The discovery of dabigatran etexilate.

Thromboembolic disease is a major cause of mortality and morbidity in the developed world and is caused by an excessive stimulation of coagulation. Thrombin is a key serine protease in the coagulation cascade and numerous efforts have been made to develop safe and effective orally active direct thrombin inhibitors (DTIs). Current anticoagulant therapy includes the use of indirect thrombin inhibitors (e.g., heparins, low-molecular-weight-heparins) and vitamin K antagonists such as warfarin. However there are several caveats in the clinical use of these agents including narrow therapeutic window, parenteral delivery, and food- and drug-drug interactions. Dabigatran is a synthetic, reversible DTI with high affinity and specificity for its target binding both free and clot-bound thrombin, and offers a favorable pharmacokinetic profile. Large randomized clinical trials have demonstrated that dabigatran provides comparable or superior thromboprophylaxis in multiple thromboembolic disease indications compared to standard of care. This minireview will highlight the discovery and development of dabigatran, the first in a class of new oral anticoagulant agents to be licensed worldwide for the prevention of thromboembolism in the setting of orthopedic surgery and stroke prevent in atrial fibrillation.

Dabigatran: an oral novel potent reversible nonpeptide inhibitor of thrombin.

Dabigatran is a highly selective, reversible, and potent thrombin inhibitor and is orally available as the prodrug, dabigatran etexilate. It has shown antithrombotic efficacy in animal models of thrombosis, with a rapid onset of action and predictable pharmacodynamic response. Peak plasma concentrations of dabigatran occur 1 to 2 hours after ingestion of the prodrug. The terminal half-life of dabigatran is 12 to 14 hours in elderly volunteers. Dabigatran is not metabolized by cytochrome P450 isoenzymes and does not interact with food. Dabigatran has a low potential for drug-drug interactions and is predominantly renally excreted. Dabigatran etexilate as chronic therapy effectively prevents the recurrence of venous thromboembolism and cardioembolic stroke. For the first time, it has been demonstrated clinically that there may be an effective and safe alternative to warfarin.

3,5-Dihydro-imidazo[4,5-d]pyridazin-4-ones: a class of potent DPP-4 inhibitors.

Systematic variations of the xanthine scaffold in close analogs of development compound BI 1356 led to the class of 3,5-dihydro-imidazo[4,5-d]pyridazin-4-ones which provided, after substituent screening, a series of highly potent DPP-4 inhibitors.

Effects of the direct thrombin inhibitor dabigatran and its orally active prodrug, dabigatran etexilate, on thrombus formation and bleeding time in rats.

Dabigatran is a reversible direct, selective thrombin inhibitor, undergoing clinical development as its orally active prodrug, dabigatran etexilate. The objective of this trial was to assess the antithrombotic and anticoagulant effects of dabigatran and dabigatran etexilate in a rat model of venous thrombosis. In order to do this a modified Wessler model was used to assess the antithrombotic and anticoagulant effects of intravenous (i.v.) dabigatran and oral dabigatran etexilate administration. In addition, a rat tail bleeding time model was used to investigate the antihemostatic effect of dabigatran. The study demonstrated that bolus administration of dabigatran (0.01-0.1 mg/kg) reduced thrombus formation dose-dependently, with an ED50 (50% of the effective dose) of 0.033 mg/kg and complete inhibition at 0.1 mg/kg. By comparison, ED50 values for heparin (0.03-0.3 mg/kg), hirudin (0.01-0.5 mg/kg) and melagatran (0.1-0.5 mg/kg) were 0.07, 0.15 and 0.12 mg/kg, respectively. Oral administration of dabigatran etexilate (5-30 mg/kg) inhibited thrombus formation in a dose- and time-dependent manner, with maximum inhibition within 30 min of pretreatment, suggesting a rapid onset of action. Following i.v. administration of dabigatran (0.1-1.0 mg/kg), a statistically significant prolongation of bleeding time was observed at doses at least 15- and 5-fold greater than ED50 and ED100 (100% of the effective dose) doses, respectively; there was no significant increase in bleeding tendency at the maximum therapeutically effective dose (0.1 mg/kg). It can be concluded that dabigatran and its oral prodrug, dabigatran etexilate, show promise in the management of thromboembolic disease.

In-vitro profile and ex-vivo anticoagulant activity of the direct thrombin inhibitor dabigatran and its orally active prodrug, dabigatran etexilate.

Dabigatran is a reversible and selective, direct thrombin inhibitor (DTI) undergoing advanced clinical development as its orally active prodrug, dabigatran etexilate. This study set out to determine the molecular potency and anticoagulant efficacy of dabigatran and its prodrug dabigatran etexilate. This was achieved through enzyme inhibition and selectivity analyses, surface plasmon resonance studies, platelet aggregation, thrombin generation and clotting assays in vitro and ex vivo. These studies demonstrated that dabigatran selectively and reversibly inhibited human thrombin (Ki: 4.5 nM) as well as thrombin-induced platelet aggregation (IC(50): 10 nM), while showing no inhibitory effect on other platelet-stimulating agents. Thrombin generation in platelet-poor plasma (PPP), measured as the endogenous thrombin potential (ETP) was inhibited concentration-dependently (IC(50): 0.56 microM). Dabigatran demonstrated concentration-dependent anticoagulant effects in various species in vitro, doubling the activated partial thromboplastin time (aPTT), prothrombin time (PT) and ecarin clotting time (ECT) in human PPP at concentrations of 0.23, 0.83 and 0.18 microM, respectively. In vivo, dabigatran prolonged the aPTT dose-dependently after intravenous administration in rats (0.3, 1 and 3 mg/kg) and rhesus monkeys (0.15, 0.3 and 0.6 mg/kg). Dose- and time-dependent anticoagulant effects were observed with dabigatran etexilate administered orally to conscious rats (10, 20 and 50 mg/kg) or rhesus monkeys (1, 2.5 or 5 mg/kg), with maximum effects observed between 30 and 120 min after administration, respectively. These data suggest that dabigatran is a potent, selective thrombin inhibitor and an orally active anticoagulant as the prodrug, dabigatran etexilate.

Heterocyclic thrombin inhibitors. Part 1: design and synthesis of amidino-phenoxy quinoline derivatives.

Amidino-phenoxy quinoline derivatives represent a new class of potent thrombin inhibitors with good selectivity and remarkably low molecular weight (M(W): 335-391). X-ray analyses of thrombin-bound inhibitors revealed that enzyme inhibition is mainly based on hydrophobic interactions.

Heterocyclic thrombin inhibitors. Part 2: quinoxalinone derivatives as novel, potent antithrombotic agents.

Quinoxalinone derivatives as prototypes of dual thrombin and factor Xa inhibitors have been discovered. Nanomolar inhibition of both coagulation enzymes resulted in very potent antithrombotic activity in vitro.

Structure-based design of novel potent nonpeptide thrombin inhibitors.

The clinical syndromes of thromboembolism are evoked by an excessive stimulation of the coagulation cascade. In this context, the serine protease thrombin plays a key role. Considerable efforts have therefore been devoted to the discovery of safe, orally active inhibitors of this enzyme. On the basis of the X-ray crystal structure of the peptide-like thrombin inhibitor NAPAP complexed with bovine thrombin, we have designed a new structural class of nonpeptidic inhibitors employing a 1,2,5-trisubstituted benzimidazole as the central scaffold. Supported by a series of X-ray structure analyses, we optimized the activity of these compounds. Thrombin inhibition in the lower nanomolar range could be achieved although the binding energy mainly results from nonpolar, hydrophobic interactions. To improve in vivo potency, we increased the overall hydrophilicity of the molecules by introducing carboxylate groups. The very polar compound 24 (BIBR 953) exhibited the most favorable activity profile in vivo. This zwitterionic molecule was converted into the double-prodrug 31 (BIBR 1048), which showed strong oral activity in different animal species. On the basis of these results, 31 was chosen for clinical development.

Mechanism of human telomerase inhibition by BIBR1532, a synthetic, non-nucleosidic drug candidate.

Telomerase, a ribonucleoprotein acting as a reverse transcriptase, has been identified as a target for cancer drug discovery. The synthetic, non-nucleosidic compound, BIBR1532, is a potent and selective telomerase inhibitor capable of inducing senescence in human cancer cells (). In the present study, the mode of drug action was characterized. BIBR1532 inhibits the native and recombinant human telomerase, comprising the human telomerase reverse transcriptase and human telomerase RNA components, with similar potency primarily by interfering with the processivity of the enzyme. Enzyme-kinetic experiments show that BIBR1532 is a mixed-type non-competitive inhibitor and suggest a drug binding site distinct from the sites for deoxyribonucleotides and the DNA primer, respectively. Thus, BIBR1532 defines a novel class of telomerase inhibitor with mechanistic similarities to non-nucleosidic inhibitors of HIV1 reverse transcriptase.