[Role of COX-2/PGE2/EP4 Axis-induced Macrophage Functional Activation 
in NSCLC Development].

BACKGROUND: Tumor microenvironment (TME) is one of the important factors in tumorigenesis and progression, in which tumor-associated macrophages (TAMs) play an important role in non-small cell lung cancer (NSCLC) progression. However, the mechanism of TAMs in NSCLC progression remains unclear, so this study aimed to investigate the role of TAMs in NSCLC progression and to find potential therapeutic targets. METHODS: Gene Expression Profiling Interactive Analysis (GEPIA) database was used to analyze the expression of prostaglandin E2 receptor 4 (EP4) mRNA in NSCLC and normal lung tissues; the protein expression levels of cyclooxygenase-2 (COX-2), EP4, cluster of differentiation 86 (CD86), CD163 and CD31 were detected by immunohistochemistry (IHC) in 120 NSCLC tissues and 24 paracancerous tissues specimens. The nude mouse lung adenocarcinoma cell A549 and macrophage RAW264.7 co-transplanted tumor model was established. And the samples were collected by gavage with EP4 inhibitor E7046, and then stained with hematoxylin-eosin (HE), IHC, and immunofluorescence (IF), and then detected by Western blot for the epithelial mesenchymal transformation (EMT) of the tumor tissues of the nude mice in each group. Western blot was used to detect the expressions of EMT related protiens in each group of nude mice; full-length transcriptome sequencing was used to screen the key genes causing liver metastasis and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis was performed. RESULTS: EP4 mRNA expression level in NSCLC tissues was generally lower than that in normal lung tissues (P<0.05); COX-2, EP4, CD163, CD31 proteins were differentially expressed in NSCLC tissues and adjacent tissues, and differences were observed in many clinicopathological parameters of NSCLC patients; RAW264.7 shortened the latency period of tumorigenesis of A549 and promoted the proliferation of tumors and liver metastasis of tumors, and E7046 could reduce tumor cell proliferation activity, tumor tissue vascular density and M2-type macrophage infiltration in nude mice; IF staining showed that macrophages were mainly distributed around the metastatic foci of tumors; Western blot results showed that compared with A549 alone transplantation group, the relative expression of E-cadherin protein in tumor tissues of mice in A549 and RAW264.7 co-transplantation group was significantly decreased, and the difference was statistically significant (P<0.05), while the relative expression of N-cadherin protein was up-regulated, but the difference was not statistically significant (P>0.05); the main pathways enriched in the differential genes of the full-length transcriptome were the PI3K-AKT and MAPK signaling pathways. CONCLUSIONS: During NSCLC development, the COX-2/PGE2/EP4 axis may promote tumor progression by inducing macrophage functional activation, and EP4 may be a potential new target for tumor immunotherapy. This study provides new perspectives and ideas for in-depth exploration of the mechanisms of NSCLC development, as well as a theoretical basis for the development of new therapeutic strategies for NSCLC.

EP4-induced mitochondrial localization and cell migration mediated by CALML6 in human oral squamous cell carcinoma.

Lymph node metastasis, primarily caused by the migration of oral squamous cell carcinoma (OSCC) cells, stands as a crucial prognostic marker. We have previously demonstrated that EP4, a subtype of the prostaglandin E2 (PGE2) receptor, orchestrates OSCC cell migration via Ca2+ signaling. The exact mechanisms by which EP4 influences cell migration through Ca2+ signaling, however, is unclear. Our study aims to clarify how EP4 controls OSCC cell migration through this pathway. We find that activating EP4 with an agonist (ONO-AE1-473) increased intracellular Ca2+ levels and the migration of human oral cancer cells (HSC-3), but not human gingival fibroblasts (HGnF). Further RNA sequencing linked EP4 to calmodulin-like protein 6 (CALML6), whose role remains undefined in OSCC. Through protein-protein interaction network analysis, a strong connection is identified between CALML6 and calcium/calmodulin-dependent protein kinase kinase 2 (CaMKK2), with EP4 activation also boosting mitochondrial function. Overexpressing EP4 in HSC-3 cells increases experimental lung metastasis in mice, whereas inhibiting CaMKK2 with STO-609 markedly lowers these metastases. This positions CaMKK2 as a potential new target for treating OSCC metastasis. Our findings highlight CALML6 as a pivotal regulator in EP4-driven mitochondrial respiration, affecting cell migration and metastasis via the CaMKK2 pathway.

Post-resolution macrophages shape long-term tissue immunity and integrity in a mouse model of pneumococcal pneumonia.

Resolving inflammation is thought to return the affected tissue back to homoeostasis but recent evidence supports a non-linear model of resolution involving a phase of prolonged immune activity. Here we show that within days following resolution of Streptococcus pneumoniae-triggered lung inflammation, there is an influx of antigen specific lymphocytes with a memory and tissue-resident phenotype as well as macrophages bearing alveolar or interstitial phenotype. The transcriptome of these macrophages shows enrichment of genes associated with prostaglandin biosynthesis and genes that drive T cell chemotaxis and differentiation. Therapeutic depletion of post-resolution macrophages, inhibition of prostaglandin E2 (PGE2) synthesis or treatment with an EP4 antagonist, MF498, reduce numbers of lung CD4+/CD44+/CD62L+ and CD4+/CD44+/CD62L-/CD27+ T cells as well as their expression of the α-integrin, CD103. The T cells fail to reappear and reactivate upon secondary challenge for up to six weeks following primary infection. Concomitantly, EP4 antagonism through MF498 causes accumulation of lung macrophages and marked tissue fibrosis. Our study thus shows that PGE2 signalling, predominantly via EP4, plays an important role during the second wave of immune activity following resolution of inflammation. This secondary immune activation drives local tissue-resident T cell development while limiting tissue injury.

Prostaglandin E2 in the Tumor Microenvironment, a Convoluted Affair Mediated by EP Receptors 2 and 4.

The involvement of the prostaglandin E2 (PGE2) system in cancer progression has long been recognized. PGE2 functions as an autocrine and paracrine signaling molecule with pleiotropic effects in the human body. High levels of intratumoral PGE2 and overexpression of the key metabolic enzymes of PGE2 have been observed and suggested to contribute to tumor progression. This has been claimed for different types of solid tumors, including, but not limited to, lung, breast, and colon cancer. PGE2 has direct effects on tumor cells and angiogenesis that are known to promote tumor development. However, one of the main mechanisms behind PGE2 driving cancerogenesis is currently thought to be anchored in suppressed antitumor immunity, thus providing possible therapeutic targets to be used in cancer immunotherapies. EP2 and EP4, two receptors for PGE2, are emerging as being the most relevant for this purpose. This review aims to summarize the known roles of PGE2 in the immune system and its functions within the tumor microenvironment. SIGNIFICANCE STATEMENT: Prostaglandin E2 (PGE2) has long been known to be a signaling molecule in cancer. Its presence in tumors has been repeatedly associated with disease progression. Elucidation of its effects on immunological components of the tumor microenvironment has highlighted the potential of PGE2 receptor antagonists in cancer treatment, particularly in combination with immune checkpoint inhibitor therapeutics. Adjuvant treatment could increase the response rates and the efficacy of immune-based therapies.

PGE2 limits effector expansion of tumour-infiltrating stem-like CD8+ T cells.

Cancer-specific TCF1+ stem-like CD8+ T cells can drive protective anticancer immunity through expansion and effector cell differentiation1-4; however, this response is dysfunctional in tumours. Current cancer immunotherapies2,5-9 can promote anticancer responses through TCF1+ stem-like CD8+ T cells in some but not all patients. This variation points towards currently ill-defined mechanisms that limit TCF1+CD8+ T cell-mediated anticancer immunity. Here we demonstrate that tumour-derived prostaglandin E2 (PGE2) restricts the proliferative expansion and effector differentiation of TCF1+CD8+ T cells within tumours, which promotes cancer immune escape. PGE2 does not affect the priming of TCF1+CD8+ T cells in draining lymph nodes. PGE2 acts through EP2 and EP4 (EP2/EP4) receptor signalling in CD8+ T cells to limit the intratumoural generation of early and late effector T cell populations that originate from TCF1+ tumour-infiltrating CD8+ T lymphocytes (TILs). Ablation of EP2/EP4 signalling in cancer-specific CD8+ T cells rescues their expansion and effector differentiation within tumours and leads to tumour elimination in multiple mouse cancer models. Mechanistically, suppression of the interleukin-2 (IL-2) signalling pathway underlies the PGE2-mediated inhibition of TCF1+ TIL responses. Altogether, we uncover a key mechanism that restricts the IL-2 responsiveness of TCF1+ TILs and prevents anticancer T cell responses that originate from these cells. This study identifies the PGE2-EP2/EP4 axis as a molecular target to restore IL-2 responsiveness in anticancer TILs to achieve cancer immune control.

PGE2 inhibits TIL expansion by disrupting IL-2 signalling and mitochondrial function.

Expansion of antigen-experienced CD8+ T cells is critical for the success of tumour-infiltrating lymphocyte (TIL)-adoptive cell therapy (ACT) in patients with cancer1. Interleukin-2 (IL-2) acts as a key regulator of CD8+ cytotoxic T lymphocyte functions by promoting expansion and cytotoxic capability2,3. Therefore, it is essential to comprehend mechanistic barriers to IL-2 sensing in the tumour microenvironment to implement strategies to reinvigorate IL-2 responsiveness and T cell antitumour responses. Here we report that prostaglandin E2 (PGE2), a known negative regulator of immune response in the tumour microenvironment4,5, is present at high concentrations in tumour tissue from patients and leads to impaired IL-2 sensing in human CD8+ TILs via the PGE2 receptors EP2 and EP4. Mechanistically, PGE2 inhibits IL-2 sensing in TILs by downregulating the IL-2Rγc chain, resulting in defective assembly of IL-2Rß-IL2Rγc membrane dimers. This results in impaired IL-2-mTOR adaptation and PGC1α transcriptional repression, causing oxidative stress and ferroptotic cell death in tumour-reactive TILs. Inhibition of PGE2 signalling to EP2 and EP4 during TIL expansion for ACT resulted in increased IL-2 sensing, leading to enhanced proliferation of tumour-reactive TILs and enhanced tumour control once the cells were transferred in vivo. Our study reveals fundamental features that underlie impairment of human TILs mediated by PGE2 in the tumour microenvironment. These findings have therapeutic implications for cancer immunotherapy and cell therapy, and enable the development of targeted strategies to enhance IL-2 sensing and amplify the IL-2 response in TILs, thereby promoting the expansion of effector T cells with enhanced therapeutic potential.

Cellular senescence and metabolic reprogramming model based on bulk/single-cell RNA sequencing reveals PTGER4 as a therapeutic target for ccRCC.

Clear cell renal cell carcinoma (ccRCC) is the prevailing histological subtype of renal cell carcinoma and has unique metabolic reprogramming during its occurrence and development. Cell senescence is one of the newly identified tumor characteristics. However, there is a dearth of methodical and all-encompassing investigations regarding the correlation between the broad-ranging alterations in metabolic processes associated with aging and ccRCC. We utilized a range of analytical methodologies, such as protein‒protein interaction network analysis and least absolute shrinkage and selection operator (LASSO) regression analysis, to form and validate a risk score model known as the senescence-metabolism-related risk model (SeMRM). Our study demonstrated that SeMRM could more precisely predict the OS of ccRCC patients than the clinical prognostic markers in use. By utilizing two distinct datasets of ccRCC, ICGC-KIRC (the International Cancer Genome Consortium) and GSE29609, as well as a single-cell dataset (GSE156632) and real patient clinical information, and further confirmed the relationship between the senescence-metabolism-related risk score (SeMRS) and ccRCC patient progression. It is worth noting that patients who were classified into different subgroups based on the SeMRS exhibited notable variations in metabolic activity, immune microenvironment, immune cell type transformation, mutant landscape, and drug responsiveness. We also demonstrated that PTGER4, a key gene in SeMRM, regulated ccRCC cell proliferation, lipid levels and the cell cycle in vivo and in vitro. Together, the utilization of SeMRM has the potential to function as a dependable clinical characteristic to increase the accuracy of prognostic assessment for patients diagnosed with ccRCC, thereby facilitating the selection of suitable treatment strategies.

Steroid-Induced Ocular Hypertension in Mice Is Differentially Reduced by Selective EP2, EP3, EP4, and IP Prostanoid Receptor Agonists.

We tested five chemically and metabolically stable prostaglandin (PG) receptor agonists in a mouse model of dexamethasone-induced ocular hypertension (OHT). Whilst all compounds significantly (p < 0.05, ANOVA) lowered intraocular pressure (IOP) after twice-daily bilateral topical ocular dosing (5 µg/dose) over three weeks, the time course and magnitude of the responses varied. The onset of action of NS-304 (IP-PG receptor agonist) and rivenprost (EP4-PG receptor agonist) was slower than that of misoprostol (mixed EP2/EP3/EP4-PG receptor agonist), PF-04217329 (EP2-PG receptor agonist), and butaprost (EP2-PG receptor agonist). The rank order of IOP-lowering efficacies aligned with the onset of actions of these compounds. Peak IOP reductions relative to vehicle controls were as follows: misoprostol (74.52%) = PF-04217329 (74.32%) > butaprost (65.2%) > rivenprost (58.4%) > NS-304 (55.3%). A literature survey indicated that few previously evaluated compounds (e.g., latanoprost, timolol, pilocarpine, brimonidine, dorzolamide, cromakalim analog (CKLP1), losartan, tissue plasminogen activator, trans-resveratrol, sodium 4-phenyl acetic acid, etc.) in various animal models of steroid-induced OHT were able to match the effectiveness of misoprostol, PF-04217329 or butaprost. Since a common feature of the latter compounds is their relatively high affinity and potency at the EP2-PG receptor sub-type, which activates the production of intracellular cAMP in target cells, our studies suggest that drugs selective for the EP2-PG receptor may be suited to treat corticosteroid-induced OHT.

Targeted Gene Deletion or Antagonism of the Prostaglandin E2 EP3 Receptor Protects Against Cardiac Injury Postmyocardial Infarction.

BACKGROUND: Prostaglandin E2 acts through 4 G-protein-coupled receptors (EP1-EP4). We previously reported that activation of the EP3 receptor reduces cardiac contractility, and its expression increases after a myocardial infarction (MI), mediating the reduction in cardiac function. In contrast, cardiac overexpression of the EP4 receptor in MI substantially improves cardiac function. Moreover, we recently reported that mice overexpressing EP3 have heart failure under basal conditions and worsened cardiac function after MI. Thus, the deleterious effects of the prostaglandin E2 EP receptors in the heart are mediated via its EP3 receptor. We, therefore, hypothesized that cardiomyocyte-specific knockout (CM-EP3 KO) or antagonism of the EP3 receptor protects the heart after MI. METHODS: To test our hypothesis, we made the novel CM-EP3 KO mouse and subjected CM-EP3 KO or controls to sham or MI surgery for 2 weeks. In separate experiments, C57BL/6 mice were subjected to 2 weeks of MI and treated with either the EP3 antagonist L798 106 or vehicle starting 3 days post-MI. RESULTS: CM-EP3 KO significantly prevented a decline in cardiac function after MI compared with WT animals and prevented an increase in hypertrophy and fibrosis. Excitingly, mice treated with L798 106 3 days after MI had significantly better cardiac function compared with vehicle-treated mice. CONCLUSIONS: Altogether, these data suggest that EP3 may play a direct role in regulating cardiac function, and pharmaceutical targeting of the EP3 receptor may be a therapeutic option in the treatment of heart failure.

EP2 and EP4 blockade prevents tumor-induced suppressive features in human monocytic myeloid-derived suppressor cells.

Tumors educate their environment to prime the occurrence of suppressive cell subsets, which enable tumor evasion and favors tumor progression. Among these, there are the myeloid-derived suppressor cells (MDSCs), their presence being associated with the poor clinical outcome of cancer patients. Tumor-derived prostaglandin E2 (PGE2) is known to mediate MDSC differentiation and the acquisition of pro-tumor features. In myeloid cells, PGE2 signaling is mediated via E-prostanoid receptor type 2 (EP2) and EP4. Although the suppressive role of PGE2 is well established in MDSCs, the role of EP2/4 on human MDSCs or whether EP2/4 modulation can prevent MDSCs suppressive features upon exposure to tumor-derived PGE2 is poorly defined. In this study, using an in vitro model of human monocytic-MDSCs (M-MDSCs) we demonstrate that EP2 and EP4 signaling contribute to the induction of a pro-tumor phenotype and function on M-MDSCs. PGE2 signaling via EP2 and EP4 boosted M-MDSC ability to suppress T and NK cell responses. Combined EP2/4 blockade on M-MDSCs during PGE2 exposure prevented the occurrence of these suppressive features. Additionally, EP2/4 blockade attenuated the suppressive phenotype of M-MDSCs in a 3D coculture with colorectal cancer patient-derived organoids. Together, these results identify the role of tumor-derived PGE2 signaling via EP2 and EP4 in this human M-MDSC model, supporting the therapeutic value of targeting PGE2-EP2/4 axis in M-MDSCs to alleviate immunosuppression and facilitate the development of anti-tumor immunity.

Prostaglandin E2 accumulation is closely associated with S. aureus-infected bovine endometritis.

S. aureus isolated from bacterial bovine endometritis is common in epidemiological reports, but is often ignored as a subclinical pathogenic microorganism. In a previous study, we showed that live S. aureus (LSA) and heat killed S. aureus (HK-SA) induce different inflammatory responses in bovine endometrial tissue, and possibly being associated with the accumulation of prostaglandin E2 (PGE2). Thus, in this study, we varied PGE2 concentrations using inhibitors or agonists in HK-SA-treated bovine endometrial tissues. The results demonstrated that PGE2 has a positive relationship with IL-6, TNF-α, and damage-associated molecular patterns (DAMPs; e.g., HMGB-1 and HABP-1) expression and tissues damage, and is regulated by the EP4-p38 MAPK pathway. We concluded that lipoproteins of S. aureus are associated with PGE2 generation. To further explore the relationship between LSA and PGE2 accumulation, we used the S. aureus strain SA113 lipoprotein knockout (SA113Δlpl) to infect bovine endometrial epithelial cells (BECs). LSA decreased PGE2, cAMP, EP4, IL-6, IL-8, cAMP secretion, and the MAPK and PKA signaling pathways when infected with SA113Δlpl, as compared with SA113-infected groups. Moreover, the adhesion and invasion of BECs were similarly downregulated when lipoproteins in S. aureus were knocked out. The results of this study show that PGE2 is involved in both HK-SA- and LSA-induced inflammatory responses in the bovine endometrium. We suggest that S. aureus infection is associated with bovine endometritis, and although HK-SA and LSA induce different inflammatory responses, the strategy of decreasing PGE2 accumulation is helpful in reducing the inflammation stage caused by S. aureus.

PGE2-EP4 signaling steers cDC2 maturation toward the induction of suppressive T-cell responses.

Dendritic cells (DCs) shape adaptive immunity in response to environmental cues such as cytokines or lipid mediators, including prostaglandin E2 (PGE2). In cancer, tumors are known to establish an enriched PGE2 microenvironment. Tumor-derived PGE2 primes regulatory features across immune cells, including DCs, facilitating tumor progression. PGE2 shapes DC function by providing signaling via its two so-called E-prostanoid receptors (EPs) EP2 and EP4. Although studies with monocyte-derived DCs have shown the importance of PGE2 signaling, the role of PGE2-EP2/EP4 on conventional DCs type 2 (cDC2s), is still poorly defined. In this study, we investigated the function of EP2 and EP4 using specific EP antagonists on human cDC2s. Our results show that EP2 and EP4 exhibit different functions in cDC2s, with EP4 modulating the upregulation of activation markers (CD80, CD86, CD83, MHC class II) and the production of IL-10 and IL-23. Furthermore, PGE2-EP4 boosts CCR type 7-based migration as well as a higher T-cell expansion capacity, characterized by the enrichment of suppressive rather than pro-inflammatory T-cell populations. Our findings are relevant to further understanding the role of EP receptors in cDC2s, underscoring the benefit of targeting the PGE2-EP2/4 axis for therapeutic purposes in diseases such as cancer.

Role of bradykinin and prostaglandin EP4 receptors in regulating TRPV1 channel sensitization in rat dorsal root ganglion neurons.

Transient receptor potential vanilloid type-1 (TRPV1) channels play key roles in chronic pain conditions and are modulated by different inflammatory mediators to elicit heat sensitisation. Bradykinin is a 9-amino acid peptide chain that promotes inflammation. The aim of present study is to investigate how bradykinin and prostaglandin receptors (EP3 and EP4 ) modulate the sensitisation of TRPV1-mediated responses. Calcium imaging studies of rat dorsal root ganglion (DRG) neurons were employed to investigate the desensitizing responses of TRPV1 ion channels by capsaicin, and the re-sensitization of TRPV1 by bradykinin, then to explore the role EP3 and EP4 receptors in mediating these bradykinin-dependent effects. Immunocytochemistry was used to study the co-expression and distribution of EP4, TRPV1, COX-1 and B2 in rat DRG neurons. Desensitization was seen upon repeated capsaicin application, we show that bradykinin-mediated sensitization of capsaicin-evoked calcium responses in rat DRG neurons occurs is dependent on COX-1 activity and utilizes a pathway that involves EP4 but not EP3 receptors. Immunocytochemical techniques revealed that EP4, TRPV1, COX-1 and B2 proteins are expressed mainly in small diameter (<1000 µm2 ) cell bodies of rat DRG neurons which are typically nociceptors. The present study provides suggestive evidence for a potential signalling pathway through which bradykinin may regulate TRPV1 ion channel function via EP4 receptors. In addition to confirming existing knowledge, the anatomical distribution and colocalization of these proteins in DRG neurons as revealed by this study offer valuable insight.

Design of Dual EP2/EP4 Antagonists through Scaffold Merging of Selective Inhibitors.

Prostaglandin E2 (PGE2) plays a key role in various stages of cancer. PGE2 signals through the EP2 and the EP4 receptors, promoting tumorigenesis, metastasis, and/or immune suppression. Dual inhibition of both the EP2 and the EP4 receptors has the potential to counteract the effect of PGE2 and to result in antitumor efficacy. We herein disclose for the first time the structure of dual EP2/EP4 antagonists. By merging the scaffolds of EP2 selective and EP4 selective inhibitors, we generated a new chemical series of compounds blocking both receptors with comparable potency. In vitro and in vivo profiling suggests that the newly identified compounds are promising lead structures for further development into dual EP2/EP4 antagonists for use in cancer therapy.

Association of PTGER4 and PRKAA1 genetic polymorphisms with gastric cancer.

BACKGROUND: Gastric cancer (GC) is one of the most common malignancies, affected by several genetic loci in the clinical phenotype. This study aimed to determine the association between PTGER4 and PRKAA1 gene polymorphisms and the risk of GC. METHODS: A total of 509 GC patients and 507 age and sex-matched healthy controls were recruited to explore the association between PTGER4 and PRKAA1 genetic polymorphisms and GC susceptibility. Logistic regression analysis was used to study the correlation between these SNPs and GC, with odd ratio (OR) and 95% confidence interval (CI) as indicators. Multifactor dimensionality reduction was utilized to analyze the genetic relationships among SNPs. was conducted to predict gene expression, the impact of SNPs on gene expression, and the signaling pathways involved in PTGER4 and PRKAA1. RESULTS: Overall, rs10036575 in PTGER4 (OR = 0.82, p = 0.029), rs10074991 (OR = 0.82, p = 0.024) and rs13361707 (OR = 0.82, p = 0.030) in PRKAA1 were associated with susceptibility to GC. Stratification analysis revealed that the effects of these SNPs in PTGER4 and PRKAA1 on GC susceptibility were dependent on smoking and were associated with a reduced risk of adenocarcinoma (p < 0.05). Bioinformatics analysis showed an association between SNPs and corresponding gene expression (p < 0.05), and PRKAA1 may affect GC by mediating RhoA. CONCLUSION: This study suggests that PTGER4 and PRKAA1 SNPs might affect the susceptibility of GC, providing a new biological perspective for GC risk assessment, pathogenesis exploration, and personalized treatment.

Prostaglandin E2 and myocarditis; friend or foe?

This review article summarizes the role of prostaglandin E2 (PGE2) and its receptors (EP1-EP4) as it relates to the inflammatory cardiomyopathy, myocarditis. During the COVID-19 pandemic, the onset of myocarditis in a subset of patients prompted a debate on the use of nonsteroidal anti-inflammatory drugs (NSAIDs), like ibuprofen, which act to inhibit the actions of prostaglandins. This review aims to further understanding of the role of PGE2 in the pathogenesis or protection of the myocardium in myocarditis. Inflammatory cardiomyopathies encompass a broad spectrum of disorders, all characterized by cardiac inflammation. Therefore, for the purpose of this review, the authors have placed particular emphasis on etiologies of myocarditis where effects of PGE2 have been documented.

Dual Blockade of EP2 and EP4 Signaling is Required for Optimal Immune Activation and Antitumor Activity Against Prostaglandin-Expressing Tumors.

While the role of prostaglandin E2 (PGE2) in promoting malignant progression is well established, how to optimally block the activity of PGE2 signaling remains to be demonstrated. Clinical trials with prostaglandin pathway targeted agents have shown activity but without sufficient significance or dose-limiting toxicities that have prevented approval. PGE2 signals through four receptors (EP1-4) to modulate tumor progression. EP2 and EP4 signaling exacerbates tumor pathology and is immunosuppressive through potentiating cAMP production. EP1 and EP3 signaling has the opposite effect through increasing IP3 and decreasing cAMP. Using available small-molecule antagonists of single EP receptors, the cyclooxygenase-2 (COX-2) inhibitor celecoxib, or a novel dual EP2/EP4 antagonist generated in this investigation, we tested which approach to block PGE2 signaling optimally restored immunologic activity in mouse and human immune cells and antitumor activity in syngeneic, spontaneous, and xenograft tumor models. We found that dual antagonism of EP2 and EP4 together significantly enhanced the activation of PGE2-suppressed mouse and human monocytes and CD8+ T cells in vitro as compared with single EP antagonists. CD8+ T-cell activation was dampened by single EP1 and EP3 antagonists. Dual EP2/EP4 PGE2 receptor antagonists increased tumor microenvironment lymphocyte infiltration and significantly reduced disease burden in multiple tumor models, including in the adenomatous polyposis coli (APC)min+/- spontaneous colorectal tumor model, compared with celecoxib. These results support a hypothesis that redundancy of EP2 and EP4 receptor signaling necessitates a therapeutic strategy of dual blockade of EP2 and EP4. Here we describe TPST-1495, a first-in-class orally available small-molecule dual EP2/EP4 antagonist. Significance: Prostaglandin (PGE2) drives tumor progression but the pathway has not been effectively drugged. We demonstrate significantly enhanced immunologic potency and antitumor activity through blockade of EP2 and EP4 PGE2 receptor signaling together with a single molecule.

A novel role for PGE2-EP4 in the developmental programming of the mouse ductus arteriosus: consequences for vessel maturation and function.

The ductus arteriosus (DA) is a vascular shunt that allows oxygenated blood to bypass the developing lungs in utero. Fetal DA patency requires vasodilatory signaling via the prostaglandin E2 (PGE2) receptor EP4. However, in humans and mice, disrupted PGE2-EP4 signaling in utero causes unexpected patency of the DA (PDA) after birth, suggesting another role for EP4 during development. We used EP4-knockout (KO) mice and acute versus chronic pharmacological approaches to investigate EP4 signaling in DA development and function. Expression analyses identified EP4 as the primary EP receptor in the DA from midgestation to term; inhibitor studies verified EP4 as the primary dilator during this period. Chronic antagonism recapitulated the EP4 KO phenotype and revealed a narrow developmental window when EP4 stimulation is required for postnatal DA closure. Myography studies indicate that despite reduced contractile properties, the EP4 KO DA maintains an intact oxygen response. In newborns, hyperoxia constricted the EP4 KO DA but survival was not improved, and permanent remodeling was disrupted. Vasomotion and increased nitric oxide (NO) sensitivity in the EP4 KO DA suggest incomplete DA development. Analysis of DA maturity markers confirmed a partially immature EP4 KO DA phenotype. Together, our data suggest that EP4 signaling in late gestation plays a key developmental role in establishing a functional term DA. When disrupted in EP4 KO mice, the postnatal DA exhibits signaling and contractile properties characteristic of an immature DA, including impairments in the first, muscular phase of DA closure, in addition to known abnormalities in the second permanent remodeling phase.NEW & NOTEWORTHY EP4 is the primary EP receptor in the ductus arteriosus (DA) and is critical during late gestation for its development and eventual closure. The "paradoxical" patent DA (PDA) phenotype of EP4-knockout mice arises from a combination of impaired contractile potential, altered signaling properties, and a failure to remodel associated with an underdeveloped immature vessel. These findings provide new mechanistic insights into women who receive NSAIDs to treat preterm labor, whose infants have unexplained PDA.

Prorelaxant E-type Prostanoid Receptors Functionally Partition to Different Procontractile Receptors in Airway Smooth Muscle.

Prostaglandin E2 imparts diverse physiological effects on multiple airway cells through its actions on four distinct E-type prostanoid (EP) receptor subtypes (EP1-EP4). Gs-coupled EP2 and EP4 receptors are expressed on airway smooth muscle (ASM), yet their capacity to regulate the ASM contractile state remains subject to debate. We used EP2 and EP4 subtype-specific agonists (ONO-259 and ONO-329, respectively) in cell- and tissue-based models of human ASM contraction-magnetic twisting cytometry (MTC), and precision-cut lung slices (PCLSs), respectively-to study the EP2 and EP4 regulation of ASM contraction and signaling under conditions of histamine or methacholine (MCh) stimulation. ONO-329 was superior (<0.05) to ONO-259 in relaxing MCh-contracted PCLSs (log half maximal effective concentration [logEC50]: 4.9 × 10-7 vs. 2.2 × 10-6; maximal bronchodilation ± SE, 35 ± 2% vs. 15 ± 2%). However, ONO-259 and ONO-329 were similarly efficacious in relaxing histamine-contracted PCLSs. Similar differential effects were observed in MTC studies. Signaling analyses revealed only modest differences in ONO-329- and ONO-259-induced phosphorylation of the protein kinase A substrates VASP and HSP20, with concomitant stimulation with MCh or histamine. Conversely, ONO-259 failed to inhibit MCh-induced phosphorylation of the regulatory myosin light chain (pMLC20) and the F-actin/G-actin ratio (F/G-actin ratio) while effectively inhibiting their induction by histamine. ONO-329 was effective in reversing induced pMLC20 and the F/G-actin ratio with both MCh and histamine. Thus, the contractile-agonist-dependent differential effects are not explained by changes in the global levels of phosphorylated protein kinase A substrates but are reflected in the regulation of pMLC20 (cross-bridge cycling) and F/G-actin ratio (actin cytoskeleton integrity, force transmission), implicating a role for compartmentalized signaling involving muscarinic, histamine, and EP receptor subtypes.

EP4 Receptor Conformation Sensor Suited for Ligand Screening and Imaging of Extracellular Prostaglandins.

Prostaglandins are important lipid mediators with a wide range of functions in the human body. They act mainly via plasma membrane localized prostaglandin receptors, which belong to the G-protein coupled receptor class. Due to their localized formation and short lifetime, it is important to be able to measure the distribution and abundance of prostaglandins in time and/or space. In this study, we present a Foerster resonance energy transfer (FRET)-based conformation sensor of the human prostaglandin E receptor subtype 4 (EP4 receptor), which was capable of detecting prostaglandin E2 (PGE2)-induced receptor activation in the low nanomolar range with a good signal-to-noise ratio. The sensor retained the typical selectivity for PGE2 among arachidonic acid products. Human embryonic kidney cells stably expressing the sensor did not produce detectable amounts of prostaglandins making them suitable for a coculture approach allowing us, over time, to detect prostaglandin formation in Madin-Darby canine kidney cells and primary mouse macrophages. Furthermore, the EP4 receptor sensor proved to be suited to detect experimentally generated PGE2 gradients by means of FRET-microscopy, indicating the potential to measure gradients of PGE2 within tissues. In addition to FRET-based imaging of prostanoid release, the sensor allowed not only for determination of PGE2 concentrations, but also proved to be capable of measuring ligand binding kinetics. The good signal-to-noise ratio at a commercial plate reader and the ability to directly determine ligand efficacy shows the obvious potential of this sensor interest for screening and characterization of novel ligands of the pharmacologically important human EP4 receptor. SIGNIFICANCE STATEMENT: The authors present a biosensor based on the prostaglandin E receptor subtype 4, which is well suited to measure extracellular prostaglandin E2 (PGE2) concentration with high temporal and spatial resolution. It can be used for the imaging of PGE2 levels and gradients by means of Foerster resonance energy transfer microscopy, and for determining PGE2 release of primary cells as well as for screening purposes in a plate reader setting.