Effects of Melagatran, a New Low-molecular-weight Thrombin Inhibitor, on Thrombin and Fibrinolytic Enzymes

Melagatran, a new, competitive and rapid inhibitor of thrombin with a molecular mass of 429 Da is described. Melagatran is well tolerated when administered in very high doses, and the oral bioavailability in the dog is relatively high. The aim of the study was to determine, in the preclinical setting, the degree of selectivity against the fibrinolytic system required for entering the clinical development phase. Melagatran was compared with two structurally similar thrombin inhibitors, inogatran and H 317/86. The potent inhibition of thrombin by melagatran was demonstrated by a low inhibition constant (Ki) for thrombin (0.002 μmol/l) and prolongation of clotting time to twice the control value in coagulation assays at low concentrations (0.010, 0.59 and 2.2 μmol/l for thrombin time, activated partial thromboplastin time and prothrombin time, respectively). Furthermore, thrombin-induced platelet aggregation was inhibited at the same concentration (IC50-value 0.002 μmol/l) as the Ki-value for thrombin. In two assays of global fibrinolysis, inhibition was observed at a concentration of 1.1 μmol/l in a euglobulin plasma fraction model, while no inhibition was observed at a concentration of ≤10 μmol/l in a plasma model. In an in vivo model of endogenous fibrinolysis in the rat, inhibition of fibrinolysis was observed at ≥1.0 μmol/l. In all assays, except the Ki-ratio determinations, the compounds could be graded with regard to selectivity against the fibrinolytic system: inogatran > melagatran > H 317/86. For melagatran, inhibition of fibrinolysis was not observed at concentrations below the upper limit of the proposed therapeutic plasma concentration interval (<0.5 μmol/l). Thus, melagatran seems to have a sufficient selectivity against the fibrinolytic system, while H 317/86 was considered to be insufficient for clinical development.

Hemostatic effects of the ticagrelor antidote MEDI2452 in pigs treated with ticagrelor on a background of aspirin

Essentials MEDI2452 is a specific antidote of the platelet P2Y12 receptor antagonist ticagrelor. Hemostatic effects of MEDI2452 were evaluated in pigs treated with ticagrelor and aspirin. MEDI2452 eliminated free ticagrelor within 5 min and gradually normalized platelet aggregation. Improvements in blood pressure (significant) and in blood-loss and survival (non-significant) were observed.

SUMMARY

Background Ticagrelor, a P2Y12 antagonist, is approved for the prevention of thromboembolic events. However, antiplatelet therapies carry a risk of bleeding. Objective To explore the hemostatic effects of MEDI2452, an antidote for ticagrelor. Methods Pigs, pre-treated with aspirin, were given an intravenous infusion of ticagrelor or vehicle. At the end of the infusion, a piece of a liver lobe was cut off and a bolus of MEDI2452 or vehicle was administered intravenously. Blood was collected to monitor blood loss, mean arterial blood pressure (MAP) was recorded and survival time was observed over 4 h. Blood samples for drug plasma exposures and platelet aggregation were collected. Results MEDI2452 eliminated the free concentrations of ticagrelor and its active metabolite AR-C124910XX within 5 min. ADP-induced platelet aggregation was close to normal at 60 min, which was not significantly different from aspirin alone. MEDI2452 numerically reduced ticagrelor-mediated effects: body-weight-adjusted blood loss in the 15- to 90-min interval, 12 (confidence interval [CI] 95% 7-28] vs. 17 (CI 95% 5-31) (ticagrelor and aspirin) vs. 5 (CI 95% 3-9) mL kg-1 (aspirin alone), survival 70% (CI 95% 47-100) vs. 45% (CI 95% 21-92) (ticagrelor and aspirin) vs. 100% (CI 95% 100-100) (aspirin alone), and median survival time, 240 (CI 95% 180-240) vs. 169 (CI 95% 64-240) (ticagrelor and aspirin) vs. 240 (CI 95% 240-240) min (aspirin alone). Finally, MEDI2452 significantly attenuated the decline in MAP, 0.08 (CI 95% 0.07-0.09) vs. 0.141 (CI 95% 0.135-0.148) (ticagrelor and aspirin) vs. 0.04 (CI 95% 0.03-0.05) mmHg per min (aspirin alone) and maintained MAP at a significantly higher level, 73 (CI 95% 51-95) vs. 48 (CI 95% 25-70) (ticagrelor and aspirin) vs. 115 (CI 95% 94-136) mmHg (aspirin alone). Conclusion MEDI2452 eliminated free ticagrelor and AR-C124910XX within 5 min. This translated into a gradual normalization of ADP-induced platelet aggregation and significant improvement in blood pressure and numerical but non-significant improvements in blood-loss and survival.

Unraveling the pharmacokinetic interaction of ticagrelor and MEDI2452 (Ticagrelor antidote) by mathematical modeling

The investigational ticagrelor‐neutralizing antibody fragment, MEDI2452, is developed to rapidly and specifically reverse the antiplatelet effects of ticagrelor. However, the dynamic interaction of ticagrelor, the ticagrelor active metabolite (TAM), and MEDI2452, makes pharmacokinetic (PK) analysis nontrivial and mathematical modeling becomes essential to unravel the complex behavior of this system. We propose a mechanistic PK model, including a special observation model for post‐sampling equilibration, which is validated and refined using mouse in vivo data from four studies of combined ticagrelor‐MEDI2452 treatment. Model predictions of free ticagrelor and TAM plasma concentrations are subsequently used to drive a pharmacodynamic (PD) model that successfully describes platelet aggregation data. Furthermore, the model indicates that MEDI2452‐bound ticagrelor is primarily eliminated together with MEDI2452 in the kidneys, and not recycled to the plasma, thereby providing a possible scenario for the extrapolation to humans. We anticipate the modeling work to improve PK and PD understanding, experimental design, and translational confidence.

Discovery of AZD8165 – a clinical candidate from a novel series of neutral thrombin inhibitors

A novel series of neutral thrombin inhibitors has been developed using a selection process based on docking experiments and property calculations and predictions.

Effects of melagatran, a new low-molecular-weight thrombin inhibitor, on thrombin and fibrinolytic enzymes

Melagatran, a new, competitive and rapid inhibitor of thrombin with a molecular mass of 429 Da is described. Melagatran is well tolerated when administered in very high doses, and the oral bioavailability in the dog is relatively high. The aim of the study was to determine, in the preclinical setting, the degree of selectivity against the fibrinolytic system required for entering the clinical development phase. Melagatran was compared with two structurally similar thrombin inhibitors, inogatran and H 317/86. The potent inhibition of thrombin by melagatran was demonstrated by a low inhibition constant (Ki) for thrombin (0.002 micromol/l) and prolongation of clotting time to twice the control value in coagulation assays at low concentrations (0.010, 0.59 and 2.2 micromol/l for thrombin time, activated partial thromboplastin time and prothrombin time, respectively). Furthermore, thrombin-induced platelet aggregation was inhibited at the same concentration (IC50-value 0.002 micromol/l) as the Ki-value for thrombin. In two assays of global fibrinolysis, inhibition was observed at a concentration of 1.1 micromol/l in a euglobulin plasma fraction model, while no inhibition was observed at a concentration of < or = 10 micromol/l in a plasma model. In an in vivo model of endogenous fibrinolysis in the rat, inhibition of fibrinolysis was observed at > or = 1.0 micromol/l. In all assays, except the Ki-ratio determinations, the compounds could be graded with regard to selectivity against the fibrinolytic system: inogatran > melagatran > H 317/86. For melagatran, inhibition of fibrinolysis was not observed at concentrations below the upper limit of the proposed therapeutic plasma concentration interval (< 0.5 micromol/l). Thus, melagatran seems to have a sufficient selectivity against the fibrinolytic system, while H 317/86 was considered to be insufficient for clinical development.