Molecular recognition and activation of the prostacyclin receptor by anti-pulmonary arterial hypertension drugs

The prostacyclin (PGI2) receptor (IP) is a Gs-coupled receptor associated with blood pressure regulation, allergy, and inflammatory response. It is a main therapeutic target for pulmonary arterial hypertension (PAH) and several other diseases. Here we report cryo-electron microscopy (cryo-EM) structures of the human IP-Gs complex bound with two anti-PAH drugs, treprostinil and MRE-269 (active form of selexipag), at global resolutions of 2.56 and 2.41 angstrom, respectively. These structures revealed distinct features governing IP ligand binding, receptor activation, and G protein coupling. Moreover, comparison of the activated IP structures uncovered the mechanism and key residues that determine the superior selectivity of MRE-269 over treprostinil. Combined with molecular docking and functional studies, our structures provide insight into agonist selectivity, ligand recognition, receptor activation, and G protein coupling. Our results provide a structural template for further improving IP-targeting drugs to reduce off-target activation of prostanoid receptors and adverse effects.

Case report: apatinib plus selexipag as a novel therapy for pulmonary tumor thrombotic microangiopathy accompanied by pulmonary hypertension associated with gastric carcinoma

RATIONALE

PTTM is a rare but fatal disease, characterized by endothelial intimal proliferation and pulmonary hypertension due to micro-vascular remodeling. In view of the poor prognosis, new effective strategies are urgently required.

PATIENT CONCERNS AND DIAGNOSIS

A 51-year-old woman was admitted to hospital for acute progressive dyspnea and dry cough. Clinical tests revealed hypercoagulable state and signs of severe pulmonary hypertension, without evidence of pulmonary embolism on contrast-enhanced CT. CT showed interlobular septal thickening and diffuse ground-glass opacity. Lung perfusion scan indicated multiple segment defect. Further right heart catherization proved a significant increase in pulmonary vascular resistance.

INTERVENTIONS

A combination therapy of apatinib and selexipag was administered for treatment of PTTM. The conventional therapies of ventilation, anticoagulation and diuretic medicines were initiated after admission.

OUTCOMES

Symptoms of PTTM were ameliorated with a reduction in pulmonary artery pressure. The resolution of interlobular septal thickening and ground-glass opacity on CT constituted the clinical benefits from treatment.

LESSONS

Patient with PTTM will benefit from the combination strategy of apatinib, a VEGF-receptor antagonist, and selexipag, an oral prostacyclin receptor agonist.

Efficacy and safety of selexipag, an oral prostacyclin receptor agonist for the treatment of pulmonary hypertension: A meta-analysis

BACKGROUND AND OBJECTIVE

This meta-analysis was performed to evaluate the effect and safety of selexipag in the treatment of pulmonary hypertension and to explore the effect of selexipag on cardiac function indexes in PAH patients.

METHODS

Electronic databases, including the Cochrane Library, EMBASE, and PubMed databases, were searched. Endnote software X9 was used for study selection, and the Cochrane Risk of Bias Tool was used for literature screening and quality assessment. Data analysis was performed using RevMan 5.3 software, and GRADE was used to assess the evidence level.

RESULTS

Ten studies were finally selected in accordance with the standard. A total of 10 papers were included. A total of 1322 patients were included, including 723 in the trial group and 599 in the control group. Patients with PAH treated with selexipag were included in the trial group, and patients with PAH treated with placebo were included in the control group. The results of the study showed that selexipag was effective in reducing mortality in patients (WMD=0.70, 95% CI: 0.53-0.94, P = 0.02). Selexipag effectively increased the 6-min walk distance (WMD=33.79, 95% CI: 2.69-64.90, P=0.03). Selexipag also effectively increased the 6-min distance between baseline and follow-up (WMD = 15.28, 95% CI: 7.76-22.80, P < 0.0001). Selexipag effectively reduced PVR (WMD = -230.96, 95% CI: 445.94 to -15.97, P = 0.04). Selexipag significantly reduced PVR between baseline and follow-up (WMD = -139.62, 95% CI: 215.32 to -63.91, P = 0.0003). The adverse reactions of selexipag were mild with headache, diarrhea and nausea reported as the main symptoms.

CONCLUSION

Selexipag is a new drug with mild adverse reactions and is safe for the treatment of PAH. This drug significantly prolongs the level of 6MWD in PAH patients, reduces the fatality rate, improves WHO FC and reduces PVR. The effects of this drug on CI, mPAP, MRAP, SvO₂ and other indicators still need to be further confirmed.

PROSPERO REGISTRATION

CRD42021245557.

Prostaglandin I2 (PGI2) inhibits Brucella abortus internalization in macrophages via PGI2 receptor signaling, and its analogue affects immune response and disease outcome in mice

To date, the implications of prostaglandin I2 (PGI₂), a prominent lipid mediator for modulation of immune responses, has not been clearly understood in Brucella infection. In this study, we found that cyclooxygenase-2 (COX-2) was significantly expressed in both infected bone marrow-derived macrophages (BMMs) and RAW 264.7 cells. Prostaglandin I2 synthase (PTGIS) expression was not significantly changed, and PGI₂receptor (PTGIR) expression was downregulated in BMMs but upregulated in RAW 264.7 macrophages at late infection. Here, we presented that PGI₂, a COX-derived metabolite, was produced by macrophages during Brucella infection and its production was regulated by COX-2 and IL-10. We suggested that PGI₂ and selexipag, a potent PGI₂ analogue, inhibited Brucella internalization through IP signaling which led to down-regulation of F-actin polymerization and p38α MAPK activity. Administration with selexipag suppressed immune responses and resulted in a notable reduction in bacterial burden in spleen of Brucella-challenged mice. Taken together, our study is the first to characterize PGI₂ synthesis and its effect in evasion strategy of macrophages against Brucella infection.

The selective PGI2 receptor agonist selexipag ameliorates Sugen 5416/hypoxia-induced pulmonary arterial hypertension in rats

Pulmonary arterial hypertension (PAH) is a lethal disease characterized by a progressive increase in pulmonary artery pressure due to an increase in vessel tone and occlusion of vessels. The endogenous vasodilator prostacyclin and its analogs are used as therapeutic agents for PAH. However, their pharmacological effects on occlusive vascular remodeling have not been elucidated yet. Selexipag is a recently approved, orally available and selective prostacyclin receptor agonist with a non-prostanoid structure. In this study, we investigated the pharmacological effects of selexipag on the pathology of chronic severe PAH in Sprague-Dawley and Fischer rat models in which PAH was induced by a combination of injection with the vascular endothelial growth factor receptor antagonist Sugen 5416 and exposure to hypoxia (SuHx). Oral administration of selexipag for three weeks significantly improved right ventricular systolic pressure and right ventricular (RV) hypertrophy in Sprague-Dawley SuHx rats. Selexipag attenuated the proportion of lung vessels with occlusive lesions and the medial wall thickness of lung arteries, corresponding to decreased numbers of Ki-67-positive cells and a reduced expression of collagen type 1 in remodeled vessels. Administration of selexipag to Fischer rats with SuHx-induced PAH reduced RV hypertrophy and mortality caused by RV failure. These effects were probably based on the potent prostacyclin receptor agonistic effect of selexipag on pulmonary vessels. Selexipag has been approved and is used in the clinical treatment of PAH worldwide. It is thought that these beneficial effects of prostacyclin receptor agonists on multiple aspects of PAH pathology contribute to the clinical outcomes in patients with PAH.

Efficacy and safety of ralinepag, a novel oral IP agonist, in PAH patients on mono or dual background therapy: results from a phase 2 randomised, parallel group, placebo-controlled trial

PURPOSE

This phase 2 study was designed to assess the efficacy, safety and tolerability of immediate-release orally administered ralinepag, a selective, non-prostanoid prostacyclin receptor agonist with a 24-h terminal half-life, compared to placebo in adult patients with symptomatic pulmonary arterial hypertension (PAH).

METHODS

61 PAH patients who were receiving standard care, including mono or dual PAH-targeted background therapy were randomised 2:1 to ralinepag (n=40) or placebo (n=21). The starting dose of ralinepag was 10 μg twice daily. Dosage was then up-titrated as tolerated over the course of the 9-week dose-titration period, to a maximum total daily dose of 600 μg (300 μg twice daily). The primary efficacy end-point was the absolute change in pulmonary vascular resistance (PVR) from baseline to week 22. Additional end-points included percentage change in PVR from baseline, other haemodynamic parameters, 6-min walk distance (6MWD) and safety and tolerability.

RESULTS

Ralinepag significantly decreased PVR by 163.9 dyn·s·cm-5 compared to an increase of 0.7 dyn·s·cm-5 with placebo (p=0.02); the least-squares mean change from baseline PVR was -29.8% compared with placebo (p=0.03). 6MWD increased from baseline by 36.2 m with ralinepag and 29.4 m with placebo (p=0.90). Serious adverse events occurred in 10% of ralinepag patients and 29% of placebo patients. Study discontinuations occurred in 13% of ralinepag patients and 10% of placebo patients.

SUMMARY

Ralinepag reduced PVR compared with placebo in PAH patients on mono (41%) or dual combination (59%) background therapy.

[Update pulmonary arterial hypertension : Definitions, diagnosis, therapy]

The term pulmonary arterial hypertension comprises a group of pulmonary vascular diseases of different etiologies that are characterized by similar precapillary vascular remodeling processes and result in exertional dyspnea and right heart insufficiency. The specific pharmacological treatment approach considers the risk of mortality and phenotypical properties and includes treatment with phosphodiesterase type 5 inhibitors, endothelin receptor antagonists and prostanoids, as well as with more novel substances, such as a soluble guanylyl cyclase stimulator and an oral prostacyclin receptor agonist. The prognosis of the disease is mainly determined by the right heart insufficiency for which there is currently no specific pharmacological treatment. Lung transplantation may be offered as a last option. This review provides an overview of the current European guidelines from 2015 and the recommendations of the Cologne Consensus Conference for pulmonary hypertension from 2016.

[Pulmonary hypertension: definition, classification and treatments]

Pulmonary hypertension (PH) is a cardio-pulmonary disorder that may involve multiple clinical conditions and can complicate the majority of cardiovascular and respiratory diseases. Its definition is an increase in mean pulmonary artery pressure (mPAP) \hbox{$\geqslant $} ⩾ 25 mmHg at rest, leading to right heart failure and ultimately death. The clinical classification of pulmonary hypertension (PH) categorizes PH into groups which share similar pathophysiological and hemodynamic characteristics and treatments. Five groups of disorders that cause PH are identified: pulmonary arterial hypertension (Group 1) which is a pre-capillary PH, defined by a normal pulmonary artery wedge pressure (PAWP) \hbox{$\leqslant $} ⩽ 15 mmH, due to remodelling of the small pulmonary arteries (<500 μm); pulmonary hypertension due to left heart disease (Group 2) which is a post-capillary PH, defined by an increased pulmonary artery wedge pressure (PAWP) >15 mmHg; pulmonary hypertension due to chronic lung disease and/or hypoxia (Group 3); chronic thrombo-embolic pulmonary hypertension (Group 4); and pulmonary hypertension due to unclear and/or multifactorial mechanisms (Group 5). PAH (PH group 1) can be treated with agents targeting three dysfunctional endothelial pathways of PAH: nitric oxide (NO) pathway, endothelin-1 pathway and prostacyclin pathway. Patients at low or intermediate risk can be treated with either initial monotherapy or initial oral combination therapy. In patients at high risk initial combination therapy including intravenous prostacyclin analogues should be considered. Patients with inadequate clinical response to maximum treatment (triple therapy with an intravenous prostacyclin) should be assessed for lung transplantation. Despite progresses, PAH remains a fatal disease with a 3-year survival rate of 58%. Treatment of group 2, group 3 and group 5 PH is the treatment of the causal disease and PAH therapeutics are not recommended. Treatment of group 4 PH is pulmonary endarteriectomy if patients are eligible, otherwise balloon pulmonary angioplasty and/or medical therapy can be considered.

Piperidine derivatives as nonprostanoid IP receptor agonists 2

We searched for a strong and selective nonprostanoid IP agonist bearing piperidine and benzanilide moieties. Through optimization of substituents on the benzanilide moiety, the crucial part of the agonist, 43 (2-((1-(2-(N-(4-tolyl)benzo[d][1,3]dioxole-5-carboxamido)ethyl)piperidin-4-yl)oxy)acetic acid monohydrate monohydrochloride) was discovered and exhibited strong platelet aggregation inhibition (IC50=21nM) and 100-fold selectivity for IP receptor over other PG receptors. The systemic exposure level and bioavailability after oral administration of 43 were also good in dog.

Prostaglandin I2 Receptor Agonism Preserves β-Cell Function and Attenuates Albuminuria Through Nephrin-Dependent Mechanisms

Discovery of common pathways that mediate both pancreatic β-cell function and end-organ function offers the opportunity to develop therapies that modulate glucose homeostasis and separately slow the development of diabetes complications. Here, we investigated the in vitro and in vivo effects of pharmacological agonism of the prostaglandin I2 (IP) receptor in pancreatic β-cells and in glomerular podocytes. The IP receptor agonist MRE-269 increased intracellular 3',5'-cyclic adenosine monophosphate (cAMP), augmented glucose-stimulated insulin secretion (GSIS), and increased viability in MIN6 β-cells. Its prodrug form, selexipag, augmented GSIS and preserved islet β-cell mass in diabetic mice. Determining that this preservation of β-cell function is mediated through cAMP/protein kinase A (PKA)/nephrin-dependent pathways, we found that PKA inhibition, nephrin knockdown, or targeted mutation of phosphorylated nephrin tyrosine residues 1176 and 1193 abrogated the actions of MRE-269 in MIN6 cells. Because nephrin is important to glomerular permselectivity, we next set out to determine whether IP receptor agonism similarly affects nephrin phosphorylation in podocytes. Expression of the IP receptor in podocytes was confirmed in cultured cells by immunoblotting and quantitative real-time PCR and in mouse kidneys by immunogold electron microscopy, and its agonism 1) increased cAMP, 2) activated PKA, 3) phosphorylated nephrin, and 4) attenuated albumin transcytosis. Finally, treatment of diabetic endothelial nitric oxide synthase knockout mice with selexipag augmented renal nephrin phosphorylation and attenuated albuminuria development independently of glucose change. Collectively, these observations describe a pharmacological strategy that posttranslationally modifies nephrin and the effects of this strategy in the pancreas and in the kidney.

Exploration of the antiplatelet activity profile of betulinic acid on human platelets

Betulinic acid, a natural pentacyclic triterpene acid, presents a diverse mode of biological actions including antiretroviral, antibacterial, antimalarial, and anti-inflammatory activities. The potency of betulinic acid as an inhibitor of human platelet activation was evaluated, and its antiplatelet profile against in vitro platelet aggregation, induced by several platelet agonists (adenosine diphosphate, thrombin receptor activator peptide-14, and arachidonic acid), was explored. Flow cytometric analysis was performed to examine the effect of betulinic acid on P-selectin membrane expression and PAC-1 binding to activated platelets. Betulinic acid potently inhibits platelet aggregation and also reduced PAC-1 binding and the membrane expression of P-selectin. Principal component analysis was used to screen, on the chemical property space, for potential common pharmacophores of betulinic acid with approved antithrombotic drugs. A common pharmacophore was defined between the NMR-derived structure of betulinic acid and prostacyclin agonists (PGI2), and the importance of its carboxylate group in its antiplatelet activity was determined. The present results indicate that betulinic acid has potential use as an antithrombotic compound and suggest that the mechanism underlying the antiplatelet effects of betulinic acid is similar to that of the PGI2 receptor agonists, a hypothesis that deserves further investigation.

Agonist-dependent internalization and trafficking of the human prostacyclin receptor: a direct role for Rab5a GTPase

The human prostacyclin receptor (hIP) undergoes rapid agonist-induced internalization by largely unknown mechanism(s). Herein the involvement of Rab5 in regulating cicaprost-induced internalization of the hIP expressed in human embryonic kidney 293 cells was investigated. Over-expression of Rab5a significantly increased agonist-induced hIP internalization. Additionally, the hIP co-localized to Rab5a-containing endocytic vesicles in response to cicaprost stimulation and there was a coincident net translocation of Rab5 from the cytosol/soluble fraction of the cell. Co-immunoprecipitation studies confirmed a direct physical interaction between the hIP and Rab5a that was augmented by cicaprost. Whilst the dominant negative Rab5a(S34N) did not show decreased interaction with the hIP or fully impair internalization, it prevented hIP sorting to endocytic vesicles. Moreover, the GTPase deficient Rab5a(Q79L) significantly increased internalization and co-localized with the hIP in enlarged endocytic vesicles. While deletion of the carboxyl terminal (C)-tail domain of the hIP did not inhibit agonist-induced internalization, co-localization or co-immunoprecipitation with Rab5a per se, receptor trafficking was altered suggesting that it contains structural determinant(s) for hIP sorting post Rab5-mediated endocytosis. Taken together, data herein and in endothelial EA.hy 926 cells demonstrate a direct role for Rab5a in agonist-internalization and trafficking of the hIP and increases knowledge of the factors regulating prostacyclin signaling.

Synthesis and evaluation of N-acylsulfonamide and N-acylsulfonylurea prodrugs of a prostacyclin receptor agonist

N-Acylsulfonamide and N-acylsulfonylurea derivatives of the carboxylic acid prostacyclin receptor agonist 1 were synthesized and their potential as prodrug forms of the carboxylic acid was evaluated in vitro and in vivo. These compounds were converted to the active compound 1 by hepatic microsomes from rats, dogs, monkeys, and humans, and some of the compounds were shown to yield sustained plasma concentrations of 1 when they were orally administered to monkeys. These types of analogues, including NS-304 (2a), are potentially useful prodrugs of 1.

Prostacyclin, atherothrombosis, and cardiovascular disease

Prostacyclin (PGI(2)) is a major product of COX-2 catalyzed metabolism of arachidonic acid in the endothelium. Recent studies have demonstrated that PGI(2) protects against atherothrombosis. The prostacyclin receptor knockout mice exhibit increased atherosclerosis, enhanced thrombosis, and enhanced proliferative response to carotid vascular injury with increased intima to media ratios [1-3]. Moreover, the recent withdrawal of rofecoxib (Vioxx) due to increased cardiovascular events further supports the critical role of prostacyclin in inhibiting atherothrombosis in humans. Such studies have paralleled intense chemical biology studies to develop more stable prostacyclin analogues. Indeed a number of these analogues are currently being successfully used for the treatment of pulmonary hypertension. In this review we will summarize the current literature on some principles of prostacyclin analogue development, our current understanding of the receptor, and recent developments which implicate prostacyclin in atherothrombotic protection. More than 68 million Americans suffer from cardiovascular disease, which causes more deaths, disability and economic loss than any other group of diseases. Further clinical investigations of orally stable prostacyclin analogues for treatment of cardiovascular diseases other than pulmonary hypertension may now be warranted.

Structure–activity studies on diphenylpyrazine derivatives: A novel class of prostacyclin receptor agonists

To develop nonprostanoid prostacyclin receptor agonists with a high degree of metabolic resistance and an extended duration of action, a novel series of diphenylpyrazine derivatives was synthesized and evaluated for their inhibition of ADP-induced human platelet aggregation. Structure-activity relationship studies on the side chain containing the carboxylic acid moiety of the lead compound 5c showed that the length of the linker and the presence of the concatenating nitrogen atom adjacent to the pyrazine ring are critical for the antiaggregatory activity. This study led to the discovery of 2-amino-5,6-diphenylpyrazine derivatives 8c, 15a, and 15b, which showed potent inhibition of platelet aggregation with IC(50) values of 0.2 microM. Among these compounds, 15b is an orally available and long-lasting prostacyclin receptor agonist which is promising for the treatment of various vascular diseases.

2-{4-[(5,6-Diphenylpyrazin-2-yl)(isopropyl)amino]butoxy}-N-(methylsulfonyl)acetamide (NS-304), an Orally Available and Long-Acting Prostacyclin Receptor Agonist Prodrug

Prostacyclin (PGI(2)) and its analogs are useful for the treatment of various vascular disorders, but their half-lives are too short for widespread clinical application. To overcome this drawback, we have synthesized a novel diphenylpyrazine derivative, 2-[4-[(5,6-diphenylpyrazin-2-yl)(isopropyl)amino]butoxy]-N-(methylsulfonyl)acetamide (NS-304), a prodrug of the active form [4-[(5,6-diphenylpyrazin-2-yl)(isopropyl)amino]butoxy]acetic acid (MRE-269). NS-304 is an orally available and potent agonist for the PGI(2) receptor (IP receptor). The inhibition constant (K(i)) of MRE-269 for the human IP receptor was 20 nM; in contrast, the K(i) values for other prostanoid receptors were >2.6 microM. MRE-269 was therefore a highly selective agonist for the IP receptor. The plasma concentrations of MRE-269 remained near peak levels for more than 8 h after oral administration of NS-304 to rats and dogs, and NS-304 increased femoral skin blood flow in rats in a long-lasting manner without affecting the hemodynamics. These findings indicate that NS-304 acts as a long-acting IP receptor agonist in vivo. The continuous vasodilation evoked by NS-304 was not attenuated by repeated treatment, indicating that NS-304 is unlikely to cause severe desensitization of the IP receptor in rats. Moreover, a microdose pharmacokinetic study in which NS-304 was orally administered to healthy male volunteers showed conversion of NS-304 to MRE-269 and a long plasma elimination half-life for MRE-269 (7.9 h). In conclusion, NS-304 is an orally available and long-acting IP receptor agonist prodrug, and its active form, MRE-269, is highly selective for the IP receptor. Therefore, NS-304 is a promising drug candidate for various vascular diseases, especially pulmonary arterial hypertension and arteriosclerosis obliterans.

Regulation of Thromboxane Receptor Trafficking Through the Prostacyclin Receptor in Vascular Smooth Muscle Cells

BACKGROUND

Prostacyclin (PGI2) and thromboxane (TxA2) effect disparate outcomes for atherogenesis and the response to vascular injury; PGI2, a vasodilator and inhibitor of platelet aggregation, limits the deleterious actions of TxA2, a vasoconstrictor and platelet activator. Dimerization of their G protein-coupled receptors, IP and TP, evokes a modified cellular response through which IP/TP counter-balance may be effected. We examined the consequence of IP/TP interaction for the regulatory pathways of both receptors.

METHODS AND RESULTS

TPalpha overexpressed in HEK293 cells or expressed endogenously in aortic smooth muscle cells (ASMCs) was internalized after selective activation of either TP or IP. Homologous trafficking of TP was unaltered by coexpression of IP. Heterologous sequestration of TPalpha required the physical presence of activated IP, in transfected and native cells, but was independent of IP signaling to adenylyl cyclase. Reciprocal heterologous regulation of IP, via activated TP, was evident in both HEK293 cells and ASMCs. Homologous TP internalization led to receptor retention and degradation. In contrast, when internalization was IP-induced, TPalpha was recycled to the cell surface in coexpressing HEK293 cells, but not in ASMCs, in accord with the postendocytotic pathway of IP.

CONCLUSIONS

IP/TPalpha interaction permits reciprocal regulation of receptor endocytosis via the trafficking pathway determined by the activated dimeric partner.

Functional role of prostacyclin receptor in rat dorsal root ganglion neurons

Recent studies on prostanoids showed that some of prostanoid receptors are expressed in rat dorsal root ganglion (DRG) neurons. These facts suggest that prostanoid receptors might be involved in the excitation mechanism of DRG neurons. In the present study, PCR experiments revealed that one of prostanoid receptor, prostacyclin receptor (IP receptor) was expressed in L6 and S1 rat DRG neurons and that the expression of IP receptor was not changed in DRG neurons obtained from the cyclophosphamide (CYP)-induced cystitis rat. We examined the functional role of IP receptor agonist and other prostanoids by measuring cyclic AMP (cAMP) accumulation and substance P (SP) release in primary cultured DRG neurons. The pretreatment of DRG neurons with prostanoid agonists such as iloprost (IP), butaprost (EP(2)), misoprostol (EP(2-4)), PGE(2) (EP(1-4)) or PGD(2) (DP and CRTH2) sensitized the DRG neurons and hence potentiated the lys-bradykinin-induced SP release. The increase of SP release by lys-BK plus prostanoid agonists was proportion to cAMP accumulation. Iloprost was the most potent agonist to induce cAMP accumulation and SP release among prostanoid agonists evaluated in this study and its effect is mediated by IP receptor. Moreover, capsaicin-, ATP- and KCl-induced SP release was also enhanced by iloprost although iloprost did not change intracellular Ca(2+) and membrane depolarization induced by these chemical stimuli. These results strongly indicate that IP receptor play an important role in the sensitization of rat sensory neuron.

Development of 3,4-dihydro-2H-benzo[1,4]oxazine derivatives as dual thromboxane A2 receptor antagonists and prostacyclin receptor agonists

We discovered a novel series of 3,4-dihydro-2H-benzo[1,4]oxazin-8-yloxyacetic acid derivatives as potent dual-acting agents to block the TXA2 receptor and to activate the PGI2 receptor. We report the synthesis, structure-activity relationship, and in vitro, ex vivo, and in vivo pharmacology of this series of compounds. 4-[2-(1,1-Diphenylethylsulfanyl)ethyl]-3,4-dihydro-2H-benzo[1,4]oxazin-8-yloxyacetic acid N-methyl-D-glucamine salt (7) is a promising candidate for a novel treatment in the anti-thrombotic and the cardiovascular fields avoiding hypotensive side effects.

Development of dual-acting benzofurans for thromboxane A2 receptor antagonist and prostacyclin receptor agonist: synthesis, structure-activity relationship, and evaluation of benzofuran derivatives

Prostacyclin (PGI(2)) is an unstable, powerful endogenous inhibitor of platelet aggregation, and thromboxane A(2) (TXA(2)) is an unstable endogenous arachidonic acid metabolite that plays a pivotal role in platelet aggregation and vasoconstriction. The balance between TXA(2) and PGI(2) greatly affects maintenance of the homeostasis of the circulatory system. A novel series of benzofuran-7-yloxyacetic acid derivatives was discovered as potent dual-acting agents to block the thromboxane A(2) receptor and to activate the prostacyclin receptor. Synthesis, structure-activity relationship, and in vitro and ex vivo pharmacology of this series of compounds are described. The most potent in the series was {3-[2-(1,1-diphenylethylsulfanyl)ethyl]-2-hydroxymethylbenzofuran-7-yloxy}acetic acid diethanolamine salt (7) with K(i) of 4.5 nM for thromboxane receptor antagonism and K(i) of 530 nM for prostacyclin receptor agonism. Remarkably, compound 7 is a promising candidate for novel treatment as an antithrombotic agent with other cardiovascular actions to avoid hypotensive side effects.

Evidence that inward rectifier K+ channels mediate relaxation by the PGI2 receptor agonist cicaprost via a cyclic AMP-independent mechanism

OBJECTIVE

We investigated the role of the inward rectifier potassium (KIR) channel and the cyclic AMP-dependent pathway in mediating vasorelaxation induced by the prostacyclin analogue cicaprost.

METHODS

Small vessel myography was used to assess responses to cicaprost in segments of rat tail artery contracted with phenylephrine. Microelectrode recordings were made from helical strips to assess effects on membrane potential.

RESULTS

Cicaprost caused relaxation and hyperpolarisation that were significantly inhibited by Ba2+ (30-100 microM), a known blocker of KIR channels. Raising extracellular K+ from 5 to 15 mM elicited membrane hyperpolarisation and an endothelium-independent relaxation that was blocked by Ba2+ (30-100 microM), suggesting the existence of functional KIR channels on the smooth muscle. In contrast, neither glibenclamide (10 microM), a blocker of ATP-sensitive K+ channels, nor fluoxetine hydrochloride (100 microM), a blocker of G-protein-gated inward rectifier K+ channels, nor pertussis toxin (PTX; 1 microg/ml), which irreversibly inhibits Gi/Go, reduced relaxation to cicaprost. Indeed, PTX significantly potentiated responses. Relaxation to cicaprost was not mediated by NO but was partially endothelium-dependent, consistent with a similar inhibition by a combination of charybdotoxin (0.1 microM) and apamin (0.5 microM), blockers of endothelium-derived hyperpolarising factor (EDHF). However, relaxation was unaffected by adenylyl cyclase (SQ22536, dideoxyadenosine) or protein kinase A (Rp-2-O-monobutyryl-cAMP) inhibitors, consistent also with Ba2+ only weakly inhibiting relaxation to the adenylyl cyclase activator forskolin.

CONCLUSION

We conclude that cicaprost relaxes rat tail artery by activating KIR channels with some involvement from EDHF. The mechanism appears to be largely independent of cyclic AMP and Gi/Go, although the latter appears to counteract relaxation through an unknown pathway and/or receptor.

Prostaglandins E1 and E2 inhibit lipopolysaccharide-induced interleukin-18 production in monocytes

The purpose of this present study was to explore the therapeutic potential of prostaglandins E1 and E2 on the systemic inflammatory response evoked by endotoxin. Since interleukin-18, a monocyte-derived cytokine, is increased during sepsis, decreasing the production of interleukin-18 is important in treating this condition. Prostaglandin E1 and E2 inhibited interleukin-18 production in human monocytes treated with lipopolysaccharide and prostanoid IP-, EP2- and EP4-receptor agonists mimicked the effects of prostaglandins E1 and E2. Therefore, prostanoid IP, EP2- and EP4-receptors might be involved in the decrease in interleukin-18 production during sepsis.

Prostacyclin receptor induces STAT1 and STAT3 phosphorylations in human erythroleukemia cells: a mechanism requiring PTX-insensitive G proteins, ERK and JNK

The ability of the human prostacyclin receptor (hIP) to regulate the activities of signal transducers and activators of transcription (STATs) has not yet been documented. In the present study, we have delineated the mechanism by which hIP induces STAT3 phosphorylations in human erythroleukemia (HEL) cells. Stimulation of endogenous hIP by its specific agonist, cicaprost, resulted in STAT3 Tyr705 and Ser727 phosphorylations in a time- and concentration-dependent manner. Cicaprost-induced STAT3 Tyr705 and Ser727 phosphorylations were resistant to pertussis toxin (PTX) treatment, suggesting that these responses were mediated through PTX-insensitive G proteins. In addition, extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK), but not p38 MAPK, were shown to be phosphorylated by cicaprost in a time- and concentration-dependent manner via PTX-insensitive G proteins. The levels of the interaction between STAT3, ERK and JNK were enhanced by cicaprost treatment. The involvement of Raf-1, MEK1/2 and JNK in cicaprost-induced phosphorylations of STAT3 was illustrated by the use of their selective inhibitors. In contrast, p38 MAPK did not appear to be required. Similar observations were obtained with STAT1 upon stimulation by cicaprost. Taken together, these results demonstrate for the first time that hIP activation by cicaprost can lead to STAT1 and STAT3 phosphorylations via signaling pathways involving PTX-insensitive G proteins, ERK and JNK.

Effects of TRA-418, a novel TP-receptor antagonist, and IP-receptor agonist, on human platelet activation and aggregation

[4-[2-(1,1-Diphenylethylsulfanyl)-ethyl]-3,4-dihydro-2H-benzo[1,4]oxazin-8-yloxy]-acetic acid N-Methyl-d-glucamine salt (TRA-418) has both thromboxane A2 (TP)-receptor antagonist and prostacyclin (IP)-receptor agonist properties. The present study examined the advantageous effects of TRA-418 based on the dual activities, over an agent having either activity alone and also the difference in the effects of TRA-418 and a glycoprotein alphaIIb/beta3 integrin (GPIIb/IIIa) inhibitor. TRA-418 inhibited platelet GPIIb/IIIa activation as well as P-selectin expression induced by adenosine 5'-diphosphate, thrombin receptor agonist peptide 1-6 (Ser-Phe-Leu-Leu-Arg-Asn-NH2), and U-46619 in the presence of epinephrine (U-46619+ epinephrine). TRA-418 also inhibited platelet aggregation induced by those platelet-stimulants in Ca2+ chelating anticoagulant, citrate and in nonchelating anticoagulant, d-phenylalanyl-l-prolyl-l-arginyl-chloromethyl ketone (PPACK). The TP-receptor antagonist SQ-29548 inhibited only U-46619+epinephrine-induced GPIIb/IIIa activation, P-selectin expression, and platelet aggregation. The IP-receptor agonist beraprost sodium inhibited platelet activation. Beraprost also inhibited platelet aggregation induced by platelet stimulants we tested in citrate and in PPACK. The GPIIb/IIIa inhibitor abciximab blocked GPIIb/IIIa activation and platelet aggregation. However, abciximab showed slight inhibitory effects on P-selectin expression. TRA-418 is more advantageous as an antiplatelet agent than TP-receptor antagonists or IP-receptor agonists separately used. TRA-418 showed a different inhibitory profile from abciximab in the effects on P-selectin expression.