New antithrombotic agents—insights from clinical trials

An eco-friendly ultra-performance liquid chromatography-mass spectrometry method for quantification of rivaroxaban and ticagrelor in rat plasma: grapefruit interactions

Aim: An eco-friendly ultra-performance liquid chromatography-tandem mass spectrometry method was developed to study the pharmacokinetics of rivaroxaban and ticagrelor in rat plasma, utilizing moxifloxacin as an internal standard. The food-drug interaction between grapefruit juice and these drugs was also investigated. Methods: Liquid-liquid extraction was used. A nonporous stationary phase Agilent® Poroshell 120EC C18 column was used with methanol: 0.1% aqueous formic acid (95:5 v/v) as a mobile phase. The detection was performed in multiple reaction monitoring mode using positive electrospray ionization. The method's validation was conducted in accordance with US FDA and European Medicines Agency guidelines. Results & conclusion: Grapefruit juice should be ingested with caution in patients treated with antithrombotic medications as it may increase their plasma concentration, inducing bleeding, and requires close clinical monitoring.

The antithrombotic activity of natural and synthetic coumarins

Thrombosis, which seriously endangers human health and life, is the leading cause of morbidity and mortality globally. Antithrombotic drugs can interfere with the occurrence and development of thrombotic diseases and play an important role in the treatment of thrombotic diseases. However, unsatisfactory efficacy and serious adverse effects of existing antithrombotic drugs increase the research for new, efficient and safer drugs. Natural and synthetic coumarins have been shown to possess antithrombotic activity, namely, anticoagulation and antiplatelet aggregation. Especially, coumarin-based warfarin, phenprocoumon and cloricromen have long been used in clinical treatment of thrombosis. Coumarin with low toxicity is the privileged structure for developing novel antithrombotic drugs with multiple mechanisms of action. The present review aims to compile current research on the development of coumarins against thrombosis, emphasizing the relationship between their chemical structures and therapeutic effectiveness. It is intended to provide promising ideas for the discovery of novel coumarin derivatives with high antithrombotic activity.

Managing the coagulopathy associated with cardiopulmonary bypass

Cardiopulmonary bypass (CPB) has allowed for significant surgical advancements, but accompanying risks can be significant and must be expertly managed. One of the foremost risks is coagulopathic bleeding. Increasing levels of bleeding in cardiac surgical patients at the time of separation from CPB are associated with poor outcomes and mortality. CPB-associated coagulopathy is typically multifactorial and rarely due to inadequate reversal of systemic heparin alone. The components of the bypass circuit induce systemic inflammation and multiple disturbances of the coagulation and fibrinolytic systems. Anticipating coagulopathy is the first step in managing it, and specific patient and procedural risk factors have been identified as predictors of excessive bleeding. Medication management pre-procedure is critical, as patients undergoing cardiac surgery are commonly on anticoagulants or antiplatelet agents. Important adjuncts to avoid transfusion include antifibrinolytics, and perfusion practices such as red cell salvage, sequestration, and retrograde autologous priming of the bypass circuit have varying degrees of evidence supporting their use. Understanding the patient's coagulation status helps target product replacement and avoid larger volume transfusion. There is increasing recognition of the role of point-of-care viscoelastic and functional platelet testing. Common pitfalls in the management of post-CPB coagulopathy include overdosing protamine for heparin reversal, imperfect laboratory measures of thrombin generation that result in normal or near-normal laboratory results in the presence of continued bleeding, and delayed recognition of surgical bleeding. While challenging, the effective management of CPB-associated coagulopathy can significantly improve patient outcomes.

Cytochrome P450 enzyme-mediated auto-enhanced photodynamic cancer therapy of co-nanoassembly between clopidogrel and photosensitizer

Reactive oxygen species (ROS)-based photodynamic therapy (PDT) has a widespread application in cancer therapy. Nevertheless, the efficiency of PDT is far from satisfactory. One major impediment is the overexpression of glutathione (GSH) in tumor cells, which could deplete the level of PDT-generated ROS. Herein, we develop a novel type of cytochrome P450 enzyme-mediated auto-enhanced photodynamic co-nanoassembly between clopidogrel (CPG) and photosensitizer pyropheophorbide a (PPa).

Methods: In this work, we prepare the co-assembled nanoparticles of CPG and PPa (CPG/PPa NPs) by using one-step precipitation method. The assembly mechanism, drug release behavior, GSH consumption, ROS generation, cellular uptake, cytotoxicity of CPG/PPa NPs are investigated in vitro. The mice bearing 4T1 tumor are employed to evaluate in vivo biodistribution and anti-tumor effect of CPG/PPa NPs.

Results: Such CPG/PPa NPs could disrupt the intracellular redox homeostasis, resulting from the elimination of GSH by CPG active metabolite mediated by cytochrome P450 enzyme (CYP2C19). The in vivo assays reveal that CPG/PPa NPs not only increase the drug accumulation in tumor sites but also significantly suppress tumor growth in BALB/c mice bearing 4T1 tumor. With CPG-mediated GSH consumption and PPa-triggered ROS generation, CPG/PPa NPs show the enhanced PDT treatment effect by breaking intracellular redox balance.

Conclusion: Our findings provide a valuable knowledge for the rational design of the PDT-based combinational cancer therapy.

A Modular Synthetic Approach to Isosteric Sulfonic Acid Analogues of the Anticoagulant Pentasaccharide Idraparinux

Heparin-based anticoagulants are drugs of choice in the therapy and prophylaxis of thromboembolic diseases. Idraparinux is a synthetic anticoagulant pentasaccharide based on the heparin antithrombin-binding domain. In the frame of our ongoing research aimed at the synthesis of sulfonic acid-containing heparinoid anticoagulants, we elaborated a modular pathway to obtain a series of idraparinux-analogue pentasaccharides bearing one or two primary sulfonic acid moieties. Five protected pentasaccharides with different C-sulfonation patterns were prepared by two subsequent glycosylation reactions, respectively, using two monosaccharide and four disaccharide building blocks. Transformation of the protected derivatives into the fully O-sulfated, O-methylated sulfonic acid end-products was also studied.

Unanswered questions in thrombolytic therapy for acute ischemic stroke

This article reviews some of the current literature in support or against extension of the intravenous tissue plasminogen activator window, use of intra-arterial therapy or devices, as well alternative pharmacologic therapies that may extend the window for treatment of patients with acute ischemic stroke, with consideration of the relative risk of thrombolytic complications, factors for worse outcomes, and unclear stroke onset, as seen in patients with wake-up stroke. The issue of newer concomitant antithrombotic therapies as they affect the decision for acute ischemic stroke thrombolytic therapy is also explored.

Implications of new anticoagulants in primary practice

BACKGROUND

Effective prophylaxis and treatment of thromboembolic disorders remain suboptimal in many healthcare systems, partly owing to limitations of traditional anticoagulants. New oral anticoagulants have been developed and among these, rivaroxaban, apixaban and dabigatran etexilate are in the most advanced stage of clinical development.

METHOD

A literature search using the PubMed and ClinicalTrials.gov databases was performed to identify English-language publications. The search was performed up to 31 December 2011 with the terms rivaroxaban OR Xarelto, apixaban OR Eliquis and dabigatran OR Pradaxa. Ongoing, completed and published phase III randomised controlled trials were selected as the primary source of information for the clinical development programme of each drug.

RESULTS

The new oral agents demonstrate several advantages over traditional anticoagulants, including administration at fixed doses and no requirement for routine coagulation monitoring On the basis of phase III clinical trials, rivaroxaban, apixaban and dabigatran etexilate have been approved in many countries for the prevention of venous thromboembolism after hip and knee replacement surgery. Dabigatran etexilate and rivaroxaban have also been approved for the prevention of stroke and systemic embolism in patients with non-valvular atrial fibrillation in Europe and the US. In addition, rivaroxaban has been approved in Europe for the treatment of acute deep vein thrombosis and prevention of recurrent venous thromboembolism. Approval of these agents and postapproval monitoring of their safety and efficacy will have implications for primary care.

CONCLUSION

Rivaroxaban, apixaban and dabigatran etexilate offer the possibility of simplified prevention and treatment strategies for thromboembolic disorders in the outpatient setting.

Identification of the Significant Involvement and Mechanistic Role of CYP3A4/5 in Clopidogrel Bioactivation

The clinical response to the antiplatelet prodrug clopidogrel is associated with high intersubject variability and a certain level of therapeutic resistance. Previous studies have suggested that genetic polymorphism of CYP2C19 might be one determinant of clopidogrel efficacy and led to the CYP2C19 genotype-tailored antithrombotic therapy. However, evidence against the role of CYP2C19 from multiple studies implied the involvement of other factors. Here, we report that prodrug activation of the thiophene motif in clopidogrel is attenuated by heavy metabolic attrition of the piperidine motif. CYP3A4/5 was identified to be the enzyme metabolizing the piperidine motif. Inhibiting CYP3A4/5-mediated attrition was shown to potentiate active metabolite formation, which was found to be catalyzed by multiple CYP enzymes. Identifying the significant involvement of CYP3A4/5 and characterizing its mechanistic role in clopidogrel bioactivation might assist future pharmacogenomic studies in exploring the full mechanism underlying clopidogrel efficacy.

Analysis of the projected utility of dabigatran, rivaroxaban, and apixaban and their future impact on existing Hematology and Cardiology Anticoagulation Clinics at The Johns Hopkins Hospital

The purpose of this study is to determine the percentage of patients in the Johns Hopkins Anticoagulation Clinics that are potential candidates for the new oral anticoagulants, dabigatran, rivaroxaban, and apixaban. A retrospective chart review was conducted of patients managed in the Johns Hopkins Cardiology and Hematology Anticoagulation Clinics between November 1, 2009 and October 31, 2010. Data elements collected include demographics, primary indication for anticoagulation, renal function, hepatic function, and concomitant medications. These factors were considered against product labeling guidelines and inclusion/exclusion criteria from clinical studies to derive candidacy status for each oral anticoagulant for each patient. Patients who met at least one caution or contraindication criteria were deemed "non-candidates"; potential dosage reductions of the new oral anticoagulants were not considered. Four hundred ninety-one patients participated in the study. Among participants, 63% would be dabigatran candidates, 62% rivaroxaban candidates, and 70% would be candidates for apixaban. Dabigatran use would be cautioned against in 34%, rivaroxaban in 18 %, and apixaban in 30%. Four percent had contraindications to dabigatran, whereas 21% had contraindications to rivaroxaban. More than 60% of patients in the Johns Hopkins Anticoagulation Clinics appear to be potential candidates for each of the new oral anticoagulants, assuming they are eventually approved for the same indications as warfarin. Many patients fell into the "cautioned" category, which demonstrates the complexity associated with selecting candidates for these new agents.

In silico discovery of a compound with nanomolar affinity to antithrombin causing partial activation and increased heparin affinity

The medical and socioeconomic relevance of thromboembolic disorders promotes an ongoing effort to develop new anticoagulants. Heparin is widely used as activator of antithrombin but incurs side effects. We screened a large database in silico to find alternative molecules and predicted d-myo-inositol 3,4,5,6-tetrakisphosphate (TMI) to strongly interact with antithrombin. Isothermal titration calorimetry confirmed a TMI affinity of 45 nM, higher than the heparin affinity (273 nM). Functional studies, fluorescence analysis, and citrullination experiments revealed that TMI induced a partial activation of antithrombin that facilitated the interaction with heparin and low affinity heparins. TMI improved antithrombin inhibitory function of plasma from homozygous patients with antithrombin deficiency with a heparin binding defect and also in a model with endothelial cells. Our in silico screen identified a new, non-polysaccharide scaffold able to interact with the heparin binding domain of antithrombin. The functional consequences of this interaction were experimentally characterized and suggest potential anticoagulant therapeutic applications.

[Periinterventional antiplatelet therapy: from bench to bedside]

The recruitment and activation of blood platelets initiate ischemic events in patients with coronary artery diseases (myocardial infarction). Moreover, platelet activation and aggregation are key events triggering early and late thrombotic complications (stent thromboses) in patients successfully treated with coronary stent implantation. Hence, the inhibition of the thromboxane A2 synthesis by aspirin and the ADP-receptor pathway by clopidogrel have drastically reduced the risk of ischemic complications following coronary stenting. However, clopidogrel has several inherent limitations, including the high incidence of non- or low-responders and the increased risk of bleeding due to the prolonged persistence of its anti-platelet effect. The latter is of particular concern in patients who require non-deferrable surgery. In recent years, novel anti-platelet substances have been clinically evaluated and are now approved for use in patients. These substances offer several potential advantages over the previous strategies and could pave the way for more individualized anti-platelet regimens. In this review, we give an overview on the available clinical data evaluating the benefits of these novel anti-platelet substances.

Novel Oral Anticoagulation in Management of Venous Thromboembolism, Atrial Fibrillation, and Acute Coronary Syndrome

Venous thromboembolism (VTE) is a major public health concern since the incidence of VTE rises substantially with age. Furthermore, the diagnosis can be elusive since patients can present differently, causing delay in diagnosis and initiation of treatment and resulting in major morbidity and mortality. In addition to accuracy and precision in diagnosis, antithrombotic therapies are the cornerstones of VTE management. In traditional paradigm, vitamin K antagonists (warfarin), indirect factor Xa inhibitors, and heparin are the foundation in management of VTE. Warfarin has been the only available oral anticoagulant therapy for several decades. Although warfarin is effective in both treatment and prophylaxis against VTE, there are several limitations. Therefore, the novel anticoagulation therapies, including rivaroxaban, apixaban, and dabigatran etexilate, have apparent advantages over warfarin in terms of clinical efficacy and adverse effects. The objective of this review is to describe the background and clinical implications of these novel anticoagulants.

Healthcare burden associated with the post-thrombotic syndrome and potential impact of the new oral anticoagulants

Deep-vein thrombosis (DVT) can have a significant impact on a patient's life. In particular, the development of post-thrombotic syndrome as a long-term complication of DVT can have devastating consequences for the individual and impose a substantial economic burden on healthcare systems. Anticoagulants are the mainstay of DVT treatment; however, the current standard of care, a parenteral anticoagulant followed by a vitamin K antagonist, is associated with complex patient management, often resulting in suboptimal therapy. New, oral anticoagulants have been developed, and a direct thrombin inhibitor--dabigatran etexilate--and two direct Factor Xa inhibitors--rivaroxaban and apixaban--have completed and/or have ongoing phase III trials in the treatment of venous thromboembolism. These agents do not have the drawbacks of the vitamin K antagonists and hold promise for more effective treatment of DVT, possibly resulting in a reduction in the incidence of post-thrombotic syndrome.

Venous thromboembolism in patients with essential thrombocythemia and polycythemia vera

Polycythemia vera (PV) and essential thrombocythemia (ET) are myeloproliferative neoplasms (MPNs), which generally follow a benign and indolent clinical course. However, venous thromboses are common and constitute the main cause of morbidity and mortality. The discovery of the JAK2V617F mutation and other biomarkers has advanced our understanding of these diseases. There is a strong association between the presence of the JAK2V617F mutation and the development of thrombosis in ET. If venous thrombosis presents with unusual manifestations, the diagnosis of a MPN, such as PV or ET, should be part of the differentials. Treatment of venous thrombosis in MPN follows the same principle as in other patients with venous thrombosis, but careful attention to primary and secondary prophylaxis in addition to heparin-induced thrombocytopenia should be given. Cytoreductive therapy is indicated in high-risk subgroups of PV and ET patients, and alternative therapeutic agents have different effects on risk of venous thrombosis. New therapeutic approaches are emerging, and JAK2 inhibitors, histone deacetylase inhibitors and next-generation anticoagulants are in various stages of clinical development for the treatment of MPN, but their exact role in thrombosis prevention and treatment remains unclear.

Antiplatelet, Antithrombotic, and Fibrinolytic Activities of Campomanesia xanthocarpa

In a previous work based on popular belief, Campomanesia xanthocarpa Berg., popularly known as “guavirova”, showed to have a potential effect in the control of a number of conditions associated with cardiovascular diseases. The aim of the present work was to investigate the effects of C. xanthocarpa extract (CXE) on antiplatelet, antithrombotic and fibrinolytic activities in mice and in human blood. Mice were treated orally for 5 days with CXE or acetylsalicylic acid and at the end of the treatment period animals were challenged for bleeding, acute thromboembolism and ulcerogenic activity. In addition, we have assessed the prothrombin time and activated partial thromboplastin time (aPTT) after oral administration. In in vitro assays, antiplatelet effects of CXE was evaluated on platelet aggregation, and fibrinolytic activity of the extract was observed by mice or human artificial blood clot degradation. Platelet citotoxicity of the extract was also determined by the LDH assay. Results demonstrated that CXE has a significant protective effect on thrombosis. It also inhibits platelet aggregation without demonstrating cytotoxicity on platelets. CXE slightly prolonged aPTT and showed no ulcerogenic activity after oral administration. In addition, CXE showed a fibrinolytic activity. Thus, C. xanthocarpa showed antiplatelet, antithrombotic and fibrinolytic activities in mice.

Historical perspective and future directions in platelet research

Platelets are a remarkable mammalian adaptation that are required for human survival by virtue of their ability to prevent and arrest bleeding. Ironically, however, in the past century, the platelets' hemostatic activity became maladaptive for the increasingly large percentage of individuals who develop age-dependent progressive atherosclerosis. As a result, platelets also make a major contribution to ischemic thrombotic vascular disease, the leading cause of death worldwide. In this brief review, I provide historical descriptions of a highly selected group of topics to provide a framework for understanding our current knowledge and the trends that are likely to continue into the future of platelet research. For convenience, I separate the eras of platelet research into the "Descriptive Period" extending from ~1880-1960 and the "Mechanistic Period" encompassing the past ~50 years since 1960. We currently are reaching yet another inflection point, as there is a major shift from a focus on traditional biochemistry and cell and molecular biology to an era of single molecule biophysics, single cell biology, single cell molecular biology, structural biology, computational simulations, and the high-throughput, data-dense techniques collectively named with the "omics postfix". Given the progress made in understanding, diagnosing, and treating many rare and common platelet disorders during the past 50 years, I think it appropriate to consider it a Golden Age of Platelet Research and to recognize all of the investigators who have made important contributions to this remarkable achievement..

Pharmacogenomics of clopidogrel: evidence and perspectives

Clopidogrel has become the mainstay oral antiplatelet regimen to prevent recurrent ischemic events after acute coronary syndromes or stent placement. However, there is marked interindividual variability in the antiplatelet effects of clopidogrel, and a reduced response to this drug may be a risk factor for ischemic complications. Pharmacogenomic analyses, including candidate-gene and genome-wide association studies, have confirmed that genetic polymorphisms in the hepatic cytochrome P450 (CYP) 2C19 dominantly affect the antiplatelet effects of clopidogrel. CYP2C19 reduced-function alleles have been associated with a significant decrease in clopidogrel responsiveness and a higher risk of adverse cardiac events including stent thrombosis, myocardial infarction, and death in several prospective studies, although these effects were not reproduced in a recent large randomized study that included a randomized control group. The US Food and Drug Administration addressed this issue by adding a boxed warning to the clopidogrel label and suggesting that adjusting the clopidogrel dose or using alternative antiplatelet agents should be potentially implemented for high-risk individuals who are identified based on the CYP2C19 genotype. Although it is promising that CYP2C19 genotyping could be used to guide personalized antiplatelet clopidogrel therapy, currently there is insufficient evidence to recommend routine genetic testing. Prospective randomized clinical trials are necessary to validate this pharmacogenomic approach to clopidogrel therapy. In the most recent trial, paraoxonase-1 (PON1) was identified as a crucial new enzyme for clopidogrel bioactivation, with its common Q192R polymorphism determining the rate of active metabolite and the clinical activity of clopidogrel. Further studies are needed to investigate the comprehensive influence of a number of different polymorphisms of CYP2C19 and PON1 variant alleles or other genetic variants on clopidogrel in various ethnic populations.

Early clopidogrel use in non-ST elevation acute coronary syndrome and subsequent coronary artery bypass grafting

Clopidogrel use is associated with a significant decrease in major adverse cardiac events when used in patients with non-ST elevation acute coronary syndromes (NSTE-ACS), and guidelines give a class I level of evidence A recommendation for the use of clopidogrel in these patients. The optimal timing of clopidogrel use has not been conclusively determined, but nearly all data available support early use in patients with NSTE-ACS. Despite this, clopidogrel usage is far less than expected based on current guidelines because of concern for bleeding at the time of possible subsequent coronary artery bypass grafting (CABG). Clopidogrel use has been associated with increased perioperative bleeding at the time of CABG, but data are mixed. Numerous studies have conclusively shown that this bleeding risk is confined to those patients receiving clopidogrel within 5 days of CABG. The absolute number of patients exposed to this possible bleeding risk is very small relative to the >1 million patients who present annually with NSTE-ACS and is estimated to be <0.8% of these patients. Recent data have shown that (1) holding clopidogrel for 5 days before CABG is safe in patients with NSTE-ACS and (2) clopidogrel use in patients with NSTE-ACS decreases ischemic events in patients referred for CABG compared to patients who are not given clopidogrel. These data strongly challenge the notion that clopidogrel should be withheld until it is determined if the patient will be referred for CABG.

Personalized medicine: understanding probabilities and managing expectations

Personalized medicine promises to represent a transformation in clinical care that will be ushered in by the unprecedented growth and development in the field of human genetics. Further examination of the scientific foundations of this new hope reveals a great number of challenges that lie ahead. While basic science research feverishly races to produce solutions, we continue to wait for the translation of deliverables. Products that have and will come to market may leave our clinical communities and systems exposed and unprepared. At each step, from basic science research to infrastructure development, a great deal of creativity and investment are required before the arsenal of more personalized tools can be assimilated into our current models of health care. This commentary seeks to share perspectives on the current status of personalized medicine from the vantage point of several potential investors, and integrate them into a common set of goals and understanding. We conclude that the stylized model of personalized medicine is more akin to a marketing tool than a literal prediction of the future.