Project Summary. Prostaglandin E2 (PGE2) regulates tissue growth and repair in multiple organs. A conserved mechanism of synthesis and degradation modulates PGE2 levels in response to trauma, inflammation and disease. In particular, the enzyme 15-prostaglandin dehydrogenase (15-PGDH) is the main PGE2-degrading enzyme and therefore a key regulator of tissue repair and regeneration. 15-PGDH is an attractive drug target for diseases characterized by tissue damage. Our team successfully developed the first small molecule inhibitors of 15-PGDH with in vivo activities in multiple rodent models of disease related to inflammatory bowel disease, renal disease, neurodegeneration and pulmonary fibrosis. This RM1 grant supports a collaborative chemical, structural and cell-signaling interrogation of the role and activity of 15-PGDH. Our expertise includes medicinal chemistry, biochemistry, neuroscience, pharmacology, and structural biology. We have obtained the first 3-dimensional structure of 15-PGDH in complex with inhibitors, and we have discovered a new class of inhibitors. Additionally, we have begun to decipher the signaling pathways that regulate 15-PGDH and the pathways that are impacted by inhibition of 15-PGDH. This supplement seeks to expand on unanticipated observations we have made during the course of our studies over the last two years. In particular, we have discovered that cells up-regulate 15-PGDH in response to inhibitors of 15-PGDH. Inhibitors block enzymatic function, but also stabilize the protein and prevent degradation. Therefore, cells have more 15-PGDH enzyme after 24h treatment with inhibitor than they had prior to drug treatment. In vivo, this pattern results in an unusual scenario in which 15-PGDH activity is suppressed for ~12h, but then rebounds and overshoots basal levels by ~24h because of new protein synthesis. A new graduate student, Mr. Max Balderas, will study this phenomenon by developing 15-PGDH degrading compounds. These PROTACs compounds will recruit E3 ligases to 15-PGDH and promote ubiquitination, leading to degradation by the proteosome. These reagents will provide tools to compare three scenarios: basal, chemical inhibition and chemical degradation of 15-PGDH. The experiments will help define the biology upstream and downstream of 15-PGDH. Through these studies, Mr. Balderas will gain exposure to synthetic chemistry, chemical biology, structural biology, biochemistry and cell biology. He will work with the larger team and interact frequently with the other PI’s and their research teams. The broad-based research project will provide a strong foundation for Mr. Balderas’ training in support of his longer term scientific and career objectives. Mr. Balderas’ research will fit into the existing objective of Aims 1 and 2, and he will lead the synthetic chemistry efforts related to the discovery of chemical degraders.