Efficacy and safety of next-generation tick transcriptome-derived direct thrombin inhibitors

Abstract

Despite their limitations, unfractionated heparin (UFH) and bivalirudin remain standard-of-care parenteral anticoagulants for percutaneous coronary intervention (PCI). We discovered novel direct thrombin inhibitors (DTIs) from tick salivary transcriptomes and optimised their pharmacologic activity. The most potent, ultravariegin, inhibits thrombin with a Ki of 4.0 pM, 445-fold better than bivalirudin. Unexpectedly, despite their greater antithrombotic effect, variegin/ultravariegin demonstrated less bleeding, achieving a 3-to-7-fold wider therapeutic index in rodent thrombosis and bleeding models. When used in combination with aspirin and ticagrelor in a porcine model, variegin/ultravariegin reduced stent thrombosis compared with antiplatelet therapy alone but achieved a 5-to-7-fold lower bleeding time than UFH/bivalirudin. Moreover, two antibodies screened from a naïve human antibody library effectively reversed the anticoagulant activity of ultravariegin, demonstrating proof-of-principle for antidote reversal. Variegin and ultravariegin are promising translational candidates for next-generation DTIs that may reduce peri-PCI bleeding in the presence of antiplatelet therapy.

Prospection of Peptide Inhibitors of Thrombin from Diverse Origins Using a Machine Learning Pipeline

“…(5) Experimental validation of these putative hits using in vitro enzyme inhibition assays and in vivo animal models should be performed to confirm the predictive power of the model [49].…”

Improving treatment for acute ischemic stroke—Clot busting innovation in the pipeline

“…Many natural inhibitors of thrombin, i.e., hirudin, hijack both exosite I and the active site to effectively terminate fibrinogen binding and clot formation. A new class of bivalent thrombin inhibitors has been recently developed based on the exosite I and active-site binding scaffolds of variegin derived from the tropical bont tick Amblyomma variegatum (54). Variegin has improved affinity (K i = 277 pM), selectivity, and almost double the in vivo half-life compared to that of the standard-ofcare bivalirudin-a therapeutic analog of hirudin-(K i = 1780 pM) (55).…”

“…Variegin has improved affinity (K i = 277 pM), selectivity, and almost double the in vivo half-life compared to that of the standard-ofcare bivalirudin-a therapeutic analog of hirudin-(K i = 1780 pM) (55). Through iterative optimization, ultravariegin was developed as a lead analog possessing 445-fold (K i = 4 pM) greater inhibitory activity than bivalirudin with 1,000,000fold selectivity for thrombin over other clotting factors (54). Importantly, variegin/ultravariegin also demonstrated improved ability to preserve the hemostatic capacity, providing three to seven-fold wider therapeutic windows in rodent thrombosis and bleeding models as compared to unfractionated heparin (UFH) and bivalirudin.…”

Purification and characterization of thrombin from camel plasma: interaction with camel tick salivary gland thrombin inhibitor

“…Thrombin has high substrate specificity through its active site selectivity and via exosite I, a strong positively charged area on its surface, which is involved in thrombin-substrate interactions. Tick molecules inhibit thrombin by targeting exosite I using different mechanisms to prevent its binding to its natural substrates [ 22 , 28 ]. Therefore, the present study aims at purification and characterization of the camel blood coagulation factor thrombin and the evaluation of the susceptibility of the camel thrombin as the natural and proper target enzyme with the previously purified camel tick salivary gland thrombin inhibitor [ 20 ].…”