History of drugs for thrombotic disease. Discovery, development, and directions for the future

New antithrombotic drugs: potential for use in oncology

For more than 50 years, heparin and vitamin K antagonists (VKAs) have been the anticoagulant drugs used to prevent and treat thrombosis. Low molecular weight heparins (LMWHs) are more recent and have been available for approximately 20 years. Patients with cancer are members of a unique patient population because of their high risk for thrombosis and the risk of anticoagulant-related bleeding. With the currently available antithrombotic agents, patients with cancer still have unmet needs in terms of the prevention and treatment of thrombosis. Although long-term LMWH is the treatment of choice for patients with cancer who have acute, symptomatic venous thromboembolism (VTE), some patients still experience recurrent VTE. More effective antithrombotic agents are needed for such patients. Convenient (ie, oral and with no laboratory monitoring), effective, and safe agents are needed to prevent thrombosis in patients taking chemotherapy and antiangiogenic drugs and in patients with central vein catheters. There are a number of new antithrombotic agents that have been studied in recent years and will soon be available for certain diseases. They target either activated factor X (ie, factor Xa) or activated thrombin, and some of them have potential therapeutic value in patients with cancer. In this article, the clinical research model used for the development of a new antithrombotic agent is discussed along with the results of recent trials that evaluate these new agents in high-risk populations.

Combination antiplatelet therapy for secondary stroke prevention: enhanced efficacy or double trouble?

The evaluation of antithrombotic agents for secondary stroke prevention has focused on stroke reduction. The aim of this analysis was to focus specifically on the increase in bleeding risk. The annualized rates of total and major bleeding events in secondary stroke prevention trials of antithrombotics were assessed and cross compared. A Medline search for major randomized clinical studies with a follow-up duration of > or =1 year identified 13 studies. Pooled data sets were used to compare mean bleeding rates for aspirin (< or =325 mg/day), clopidogrel, anticoagulants (warfarin and other vitamin K antagonists), aspirin plus clopidogrel, and aspirin plus extended-release dipyridamole (ER-DP). Total bleeding occurred at mean rates of 4.8% with aspirin (< or =325 mg/day) alone, 2.9% with clopidogrel alone, 3.6% with aspirin plus ER-DP, 10.1% with aspirin plus clopidogrel, and 16.8% with anticoagulation. Major bleeding occurred at mean rates of 1% with aspirin (< or =325 mg/day) alone, 0.85% with clopidogrel, 0.93% with aspirin plus ER-DP, 1.7% with aspirin plus clopidogrel, and 2.5% with anticoagulation. In conclusion, the combination of aspirin and clopidogrel is associated with significantly greater bleeding than either aspirin (< or =325 mg/day) or clopidogrel alone. Aspirin plus ER-DP has a greater bleeding rate than clopidogrel but a lower rate than aspirin (< or =325 mg/day) alone.

Reduced paxillin expression contributes to the antimetastatic effect of 4-hydroxycoumarin on B16-F10 melanoma cells

BACKGROUND

4-Hydroxycoumarin (4-HC) is a coumarin that lacks anticoagulant activity. 4-HC affects the cytoskeletal stability and decreases cell adhesion and motility of the melanoma cell line B16-F10. Together with integrins and other cytoskeletal proteins, paxillin participates in the regulation of cell adhesion and motility, acting as an adapter protein at focal adhesions. The present study determined the participation of paxillin in the reported effects of 4-HC and analyzed the role of paxillin in the formation of melanoma metastases.

RESULTS

4-HC decreased protein and mRNA levels of alpha- and beta-paxillin isoforms in B16-F10 cells. Paxillin downregulation correlated with an inadequate translocation of paxillin to focal adhesions and a reduced phosphotyr118-paxillin pool. Consequently, 4-HC altered paxillin-mediated signaling, decreasing the phosphorylation of FAK and the level of GTP-bound Rac-1. These results partially explain the mechanism of the previously reported effects of 4-HC. Additionally, we studied the effect of 4-HC on metastatic potential of B16-F10 cells through experimental metastasis assays. In vitro treatment of cells with 4-HC inhibited their capability to originate pulmonary metastases. 4-HC did not affect cell proliferation or survival, demonstrating that its antimetastatic effect is unrelated to changes on cell viability. We also studied the importance of paxillin in metastasis by transfecting melanoma cells with paxillin-siRNA. Transfection produced a modest reduction on metastatic potential, indicating that: i) paxillin plays a role as inducer of melanoma metastasis; and ii) paxillin downregulation is not sufficient to explain the antimetastatic effect of 4-HC. Therefore, we evaluated other changes in gene expression by differential display RT-PCR analysis. Treatment with 4-HC produced a downregulation of Adhesion Regulating Molecule-1 (ARM-1), which correlated with a decreased adhesion of melanoma cells to lung slides.

CONCLUSION

This study shows that reduced paxillin expression is associated with the impaired cell adhesion and motility seen in 4-HC-treated cells and partially contributes to the antimetastatic effect of 4-HC. In contrast, the role of ARM-1 reduced expression in the effects of 4-HC is still to be clarified. The antimetastatic effect of 4-HC suggests that this compound, or others with similar mode of action, might be useful for the development of adjuvant therapies for melanoma.

Advancement in antithrombotics for stroke prevention in atrial fibrillation

The focus of this review is the evolving field of antithrombotic drug therapy for stroke prevention in patients with atrial fibrillation (AF). The current standard of therapy includes warfarin, acenocoumarol and phenprocoumon which have proven efficacy by reducing stroke by 68% against placebo. However, a narrow therapeutic index, wide variation in metabolism, and numerous food and drug interactions have limited their clinical application to only 50% of the indicated population. Newer agents such as direct thrombin inhibitors, factor Xa inhibitors, factor IX inhibitors, tissue factor inhibitors and a novel vitamin K antagonist are being developed to overcome the limitations of current agents. The direct thrombin inhibitor dabigatran is farthest along in development. Further clinical trial testing, and eventual incorporation into clinical practice will depend on safety, efficacy and cost. Development of a novel vitamin K antagonist with better INR control will challenge the newer mechanistic agents in their quest to replace the existing vitamin K antagonists. Till then, the large unfilled gap to replace conventional agents remains open. This review will assess all these agents, and compare their mechanism of action, stage of development and pharmacologic profile.

Tabebuia avellanedae extracts inhibit IL-2-independent T-lymphocyte activation and proliferation

In order to identify new, immune modulating compounds, aqueous extracts of plants pre-selected on ethno-pharmacological knowledge were screened for inhibitory effects in an anti-CD3 driven lymphocyte proliferation assay (MTT-assay). We found for the extract of the inner bark of Tabebuia avellanedae (Tabebuia) dose dependent and reproducible inhibitory effects on lymphocyte proliferation. We further analyzed Tabebuia in flow cytometry based whole blood T-cell function assays. We found that Tabebuia inhibited dose dependent ConA stimulated T-cell proliferation. Decreased T-lymphocyte proliferation was associated with dose dependent reduction of CD25 and CD71 expression on T-lymphocytes. In contrast Tabebuia exerted no effects on cytokine expression (Il-2 and TNF-alpha) by PMA/Ionomycin stimulated T-lymphocytes. Concentrations of Tabebuia used were not toxic for lymphocytes as verified by trypan blue exclusion assay. Further experiments showed that the immune inhibitory effects by Tabebuia were not mediated by its pharmacological lead compound beta-lapachone and only observed in aqueous but not in ethanol plant extracts.

Emergency department management of the salicylate-poisoned patient

Salicylate toxicity continues to be encountered commonly in emergency medicine. This article portrays the signs and symptoms of salicylate toxicity, reviews the erratic absorption and elimination kinetics, describes the devastating physiologic effects of overdose, and illustrates the potentially subtle manifestations of chronic aspirin toxicity.

Place of drug therapy in the treatment of carotid stenosis

Carotid stenosis is an important cause of transient ischaemic attacks and stroke. The cause of carotid stenosis is most often atherosclerosis; contributing to the pathogenesis of the lesion are endothelial injury, inflammation, lipid deposition, plaque formation, fibrin, platelets and thrombin. Carotid stenosis accounts for 10-20% of cases of brain infarction, depending on the population studied. Despite successful treatment of selected patients who have had an acute ischaemic stroke with tissue plasminogen activator and the promise of other experimental therapies, prevention remains the best approach to reducing the impact of ischaemic stroke. High-risk or stroke-prone patients can be identified and targeted for specific interventions. At this juncture, treatment of carotid stenosis is a well established therapeutic target and a pillar of stroke prevention. There are two main strategies for the treatment of carotid stenosis. The first approach is to stabilise or halt the progression of the carotid plaque through risk factor modification and medication. Hypertension, diabetes mellitus, smoking, obesity and high cholesterol levels are closely associated with carotid stenosis and stroke; control of these factors may decrease the risk of plaque formation and progression. The second approach is to eliminate or reduce carotid stenosis through carotid endarterectomy or carotid angioplasty and stenting. Carotid endarterectomy, which is the mainstay of therapy for severe carotid stenosis, is beyond the scope of this review. Anticoagulants seem to play little role (if any) in the medical (i.e. non-surgical) treatment of carotid stenosis. Adoption of a healthy lifestyle combined with the reduction of risk factors has been shown to lead to a reduction in the extent of carotid stenosis. The medical treatment of carotid stenosis should be based on the triad of the reduction of risk factors, patient education, and use of antiplatelet agents.

Ximelagatran: An orally active direct thrombin inhibitor

PURPOSE

The chemistry, pharmacology, pharmacokinetics, clinical efficacy, dosage and administration, contraindications, and adverse effects of ximelagatran are reviewed.

SUMMARY

Ximelagatran is the first orally active direct thrombin inhibitor to be tested in Phase III clinical trials. After oral administration, ximelagatran is rapidly converted to its active metabolite, melagatran. Melagatran (after oral ximelagatran administration) predictably inhibits thrombin function without need for routine anticoagulation monitoring. Melagatran effectively inhibits both free and clot-bound thrombin-a potential pharmacodynamic advantage over heparin products. Melagatran has a half-life of 2.4-4.6 hours, necessitating twice-daily administration. Melagatran is primarily eliminated by the kidneys and has not been studied clinically in patients with severe renal failure. Ximelagatran has undergone 10 Phase III trials (6 for prophylaxis of venous thromboembolism [VTE] due to orthopedic surgery, 1 for initial treatment of VTE, 1 for long-term prevention of VTE recurrence, and 2 for stroke prophylaxis due to atrial fibrillation). Results were generally positive. AstraZeneca applied in December 2003 for marketing approval of ximelagatran for prevention of VTE after total knee replacement surgery, long-term prevention of VTE recurrence after standard therapy, and stroke prevention due to atrial fibrillation. FDA denied approval of ximelagatran for all indications, mainly because of increased rates of coronary artery disease events in ximelagatran recipients in some studies and the possibility of hepatic failure when the medication is used for long-term therapy.

CONCLUSION

Ximelagatran has shown promise as a possible alternative to warfarin and other anticoagulants but will require further study to ensure its safety.

Direct thrombin inhibitors: pharmacology and clinical relevance

Although heparin has been a cornerstone of treatment for the prevention of thrombosis, it is limited by its adverse effects and unpredictable bioavailability. Direct thrombin inhibitors are a novel class of drugs that have been developed as an effective alternative mode of anticoagulation in patients who suffer from heparin-induced thrombocytopaenia, and for the management of thromboembolic disorders and acute coronary syndromes. The main disadvantages of the direct thrombin inhibitors are the lack of an antidote or readily available clinical monitoring. The mechanism of action, the properties of direct thrombin inhibitors and their potential to replace currently available anticoagulants are reviewed.

Allergy to heparin: a new in vitro diagnostic technique

INTRODUCTION

Few descriptions of allergic reactions to heparin have been published, because these reactions are not well known, their prevalence is low and they are difficult to diagnose due to the lack of an in vitro test until now. We propose a new technique, the basophil activation test (BAT) for the diagnosis of these reactions.

METHODS AND RESULTS

We performed in vivo and in vitro studies with heparin and its derivatives in two patients with heparin-induced acute urticaria. In both patients the results of prick tests with sodium and calcium heparin, enoxaparin and nadroparin with immediate reading were negative. Intradermal skin tests with immediate reading and reading at 48 and at 96 hours with calcium heparin, enoxaparin and nadroparin were positive in the immediate reading and after 48 hours in the first patient. The second patient showed positivity to nadroparin in the immediate reading. The same drugs were also tested using patch tests, with reading after 48 and 72 hours. The second patient showed positivity to nadroparin after 48 hours. The BAT was positive to enoxaparin in the first patient and revealed showed slight positivity to sodium heparin in the second patient.

CONCLUSIONS

We consider the BAT to be a useful, safe and reliable test for the in vitro diagnosis of heparin allergy. This test avoids the use of provocation tests, which present a risk to the patient.

First-generation agents: aspirin, heparin and coumarins

Aspirin, heparin and the coumarins are the classical anti-thrombotic agents. They represent the platform upon which newer drugs holding the promise of greater efficacy and less toxicity are being developed. Even as such newer drugs arrive into clinical practice, the older agents remain remarkable for their decades-long pre-eminence. All derive from natural sources, and none from a search for therapeutic anti-thrombotic agents; they have saved countless lives but also served as essential probes into basic mechanisms of thrombosis. Testament to their clinical importance is that these agents are the only drugs profiled on a regular basis in special scientific statements by the American Heart Association/American College of Cardiology and by the American College of Chest Physicians. This chapter reviews their biology, uses and limitations.

Ximelagatran

Although there have been many significant advances over the last 50 years with regards to anticoagulant therapy, warfarin remains the definitive standard for the long-term prevention of thromboembolic events in many patients at risk for these complications. Although effective, warfarin has a narrow therapeutic window, necessitating frequent laboratory monitoring for anticoagulant effect. Ximelagatran is an investigational anticoagulant that directly inhibits thrombin, unlike heparin or warfarin, which are indirect inhibitors. Although indirect thrombin inhibitors are mainly only effective at inhibiting circulating thrombin, direct thrombin inhibitors are able to inhibit both free and clot-bound thrombin, thereby producing more effective anticoagulation. Ximelagatran is the first orally available direct thrombin inhibitor to reach phase 3 clinical trials. Ximelagatran is a prodrug for the active metabolite melagatran, and has been demonstrated to have a relatively wide therapeutic window in terms of bleeding and antithrombotic effect compared with warfarin. Clinical studies have demonstrated ximelagatran to be comparable in efficacy to warfarin and low-molecular-weight heparins (LMWH) for prophylaxis of venous thromboembolism, comparable to warfarin for stroke prevention in the setting of atrial fibrillation, and, when combined with aspirin, possible more effective than aspirin alone at preventing major adverse cardiovascular events in patients with a recent myocardial infarction. Adverse effects with ximelagatran primarily involve bleeding complications, which are more frequent than with placebo, but appear comparable to those occurring with standard anticoagulant treatment (ie, warfarin and LMWH). Ximelagatran has also been demonstrated to cause transient increases in liver enzymes, the significance of which will need to be addressed in ongoing phase 3 studies. Should ongoing trials prove ximelagatran to have at least similar therapeutic efficacy and safety as warfarin, ximelagatran may become a first-line anticoagulant due to its ease of administration and lack of a need for drug monitoring. The results of these trials are eagerly awaited in helping to defining the place in therapy for this promising new agent.

The role of eicosanoids, cyclooxygenases, and nonsteroidal anti-inflammatory drugs in colorectal tumorigenesis and chemoprevention

There is mounting evidence from studies on experimental cancer in rodents, interventional studies in patients with familial adenomatous polyposis, and some, but not all, epidemiologic investigations, that suggests a chemopreventive effect of aspirin and nonaspirin nonsteroidal anti-inflammatory drugs (NSAIDs) against colorectal cancer. In addition, the mechanisms by which these agents modulate tumorigenesis are being elucidated in laboratory experiments. Currently available NSAIDs are unlikely to have an acceptable benefit-to-risk ratio for long-term use in an asymptomatic population. Once the discrete chemopreventive mechanisms are established and the genetic background and risk factor profile of individuals who will benefit from chemoprevention are clarified, a low-dose combination of NSAIDs with different targets may optimize efficacy and minimize toxicity. At present, however, colectomy is still the treatment of choice for patients with familial adenomatous polyposis, and early screening and regular surveillance colonoscopies are the choices for those at risk for hereditary nonpolyposis colorectal cancer. In the average-risk individual, endoscopic screening and surveillance will remain the core of efforts to prevent sporadic colorectal cancer.

Seizure activity and unresponsiveness after hydroxycut ingestion

A 22-year-old man was hospitalized after unexplained seizure-like activity and unresponsiveness. A urine toxicology screen was negative for salicylates, acetaminophen, alcohol, and drugs of abuse. Medical history was insignificant with the exception of recent (within 2 wks) ingestion of Hydroxycut is a dietary supplement purported to be energy enhancing, muscle building, and fat burning. The agent contains ephedra alkaloids and caffeine, which are both central nervous system stimulants; the etiology of seizure was attributed to their consumption. Due to a significant number of reported adverse events, the United States Food and Drug Administration (FDA) proposed regulations for dietary supplements containing ephedra alkaloids and requested an independent review of case reports linked to these products. Because herbal products are not subject to the same rigorous FDA regulations required for prescription and over-the-counter products, consumers unknowingly risk adverse effects when taking these products. Questioning patients about consumption of herbal products should be part of routine medical visits.

Antiplatelet and anticoagulant effects of "HN-11 500," a selective thromboxane receptor antagonist

The antiplatelet and anticoagulant effect of a thromboxane receptor (TX receptor) antagonist developed by Nycomed (Linz) has been studied in a placebo-controlled double-blind phase I study. Sixteen healthy male volunteers received different single oral doses of "HN-11 500" (C(14)H(15)NO(5)S(2); 1, 10, 100, 200, and 400 mg). Eight volunteers received placebo. The washout period between each dosage applied was at least 12 days. Platelet aggregation induced by the thromboxane mimetic "U 46 619" (C(21)H(34)0(4)) and platelet adhesion to siliconized glass were significantly and dose-dependently inhibited. The effect lasted between 3 and 4 h (10 mg) and 8 h (400 mg), respectively, and correlated well with the pharmacokinetic data. Platelet aggregation seems to be more sensitive to monitor the effects of HN-11 500 on platelet function than platelet adhesion. Plasma levels of 300 ng/ml HN-11 500 probably leads to >90% inhibition of platelet aggregation. The template bleeding time slightly increased but did not exceed the normal range. Furthermore, there was a wide variation of results. There were no significant changes in platelet counts, platelet-induced thrombin generation time (PITT), and blood coagulation parameters. All doses of HN-11 500 were well tolerated. HN-11 500 is a potent TX receptor antagonist (TXRA), which inhibits either platelet aggregation or platelet adhesion, which has not yet been described. In clinical routine, TXRAs have to demonstrate the effectiveness in large clinical trials for different clinical indications and to compete with single or combined administrations of cyclooxygenase (COX) inhibitors, thienovridines, thromboxane synthase inhibitors, and GIIb/IIIa inhibitors.

The role of adenosine 5'-diphosphate receptor blockade in patients with cardiovascular disease

Aspirin, which has been the mainstay of antiplatelet agent for many decades, affects a single pathway in the platelet activation process and provides incomplete protection against cardiovascular events. Aspirin also may blunt the hemodynamic effect of angiotensin-converting enzyme inhibitors. Dipyridamole may provide some additional benefit, but there is little evidence to suggest its superiority alone or in combination with aspirin compared to standard doses of aspirin. Oral platelet glycoprotein IIb/IIIa inhibitors, although initially promising, have had disappointing results in recent clinical studies. A new class of medications, the thienopyridines, blocks the activity of platelet adenosine 5'-diphosphate (ADP) receptors, thereby reducing platelet activation. This review discusses the pharmacology, clinical studies, and potential uses of these agents, which include ticlopidine and clopidogrel. ADP inhibitors, by blocking an alternate pathway of platelet activation, are slightly more effective than aspirin in reducing cardiovascular events.

Development of oral heparin therapy for prophylaxis and treatment of deep venous thrombosis

OBJECTIVE

To review the current research and published literature regarding the development of oral heparin therapy for the prophylaxis and treatment of deep venous thrombosis.

BACKGROUND

Currently, the accepted practice of prophylaxis and/or treatment of acute deep venous thrombosis (DVT) is intravenous or subcutaneous (SQ) heparin followed by oral warfarin or SC low molecular weight heparin (LMWH) therapy followed by warfarin. Both of which are less than ideal. More recently, advances have been made towards an effective oral heparin preparation that would resolve many of the drawbacks to the current therapies.

METHODS

A review of the current and relevant English literature identified via a search of the Medline database from January 1990 to present.

RESULTS

Initial oral heparin therapy for DVT was unsuccessful due to presumed inadequate intestinal absorption as a result of heparin's molecular and structural characteristics. The development of oral heparin therapy, based on combining heparin with the carrier molecule Sodium N-(8[2-hydroxybenzoyl]amino) caprylate (SNAC) to enhance its intestinal absorption and bioavailability for the prophylaxis and treatment of DVT has been demonstrated to be effective in animal models. More recent efforts have been aimed at human trials.

CONCLUSION

Recent advances in prophylaxis and treatment of DVT have stimulated great interest among researchers to develop an effective, convenient, and well tolerated oral therapy. An effective oral heparin therapy may represent an ideal method of prophylaxis and treatment of DVT.

Exploiting human genetic variation in drug discovery and development

'The right drug for the right patient at the right time'Is this a realistic goal for today's pharmaceutical industry and tomorrow's medical practitioner? Or merely an over-simplistic refrain that can only ever be an unfulfilled dream? Here we discuss the reality behind the dream and illustrate how the analysis of genetic variation is a complex science that has the capacity to make significant contributions to drug discovery and development strategies. An understanding of the impact of human variation must be a central consideration in the future practice of pharmaceutical R&D.

[Aspirin and hemostasis]

Aspirin is one hundred years old, though its use has clearly evolved during the last 25 years. Identifying its action mechanism has allowed us to better understand the antithrombotic impact. Prostaglandin H synthetase (PGHS) is a bifunctional enzyme with cyclooxygenase and peroxydase activities. There are two isoforms: constitutive PGHS-1 and inducible PGHS-2. Aspirin irreversive acetylates the platelet cyclooxygenase involved in the formation of thromboxane A2, a powerful proaggregating agent and vasoconstrictor. More than 95% of inhibition of this synthesis takes place in two to three days using very weak doses of aspirin, on the order of 30 to 50 mg per day. Under some circumstances, this inhibition requires higher dosages. Certain clinical and biological circumstances could lead to a resistance to aspirin, making a readjustment of doses and sometimes complementary explorations necessary. The ISIS 2 study showed in an apparently irrefutable way the entry of aspirin into the antithrombotics arsenal, with a significant risk reduction of vascular death and recurrence of infarctus. Numerous studies have confirmed this efficacy. Consensus studies are based on information showing total coherence between the dose necessary to acetylate the enzyme to inhibit thromboxane A2 platelet production and the clinical antithrombotic effect. Aspirin seems to have a secure place, and it begins the third millennium in relative peace with new extra-platelet potentialities outside the framework of hemostasis and thrombosis.

[Aspirin throughout the ages: a historical review]

Even at the beginning of the next millennium, aspirin will still offer surprises. Its relatively young pharmacological history compares with the early use of salicylate-containing plants since antiquity. The Assyrians and the Egyptians were aware of the analgesic effects of a decoction of myrtle or willow leaves for joint pains. Hippocrates recommended chewing willow leaves for analgesia in childbirth and the Reverend Edward Stones is acknowledged as the first person to scientifically define the beneficial antipyretic effects of willow bark. At the beginning of the 19th century salicin was extracted from willow bark and purified. Although a French chemist, Charles Gerhardt, was the first to synthesize aspirin in a crude form, the compound was ignored, and later studied by Felix Hoffmann. He reportedly tested the rediscovered agent on himself and on his father, who suffered from chronic arthritis--a legend was born and Bayer Laboratories rose to the heights of the pharmacological world. First used for its potent analgesic, antipyretic and anti-inflammatory properties, aspirin was successfully used as an antithrombotic agent. Sir John Vane elucidated aspirin's active mechanism as an inhibitor of prostaglandin synthetase and received the Nobel Price in Medicine for this work in 1982. Two isoform of cyclooxygenase (COX-1 and COX-2) have now been identified, each possessing similar activities, but differing in characteristic tissue expression. The cox enzyme is now a target of drug interventions against the inflammatory process. After two centuries of evaluation, aspirin remains topical, and new therapeutic indications are increasingly being studied.

Enhancement of heparin cofactor II anticoagulant activity

Heparin cofactor II (HCII) is a serpin whose thrombin inhibition activity is accelerated by glycosaminoglycans. We describe the novel properties of a carboxyl-terminal histidine-tagged recombinant HCII (rHCII-CHis(6)). Thrombin inhibition by rHCII-CHis(6) was increased >2-fold at approximately 5 microgram/ml heparin compared with wild-type recombinant HCII (wt-rHCII) at 50-100 microgram/ml heparin. Enhanced activity of rHCII-CHis(6) was reversed by treatment with carboxypeptidase A. We assessed the role of the HCII acidic domain by constructing amino-terminal deletion mutants (Delta1-52, Delta1-68, and Delta1-75) in wt-rHCII and rHCII-CHis(6). Without glycosaminoglycan, unlike wt-rHCII deletion mutants, the rHCII-CHis(6) deletion mutants were less active compared with full-length rHCII-CHis(6). With glycosaminoglycans, Delta1-68 and Delta1-75 rHCIIs were all less active. We assessed the character of the tag by comparing rHCII-CHis(6), rHCII-CAla(6), and rHCII-CLys(6) to wt-rHCII. Only rHCII-CHis(6) had increased activity with heparin, whereas all three mutants have increased heparin binding. We generated a carboxyl-terminal histidine-tagged recombinant antithrombin III to study the tag on another serpin. Interestingly, this mutant antithrombin III had reduced heparin cofactor activity compared with wild-type protein. In a plasma-based assay, the glycosaminoglycan-dependent inhibition of thrombin by rHCII-CHis(6) was significantly greater compared with wt-rHCII. Thus, HCII variants with increased function, such as rHCII-CHis(6), may offer novel reagents for clinical application.

The early clinical history of salicylates in rheumatology and pain

The first clinical reports on the treatment of fever and pain with salicylate-containing natural willow bark remedies were made by the English clergyman Edward Stone in 1763. The pharmacologically active principles were isolated from natural sources by Italian, German and French scientists between 1826 and 1829. Salicylic acid was first synthesised by the German Gerland in 1852 and a year later the Frenchman Gerhardt synthesised acetylsalicylic acid. The first reports on the clinical use of salicylic acid in rheumatic disorders were made independently by the two German physicians Stricher and Reiss in 1876. Acetylsalicylic acid was rediscovered by Hoffmann in 1897 and by the turn of the century it had gained worldwide recognition in the treatment of pain and rheumatological disorders. Reports on adverse events relating to gastrointestinal intolerance and bleeding appeared early, but were largely neglected until the 1950s. Today, salicylates are still widely used as analgesic, antipyretic and anti-inflammatory drugs. New indications, such as thrombosis prophylaxis, have emerged during the last decades, and yet others are being explored.

Identification and initial structure-activity relationships of a novel class of nonpeptide inhibitors of blood coagulation factor Xa

The discovery and some of the basic structure-activity relationships of a series of novel nonpeptide inhibitors of blood coagulation Factor Xa is described. These inhibitors are functionalized beta-alanines, exemplified by 2a. Docking experiments placing 2a in the active site of Factor Xa implied that the most expeditious route to enhancing in vitro potency was to modify the group occupying the S3 site of the enzyme. Increasing the hydrophobic contacts between the inhibitor and the enzyme in this region led to 8, which has served as the prototype for this series. In addition, an enantioselective synthesis of these substituted beta-alanines was also developed.

New antiplatelet drugs

Antiplatelet drugs are used in a wide range of disorders, either as sole agents or as adjuncts to other therapies. Aspirin has been shown to be clinically effective in a number of ischaemic conditions and has been in use for many years. The newer agents, ticlopidine and clopidogrel (which are thought to inhibit ADP-mediated platelet reactions) are also effective and may prove to be superior to aspirin in certain indications. However, ticlopidine in particular has a different spectrum of side-effects, which may eventually limit its widespread use. The Gp IIb/IIIa antagonists have been most extensively investigated in the acute coronary syndromes, and shown to significantly improve outcome. Most of these studies have utilized agents which need to be given parenterally, and subsequently oral compounds are currently being developed. A number of other antiplatelet drugs such as prostacyclin and its analogues, as well as thromboxane inhibitors have been studied over the years, but overall they have failed to demonstrate any real clinical advantage.

Antiplatelet therapy

The major clinical indication for antiplatelet therapy has been the prevention of arterial thrombosis. Arterial thrombi are composed of predominantly platelets formed under conditions of elevated shear stress at sites of atherosclerotic vascular injury and disturbed blood flow. Aspirin, the prototype antiplatelet agent, has been in clinical use as an antithrombotic for almost a half century. However, clinical trials have exposed the limitations of aspirin, and there has been considerable recent progress in the development of more effective antiplatelet agents. These newer agents are rationally based on interrupting specific sites in the sequence of platelet activation. Inhibitors of the initial step of platelet adhesion remain experimental. Inhibitors of specific platelet agonist-receptor interactions include antithrombins, thromboxane A2 receptor antagonists, and adenosine diphosphate (ADP) receptor blockers including ticlopidine and clopidogrel. Inhibitors of arachidonic acid metabolism and thromboxane A2 include omega-3 fatty acids, aspirin and other nonsteroidal antiinflammatory drugs that inhibit cyclooxygenase, and thromboxane synthase inhibitors. The clinical efficacy of many of these agents may be limited by their actions, which are restricted to single, specific platelet receptors or metabolic pathways. Global interruption of the final step of platelet aggregation can be achieved with monoclonal antibodies and RGD (arginine-glycine-aspartic acid) analogs that block ligand binding to the platelet glycoprotein IIb/IIIa complex. Initial clinical trials with these novel agents have demonstrated superior efficacy in preventing reocclusion and restenosis following coronary angioplasty and atherectomy.