Cangrelor for treatment of coronary thrombosis

Best Practices in Pharmacotherapy for Acute Coronary Syndromes

Numerous advances have been made in the therapy of acute coronary syndromes. Despite these advances, acute coronary syndromes still cause significant morbidity and mortality. Decisions as to the best therapy vary depending on other patient factors, such as age, need for chronic anticoagulation, tolerability of medications, and the degree of myocardial damage. Recent evidence suggests that a shorter duration of therapy may be beneficial in decreasing bleeding events without compromising benefits of preventing ischemic complications. For those who have an indication for chronic anticoagulation, less intensive therapy may also be beneficial, again without increasing ischemic complications. Data regarding agents that inhibit the renin–angiotensin–aldosterone system are available and these data are reviewed. Knowledge of the pharmacology, potency, and pharmacokinetics of drugs, as well as adverse drug events, may direct clinicians in choosing the optimal pharmacotherapy strategy for their patients.

Cardiac purinergic signalling in health and disease

This review is a historical account about purinergic signalling in the heart, for readers to see how ideas and understanding have changed as new experimental results were published. Initially, the focus is on the nervous control of the heart by ATP as a cotransmitter in sympathetic, parasympathetic, and sensory nerves, as well as in intracardiac neurons. Control of the heart by centers in the brain and vagal cardiovascular reflexes involving purines are also discussed. The actions of adenine nucleotides and nucleosides on cardiomyocytes, atrioventricular and sinoatrial nodes, cardiac fibroblasts, and coronary blood vessels are described. Cardiac release and degradation of ATP are also described. Finally, the involvement of purinergic signalling and its therapeutic potential in cardiac pathophysiology is reviewed, including acute and chronic heart failure, ischemia, infarction, arrhythmias, cardiomyopathy, syncope, hypertrophy, coronary artery disease, angina, diabetic cardiomyopathy, as well as heart transplantation and coronary bypass grafts.

Cangrelor for treatment of arterial thrombosis

INTRODUCTION

Percutaneous coronary intervention (PCI) is a highly effective treatment for obstructive coronary artery disease. Oral platelet P2Y12 receptor antagonists reduce ischemic events in patients treated with PCI. However, there are several limitations to their use, including variable pharmacodynamics, a slow onset and offset, and in those patients who are pretreated but subsequently require cardiac surgery, increased bleeding. Cangrelor is an intravenous agent that provides rapid and intensive inhibition of the P2Y12 receptor that quickly dissipates after discontinuation. A recent, Phase III randomized clinical trial of PCI patients demonstrated that cangrelor bolus and infusion reduced ischemic events compared with conventional clopidogrel therapy without increasing major bleeding.

AREAS COVERED

This review outlines the pharmacodynamics, pharmacokinetics, and the safety and efficacy of cangrelor for the acute treatment of patients undergoing planned PCI.

EXPERT OPINION

Cangrelor is an important addition to the current armamentarium of platelet inhibitors as it significantly reduces periprocedural myocardial infarction and stent thrombosis in a broad spectrum of patients, without increasing major bleeding or the need for transfusion. Cangrelor will have particular benefit in clopidogrel-naïve patients with high anatomical complexity and/or increased clinical risk (where the absolute risk for thrombotic and ischemic complications of PCI is greatest).

Aspirin and platelet adenosine diphosphate receptor antagonists in acute coronary syndromes and percutaneous coronary intervention: role in therapy and strategies to overcome resistance

Platelet activation and aggregation are key components in the cascade of events causing thrombosis following plaque rupture. Antiplatelet therapy is essential in the treatment of patients with acute coronary syndromes (ACS) and for those requiring percutaneous coronary intervention (PCI). Aspirin (acetylsalicylic acid) is a well established antiplatelet therapy and is mandated for secondary prevention of cardiovascular events following ACS. In patients with ACS, the addition of clopidogrel to aspirin is more effective than aspirin alone. For patients undergoing PCI, dual antiplatelet therapy with aspirin and clopidogrel is warranted. Aspirin should be continued indefinitely after PCI. Pretreatment of patients with clopidogrel prior to PCI lowers the incidence of cardiovascular events, yet the optimum timing of drug administration and dose are still being investigated, as is the duration of therapy following PCI. Late-stent thrombosis with drug-eluting stents has pushed the recommendation for duration of clopidogrel therapy up to 1 year and perhaps beyond, in patients without risks for bleeding. The concepts of aspirin and clopidogrel resistance are important clinical questions. No uniform definition exists for aspirin or clopidogrel resistance. Measurements of resistance are often highly variable and do not necessarily correlate with clinical resistance. Noncompliance remains the most prominent mode of resistance. Screening of selected patient populations for resistance or pharmacologic intervention of those patients termed 'resistant' warrants further study.

New antithrombotic drugs: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

This article focuses on new antithrombotic drugs that are in or are entering phase 3 clinical testing. Development of these new agents was prompted by the limitations of existing antiplatelet, anticoagulant, or fibrinolytic drugs. Addressing these unmet needs, this article (1) outlines the rationale for development of new antithrombotic agents; (2) describes the new antiplatelet, anticoagulant, and fibrinolytic drugs; and (3) provides clinical perspectives on the opportunities and challenges faced by these novel agents.

Short-acting P2Y12 blockade to reduce platelet dysfunction and coagulopathy during experimental extracorporeal circulation and hypothermia

BACKGROUND

Extracorporeal circulation (ECC) and hypothermia are routinely used in cardiac surgery to maintain stable circulatory parameters and to increase the ischaemic tolerance of the patient. However, ECC and hypothermia cause platelet activation and dysfunction possibly followed by a devastating coagulopathy. Stimulation of the adenosinediphosphate (ADP) receptor P(2)Y(12) plays a pivotal role in platelet activation. This experimental study tested P(2)Y(12) receptor blockade as an approach to protect platelets during ECC.

METHODS

Human blood was treated with the short-acting P(2)Y(12) blocker cangrelor (1 µM, t(1/2)<5 min) or the P(2)Y(12) inhibitor 2-MeSAMP (100 µM) and circulated in an ex vivo ECC model at normothermia (37°C) and hypothermia (28°C). Before and after circulation, markers of platelet activation and of coagulation (thrombin-antithrombin complex generation) were analysed. During hypothermic ECC in pigs, the effect of reversible P(2)Y(12) blockade on platelet function was evaluated by cangrelor infusion (0.075 µg kg(-1) min(-1)).

RESULTS

During ex vivo hypothermic ECC, P(2)Y(12) blockade inhibited platelet granule release (P<0.01), platelet-granulocyte binding (P<0.05), and platelet loss (P<0.001), whereas no effects on platelet-ECC binding, platelet CD42bα expression, glycoprotein IIb/IIIa activation, or thrombin-antithrombin complex generation were observed. During hypothermic ECC in pigs, cangrelor inhibited platelet-fibrinogen binding (P<0.05) and ADP-induced platelet aggregation (P<0.001). Platelet function was rapidly restored after termination of cangrelor infusion.

CONCLUSIONS

P(2)Y(12) blockade by cangrelor prevents platelet activation during ECC and hypothermia. Owing to its short half-life, platelet inhibition can be well controlled, thus potentially reducing bleeding complications. This novel pharmacological strategy has the potential to reduce complications associated with ECC and hypothermia.

Evidence of platelet activation at medically used hypothermia and mechanistic data indicating ADP as a key mediator and therapeutic target

OBJECTIVE

Hypothermia is used in various clinical settings to inhibit ischemia-related organ damage. However, prothrombotic effects have been described as potential side effects. This study aimed to elucidate the mechanism of hypothermia-induced platelet activation and subsequent prothrombotic events and to develop preventative pharmacological strategies applicable during clinically used hypothermia.

METHODS AND RESULTS

Platelet function was investigated ex vivo and in vivo at clinically used hypothermia (28°C/18°C). Hypothermic mice demonstrated increased expression of platelet activation marker P-selectin, platelet-leukocyte aggregate formation, and thrombocytopenia. Intravital microscopy of FeCl(3)-injured murine mesenteric arteries revealed increased platelet thrombus formation with hypothermia. Ex vivo flow chamber experiments indicated increased platelet-fibrinogen adhesion under hypothermia. We show that hypothermia results in reduced ADP hydrolysis via reduction of CD39 (E-NTPDase1) activity, resulting in increased levels of ADP and subsequent augmented primary and secondary platelet activation. In vivo administration of ADP receptor P(2)Y(12) antagonists and recombinant soluble CD39 prevented hypothermia-induced thrombus formation and thrombocytopenia, respectively.

CONCLUSIONS

The platelet agonist ADP plays a key role in hypothermia-induced platelet activation. Inhibition of receptor binding or hydrolysis of ADP has the potential to protect platelets against hypothermia-induced activation. Our findings provide a rational basis for further evaluation of novel antithrombotic strategies in clinically applied hypothermia.

Antiplatelet therapy in acute coronary syndromes

Antiplatelet therapy is integral to the acute and long-term management of acute coronary syndromes (ACSs) and for minimizing the thrombotic complications of percutaneous coronary intervention (PCI). This article reviews the most commonly used antiplatelet agents in ACS therapy--aspirin, adenosine diphosphate (ADP)-receptor blockers, and glycoprotein IIb/IIIa inhibitors. More recent data are also reviewed on novel ADP-receptor blockers and thrombin inhibitors before addressing issues of adherence to antiplatelet regimens.

Antiplatelet therapy in percutaneous coronary intervention: a critical review of the 2007 AHA/ACC/SCAI guidelines and beyond

Antiplatelet therapy is a mainstay in the treatment of patients who have undergone percutaneous coronary intervention (PCI). Although the 2007 PCI treatment guidelines were published by the American College of Cardiology, the American Heart Association, and the Society for Cardiovascular Angiography and Interventions, new clinical evidence has emerged, expanding our understanding of antiplatelet use and potentially affecting the treatment guidelines. For example, clinical trial results prompted a Science Advisory to recommend that dual therapy with aspirin and clopidogrel be used for longer periods-up to 1 year in patients who receive bare metal stents and at least 1 year in patients receiving drug-eluting stents. New trial results have also emerged regarding the use of glycoprotein IIb/IIIa antagonists such as abciximab, eptifibatide, and tirofiban. This article reviews the current recommendations for antiplatelet therapy in PCI patients, recent trial results, newly developed agents, ongoing clinical trials, and the future direction of antiplatelet therapy in patients who undergo PCI.

New antiplatelet agents: why they are needed

Despite recent advances in the treatment of acute coronary syndromes (ACS), including dual antiplatelet therapy with aspirin and a thienopyridine during the acute phase and for secondary prevention, this condition remains a leading cause of morbidity and mortality. The limitations of the currently available antiplatelet agents have triggered the development of newer drugs. In this review we summarize the mechanisms of actions and results of current clinical trials of novel antiplatelet agents. These include prasugrel, a thienopyridine prodrug which has a mechanism similar to that of clopidogrel but superior pharmacokinetic features; ticagrelor, a non-thienopyridine that binds reversibly to the platelet P2Y(12) receptor; cangrelor, an intravenously administered analog of ticagrelor; the thrombin receptor antagonist SCH 53048; and terutroban (S18886), a thromboxane A(2) receptor inhibitor.

Antithrombotics in acute coronary syndromes

Antithrombotic agents are an integral component of the medical regimens and interventional strategies currently recommended to reduce thrombotic complications in patients with acute coronary syndromes (ACS). Despite great advances with these therapies, associated high risks for thrombosis and hemorrhage remain as the result of complex interactions involving patient comorbidities, drug combinations, multifaceted dosing adjustments, and the intricacies of the care environment. As such, the optimal combinations of antithrombotic therapies, their timing, and appropriate targeted subgroups remain the focus of intense research. During the last several years a number of new antithrombotic treatments have been introduced, and new data regarding established therapies have come to light. Although treatment guidelines include the most current available data, subsequent findings can be challenging to integrate. This challenge is compounded by the complexity associated with different efficacy and safety measures and the variability in study populations, presenting syndromes, physician, and patient preferences. In this work we review recent data regarding clinically available antiplatelet and anticoagulation agents used in the treatment of patients with ACS. We address issues including relative efficacy, safety, and timing of therapies with respect to conservative and invasive treatment strategies. In specific cases we will highlight remaining questions and controversies and ongoing trials, which will hopefully shed light in these areas. In addition to reviewing existing agents, we take a look forward at the most promising new antithrombotics currently in late-stage clinical development and their potential role in the context of ACS management.

New antithrombotic drugs

Thrombosis, both venous and arterial, is a major cause of morbidity and mortality worldwide. Consequently, there is an ongoing search for new antithrombotic drugs, particularly novel antiplatelet agents and anticoagulants. A better understanding of the biochemical pathways involved in platelet activation and coagulation and of the links between these systems and the impact of thrombosis on inflammation has led to the identification of new targets for antithrombotic drugs. This paper focuses on these new targets and new antiplatelet drugs and anticoagulants and describes the major advances in the continuing search for more potent antithrombotic drugs that have limited effects on hemostasis.

Cangrelor increases the magnitude of platelet inhibition and reduces interindividual variability in clopidogrel-pretreated subjects

BACKGROUND

Inadequate platelet inhibition despite aspirin and clopidogrel therapy during and after a percutaneous coronary intervention is associated with an impaired clinical outcome. Cangrelor, a direct and reversible P2Y(12) inhibitor that is currently in development, has the potential to achieve higher levels of inhibition of ADP-induced platelet aggregation than clopidogrel. The aim of the present study was to compare the magnitude of platelet inhibition in clopidogrel-pretreated patients before and after the in vitro addition of a subtherapeutic dose of cangrelor.

METHODS

Blood samples were drawn from patients pretreated with clopidogrel and aspirin who were undergoing elective percutaneous coronary intervention (n=39). Platelet function analysis with 'classical' light transmittance aggregometry (both peak and late aggregation [at 6 min]) was performed before and after the in vitro addition of cangrelor (0.25 mumol/l) to platelet-rich plasma (PRP). After an incubation period of five minutes, platelet aggregation was induced by 5 and 20 mumol/l ADP.

RESULTS

The in vitro addition of 0.25mumol/l cangrelor to the PRP from clopidogrel-treated subjects resulted in an additional reduction in ADP-induced platelet aggregation. For ADP concentrations of 5 and 20 mumol/l, peak aggregation showed a decrease of 75 and 85%, respectively (p<0.001 for both), while late aggregation was almost completely diminished (p=0.003 and p<0.001, respectively). Furthermore, the interindividual variation in inhibition of ADP-induced platelet aggregation by clopidogrel was greatly reduced after the addition of cangrelor.

CONCLUSION

We demonstrate that the in vitro addition of even a subtherapeutic dose of cangrelor to the PRP of clopidogrel-pretreated patients results in an additional reduction of ADP-induced platelet aggregation. Moreover, cangrelor was able to diminish the interindividual variation observed in clopidogrel-inhibited platelet aggregation. (Neth Heart J 2009;17:195-8.).

New antithrombotic drugs: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition)

This chapter focuses on new antithrombotic drugs that are in phase II or III clinical testing. Development of these new agents was prompted by limitations of existing antiplatelet, anticoagulant, or fibrinolytic drugs. Addressing these unmet needs, this chapter (1) outlines the rationale for development of new antithrombotic agents, (2) describes the new antiplatelet, anticoagulant, and fibrinolytic drugs, and (3) provides clinical perspectives on the opportunities and challenges faced by these novel agents.

Novel P2Y12 adenosine diphosphate receptor antagonists for inhibition of platelet aggregation (I): in vitro effects on platelets

ADP plays a key role in platelet aggregation which has led to the development of antiplatelet drugs that target the P2Y12 receptor. The aim of this study was to characterize the effects of two novel P2Y12 receptor antagonists, BX 667 and its active metabolite BX 048, on platelets. BX 667 and BX 048 block the binding of 2MeSADP to platelets and antagonize ADP-induced platelet aggregation in human, dog and rat washed platelets. Both compounds were shown to be reversible inhibitors of platelet aggregation. BX 048 prevents the decrease in cAMP induced by treatment of platelets with ADP. The specificity of BX 667 and BX 048 was demonstrated against cell lines expressing P2Y1 and P2Y6 as well as against a panel of receptors and enzymes. Taken all together these data show that both BX 048 and BX 667 are potent P2Y12 antagonists with high specificity which, in the accompanying paper are demonstrated to behave predictably in vivo.

Clinical aspects of platelet inhibitors and thrombus formation

The platelet, once thought to be solely involved in clot formation, is now known to be a key mediator in various others processes such as inflammation, thrombosis, and atherosclerosis. Supported by the wealth of evidence from clinical trials demonstrating their benefits in patient outcomes, antiplatelet agents have become paramount in the prevention and management of various diseases involving the cardiovascular, cerebrovascular, and peripheral arterial systems. Despite being among the most widely used and studied classes of medical therapies, new discoveries regarding important clinical aspects and properties of these agents continue to be made. As our understanding of platelet biology expands, more effective and safer novel therapies continue to be developed. The use of more refined agents in conjunction with a better understanding of their effects will further the ability to provide more optimized care on an individual basis.