– EP4 antagonist 14 is a prostaglandin E2 receptor subtype EP4 antagonist, demonstrating an IC50 of 1.1 nM in a HEK293 human receptor reporter assay and blocking β-arrestin recruitment due to PGE2 with an IC50 of 0.9 nM. At 10 µM, it reduces PGE2-stimulated mRNA levels of Il-4, macrophage mannose receptor 1 (Mrc1), chitinase-like protein 3 (Chil3), chemokine (C-X-C) motif ligand 1 (Cxcl1), triggering receptor expressed on myeloid cells 2 (Trem2), and arginase-1 (Arg1) in RAW 264.7 macrophages. When used at 30 mg/kg per day alongside anti-PD-1 antibodies, it curbs tumor growth and enhances CD8+ T cell infiltration in tumors using a CT26 murine colon cancer model.