Hematopoietic modulators as potential agents for the treatment of leukemia.

Leukemias are the most common malignancy of childhood and have the highest mortality among aging people. Leukemias are a group of blood disorders characterized by an accumulation of leukemic cells in the peripheral blood of patients as a result of disturbances in proliferation and differentiation. Refractory leukemia remains the most common therapeutic challenge. In recent years, the presence of a cancer stem cell population in leukemias has been proposed as a cause for the refractory phenomenon. Insights into the cellular and molecular features of leukemia led to a new point of view in the choice of novel therapeutic agents. New agents for the treatment of this disease should selectively target leukemia stem cells or exhibit higher cytotoxic effects in cancer cells than in normal cells. A special interest is focused on anticancer agents from biological and natural sources that can be used in the treatment of leukemia. This review discusses the characteristics of some of these potential new agents.

What is the risk of intensifying platelet inhibition beyond clopidogrel? A systematic review and a critical appraisal of the role of prasugrel.

Thienopyridines are a class of drug targeting the platelet adenosine diphosphate 2 receptor. They have been shown to significantly reduce platelet activity exerting an important role in those clinical settings in which such an effect is beneficial. Ticlopidine was first to be introduced several years ago but it was quickly replaced by clopidogrel as it had a better risk/benefit profile. Recently, prasugrel has been developed and tested in several ex vivo studies and clinical trials showing able to provide a more powerful antiplatelet effect at the expense of a higher risk of bleeding complications. Great debate rose around its recent approval in the US as well as in Europe. This review aims at exploring the development and available clinical data of this third-generation thienopyridine while discussing its practical implementation in routine practice.

Functional expression of purinergic P2X7 receptors in pregnant rat myometrium.

ATP has been reported to enhance the membrane conductance of myometrial cells and uterine contractility. Purinergic P2 receptor expression has been reported in the myometrium, using molecular biology, but the functional identity of the receptor subtype has not been determined. In this study, ATP-induced currents were recorded and characterized in single myometrial cells from pregnant rats using whole cell patch clamping. Extracellular ATP was applied in the range of 10 muM-1 mM and induced currents with an EC(50) of 74 muM, with no desensitization, time dependency, or voltage dependency. The currents induced carried multiple monovalent cations, with conductances ranked as K(+) > Cs(+) > Li(+) > Na(+). They were activated by P2X receptor agonists, with their effectiveness ranked as 2',3'-O-(4-benzoylbenzoyl)-ATP >> ATP > alphabeta-methylene-ATP > 2-methylthio ATP > or = UTP > or = GTP > ADP. These currents were blocked by the selective P2X7 receptor antagonist 3-[5-(2,3-dichlorophenyl)-1 H-tetrazol-1-yl]methyl pyridine (A-438079). We therefore concluded that ATP-induced currents in rat myometrial cells crossed cell membranes via P2X7 receptors. We further showed that the ATP-induced currents were blocked by extracellular Mg(2+) (IC(50) = 0.26 mM). Clinically, administering extracellular Mg(2+) is known to inhibit uterine contraction. It therefore seems likely that uterine contraction may be induced by raised extracellular ATP and suppressed via Mg(2+) inhibiting P2X7 receptors. Further research is needed into the P2X7 receptor as a therapeutic target in abnormal uterine contraction, as a possible treatment for premature labor.

Inhibición del receptor plaquetario P2Y12 de adenosina difosfato plaquetario: efectos beneficiosos y limitaciones de las estrategias terapéuticas actuales y perspectivas futuras / Platelet adenosine diphosphate P2Y12 recep tor antagonism: benefits and limitations of current treatment strategies and future directions

La inhibición del receptor plaquetario P2Y 12 con el empleo de clopidogrel ha representado un importante avance en el tratamiento farmacológico de los pacientes con enfermedad aterotrombótica, especialmente en los síndromes coronarios agudos y en el intervencionismo coronario percutáneo. A pesar de los efectos beneficiosos asociados al tratamiento con clopidogrel en estos contextos de alto riesgo, las experiencias clínicas y de laboratorio ha permitido identificar algunas de sus limitaciones, la más relevante de las cuales es la amplia variabilidad existente en la respuesta inhibitoria plaquetaria. En esta variabilidad de la respuesta al clopidogrel se han involucrado diferentes factores clínicos, genéticos y celulares. Es importante señalar que los hallazgos farmacodinámicos han demostrado tener repercusiones pronósticas, lo cual subraya la necesidad de mejores estrategias de tratamiento antiagregante plaquetario. El objetivo de este artículo es aportar una visión general del estado actual y las perspectivas futuras sobre el antagonismo del receptor P2Y12, con especial referencia a la variabilidad interindividual en la respuesta a clopidogrel y a las estrategias destinadas a mejorar la inhibición del receptor P2Y12, incluidos los fármacos antiagregantes plaquetarios más recientes (AU)

Platelet P2Y 12 receptor antagonism with clopidogrel has represented a major advancement in the pharmacological management of patients with atherothrombotic disease, in particular those with acute coronary syndromes and undergoing percutaneous coronary interventions. Despite the benefit associated with clopidogrel therapy in these high risk settings, laboratory and clinical experience have led to identify some of its caveats, among which its wide range of platelet inhibitory response is the most relevant. Genetic, cellular and clinical factors are implied in variability in response to clopidogrel. Importantly, pharmacodynamic findings have shown to have important prognostic implications, underscoring the need for more optimal antiplatelet treatment strategies. The aim of this manuscript is to provide an overview on the current status and future directions in P2Y12 receptor antagonism, with particular emphasis on interindividual variability in response to clopidogrel and strategies, including novel antiplatelet agents, to improve platelet P2Y12 inhibition (AU)

Impact of P2Y12-ADP receptor polymorphism on the efficacy of clopidogrel dose-adjustment according to platelet reactivity monitoring in coronary artery disease patients.

INTRODUCTION: High on-treatment platelet reactivity (HTPR) after clopidogrel loading dose (LD) is associated with a high risk of thrombotic events after percutaneous coronary intervention(PCI). We have demonstrated that HTPR could be overcome in the majority of cases using LD adjustment resulting in an improved clinical outcome. However this strategy failed in nearly 10% of patients with HTPR. We aimed to determine if P2Y12-ADP receptor polymorphisms were associated with failed dose adjustment. MATERIAL AND METHOD: Forty-three patients undergoing PCI were included in this prospective study. A VASP index >or=50% after a 600 mg LD of clopidogrel defined HTPR. Dose adjustment was performed according to PR monitoring to reach a VASP index <50%. Genetic polymorphism of the P2Y12-ADP receptor was determined by direct sequencing. RESULTS: Patients with successful dose-adjustment (SDA) (n=33) and failed (FDA) (n=10) dose-adjustment groups were compared. The 2 groups were similar in terms of cardiovascular risk factors including diabetes mellitus (SDA vs FDA: 42 vs 20%; p=0.3). The prevalence of the H2 allele of the P2Y12-ADP receptor was also similar between the 2 groups (p=0.3). The H2 allele was found in 6 patients which are all included in the SDA group. After the first 600 mg loading dose of clopidogrel, patients carrying at least one H2 allele had similar VASP index compared to those carrying two copies of the wild type allele (H1) (SDA vs FDA: 44.9+/-14.9 vs 43.5+/-10%; p=0.8). CONCLUSION: The present study suggests that the H2 allele of the P2Y12-ADP receptor is not involved in clopidogrel failed dose adjustment according to platelet reactivity monitoring.

Frontiers in platelet inhibition.

Anti-platelet drugs play a key role in cardiovascular medicine since the introduction of aspirin as an anti-thrombotic agent some 50 years ago. After many years of a "monopoly" of aspirin, ADP receptor P2Y12 inhibitors were introduced with a significant improvement in clinical outcome. Nowadays dual anti-platelet therapy is the common practice for both acute events and secondary prevention in selected groups of patients. The improved efficacy of multiple drug therapy is associated with an increased risk of bleeding, which raises the issue of the dosing of these drugs. Recently, numerous studies have reported a variable laboratory response to aspirin and clopidogrel, which correlates with clinical outcome. Several mechanisms for causing this variable response have been proposed, including genetic variability, disease burden, and others. A major obstacle in this field is the lack of a standardized method for testing these responses. New drugs are currently under different stages of development, including new P2Y12 receptors inhibitors, thrombaxane receptor blockers, direct thrombin inhibitors, and inhibitors for other signaling pathways including oral GPIIbIIIa inhibitors. Thus anti-platelet therapy is currently under intensive developments toward multiple drug therapy and personal dose adjustment, which may improve clinical outcome.

Prasugrel: new drug. After angioplasty and stenting: continue to use aspirin + clopidogrel.

(1) For patients with acute coronary syndromes who have undergone percutaneous angioplasty and stenting, the best-assessed treatment for preventing relapses is a combination of aspirin and clopidogrel; (2) Prasugrel, an antiplatelet drug belonging the same chemical class as clopidogrel, is authorized in the EU for use in this indication; (3) Clinical evaluation is based on a randomized double-blind trial comparing prasugrel + aspirin versus clopidogrel + aspirin in 13 608 patients with acute coronary syndromes, half of whom were treated for at least 15 months. Prasugrel did not reduce overall mortality (about 3%) or the incidence of non-fatal stroke after 15 months (1% of patients). The only advantage reported with prasugrel was a significant reduction in the risk of non-fatal myocardial infarction (7.3% versus 9.5%); (4) In this trial, bleeding events, excluding those related to revascularisation procedures, were more frequent in the prasugrel group than in the clopidogrel group (2.4% versus 1.8%). Haemorrhages associated with revascularisation were also significantly more numerous with prasugrel (11.3% and 3.6%); (5) Subgroup analyses suggest that the risk-benefit balance of prasugrel is unfavourable in patients weighing less than 60 kg, patients over 75 years of age, and patients with a history of transient ischaemic attack or stroke; (6) The trial comparing prasugrel versus clopidogrel, as well as some animal studies, raise the possibility that prasugrel might increase the risk of cancer. In the main trial, prasugrel caused fewer cases of neutropenia than clopidogrel, but more cases of respiratory failure, hypotension and atrial flutter were observed; (7) In practice, for secondary prevention in patients with acute coronary syndromes treated with angioplasty and stenting, the risk-benefit balance of prasugrel, used in combination with aspirin, appears to be no better than that of clopidogrel + aspirin.

International Union of Pharmacology LVIII: update on the P2Y G protein-coupled nucleotide receptors: from molecular mechanisms and pathophysiology to therapy.

There have been many advances in our knowledge about different aspects of P2Y receptor signaling since the last review published by our International Union of Pharmacology subcommittee. More receptor subtypes have been cloned and characterized and most orphan receptors de-orphanized, so that it is now possible to provide a basis for a future subdivision of P2Y receptor subtypes. More is known about the functional elements of the P2Y receptor molecules and the signaling pathways involved, including interactions with ion channels. There have been substantial developments in the design of selective agonists and antagonists to some of the P2Y receptor subtypes. There are new findings about the mechanisms underlying nucleotide release and ectoenzymatic nucleotide breakdown. Interactions between P2Y receptors and receptors to other signaling molecules have been explored as well as P2Y-mediated control of gene transcription. The distribution and roles of P2Y receptor subtypes in many different cell types are better understood and P2Y receptor-related compounds are being explored for therapeutic purposes. These and other advances are discussed in the present review.

Purinergic signalling: therapeutic potential

El concepto de un sistema de señalización purinérgica, empleando los nucleótidos y nucleósidos de purina como mensajeros extracelulares, fue propuesto hace unos 30 años. Después de una breve introducción y puesta al día de los subtipos de receptores purinérgicos, este artículo se centra en los aspectos fisiopatológicos desempeñados por el ATP, ADP, UTP y adenosina. Estas moléculas median respuestas a corto plazo (agudas), como en la neurotransmisión, secreción y vasodilatación, y también respuestas a largo plazo (crónicas), como la señalización en el desarrollo, regeneración, proliferación y muerte celular. En condiciones patológicas, se observa que la expresión de los purinoceptores es muy versátil, incluyendo un incremento en el componente purinérgico del control nervioso parasimpático de la vejiga humana en el caso de sufrir cistitis intersticial y obstrucción del flujo, y también como cotransmisor en el control simpático de los vasos sanguíneos en ratas hipertensas. La acción antitrombótica del clopidogrel, un antagonista del receptor P2Y12, ha demostrado ser particularmente útil en la prevención de los infartos cerebrales recurrentes e infartos cardíacos en recientes ensayos clínicos. El papel del receptor P2X3 en la nocicepción y una nueva hipótesis sobre la transducción mecano-sensible en el dolor visceral, serán consideradas, así como el potencial terapéutico de los agonistas y antagonistas purinérgicos para el tratamiento de la taquicardia supraventricular, cáncer, ojo seco, hiperactividad de vejiga, disfunción eréctil, osteoporosis, diabetes, motilidad intestinal y anomalías respiratorias y vasculares

The concept of a purinergic signalling system, using purine nucleotides and nucleosides as extracellular messengers, was first proposed over 30 years ago. After a brief introduction and update of purinoceptor subtypes, this article focuses on the diverse pathophysiological roles of ATP, ADP, UTP and adenosine. These molecules mediate short-term (acute) signalling functions in neurotransmission, secretion and vasodilatation and long-term (chronic) signalling functions in development, regeneration, proliferation and cell death. Plasticity of purinoceptor expression in pathological conditions is frequently observed, including an increase in the purinergic component of parasympathetic nervous control of the human bladder in interstitial cystitis and outflow obstruction, and in sympathetic cotransmitter control of blood vessels in hypertensive rats. The antithrombotic action of clopidogrel, a P2Y12 receptor antagonist, has been shown to be particularly useful in the prevention of recurrent strokes and heart attacks in recent clinical trials. The role of P2X3 receptors in nociception and a novel hypothesis about purinergic mechano-sensory transduction in visceral pain will be considered, as well as the therapeutic potential of purinergic agonists or antagonists for the treatment of supraventricular tachycardia, cancer, dry eye, bladder hyperactivity, erectile dysfunction, osteoporosis, diabetes, gut motility, respiratory and vascular disorders

From CURE to MATCH: ADP receptor antagonists as the treatment of choice for high-risk atherothrombotic patients.

Patients with a clinical manifestation of atherothrombosis such as a recent ischaemic cerebrovascular event are at high risk of subsequent events. Atherothrombosis often reflects disseminated disease; thus, further events may occur not only in the same arterial distribution but also in other vascular beds. To achieve adequate secondary prevention in these patients, long-term antiplatelet therapy with consistent benefit across the atherothrombosis spectrum is required. In the CAPRIE (Clopidogrel versus Aspirin in Patients at Risk of Ischaemic Events) Trial, clopidogrel (clopidogrel bisulphate) was superior to acetylsalicylic acid (ASA) in reducing the combined risk of ischaemic stroke (IS), myocardial infarction (MI) or vascular death in patients with symptomatic atherosclerosis. Post hoc analyses demonstrated that the benefit of clopidogrel was amplified in high-risk patients, including patients with a history of previous ischaemic events, diabetic patients and patients with hypercholesterolaemia. The synergistic antiplatelet effect produced by using clopidogrel on top of ASA may be beneficial in high-risk patients. The benefit of dual antiplatelet therapy was recently examined in the CURE (Clopidogrel in Unstable Angina to Prevent Recurrent Events) Study, which demonstrated that long-term treatment with clopidogrel on top of standard therapy including ASA was superior to standard therapy alone in the prevention of major vascular ischaemic events in patients with unstable angina or non-Q-wave MI. The ongoing MATCH (Management of Atherothrombosis with Clopidogrel in High-risk Patients with Recent Transient Ischaemic Attack or Ischaemic Stroke) trial will evaluate the efficacy and safety of clopidogrel plus ASA versus clopidogrel alone in patients with recent transient ischaemic attack (TIA) or IS and with at least one additional risk factor. Approximately 7,600 patients will be enroled, with treatment and follow-up for each patient lasting 18 months. The primary combined efficacy endpoint will be the first occurrence of an event in the composite of IS, MI, vascular death or rehospitalization for an acute ischaemic event during the follow-up period. MATCH will explore the potential benefit of clopidogrel in high-risk stroke/TIA patients and together with CAPRIE and CURE could provide further evidence of the long-term benefit of clopidogrel in patients with major atherothrombotic manifestations.