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Coagulation & its Disorders
Novel aptamer to von Willebrand factor A1 domain (TAGX-0004) shows total inhibition of thrombus formation superior to ARC1779 and comparable to caplacizumab
Ferrata Storti Foundation
Haematologica 2020 Volume 105(11):2631-2638
Kazuya Sakai,1 Tatsuhiko Someya,2 Kaori Harada,2 Hideo Yagi,1 Taei Matsui3 and Masanori Matsumoto1
1Department of Blood Transfusion Medicine, Nara Medical University, Kashihara and 2TAGCyx Biotechnologies Inc, Tokyo and 3Clinical Laboratory Medicine, Fujita Health University School of Medical Sciences, Toyoake, Japan
ABSTRACT
Von Willebrand factor (VWF) is a blood glycoprotein that plays an important role in platelet thrombus formation through interaction between its A1 domain and platelet glycoprotein Ib. ARC1779, an aptamer to the VWF A1 domain, was evaluated in a clinical trial for acquired thrombotic thrombocytopenic purpura (aTTP). Subsequently, caplacizumab, an anti-VWF A1 domain nanobody, was approved for aTTP in Europe and the USA. We recently developed a novel DNA aptamer, TAGX-0004, to the VWF A1 domain; it contains an artificial base and demonstrates high affinity for VWF. To compare the effects of these three agents on VWF A1, their ability to inhibit ristocetin- or botrocetin-induced platelet aggregation under static conditions was analyzed, and the inhibition of thrombus formation under high shear stress was investigated in a microchip flow chamber system. In both assays, TAGX-0004 showed stronger inhibition than ARC1779, and had comparable inhibitory effects to caplacizumab. The binding sites of TAGX-0004 and ARC1779 were ana- lyzed with surface plasmon resonance performed using alanine scanning mutagenesis of the VWF A1 domain. An electrophoretic mobility shift assay showed that R1395 and R1399 in the A1 domain bound to both aptamers. R1287, K1362, and R1392 contributed to ARC1779 binding, and F1366 was essential for TAGX-0004 binding. Surface plasmon resonance analysis of the binding sites of caplacizumab identified five amino acids in the VWF A1 domain (K1362, R1392, R1395, R1399, and K1406). These results suggest that TAGX-0004 possesses better pharmacological properties than capla- cizumab in vitro and might be similarly promising for aTTP treatment.
Introduction
Von Willebrand factor (VWF) is a large multimeric plasma glycoprotein that plays an essential role in tethering circulating platelets to damaged endothelial cells.1 Interaction between the VWF A1 domain and the platelet glycoprotein (GP) Ib receptor leads to rapid development of VWF-rich platelet thrombi, thus preventing further bleeding.2 Although normal amounts of VWF are usually helpful in hemo- stasis reactions, several VWF-mediated diseases, such as acute coronary syn- drome,3,4 cerebral infarction,5 and thrombotic thrombocytopenic purpura (TTP),6 demonstrate remarkably elevated plasma levels of VWF. Inhibiting VWF activity by blocking its A1 domain has recently been demonstrated to be an attractive thera- peutic target in these arterial thromboses.7-10
Caplacizumab (Ablynx), an anti-VWF A1 humanized nanobody,11,12 was approved by the European Medicines Agency in 2018 and by the US Food and Drug Administration in 2019 for the treatment of acquired TTP (aTTP). The anti- VWF A1 aptamer ARC1779 (Archemix) was developed as an antithrombotic agent for use in patients with aTTP, and it showed sufficient inhibitory effects on VWF activity without any severe bleeding events in a randomized control trial.13 However, ARC1779 has not yet been approved for the treatment of VWF-mediated
Correspondence:
MASANORI MATSUMOTO
mmatsumo@naramed-u.ac.jp
Received: August 16, 2019. Accepted: December 18, 2019. Pre-published: December 19, 2019.
doi:10.3324/haematol.2019.235549 ©2020 Ferrata Storti Foundation
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