic cancer. Citation Format: Nune Markosyan, Il-Kyu Kim, Charu Arora, Liz Quinones, Noah Cheng, Ben Z. Stanger, Robert H. Vonderheide. Tumor cell-intrinsic mPGES-1-PGE2-EP4 signaling is a major immunosuppressive pathway in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr B033.