vorapaxar and Thrombosis

Protease-activated receptors (PARs) are a family of four GPCRs with a variety of cellular functions, yet the only advanced clinical endeavours to target these receptors for therapeutic gain to date relates to the impairment of platelet function for anti-thrombotic therapy. The only approved PAR antagonist is the PAR1 inhibitor, vorapaxar-the sole anti-platelet drug against a new target approved in the past 20 years. However, there are two PARs on human platelets, PAR1 and PAR4, and more recent efforts have focused on the development of the first PAR4 antagonists, with first-in-class agents recently beginning clinical trial. Here, we review the rationale for this approach, outline the various modes of PAR4 inhibition, and speculate on the specific therapeutic potential of targeting PAR4 for the prevention of thrombotic conditions.

Topics: Animals; Blood Platelets; Humans; Lactones; Platelet Aggregation Inhibitors; Pyridines; Receptors, Thrombin; Thrombosis

In spite of treatment with the current standard of care antiplatelet regimens including dual antiplatelet therapy, recurrence rates of ischemic events remain elevated for high-risk patients with atherosclerotic disease. This may be in part attributed to the fact that other key platelet activation pathways remain uninhibited and can thus continue to trigger platelet activation and lead to thrombotic complications. Thrombin is a powerful inducer of platelet activation and mediates its effects directly on platelets through protease activator receptors (PARs), particularly the PAR-1 subtype, making PAR-1 inhibition an attractive approach for reducing atherothrombotic events. These observations have led to the development of several PAR-1 antagonists. Vorapaxar is a direct inhibitor of PAR-1 and the only agent of this class approved for the prevention of recurrent ischemic events in patients with prior myocardial infarction or peripheral artery disease. In the present manuscript, we present a review of the pathophysiologic role of thrombin on thrombotic complications, the impact of vorapaxar on outcomes, including the most recent updates deriving from clinical trials, as well as future perspectives in the field.

Topics: Atherosclerosis; Humans; Lactones; Myocardial Infarction; Myocardial Ischemia; Peripheral Arterial Disease; Platelet Aggregation Inhibitors; Pyridines; Receptor, PAR-1; Secondary Prevention; Thrombin; Thrombosis

Since the identification of the proteinase-activated receptor (PAR) family as mediators of serine protease activity in the 1990s, there has been tremendous progress in the elucidation of their pathophysiological roles. The development of drugs that target PARs has been the focus of many laboratories for the potential treatment of thrombosis, cancer and other inflammatory diseases. Understanding the mechanisms of PAR activation and G protein signalling pathways evoked in response to the growing list of endogenous proteases has yielded great insight into receptor regulation at the molecular level. This has led to the development of new selective modulators of PAR activity, particularly PAR1. The mixed success of targeting PARs has been best exemplified in the context of inhibiting PAR1 as a new antiplatelet therapy. The development of the competitive PAR1 antagonist, vorapaxar (Zontivity), has clearly shown the value in targeting PAR1 in acute coronary syndrome (ACS); however the severity of associated bleeding with this drug has limited its use in the clinic. Due to the efficacy of thrombin acting via PAR1, strategies to selectively inhibit specific PAR1-mediated G protein signalling pathways or to target the second thrombin platelet receptor, PAR4, are being devised. The rationale behind these alternative approaches is to bias downstream thrombin activity via PARs to allow for inhibition of pro-thrombotic pathways but maintain other pathways that may preserve haemostatic balance and improve bleeding profiles for widespread clinical use. This review summarizes the structural determinants that regulate PARs and the modulators of PAR activity developed to date.

Topics: Humans; Hydrolysis; Lactones; Ligands; Platelet Aggregation Inhibitors; Pyridines; Receptors, Proteinase-Activated; Signal Transduction; Thrombosis

Twenty-three years after the discovery of the first thrombin receptor, now known as protease-activated receptor 1 (PAR1), the first drug targeting this receptor is available for human use. The PAR1 inhibitor, vorapaxar (Zontivity, MSD), was recently approved by the FDA for use in the USA for the prevention of thrombotic cardiovascular events in patients with a history of myocardial infarction or peripheral artery disease. In this review, we detail the rationale, development, as well as the clinical significance and considerations of vorapaxar, the original PAR antagonist and the latest anti-platelet agent in the pharmaco-armoury against arterial thrombosis.

Topics: Blood Platelets; Clinical Trials as Topic; Drug Approval; Humans; Lactones; Molecular Targeted Therapy; Platelet Aggregation Inhibitors; Pyridines; Receptor, PAR-1; Thrombosis; Treatment Outcome; United States; United States Food and Drug Administration

Atherothrombosis and its clinical manifestations are among the leading causes of death in the developed world. The current standard-of-care antiplatelet therapy for the treatment of such events comprises aspirin and a thienopyridine or ticagrelor. However, recurrent ischemic events due to residual cardiovascular risk are a common phenomenon in these patients. It is believed that this residual risk is caused, at least in part, by thrombin, which signals through protease-activated receptors (PARs) and especially PAR-1. Thus, PAR-1 antagonism could represent an effective approach in the treatment of atherothrombotic disease. In this context, two potent and selective agents have been developed, vorapaxar and atopaxar. However, only vorapaxar has completed phase 3 clinical trials. In the present review, the main pharmacodynamic and pharmacokinetic properties of the PAR-1 antagonists are briefly described and the latest clinical data on vorapaxar are presented.

Topics: Clinical Trials as Topic; Coronary Artery Bypass; Drug Therapy, Combination; Hemorrhage; Humans; Imines; Lactones; Myocardial Infarction; Percutaneous Coronary Intervention; Peripheral Arterial Disease; Platelet Aggregation Inhibitors; Pyridines; Receptor, PAR-1; Receptors, Thrombin; Stents; Stroke; Thrombosis

Vorapaxar (Zontivity®) is a first-in-class, potent and orally-active protease-activated receptor 1 (PAR-1) antagonist that blocks thrombin-mediated platelet activation without interfering with thrombin-mediated fibrin deposition. The long-term efficacy of once-daily vorapaxar added to standard antiplatelet therapy (aspirin with or without clopidogrel) in the secondary prevention of atherothrombotic events in patients with a history of myocardial infarction (MI), ischaemic stroke or peripheral arterial disease was investigated in the large, multinational TRA 2°P-TIMI 50 trial. Compared with placebo, vorapaxar significantly reduced the risk of the composite endpoints of cardiovascular (CV) death, MI or stroke, and CV death, MI, stroke or urgent coronary revascularization in the overall trial population. Vorapaxar also significantly reduced the risk of these composite endpoints in the subgroup of patients with prior MI (the largest qualifying disease cohort) and the subset of post-MI patients with no history of stroke or transient ischaemic attack (TIA). Vorapaxar significantly increased the risk of GUSTO moderate and/or severe bleeding in the overall trial population and all key subgroups (including post-MI patients with no history of stroke or TIA). Vorapaxar also significantly increased the risk of intracranial haemorrhage (ICH) in the overall trial population and the subgroup of patients with prior stroke, but not the subgroup of post-MI patients or the subset of post-MI patients with no history of stroke or TIA. Based on these results, vorapaxar has been approved in the EU as an adjunctive treatment for the secondary prevention of atherothrombotic events in patients with prior MI who do not have a history of stroke, TIA or ICH.

Topics: Clinical Trials as Topic; Humans; Lactones; Myocardial Infarction; Platelet Aggregation Inhibitors; Pyridines; Randomized Controlled Trials as Topic; Secondary Prevention; Stroke; Thrombosis

Acute myocardial infarction (AMI) is generally attributed to coronary atherothrombotic disease. Platelet activation is essential for thrombus formation and is thus an important target for pharmacological intervention to prevent and treat AMI. Despite contemporary treatment with dual antiplatelet therapy, including acetylsalicylic acid and adenosine diphosphate receptor antagonists, patients with prior AMI remain at increased risk of future thrombotic events. This has stimulated the search for more potent antithrombotic agents. Among these is the oral protease-activated receptor-1 antagonist vorapaxar, which represents a new oral antiplatelet agent to reduce thrombotic risk in patients with atherothrombotic disease. The TRACER and the TRA 2°P-TIMI 50 trials concluded that vorapaxar in addition to standard therapy reduced ischemic adverse cardiac events. A remarkable benefit was observed in patients with stable atherosclerotic disease, particularly those with a previous history of AMI. Although favorable effects were seen in reduction of adverse cardiac events, this was associated with excess major and intracranial bleeding, particularly in patients at high risk of bleeding and those with a history of stroke or transient ischemic attack. Currently, the lack of a reliable individualized risk stratification tool to assess patients for thrombotic and bleeding tendencies in order to identify those who might gain most net clinical benefit has led to limited use of vorapaxar in clinical practice. Vorapaxar may find a niche as an adjunct to standard care in patients at high risk of thrombotic events and who are at low risk of bleeding.

Topics: Animals; Hemorrhage; Humans; Lactones; Myocardial Infarction; Platelet Aggregation Inhibitors; Pyridines; Thrombosis

The pharmacology, pharmacokinetics, clinical efficacy, adverse effects, dosage and administration, cost, and place in therapy of vorapaxar in the secondary prevention of atherosclerotic events are reviewed.. Vorapaxar is a highly selective, reversible antagonist of protease-activated receptor-1 expressed on platelets. Vorapaxar competitively inhibits thrombin from activating the receptor, thereby decreasing platelet aggregation. Vorapaxar is rapidly absorbed and distributed, with peak plasma levels being reached within 60-90 minutes. Vorapaxar's effective half-life is three to four days and its terminal elimination half-life is eight days. Vorapaxar sulfate 2.5 mg (equivalent to 2.08 mg of vorapaxar) orally daily without a loading dose was clinically effective for the secondary prevention of ischemic events in patients with a history of myocardial infarction (MI) or with peripheral arterial disease (PAD) without a history of stroke. Phase II and III trials of vorapaxar given with aspirin or a thienopyridine or both demonstrated a reduction in the primary endpoint of cardiovascular death, MI, and stroke in patients with a history of MI or coronary artery disease and PAD. Patients with a history of stroke were found to have an increased rate of intracranial hemorrhage (ICH), which led to a boxed warning placed on vorapaxar's labeling to warn of the increased risk for bleeding in patients with a history of stroke.. Vorapaxar is a novel antiplatelet agent that has demonstrated efficacy in reducing atherosclerotic events in patients with a history of MI or PAD without a history of stroke, transient ischemic attack, or ICH when taken in combination with aspirin and clopidogrel.

Topics: Aspirin; Clopidogrel; Drug Interactions; Drug Therapy, Combination; Half-Life; Hemorrhage; Humans; Lactones; Myocardial Infarction; Myocardial Ischemia; Peripheral Arterial Disease; Platelet Aggregation Inhibitors; Pyridines; Randomized Controlled Trials as Topic; Receptor, PAR-1; Secondary Prevention; Stroke; Thrombosis; Ticlopidine

Atherosclerosis is frequently caused by clot blockage of the coronary or peripheral arteries, and may lead to myocardial infarction (MI) or peripheral arterial disease (PAD). Despite advancements in management of atherosclerosis, mortality and ischemic rates remain high. Vorapaxar is a protease activated receptor-1 (PAR-1) antagonist, and prevents thrombin activation of PAR-1 receptors on platelets.. Vorapaxar was studied in 2 landmark trials in patients with acute coronary syndrome (ACS) and in those with history of atherosclerosis. For patients with ACS, vorapaxar did not significantly reduce rates of the primary efficacy outcome as compared to placebo. For patients with a history of atherosclerosis, vorapaxar significantly reduced rates of primacy outcome. However, in both landmark trials, vorapaxar significantly increased risks of bleeding, and significantly increases risks of intracranial hemorrhage in patients with a history of stroke. Vorapaxar was approved in 2014 in the US for patients with a history of MI or PAD, and in the European Union for patients with a history of MI.. Use of vorapaxar may be limited due to its high potential for causing bleeding. Efficacy of vorapaxar in addition to aspirin and prasugrel or ticagrelor for the management of ACS should be studied in the future.

Topics: Acute Coronary Syndrome; Animals; Atherosclerosis; Hemorrhage; Humans; Lactones; Platelet Aggregation Inhibitors; Pyridines; Randomized Controlled Trials as Topic; Receptor, PAR-1; Risk; Stroke; Thrombosis

Dual antiplatelet therapy with aspirin, a platelet cyclooxygenase-1 inhibitor and P2Y12 receptor blockers, remains the major drug strategy to prevent ischemic event occurrence in patients with acute coronary syndromes and in patients undergoing coronary stenting, but there some limitations that can be overcome by targeting novel targets. Unlike direct thrombin inhibitors that bind directly to thrombin, targeting the platelet thrombin receptor, protease activated receptor (PAR)-1, may offer a better choice for the attenuation of atherosclerosis progression, thrombus-mediated ischemic events and restenosis without interfering with primary hemostasis. Vorapaxar - a synthetic analogue of himbacine, is a high affinity and highly selective PAR-1 antagonist that can effectively inhibit thrombin-induced platelet aggregation. In the TRACER trial, the addition of vorapaxar to standard therapy in patients with non-stent thrombosis-elevation- acute coronary syndromes did not significantly reduce the primary composite end point occurrence of cardiovascular (CV) death, myocardial infarction (MI), stroke, hospitalization for ischemia, or urgent revascularization, but significantly increased the GUSTO moderate and severe bleeding (p < 0.001) and intracranial hemorrhage (ICH). In the TRA 2°P-TIMI 50 trial, in patients with a history of MI and peripheral arterial disease (PAD) (67% of the total population), the end point of CV death, MI, or stroke was significantly (20%) reduced with vorapaxar whereas GUSTO moderate or severe bleeding was increased (1.5-fold), but not ICH or fatal bleeding and the net clinical outcome favoring the vorapaxar therapy. Based on these favorable results, the FDA approved vorapaxar for the reduction of thrombotic cardiovascular events in patients with prior MI or with PAD for long term therapy. A careful patient selection is needed to balance efficacy versus safety. At this time, patients with high risk for recurrent ischemic event occurrence such as patients with diabetes mellitus and previous MI can be safely treated with vorapaxar for long-term therapy.

Topics: Clinical Trials as Topic; Humans; Lactones; Myocardial Ischemia; Outcome and Process Assessment, Health Care; Patient Selection; Platelet Aggregation Inhibitors; Pyridines; Receptor, PAR-1; Risk Assessment; Secondary Prevention; Stroke; Thrombosis

Proteinase Activated Receptors (PARs) are G-protein coupled receptors (GPCRs) that were discovered in the early 1990's. They are unusual among GPCRs in being activated through proteolytic cleavage of the receptor N-terminus by serine proteinases such as thrombin. Over the last two decades major advances have been made in our understanding of how these receptors function and the roles they play in (patho)physiology. They have also emerged as drug targets for a number of conditions, most notably thrombosis. Recently two different drugs targeting PAR1 have entered clinical trials as anti-platelet agents. This review provides an overview of the proteinase activated receptor family and focuses on the role of PAR1 in regulating the endothelial barrier integrity and its implication on developing PAR antagonists for anti-platelet therapy.

Topics: Animals; Cardiovascular Diseases; Endothelial Cells; Humans; Lactones; Platelet Aggregation Inhibitors; Pyridines; Receptors, Proteinase-Activated; Thrombosis

Stroke and myocardial infarction are leading causes of death and disability worldwide. Typically, these events are triggered by the rupture or erosion of "vulnerable" atherosclerotic plaque, a phenomenon termed atherothrombosis.Three platelet activation pathways are presumed to be particularly important in the genesis of atherothrombosis and are triggered by 1) cyclo-oxygenase (COX)-1 mediated thromboxane A2 (TXA2) synthesis and activation via the TXA2 receptor, 2) adenosine diphosphate (ADP) via the P2Y12 receptor, and 3) thrombin via the protease activated receptor (PAR)-1.Despite the efficacy of aspirin and of a growing family of P2Y12 receptor antagonists on the first 2 pathways, major cardiovascular events continue to occur in patients with coronary and cerebrovascular disease, suggesting that thrombin-mediated platelet activation may contribute to these adverse events.Recently, a novel class of antiplatelet agents able to inhibit thrombin-mediated platelet activation has been developed, PAR-1 inhibitors. In this chapter, we will discuss the rationale underlying the development of this novel class of agents focus on the two drugs in the most advanced stages of development: vorapaxar (SCH530348) and atopaxar (E5555).

Topics: Animals; Clinical Trials as Topic; Humans; Imines; Lactones; Plaque, Atherosclerotic; Platelet Aggregation Inhibitors; Pyridines; Receptor, PAR-1; Thrombosis

Recent clinical trial data suggest that protease-activated receptor-1 (PAR-1) antagonists may increase the risk of intracranial hemorrhage. Our objective was to investigate the qualitative and quantitative risks of intracranial hemorrhage in patients receiving PAR-1 antagonist therapy.. Pubmed, EMBASE, Cochrane Central Register of Controlled Trials, and Clinicaltrials.gov from 1966 to May 2012, were searched to identify relevant studies. We included randomized controlled trials that included a comparison of PAR-1 antagonist with placebo and in which the total number of patients and intracranial hemorrhage events were reported separately for active treatment and control groups. Summary incidence rates, relative risks, and 95% confidence intervals (CIs) were calculated using random-effects models. Between-study heterogeneity was assessed using the I2 statistic.. In 9 PAR-1 antagonist trials with 42000 patients with a history of thrombotic vascular disease or acute coronary syndrome, PAR-1 antagonist treatment was associated with increased risk of intracranial hemorrhage (0.59% vs 0.30%; relative risk, 1.98; 95% CI, 1.46-2.68; P<0.00001; number needed to harm, 345). There was no heterogeneity across trials (P=0.84; I2=0%), PAR-1 antagonist agent (P=0.52), treatment duration (P=0.38), or trial-qualifying event (P=0.59). Risk of death from any cause or a cardiovascular cause did not differ between active treatment and control groups.. In a pooled analysis of data from 9 trials, PAR-1 antagonist therapy was associated with an increased risk for intracranial hemorrhage.

Topics: Acute Coronary Syndrome; Humans; Imines; Incidence; Intracranial Hemorrhages; Lactones; Placebos; Pyridines; Randomized Controlled Trials as Topic; Receptor, PAR-1; Risk Factors; Thrombosis

Activated platelets stimulate thrombus formation in response to rupture of an atherosclerotic plaque or endothelial cell erosion, promoting atherothrombotic disease. Multiple pathways contribute to platelet activation. Aspirin, an irreversible inhibitor of thromboxane A2 synthesis, in combination with clopidogrel, an inhibitor of P2Y(12) adenosine diphosphate platelet receptors, represent the current standard-of-care of antiplatelet therapy for patients with acute coronary syndrome and for those undergoing percutaneous coronary intervention. Although these agents have demonstrated significant clinical benefit, the increased risk of bleeding and the recurrence of thrombotic events represent substantial limitations. Thrombin is one of the most important platelet activators. The inhibition of protease-activated receptor 1 showed a good safety profile in preclinical studies. In fact, phase II studies with vorapaxar (SCH530348) and atopaxar (E5555) showed no increase of bleeding events in addition to the current standard-of-care of antiplatelet therapy. Although the results of phase III trials for both drugs are awaited, this family is a promising new addition to the current clinical practice for patients with atherothrombotic disease, not only as an alternative, but also as additional therapy.

Topics: Aspirin; Blood Platelets; Humans; Imines; Lactones; Platelet Aggregation; Platelet Aggregation Inhibitors; Pyridines; Receptors, Thrombin; Thrombosis

Clinical manifestations of atherothrombotic disease, such as acute coronary syndromes, cerebrovascular events, and peripheral arterial disease, are major causes of mortality and morbidity worldwide. Platelet activation and aggregation are ultimately responsible for the progression and clinical presentations of atherothrombotic disease. The current standard of care, dual oral antiplatelet therapy with aspirin and the P2Y(12) adenosine diphosphate (ADP) receptor inhibitor clopidogrel, has been shown to improve outcomes in patients with atherothrombotic disease. However, aspirin and P2Y(12) inhibitors target the thromboxane A(2) and the ADP P2Y(12) platelet activation pathways and minimally affect other pathways, while agonists such as thrombin, considered to be the most potent platelet activator, continue to stimulate platelet activation and thrombosis. This may help explain why patients continue to experience recurrent ischaemic events despite receiving such therapy. Furthermore, aspirin and P2Y(12) receptor antagonists are associated with bleeding risk, as the pathways they inhibit are critical for haemostasis. The challenge remains to develop therapies that more effectively inhibit platelet activation without increasing bleeding complications. The inhibition of the protease-activated receptor-1 (PAR-1) for thrombin has been shown to inhibit thrombin-mediated platelet activation without increasing bleeding in pre-clinical models and small-scale clinical trials. PAR-1 inhibition in fact does not interfere with thrombin-dependent fibrin generation and coagulation, which are essential for haemostasis. Thus PAR-1 antagonism coupled with existing dual oral antiplatelet therapy may potentially offer more comprehensive platelet inhibition without the liability of increased bleeding.

Topics: Fibrinolytic Agents; Humans; Imines; Lactones; Platelet Activation; Platelet Aggregation Inhibitors; Pyridines; Receptor, PAR-1; Thrombosis

Coronary artery disease is a leading cause of morbidity and mortality worldwide. Platelet activation and subsequent thrombus formation play a central role in disease progression and development of acute coronary syndromes (ACS). Despite widespread use of single and dual antiplatelet therapies in atherothrombotic disease, ischemic complications remain common. Therefore, the need exists for new antiplatelet agents that are more effective, but with acceptable safety profiles (i.e., do not increase risk of bleeding). Antiplatelet agents available at present are effective in blocking the cyclo-oxygenase, ADP-mediated and final common (IIb/IIIa receptor) pathways for platelet activation. Recently, there has been more interest in inhibition of the proteinase-activated receptor-1 (PAR-1), which blocks thrombin-mediated platelet activation.. This review covers the pharmacology, pharmacokinetics and development of the new PAR(1) antagonist, SCH 530348 in a review of all publications relevant to the topic over the last 10 years. Phase II clinical trials indicate that addition of this agent to current antiplatelet regimens may provide additional antithrombotic protection without an increase in bleeding. Results of the ongoing Phase III trials, examining the use of SCH 530348 in patients with ACS and for secondary prevention of ischemic events are anxiously awaited.. The review is a summary of all pharmacologic properties and current clinical data available on the PAR1 antagonist SCH 530348. The readers will be introduced to its novel mechanism of action, advantages over current antiplatelet agents and potential future applications should ongoing clinical trials confirm its efficacy in reducing platelet activity.. SCH 530348 is a new, orally administered antiplatelet agent that blocks the protease-activated thrombin receptor on the platelet. Early clinical data indicate that it is associated with a lower risk of bleeding. However, its efficacy in improving clinical outcomes in patients with coronary disease remains to be confirmed in ongoing Phase III clinical trials.

Topics: Administration, Oral; Animals; Blood Platelets; Clinical Trials as Topic; Coronary Disease; Evidence-Based Medicine; Hemorrhage; Humans; Lactones; Platelet Aggregation Inhibitors; Pyridines; Receptor, PAR-1; Thrombosis; Treatment Outcome

Atherothrombotic disease is the leading cause of death worldwide. Currently, dual antiplatelet therapy with aspirin and ADP receptor antagonists has shown improved short- and long-term clinical outcomes but is associated with increased bleeding risk, and the rates of recurrent ischemic events still remain high. Selective inhibition of the principal protease-activated receptor (PAR)-1 for thrombin, the most potent platelet activator, represents a promising novel strategy to reduce ischemic events without increasing the risk of bleeding. Two PAR-1 antagonists are currently being tested in clinical trials: SCH 530348 and E5555. Both have demonstrated an antiplatelet effect without increasing bleeding time in preclinical trials. Results of Phase II trials showed that SCH 530348, in addition to standard antiplatelet therapy, was well tolerated and not associated with increased bleeding risk. The safety and tolerability of E5555 is being evaluated in patients with coronary artery disease and non-ST-segment elevation acute coronary syndrome in four Phase II clinical trials. Two large-scale Phase III trials assessing the efficacy of SCH 530348 in addition to the standard of care are currently ongoing. This article provides an overview of the current status of knowledge on platelet thrombin receptor antagonists, focusing on pharmacologic properties and clinical development.

Topics: Animals; Clinical Trials as Topic; Hemorrhage; Humans; Imines; Lactones; Platelet Aggregation Inhibitors; Pyridines; Receptor, PAR-1; Receptors, Thrombin; Thrombosis

Antiplatelet agents are a cornerstone in the treatment of acute arterial thrombotic events and in the prevention of thrombus formation. However, existing antiplatelet agents (mainly aspirin, the combination of aspirin and dipyridamole and clopidogrel) reduce the risk of vascular events only by about one quarter compared with placebo. As a consequence, more efficacious antiplatelet therapies with a reduced bleeding risk are needed. We give an overview of several new antiplatelet agents that are currently investigated in secondary stroke prevention: adenosine 5'-diphosphonate receptor antagonists, cilostazol, sarpogrelate, terutroban and SCH 530348. There are unique features in secondary stroke prevention that have to be taken into account: ischaemic stroke is a heterogeneous disease caused by multiple aetiologies and the blood-brain barrier is disturbed after stroke which may result in a higher intracerebral bleeding risk. Several small randomized trials indicated that the combination of aspirin and clopidogrel might be superior to antiplatelet monotherapy in the acute and early post-ischaemic phase. There is an ongoing debate about antiplatelet resistance. Decreasing response to aspirin is correlated independently with an increased risk of cardiovascular events. However, there is still no evidence from randomized trials linking aspirin resistance and recurrent ischaemic events. Similarly, randomized trials have not demonstrated a clinical significantly decreased antiplatelet effect by the concomitant use of clopidogrel and proton pump inhibitors. Nevertheless, a routine use of this drug combination is not recommended.

Topics: Aspirin; Blood-Brain Barrier; Cilostazol; Clopidogrel; Dipyridamole; Drug Interactions; Drug Therapy, Combination; Humans; Lactones; Naphthalenes; Platelet Aggregation Inhibitors; Propionates; Pyridines; Randomized Controlled Trials as Topic; Secondary Prevention; Stroke; Succinates; Tetrazoles; Thrombosis; Ticlopidine

Platelet activation, achieved through a variety of surface receptors and biochemical mediators, represents a key event in the pathogenesis of atherothrombosis and its clinical manifestations. The major pathways involved in platelet activation are triggered by thromboxane A(2), adenosine diphosphate and thrombin, with the latter being the most potent of these agonists. Despite the effective inhibition of the first two pathways with aspirin and several generations of P2Y(12) receptor antagonists, respectively, the recurrence of ischaemic events in patients with atherothrombosis remains high. In addition, there is a growing concern over the safety profile of increasingly powerful antiplatelet drugs in terms of bleeding, which has tempered expectations of newly developed compounds. Thrombin receptor antagonists are a novel class of antiplatelet agents that inhibit thrombin-mediated platelet activation. Preliminary data indicate that these compounds may have the potential to improve ischaemic outcomes without significantly increasing the bleeding liability. Currently, two agents of this class are under clinical development: vorapaxar (previously known as SCH 530348) and E-5555. In this review we discuss this novel class of antiplatelet agents, focusing in particular on their therapeutic potential.

Topics: Atherosclerosis; Humans; Imines; Lactones; Platelet Activation; Platelet Aggregation Inhibitors; Pyridines; Receptors, Thrombin; Thrombosis

Despite the availability of dual antiplatelet therapy comprised of aspirin and clopidogrel, there is still significant unmet medical need for treating and preventing arterial thrombotic diseases. To achieve further reduction of cardiovascular events without exceeding bleeding tolerability and safety limits, novel antiplatelet strategies might need to trade in antiplatelet efficacy by partial inhibition of an important platelet activation pathway or by differentially targeting pathological versus physiological thrombogenesis pathways. Thrombin, the central enzyme in coagulation and the most potent platelet agonist tested in vitro, is one of the key factors driving the formation of occlusive thrombi. Platelet thrombin receptors, namely protease-activated receptor 1 (PAR-1) and protease-activated receptor 4 (PAR-4), act in concert to elicit robust platelet responses to thrombin. PAR-1 is the high affinity thrombin receptor and represents a novel antithrombotic target. PAR-4 is a low affinity thrombin receptor with less understood function. This review discusses the genetic and pharmacological evidence for PAR-1 target validation and highlights the progresses and challenges in developing oral PAR-1 antagonists, especially SCH 530348 from Merck/Schering-Plough and E-5555 from Eisai Co. Recent patents disclosing several novel chemical series of PAR-1 antagonists from Sanofi-Aventis and Pierre Fabre are also presented.

Topics: Administration, Oral; Animals; Cardiovascular Diseases; Humans; Imines; Lactones; Platelet Aggregation Inhibitors; Pyridines; Receptor, PAR-1; Receptors, Thrombin; Thrombin; Thrombosis

Aspirin, an irreversible inhibitor of thromboxane A(2) production, in combination with clopidogrel, an inhibitor of PY(12) ADP platelet receptors, represents the current standard-of-care of antiplatelet therapy for patients with acute coronary syndrome and those undergoing percutaneous coronary intervention. Although these agents have demonstrated significant clinical benefit, the increased risk of bleeding and the recurrence of thrombotic events represent substantial limitations.. The inhibition of protease-activated receptors (PAR)-1, is the target for novel antiplatelet drugs, which showed a good safety profile in preclinical studies. The drugs most developed are vorapaxar (SCH530348) and atopaxar (E5555), which will be further evaluated in ongoing Phase III and II clinical trials respectively.. This review is focused on the current knowledge of PAR-1 antagonists, analyzing the pharmacological and early phase clinical investigation findings on these new drugs.. The PAR-1 receptor offers a new target for the inhibition of platelet activation and aggregation. Preliminary results showed the good safety profile of these new agents. The results of the Phase III ongoing trials will provide important clinical insight into the blockade of thrombin-induced platelet activation.

Topics: Animals; Atherosclerosis; Clinical Trials as Topic; Humans; Imines; Lactones; Pyridines; Receptor, PAR-1; Thrombosis; Treatment Outcome

SCH-530348 is a novel antiplatelet agent undergoing development by Schering-Plough Corp for the treatment and prevention of atherothrombosis. The compound is an orally administered himbacine analog that potently antagonizes the platelet thrombin receptor protease-activated receptor 1 (PAR-1), which leaves the procoagulant function of thrombin intact. In preclinical studies, SCH-530348 demonstrated no effect on bleed time or coagulation parameters. In both cynomolgus monkeys and humans, the compound had high bioavailability and inhibited ex vivo TRAP (thrombin receptor-activating peptide)-stimulated platelet aggregation in a potent and long-lasting manner. In a phase II clinical trial of patients undergoing percutaneous coronary intervention, SCH-530348 added to standard therapy with aspirin and clopidogrel did not increase major or minor thrombolysis in myocardial infarction bleeding, and demonstrated a trend toward decreased major adverse cardiovascular events versus placebo. At the time of publication, three phase III trials were underway to assess the efficacy and safety of SCH-530348 for at least 1 year in up to 35,000 patients with acute coronary syndromes or atherosclerosis. The distinct mechanism of action of SCH-530348 allows for cardiovascular protection without the liability of increased bleeding associated with other antiplatelet therapies. Phase III trials in high-risk patients will determine the use of SCH-530348 in cardiological practice.

Topics: Absorption; Animals; Area Under Curve; Biological Availability; Clinical Trials as Topic; Dose-Response Relationship, Drug; Double-Blind Method; Humans; Lactones; Molecular Structure; Platelet Aggregation Inhibitors; Pyridines; Randomized Controlled Trials as Topic; Receptor, PAR-1; Structure-Activity Relationship; Thrombosis

Vorapaxar is a first-in-class protease-activated receptor-1 antagonist indicated for the reduction of cardiovascular death, myocardial infarction, and stroke in stable patients with prior atherothrombosis, who have not had a prior stroke or transient ischemic attack. The aims of this study were to investigate: 1) the role of vorapaxar in patients with severe coronary artery disease treated previously with coronary artery bypass grafting (CABG); and 2) safety in patients undergoing CABG while receiving vorapaxar.. TRA 2°P-TIMI 50 was a randomized, double-blinded, placebo-controlled trial of vorapaxar in 26,449 stable patients with prior atherothrombosis followed for a median of 30 months. We 1) investigated the efficacy of vorapaxar among patients with a history of CABG prior to randomization ( n=2942); and 2) assessed the safety among 367 patients who underwent a new CABG during the trial.. Patients with a prior CABG were at higher risk for cardiovascular death, myocardial infarction, or stroke at three years compared with patients without a prior CABG (13.7% vs. 7.8%, p<0.001). Among patients with a prior CABG, vorapaxar significantly reduced the risk of cardiovascular death, myocardial infarction, or stroke (11.9% vs. 15.6%, hazard ratio 0.71, 95% confidence interval 0.58-0.88, p=0.001; number-needed-to-treat = 27). In patients undergoing CABG while receiving vorapaxar, the rate of Thrombolysis in Myocardial Infarction CABG major bleeding was 6.3% vs. 4.1% with placebo (hazard ratio 1.53, 95% confidence interval 0.58-4.01, p=0.39).. In patients with a prior CABG, vorapaxar significantly reduced the risk of recurrent major cardiovascular events. In patients undergoing CABG while receiving vorapaxar, bleeding risk appeared similar to that seen in the overall trial population.

Topics: Aged; Coronary Artery Bypass; Double-Blind Method; Female; Heart Diseases; Humans; Lactones; Male; Middle Aged; Myocardial Infarction; Platelet Aggregation Inhibitors; Pyridines; Secondary Prevention; Stroke; Thrombosis; Treatment Outcome

Stent thrombosis (ST) is an important end point in cardiovascular clinical trials. Adjudication is traditionally based on clinical event committee (CEC) review of case report forms and source documentation rather than angiograms. However, the degree to which this method of adjudication is concordant with the review of independent angiographic core laboratories (ACLs) has not been studied. This report represents the first assessment of variability between local investigators (LIs), a CEC, and an ACL.. Serial angiograms of 329 patients with acute coronary syndrome without ST-segment-elevation who underwent percutaneous coronary intervention at entry in the Trial to Assess the Effects of Vorapaxar in Preventing Heart Attack and Stroke in Particpants With Acute Coronary Syndrome (TRACER) and who met criteria for possible ST subsequent to the index event were reviewed by an ACL. The ACL was blinded to the assessment by both LIs and the CEC regarding the presence or absence of ST. CEC adjudication was based on Academic Research Consortium definitions of ST, using case report form data and source documents, including catheterization laboratory reports. The ACL, CEC, and LIs agreed on the presence or absence of ST in 52.9% events (κ=0.32; 95% confidence interval, 0.26-0.39). The ACL and CEC agreed on 82.7% of events (κ=0.57; 95% confidence interval, 0.47-0.67); the ACL and LIs agreed on 61.1% of events (κ=0.25; 95% confidence interval, 0.16-0.34); and the CEC and LIs agreed on 62% of events (κ=0.28; 95% confidence interval, 0.21-0.36).. ST reporting by an ACL, a CEC, and LIs is discordant. The assessment of ST is more often detected by direct review of angiograms by an ACL.. URL: http://www.clinicaltrials.gov. Unique identifier: NCT00527943.

Topics: Acute Coronary Syndrome; Angiography; Animals; Blood Vessel Prosthesis Implantation; Chick Embryo; Clinical Laboratory Techniques; Drug-Eluting Stents; Electrocardiography; Female; Follow-Up Studies; Humans; Lactones; Male; Outcome Assessment, Health Care; Percutaneous Coronary Intervention; Postoperative Complications; Pyridines; Reproducibility of Results; Thrombosis

Vorapaxar reduces cardiovascular death, myocardial infarction (MI), or stroke in patients with previous MI while increasing bleeding. Patients with diabetes mellitus (DM) are at high risk of recurrent thrombotic events despite standard therapy and may derive particular benefit from antithrombotic therapies. The Thrombin Receptor Antagonist in Secondary Prevention of Atherothrombotic Ischemic Events-TIMI 50 trial was a randomized, double-blind, placebo-controlled trial of vorapaxar in patients with stable atherosclerosis.. We examined the efficacy of vorapaxar in patients with and without DM who qualified for the trial with a previous MI. Because vorapaxar is contraindicated in patients with a history of stroke or transient ischemic attack, the analysis (n=16 896) excluded such patients. The primary end point of cardiovascular death, MI, or stroke occurred more frequently in patients with DM than in patients without DM (rates in placebo group: 14.3% versus 7.6%; adjusted hazard ratio, 1.47; P<0.001). In patients with DM (n=3623), vorapaxar significantly reduced the primary end point (11.4% versus 14.3%; hazard ratio, 0.73 [95% confidence interval, 0.60-0.89]; P=0.002) with a number needed to treat to avoid 1 major cardiovascular event of 29. The incidence of moderate/severe bleeding was increased with vorapaxar in patients with DM (4.4% versus 2.6%; hazard ratio, 1.60 [95% confidence interval, 1.07-2.40]). However, net clinical outcome integrating these 2 end points (efficacy and safety) was improved with vorapaxar (hazard ratio, 0.79 [95% confidence interval, 0.67-0.93]).. In patients with previous MI and DM, the addition of vorapaxar to standard therapy significantly reduced the risk of major vascular events with greater potential for absolute benefit in this group at high risk of recurrent ischemic events.. URL: http://www.clinicaltrials.gov. Unique identifier: NCT00526474.

Topics: Aged; Death; Diabetes Mellitus; Double-Blind Method; Female; Humans; Lactones; Male; Middle Aged; Myocardial Infarction; Pyridines; Receptors, Thrombin; Secondary Prevention; Stroke; Thrombosis; Treatment Outcome

To assess the effect of vorapaxar on global thrombotic and thrombolytic status. The propensity for thrombus formation is determined by the balance between prothrombotic factors and endogenous thrombolysis. Impaired thrombolytic status increases cardiovascular risk. Vorapaxar is a novel, oral, protease-activated receptor-1 antagonist that inhibits thrombin-induced platelet activation. In the TRACER and TRA 2°P-TIMI 50 studies, patients with acute coronary syndromes and established atherosclerosis were randomized to vorapaxar 2.5 mg daily or placebo, in addition to standard care. In 57 patients enrolled in a single center, blood was tested with the point-of-care global thrombosis test, on and off treatment. This automated test employs non-anticoagulated blood to assess thrombotic and thrombolytic status, measuring the time required to form a shear-induced thrombus under physiological conditions (occlusion time, OT), and subsequently, the time to achieve endogenous lysis of the thrombus (lysis time, LT). Patients on vorapaxar exhibited longer OT on vs. off treatment [median 561 s (interquartile range 422-654) vs. 372 s(338-454), P = 0.003] and shorter LT on treatment than off [1,158 s(746-1,492) vs. 1,733 s(1,388-2,230), P = 0.016]. Patients on placebo showed no difference in OT [419 s(343-514) vs. 411 s(346-535), P = 0.658] or LT [1,236 s(985-1,594) vs. 1,400 s(1,092-1,686), P = 0.524] on and off treatment. During treatment, OT was longer in patients taking vorapaxar [561 s(422-654) vs. 419 s(343-514), P = 0.009], but LT was similar in vorapaxar and placebo arms [1,158 s(746-1,492) vs. 1,236 s(985-1,594), P = 0.277]. Vorapaxar prolongs OT and shortens LT, with favorable effects on thrombotic and thrombolytic status. In addition to its antiplatelet effect, vorapaxar may enhance endogenous thrombolysis, which is frequently impaired in coronary disease.

Topics: Aged; Coronary Disease; Double-Blind Method; Female; Humans; Lactones; Longitudinal Studies; Male; Middle Aged; Pyridines; Receptor, PAR-1; Thrombosis

Vorapaxar inhibits platelet activation by antagonising thrombin-mediated activation of the protease-activated receptor 1 on human platelets. The effect of adding other antiplatelet drugs to aspirin for long-term secondary prevention of thrombotic events in stable patients with previous myocardial infarction is uncertain. We tested this effect in a subgroup of patients from the Thrombin Receptor Antagonist in Secondary Prevention of Atherothrombotic Ischemic Events (TRA 2°P)-TIMI 50 trial.. In TRA 2°P-TIMI 50--a randomised, placebo-controlled, parallel trial--we randomly assigned patients with a history of atherothrombosis to receive vorapaxar (2·5 mg daily) or matching placebo in a 1:1 ratio. Patients, and those giving treatment, assessing outcomes, and analysing results were masked to treatment allocation. Patients with a qualifying myocardial infarction within the previous 2 weeks to 12 months were analysed as a pre-defined subgroup. The primary efficacy endpoint was cardiovascular death, myocardial infarction, or stroke, analysed by intention to treat. We analysed events by Kaplan-Meier analysis and compared groups with a Cox proportional hazard model. TRA 2°P-TIMI 50 is registered at ClinicalTrials.gov (NCT00526474).. 17,779 of 26,449 patients had a qualifying myocardial infarction and were assigned treatment (8898 to vorapaxar and 8881 to placebo). Median follow-up was 2·5 years (IQR 2·0-2·9). Cardiovascular death, myocardial infarction, or stroke occurred in 610 of 8898 patients in the vorapaxar group and 750 of 8881 in the placebo group (3-year Kaplan-Meier estimates 8·1%vs 9·7%, HR 0·80, 95% CI 0·72-0·89; p<0·0001). Moderate or severe bleeding was more common in the vorapaxar group versus the placebo group (241/8880 [3·4%, 3-year Kaplan-Meier estimate] vs 151/8849 [2·1%, 3-year Kaplan-Meier estimate], HR 1·61, 95% CI 1·31-1·97; p<0·0001). Intracranial haemorrhage occurred in 43 of 8880 patients (0·6%, 3-year Kaplan-Meier estimate) with vorapaxar versus 28 of 8849 (0·4%, 3-year Kaplan-Meier estimate) with placebo (p=0·076). Other serious adverse events were equally distributed between groups.. For patients with a history of myocardial infarction, inhibition of protease-activated receptor 1 with vorapaxar reduces the risk of cardiovascular death or ischaemic events when added to standard antiplatelet treatment, including aspirin, and increases the risk of moderate or severe bleeding.. Merck.

Topics: Aged; Cardiovascular Diseases; Double-Blind Method; Female; Humans; Lactones; Male; Middle Aged; Myocardial Infarction; Pyridines; Receptor, PAR-1; Secondary Prevention; Stroke; Thrombosis

Topics: Humans; Lactones; Membranes, Artificial; Polymers; Pyridines; Sulfones; Thrombosis

Topics: Age Factors; Aged; Aged, 80 and over; Female; Hemorrhage; Humans; Lactones; Male; Middle Aged; Myocardial Infarction; Peripheral Arterial Disease; Platelet Aggregation Inhibitors; Pyridines; Randomized Controlled Trials as Topic; Risk Assessment; Risk Factors; Secondary Prevention; Stroke; Thrombosis; Time Factors; Treatment Outcome

Topics: Afibrinogenemia; Humans; Lactones; Platelet Aggregation Inhibitors; Pyridines; Thrombosis

To evaluate long-term health benefits and risks of adding vorapaxar (VOR) to the standard care antiplatelet therapy (SC) of aspirin and/or clopidogrel, among a population with a recent myocardial infarction (MI) and/or peripheral artery disease (PAD).. In a state-transition model, patients transition between health states (event-free, recurrent MI, stroke, death), while at risk of experiencing non-transition-related revascularization and non-fatal bleeding events. Risk equations developed from the TRA 2°P-TIMI 50 trial's patient-level data were used to predict cardiovascular (CV) outcomes over longer time horizons. Additional sources, including trials and US-based observational studies, informed the inputs for short-term CV risk, non-CV death, and health-related quality of life. Survival and quality-adjusted life-years (QALYs) were estimated over a lifetime horizon, discounted at 3% per year.. Within a cohort of 7361 patients with recent MI and/or PAD, VOR + SC relative to SC alone yielded 176 fewer CV events (MIs, strokes, or CV deaths), but 27 more major bleeding events. VOR + SC was associated with increased life expectancy and health benefits (19.93 undiscounted life-years [LYs], 9.57 discounted QALYs vs. 19.61 undiscounted LYs, 9.41 discounted QALYs). The results were most sensitive to scenarios varying time of vorapaxar initiation, and the assumptions in the 90 day period post-MI. Additional analyses showed that add-on vorapaxar provides consistent incremental benefits in high-risk subgroups.. This study contributes to the growing literature on secondary prevention add-on therapy, as results from these modeling analyses suggest that adding vorapaxar to SC for patients at high atherothrombotic risk can provide long-term health benefits.

Topics: Aspirin; Clopidogrel; Female; Hemorrhage; Humans; Lactones; Male; Middle Aged; Myocardial Infarction; Peripheral Arterial Disease; Platelet Aggregation Inhibitors; Pyridines; Quality of Life; Quality-Adjusted Life Years; Secondary Prevention; Stroke; Thrombosis; Ticlopidine

Essentials The platelet thrombin receptor, PAR4, is an emerging anti-thrombotic drug target. We examined the anti-platelet & anti-thrombotic effects of PAR4 inhibition in human blood. PAR4 inhibition impaired platelet procoagulant activity in isolated cells and during thrombosis. Our study shows PAR4 is required for platelet procoagulant function & thrombosis in human blood.. Background Thrombin-induced platelet activation is important for arterial thrombosis. Thrombin activates human platelets predominantly via protease-activated receptor (PAR)1 and PAR4. PAR1 has higher affinity for thrombin, and the first PAR1 antagonist, vorapaxar, was recently approved for use as an antiplatelet agent. However, vorapaxar is contraindicated in a significant number of patients, owing to adverse bleeding events. Consequently, there is renewed interest in the role of platelet PAR4 in the setting of thrombus formation. Objectives To determine the specific antiplatelet effects of inhibiting PAR4 function during thrombus formation in human whole blood. Methods and Results We developed a rabbit polyclonal antibody against the thrombin cleavage site of PAR4, and showed it to be a highly specific inhibitor of PAR4-mediated platelet function. This function-blocking anti-PAR4 antibody was used to probe for PAR4-dependent platelet functions in human isolated platelets in the absence and presence of concomitant PAR1 inhibition. The anti-PAR4 antibody alone was sufficient to abolish the sustained elevation of cytosolic calcium level and consequent phosphatidylserine exposure induced by thrombin, but did not significantly inhibit integrin αII b β3 activation, α-granule secretion, or aggregation. In accord with these in vitro experiments on isolated platelets, selective inhibition of PAR4, but not of PAR1, impaired thrombin activity (fluorescence resonance energy transfer-based thrombin sensor) and fibrin formation (anti-fibrin antibody) in an ex vivo whole blood flow thrombosis assay. Conclusions These findings demonstrate that PAR4 is required for platelet procoagulant function during thrombus formation in human blood, and suggest PAR4 inhibition as a potential target for the prevention of arterial thrombosis.

Topics: Adult; Animals; Antibodies; Blood Platelets; Calcium; Cytosol; Female; Fibrin; Fluorescence Resonance Energy Transfer; Healthy Volunteers; Humans; Lactones; Male; Mice; Mice, Transgenic; Middle Aged; P-Selectin; Phosphatidylserines; Platelet Activation; Platelet Aggregation; Platelet Aggregation Inhibitors; Pyridines; Receptor, PAR-1; Receptors, Thrombin; Signal Transduction; Thrombin; Thrombosis; Young Adult

The TRA 2°P-TIMI 50 trial showed the addition of vorapaxar to standard care (SC) antiplatelet therapy reduced the combined risk of death, myocardial infarction (MI), and stroke, while exhibiting an increase in moderate, but not other bleeding events.. Our objective was to estimate the long-term health benefits and risks of vorapaxar as an add-on to SC treatment (lifetime aspirin and up to 12 months of clopidogrel) for patients with a prior MI and without a history of cerebrovascular disease.. In the state transition model we developed, the patients transition between states due to recurrent MI, stroke, or death, and are at risk of non-fatal bleeding. Risk equations were developed from individual patient-level data from the TRA 2°P-TIMI 50 trial to predict long-term cardiovascular (CV) outcomes. Additional sources informed inputs for case fatality, bleeding rates on SC, risk of non-CV death, and utilities.. Over a lifetime horizon, fewer CV events and more bleeding events occurred in the vorapaxar (VOR) + SC arm, relative to the SC-only arm. These results were ultimately accompanied by an increase in life expectancy and health benefits associated with add-on vorapaxar treatment, as the VOR + SC arm yielded an average of 8.27 discounted quality-adjusted life-years (QALYs) compared with an average of 7.96 discounted QALYs in the SC-only arm.. This model framework leveraged novel risk equations to make long-term projections of CV events in a population at high risk of recurrence. Model results suggest vorapaxar is most effective as add-on therapy to SC antiplatelet treatment when initiated upon hospital discharge post-MI.

Topics: Aspirin; Cardiovascular System; Clopidogrel; Hemorrhage; Humans; Lactones; Myocardial Infarction; Platelet Aggregation Inhibitors; Pyridines; Secondary Prevention; Stroke; Thrombosis; Ticlopidine; Treatment Outcome

Protease-activated receptor-1 (PAR1) couples the coagulation cascade to platelet activation during myocardial infarction and to endothelial inflammation during sepsis. This receptor demonstrates marked signaling bias. Its activation by thrombin stimulates prothrombotic and proinflammatory signaling, whereas its activation by activated protein C (APC) stimulates cytoprotective and antiinflammatory signaling. A challenge in developing PAR1-targeted therapies is to inhibit detrimental signaling while sparing beneficial pathways. We now characterize a novel class of structurally unrelated small-molecule PAR1 antagonists, termed parmodulins, and compare the activity of these compounds to previously characterized compounds that act at the PAR1 ligand-binding site. We find that parmodulins target the cytoplasmic face of PAR1 without modifying the ligand-binding site, blocking signaling through Gαq but not Gα13 in vitro and thrombus formation in vivo. In endothelium, parmodulins inhibit prothrombotic and proinflammatory signaling without blocking APC-mediated pathways or inducing endothelial injury. In contrast, orthosteric PAR1 antagonists such as vorapaxar inhibit all signaling downstream of PAR1. Furthermore, exposure of endothelial cells to nanomolar concentrations of vorapaxar induces endothelial cell barrier dysfunction and apoptosis. These studies demonstrate how functionally selective antagonism can be achieved by targeting the cytoplasmic face of a G-protein-coupled receptor to selectively block pathologic signaling while preserving cytoprotective pathways.

Topics: Animals; Apoptosis; Binding Sites; Chlorocebus aethiops; COS Cells; Cytoplasm; Endothelium, Vascular; Exocytosis; Human Umbilical Vein Endothelial Cells; Humans; Inflammation; Lactones; Ligands; Platelet Aggregation Inhibitors; Protein C; Pyridines; Receptor, PAR-1; RNA, Small Interfering; Signal Transduction; Thrombosis

Topics: Diabetes Mellitus; Female; Humans; Lactones; Male; Myocardial Infarction; Pyridines; Receptors, Thrombin; Secondary Prevention; Stroke; Thrombosis

In this issue of Blood, Aisiku et al describe a novel class of protease-activated receptor-1 (PAR1) inhibitors that block proinflammatory pathways but spare cytoprotective signaling in endothelial cells. These compounds, parmodulins, target the cytoplasmic face of PAR1, where they selectively interfere with Gαq, but not Gα12/13. This strategy of blocking specific pathways provides the ability to modulate the activity of receptors with multiple functions (such as PAR1) and may have therapeutic advantages.

Topics: Animals; Endothelium, Vascular; Humans; Lactones; Pyridines; Receptor, PAR-1; Thrombosis

Topics: Hemorrhage; Humans; Lactones; Myocardial Infarction; Patient Selection; Peripheral Arterial Disease; Platelet Aggregation Inhibitors; Pyridines; Randomized Controlled Trials as Topic; Receptor, PAR-1; Thrombosis

Topics: Drug Approval; Humans; Lactones; Platelet Aggregation Inhibitors; Pyridines; Thrombosis; United States; United States Food and Drug Administration

Topics: Drug Approval; Drug Interactions; Drug Therapy, Combination; Humans; Lactones; Myocardial Infarction; Peripheral Arterial Disease; Pyridines; Receptor, PAR-1; Thrombosis; United States; United States Food and Drug Administration

Vorapaxar is a novel platelet inhibitor that potently and selectively inhibits thrombin-mediated platelet activation without interfering with thrombin-mediated cleavage of fibrinogen via antagonism of the platelet proteinase-activated receptor PAR1. Vorapaxar is a non-peptide himbacine analogue that has been developed for the reduction of thrombotic cardiovascular events in patients with a history of myocardial infarction or peripheral arterial disease.

Topics: Drug Interactions; Food-Drug Interactions; Humans; Lactones; Platelet Aggregation Inhibitors; Pyridines; Receptor, PAR-1; Thrombosis

Vorapaxar is the first substance of a new class of antiplatelet drugs that has been tested in large clinical trials. The protease-activated receptor 1 (PAR-1) antagonist inhibits thrombin-induced platelet activation to prevent atherothrombosis. In the phase 3 trials TRACER (acute coronary syndrome) and TRA 2P-TIMI 50 (stable atherosclerosis) reducing ischemic events with vorapaxar came at the cost of bleeding. TRACER compared vorapaxar to placebo in 12,944 patients who had non-ST-segment elevation acute coronary syndromes on top of contemporary treatment including dual antiplatelet therapy (aspirin and clopidogrel). Vorapaxar reduced ischemic events non-significantly, but increased bleeding significantly, therefore not justifying triple antiplatelet therapy in this setting. Follow-up was stopped early because of bleeding. TRA 2P-TIMI 50 examined 26,449 patients who had a history of myocardial infarction, ischemic stroke, or peripheral arterial disease. Vorapaxar reduced ischemic events and increased bleeding both significantly. Recruitment of patients with prior stroke was stopped early. Net clinical outcome and subgroup analyses suggested that vorapaxar could be beneficial for patients with prior myocardial infarction - but no history of stroke.

Topics: Evidence-Based Medicine; Fibrinolytic Agents; Humans; Lactones; Patient Selection; Platelet Aggregation Inhibitors; Pyridines; Receptors, Thrombin; Thrombosis; Treatment Outcome

Topics: Female; Humans; Lactones; Male; Pyridines; Receptor, PAR-1; Secondary Prevention; Thrombosis

The rising costs and time associated with bringing new medicines to the market have created a need for a new paradigm for reducing the attrition rates of drug candidates in both preclinical and clinical development stages. Early appraisal of drug metabolism and pharmacokinetic (DMPK) parameters is now possible due to several higher throughput in vitro and in vivo screens. This knowledge of DMPK properties should not only shorten the timelines for the selection of drug candidates but also enhance the probability of their success for development. The role of DMPK researchers in the drug research paradigm should not be limited to screening a large array of compounds during the lead optimization process but should include a strive for an understanding of the absorption, distribution, metabolism, excretion, and potential drug-related toxicities of a chemical series. As an example, in this article we present a specific DMPK research screening paradigm and describe a case study using the Thrombin Receptor Antagonist program. This screening paradigm followed by the extensive lead optimization process culminated in the selection of SCH 530348, a potent, selective and orally active thrombin receptor antagonist for the treatment of thrombosis.

Topics: Animals; Drug Design; Drug Evaluation, Preclinical; Drug Industry; Drug-Related Side Effects and Adverse Reactions; Humans; Lactones; Pharmaceutical Preparations; Pyridines; Receptors, Thrombin; Thrombosis

Atherothrombotic disease is a leading public health problem. Although current antiplatelet agents, such as aspirin and adenosine diphosphate (ADP)-receptor antagonists, reduce the morbidity and mortality associated with atherothrombotic disease, the residual risk for ischemic events remains substantial. The high residual risk despite dual antiplatelet therapy can be attributed to the fact that platelets possess multiple pathways of activation that are not all inhibited by aspirin and ADP-receptor antagonists. Among these, binding of thrombin to the proteinase-activated receptor 1 (PAR(1)) is the most potent platelet activation pathway. In addition, the PAR(1) pathway does not appear to be essential for initiating hemostasis. Inhibition of the PAR(1) receptor thus offers a possible new therapeutic approach with a potentially improved benefit-to-risk profile for treatment of patients with atherothrombotic disease. Preclinical and clinical studies have confirmed that SCH 530348, a potent, orally active thrombin-receptor antagonist selective for PAR(1), does not increase bleeding liability when added to dual antiplatelet therapy. Currently, two large ongoing phase 3 clinical trials are evaluating the efficacy and safety of SCH 530348 in combination with the standard of care in patients with acute coronary syndromes as well as for secondary prevention in patients with previous history of atherothrombotic disease.

Topics: Animals; Atherosclerosis; Clinical Trials as Topic; Disease Models, Animal; Drug Therapy, Combination; Hemorrhage; Humans; Lactones; Platelet Aggregation Inhibitors; Pyridines; Receptor, PAR-1; Risk Factors; Thrombosis