Phase I--study with aprosulate, a new synthetic anticoagulant

Heparin mimetics

Explorations of the therapeutic potential of heparin mimetics, anionic compounds that are analogues of glycosaminoglycans (GAGs), have gone hand-in-hand with the emergence of understanding as to the role of GAGs in many essential biological processes. A myriad of structurally different heparin mimetics have been prepared and examined in many diverse applications. They range in complexity from heterogeneous polysaccharides that have been chemically sulphated to well-defined compounds, designed in part to mimic the natural ligand, but with binding specificity and potency increased by conjugation to non-carbohydrate pharmacophores. The maturity of the field is illustrated by the seven heparin mimetics that have achieved marketing approval and there are several more in late-stage clinical development. An overview of the structural determinants of heparin mimetics is presented together with an indication of their activities. The challenges in developing heparin mimetics as drugs, specificity and potential toxicity issues, are highlighted. Finally, the development path of three structurally very different mimetics, PI-88(®), GMI-1070 and RGTAs, each of which is in clinical trials, is described.

Ecarin clotting time is sensitive to heparinoids: comparison of two different techniques

Ecarin clotting time (ECT) is currently developed for the specific monitoring of antithrombin drugs, such as hirudin, argatroban, and hirulog. Aqueous reagent and dry chemistry technology have become available for ECT monitoring of antithrombin agents. Currently, many heparinoids and heparinomimetic drugs are being developed. These agents activate heparin cofactor II (HCII) and primarily mediate their effects by inhibiting thrombin. Although the test is specific for antithrombin agents, heparin cofactor II-mediated thrombin inhibitors are capable of prolonging the ECT. In order to study the relative effects of some of these agents, ECT was measured in human plasma supplemented with Pl-88 (a sulfated pentomanose; Progen Industries Limited, Sydney, Australia), aprosulate, pentosan polysulfate, dermatan sulfate, unfractionated heparin (UFH), and recombinant hirudin (r-hirudin). All agents were supplemented to the citrated-pooled plasma prepared from 10 healthy volunteers at a graded dosage of 0 to 100 microg/ml. These techniques gave comparable results for all of the agents used (PI-88, r2 = 0.99; r-hirudin, r2 = 0.98; UFH, r2 = 0.98; dermatan sulfate, r2 = 0.95; aprosulate, r2 = 0.95; pentosan polysulfate, r2 = 0.94). The relative anticoagulant effects of various agents used on ECT varied widely, exhibiting their potency in the following order: r-hirudin = pentosan polysulfate > dermatan sulfate > PI-88 > aprosulate > UFH. The sensitivity of ECT was adjusted by varying the concentration of the ecarin reagent. The results suggest that HCII-mediated inhibition of thrombin can be detected by using ECT reagents.

Effects of aprosulate, a novel synthetic glycosaminoglycan, on coagulation and platelet function parameters: a prospective, randomized phase I study

In a phase I clinical trial the effect of the highly sulfated polyanion "Aprosulate" was studied in healthy volunteers using different coagulation and platelet function parameters. Eighteen healthy volunteers aged 21 to 30 years received two single subcutaneous doses of aprosulate (0.5 mg/kg body weight; 1.0 mg/kg body weight), or unfractionated heparin (Calciparin 7,500 IU). The washout period between the different drugs/doses was at least 7 days. Coagulation and platelet function parameters (activated partial thromboplastin time, Heptest, fibrinogen, von Willebrand factor, ristocetin cofactor, platelet adhesion to siliconized glass, and platelet-induced thrombin generation time [a new method for measuring thrombin generation in platelet-rich plasma in the presence of platelets]) were assessed during 24 hours after each injection. Aprosulate led to a significant and dose-dependent prolongation of activated partial thromboplastin time and Heptest. This effect lasted for 4 hours (activated partial thromboplastin time) to 8 hours (Heptest). Activated partial thromboplastin time was not prolonged after the injection of unfractionated heparin (7,500 IU). Fibrinogen, von Willebrand factor, and ristocetin cofactor remained unchanged with both drugs. Platelet induced thrombin generation time was slightly prolonged and platelet adhesion was slightly diminished up to 2 hours using 0.5 mg/kg aprosulate, and up to 4 hours using 1.0 mg/kg aprosulate while the platelet induced thrombin generation time system was not influenced by the subcutaneous injection (7,500 IU) of unfractionated heparin. Both drugs and doses were well tolerated. Plasma transaminase concentrations alanin aminotransferase and aspartate aminotransferase serum values were slightly increased in some volunteers but returned to normal during or after the study (< 4 weeks). Further clinical trials will have to establish whether aprosulate is an effective drug for the prophylaxis of deep venous thrombosis.