CJ-023,423, a novel, potent and selective prostaglandin EP4 receptor antagonist with antihyperalgesic properties

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.

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.

Docking for EP4R antagonists active against inflammatory pain

The lipid prostaglandin E2 (PGE2) mediates inflammatory pain by activating G protein-coupled receptors, including the prostaglandin E2 receptor 4 (EP4R). Nonsteroidal anti-inflammatory drugs (NSAIDs) reduce nociception by inhibiting prostaglandin synthesis, however, the disruption of upstream prostanoid biosynthesis can lead to pleiotropic effects including gastrointestinal bleeding and cardiac complications. In contrast, by acting downstream, EP4R antagonists may act specifically as anti-inflammatory agents and, to date, no selective EP4R antagonists have been approved for human use. In this work, seeking to diversify EP4R antagonist scaffolds, we computationally dock over 400 million compounds against an EP4R crystal structure and experimentally validate 71 highly ranked, de novo synthesized molecules. Further, we show how structure-based optimization of initial docking hits identifies a potent and selective antagonist with 16 nanomolar potency. Finally, we demonstrate favorable pharmacokinetics for the discovered compound as well as anti-allodynic and anti-inflammatory activity in several preclinical pain models in mice.

Pharmacokinetics of a single oral dose of grapiprant in juvenile pigs (Sus scrofa domestica)

Both pet and research pigs can suffer from some degree of pain from surgery, injuries, or osteoarthritis (OA). Despite this, there is a paucity of data on safe and effective analgesia agents in pigs. Grapiprant is an EP4 antagonist that blocks the action of the pro-inflammatory prostanoid, PGE2 . It has shown efficacy in attenuating pain associated with ovariohysterectomy and OA in dogs. However, there are no data regarding grapiprant in pigs. Therefore, the pharmacokinetic profile of orally administered grapiprant to juvenile pigs (Sus scrofa domestica) was evaluated in this study. Seven juvenile pigs received 12 mg/kg grapiprant orally. Blood was collected from an indwelling jugular catheter using the push-pull method at set timepoints up to 48 hours. Sample analysis was performed with high-performance liquid chromatography. Mean grapiprant plasma concentration was 164.3 ± 104.7 ng/mL which occurred at 0.8 ± 0.3 h. This study demonstrated that grapiprant concentrations consistent with analgesia in dogs were reached at this dosage in pigs. Further studies are needed to evaluate the efficacy of grapiprant in pigs.

Discovery of Novel, Selective Prostaglandin EP4 Receptor Antagonists with Efficacy in Cancer Models

Prostaglandin E2 (PGE2) receptor 4 (EP4) is one of four EP receptors commonly upregulated in the tumor microenvironment and plays vital roles in stimulating cell proliferation, invasion, and metastasis. Biochemical blockade of the PGE2-EP4 signaling pathway is a promising strategy for controlling inflammatory and immune related disorders. Recently combination therapies of EP4 antagonists with anti-PD-1 or chemotherapy agents have emerged in clinical studies for lung, breast, colon, and pancreatic cancers. Herein, a novel series of indole-2-carboxamide derivatives were identified as selective EP4 antagonists, and SAR studies led to the discovery of the potent compound 36. Due to favorable pharmacokinetics properties and good oral bioavailability (F = 76%), compound 36 was chosen for in vivo efficacy studies. Compound 36 inhibited tumor growth in a CT-26 colon cancer xenograft better than E7046 and a combination of 36 with capecitabine significantly suppressed tumor growth (TGI up to 94.26%) in mouse models.

Discovery of 2H-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 PGE₂/EP4 signaling to induce robust antitumor immune response represents an attractive immunotherapy strategy. Herein, a 2H-indazole-3-carboxamide containing compound 1 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 14, which displayed single-nanomolar EP4 antagonistic activity in a panel of cell functional assays, high subtype selectivity, and favorable drug-like profiles. Moreover, compound 14 profoundly inhibited the up-regulation of multiple immunosuppression-related genes in macrophages. Oral administration of compound 14, 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 14 as a candidate for developing novel EP4 antagonists for tumor immunotherapy.

Evaluation of the perioperative analgesic effects of grapiprant compared with carprofen in dogs undergoing elective ovariohysterectomy

OBJECTIVE

To evaluate and compare postoperative analgesic effects of grapiprant and carprofen in dogs undergoing ovariohysterectomy.

ANIMALS

42 sexually intact female healthy dogs (< 35 kg and 0.5 to 7 years old) were enrolled.

PROCEDURES

In a masked, randomized, noninferiority clinical trial, dogs received either 2 mg/kg of grapiprant or 4.4 mg/kg of carprofen orally 2 hours prior to ovariohysterectomy. Postoperative pain was assessed using the Glasgow Composite Pain Scale-Short Form (GCPS-SF) at extubation and 2, 4, 6, 8, 18, and 24 hours postextubation and compared to baseline. After each pain scoring, mechanical nociceptive testing with von Frey monofilaments (vF) was performed to assess hyperalgesia. Hydromorphone (0.05 mg/kg, IM) was administered to any dog with a GCPS-SF of ≥ 5/24. The noninferiority limit (NI) for the GCPS-SF was Δ = 3. The NI for vF was Δ = -0.2. Following noninferiority, a mixed-effect ANOVA and post hoc comparisons were made with the Tukey correction method (P < .05).

RESULTS

3 dogs required rescue analgesia and were excluded from statistical analysis. Of the remaining 39 dogs, the upper CI for GCPS-SF was below the NI of 3 and the lower CI for vF was greater than the NI of -0.2, indicating noninferiority of grapiprant as compared to carprofen. There was no difference between treatment (P = .89) nor treatment by time (P = .62) for GCPS-SF. There was no difference between groups at any time point or over time when vF were used.

CLINICAL RELEVANCE

Our study results support the use of grapiprant as an analgesic alternative to carprofen in dogs undergoing ovariohysterectomy.

Quantification of Grapiprant and Its Stability Testing under Changing Environmental Conditions

Grapiprant is a new analgesic and anti-inflammatory drug belonging to the piprant class, approved in 2016 by the FDA Veterinary Medicine Center for the treatment of pain and inflammation associated with osteoarthritis in dogs. It acts as a highly selective antagonist of the EP4 receptor, one of the four prostaglandin E2 (PGE2) receptor subtypes. It has been shown to have anti-inflammatory effects in rat models of acute and chronic inflammation and clinical studies in people with osteoarthritis. The current state of knowledge suggests the possibility of using it in oncological therapy. The manuscript presents the development of conditions for the identification and quantitative determination of grapiprant by thin-layer chromatography with densitometric detection. The optimal separation of the substance occurs using silica gel 60F254 chromatographic plates and the mobile phase containing ethyl acetate-toluene-butylamine. Validation (according to ICH requirements) showed that the developed method is characterized by straightness of results in a wide concentration range with the limit of detection of 146.65 µg/mL. The %RSD values of the precision and accuracy confirm the sensitivity and reliability of the developed procedure. Next, the method was used for quantification of grapiprant in a pharmaceutical preparation, and for stability studies under various environmental conditions. Additionally, the mass studies were carried out on the stressed samples using the UPLC-MS/MS method. The degradation products were primarily characterized by comparing their mass fragmentation profiles with those of the drug. The results indicated a potential degradation pathway for grapiprant.

Advances in the pharmaceutical treatment options for canine osteoarthritis

Canine osteoarthritis is a significant cause of pain in many dogs and can therefore compromise animal welfare. As the understanding of the biology and pain mechanisms underpinning osteoarthritis grows, so do the number of treatments available to manage it. Over the last decade, there have been a number of advances in the pharmaceutical treatment options available for dogs with osteoarthritis, as well as an increasing number of clinical trials investigating the efficacy of pre-existing treatments. This review aims to examine the current evidence behind pharmaceutical treatment options for canine osteoarthritis, including non-steroidal anti-inflammatory drugs, piprants, monoclonal antibodies, adjunctive analgesics, structure modifying osteoarthritis drugs and regenerative therapies.

Pharmacokinetics of grapiprant and effects on TNF-alpha concentrations following oral administration to horses

Grapiprant is a prostaglandin E2 receptor antagonist that has been found to be an effective anti-inflammatory in dogs and that is devoid of some of the adverse effects associated with traditional NSAIDs that elicit their effects through inhibition of PGE2 production. Previously published reports have described the pharmacokinetics of this drug in horses when administered at 2 mg/kg; however, pharmacodynamic effects in this species have yet to be described. The objective of the current study was to describe the pharmacokinetics and pharmacodynamics of grapiprant at a higher dose. Eight horses received a single oral administration of 15 mg/kg. Plasma concentrations were determined for 96 h using liquid chromatography-tandem mass spectrometry. Non-compartmental analysis was used to determine pharmacokinetic parameters. Pharmacodynamic effects were assessed ex vivo by stimulating blood samples with PGE2 and determining TNF-ɑ concentrations. Maximum concentration, time to maximum concentration and area under the curve were 327.5 (188.4-663.0) ng/ml, 1 (0.75-2.0) hour and 831.8 (512.6-1421.6) h*ng/ml, respectively. The terminal half-life was 11.1 (8.27-21.2) hr. Significant stimulation of TNF alpha was noted for 2-4 h post-drug administration. Results of this study suggest a short duration of EP4 receptor engagement when administered at a dose of 15 mg/kg.

Grapiprant or carprofen following ovariohysterectomy in the cat: analgesic efficacy, hematological, biochemical and urinalysis evaluation

OBJECTIVES

This study aimed to compare the analgesic effect between carprofen and grapiprant every 12 or 24 h on postoperative pain in cats undergoing ovariohysterectomy, in addition to the effects on the hematological, biochemical and urinalysis variables.

METHODS

A total of 32 female cats were randomly divided into three groups, according to the treatment administered with the first dose given orally 90 mins before surgery, as follows: CAR (cats received 4 mg/kg carprofen, n = 11); GRA1 (cats received 2 mg/kg grapiprant, n = 10); and GRA2 (cats received 2 mg/kg grapiprant q12h, n = 11). Pain was assessed by UNESP-Botucatu Multidimensional Composite Pain Scale (UNESP) and Glasgow Feline Composite Measure Pain Scale (GLASGOW) for cats preoperatively (baseline) and at 1, 3, 6, 8, 12 and 24 h after extubation. Venous blood was collected at baseline, and 12 and 24 h after the administration of carprofen or grapiprant to perform a complete blood count (CBC), the percentage of Heinz bodies and serum biochemistry (alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, gamma-glutamyltransferase, creatinine and urea). Urinalysis was performed at baseline and 24 h after extubation. Glucose levels were evaluated at baseline and 1 h postoperatively.

RESULTS

Pain scores were not significantly different among groups in both scales, although pain was higher at 3 h in comparison with 24 h in all groups. In the GRA1 and GRA2 groups, 67% (14/21) of cats needed rescue analgesia compared with 18% (2/11) in the CAR group. Glucose increased from baseline to 1 h in the GRA1 and GRA2 groups. None of the CBC, serum biochemistry and urinalysis variables differed among groups.

CONCLUSIONS AND RELEVANCE

Grapiprant did not promote adequate analgesia during the first 3 h postoperatively in cats undergoing ovariohysterectomy compared with carprofen, and no benefits were observed by administering grapiprant every 12 h.

A Novel Small Molecular Prostaglandin Receptor EP4 Antagonist, L001, Suppresses Pancreatic Cancer Metastasis

Metastatic pancreatic cancer remains a major clinical challenge, emphasizing the urgent need for the exploitation of novel therapeutic approaches with superior response. In this study, we demonstrate that the aberrant activation of prostaglandin E₂ (PGE₂) receptor 4 (EP4) is a pro-metastatic signal in pancreatic cancer. To explore the therapeutic role of EP4 signaling, we developed a potent and selective EP4 antagonist L001 with single-nanomolar activity using a panel of cell functional assays. EP4 antagonism by L001 effectively repressed PGE₂-elicited cell migration and the invasion of pancreatic cancer cells in a dose-dependent manner. Importantly, L001 alone or combined with the chemotherapy drug gemcitabine exhibited remarkably anti-metastasis activity in a pancreatic cancer hepatic metastasis model with excellent tolerability and safety. Mechanistically, EP4 blockade by L001 abrogated Yes-associated protein 1 (YAP)-driven pro-metastatic factor expression in pancreatic cancer cells. The suppression of YAP’s activity was also observed upon L001 treatment in vivo. Together, these findings support the notions that EP4–YAP signaling axis is a vital pro-metastatic pathway in pancreatic cancer and that EP4 inhibition with L001 may deliver a therapeutic benefit for patients with metastatic pancreatic cancer.

Inflammation, Fibrosis and Cancer: Mechanisms, Therapeutic Options and Challenges

Uncontrolled inflammation is a salient factor in multiple chronic inflammatory diseases and cancers. In this review, we provided an in-depth analysis of the relationships and distinctions between uncontrolled inflammation, fibrosis and cancers, while emphasizing the challenges and opportunities of developing novel therapies for the treatment and/or management of these diseases. We described how drug delivery systems, combination therapy and the integration of tissue-targeted and/or pathways selective strategies could overcome the challenges of current agents for managing and/or treating chronic inflammatory diseases and cancers. We also recognized the value of the re-evaluation of the disease-specific roles of multiple pathways implicated in the pathophysiology of chronic inflammatory diseases and cancers-as well as the application of data from single-cell RNA sequencing in the success of future drug discovery endeavors.

Pharmacokinetics of grapiprant administered to red-tailed hawks (Buteo jamaicensis) after food was withheld for 24 hours

OBJECTIVE

To identify an oral dose of grapiprant for red-tailed hawks (RTHAs; Buteo jamaicensis) that would achieve a plasma concentration > 164 ng/mL, which is considered therapeutic for dogs with osteoarthritis.

ANIMALS

6 healthy adult RTHAs.

PROCEDURES

A preliminary study, in which grapiprant (4 mg/kg [n = 2], 11 mg/kg [2], or 45 mg/kg [2]) was delivered into the crop of RTHAs from which food had been withheld for 24 hours, was performed to obtained pharmacokinetic data for use with modeling software to simulate results for grapiprant doses of 20, 25, 30, 35, and 40 mg/kg. Simulation results directed our selection of the grapiprant dose administered to the RTHAs in a single-dose study. Plasma grapiprant concentration, body weight, and gastrointestinal signs of RTHAs were monitored.

RESULTS

On the basis of results from the preliminary study and simulations, a grapiprant dose of 30 mg/kg was used in the single-dose study. The geometric mean maximum observed plasma concentration of grapiprant was 3,184 ng/mL, time to maximum plasma grapiprant concentration was 2.0 hours, and the harmonic mean terminal half-life was 17.1 hours. No substantial adverse effects were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Although the single dose of grapiprant (30 mg/kg) delivered into the crop achieved plasma concentrations > 164 ng/mL in the RTHAs, it was unknown whether this concentration would be therapeutic for birds. Further research that incorporates multidose assessments, safety monitoring, and pharmacodynamic data collection is warranted on the use of grapiprant in RTHAs from which food was withheld versus not withheld.

TRPV1 Channel Activated by the PGE2/EP4 Pathway Mediates Spinal Hypersensitivity in a Mouse Model of Vertebral Endplate Degeneration

Low back pain (LBP) is the primary cause of disability globally. There is a close relationship between Modic changes or endplate defects and LBP. Endplates undergo ossification and become highly porous during intervertebral disc (IVD) degeneration. In our study, we used a mouse model of vertebral endplate degeneration by lumbar spine instability (LSI) surgery. Safranin O and fast green staining and μCT scan showed that LSI surgery led to endplate ossification and porosity, but the endplates in the sham group were cartilaginous and homogenous. Immunofluorescent staining demonstrated the innervation of calcitonin gene-related peptide- (CGRP-) positive nerve fibers in the porous endplate of LSI mice. Behavior test experiments showed an increased spinal hypersensitivity in LSI mice. Moreover, we found an increased cyclooxygenase 2 (COX2) expression and an elevated prostaglandin E2 (PGE2) concentration in the porous endplate of LSI mice. Immunofluorescent staining showed the colocalization of E-prostanoid 4 (EP4)/transient receptor potential vanilloid 1 (TRPV1) and CGRP in the nerve endings in the endplate and in the dorsal root ganglion (DRG) neurons, and western blotting analysis demonstrated that EP4 and TRPV1 expression significantly increased in the LSI group. Our patch clamp study further showed that LSI surgery significantly enhanced the current density of the TRPV1 channel in small-size DRG neurons. A selective EP4 receptor antagonist, L161982, reduced the spinal hypersensitivity of LSI mice by blocking the PGE2/EP4 pathway. In addition, TRPV1 current and neuronal excitability in DRG neurons were also significantly decreased by L161982 treatment. In summary, the PGE2/EP4 pathway in the porous endplate could activate the TRPV1 channel in DRG neurons to cause spinal hypersensitivity in LSI mice. L161982, a selective EP4 receptor antagonist, could turn down the TRPV1 current and decrease the neuronal excitability of DRG neurons to reduce spinal pain.

PGE2/EP4 skeleton interoception activity reduces vertebral endplate porosity and spinal pain with low-dose celecoxib

Skeletal interoception regulates bone homeostasis through the prostaglandin E2 (PGE2) concentration in bone. Vertebral endplates undergo ossification and become highly porous during intervertebral disc degeneration and aging. We found that the PGE2 concentration was elevated in porous endplates to generate spinal pain. Importantly, treatment with a high-dose cyclooxygenase 2 inhibitor (celecoxib, 80 mg·kg⁻¹ per day) decreased the prostaglandin E2 concentration and attenuated spinal pain in mice with lumbar spine instability. However, this treatment impaired bone formation in porous endplates, and spinal pain recurred after discontinuing the treatment. Interestingly, low-dose celecoxib (20 mg·kg⁻¹ per day, which is equivalent to one-quarter of the clinical maximum dosage) induced a latent inhibition of spinal pain at 3 weeks post-treatment, which persisted even after discontinuing treatment. Furthermore, when the prostaglandin E2 concentration was maintained at the physiological level with low-dose celecoxib, endplate porosity was reduced significantly, which was associated with decreased sensory nerve innervation and spinal pain. These findings suggest that low-dose celecoxib may help to maintain skeletal interoception and decrease vertebral endplate porosity, thereby reducing sensory innervation and spinal pain in mice.

Mapping the Molecular Architecture Required for Lipid-Binding Pockets Using a Subset of Established and Orphan G-Protein Coupled Receptors

G-protein coupled receptors (GPCRs) sense a wide variety of stimuli, including lipids, and transduce signals to the intracellular environment to exert various physiological responses. However, the structural features of GPCRs responsible for detecting and triggering responses to distinct lipid ligands have only recently begun to be revealed. 14,15-epoxyeicosatrienoic acid (14,15-EET) is one such lipid mediator that plays an essential role in the vascular system, displaying both vasodilatory and anti-inflammatory properties. We recently reported multiple low-affinity 14,15-EET-binding GPCRs, but the mechanism by which these receptors sense 14,15-EET remains unclear. Here, we have taken a combined computational and experimental approach to identify and confirm critical residues and properties within the lipid-binding pocket. Furthermore, we generated mutants to engineer selected GPCR-predicted binding sites to either confer or abolish 14,15-EET-induced signaling. Our structure-function analyses indicate that hydrophobic and positively charged residues of the receptor-binding pocket are prerequisites for recognizing lipid ligands such as 14,15-EET and possibly other eicosanoids.

Tolerance and Pharmacokinetics of Galliprant™ Administered Orally to Collies Homozygous for MDR1-1Δ

The objectives of the study were to evaluate the pharmacokinetics and tolerance of grapiprant, a substrate of the human P-gp transporter, in collies homozygous for MDR1-1Δ when administered at the labeled dosage of 2 mg/kg once daily for 28 days. Twelve collie dogs with homozygous for MDR1-1Δ genotype from a commercial colony were used in the study, eight in the treated group and four as placebo-treated controls. The only treatment-related clinical sign was self-limiting vomiting (in 2/8 treated animals) and the only treatment-related clinical pathological changes seen were a slight decrease in serum albumin in one dog (2.6 g/dL; reference 2.7 to 3.9 g/dL) and total protein (5.1 g/dL; reference 5.5 to 7.7 g/dL). Absorption of grapiprant was rapid with a median T_max of 1 h, C_max of 5.2 μg/mL, AUC_0-24 of 17.3 ± 7.1 h^* μg/mL and median terminal t½ of 4.3 h after the first dose. To determine whether MDR1-1Δ animals handle grapiprant differently from normal dogs, a population pharmacokinetic analysis was performed utilizing data from the collies and historical beagle data. Volume of the peripheral compartment of collies was estimated to be 45% that of beagles, and clearance from the central compartment was 71% less in collies than in beagles. Self-liming vomiting events occurred at a numerically higher rate (2/8; 25%) in this group of P-gp-deficient dogs than seen in a clinical study (17%) composed of various dog breeds but limited numbers in this PK study make comparisons difficult. Grapiprant was otherwise well tolerated in collies homozygous for MDR1-1Δ despite increased drug exposure compared to dogs without this mutation.

Grapiprant: A snapshot of the current knowledge

Grapiprant is the pioneer member of the novel piprant class, a potent and specific antagonist of the prostaglandin E2 receptor 4. It has been approved in veterinary medicine for the control of pain and inflammation associated with osteoarthritis in dogs at the dose regimen of 2 mg/kg once a day by the FDA and EMA (for pain only) in 2016 and 2018, respectively. The aim of this narrative review was to report the analytical methods, pharmacokinetics, pharmacodynamics and safety of grapiprant in several animal species using the best available published scientific evidence. In conclusion, most of the analytical methods proposed for grapiprant detection are simple, reliable, sensitive and validated. The pharmacokinetics show discrepancies between animal species. The therapeutic efficacy seems more suited to chronic rather than acute pain.

Ibuprofen-based advanced therapeutics: breaking the inflammatory link in cancer, neurodegeneration, and diseases

Ibuprofen is a classical nonsteroidal anti-inflammatory drug (NSAID) highly prescribed to reduce acute pain and inflammation under an array of conditions, including rheumatoid arthritis, osteoarthritis, dysmenorrhea, and gout. Ibuprofen acts as a potential inhibitor for cyclooxygenase enzymes (COX-1 and COX-2). In the past few decades, research on this small molecule has led to identifying other possible therapeutic benefits. Anti-tumorigenic and neuroprotective functions of Ibuprofen are majorly recognized in recent literature and need further consideration. Additionally, several other roles of this anti-inflammatory molecule have been discovered and subjected to experimental assessment in various diseases. However, the major challenge faced by Ibuprofen and other drugs of similar classes is their side effects, and tendency to cause gastrointestinal injury, generate cardiovascular risks, modulate hepatic and acute kidney diseases. Future research should also be conducted to deduce new methods and approaches of suppressing the unwanted toxic changes mediated by these drugs and develop new therapeutic avenues so that these small molecules continue to serve the purposes. This article primarily aims to develop a comprehensive and better understanding of Ibuprofen, its pharmacological features, therapeutic benefits, and possible but less understood medicinal properties apart from major challenges in its future application.KEY POINTSIbuprofen, an NSAID, is a classical anti-inflammatory therapeutic agent.Pro-apoptotic roles of NSAIDs have been explored in detail in the past, holding the key in anti-cancer therapies.Excessive and continuous use of NSAIDs may have several side effects and multiple organ damage.Hyperactivated Inflammation initiates multifold detrimental changes in multiple pathological conditions.Targeting inflammatory pathways hold the key to several therapeutic strategies against many diseases, including cancer, microbial infections, multiple sclerosis, and many other brain diseases.

In silico identification of available drugs targeting cell surface BiP to disrupt SARS-CoV-2 binding and replication: Drug repurposing approach

Aims

Cell surface binding immunoglobin protein (csBiP) is predicted to be susceptible to SARS-CoV-2 binding. With a substrate-binding domain (SBD) that binds to polypeptides and a nucleotide-binding domain (NBD) that can initiate extrinsic caspase-dependent apoptosis, csBiP may be a promising therapeutic target for COVID-19. This study aims to identify FDA-approved drugs that can neutralize viral binding and prevent viral replication by targeting the functional domains of csBiP.

Methods

In silico screening of 1999 FDA-approved drugs against the functional domains of BiP were performed using three molecular docking programs to avoid bias from individual docking programs. Top ligands were selected by averaging the ligand rankings from three programs. Interactions between top ligands and functional domains of BiP were analyzed.

Key findings

The top 10 SBD-binding candidates are velpatasvir, irinotecan, netupitant, lapatinib, doramectin, conivaptan, fenoverine, duvelisib, irbesartan, and pazopanib. The top 10 NBD-binding candidates are nilotinib, eltrombopag, grapiprant, topotecan, acetohexamide, vemurafenib, paritaprevir, pixantrone, azosemide, and piperaquine-phosphate. Among them, Velpatasvir and paritaprevir are antiviral agents that target the protease of hepatitis C virus. Netupitant is an anti-inflammatory drug that inhibits neurokinin-1 receptor, which contributes to acute inflammation. Grapiprant is an anti-inflammatory drug that inhibits the prostaglandin E₂ receptor protein subtype 4, which is expressed on immune cells and triggers inflammation. These predicted SBD-binding drugs could disrupt SARS-CoV-2 binding to csBiP, and NBD-binding drugs may falter viral attachment and replication by locking the SBD in closed conformation and triggering apoptosis in infected cells.

Significance

csBiP appears to be a novel therapeutic target against COVID-19 by preventing viral attachment and replication. These identified drugs could be repurposed to treat COVID-19 patients.

Prostaglandin E2 receptors and their role in gastrointestinal motility - Potential therapeutic targets

Prostaglandin E2 (PGE2) is found throughout the gastrointestinal tract in a diverse variety of functions and roles. The recent discovery of four PGE2 receptor subtypes in intestinal muscle layers as well as in the enteric plexus has led to much interest in the study of their roles in gut motility. Gut dysmotility has been implicated in functional disease processes including irritable bowel syndrome (IBS) and slow transit constipation, and lubiprostone, a PGE2 derivative, has recently been licensed to treat both conditions. The diversity of actions of PGE2 in the intestinal tract is attributed to its differing effects on its downstream receptor types, as well as their varied distribution in the gut, in both health and disease. This review aims to identify the role and distribution of PGE2 receptors in the intestinal tract, and aims to elucidate their distinct role in gut motor function, with a specific focus on functional intestinal pathologies.

Aberrant subchondral osteoblastic metabolism modifies NaV1.8 for osteoarthritis

Pain is the most prominent symptom of osteoarthritis (OA) progression. However, the relationship between pain and OA progression remains largely unknown. Here we report osteoblast secret prostaglandin E2 (PGE2) during aberrant subchondral bone remodeling induces pain and OA progression in mice. Specific deletion of the major PGE2 producing enzyme cyclooxygenase 2 (COX2) in osteoblasts or PGE2 receptor EP4 in peripheral nerve markedly ameliorates OA symptoms. Mechanistically, PGE2 sensitizes dorsal root ganglia (DRG) neurons by modifying the voltage-gated sodium channel Na_V1.8, evidenced by that genetically or pharmacologically inhibiting Na_V1.8 in DRG neurons can substantially attenuate OA. Moreover, drugs targeting aberrant subchondral bone remodeling also attenuates OA through rebalancing PGE2 production and Na_V1.8 modification. Thus, aberrant subchondral remodeling induced Na_V1.8 neuronal modification is an important player in OA and is a potential therapeutic target in multiple skeletal degenerative diseases.

Many people will suffer from joint pain as they age, particularly in their knees. The most common cause of this pain is osteoarthritis, a disease that affects a tissue inside joints called cartilage. In a healthy knee, cartilage acts as a shock absorber. It cushions the ends of bones and enables them to move smoothly against one another. But in osteoarthritis, cartilage gradually wears away. As a result, the bones within a joint rub against each other whenever a person moves. This makes activities such as running or climbing stairs painful.

But how does this pain arise? Previous work has implicated cells called osteoblasts. Osteoblasts are found in the area of the bone just below the cartilage. They produce new bone tissue throughout our lives, enabling our bones to regenerate and repair. Each time we move, forces acting on the knee joint activate osteoblasts. The cells respond by releasing a key molecule called PGE2, which is a factor in pain pathways. The joints of people with osteoarthritis produce too much PGE2. But exactly how this leads to increased pain sensation has been unclear.

Zhu et al. now complete this story by working out how PGE2 triggers pain. Experiments in mice reveal that PGE2 irritates the nerve fibers that carry pain signals from the knee joint to the brain. It does this by activating a channel protein called Na_v1.8, which allows sodium ions through the membranes of those nerve fibers. Zhu et al. show that, in a mouse model of osteoarthritis, Na_v1.8 opens too widely in response to binding of PGE2, so the nerve cells become overactive and transmit a stronger pain sensation. This means that even small movements cause intense pain signals to travel from the joints to the brain.

Building on their findings, Zhu et al. developed a drug that acts directly on bone to reduce PGE2 production, and show that this drug reduces pain in mice with osteoarthritis. At present, there are no treatments that reverse the damage that occurs during osteoarthritis, but further testing will determine whether this new drug could one day relieve joint pain in patients.

Determination of grapiprant plasma and urine concentrations in horses

OBJECTIVE

Non-steroidal anti-inflammatory drugs are inhibitors of cyclooxygenase (COX) in tissues and used as therapeutic agents in different species. Grapiprant, a member of the piprant class of compounds, antagonizes prostaglandin receptors. It is a highly selective EP4 prostaglandin E₂ receptor inhibitor, thereby limiting the potential for adverse effects caused by wider COX inhibition. The objectives of this study were to determine if the approved canine dose would result in measurable concentrations in horses, and to validate a chromatographic method of analysis for grapiprant in urine and plasma.

STUDY DESIGN

Experimental study.

ANIMALS

A total of six healthy, adult mixed-breed mares weighing 502 ± 66 (397-600) kg and aged 14.8 ± 5.3 (6-21) years.

METHODS

Mares were administered one dose of 2 mg kg^-1 grapiprant via nasogastric tube. Blood and urine samples were collected prior to and up to 48 hours after drug administration. Drug concentrations were measured using high-performance liquid chromatography.

RESULTS

Grapiprant plasma concentrations ranged from 71 to 149 ng mL^-1 with the mean peak concentration (106 ng mL^-1) occurring at 30 minutes. Concentrations were below the lower limit of quantification (50 ng mL^-1) in four of six horses at 1 hour and in all six horses by 2 hours after drug administration. Grapiprant urine concentrations ranged from 40 to 4077 ng mL^-1 and were still detectable at 48 hours after administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Currently, there are no published studies looking at the pharmacodynamics of grapiprant in horses. The effective concentration needed to control pain in dogs ranges 114-164 ng mL^-1. Oral administration of grapiprant (2 mg kg^-1) in horses did not achieve those concentrations. The dose was well tolerated; therefore, studies with larger doses could be conducted.

Comparison of two inhibitors of E-type prostanoid receptor four and carprofen in dogs with experimentally induced acute synovitis

OBJECTIVE

To investigate the ability of a proprietary antagonist of E-type prostanoid receptor (EP) 4, grapiprant, and carprofen to attenuate lameness attributable to urate-induced synovitis in dogs.

ANIMALS

5 purpose-bred hound-cross dogs.

PROCEDURES

A blinded, 3-way crossover study was performed. Dogs received each of 3 treatments (L-766, a proprietary antagonist of EP4; 4.0 mg/kg), grapiprant (an antagonist of EP4; 2.0 mg/kg), and carprofen (4.4 mg/kg); dogs received 4 doses of each treatment (14 and 2 hours before and 22 and 46 hours after urate injection). Synovitis was induced by intra-articular injection of sodium urate. Measurements (vertical ground reaction forces and clinical lameness scores) were obtained immediately before (0 hours; baseline) and 6, 12, 24, 36, and 48 hours after sodium urate injection. All data were analyzed with repeated-measures ANOVA.

RESULTS

Lameness scores at 6 hours were significantly higher than baseline lameness scores for all treatments. Lameness scores for the grapiprant treatment remained significantly higher at 12 and 24 hours, compared with baseline lameness scores. Lameness scores for the carprofen treatment were significantly lower than lameness scores for the grapiprant treatment at 6, 12, and 24 hours. Analysis of peak vertical force and vertical impulse data revealed a pattern similar to that for lameness scores. Treatment with L-766 resulted in a significantly higher vertical impulse at 48 hours than did treatment with carprofen or grapiprant.

CONCLUSIONS AND CLINICAL RELEVANCE

In these dogs, carprofen was the most effective treatment for attenuating lameness induced by injection of sodium urate, and grapiprant was the least effective treatment.

Discovery and Characterization of 1H-1,2,3-Triazole Derivatives as Novel Prostanoid EP4 Receptor Antagonists for Cancer Immunotherapy

The prostanoid EP4 receptor is one of the key receptors associated with inflammatory mediator PGE₂-elicited immunosuppression in the tumor microenvironment. Blockade of EP4 signaling to enhance immunity-mediated tumor elimination has recently emerged as a promising strategy for cancer immunotherapy. In our efforts to discover novel subtype-selective EP4 antagonists, we designed and synthesized a class of 1H-1,2,3-triazole-based ligands that display low nanomolar antagonism activity toward the human EP4 receptor and excellent subtype selectivity. The most promising compound 59 exhibits single-digit nanomolar potency in the EP4 calcium flux and cAMP-response element reporter assays and effectively suppresses the expression of multiple immunosuppression-related genes in macrophage cells. On the basis of its favorable ADMET properties, compound 59 was chosen for further in vivo biological evaluation. Oral administration of compound 59 significantly inhibited tumor growth in the mouse CT26 colon carcinoma model accompanied by enhanced infiltration of cytotoxic T lymphocytes in the tumor tissue.

Druggable Prostanoid Pathway

Prostanoids (prostaglandins, prostacyclin and thromboxane) belong to the oxylipin family of biologically active lipids generated from arachidonic acid (AA). Protanoids control numerous physiological and pathological processes. Cyclooxygenase (COX) is a rate-limiting enzyme involved in the conversion of AA into prostanoids. There are two COX isozymes: the constitutive COX-1 and the inducible COX-2. COX-1 and COX-2 have similar structures, catalytic activities, and subcellular localizations but differ in patterns of expression and biological functions. Non-selective COX-1/2 or traditional, non-steroidal anti-inflammatory drugs (tNSAIDs) target both COX isoforms and are widely used to relieve pain, fever and inflammation. However, the use of NSAIDs is associated with various side effects, particularly in the gastrointestinal tract. NSAIDs selective for COX-2 inhibition (coxibs) were purposefully designed to spare gastrointestinal toxicity, but predisposed patients to increased cardiovascular risks. These health complications from NSAIDs prompted interest in the downstream effectors of the COX enzymes as novel drug targets. This chapter describes various safety issues with tNSAIDs and coxibs, and discusses the current development of novel classes of drugs targeting the prostanoid pathway, including nitrogen oxide- and hydrogen sulfide-releasing NSAIDs, inhibitors of prostanoid synthases, dual inhibitors, and prostanoid receptor agonists and antagonists.

Sensory innervation in porous endplates by Netrin-1 from osteoclasts mediates PGE2-induced spinal hypersensitivity in mice

Spinal pain is a major clinical problem, however, its origins and underlying mechanisms remain unclear. Here we report that in mice, osteoclasts induce sensory innervation in the porous endplates which contributes to spinal hypersensitivity in mice. Sensory innervation of the porous areas of sclerotic endplates in mice was confirmed. Lumbar spine instability (LSI), or aging, induces spinal hypersensitivity in mice. In these conditions, we show that there are elevated levels of PGE2 which activate sensory nerves, leading to sodium influx through Na_v 1.8 channels. We show that knockout of PGE2 receptor 4 in sensory nerves significantly reduces spinal hypersensitivity. Inhibition of osteoclast formation by knockout Rankl in the osteocytes significantly inhibits LSI-induced porosity of endplates, sensory innervation, and spinal hypersensitivity. Knockout of Netrin-1 in osteoclasts abrogates sensory innervation into porous endplates and spinal hypersensitivity. These findings suggest that osteoclast-initiated porosity of endplates and sensory innervation are potential therapeutic targets for spinal pain.

Spinal pain is a major clinical problem. Here the authors show that osteoclasts create porous area of endplates of the vertebrae and sensory innervation of porous endplates by Netrin-1 release from osteoclasts mediates PGE2-induced spinal hypersensitivity in mice.

Detection and pharmacokinetics of grapiprant following oral administration to exercised Thoroughbred horses

Traditional therapeutic options for the treatment of lameness associated with inflammation in performance horses include administration of cyclooxygenase enzyme inhibiting non-steroidal anti-inflammatory drugs (NSAID). As long-term use of these drugs can adversely impact the health of the horse, anti-inflammatories with a more favorable safety profile are warranted. Grapiprant is a newly approved non-cyclooxygenase inhibiting NSAID that has demonstrated efficacy and safety in other species and which may be a valuable alternative to traditional NSAIDs used in the horse. The objectives of the current study were to describe drug concentrations and the pharmacokinetics of grapiprant in exercised Thoroughbred horses and to develop an analytical method that could be used to regulate its use in performance horses. To that end, grapiprant, at a dose of 2 mg/kg was administered orally to 12 exercised Thoroughbred horses. Blood and urine samples were collected prior to and for up to 96 hours post drug administration. Drug concentrations were measured using liquid chromatography-tandem mass spectrometry. Grapiprant remained above the LOQ of the assay (0.005 ng/mL) in serum for 72 hours post administration and urine concentrations were above the LOQ until 96 hours. The Cmax , Tmax and elimination half-life were 31.9 ± 13.9 ng/mL, 1.5 ± 0.5 hours and 5.86 ± 2.46 hours, respectively. The drug was well tolerated in all horses at a dose of 2 mg/kg. Results support further study of this compound in horses. Furthermore, development of a highly sensitive analytical method demonstrate that this compound can be adequately regulated in performance horses.

Prostaglandin E2 suppresses hCAP18/LL-37 expression in human macrophages via EP2/EP4: implications for treatment of Mycobacterium tuberculosis infection

Prostaglandin (PG)E₂ is an arachidonic acid-derived lipid mediator that plays an important role in inflammation and immunity. In this study, we demonstrate that PGE₂ suppresses basal and 1,25-dihydroxy vitamin D₃ (VD₃)-induced expression of hCAP18/LL-37 via E prostanoid (EP)2 and EP4 receptors. In humans, VD₃ up-regulates vitamin D receptor (VDR) expression and promotes transcription of the cathelicidin hCAP18/LL-37 gene, whereas PGE₂ counteracts this effect. We find that PGE₂ induces the cAMP/PKA-signaling pathway and enhances the expression of the inhibitory transcription factor cAMP-responsive modulator/inducible cAMP early repressor, which prevents VDR expression and induction of hCAP18/LL-37 in human macrophages. The negative regulation by PGE₂ was evident in M1- and M2-polarized human macrophages, although PGE₂ displayed more profound inhibitory effects in M2 cells. PGE₂ impaired VD₃-induced expression of cathelicidin and concomitant activation of autophagy during Mycobacterium tuberculosis (Mtb) infection and facilitated intracellular Mtb growth in human macrophages. An EP4 agonist also significantly promoted Mtb survival in human macrophages. Our results indicate that PGE₂ inhibits hCAP18/LL-37 expression, especially VD₃-induced cathelicidin and autophagy, which may reduce host defense against Mtb. Accordingly, antagonists of EP4 may constitute a novel adjunctive therapy in Mtb infection.-Wan, M., Tang, X., Rekha, R. S., Muvva, S. S. V. J. R., Brighenti, S., Agerberth, B., Haeggström, J. Z. Prostaglandin E₂ suppresses hCAP18/LL-37 expression in human macrophages via EP2/EP4: implications for treatment of Mycobacterium tuberculosis infection.

Analgesic and anti-inflammatory properties of novel, selective, and potent EP4 receptor antagonists

Prostaglandin (PG) E2 is the key driver of inflammation associated with arthritic conditions. Inhibitors of PGE 2 production (NSAIDs and Coxibs) are used to treat these conditions, but carry significant side effect risks due to the inhibition of all prostanoids that play important physiological function. The activities of PGE 2 are transduced through various receptor sub-types. Prostaglandin E2 type 4 receptor (EP4) is associated with the development of inflammation and autoimmunity. We therefore are interested in identifying novel EP4 antagonists to treat the signs and symptoms of arthritis without the potential side effects of PGE 2 modulators such as NSAIDs and Coxibs. Novel EP4 antagonists representing distinct chemical scaffolds were identified using a variety of in vitro functional assays and were shown to be selective and potent. The compounds were shown to be efficacious in animal models of analgesia, inflammation, and arthritis.

Pharmacokinetic/pharmacodynamic evaluation of grapiprant in a carrageenan-induced inflammatory pain model in the rabbit

Grapiprant is the novel selective EP4 receptor inhibitor recently issued on the veterinary market for dogs affected by osteoarthritis. The aim of this study was twofold: to evaluate the pharmacokinetics and the pharmacodynamics of grapiprant in the induced inflammatory pain model in the rabbit after a single IV injection of 2 mg/kg; to compare the thermal antinociception effect after 2 mg/kg IV grapiprant, with that generated by 0.5 mg/kg meloxicam SC injected. Rabbits (n = 12) were randomly assigned to two crossover studies (single-dose, two-period crossover). The first study group A (n = 3) received a single IV dose of grapiprant at 2 mg/kg dissolved in ethanol. Group B (n = 3) received a single IV injection of ethanol (equivalent volume to grapiprant volume) at the same site. The second study group C (n = 3) received a single SC dose of meloxicam at 0.5 mg/kg. Group D (n = 3) received a single SC injection of 15% ethanol (equivalent volume to grapiprant volume) at the same site. After a 2-week washout period, the groups were rotated and the experiments repeated. Blood samples (0.7 mL) were collected from the right ear artery at assigned times and grapiprant plasma concentrations determined by a validated HPLC-FL method. Three hours prior to administration of the drugs, inflammation was induced by SC injection of lambda carrageenan (200 μL, 3% in physiological saline) under the plantar surface of the right hind paw. At a similar time to the blood collection, an infrared thermal stimuli (40 °C) was applied to the plantar surface of the rabbits' hindlimbs to evaluate the thermal withdrawal latency (TWL). The thermal antinociceptive effect was expressed as maximum possible response (% MPR). Grapiprant plasma concentrations were detectable up to the 10-h time point (concentration range 17-7495 ng/mL). The grapiprant-treated group showed a significant increase in TWL from 1 h and up to 10 h after drug administration compared to the control. In contrast, the meloxicam group showed a significant increase in TWL from 4 up to 10 h after drug administration, compared to control. The maximal MPR% was not statistically different between the grapiprant and meloxicam group from 4 to 8 h, while significant differences were shown at 1, 1.5, 2, 10 and 24 h. Given these findings, grapiprant appears to be an attractive option for antinociception in rabbits, due to its rapid onset and extended duration of effect.

Pharmacological interrogation of a rodent forced ambulation model: leveraging gait impairment as a measure of pain behavior pre-clinically

OBJECTIVE

The aim of this study was to investigate whether inflammogen-induced temporal and spatial gait changes in a rodent forced-ambulation paradigm were sensitive to pharmacological intervention with both clinically validated and novel analgesics.

METHODS

Using the GaitScan (CleverSys Inc., Reston, VA) treadmill system, we identified four functional endpoints inspired by clinical literature and sensitive to unilateral joint injury induced by intra-articular Complete Freund's Adjuvant (CFA). These endpoints included: range of motion, normalized stance distance, stance/swing ratio, and paw print size as a measure of guarding; collectively, these measures are proposed to serve as a high fidelity index of joint pain. We then examined the ability of known analgesic mechanisms to attenuate gait impairment as measured by this index.

RESULTS

Clinically efficacious opioids, Nonsteroidal anti-inflammatory drugs (NSAIDs), and the yet unapproved anti-NGF antibody dose-dependently attenuated the CFA)-induced gait deficits, while a TNF-alpha fusion protein blocker had no effect on gait, but did produce a reduction in swelling. As well, the time course for gait impairment in the model appears to be distinct from the traditional endpoint of tactile hypersensitivity, offering the potential to assess a novel functional pain phenotype.

CONCLUSIONS

In response to the call for more functional pain measures, we submit this composite gait score as a novel endpoint to interrogate joint pain pre-clinically. As the etiology of human osteoarthritis (OA) remains unclear, this model/endpoint cannot attempt to improve construct validity, but may provide an additional dimension to interrogate pain-induced gait deficits.

Structural features of subtype-selective EP receptor modulators

Prostaglandin E2 is a potent endogenous molecule that binds to four different G-protein-coupled receptors: EP1-4. Each of these receptors is a valuable drug target, with distinct tissue localisation and signalling pathways. We review the structural features of EP modulators required for subtype-selective activity, as well as the structural requirements for improved pharmacokinetic parameters. Novel EP receptor subtype selective agonists and antagonists appear to be valuable drug candidates in the therapy of many pathophysiological states, including ulcerative colitis, glaucoma, bone healing, B cell lymphoma, neurological diseases, among others, which have been studied in vitro, in vivo and in early phase clinical trials.

Mapping PTGERs to the Ovulatory Follicle: Regional Responses to the Ovulatory PGE2 Signal

Prostaglandin E2 (PGE2) is a key intrafollicular mediator of ovulation in many, if not all, mammalian species. PGE2 acts at follicular cells via four distinct PGE2 receptors (PTGERs). Within the ovulatory follicle, each cell type (e.g., oocyte, cumulus granulosa cell, mural granulosa cell, theca cell, endothelial cell) expresses a different subset of the four PTGERs. Expression of a subset of PTGERs has consequences for the generation of intracellular signals and ultimately the unique functions of follicular cells that respond to PGE2. Just as the ovulatory LH surge regulates PGE2 synthesis, the LH surge also regulates expression of the four PTGERs. The pattern of expression of the four PTGERs among follicular cells before and after the LH surge forms a spatial and temporal map of PGE2 responses. Differential PTGER expression, coupled with activation of cell-specific intracellular signals, may explain how a single paracrine mediator can have pleotropic actions within the ovulatory follicle. Understanding the role of each PTGER in ovulation may point to previously unappreciated opportunities to both promote and prevent fertility.

Simultaneous Inhibition of PGE2 and PGI2 Signals Is Necessary to Suppress Hyperalgesia in Rat Inflammatory Pain Models

Prostaglandin E2 (PGE2) is well known as a mediator of inflammatory symptoms such as fever, arthritis, and inflammatory pain. In the present study, we evaluated the analgesic effect of our selective PGE2 synthesis inhibitor, compound I, 2-methyl-2-[cis-4-([1-(6-methyl-3-phenylquinolin-2-yl)piperidin-4-yl]carbonyl amino)cyclohexyl] propanoic acid, in rat yeast-induced acute and adjuvant-induced chronic inflammatory pain models. Although this compound suppressed the synthesis of PGE2 selectively, no analgesic effect was shown in both inflammatory pain models. Prostacyclin (PGI2) also plays crucial roles in inflammatory pain, so we evaluated the involvement of PGI2 signaling in rat inflammatory pain models using prostacyclin receptor (IP) antagonist, RO3244019. RO3244019 showed no analgesic effect in inflammatory pain models, but concomitant administration of compound I and RO3244019 showed analgesic effects comparable to celecoxib, a specific cyclooxygenase- (COX-) 2 inhibitor. Furthermore, coadministration of PGE2 receptor 4 (EP4) antagonist, CJ-023423, and RO3244019 also showed an analgesic effect. These findings suggest that both PGE2 signaling, especially through the EP4 receptor, and PGI2 signaling play critical roles in inflammatory pain and concurrent inhibition of both signals is important for suppression of inflammatory hyperalgesia.

A Prospective, Randomized, Masked, Placebo-Controlled Multisite Clinical Study of Grapiprant, an EP4 Prostaglandin Receptor Antagonist (PRA), in Dogs with Osteoarthritis

Background

This study evaluated the effectiveness and safety of grapiprant for treatment of pain in dogs with osteoarthritis (OA).

Hypothesis/Objectives

Grapiprant will relieve pain as measured by the owner's and veterinarian's evaluation of pain in dogs with OA. Another objective was evaluation of the safety of grapiprant.

Animals

Two hundred and eighty‐five client‐owned dogs with OA were enrolled and treated with grapiprant or placebo with 262 cases (N = 131 in each group) evaluable for the effectiveness analysis.

Methods

In this prospective, randomized, masked, placebo‐controlled study dogs were treated daily with grapiprant (2 mg/kg) per OS or placebo. Owners completed an evaluation using the Canine Brief Pain Inventory (CBPI) on days 0, 7, 14, 21, and 28. Success was defined as improvement in the CBPI. Veterinary assessments were made on screening and days 14 and 28. Safety was evaluated by physical examination, evaluation of clinical pathology results, and owner observations.

Results

Grapiprant treatment improved pain compared to placebo on day 28 (48.1 and 31.3% treatment successes respectively; P = .0315). The pain interference score (PIS) and pain severity score (PSS) improved in the grapiprant group compared to placebo (P = .0029 and 0.0022, respectively). Veterinary assessments were significantly better in the grapiprant‐treated dogs (P = .0086). Grapiprant generally was well tolerated, but a higher percentage of treated dogs (17.02%) had occasional vomiting as compared to the placebo group (6.25%).

Conclusions and Clinical Importance

Grapiprant is an effective treatment for alleviation of pain in dogs with OA, and represents a modality of treatment that may be better tolerated than current options.

Pharmacokinetic comparison of oral tablet and suspension formulations of grapiprant, a novel therapeutic for the pain and inflammation of osteoarthritis in dogs

A new anti-inflammatory drug for pain (grapiprant) was recently shown to have minimal side effects following chronic (9-month) daily oral dose of 6 or 50 mg/kg suspension. The current study compares the pharmacokinetics of the formulation used in the chronic safety study to those of the tablet formulation that will be marketed upon FDA approval. Sixteen Beagle dogs were randomized to receive single doses of either 6 or 50 mg/kg grapiprant as both suspension and table formulations within a cross-over design with a 15-day washout. Clinical observations were vomiting in one high-dose suspension dog and loose stools in two dogs, one in each 6 mg/kg formulation group. For both formulations, grapiprant reached a maximum concentration within two hours. The tablet formulation had better bioavailability, with AUC_last values 34% higher at 6 mg/kg and 64% higher at 50 mg/kg compared to the suspension. Results on Day 0 were similar to those reported on Day 15, suggesting little to no accumulation. Using conversion factors of 1.34 and 1.64, these findings suggest that the 6 and 50 mg/kg suspension doses are equivalent to 4.5 and 30 mg/kg tableted doses, respectively. Combining these findings with the 9-month safety study demonstrates that safety was evaluated at doses approximately 15-fold above the demonstrated therapeutic dose of 2 mg/kg and 10-fold over the 'safety dose', defined as the maximum dose a dog of any body weight could receive when dosed at 2 mg/kg with whole or half-tablets.