Abstract 4159: The COX-2/PGE2 pathway as a mediator of resistance to anti-PD-1 therapy

Background: We previously found upregulation of the cyclooxygenase-2/prostaglandin E2 (COX-2/PGE2) pathway in the tumor microenvironment (TME) of cancer types that respond poorly to anti-PD-1 therapy, and showed that TME-resident cytokines such as IL-1B induce COX-2 expression in human tumor and myeloid cells. To investigate a potential role for COX-2/PGE2 in anti-PD-1 resistance, we studied PGE2-mediated effects on human myeloid and T cells and their dependence on prostaglandin (EP) receptor signaling. Methods: Monocytes (Monos) and T cells were enriched from normal donor peripheral blood by negative selection. PGE2 effects were tested on Monos activated with IFN-g (PD-L1 expression; FACS) or LPS (cytokine secretion; ELISA). PGE2 effects on monocytic dendritic cells (DCs) generated with GM-CSF+IL-4 and matured with CD40L were assessed by phenotyping for costimulatory molecules (CD80, CD86) and subpopulation markers (CD14, CD16, CD83). T cells activated with anti-CD3/CD28 +/- PGE2 for 2-6 days were assessed for expression of CD25, CD69, CD107a, CD137, OX40, GITR, LAG-3, PD-1, PD-1, PD-L1 and TIM3 (FACS); proliferation markers (Ki67, CFSE; FACS); cytokine secretion (IFN-g, IL-2, IL-10, TGF-b; ELISA); and metabolic function (Seahorse assay). In some experiments, cells were pre-incubated with inhibitors of EP2 (PF-04418948), EP4 (ONO-AE3-208), or the dual inhibitor TPST-1495 (Tempest Therapeutics). Results: Myeloid cell functions were suppressed by PGE2, which reduced IFNg-induced PD-L1 expression and modulated LPS-induced cytokine secretion. Furthermore, PGE2 inhibited DC maturation, evidenced by persistent CD14 and CD16 expression and a decreased CD83+ subset. In CD4 and CD8 T cells activated with anti-CD3/CD28, PGE2 reduced expression of CD25 and CD69 (early activation markers), CD107a (cytolytic potential), Ki67 (cell proliferation), co-stimulatory molecules (CD137, OX40, GITR) and checkpoint molecules (LAG-3, PD-1, PD-L1, TIM3) in a dose-dependent manner. PGE2 also reduced the CFSE-low (proliferating) population in activated CD4, CD8 and Treg cells. Secretion of proinflammatory cytokines IFN-g and IL-2, and inhibitory cytokines IL-10 and TGF-b from activated T cells was also suppressed by PGE2. These effects were specifically reversed by chemical inhibitors of EP2 and/or EP4. PGE2 exposure at the time of T cell activation was associated with depressed mitochondrial oxidation and cellular glycolysis, suggesting global effects on T cell metabolism. Conclusion: Understanding and preventing anti-PD-1 resistance is a critical goal in oncology. Our results suggest that the COX-2/PGE2 pathway exerts immunosuppressive effects on myeloid and T cells via the EP2 and EP4 receptors. COX-2 and PD-L1 are distinct immune checkpoints, providing a rationale to test anti-PD-1 in conjunction with COX-2 pathway inhibitors such as IL-1B antagonists and highly specific EP2 and EP4 inhibitors in patients with cancer. Citation Format: Shuming Chen, Seoho Lee, Tracee L. McMiller, Isaac Morales, Preethi Sankaran, Brian Francica, Robert D. Leone, Tom W. Dubensky, Suzanne L. Topalian. The COX-2/PGE2 pathway as a mediator of resistance to anti-PD-1 therapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4159.