Abstract 4607: Specific inhibition of PGE2-EP4 signaling by E7046 promotes anti-tumor activity of checkpoint blockade agents through boosting cytotoxic T cell activity
Authors: Albu Diana I. , Verbel David , Huang Yuan , Kolber-Simonds Donna , Wang Zichun , Wang Xulong , Dezso Zoltan , Ingersoll Christy , Huang Kuan-Chun , Hutz Janna , Woodall-Jappe Mary , Bao Xingfeng 
Published: July 2017

Abstract
Purpose: Immunotherapies targeting immune checkpoint receptors have shown great promise for a subset of cancer patients; however, robust and safe combination therapies are still needed. In the tumor microenvironment, prostaglandin E2 receptor type 4 (EP4) signaling has been implicated in both protumoral myeloid cell differentiation and cytotoxic T cell exhaustion. We evaluated the combination of the EP4 antagonist E7046 (clinical trial NCT02540291) with anti-PD1 or anti-CTLA4 in preclinical tumor models, and also interrogated the relationship between PGE2 pathway activation and cancer patient survival. Materials/Methods: Mouse syngeneic tumor models CT-26 and 4T1 were used for pharmacological investigation. GMP grade E7046 was administered to tumor-bearing animals by oral gavage. Co-culture of EG7-OVA and OT1 cells in an antigen-specific cytotoxic T cell (CTL) activation assay provided mechanistic insights. For translational validation, transcripts of five major genes involved in PGE2 synthesis, transport and degradation were compared between malignant and normal tissues across all TCGA tumor types, and correlation of their expression with overall survival was assessed.
Results: In the CT26 tumor model, the combination of E7046 and anti-PD1 resulted in significantly more tumor-free animals compared with either agent alone. In the 4T1 tumor model, the combination of E7046 and anti-CTLA4 was also more effective in suppressing tumor growth and tumor rejection compared with anti-CTLA4 alone, and was accompanied by a markedly increased accumulation of GZMB+CD8T+ CTLs in the treated tumors. Consistent with those findings, addition of anti-PD1 antibody promoted OVA-specific CTL activation in vitro while addition of PGE2 strongly inhibited it, as measured by IFNγ secretion. Inclusion of E7046 dose-dependently reversed the PGE2-induced suppressive activity in the presence of anti-PD1 antibody. Among major human PGE2 pathway genes, TCGA analysis showed that PTGES1 was upregulated and HPGD downregulated across a broad range of tumor types. In contrast, COX1, COX2 and PGT showed less difference between malignant and normal tissues. Importantly, these differences of one or multiple PGE2 pathway genes were strongly associated with patient survival in certain cancer types.
Conclusions: A subset of human cancer types displays upregulated PGE2 pathway that is associated with a poorer prognosis. PGE2-EP4 signaling potently suppresses antigen-specific CTL activation in the presence of PD1 signaling blockade. The combination of EP4 antagonist E7046 with either anti-PD1 or anti-CTLA4 demonstrated superior anti-tumor activity compared with anti-PD1 or anti-CTLA4 alone. This increased activity was accompanied by increased CTL activation.
Citation Format: Diana I. Albu, David Verbel, Yuan Huang, Donna Kolber-Simonds, Zichun Wang, Xulong Wang, Zoltan Dezso, Christy Ingersoll, Kuan-Chun Huang, Janna Hutz, Mary Woodall-Jappe, Xingfeng Bao. Specific inhibition of PGE2-EP4 signaling by E7046 promotes anti-tumor activity of checkpoint blockade agents through boosting cytotoxic T cell activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4607. doi:10.1158/1538-7445.AM2017-4607