Randomized trial of an oral platelet glycoprotein IIb/IIIa antagonist, sibrafiban, in patients after an acute coronary syndrome: results of the TIMI 12 trial. Thrombolysis in Myocardial Infarction

Accuracy of the TIMI and GRACE scores in predicting coronary disease in patients with non-ST-elevation acute coronary syndrome

INTRODUCTION

The GRACE and TIMI scores have been well validated for assessment of prognosis in non-ST-elevation acute coronary syndrome (NSTE-ACS). However, their value in predicting coronary artery disease (CAD) has been little studied. We aimed to assess the relationship between these scores and the extent of coronary disease.

METHODS

We analyzed 238 consecutive patients admitted for NSTE-ACS and undergoing a coronary angiogram during hospitalization. The severity of CAD was assessed using the SYNTAX score. Obstructive CAD was defined as ≥50% stenosis in the left main or ≥70% stenosis in other vessels. Severe CAD was defined as a SYNTAX score >32. The Pearson test was used to assess the correlation between scores.

RESULTS

The SYNTAX score was higher in patients at high risk (GRACE score: p<0.001 and TIMI score: p=0.001). Moreover, there was a significant positive correlation between the GRACE and SYNTAX scores (r=0.23, p<0.001) as well as between TIMI and SYNTAX (r=0.2, p=0.002). Both clinical scores can predict obstructive CAD moderately well (area under the curve [AUC] for GRACE score: 0.599, p=0.015; TIMI score: AUC 0.639, p=0.001) but not severe disease. A GRACE score of 120 and a TIMI score of 2 were predictive of obstructive CAD with, respectively, a sensitivity of 57% and 75.7% and a specificity of 61.8% and 47.9%.

CONCLUSION

The GRACE and TIMI scores correlate moderately with the extent of coronary disease assessed by the SYNTAX score. They can predict obstructive CAD but not severe disease.

The progress in the research of antiplatelet agents (1995-2017)

Antiplatelet therapy displays a critical role in the treatment and prevention of antithrombotic disorders. Many new antiplatelet agents have been developed following the emergence of various clinical limitations of classical antiplatelet drugs. This review covers mainly the recent advances in the development of P2Y₁₂ antagonists and GPIIb/IIIa antagonists. Meanwhile, it summarizes promising approaches to new platelet surface receptors such as prostanoid EP3 receptor, thromboxane A₂ prostanoid receptor, protease-activated receptors, GPIb-IX-V receptor and P-selectin. In addition, PI3K_β, a critical protein at the inside signaling pathway of platelet activation is also mentioned as an important antiplatelet target. Moreover, the development of respective drug candidates is discussed in detail.

Platelet glycoprotein IIb/IIIa blockers during percutaneous coronary intervention and as the initial medical treatment of non-ST segment elevation acute coronary syndromes

BACKGROUND

During percutaneous coronary intervention (PCI), and in non-ST segment elevation acute coronary syndromes (NSTEACS), the risk of acute vessel occlusion by thrombosis is high. Glycoprotein IIb/IIIa blockers strongly inhibit platelet aggregation and may prevent mortality and myocardial infarction. This is an update of a Cochrane review first published in 2001, and previously updated in 2007 and 2010.

OBJECTIVES

To assess the efficacy and safety effects of glycoprotein IIb/IIIa blockers when administered during PCI, and as initial medical treatment in patients with NSTEACS.

SEARCH METHODS

We updated the searches of the Cochrane Central Register of Controlled Trials (CENTRAL) on The Cochrane Library (Issue 12, 2012), MEDLINE (OVID, 1946 to January Week 1 2013) and EMBASE (OVID, 1947 to Week 1 2013) on 11 January 2013.

SELECTION CRITERIA

Randomised controlled trials comparing intravenous IIb/IIIa blockers with placebo or usual care.

DATA COLLECTION AND ANALYSIS

Two authors independently selected studies for inclusion, assessed trial quality and extracted data. We collected major bleeding as adverse effect information from the trials. We used odds ratios (OR) and 95% confidence intervals (CI) for effect measures.

MAIN RESULTS

Sixty trials involving 66,689 patients were included. During PCI (48 trials with 33,513 participants) glycoprotein IIb/IIIa blockers decreased all-cause mortality at 30 days (OR 0.79, 95% CI 0.64 to 0.97) but not at six months (OR 0.90, 95% CI 0.77 to 1.05). All-cause death or myocardial infarction was decreased both at 30 days (OR 0.66, 95% CI 0.60 to 0.72) and at six months (OR 0.75, 95% CI 0.64 to 0.86), although severe bleeding was increased (OR 1.39, 95% CI 1.21 to 1.61; absolute risk increase (ARI) 8.0 per 1000). The efficacy results were homogeneous for every endpoint according to the clinical condition of the patients, but were less marked for patients pre-treated with clopidogrel, especially in patients without acute coronary syndromes.As initial medical treatment of NSTEACS (12 trials with 33,176 participants), IIb/IIIa blockers did not decrease mortality at 30 days (OR 0.90, 95% CI 0.79 to 1.02) or at six months (OR 1.00, 95% CI 0.87 to 1.15), but slightly decreased death or myocardial infarction at 30 days (OR 0.91, 95% CI 0.85 to 0.98) and at six months (OR 0.88, 95% CI 0.81 to 0.96), although severe bleeding was increased (OR 1.29, 95% CI 1.14 to 1.45; ARI 1.4 per 1000).

AUTHORS' CONCLUSIONS

When administered during PCI, intravenous glycoprotein IIb/IIIa blockers reduce the risk of all-cause death at 30 days but not at six months, and reduce the risk of death or myocardial infarction at 30 days and at six months, at a price of an increase in the risk of severe bleeding. The efficacy effects are homogeneous but are less marked in patients pre-treated with clopidogrel where they seem to be effective only in patients with acute coronary syndromes. When administered as initial medical treatment in patients with NSTEACS, these agents do not reduce mortality although they slightly reduce the risk of death or myocardial infarction.

Platelet glycoprotein IIb/IIIa blockers during percutaneous coronary intervention and as the initial medical treatment of non-ST segment elevation acute coronary syndromes

BACKGROUND

During percutaneous coronary intervention (PCI), and in non-ST segment elevation acute coronary syndromes (NSTEACS), the risk of acute vessel occlusion by thrombosis is high. Glycoprotein IIb/IIIa blockers strongly inhibit platelet aggregation and may prevent mortality and myocardial infarction. This is an update of a Cochrane review first published in 2001, and previously updated in 2007 and 2010.

OBJECTIVES

To assess the efficacy and safety effects of glycoprotein IIb/IIIa blockers when administered during PCI, and as initial medical treatment in patients with NSTEACS.

SEARCH METHODS

We updated the searches of the Cochrane Central Register of Controlled Trials (CENTRAL) on The Cochrane Library (Issue 12, 2012), MEDLINE (OVID, 1946 to January Week 1 2013) and EMBASE (OVID, 1947 to Week 1 2013) on 11 January 2013.

SELECTION CRITERIA

Randomised controlled trials comparing intravenous IIb/IIIa blockers with placebo or usual care.

DATA COLLECTION AND ANALYSIS

Two authors independently selected studies for inclusion, assessed trial quality and extracted data. We collected major bleeding as adverse effect information from the trials. We used odds ratios (OR) and 95% confidence intervals (CI) for effect measures.

MAIN RESULTS

Sixty trials involving 66,689 patients were included. During PCI (48 trials with 33,513 participants) glycoprotein IIb/IIIa blockers decreased all-cause mortality at 30 days (OR 0.79, 95% CI 0.64 to 0.97) but not at six months (OR 0.90, 95% CI 0.77 to 1.05). All-cause death or myocardial infarction was decreased both at 30 days (OR 0.66, 95% CI 0.60 to 0.72) and at six months (OR 0.75, 95% CI 0.64 to 0.86), although severe bleeding was increased (OR 1.39, 95% CI 1.21 to 1.61; absolute risk increase (ARI) 8.0 per 1000). The efficacy results were homogeneous for every endpoint according to the clinical condition of the patients, but were less marked for patients pre-treated with clopidogrel, especially in patients without acute coronary syndromes.As initial medical treatment of NSTEACS (12 trials with 33,176 participants), IIb/IIIa blockers did not decrease mortality at 30 days (OR 0.90, 95% CI 0.79 to 1.02) or at six months (OR 1.00, 95% CI 0.87 to 1.15), but slightly decreased death or myocardial infarction at 30 days (OR 0.91, 95% CI 0.85 to 0.98) and at six months (OR 0.88, 95% CI 0.81 to 0.96), although severe bleeding was increased (OR 1.29, 95% CI 1.14 to 1.45; ARI 1.4 per 1000).

AUTHORS' CONCLUSIONS

When administered during PCI, intravenous glycoprotein IIb/IIIa blockers reduce the risk of all-cause death at 30 days but not at six months, and reduce the risk of death or myocardial infarction at 30 days and at six months, at a price of an increase in the risk of severe bleeding. The efficacy effects are homogeneous but are less marked in patients pre-treated with clopidogrel where they seem to be effective only in patients with acute coronary syndromes. When administered as initial medical treatment in patients with NSTEACS, these agents do not reduce mortality although they slightly reduce the risk of death or myocardial infarction.

Platelet glycoprotein IIb/IIIa blockers during percutaneous coronary intervention and as the initial medical treatment of non-ST segment elevation acute coronary syndromes

BACKGROUND

During percutaneous coronary intervention (PCI), and in non-ST segment elevation acute coronary syndromes (NSTEACS), the risk of acute vessel occlusion by thrombosis is high. IIb/IIIa blockers strongly inhibit platelet aggregation and may prevent mortality and myocardial infarction (MI). This is an update of a Cochrane review first published in 2001, and previously updated in 2007.

OBJECTIVES

To assess the effects and safety of IIb/IIIa blockers when administered during PCI, and as initial medical treatment in patients with NSTEACS.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) on The Cochrane Library (Issue 3, 2009), MEDLINE (1966 to October 2009), and EMBASE (1980 to October 2009).

SELECTION CRITERIA

Randomised controlled trials comparing intravenous IIb/IIIa blockers with placebo or usual care.

DATA COLLECTION AND ANALYSIS

Two authors independently selected studies for inclusion, assessed trial quality and extracted data. We collected major bleeding as adverse effect information from the trials. Odds ratios (OR) and 95% confidence intervals (CI) were used for effect measures.

MAIN RESULTS

Forty-eight trials involving 62,417 patients were included. During PCI, IIb/IIIa blockers decreased mortality at 30 days (OR 0.76, 95% CI 0.62 to 0.95) and at six months (OR 0.84, 95% CI 0.71 to 1.00). Death or MI was decreased both at 30 days (OR 0.65, 95% CI 0.60 to 0.72), and at 6 months (OR 0.70, 95% CI 0.61 to 0.81), although severe bleeding was increased (OR 1.38, 95% CI 1.20 to 1.59; absolute risk increase (ARI) 8.0 per 1000). The efficacy results were homogeneous for every endpoint according to the clinical condition of the patients, but were less marked for patients pre-treated with clopidogrel, especially in patients without ACS.As initial medical treatment of NSTEACS, IIb/IIIa blockers did not decrease mortality at 30 days (OR 0.91, 95% CI 0.80 to 1.03) or at six months (OR 1.00, 95% CI 0.87 to 1.15), but slightly decreased death or MI at 30 days (OR 0.92, 95% CI 0.86 to 0.99) and at six months (OR 0.88, 95% CI 0.81 to 0.96), although severe bleeding was increased (OR 1.27, 95% CI 1.12 to 1.43; ARI 1.4 per 1000).

AUTHORS' CONCLUSIONS

When administered during PCI, intravenous IIb/IIIa blockers reduce the risk of death and of death or MI at 30 days and at six months, at a price of an increase in the risk of severe bleeding. The efficacy effects are homogeneous but are less marked in patients pre-treated with clopidogrel where they seem to be effective only in patients with ACS. When administered as initial medical treatment in patients with NSTEACS, these agents do not reduce mortality although they slightly reduce the risk of death or MI.

Adhesion molecules: potential therapeutic and diagnostic implications

The role of cell adhesion molecules (CAMs) and extracellular matrix (ECM) proteins in various pathological processes, including angiogenesis, thrombosis, inflammation, apoptosis, cell migration, and proliferation is well documented. These processes can lead to both acute and chronic disease states such as ocular diseases, metastasis, unstable angina, myocardial infarction, stroke, osteoporosis, a wide range of inflammatory diseases, vascular remodeling, and neurodegenerative disorders. A key success in this field was identification of the role of platelet glycoprotein (GP)IIb/IIIa in the prevention and diagnosis of various thromboembolic disorders. The use of soluble adhesion molecules as potential diagnostic markers for acute and chronic leukocyte, platelet, and endothelial cell insult is becoming increasingly common. The development of various therapeutic and diagnostic candidates based on the key role of CAMs, with special emphasis on integrins in various diseases, as well as the structure-function aspects of cell adhesion and signaling of the different CAMs and ECM are highlighted.

Inhibitory effects of oligopeptides from hen egg white on both human platelet aggregation and blood coagulation

Egg white proteins have many biological functions and substantial nutritional benefits when used as a food source; however, they also contain allergens such as ovalbumin, ovomucoid, and ovotransferrin. We prepared oligopeptides without allergens from hen egg whites via the use of several proteases, and assessed their effects on platelet aggregation and blood coagulation, known to both of which are known to be major risk factors in thrombogenesis. Egg white oligopeptides (EWOP) inhibited collagen-induced human platelet aggregation in a dose-dependent manner. Additionally, we attempted to determine whether cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), aggregation-inhibiting intracellular molecules, regulate EWOP-inhibited platelet aggregation. EWOP caused an increase in cAMP levels, but did not affect cGMP levels, which suggests that the anti-platelet activity of EWOP operates in a cAMP-dependent manner, rather than via a cGMP-dependent process, in collagen-induced platelet aggregation. In addition, EWOP induced a significantly prolonged prothrombin time (PT) as compared with the controls. These data show that EWOP inhibits the conversion of fibrinogen to fibrin in a plasmatic atmosphere on an extrinsic pathway. Accordingly, these findings suggest that EWOP may be an excellent candidate as a crucial inhibitor of platelet activation, and its anti-platelet effects appear to involve the inhibition of both platelet aggregation and blood coagulation within the cardiovascular system.

Platelet-endothelial interactions in atherothrombotic disease: therapeutic implications

The role of the platelet and the endothelium in the pathogenesis of atherosclerosis and subsequent ischemic events has been the subject of extensive investigation. Arterial sites where endothelial function is severely impaired are often the sites of atheroma development. Lesion evolution impairs endothelial function, leading to a self-perpetuating cycle of growth. During early lesion development, overt thrombotic events are rare. However, rupture of an advanced, necrotic plaque or intimal ulceration triggers arterial thrombosis, at which point the importance of platelet function may be seen clearly. The Antiplatelet Trialists' Collaboration meta-analysis demonstrated the benefit of antiplatelet therapy to patients with atherosclerotic disease. Aspirin is the most widely studied agent and is considered the standard of antiplatelet therapy. Newer agents that intervene at different stages of the platelet activation pathway have been developed. Clopidogrel, a new adenosine diphosphate receptor antagonist, is more effective than aspirin in reducing vascular events in patients with prior myocardial infarction, stroke, or established peripheral arterial disease. The glycoprotein IIb-IIIa antagonists such as abciximab have proven effective in the setting of active arterial thrombosis and percutaneous revascularization, but their value in secondary prevention remains unknown. All patients with atherosclerosis should be treated with an antiplatelet drug. Current evidence suggests that either aspirin or clopidogrel are appropriate first-line agents. There is urgent need for an analysis of the risk/benefit ratio in various populations and clinical settings to determine the most appropriate type and intensity of therapy for a given patient.

Learning from the recently completed oral glycoprotein IIb/IIIa receptor antagonist trials

Although parenteral therapy with glycoprotein (GP) IIb/IIIa inhibitors has resulted in a reduced risk of death or myocardial infarction in patients with acute coronary syndromes and in patients undergoing percutaneous coronary intervention, the benefit is achieved only during the infusion period. Oral GP IIb/IIIa inhibitors may offer an opportunity to expand the application of this therapy to additional vascular indications and to extend therapy beyond the in-hospital period. A number of oral GP IIb/IIIa inhibiting agents have been evaluated; however, no benefit has been observed. Oral GP IIb/IIIa inhibitors have been associated with an increased incidence of bleeding, but additional experience may permit the design of dosing regimens that decrease this risk. The recent Orbofiban in Patients with Unstable Coronary Syndromes (OPUS/TIMI-16) trial showed a small but significant increase in mortality in orbofiban-treated patients. It appears that this agent, and perhaps other oral GP IIb/IIIa inhibitors including sibrafiban and xemilofiban, may have a pro-aggregatory effect. This may be caused by the drug dissociating from the GP IIb/IIIa receptor, leaving an activated receptor that can then bind fibrinogen and form a platelet aggregate. Further studies are needed to elucidate the mechanism of this effect and to evaluate whether the second-generation of oral GP IIb/IIIa inhibitors, which have tight binding and a longer duration of antiplatelet effect, will be of clinical benefit.

In vitro and clinical investigation of the relationship between CCR5 receptor occupancy and anti-HIV activity of Aplaviroc

Aplaviroc (GW873140) binds specifically to human cellular CC chemokine receptor 5 (CCR5) and demonstrates potent anti-human immunodeficiency virus activity in vitro in the subnanomolar range. In vitro studies show that aplaviroc selectively inhibits the binding of a particular monoclonal antibody, 45531, to CCR5. Based on this observation, a flow cytometry-based assay was developed to determine percentage CCR5 receptor occupancy (RO). CCR5 receptor occupancy was aplaviroc concentration-dependent and related to anti-human immunodeficiency virus activity in vitro. In the clinical setting, CCR5 receptor occupancy in peripheral blood was >98% in all subjects within 2 to 3 hours of dosing, which is consistent with the peak plasma concentrations of drug. Longitudinal analysis in the drug washout period revealed the time to 50% CCR5 receptor occupancy averaged >100 hours, in both human immunodeficiency virus-positive and human immunodeficiency virus-negative subjects, substantially longer than the plasma pharmacokinetic half-life of 3 hours. The duration of CCR5 receptor occupancy appeared to be dose-dependent and associated with antiviral activity as measured by plasma human immunodeficiency virus RNA nadir following 10 days of multiple dose administration. These data demonstrate that the analysis of CCR5 receptor occupancy, in addition to conventional plasma-based pharmacokinetic measures, provides an informative tool to assist in evaluating the pharmacodynamic and antiviral effects of cellular CC chemokine receptor antagonists.

Blockade of glycoprotein IIb/IIIa mediates the antithrombotic activity of butanol fraction of Actinostemma lobatum Maxim

AIM OF THE STUDY

Actinostemma lobatum Maxim, a wildlife plant of Cucurbitaceae family, has been utilized for the prevention or treatment of cardiovascular diseases as a folk remedy in Korea. However, its scientific evidence remains unclear. Thus, in the present study, we examined the effects of butanol fraction of Actinostemma lobatum Maxim (BFALM) on the in vitro and in vivo antithrombotic activity and possible mechanisms were elucidated for the first time.

MATERIAL AND METHODS

To elucidate the antithrombotic mechanism of BFALM, platelet aggregation assay, coagulation assay, glycoprotein IIb/IIIa assay, thromboxane A(2) assay and in vivo pulmonary thromboembolism experiment were performed.

RESULTS

BFALM significantly inhibited collagen, adenosine diphosphate (ADP) and thrombin-induced platelet aggregation in a concentration dependent manner. Consistently, oral administration of BFALM resulted in a dose-dependent increase of survival rates of mice with pulmonary thromboembolism induced by intravenous injection of collagen and epinephrine. In mechanism assays for the antithrombotic activity of BFALM, BFALM significantly inhibited the fibrinogen binding to the platelet surface Glycoprotein IIb/IIIa (GP IIb/IIIa) receptor in a concentration dependent fashion, as well as reduced the level of thromboxane A(2) at 400microg/ml. Furthermore, BFALM significantly prolonged the prothrombin time (PT) and activated partial thromboplastin time (APTT) compared with untreated control.

CONCLUSIONS

These results suggest that BFALM may exert antithrombotic activity through inhibition of platelet aggregation via GP IIb/IIIa and thromboxane A(2) pathways, along with anticoagulatory activity through intrinsic and extrinsic pathways.

The independent and combined risk of diabetes and non-endstage renal impairment in non-ST-segment elevation acute coronary syndromes

OBJECTIVES

To assess the effect of renal impairment (RI) and diabetes (DM) on outcomes in non-ST-segment elevation acute coronary syndromes (NSTE-ACS).

METHODS

Data were pooled from 13,126 patients in five NSTE-ACS TIMI trials (TIMI 11A and B, TIMI 12, OPUS-TIMI 16, and TACTICS-TIMI 18). Patients were divided based on DM status and RI (none, mild, or moderate if the glomerular filtration rate (GFR, ml/min/1.73 m(2)) was > or = 90, 60-89 and 30-59 respectively).

RESULTS

Patients with DM and moderate RI (n=609) were older and had more prior MI (p<0.01 for all) than other subgroups. Compared with no RI/DM (n=3,832), the 12-month adjusted risks of death, MI, and death/MI increased with advancing RI and were highest with DM and moderate RI (H.R. 1.7, (1.2-2.4), p=0.002; H.R. 2.0 (1.5-2.6), p<0.001; and H.R. 1.7 (1.3-2.2), p<0.001 respectively). These events were also increased with DM and mild RI (H.R. 1.4, (1.0-1.9), p=0.06, H.R. 1.4 (1.1-1.8), p=0.006 and H.R. 1.3 (1.1-1.7), p=0.007 respectively) but not with 1) mild or moderate RI without DM or 2) DM without RI. The interaction terms for RI and DM in their association with MI and death/MI were significant.

CONCLUSIONS

In the absence of DM, RI and in the absence of RI, DM did not increase the risk of MI or death/MI. However, the combination of RI and DM was associated with a particularly high risk of MI and death/MI suggesting that attention to preserving renal function may be of particular benefit for reducing cardiovascular risk in diabetic patients.

Cell adhesion molecules: potential therapeutic & diagnostic implications

The role of cell adhesion molecules (CAM) and extracellular matrix proteins (ECM) in various pathological processes including angiogenesis, thrombosis, apoptosis, cell migration & proliferation are well documented. These processes can lead to both acute and chronic disease states such as ocular diseases, metastasis, unstable angina, myocardial infarction, stroke, osteoporosis, a wide range of inflammatory diseases, vascular remodeling, and neurodegenerative disorders. A key success in this field is evident from the potential role of the platelet GPIIb/IIIa integrin in the prevention and diagnosis of various thromboembolic disorders. Additionally, the use of soluble adhesion molecules as potential diagnostic markers for acute and chronic leukocyte, platelet, and endothelial cellular insult are increasingly utilized. The development of various therapeutic and diagnostic candidates based on the key role of CAM, with special emphasis on integrins in various diseases as well as the structure-function aspects of cell adhesion and signaling of the different CAM and ECM are highlighted.

Laboratory Evaluation of Platelet Function

Platelets play a central role in hemostasis. Consequently, they lie at the heart of many inherited and acquired bleeding disorders and thrombotic events. The diagnosis of these disorders and monitoring of antiplatelet therapy require a thorough understanding of tests that measure platelet quantity and function. This article outlines basic concepts of platelet physiology and describes the tests that are commonly used in the clinical assessment of platelet function.

In-vitro efficacy of different platelet glycoprotein IIb/IIIa antagonists and thrombolytics on platelet/fibrin-mediated clot dynamics in human whole blood using thrombelastography

Suppressing platelet activation improves efficacy of thrombolytic therapy for stroke and acute myocardial infarction. Combination treatment with recombinant tissue plasminogen activator (r-tPA) and glycoprotein IIb/IIIa (GPIIb/IIIa) inhibitor that binds with high affinity to platelets may therefore improve the efficacy of thrombolytic therapy. The effect of platelet GPIIb/IIIa antagonists and/or r-tPA on the dynamics of platelet/fibrin clot formation, strength, and lysis was determined using thrombelastography in human blood under thrombin or tissue factor stimulation. The study utilized platelet GPIIb/IIIa antagonists with high affinity and slow off-rate (Class I) from resting and activated platelets in comparison with Class II antagonists (lower affinity and fast off-rate from platelet GPIIb/IIIa receptors). The combination of the active form of roxifiban (XV459; Class I) or the active form of orbofiban (Class II) with a subeffective concentration of r-tPA resulted in a synergistic effect in clot lysis with roxifiban active form XV459 but not with that of orbofiban at therapeutically achievable concentrations that inhibit human platelet aggregation. These data indicate differential enhanced thrombolysis of low levels of r-tPA with high-affinity Class I but not with low-affinity Class II GPIIb/IIIa antagonists in the absence of anticoagulants.

Oral platelet glycoprotein IIb/IIIa receptor inhibitors--Part I

With the central importance of antiplatelet therapy in patients with coronary artery disease and the numerous positive trials with glycoprotein (GP) IIb/IIa inhibitors given intravenously, it was hoped that one could extend the benefit of IIb/IIIa inhibition to long-term treatment. Although the hypothesis that prolonged oral IIb/IIIa inhibition was appealing, many issues have been identified in the initial Phase II trials that would limit the usefulness of these compounds. Variability of the level of platelet inhibition was one major culprit that distinguished the oral compounds from intravenous ones. The problems that arose were that increased bleeding has been seen when levels of platelet inhibition are high (e.g., > 90%) and that, conversely, efficacy would likely be limited when levels of platelet inhibition were low. If further development of this class of drugs is undertaken, formal dosing studies would have to establish an oral dosing strategy that achieves appropriately high (80-95% inhibition) and steady levels of inhibition.

Association of a history of systemic hypertension with mortality, thrombotic, and bleeding complications following non-ST-segment elevation acute coronary syndrome

Chronic hypertension is a well established risk factor for the development of cardiovascular disease; however, its prognostic significance after a non-ST-segment elevation acute coronary syndrome remains to be established. Data from 15,414 patients included in six randomized Thrombolysis in Myocardial Infarction (TIMI) trials (TIMI 3B, TIMI 11A, TIMI 11B, TIMI 12, the Orbofiban in Patients With Unstable Coronary Syndromes [OPUS]-TIMI 16, and the Treat Angina With Aggrastat and Determine Cost of Therapy With an Invasive or Conservative Strategy [TACTICS]-TIMI 18) were analyzed. A history of hypertension was present in 10,998 (71.35%) patients; comorbidities and higher TIMI risk scores were more likely in these patients. However, positive troponin and ST-segment deviations were less frequent among hypertensive patients. After multivariate analysis, the history of hypertension was associated with more adverse outcomes, specifically the composite end point of death/myocardial infarction at 30 days and 1 year (odds ratio [OR] 1.54, 95% confidence interval [CI] 1.31-1.81; p<0.001 at 1 year) than in patients without this history. An independent relationship was also observed with mortality (OR 1.70, 95% CI 1.34-2.16; p<0.001 at 1 year), myocardial infarction (OR 1.50, 95% CI 1.23-1.82; p<0.001 at 1 year), recurrent ischemia (OR 1.24, 95% CI 1.11-1.38; p<0.001 at 1 year), and major bleeding (OR 1.45, 95% CI 1.03-2.06; p=0.036 at 30 days). It was concluded that chronic hypertension remains an independent marker for major short- and long-term cardiac adverse outcomes after non-ST-segment elevation acute coronary syndrome.

Association of platelet counts on presentation and clinical outcomes in ST-elevation myocardial infarction (from the TIMI Trials)

Platelet activation and aggregation play pivotal roles in the thrombotic process of acute coronary syndromes. However, data regarding platelet count and its association with clinical outcomes in the setting of ST-elevation myocardial infarction (STEMI) are limited. We hypothesized that higher platelet counts on presentation would be associated with poorer clinical outcomes. Data from 10,793 patients with STEMI in the Thrombolysis In Myocardial Infarction (TIMI) trials database were analyzed. Mean platelet count on presentation was 254.8 x 10(3)/microl. Higher platelet counts were associated with higher rates of adverse clinical outcomes at 30 days. In a multivariable analysis that adjusted for confounders of platelet counts (age, gender, weight, diabetes, and smoking), higher platelet counts remained associated with an increased risk of the combined end point of death, reinfarction, and congestive heart failure. With a reference group of platelet counts <200 x 10(3)/microl, the multivariable odds ratios were 1.22 (95% confidence interval 1.05 to 1.42, p = 0.009) for platelet counts of 201 to 300 x 10(3)/microl, 1.37 (95% confidence interval 1.11 to 1.68, p = 0.002) for counts of 301 to 400 x 10(3)/microl, and 1.71 (95% confidence interval 1.16 to 2.51, p = 0.005) for counts >400 x 10(3)/microl. Further, a greater decrease in follow-up platelet counts (compared with baseline values) was independently associated with an increased risk of reinfarction at 30 days (odds ratio 1.44 for every decrease of 100 x 10(3)/microl unit of platelets, 95% confidence interval 1.13 to 1.82, p = 0.03). In conclusion, in STEMI, a higher platelet count on presentation was independently associated with adverse clinical outcomes, whereas a greater subsequent platelet count decrease was associated with an increased risk of reinfarction.

Using thrombelastography to determine the efficacy of the platelet glycoprotein IIb/IIIa antagonist, roxifiban, on platelet/fibrin-mediated clot dynamics in humans

The effect of platelet glycoprotein IIb/IIIa antagonists on the dynamics of platelet/fibrin clot formation and strength was determined using thrombelastography (TEG) under conditions of recalcification or tissue factor addition. In the present investigation, the effect of roxifiban (class I) on ex vivo clot dynamics using recalcified blood was tested in normal, healthy volunteers (n = 7) dosed with 1 mg BID roxifiban for 9 days. Roxifiban inhibited platelet aggregation induced by 20 mumol/l adenosine diphosphate by 60-90% but did not significantly affect any of the TEG parameters either at peak, trough, or subtrough drug levels. Addition of 30 nmol/l roxifiban free acid (XV459; which is ineffective by itself to modify TEG parameters) to human blood obtained from roxifiban-treated subjects resulted in 45-60% (P < 0.01) inhibition of clot strength (maximum amplitude), 90-100% (P < 0.01) inhibition of initial kinetic of clot development (angle alpha), and 50-70% (P < 0.01) inhibition of early clot initiation (K). These data suggest that a subthreshold blood level of 40-50 nmol/l roxifiban active form was achieved in those subjects, as estimated from an in vitro calibration with XV459. These data indicate (not studied) that roxifiban, at a targeted clinical dosing regimen, failed to achieve sufficient exposure to modulate platelet-mediated clot retraction.

Ongoing clinical trials of anti-platelet agents in the management of acute ischaemic coronary syndromes

Acute ischaemic coronary syndromes, the clinical sequelae of thrombosis over a fissured atherosclerotic plaque within the coronary circulation, are the leading cause of death and hospitalisation in Western countries. Platelets are fundamental for the initiation and continuation of thrombosis, and currently available anti-platelet agents such as aspirin significantly improve the clinical outcome of patients with these syndromes. Therapeutic success with available therapy is however not universal, and adverse clinical event rates remain high. Several new classes of agents with a variety of anti-platelet actions are currently under development. Those which inhibit the final common pathway of platelet aggregation, the glycoprotein (GP) IIb/IIIa receptor, appear to show the most promise. Much clinical trial evidence already exists supporting the use of GP IIb/IIIa receptor antagonists in the management of acute ischaemic coronary syndromes. Several clinical studies are underway to further refine this knowledge base, and to assess their efficacy in a variety of novel applications.

Antiplatelet and antithrombotic activity of L-3-n-butylphthalide in rats

3-n-butylphthalide (NBP) is a potentially beneficial drug for the treatment of ischemic stroke with multiple actions on different pathophysiological processes. In the present study, the effect of l-, d-, and dl-NBP was investigated on ADP-, collagen-, and AA-induced platelet aggregation. l-NBP was the most potent among l-, d-, and dl-NBP. At higher concentration the effect of dl-NBP on platelet aggregation was greater than that of l- or d-NBP alone. The ex vivo antiaggregatory activity of l-NBP 100mg/kg declined gradually after 2 hours, but a considerable antiplatelet activity was still observed 4h after l-NBP administration. NBP was given orally and resulted in a dose-dependent inhibition of thrombus formation. Of the two isomers, l-NBP was the most potent. It significantly protected mice from a mixture of collagen and epinephrine induced thromboembolic death. When 100 mg/kg of l-NBP were administered orally to rats, the bleeding time increased 2.1-fold compared with the control group. At the same dose, ex vivo platelet aggregation induced by ADP, collagen, and AA was inhibited by l-NBP and the antithrombotic effects of the compound were also observed. Thus, NBP exerts oral anti-platelet and anti-thrombotic efficacy without perturbing systemic hemostasis in rats. l-NBP is more potent than d- and dl-NBP as antiplatelet agent.

Risk of bleeding complications with antiplatelet agents: meta-analysis of 338,191 patients enrolled in 50 randomized controlled trials

Antiplatelet therapy has been the focus of extensive clinical investigations over the last two decades. A variety of agents and regimens have been advanced for the prevention and treatment of vascular disease. Despite the proven life-saving clinical benefits of inhibiting platelets, this therapy is associated with an increased risk of bleeding. The objective of this study was to determine the risk of hemorrhage in the major classes of antiplatelet agents. Data from clinical trials published 1988-2002 in English were retrieved from MEDLINE, OVID, and CARDIOSOURCE. Only those studies in which patients had clinical follow-up for at least 1 month and in which a full description of hemorrhagic complications was reported were included. Information on sample size, study design, duration, agent, patient characteristics, and bleeding severity was independently and blindly reviewed. Data from 51 clinical trials with a total of 338,191 patients were analyzed. The antiplatelet agents were divided into 6 groups: aspirin (ASA) < 100 mg; ASA > or = 100 mg; dipyridamole, thienopyridines; intravenous and oral GP IIb/IIIa inhibitors. The variance estimate and confidence intervals were calculated for each treatment assignment. Low-dose aspirin and dipyridamole therapy were associated with the lowest risk of bleeding (3.6% and 6.7%, respectively). The highest rate of bleeding complications (44.6%) was associated with the GP IIa/IIIb inhibitors. Despite substantial differences in the reporting patterns of bleeding complications, low-dose ASA and dipyridamole therapy were associated with the lowest risk. Surprisingly, doses of ASA >/= 100 mg caused a relatively high hemorrhagic event rate, which was comparable to that of ADP-receptor blockers. These findings should be considered when using combination antiplatelet and/or anticoagulant therapy with conventional doses of ASA.

Oral platelet glycoprotein IIb/IIIa receptor inhibitors--part II

Although the hypothesis of benefit from prolonged oral IIb/IIIa inhibition was appealing, the large Phase III trials have uniformly shown there was no improvement in outcome. In addition, there was an increased mortality seen in patients treated with the oral IIb/IIIa inhibitor. This latter finding is not adequately explained, but is likely a multifactorial problem of this strategy of platelet inhibition. The trials found that, even with no improvement in efficacy, there was increased bleeding, meaning that for chronic therapy with IIb/IIIa inhibition there does not appear to be a therapeutic window. Accordingly, chronic oral IIb/IIIa inhibition appears to have been well tested but has not worked. Fortunately, there are several other oral antiplatelet agents available that have shown beneficial results, including clopidogrel. In addition, other newer classes of antiplatelet agents are in earlier stages of development. Thus, agents targeted more "upstream" in platelet activation pathways may offer a more tolerable and efficacious approach to long-term antiplatelet therapy.

Antithrombotic properties of SSR182289A, a new, orally active thrombin inhibitor

N-[3-[[[(1S)-4-(5-Amino-2-pyridinyl)-1-[[4-difluoromethylene)-1-piperidinyl]carbonyl]butyl]amino]sulfonyl][1,1'-biphenyl]-2-yl]acetamide hydrochloride (SSR182289A) is a novel, potent, and selective thrombin inhibitor. We have examined the antithrombotic properties of SSR182289A administered by i.v. and p.o. routes in several different animal thrombosis models in comparison with reference antithrombotic agents. Oral administration of SSR182289A produced dose-related antithrombotic effects in the following models; rat venous thrombosis (ED(50) 0.9 mg/kg p.o.), rat silk thread arterio-venous (AV) shunt (ED(50) 3.8 mg/kg p.o.), rat thromboplastin-induced AV shunt (ED(50) 3.1 mg/kg p.o.), rat carotid artery thrombosis (ED(200) 5.9 mg/kg p.o.), and rabbit venous thrombosis (ED(50) 7.5 mg/kg p.o.). Administered as an i.v. bolus, SSR182289A showed antithrombotic activity in the above models with ED(50)/ED(200) values in the range of 0.2 to 1.9 mg/kg i.v. SSR182289A increased rat tail transection bleeding time at doses > or =10 mg/kg p.o. In the rat thromboplastin-induced AV shunt model, SSR182289A 10 mg/kg p.o. produced marked antithrombotic effects at 30, 60, 120, and 240 min after administration. Hence, SSR182289A demonstrates potent oral antithrombotic properties in animal venous, AV-shunt, and arterial thrombosis models.

Ethanol enhances the inhibitory effect of an oral GPIIb/IIIa antagonist on human platelet function

Ethanol is a commonly used substance that can significantly influence platelet responses when combined with therapeutic drugs. In in vitro studies, we combined ethanol with LY309562, a novel 2,6-disubstituted isoquinolone RGD mimic that competes for fibrinogen binding to GPIIb/IIIa. Ethanol inhibits aggregation and secretion, partly by inhibiting thromboxane A(2) formation. We measured aggregation and secretion of dense granule contents by platelets labeled with [(14)C] serotonin in plasma from blood anticoagulated with FPRCH(2)Cl (PPACK). Alone, LY309562 dose-dependently inhibited aggregation induced by 10 micromol/L adenosine diphosphate, 1 microg/mL collagen, 2 micromol/L U46619 (a thromboxane A(2) mimetic), or 15 micromol/L SFLLRN (protease-activated receptor-1-activating peptide); inhibition was complete at 1 micromol/L LY309562 and partial at 0.1 micromol/L (50% inhibitory concentration [IC(50)] 0.19-0.33 micromol/L). Secretion induced by collagen, U46619, and SFLLRN was also inhibited by LY309562 (IC(50) 0.08-0.31 micromol/L). At inhibitory concentrations of LY309562, ethanol (2 or 4 mg/mL) further inhibited responses to collagen, U46619, and SFLLRN (IC(50) for aggregation 0.12-0.16 micromol/L; for secretion 0.04-0.12 micromol/L). Responses of aspirin-treated platelets to U46619 were also inhibited, indicating that ethanol was not acting solely by inhibiting thromboxane A(2) formation. Because it is likely that our results with LY309562 are representative of results with other GPIIb/IIIa antagonists, our in vitro data suggest that the concomitant use of GPIIb/IIIa antagonists and consumption of alcoholic beverages may result in further impairment of platelet participation in hemostasis and thrombosis.

Integrated pharmacokinetic/pharmacodynamic model of XV459, a potent and specific GPIIb/IIIa inhibitor, in healthy male volunteers

Roxifiban is an oral prodrug of XV459, a potent and specific inhibitor of the glycoprotein (GP) IIb/IIIa receptor previously under investigation for the treatment of peripheral arterial disease and acute coronary care syndrome. The objective of the present analysis was to develop a pharmacokinetic/pharmacodynamic (PK/PD) model that would be used to guide dose selection in Phase 2. This was a randomized, sequential, rising multiple-dose study in 41 healthy male volunteers given doses of 0.5 to 1.25 mg daily for 7 to 10 days. Total XV459 was measured in plasma by a sensitive and specific LC/MS/MS method. The percent inhibition of platelet aggregation (%IPA) was evaluated in citrated plasma in response to 10 microM ADP using the initial slope of the response. The resulting PK data were fit to a two-compartment model with first-order absorption and saturable oral absorption. The pharmacodynamics was modeled using a direct sigmoidal Emax model. Modeling was performed using NONMEM V. Intersubject variability was moderate in both PK and PD (15.3%-18.5%), except for V2/F (64.8%). Residual variability was low at 11.8%. Platelet count influenced both CL/F and EC50. Age and weight did not explain any additional variability in either PK or PD. The model was shown to produce realistic data when used for simulation. Overall, the results suggest that XV459 concentrations in the range of 10 to 20 ng/ml will yield %IPA values in the range of 40% to 80% inhibition. Because of the pharmacodynamically mediated PK of XV459 (due to platelet binding), the EC50 and CL/F are negatively correlated, limiting the utility of plasma concentration monitoring.

Glicoprotein (GP) IIb/IIIa inhibitors for acute stroke treatment

The benefit of antiplatelet therapy remains unclear, although it does appear that aspirin monotherapy started within 48 hours of stroke onset may result in a modest clinical improvement. Glicoprotein (GP) IIb/IIIa antagonists are currently considered the most powerful specific inhibitors of platelet activation in acute thrombosis. Glicoprotein IIb/IIIa inhibitor therapy could merit a prominent role also in the initial management of patients with acute ischemic stroke. Abciximab may be promising in this setting and should be evaluated in further clinical trials.

Anti-integrin as novel drug-discovery targets: potential therapeutic and diagnostic implications

The role of integrin and extracellular matrix proteins in various pathological processes (including angiogenesis, thrombosis, apoptosis and cell migration and proliferation), leading to both acute and chronic disease states (e.g. ocular diseases, metastasis, unstable angina, myocardial infarction, stroke, osteoporosis, a wide range of inflammatory diseases, vascular remodeling and neurodegenerative disorders) has been recently documented. A key success in this field is evident from the potential role of the platelet GPIIb/IIIa (alphaIIbbeta3) integrin in the prevention, treatment and perhaps diagnosis of various thromboembolic disorders. Additionally, progress has been shown in the development of leukocyte alpha4beta1 antagonists for various inflammatory indications and alphav integrin antagonists for angiogenesis and vascular-related disorders. However, the exact modes of action of certain integrin antagonists are still not fully clear. Integrin antagonists in clinical or pre-clinical development are expected to be used as a stand-alone therapy or, better, as an adjunct to other pharmacotherapy, radiotherapy or interventional procedures.

Reduction of N-hydroxylated compounds: amidoximes (N-hydroxyamidines) as pro-drugs of amidines

In order to examine the importance of metabolic cycles and in particular of reductions of N-hydroxylated compounds, the reversible metabolism at the amidine, guanidine, and amidinohydrazone nitrogen atoms of various drugs and model compounds was investigated. Many of these N-oxygenated metabolites are very easily reduced back into the starting materials. A comparison of the kinetic data for the N-hydroxylation and reduction suggests that the reduction should predominate in vivo. This could be verified by in vivo studies. Thus, N-hydroxylated amidines (amidoximes) can be used as pro-drugs of amidines. Because of their strong basicity, amidines, guanidines, and amidinohydrazones are protonated under physiological conditions, are very hydrophilic, and are usually not absorbed from the gastrointestinal tract. The N-hydroxylated derivatives of amidines (amidoximes), guanidines (N-hydroxyamidines), and amidinohydrazones (N-hydroxyamidinohydrazones) are less basic because of the introduction of the oxygen atom. They are absorbed from the gastrointestinal tract and then reduced to the active amidines, guanidines, and amidinohydrazones. The pro-drug principle was originally developed in our laboratory for pentamidine and then applied to other amidines such as sibrafiban and melagatran (ximelagatran). The enzymatic basis of N-oxidative processes is very well understood, whereas reductions have been less extensively investigated. We purified an enzyme system from pig and human liver consisting of cytochrome b5, its reductase, and a P450 enzyme, which is involved in the reduction of the N-hydroxylated compounds. Similar activities were found in all species studied so far. Furthermore, comparable reductive reactions could also be demonstrated with microsomal fractions from organs other than liver. In addition, mitochondria are highly capable of performing the reductions of these N-hydroxylated compounds. Thus, several organs and cell organelles are involved in the reduction explaining the extensive reduction of the pro-drugs in vivo underlying the suitability of the concept for drug development.

Safety, tolerability, pharmacokinetics, and time course of pharmacologic response of the active metabolite of roxifiban, XV459, a glycoprotein IIb/IIIa antagonist, following oral administration in healthy volunteers

Roxifiban is an esterprodrug that is hydrolyzed, after oral administration, to the active glycoprotein (GP) IIb/IIIa antagonist, XV459. The objectives of the study were to investigate the safety, tolerability, pharmacokinetics, and the time course of the pharmacologic response of XV459 in escalating doses of roxifiban and to assess the effect of age, loading dose of roxifiban, and aspirin pretreatment on XV459 pharmacokinetics, pharmacologic response, and safety profile in a five-part double-blind, placebo-controlled study. Healthy male volunteers (ages 18-46 years) received 7 (0.75-1.5 mg; n = 20) and 10 (0.75-1.0 mg; n = 8) multiple, oral, qd doses of roxifiban or placebo (n = 5). Healthy older male and female volunteers (ages 47-75 years) received roxifiban qd doses (0.5-0.75 mg; n = 8) or placebo (n = 3) for 7 days. Healthy male subjects (ages 18-46 years; n = 16) received a 1.5 or 1.0 mg loading dose either with or without pretreatment of 325 mg aspirin once daily for 3 days followed by single daily doses of 1.0 mg roxifiban for 6 days. Measurable plasma concentrations of XV459 appeared rapidly and were sustained throughout the dosing interval of 24 hours. The pharmacokinetics of XV459 were nonlinear. Systemic exposure of XV459 plateaued at the 1-mg dose level; plasma concentrations approached steady state in 4 to 6 days for doses greater than 1.0 mg. The time course of pharmacologic response as measured by the inhibition of platelet aggregation in response to an ex vivo 10 microM adenosine 5'-diphosphate (ADP) agonist correlated closely to the plasma concentration of XV459. Potent inhibition of ADP-induced platelet aggregation (IPA) persisted over the entire dosing interval. A clear dose response was achieved with roxifiban doses of 0.5 and 1.0 mg. For doses greater than 1.0 mg, a dose-proportional increase in IPA was not observed. Both the pharmacokinetics and pharmacologic response of XV459 exhibited low intraindividual variability (coefficient of variation [CV] < 15%) and higher interindividual variability (CV < 30%). Pretreatment with aspirin and/or a loading dose of 1.5 mg roxifiban had no significant effect on the pharmacokinetics and pharmacologic response of XV459. A dose-related increase in template bleeding time was observed at 1.25- and 1.5-mg doses of roxifiban, as compared to placebo. However, these bleeding time increases in the 1.25- and 1.5-mg dose groups were not significantly different from those at the lower dose groups. Overall, once-daily oral administration of roxifiban was fairly well tolerated and provided sustained systemic drug exposure and pharmacologic response over the entire administration interval.

The failure of orally administered glycoprotein IIb/IIIa inhibitors to prevent recurrent cardiac events

PURPOSE

Despite the success of intravenous glycoprotein IIb/IIIa antagonists, oral formulations have failed to show benefit and have been associated with increased mortality. To understand these findings, we performed a meta-analysis of results from four phase 3 trials.

SUBJECTS AND METHODS

Trials were identified by MEDLINE search; review of abstracts from American College of Cardiology, European Society of Cardiology, and American Heart Association scientific sessions; or querying investigators in the field. Published, phase 3, randomized, placebo-controlled trials involving more than 1000 patients with coronary artery disease that compared an oral glycoprotein IIb/IIIa antagonist with or without background aspirin versus aspirin, and that had a planned follow-up of > or =30 days, were included. Four trials met these criteria. Odds ratios (ORs) and 95% confidence intervals (CIs) were generated from results, and combined using an empirical Bayes random-effects model.

RESULTS

Among 33,326 patients, oral glycoprotein IIb/IIIa agents were associated with 31% increased mortality (OR = 1.31; 95% CI: 1.12 to 1.53; P= 0.0001). Results were similar whether the agent was added to (OR = 1.38; 95% CI: 1.15 to 1.67) or substituted for (OR = 1.37; 95% CI: 1.00 to 1.86) aspirin. Ischemic events or sudden death (OR = 1.22; 95% CI: 0.91 to 1.63) were also more common. Among patients with acute coronary syndromes, the incidence of myocardial infarction was increased (OR = 1.16; 95% CI: 1.03 to 1.29).

CONCLUSION

Oral glycoprotein IIb/IIIa inhibitor therapy is associated with increased mortality and myocardial infarction. No single explanation for these findings is satisfactory; the problem is likely to be multifactorial.

Differential efficacy of different platelet glycoprotein IIb/IIIa antagonists on platelet/fibrin-mediated clot dynamics under different conditions using thrombelastography: the critical need for anticoagulant

BACKGROUND

Intravenous GpIIb/IIIa antagonists demonstrate various significant clinical benefits depending on the agent used. In contrast, oral delivery of GpIIb/IIIa antagonists failed in achieving clinical benefits. This raises the question about the differences among different GpII/IIIa antagonists.

METHODS

The effect of various platelet glycoprotein (GP) IIb/IIIa antagonists on the dynamics of platelet/fibrin clot formation and strength was determined using thrombelastography under different conditions.

RESULTS

GPIIb/IIIa antagonists with high affinity for resting and activated platelets and with slow rates of dissociation from GPIIb/IIIa (Class I antagonists) demonstrated potent and comparable inhibition of platelet aggregation and platelet-mediated clot strength under different conditions. In contrast to antagonists that dissociate rapidly from GPIIb/IIIa (class II antagonists). Class I antagonists such as the free acid form of roxifiban inhibited platelet-mediated clot strength, with the inhibiting concentration required for 50% effect (IC50) = 70 n mol/l, whereas the IC50 of the class II antagonists such as the free acid forms of orbofiban, sibrafiban, lotrafiban, integrilin or aggrastat ranged from 1 to 15 micromol/l. The IC50s for class II antagonists in inhibiting platelet/fibrin clot formation and strength were substantially greater (10-15 fold) than their clinically achievable concentrations. The limited efficacy for class II antagonists in inhibiting platelet-mediated clot dynamics was enhanced by the combination with heparin.

CONCLUSIONS

Thus, these data indicated that there are differences in the efficacy of various GPIIb/IIIa antagonists in inhibiting platelet/fibrin clot formation and strength, which might be corrected by heparin. Data also suggest that inhibition of platelet aggregation may not be the sole determinant for the in-vivo efficacy of various GPIIb/IIIa antagonists.

The role of platelets in peripheral arterial disease: therapeutic implications

Peripheral arterial disease (PAD) is associated with platelet hyperaggregability as well as an increase in morbidity and mortality from myocardial infarction and stroke. Enhanced platelet activation in PAD may substantially contribute to these adverse outcomes. A relative resistance to aspirin therapy has been reported in patients with PAD. Therefore, clopidogrel may be superior to aspirin in treatment of PAD. Furthermore, the aspirin + clopidogrel combination could be more effective than monotherapy but its risk-benefit ratio has yet to be evaluated. Clopidogrel is preferable to ticlopidine because of its safer profile and the convenience of once-daily administration. The glycoprotein (Gp) IIb/IIIa inhibitors may also find a place as short-term therapy after peripheral angioplasty. There is a need to consider the use of clopidogrel in patients who cannot tolerate aspirin. Patients who have an event while taking aspirin also present a problem. One possibility here is to substitute aspirin with clopidogrel or to add clopidogrel to the aspirin. Although these options are currently not evidence based in patients with PAD, there is emerging evidence showing that they are realistic choices.

Monitoring of platelet function in the setting of glycoprotein IIb/IIIa inhibitor therapy

The role of the platelet in the pathogenesis of acute coronary syndromes is clearly established. In addition, the beneficial effects of oral and intravenous platelet inhibitor therapies were demonstrated in multiple, large, randomized clinical trials. However, despite these advances, current antiplatelet therapy fails to prevent coronary events in a substantial proportion of patients. One possible explanation for this phenomenon is that antiplatelet medications are administered without monitoring of the response to therapy. For example, oral antiplatelet therapy is administered as a standard dose for all patients, while intravenous inhibitors of the platelet glycoprotein (GP) IIb/IIIa receptor are dosed based on patient body weight. A major limitation of measuring platelet function has been that no practical test exists. The historic gold standard, bleeding time, was a very crude measure of platelet function with limited clinical utility. The current "gold standard," turbidimetric aggregometery, requires a central laboratory and is cumbersome to perform. Fortunately, a number of new tests with rapid turnaround time can be performed at the patient's bedside. This article discusses the details regarding the performance, advantages, disadvantages, and available data related to clinical use of each test in populations with coronary disease and patients treated with antiplatelet therapy.

Anti-platelet and anti-thrombotic effects of triacetylshikimic acid in rats

Because shikimic acid is the key intermediate in the shikimate pathway in plants and microorganisms, shikimic acid and its derivatives have been described as herbicides and anti-microbial agents. Triacetylshikimic acid (TSA) is an acetylate derivative of shikimic acid. The possible anti-platelet activity and anti-thrombotic efficacy of TSA were evaluated and its effect on arachidonic acid (AA) metabolism and second messengers including cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) was evaluated. After oral pretreatment with TSA, adenosine diphosphate (ADP)-, collagen-, and AA-induced rat platelet aggregation was inhibited ex vivo in a dose-dependent manner. In an arteriovenous-shunt thrombosis model, oral administration of TSA resulted in a dose-dependent inhibition of thrombus growth. TSA markedly increased the cAMP level and showed no effect on the cGMP level in rat platelets. Also, no significant changes in ADP-induced thromboxane B2 formation in rat platelets or 6-keto-prostaglandin F 1alpha production from the abdominal aorta were observed after oral administration of low and medium doses of TSA (12.5 and 50 mg/kg). Additionally, prothrombin time, activated partial thromboplastin time, and thrombin time were unchanged at effective anti-platelet doses of TSA. These results demonstrate that TSA exerts oral anti-platelet and anti-thrombotic efficacy without perturbation of systemic hemostasis in rats, which was partially concerned with the elevation of cAMP in platelets.

Antiplatelet and antithrombotic activity of RWJ-53308, a novel orally active glycoprotein IIb/IIIa antagonist

RWJ-53308 is a novel nonpeptide glycoprotein IIb/IIIa (GPIIb/IIIa) antagonist that inhibits fibrinogen binding to GPIIb/IIIa with an IC(50) of 0.4+/-0.3 nM. RWJ-53308 inhibits thrombin-induced platelet aggregation in human gel-filtered platelets (IC(50)=60+/-12 nM) and platelet aggregation in human platelet-rich plasma (PRP) in response to collagen, arachidonic acid, ADP, and SFLLRN-NH(2) (IC(50)=60+/-10, 150+/-30, 70+/-4, and 160+/-80 nM, respectively). The potency of RWJ-53308 in dog and guinea pig PRP is similar to human PRP. RWJ-53308 inhibits ex vivo collagen- and ADP-induced platelet aggregation in conscious dogs for up to 4 h following 0.3 mg/kg iv, and through 4 and 6 h following 1 and 3 mg/kg po. Oral bioavailability is 16+/-7%. RWJ-53308 reduces thrombus weight in a canine arteriovenous (AV) shunt model following intravenous (0.01-0.1 mg/kg) and oral (3 mg/kg) administration. In a guinea pig carotid artery pinch-injury model, RWJ-53308 completely suppresses thrombus-induced cyclic flow reductions (CFR) at 0.7 mg/kg iv. RWJ-53308 also blocks thrombus formation in photoactivation- and ferric chloride-induced models of thrombosis in guinea pigs at 0.3 and 1 mg/kg iv, respectively. In summary, RWJ-53308 is a potent orally active GPIIb/IIIa antagonist that may be useful for both acute and chronic treatment of arterial thrombotic disorders.

Comparison of the effect of different platelet GPIIb/IIa antagonists on the dynamics of platelet/fibrin-mediated clot strength induced using thromboelastography

The effect of various platelet glycoprotein IIb/IIIa (GPIIb/IIIa) antagonists on the dynamics of platelet-fibrin clot formation and strength induced by various stimuli was measured by thromboelastography (TEG). GPIIb/IIIa antagonists with high affinity for resting and activated platelets and with slow rates of dissociation from GPIIb/IIIa (Class I antagonists) demonstrated potent and comparable inhibition of platelet aggregation and tissue factor (TF), lipopolysaccharide (LPS), Factor Xa, and thrombin-induced clot strength, in contrast to antagonists that dissociate rapidly from GPIIb/IIIa (Class II antagonists). For example, the Class I antagonist XV459 (the free acid form of roxifiban) inhibited TF, endotoxin, Factor Xa, and thrombin-induced maximal clot strength and platelet aggregation with an IC(50)=30-70 nM, whereas the IC(50) of the Class II antagonist YZ211 (the free acid form of sibrafiban) for altering clot formation and strength was 0.3-4.7 microM. Moreover, the IC(50)'s of sibrafiban, and another Class II antagonist, orbofiban, for inhibiting platelet-fibrin clot formation and strength were substantially greater than their clinically achievable concentrations. Further, although aspirin treatment improved the efficacy of all GPIIb/IIIa antagonists, it did not alter the differences between Classes I and II antagonists. Thus, these data indicate that there are differences in the efficacy of various GPIIb/IIIa antagonists in inhibiting platelet-fibrin clot formation and strength. They also suggest that inhibiting platelet aggregation may not be the sole determinant for the in vivo efficacy of various GPIIb/IIIa antagonists.

Comparison of GP IIB/IIIA inhibitors and their activity as measured by aggregometry, flow cytometry, single platelet counting, and the rapid platelet function analyzer

BACKGROUND

GP IIb/IIIa inhibitors have primarily been used short-term e.g., during PTCA. They failed to show clinical benefit during long-term therapy. One reason might be the absence of a method to monitor inhibitor activity. This study compared platelet aggregometry, the rapid platelet function analyzer (RPFA) test, single platelet counting, and flow cytometric determination of receptor occupancy to measure GP IIb/IIIa-receptor inhibitor activity.

METHODS

Increasing doses of abciximab, tirofiban, and eptifibatide were added to whole blood in vitro. Whole blood was used for the RPFA, for single platelet counting and flow cytometry. Platelet rich plasma was prepared for aggregometry.

RESULTS

The correlation between aggregometry and RPFA results was linear for abciximab and eptifibatide. Tirofiban was a stronger inhibitor with the RPFA (IC(50) 7.7nM) than with aggregometry (IC(50) 19.6nM). The single platelet counting technique showed that even supratherapeutic concentrations of all three inhibitors could not completely suppress microaggregation. Abciximab concentrations that were equipotent to tirofiban with aggregometry were less potent with regards to the inhibition of microaggregation. This difference was more pronounced with TRAP induced microaggregation than with ADP. The flow cytometric receptor occupancy test showed that occupancy was 95% with 5 microg/ml abciximab and almost 97% with 10 microg/ml. Tirofiban reached a maximum receptor occupancy of 56%, eptifibatide 64%.

CONCLUSIONS

While aggregometry is time consuming the RPFA provides results fast and with little variability. There is still a discrepancy between aggregometry and RPFA results for tirofiban. The single platelet counting technique detects the inhibition of microaggregation the relevance of which for the clinical outcome is not known. The flow cytometric receptor occupancy assay is best suited for abciximab.

Oral glycoprotein IIb/IIa antagonists for unstable angina--is there still a chance for the oral substances?

The intravenous glycoprotein IIb/IIIa antagonists abciximab, tirofiban and eptifibatide are well accepted for the therapy of patients with unstable angina and/or as concomitant medication during coronary interventions. Despite the fact that these drugs are not used in all patients presenting with unstable angina during coronary interventions, the scientific evidence is overwhelming including the substantial reduction in mortality 3 years after utilisation of abciximab for coronary interventions in patients with unstable angina. In addition to these two indications, intravenous glycoprotein IIb/IIIa antagonists are currently being investigated for use in patients undergoing carotid artery interventions, peripheral arterial interventions and stroke, as well as adjunct therapy in patients undergoing fibrinolytic therapy during acute myocardial infarction. In contrast, the large trials being performed in patients with unstable angina and following coronary interventions using oral glycoprotein IIb/IIIa antagonists have been very disappointing. There were only minor therapeutic effects detectable, resulting in a slight reduction in ischemic cardiac events in some investigations, however, in all studies, there was a slight trend towards an increased mortality in the glycoprotein IIb/IIIa receptor-antagonist-treated group of patients. In meta-analysis, an approximately 35% relative increase in mortality has been calculated for patients being treated long term with the oral glycoprotein antagonists. The reason for this therapeutic failure is still unknown, however, the limited bioavailability of these drugs, together with our still very limited knowledge about the regulation of the platelet fibrinogen receptor, may be partially responsible for this therapeutic failure. Other compounds with improved pharmacokinetic properties are currently in clinical development.

Platelet GPIIb/IIIa binding characteristics of small molecule RGD mimetic: distinct binding profile for Roxifiban

A number of non-peptide orally active RGD mimetic prodrug such as Orbofiban, Sibrafiban, SR121566, Roxifiban and others entered into the clinical evaluation stage. Some of these agents were terminated and some are still in clinical trials. The present study examined the platelet GPIIb/IIIa binding profiles for the active form of Roxifiban, Sibrafiban, SR121566 and Orbofiban using 3H-Roxifiban active form (XV459), 3H-DMP728, 125I-Echistatin, and 125I-Fibrinogen. Either DMP728, Orbofiban, Sibrafiban, SR121566 or Roxifiban active form as well as other RGD mimetic bind to the same binding site(s) on human platelets as evident from the competitive inhibition of binding of each other to human platelet. Additionally, Roxifiban active form competed with FITC labeled GPIIb/IIIa antagonist cyclic RGD peptidomimetic (XL086) as demonstrated using confocal microscopy technique. Roxifiban active form (XV459) demonstrated the highest potency in inhibiting 3H-XV459, 3H-DMP728, 125I-Echistatin, and 125I-Fibrinogen binding to human platelets as compared to the others. Structure activity relationship within the isoxazoline Roxifiban series showed that substituent at the alpha-carbon next to the carboxy terminal represents an exosite for the affinity binding to human platelets leading to slow platelet dissociation rate. These data indicated a distinct binding profile for Roxifiban (high affinity to both activated and resting platelets associated with a relatively slow K(off)) as compared to others. These differences might determine the pharmacodynamics and pharmackokinetics of the different GPIIb/IIIa antagonists.

UR-3216: a manageable oral GPIIb/IIIa antagonist

UR-3216, a prodrug, is a novel, selective, and orally active platelet surface glycoprotein (GPIIb/IIIa) receptor antagonist. The most important property of UR-3216 is the very tight binding of its active metabolite to platelets (Ki for resting platelets is < 1 nM). UR-2992, the active form of UR-3216, binds to platelets for a long period of time, while the unbound drug is rapidly cleared. Therefore, after an initial loading dose of 0.1 mg/kg, only once daily repeated low maintenance doses of UR-3216 (< 0.05 mg/kg p.o.) are required. This regimen maintains a high level of inhibition of platelet aggregation and, due to a small peak-to-trough ratio, severe bleeding is avoided. The therapy with UR-3216 is easy to manage, because it has low peak-to-trough ratio and high efficacy (> 80% inhibition of platelet aggregation). In addition, UR-3216 does not produce excessive bleeding or thrombocytopenia and does not interact with abciximab. UR-3216 is excreted mostly in bile, so that it will not accumulate in patients with chronic renal dysfunction. UR-2316 has the following abciximab-like features: (a) its half-lives for residence on platelets, inhibition of platelets aggregation and bleeding time prolongation are 60 to 80 h, 24, and 2 h, respectively; (b) its receptor binding occupancy is similar to that of abciximab (Mab1 is inhibited and Mab2 is unaltered). In conclusion, UR-3216 is a promising, orally active GPIIb/IIIa antagonist for the treatment of cardiovascular diseases.

Glycoprotein IIb/IIIa antagonists and low-molecular weight heparin in acute coronary syndromes

The glycoprotein (GP) IIb/IIIa antagonists and the low-molecular weight heparins are the newest additions to the armamentarium of antiplatelet drugs for the treatment of acute coronary syndromes. They are extremely potent inhibitors of platelet aggregation and thrombin generation, respectively. There are currently three GP IIb/IIIa inhibitors (abciximab, eptifibatide, and tirofiban) and two low-molecular weight heparins (dalteparin and enoxaparin) approved for use with acute coronary syndromes. Data continue to accumulate outlining the specific roles for these drugs in the treatment of patients with acute coronary syndromes. Clinical trials in patients with acute coronary syndromes have demonstrated that the GP IIb/IIIa antagonists and low-molecular weight heparins offer significant benefit with acceptable safety profiles. Future issues that need to be addressed include refinement of indications for administration and patient selection, comparison between existing agents, evaluation of newer agents, and optimization of dosing to maximize benefit and safety in the use of these powerful new classes of drugs.