Development and Testing of Thrombolytics in Stroke

Abstract

Despite recent advances in recanalization therapy, mechanical thrombectomy will never be a treatment for every ischemic stroke because access to mechanical thrombectomy is still limited in many countries. Moreover, many ischemic strokes are caused by occlusion of cerebral arteries that cannot be reached by intra-arterial catheters. Reperfusion using thrombolytic agents will therefore remain an important therapy for hyperacute ischemic stroke. However, thrombolytic drugs have shown limited efficacy and notable hemorrhagic complication rates, leaving room for improvement. A comprehensive understanding of basic and clinical research pipelines as well as the current status of thrombolytic therapy will help facilitate the development of new thrombolytics. Compared with alteplase, an ideal thrombolytic agent is expected to provide faster reperfusion in more patients; prevent re-occlusions; have higher fibrin specificity for selective activation of clot-bound plasminogen to decrease bleeding complications; be retained in the blood for a longer time to minimize dosage and allow administration as a single bolus; be more resistant to inhibitors; and be less antigenic for repetitive usage. Here, we review the currently available thrombolytics, strategies for the development of new clot-dissolving substances, and the assessment of thrombolytic efficacies <i>in vitro</i> and <i>in vivo</i>.

Computer-aided engineering of staphylokinase toward enhanced affinity and selectivity for plasmin

“…Therefore, the assay monitors mainly the fibrin-SAK interaction. Alteplase showed a significantly lower penetration rate than the control protein BSA, indicating a substantial level of binding within the fibrin network [5] , [6] , [48] . Conversely, the penetration rates of SAK-wt and SAK01 did not differ from the control.…”

“…Conversely, the penetration rates of SAK-wt and SAK01 did not differ from the control. We speculate that this could be due to the limited supply of plasminogen in the microarray, suggesting a plasmin and/or plasminogen dependency of SAKs [5] , [6] , [49] , [50] . Both SAKs accumulated in the surface layer of the fibrin network and then penetrated at the same rate as the non-interacting control protein α-LA, suggesting a weak interaction with fibrin.…”

“…The greater loss of clot mass following treatment with SAK-wt suggests that clot lysis proceeded mainly in the fibrin component, while RBCs remained densely packed in the remaining clot. The high penetration capability and relatively low plasmin affinity of SAK-wt could lead to rapid clot penetration followed by fibrin degradation inside the clot [5] , [6] . However, SAK01 has a ∼7-fold higher affinity for plasmin than SAK-wt; this might be expected to limit its penetration into clots, explaining its lower thrombolytic efficacy in the static model.…”

“…Two important plasminogen activators, urokinase and tissue plasminogen activator (tPA), were subsequently discovered in human urine and animal tissues, respectively [3] , [4] . Both are serine proteases that promote the conversion of plasminogen into active plasmin capable of degrading fibrin clots [5] , [6] . All three factors are still widely used to treat pathologies caused by blood vessel occlusions, generating annual revenues estimated to be in the billions of dollars.…”

“…In contrast, staphylokinase (SAK) is an inexpensive indirect plasminogen activator first discovered in Staphylococcus aureus in 1948 [10] . It has a molecular weight of ∼15.5 kDa and consists of only 136 amino acids [5] , [6] . It lacks enzymatic activity; instead, it changes the substrate specificity of plasmin, promoting the conversion of plasminogen into plasmin [11] .…”