Structural Biology and Protein Engineering of Thrombolytics

Abstract

Myocardial infarction and ischemic stroke are the most frequent causes of death or disability worldwide. Due to their ability to dissolve blood clots, the thrombolytics are frequently used for their treatment. Improving the effectiveness of thrombolytics for clinical uses is of great interest. The knowledge of the multiple roles of the endogenous thrombolytics and the fibrinolytic system grows continuously. The effects of thrombolytics on the alteration of the nervous system and the regulation of the cell migration offer promising novel uses for treating neurodegenerative disorders or targeting cancer metastasis. However, secondary activities of thrombolytics may lead to life-threatening side-effects such as intracranial bleeding and neurotoxicity. Here we provide a structural biology perspective on various thrombolytic enzymes and their key properties: (i) effectiveness of clot lysis, (ii) affinity and specificity towards fibrin, (iii) biological half-life, (iv) mechanisms of activation/inhibition, and (v) risks of side effects. This information needs to be carefully considered while establishing protein engineering strategies aiming at the development of novel thrombolytics. Current trends and perspectives are discussed, including the screening for novel enzymes and small molecules, the enhancement of fibrin specificity by protein engineering, the suppression of interactions with native receptors, liposomal encapsulation and targeted release, the application of adjuvants, and the development of improved production systems.

The multifaceted role of plasminogen in inflammation

“…The kringle 1 domain of tPA is involved in the uptake of tPA in the liver [ 35 ], while the Kringle 2 domain is important for interactions with N -methyl-D-aspartic acid receptor (NMDA-R) and platelet-derived growth factors (PDGFs) [ 36 ]. tPA also associates with the annexinA2S100A10 complex, Plg-RKT, and mannose receptors [ [37] , [38] , [39] , [40] , [41] ]. Natural inhibitors of tPA's fibrinolytic activity are plasminogen activator inhibitor-1 (PAI-1), a circulating serpin (serine protease inhibitor), and PAI-2 [ 32 , 42 ].…”

Fibrin Matrices as (Injectable) Biomaterials: Formation, Clinical Use, and Molecular Engineering

“…Also a number of other factors can contribute to plasmin activation (Figure B), for example, the bacteria‐derived streptokinase and staphylokinase, which have been clinically employed in fibrinolytic therapies for the treatment of thrombosis, although with concerns about the risk of hemorrhage . Another clinically evaluated fibrinolytic agent is desmoteplase (derived from vampire bat saliva), which shows a highly selective fibrin‐bound activation of plasminogen, thereby avoiding the problematic systemic activation of plasmin . In this mechanism of locally enhanced plasmin activation, cleavage events predominantly occur transversally rather than longitudinally in the fibers .…”

“…Streptokinase and staphylokinase activate plasminogen, the first by binding to both plasminogen and plasmin to activate other plasminogen molecules in solution, the second only binding to plasmin bound to fibrin (as it is strongly inhibited by α 2 ‐antiplasmin when in solution). Desmoteplase mimics the mechanism of tPA, but is more selective, only activating plasminogen when bound . C) SEM images and sketches of fibrin networks; at a few mg mL −1 (physiological), they have thicker fibers and a larger pore size, allowing faster plasmin diffusion and degradation.…”

Impact of SMTP Targeting Plasminogen and Soluble Epoxide Hydrolase on Thrombolysis, Inflammation, and Ischemic Stroke

“…Recanalization therapy, especially thrombolysis and endovascular thrombectomy, is currently the major choice for acute phase treatment [ 147 , 148 , 149 ]. Among several thrombolytics developed to date, t-PA (alteplase) is highly recommended for ischemic stroke treatment (see [ 150 , 151 , 152 ] for historical and comparative perspectives on the thrombolytics). Despite the robust evidence backing t-PA therapy and endovascular thrombectomy, these therapies are not a panacea; they have some limitations.…”