Desirudin: a review of the pharmacology and clinical application for the prevention of deep vein thrombosis

Novel drug delivery systems for hirudin-based product development and clinical applications

Hirudin, a natural biological polypeptide macromolecule secreted by the salivary glands of medicinal leech, is a specific thrombin inhibitor with multiple favourable bioactivities, including anti-coagulation, anti-fibrotic, and anti-tumour. Despite several anticoagulants have been widely applied in clinic, hirudin shows advantages in reducing the incidence of bleeding side effects by virtue of its high specificity in binding to thrombin. As a result, hirudin has been tested in clinical practice to prevent and treat several complex diseases. However, the application of this polypeptide macromolecule is compromised by its low bioavailability and bioactivity due to poor serum stability and susceptibility to protease degradation in vivo. To overcome these drawbacks, several studies have proposed novel drug delivery systems (NDDSs) to prevent the degradation and increase the targeting efficiency of hirudin. This systematic review summarises the clinical research on hirudin, including its classification and bioactivities, and highlights the opportunities and challenges in the clinical use of hirudin. The NDDSs designed to enhance the bioavailability and bioactivity of hirudin are discussed to explore its application in the treatment of related diseases. This review may considerably contribute to the advancement of delivery science and technology, particularly in the context of polypeptide-based therapeutics.

Unified Methodology for the Primary Preclinical In Vivo Screening of New Anticoagulant Pharmaceutical Agents from Hematophagous Organisms

The development of novel anticoagulants requires a comprehensive investigational approach that is capable of characterizing different aspects of antithrombotic activity. The necessary experiments include both in vitro assays and studies on animal models. The required in vivo approaches include the assessment of pharmacokinetic and pharmacodynamic profiles and studies of hemorrhagic and antithrombotic effects. Comparison of anticoagulants with different mechanisms of action and administration types requires unification of the experiment scheme and its adaptation to existing laboratory conditions. The rodent thrombosis models in combination with the assessment of hemostasis parameters and hematological analysis are the classic methods for conducting preclinical studies. We report an approach for the comparative study of the activity of different anticoagulants in vivo, including the investigation of pharmacodynamics and the assessment of hemorrhagic effects (tail-cut bleeding model) and pathological thrombus formation (inferior vena cava stenosis model of venous thrombosis). The reproducibility and uniformity of our set of experiments were illustrated on unfractionated heparin and dabigatran etexilate (the most common pharmaceuticals in antithrombic therapy) as comparator drugs and an experimental drug variegin from the tick Amblyomma variegatum. Variegin is notorious since it is a potential analogue of bivalirudin (Angiomax, Novartis AG, Basel, Switzerland), which is now being actively introduced into antithrombotic therapy.

In situ formed depot of elastin-like polypeptide-hirudin fusion protein for long-acting antithrombotic therapy

Thrombosis, induced by abnormal coagulation or fibrinolytic systems, is the most common pathology associated with many life-threatening cardio-cerebrovascular diseases. However, first-line anticoagulant drugs suffer from rapid drug elimination and risk of hemorrhagic complications. Here, we developed an in situ formed depot of elastin-like polypeptide (ELP)-hirudin fusion protein with a prodrug-like feature for long-term antithrombotic therapy. Highly secretory expression of the fusion protein was achieved with the assistance of the Ffu312 tag. Integration of hirudin, ELP, and responsive moiety can customize fusion proteins with properties of adjustable in vivo retention and controllable recovery of drug bioactivity. After subcutaneous injection, the fusion protein can form a reservoir through temperature-induced coacervation of ELP and slowly diffuse into the blood circulation. The biological activity of hirudin is shielded due to the N-terminal modification, while the activated key proteases upon thrombus occurrence trigger the cleavage of fusion protein together with the release of hirudin, which has antithrombotic activity to counteract thrombosis. We substantiated that the optimized fusion protein produced long-term antithrombotic effects without the risk of bleeding in multiple animal thrombosis models.

Tyrosine phosphorylation of recombinant hirudin increases affinity to thrombin and antithrombotic activity

Thrombin is one of the key enzymes of the blood coagulation system and a promising target for the development of anticoagulants. One of the most specific natural thrombin inhibitors is hirudin, contained in the salivary glands of medicinal leeches. The medicinal use of recombinant hirudin is limited because of the lack of sulfation on Tyr63, resulting in a 10-fold decrease in activity compared to native (sulfated) hirudin. In the present work, a set of hirudin derivatives was tested for affinity to thrombin: phospho-Tyr63, Tyr63(carboxymethyl)Phe, and Tyr63Glu mutants, which mimic Tyr63 sulfation and Gln65Glu mutant and lysine-succinylated hirudin, which enhance the overall negative charge of hirudin, as well as sulfo-hirudin and desulfo-hirudin as references. Using steered molecular dynamics simulations with subsequent umbrella sampling, phospho-hirudin was shown to exhibit the highest affinity to thrombin among all hirudin analogs, including native sulfo-hirudin; succinylated hirudin was also prospective. Phospho-hirudin exhibited the highest antithrombotic activity in in vitro assay in human plasma. Taking into account the modern methods for obtaining phospho-hirudin and succinylated hirudin, they are prospective as anticoagulants in clinical practice.

From haemadin to haemanorm: Synthesis and characterization of full-length haemadin from the leech Haemadipsa sylvestris and of a novel bivalent, highly potent thrombin inhibitor (haemanorm)

Hirudin from Hirudo medicinalis is a bivalent α-Thrombin (αT) inhibitor, targeting the enzyme active site and exosite-I, and is currently used in anticoagulant therapy along with its simplified analogue hirulog. Haemadin, a small protein (57 amino acids) isolated from the land-living leech Haemadipsa sylvestris, selectively inhibits αT with a potency identical to that of recombinant hirudin (KI  = 0.2 pM), with which it shares a common disulfide topology and overall fold. At variance with hirudin, haemadin targets exosite-II and therefore (besides the free protease) it also blocks thrombomodulin-bound αT without inhibiting the active intermediate meizothrombin, thus offering potential advantages over hirudin. Here, we produced in reasonably high yields and pharmaceutical purity (>98%) wild-type haemadin and the oxidation resistant Met5 → nor-Leucine analogue, both inhibiting αT with a KI of 0.2 pM. Thereafter, we used site-directed mutagenesis, spectroscopic, ligand-displacement, and Hydrogen/Deuterium Exchange-Mass Spectrometry techniques to map the αT regions relevant for the interaction with full-length haemadin and with the synthetic N- and C-terminal peptides Haem(1-10) and Haem(45-57). Haem(1-10) competitively binds to/inhibits αT active site (KI  = 1.9 μM) and its potency was enhanced by 10-fold after Phe3 → β-Naphthylalanine exchange. Conversely to full-length haemadin, haem(45-57) displays intrinsic affinity for exosite-I (KD  = 1.6 μM). Hence, we synthesized a peptide in which the sequences 1-9 and 45-57 were joined together through a 3-Glycine spacer to yield haemanorm, a highly potent (KI  = 0.8 nM) inhibitor targeting αT active site and exosite-I. Haemanorm can be regarded as a novel class of hirulog-like αT inhibitors with potential pharmacological applications.

Screening of the Promising Direct Thrombin Inhibitors from Haematophagous Organisms. Part I: Recombinant Analogues and Their Antithrombotic Activity In Vitro

The success in treatment of venous thromboembolism and acute coronary syndromes using direct thrombin inhibitors has stimulated research aimed at finding a new anticoagulant from haematophagous organisms. This study deals with the comparison between hirudin-1 from Hirudomedicinalis(desirudin), being the first-known and most well-studied natural anticoagulant, along with recombinant analogs of haemadin from the leech Haemadipsa sylvestris, variegin from the tick Amblyomma variegatum, and anophelin from Anopheles albimanus. These polypeptides were chosen due to their high specificity and affinity for thrombin, as well as their distinctive inhibitory mechanisms. We have developed a universal scheme for the biotechnological production of these recombinant peptides as pharmaceutical substances. The anticoagulant activities of these peptides were compared using the thrombin amidolytic activity assay and prolongation of coagulation time (thrombin time, prothrombin time, and activated partial thromboplastin time) in mouse and human plasma. The preliminary results obtained suggest haemadin as the closest analog of recombinant hirudin-1, the active substance of the medicinal product Iprivask (Aventis Pharmaceuticals, USA) for the prevention of deep venous thrombosis in patients undergoing elective hip or knee replacement surgery. In contrast, variegin can be regarded as a natural analog of bivalirudin (Angiomax, The Medicines Company), a synthetic hirudin-1 derivative certified for the treatment of patients undergoing percutaneous coronary intervention and of patients with unstable angina pectoris after percutaneous transluminal coronary angioplasty.

Paracelsus' legacy in the faunal realm: Drugs deriving from animal toxins

Given the vast number of venomous and poisonous animals, it is surprising that only relatively few animal-derived toxins have been explored and made their way into marketed drugs or are being investigated in ongoing clinical trials. In this review, we highlight marketed drugs deriving from animal toxins as well as ongoing clinical trials and preclinical investigations in the field. We emphasize that more attention should be paid to the rich supply of candidates that nature provides as valuable starting points for addressing serious unmet medical needs.

From Animal Poisons and Venoms to Medicines: Achievements, Challenges and Perspectives in Drug Discovery

Animal poisons and venoms are comprised of different classes of molecules displaying wide-ranging pharmacological activities. This review aims to provide an in-depth view of toxin-based compounds from terrestrial and marine organisms used as diagnostic tools, experimental molecules to validate postulated therapeutic targets, drug libraries, prototypes for the design of drugs, cosmeceuticals, and therapeutic agents. However, making these molecules applicable requires extensive preclinical trials, with some applications also demanding clinical trials, in order to validate their molecular target, mechanism of action, effective dose, potential adverse effects, as well as other fundamental parameters. Here we go through the pitfalls for a toxin-based potential therapeutic drug to become eligible for clinical trials and marketing. The manuscript also presents an overview of the current picture for several molecules from different animal venoms and poisons (such as those from amphibians, cone snails, hymenopterans, scorpions, sea anemones, snakes, spiders, tetraodontiformes, bats, and shrews) that have been used in clinical trials. Advances and perspectives on the therapeutic potential of molecules from other underexploited animals, such as caterpillars and ticks, are also reported. The challenges faced during the lengthy and costly preclinical and clinical studies and how to overcome these hindrances are also discussed for that drug candidates going to the bedside. It covers most of the drugs developed using toxins, the molecules that have failed and those that are currently in clinical trials. The article presents a detailed overview of toxins that have been used as therapeutic agents, including their discovery, formulation, dosage, indications, main adverse effects, and pregnancy and breastfeeding prescription warnings. Toxins in diagnosis, as well as cosmeceuticals and atypical therapies (bee venom and leech therapies) are also reported. The level of cumulative and detailed information provided in this review may help pharmacists, physicians, biotechnologists, pharmacologists, and scientists interested in toxinology, drug discovery, and development of toxin-based products.

Role of direct oral anticoagulants in patients with kidney disease

The anticoagulation field is experiencing a renaissance that began with regulatory approval of the direct thrombin inhibitor dabigatran, a direct oral anticoagulant (DOAC), in 2010. The DOAC medication class has rapidly evolved to include the additional approval of 4 direct factor Xa inhibitors. Commensurately, DOAC use has increased and collectively account for the majority of new anticoagulant prescriptions. Despite exclusion of patients with moderate-to-severe kidney disease from most pivotal DOAC trials, DOACs are increasingly used in this setting. An advantage of DOACs is similar or improved antithrombotic efficacy with less bleeding risk when compared with traditional agents. Several post hoc analyses, retrospective studies, claims data studies, and meta-analyses suggest that these benefits extend to patients with kidney disease. However, the lack of randomized controlled trial data in specific kidney disease settings, with their unique pathophysiology, should be a call to action for the kidney community to systematically study these agents, especially because early data suggest that DOACs may pose less risk of anticoagulant-related nephropathy than do vitamin K antagonists. Most DOACs are renally cleared and are significantly protein bound in circulation; thus, the pharmacokinetics of these drugs are influenced by reduced renal function and proteinuria. DOACs are susceptible to altered metabolism by P-glycoprotein inhibitors and inducers, including drugs commonly used for the management of kidney disease comorbidities. We summarize the currently available literature on DOAC use in kidney disease and illustrate knowledge gaps that represent important opportunities for prospective investigation.

The Research Progress of Direct Thrombin Inhibitors

Blood coagulation is the process of changing the blood from the flowing state to the gel state. It is an important part of the hemostatic function. Coagulation is a process by which a series of coagulation factors are sequentially activated, and finally thrombin is formed to form fibrin clot. Direct thrombin inhibitors are important anticoagulant drug. These drugs can selectively bind to the active site of thrombin, inhibit thrombin activity, have strong action and high specificity, and have important significance in the clinical treatment of thrombus diseases. Some of them come from natural products of animals or plants, and many of them have been applied in the clinic. The other part is derived from the design, synthesis and activity studies of small molecule inhibitors. This review discusses the progress of direct thrombin inhibitors in recent years.

Evaluating prodrug characteristics of a novel anticoagulant fusion protein neorudin, a prodrug targeting release of hirudin variant 2-Lys47 at the thrombosis site, by means of in vitro pharmacokinetics

Recombinant neorudin (EPR-hirudin, EH), a low-bleeding anticoagulant fusion protein, is an inactive prodrug designed to be converted to the active metabolite, hirudin variant 2-Lys47 (HV2), locally at the thrombus site by FXa and/or FXIa, following activation of the coagulation system. Our aim was to evaluate the prodrug characteristics of EH by comparing the biotransformation of EH and HV2 in biological matrices, including rat blood, liver, and kidney homogenates, demonstrating the cleavage of EH to HV2 by FXa and FXIa, and comparing the conversion of EH to HV2 between fresh whole blood and whole-blood clot homogenate, using ultra-performance liquid chromatography-mass spectrometry (UPLC-MS/MS). Both EH and HV2 were stable in blood and unstable in the liver and kidney homogenates. Eight EH metabolites and eight HV2 metabolites identified as N-terminal fragments were found in the liver and kidney. C-terminal proteolysis is therefore the major metabolic pathway, with serine/cysteine carboxypeptidases and metallocarboxypeptidases being responsible for the degradation of EH and HV2 in the liver and kidney, respectively. EH was cleaved to release HV2 by FXIa. Higher levels of HV2 were produced from EH in the whole-blood clot homogenate, in which the coagulation system was activated compared with those in fresh whole blood. In conclusion, the metabolism of EH and HV2 shares the same cleavage pattern, and EH is transformed into HV2 when the coagulation system is activated, where FXIa is a specific enzyme. Our in vitro study revealed the anticipated prodrug characteristics of EH newly designed as an inactive prodrug of hirudin.

A novel hirudin derivative inhibiting thrombin without bleeding for subcutaneous injection

Currently, anticoagulants would be used to prevent thrombosis. Thrombin is an effector enzyme for haemostasis and thrombosis. We designed a direct thrombin inhibitor peptide (DTIP) using molecular simulation and homology modelling and demonstrated that the C-terminus of DTIP interacts with exosite I, and N-terminus with the activity site of thrombin, respectively. DTIP interfered with thrombin-mediated coagulation in human, rat and mouse plasma (n=10 per group) and blocked clotting in human whole blood in vitro. When administered subcutaneously, DTIP showed potent and dose-dependent extension of aPTT, PT, TT and CT in rats (n=10 per group). The antithrombotic dose of DTIP induced significantly less bleeding than bivalirudin determined by transecting distal tail assay in rats. Furthermore, DTIP reached peak blood concentration in 0.5-1 hour and did not cause increased bleeding after five days of dosing compared to dabigatran etexilate. The antithrombotic effect of DTIP was evaluated in mice using lethal pulmonary thromboembolism model and FeCl₃-induced mesenteric arteriole thrombus model. DTIP (1.0 mg/kg, sc) prevented deep venous thrombosis and increased the survival rate associated with pulmonary thromboembolism from 30 % to 80 %. Intravital microscopy showed that DTIP (1.0 mg/kg, sc) decelerated mesenteric arteriole thrombosis caused by FeCl₃ injury. These data establish that DTIP is a novel antithrombotic agent that could be used to prevent thrombosis without conferring an increased bleeding risk.

Recent advances in developing insect natural products as potential modern day medicines

Except for honey as food, and silk for clothing and pollination of plants, people give little thought to the benefits of insects in their lives. This overview briefly describes significant recent advances in developing insect natural products as potential new medicinal drugs. This is an exciting and rapidly expanding new field since insects are hugely variable and have utilised an enormous range of natural products to survive environmental perturbations for 100s of millions of years. There is thus a treasure chest of untapped resources waiting to be discovered. Insects products, such as silk and honey, have already been utilised for thousands of years, and extracts of insects have been produced for use in Folk Medicine around the world, but only with the development of modern molecular and biochemical techniques has it become feasible to manipulate and bioengineer insect natural products into modern medicines. Utilising knowledge gleaned from Insect Folk Medicines, this review describes modern research into bioengineering honey and venom from bees, silk, cantharidin, antimicrobial peptides, and maggot secretions and anticoagulants from blood-sucking insects into medicines. Problems and solutions encountered in these endeavours are described and indicate that the future is bright for new insect derived pharmaceuticals treatments and medicines.

Pathology consultation on monitoring direct thrombin inhibitors and overcoming their effects in bleeding patients

OBJECTIVES

Direct thrombin inhibitors (DTIs), a relatively new class of anticoagulants, present several challenges regarding monitoring of their anticoagulant effects and overcoming bleeding associated with their use. The aim of this article is to (1) briefly present the pharmacologic properties of currently available DTIs, (2) discuss approaches to laboratory assessment of these drugs, and (3) review management of bleeding associated with their use.

METHODS

Published literature on DTIs, including clinical trials, case reports, and experimental animal models, was reviewed. The primary authors also reviewed their first-hand experiences with DTI anticoagulation.

RESULTS

Based on the literature review and the practical experiences of the authors, suggestions for the monitoring of DTIs and algorithmic approaches for the management of DTI-associated bleeding were developed.

CONCLUSIONS

Routine coagulation assays (eg, the prothrombin time) show a relatively poor correlation with the degree of anticoagulation and DTI drug concentrations. Newer assays, such as the ecarin clotting time and dilute thrombin time, may be more useful in assessing DTI anticoagulation, but these assays are not yet widely available. Low-grade DTI-associated bleeds are best managed with cessation of the drug and supportive care, while higher-grade and/or life-threatening bleeds may best be reversed by active drug removal (eg, via the administration of activated charcoal or hemodialysis). At present there is little evidence to suggest that transfusion products such as factor concentrates or thawed plasma are of any particular benefit in DTI reversal; however, these products may play a supportive role in the management of bleeding.