Population Pharmacokinetics of Melagatran, the Active Form of the Oral Direct Thrombin Inhibitor Ximelagatran, in Atrial Fibrillation Patients Receiving Long-Term Anticoagulation Therapy

A fully automatic tool for development of population pharmacokinetic models

Population pharmacokinetic (PK) models are widely used to inform drug development by pharmaceutical companies and facilitate drug evaluation by regulatory agencies. Developing a population PK model is a multi-step, challenging, and time-consuming process involving iterative manual model fitting and evaluation. A tool for fully automatic model development (AMD) of common population PK models is presented here. The AMD tool is implemented in Pharmpy, a versatile open-source library for pharmacometrics. It consists of different modules responsible for developing the different components of population PK models, including the structural model, the inter-individual variability (IIV) model, the inter-occasional variability (IOV) model, the residual unexplained variability (RUV) model, the covariate model, and the allometry model. The AMD tool was evaluated using 10 real PK datasets involving the structural, IIV, and RUV modules in three sequences. The different sequences yielded generally consistent structural models; however, there were variations in the results of the IIV and RUV models. The final models of the AMD tool showed lower Bayesian Information Criterion (BIC) values and similar visual predictive check plots compared with the available published models, indicating reasonable quality, in addition to reasonable run time. A similar conclusion was also drawn in a simulation study. The developed AMD tool serves as a promising tool for fast and fully automatic population PK model building with the potential to facilitate the use of modeling and simulation in drug development.

Prolongation of clot lysis time by a direct thrombin inhibitor melagatran mediated by paradoxical enhancement of thrombin generation: comparison with a direct factor Xa inhibitor edoxaban

Previously, we reported that a direct thrombin inhibitor melagatran paradoxically increased thrombin generation in human plasma in the presence of thrombomodulin. The aim of this study is to test the hypothesis that melagatran may exert a deleterious effect on tissue-type plasminogen activator (t-PA)-induced fibrinolysis via enhancement of thrombin generation and subsequent activation of thrombin-activatable fibrinolysis inhibitor (TAFI) and factor XIII (FXIII). Clot formation in human plasma containing t-PA and thrombomodulin was induced by tissue factor. The absorbance at 405 nm was measured to obtain clot lysis time. Effects of melagatran and a factor Xa inhibitor edoxaban on clot lysis time were determined. In the presence of thrombomodulin, melagatran significantly prolonged clot lysis time, but edoxaban shortened it. In the absence of thrombomodulin, melagatran did not inhibit fibrinolysis. Prolongation of clot lysis time by melagatran was reversed by activated protein C (which suppressed thrombin generation increased by melagatran) and a TAFIa inhibitor. Melagatran significantly suppressed plasmin generation, while edoxaban significantly increased it. However, both melagatran and edoxaban suppressed FXIII activation. In the clot formed in the presence of melagatran and edoxaban, the fibrin fibre was thin compared with control, showing no clear difference in the clot structures between melagatran and edoxaban. These results indicated that melagatran, not edoxaban, prolonged clot lysis time through the paradoxical enhancement of thrombin generation, and subsequent TAFI activation and inhibition of plasmin generation. Neither FXIII activation nor change in fibrin clot structure contributed to the inhibition of fibrinolysis by melagatran.

Molecular modeling studies, synthesis and biological evaluation of dabigatran analogues as thrombin inhibitors

In this work, 48 thrombin inhibitors based on the structural scaffold of dabigatran were analyzed using a combination of molecular modeling techniques. We generated three-dimensional quantitative structure-activity relationship (3D-QSAR) models based on three alignments for both comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA) to highlight the structural requirements for thrombin protein inhibition. In addition to the 3D-QSAR study, Topomer CoMFA model also was established with a higher leave-one-out cross-validation q(2) and a non-cross-validation r(2), which suggest that the three models have good predictive ability. The results indicated that the steric, hydrophobic and electrostatic fields play key roles in QSAR model. Furthermore, we employed molecular docking and re-docking simulation explored the binding relationship of the ligand and the receptor protein in detail. Molecular docking simulations identified several key interactions that were also indicated through 3D-QSAR analysis. On the basis of the obtained results, two compounds were designed and predicted by three models, the biological evaluation in vitro (IC50) demonstrated that these molecular models were effective for the development of novel potent thrombin inhibitors.

Synthesis and Biological Evaluation of Some New 2,5-Substituted 1-Ethyl-1H-benzoimidazole Fluorinated Derivatives as Direct Thrombin Inhibitors

A new series of fluorinated 2,5-substituted 1-ethyl-1H-benzimidazole derivatives were synthesized from starting compounds 3a-i, which were prepared from acrylic acid ethyl ester and the appropriate amines using trifluoromethanesulfonic acid as a catalyst. A total of 9 novel derivatives were synthesized through 9 steps. All of them were evaluated for thrombin inhibition activity in vitro for the first time. We have altered their structures using different substituents on the amines to assess their structure-activity relationships as direct thrombin inhibitors. All the compounds were effective thrombin inhibitors, with IC50 values ranging from 3.39 to 23.30 nM. Among the compounds synthesized, compounds 14a, 14b, 14d, 14e, and 14h exhibited greater anticoagulant activity than argatroban (IC50 = 9.36 nM). Furthermore, compound 14h synthesized starting with 2-amino-pyridine was the most potent thrombin inhibitor with an IC50 value of 3.39 nM. Molecular modeling studies were performed to determine the probable interactions of the most potent compounds 14a, 14e, and 14h with their protein receptor (PDB ID: 1KTS). Docking data show that the active compounds inhibit thrombin in a similar mode to that of the potent anticoagulant dabigatran.