G-Quadruplex Aptamers to Human Thrombin Versus Other Direct Thrombin Inhibitors: The Focus on Mechanism of Action and Drug Efficiency as Anticoagulants

Abstract

Thrombin is a key enzyme of blood coagulation system which has multiple functions including pro- and anticoagulant, platelet aggregating and inflammatory activities. Unsurprisingly, this enzyme has been a target for anticoagulant drug development for decades. Among the most interesting direct thrombin inhibitors with intravenous administration route are the following ones: 1) hirudins, proteins with bivalent binding mode to the thrombin, 2) bivalirudin, the peptide with bivalent binding mode to the thrombin, 3) argatroban, the chemical that binds to the thrombin active site, and 4) G-quadruplex DNA aptamers, structured oligonucleotides with an affinity to protein-binding site of the thrombin. Efficiency of all these inhibitors has been studied in vivo in preclinical and clinical trials, as well as in vitro with various tests, allowing to compare them thoroughly. In the review three levels of comparison were used to highlight the features of each inhibitor: 1) thrombin inhibition constants as a characteristic of inhibitor potency in simple enzymatic system; 2) inhibition of fibrin fiber formation and thrombin generation in coagulation cascade as a characteristic of anticoagulant potency in human blood plasma; and 3) therapeutic doses used and therapeutic profiles obtained after intravenous administration into animals and humans. The data clearly demonstrate weak and strong aspects of thrombin binding aptamers providing a solid background for further novel anticoagulant development. </p><p&gt.

The Evaluation of Pharmacodynamics and Pharmacokinetics of Anti-thrombin DNA Aptamer RA-36

“…Both compounds have inhibition constants in the nanomolar range: 2 nM for bivalirudin and 7 nM for aptamer RA-36. The compounds inhibits coagulation cascade in the same concentration range, although bivalirudin is more efficient inhibitor than RA-36 ( Zavyalova et al, 2016b ). The difference in a type of thrombin binding is seen in the sophisticated thrombin generation test.…”

“…In blood plasma, bivalirudin prevents temporally any thrombin activity; then, the peptide is slowly hydrolyzed, fully restoring thrombin activity. On the contrary, RA-36 provides permanent inhibitory effect inhibiting those thrombin activities that are mediated with thrombin exosite I ( Ustinov et al, 2016 ; Zavyalova et al, 2016b ).…”

“…A dozen DNA and RNA aptamers to thrombin have since been developed, being adopted to a large variety of applications in biochemistry, bioanalytics and medicine. Two DNA aptamers to thrombin, HD1 and NU172, successfully passed preclinical trials; they entered clinical trials as agents for the treatment of cardiovascular diseases, but no drug has been developed to date ( Woodruff and Sullenger, 2015 ; Nimjee et al, 2016 ; Zavyalova et al, 2016a , b ). The trials of aptamer HD1 were terminated due to suboptimal dosing profiles in humans.…”

“…The peptide counterpart, bivalirudin, was chosen as a reference drug, because it is close due to the pharmacokinetics and pharmacodynamics, and is already used in the clinic. In addition, both compounds are direct thrombin inhibitors; they are administered intravenously, and have a short lifetime in blood ( Zavyalova et al, 2016b ). Anticoagulant efficiency was assessed in vivo after both single and repeated intravenous injections into rats and monkeys.…”

Exploring the efficiency of thrombin inhibitors with a quantitative model of the coagulation cascade

“…All four inhibitors bind and inhibit thrombin but yield different thrombin generation profiles . The designed mathematical model was applied to describe the mechanism of action of each inhibitor as well as to estimate their power in inhibiting thrombin activity.…”