Discovery of 2 H -Indazole-3-carboxamide Derivatives as Novel Potent Prostanoid EP4 Receptor Antagonists for Colorectal Cancer Immunotherapy.

Nowadays, small-molecule drugs have become an indispensable part of tumor immunotherapy. Accumulating evidence has indicated that specifically blocking PGE/EP4 signaling to induce robust antitumor immune response represents an attractive immunotherapy strategy. Herein, a 2-indazole-3-carboxamide containing compound was identified as a EP4 antagonist hit by screening our in-house small-molecule library. Systematic structure-activity relationship exploration leads to the discovery of compound , which displayed single-nanomolar EP4 antagonistic activity in a panel of cell functional assays, high subtype selectivity, and favorable drug-like profiles. Moreover, compound profoundly inhibited the up-regulation of multiple immunosuppression-related genes in macrophages. Oral administration of compound , either as monotherapy or in combination with an anti-PD-1 antibody, significantly impaired tumor growth via enhancing cytotoxic CD8 T cell-mediated antitumor immunity in a syngeneic colon cancer model. Thus, these results demonstrate the potential of compound as a candidate for developing novel EP4 antagonists for tumor immunotherapy.