Structural Insights into Novel 15-Prostaglandin Dehydrogenase Inhibitors

We discovered SW033291 in a high throughput chemical screen aimed at identifying 15-prostaglandin dehydrogenase (15-PGDH) modulators. The compound exhibited inhibitory activity in in vitro biochemical and cell-based assays of 15-PGDH activity. We subsequently demonstrated that this compound, and several analogs thereof, are effective in in vivo mouse models of bone marrow transplant, colitis, and liver regeneration, where increased levels of PGE2 positively potentiate tissue regeneration. To better understand the binding of SW033291, we carried out docking studies for both the substrate, PGE2, and an inhibitor, SW033291, to 15-PGDH. Our models suggest similarities in the ways that PGE2 and SW033291 interact with key residues in the 15-PGDH-NAD+ complex. We carried out molecular dynamics simulations (MD) of SW033291 bound to this complex, in order to understand the dynamics of the binding interactions for this compound. The butyl side chain (including the sulfoxide) of SW033291 participates in crucial binding interactions that are similar to those observed for the C15-OH and the C16-C20 alkyl chain of PGE2. In addition, interactions with residues Ser138, Tyr151, and Gln148 play key roles in orienting and stabilizing SW033291 in the binding site and lead to enantioselectivity for the R-enantiomer. Finally, we compare the binding mode of (R)-S(O)-SW033291 with the binding interactions of published 15-PGDH inhibitors.

Prostaglandin dehydrogenase is a target for successful induction of cervical ripening

The cervix represents a formidable structural barrier for successful induction of labor. Approximately 10% of pregnancies undergo induction of cervical ripening and labor with prostaglandin (PG) E2 or PGE analogs, often requiring many hours of hospitalization and monitoring. On the other hand, preterm cervical ripening in the second trimester predicts preterm birth. The regulatory mechanisms of this paradoxical function of the cervix are unknown. Here, we show that PGE2 uses cell-specific EP2 receptor-mediated increases in Ca2+ to dephosphorylate and translocate histone deacetylase 4 (HDAC4) to the nucleus for repression of 15-hydroxy prostaglandin dehydrogenase (15-PGDH). The crucial role of 15-PGDH in cervical ripening was confirmed in vivo. Although PGE2 or 15-PGDH inhibitor alone did not alter gestational length, treatment with 15-PGDH inhibitor + PGE2 or metabolism-resistant dimethyl-PGE2 resulted in preterm cervical ripening and delivery in mice. The ability of PGE2 to selectively autoamplify its own synthesis in stromal cells by signaling transcriptional repression of 15-PGDH elucidates long sought-after molecular mechanisms that govern PG action in the cervix. This report details unique mechanisms of action in the cervix and serves as a catalyst for (i) the use of 15-PGDH inhibitors to initiate or amplify low-dose PGE2-mediated cervical ripening or (ii) EP2 receptor antagonists, HDAC4 inhibitors, and 15-PGDH activators to prevent preterm cervical ripening and preterm birth.

Expression of COX-2 and 15-PGDH in adenomas removed during pretreatment colonoscopy to predict chemopreventive efficacy of the selective COX-2 inhibitor, celecoxib.

524 Background: The APC trial showed that patients at high risk for colorectal adenoma development experienced a 33-45% reduction in post-polypectomy adenoma detection when treated with the selective cyclooxygenase-2 (cox-2) inhibitor, celecoxib. Unfortunately, this study also found a small increased risk of cardiovascular toxicity among celecoxib users, preventing broad use of this agent for chemoprevention. Celecoxib inhibits expression of prostaglandin E2 (PGE2), an inflammatory mediator produced by fatty acid metabolism via cyclooxygenases, and degraded through the activity of 15-prostaglandin dehydrogenase (15-PGDH). Methods: Adenomas collected from APC trial participants prior to treatment were examined using immunohistochemistry (IHC) to assess expression of cox-2 (high vs. low) and 15-PGDH (present vs. absent). A combined variable to estimate tumor PGE2 levels identified cases as PGE2 low (Cox-2 low/15-PGDH present) or PGE2 high (Cox-2 high/15-PGDH present; Cox-2 high/15-PGDH absent; or Cox-2 low/15-PGDH absent). Mantel–Cox test was used to evaluate whether markers of PGE2 expression in these adenomas predicted benefit from celecoxib treatment for the primary study outcome of adenoma detection. Results: Biomarker determinations were achieved for 1295 cases, or 71% of patients with available outcome data. Patients whose baseline adenomas demonstrated elevated Cox-2 achieved the greatest overall reduction in adenoma risk with celecoxib treatment (RR 0.37; p = 0.0001). This risk reduction was less significant in the low Cox-2 category (RR 0.64). Patients with low estimated tumor PGE2 did not benefit from celecoxib for adenoma prevention (RR 0.95; p = 0.83). This is compared to a 41% reduction in adenoma detection with celecoxib treatment for patients in the high PGE2 category (RR 0.59; p < 0.0001). Conclusions: IHC to determine expression of target enzymes in pre-malignant adenomas provides significant prognostic and predictive information in patients treated with celecoxib for prevention of colorectal adenomas.

Upregulation of Cyclooxygenase-2/Prostaglandin E2 (COX-2/PGE2) Pathway Member Multiple Drug Resistance-Associated Protein 4 (MRP4) and Downregulation of Prostaglandin Transporter (PGT) and 15-Prostaglandin Dehydrogenase (15-PGDH) in Triple-Negative Breast Cancer

Elevated levels of cyclooxygenase-2 (COX-2) and prostaglandin E2 (PGE2) are indicators of a poor prognosis in breast cancer. Using several independent publicly available breast cancer gene expression databases, we investigated other members of the PGE2 pathway. PGE2 is produced by COX-2 and actively exported by multiple drug resistance-associated protein 4 (MRP4) into the extracellular microenvironment, where PGE2 can bind four cognate EP receptors (EP1–EP4) and initiate diverse biological signaling pathways. Alternatively, PGE2 is imported via the prostaglandin transporter (PGT) and metabolized by 15-prostaglandin dehydrogenase (15-PGDH/HPGD). We made the novel observation that MRP4, PGT, and 15-PGDH are differentially expressed among distinct breast cancer molecular subtypes; this finding was confirmed in independent datasets. In triple-negative breast cancer, the observed gene expression pattern (high COX-2, high MRP4, low PGT, and low 15-PGDH) would favor high levels of tumor-promoting PGE2 in the tumor microenvironment that may contribute to the overall poor prognosis of triple-negative breast cancer.