Title Emerging Adjuvant Thrombolytic Therapies for Acute Ischemic Stroke Reperfusion.pdf ✅

Stroke Stroke is available at www.ahajournals.org/journal/str 2536 October 2024 Stroke. 2024;55:2536–2546. DOI: 10.1161/STROKEAHA.124.045755 TOPICAL REVIEW Emerging Adjuvant Thrombolytic Therapies for Acute Ischemic Stroke Reperfusion Vignan Yogendrakumar , PhD; Sarah Vandelanotte, MSc; Eva A. Mistry , MBBS; Michael D. Hill , MD; Shelagh B. Coutts , MD; Raul G. Nogueira , MD; Thanh N. Nguyen , MD; Robert L. Medcalf , PhD; Joseph P. Broderick , MD; Simon F. De Meyer , PhD; Bruce C.V. Campbell , PhD ABSTRACT: Thrombolytic therapies for acute ischemic stroke are widely available but only result in recanalization early enough, to be therapeutically useful, in 10% to 30% of cases. This large gap in treatment effectiveness could be filled by novel therapies that can increase the effectiveness of thrombus clearance without significantly increasing the risk of harm. This focused update will describe the current state of emerging adjuvant treatments for acute ischemic stroke reperfusion. We focus on new treatments that are designed to (1) target different components that make up a stroke thrombus, (2) enhance endogenous fibrinolytic systems, (3) reduce stagnant blood flow, and (4) improve recanalization of distal thrombi and postendovascular thrombectomy. GRAPHIC ABSTRACT: A graphic abstract is available for this article. Key Words: reperfusion ◼ stroke ◼ thrombectomy ◼ thrombolytic therapy ◼ treatment outcome While highly effective, only a portion of acute isch- emic stroke patients are eligible for and have access to endovascular therapy (EVT).1–3 EVT is a technology- and expertise-dependent treatment only available in larger and more advanced hospitals. The disparity in access to EVT is particularly marked in low- and middle-income countries.4 Even in devel- oped countries, the majority of patients with ischemic stroke do not present to EVT-capable centers and often require time-consuming inter-hospital transfers. In contrast, intravenous thrombolytic therapies are more readily available3,5,6 and less resource-intensive. Throm- bolytic treatments can benefit patients during inter- hospital transfers for EVT and have also been shown to be superior to EVT alone if administered within several hours after symptom onset.7 With growing innovations in prehospital care, rapid treatment with thrombolytics is becoming possible.8–10 Patients who are treated quickly with thrombolytics are more likely to achieve early recanalization (defined as the reopening of an occluded vessel) and reperfusion (defined as the restoration of blood flow in the formerly occluded vasculature).11 This translates into improved long-term outcomes, even when compared with reperfusion achieved following EVT.12 Intra-arterial delivery of thrombolytic agents may also play a role in situations where EVT is unsuccessful or leaves behind distal thrombi that cannot be mechani- cally retrieved. The key to any successful thrombolytic therapy is achieving reperfusion as rapidly as possible without increasing the risk of significant harm. With currently available plasminogen activators, the majority of patients with a visible occlusion on imaging do not achieve rapid (within 2–4 hours of treatment) or complete reperfu- sion.13,14 Innovative pharmacotherapeutics targeting the primary occlusion and new therapeutic options to treat distal nonretrievable thrombi following EVT are required. This review will describe the current state of emerging adjuvant treatments for acute ischemic stroke reperfusion. Correspondence to: Vignan Yogendrakumar PhD, Division of Neurology, Department of Medicine, The Ottawa Hospital Civic Campus, 1053 Carling Ave, K1Y4E9, Ottawa, Ontario, Canada. Email [email protected] For Sources of Funding and Disclosures, see page 2543. © 2024 American Heart Association, Inc. Downloaded from http://ahajournals.org by on December 17, 2024
TOPICAL REVIEW Stroke. 2024;55:2536–2546. DOI: 10.1161/STROKEAHA.124.045755 October 2024 2537 Yogendrakumar et al Emerging Adjuvant Thrombolytic Strategies CONSIDERING BOTH THE MACROVASCULAR AND MICROVASCULAR CIRCULATION There are 2 related but distinct pathophysiologic entities that may be targeted by thrombolytic therapies (Figure 1). Traditionally, visible (macrovascular) arterial occlusions have been the target of all EVT and many intravenous thrombolytic studies. In addition to primary thrombus removal, macrovascular reperfusion strategies can also be used to treat smaller distal emboli, often created as a secondary complication of EVT. These thromboembolic events can affect new vascular territories and are not always visible or accessible to mechanical removal dur- ing angiography.15,16 Emerging data suggest that clearing these smaller thrombi and achieving complete reperfu- sion, even in the hours following EVT, is associated with favorable clinical outcomes, similar to patients who achieve complete reperfusion following EVT.17 The cerebral microcirculation, which is not visualized on cerebral angiography, may be another important tar- get in reperfusion. Preclinical models of the heart and brain describe the concept of reduced microvascular flow after macrovascular recanalization, termed no-reflow.18 The underlying causes of microvascular no-reflow are not well understood but may include intravascular plug- ging by fibrin, platelets, or leukocytes, capillary endothe- lial thickening, or contraction by pericytes.19 Clinically, perfusion imaging has been used in an attempt to iden- tify the no-reflow phenomenon in acute ischemic stroke patients.20 The CHOICE trial (Intraarterial Alteplase Versus Placebo After Mechanical Thrombectomy)21 highlighted the potential of the cerebral microcircula- tion as a therapeutic target. Randomizing patients with anterior circulation large vessel occlusion who achieved successful macrovascular recanalization following EVT (expanded Treatment in Cerebral Ischemia [eTICI] 2b-3) to intra-arterial alteplase or placebo, CHOICE suggested that intra-arterial treatment was associated with higher rates of improved outcomes at 90 days. The results of CHOICE are limited by its sample size (the study was terminated early) and the use of a nonsaline placebo. The results require replication, but the trial illustrates the potential benefits of targeting the microvascular circulation. TARGETING THE PRIMARY OCCLUSION Using Clot Composition to Our Advantage The composition of stroke thrombi is highly variable and can evolve with time, impacting their susceptibility to thrombolytic treatments. Acute thrombi are primarily made up of red blood cells (RBCs), fibrin, white blood cells, platelets, neutrophil extracellular traps (NETs; com- posed of DNA), and von Willebrand Factor (VWF).22,23 Via histological studies of stroke thrombi, Staessens et al24 defined 2 distinct types of thrombus material, referred to as RBC-rich and platelet-rich. RBC-rich thrombi are composed of packed RBCs entangled in a loose mesh- work of thin fibrin, whereas platelet-rich thrombi have a more complex structural organization, characterized by the presence of platelets within dense fibrin structures together with significant amounts of VWF and extracel- lular DNA.24 An outer shell made of densely compacted thrombus components, including fibrin, VWF, and aggre- gated platelets, has also been described as a common structural feature of ischemic stroke thrombi.25 Increasing evidence indicates that platelet-rich thrombi are resistant to intravenous thrombolytic thera- pies. In animal stroke models using platelet-rich thrombi, the administration of recombinant tissue-type plasmino- gen activator was not associated with successful recan- alization.26–28 In humans, alteplase is less effective in patients whose diagnostic CT imaging conducted before treatment shows a low-density thrombus associated with fibrin or platelet-rich thrombi.29 Conversely, the pres- ence of a hyperdense thrombus on CT, or a hypointense thrombus on T2* susceptibility-weighted magnetic reso- nance imaging, is associated with RBC-rich thrombi and improved response to thrombolysis.30,31 Using retrieved thrombi from stroke patients, Vandelanotte et al32 have recently demonstrated that the efficacy of alteplase is linked with thrombus composition, with platelet-rich thrombi showing resistance to alteplase. The reason why platelet-rich thrombi are less respon- sive to thrombolytics is attributed to several factors. First, the presence of nonfibrin components such as VWF and extracellular DNA creates an additional scaffold that is resistant to fibrinolysis. The presence of such fibrinolysis- resistant scaffolds reduces the ability of conventional fibrinolytic agents to permeate the thrombus and reach their therapeutic targets, especially when present in the Nonstandard Abbreviations and Acronyms ADAMTS13 a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 diNAC di-N-acetylcysteine eTICI expanded Treatment in Cerebral Ischemia EVT endovascular therapy GP glycoprotein NET neutrophil extracellular trap RBC red blood cells TAFI thrombin-activatable fibrinolysis inhibitor VWF von Willebrand Factor Downloaded from http://ahajournals.org by on December 17, 2024
TOPICAL REVIEW 2538 October 2024 Stroke. 2024;55:2536–2546. DOI: 10.1161/STROKEAHA.124.045755 Yogendrakumar et al Emerging Adjuvant Thrombolytic Strategies outer shell that encapsulates a looser thrombus core.25 Platelet-mediated thrombus contraction may also further decrease the overall permeability of the thrombus, ren- dering the internal structures less accessible to throm- bolysis.33,34 Second, NET components such as DNA and histones can alter the fibrin structure, resulting in thicker fibrin fibers that are more resistant to fibrinolysis.35,36 Furthermore, NETs can bind to VWF and plasminogen activator inhibitor-1 under shear conditions and further enhance thrombus stability.37 Novel approaches are emerging to increase thrombolysis rates, including the targeting of VWF, NETs, or platelets. von Willebrand Factor VWF is a circulating plasma glycoprotein that normally facilitates hemostasis by recruiting platelets to a site of vascular injury via interactions with the platelet GP (gly- coprotein) Ibα receptor. This promotes the development of a platelet plug via fibrinogen, or VWF, which, by bind- ing to glycoprotein IIb-IIIa, can cross-link platelets in the growing thrombus.38 In stroke thrombi, VWF is mainly found among platelet-rich material and throughout the outer shell. Based on the idea that VWF is a substantial component of platelet-rich thrombi, VWF has become a novel target for candidate treatments to improve thrombolysis. Several strategies include the use of N-acetylcysteine (NAC), ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13), and agents that block the binding of plate- lets to VWF (Figure 2). NAC is a reducing agent used for a variety of clinical indications and is known to be both affordable and safe. It is being investigated as a novel strategy to improve the dissolution of stroke thrombi because NAC has been previously shown to reduce the disulfide bonds within VWF multimers.39 This can lead to the degradation of large multimeric VWF molecules, and in mouse mod- els, NAC (stand-alone) exerts an improved thrombolytic effect on arterial thrombi compared with plasminogen activators without worsening hemorrhagic side effects.40 The dimerized form of NAC (diNAC) was shown to be superior to NAC in lysing VWF-platelet–rich thrombi in vitro arterial stenosis models.41 An ex vivo analysis of human stroke thrombi retrieved via EVT has demon- strated a significant reduction in thrombus weight when diNAC is combined with alteplase, specifically when the thrombus is platelet-rich.32 A phase 2, single-arm trial using intravenous NAC in acute ischemic stroke patients is registered (NAC-S, NCT04920448; Table). ADAMTS13 is a metalloprotease that cleaves large, prothrombotic VWF multimers into smaller, less active fragments within the circulation (Figure 2). The VWF- degrading activity of ADAMTS13 has been used to pro- mote the thrombolysis of platelet-rich thrombi, which Figure 1. Schematic overview of emerging adjuvant therapies. Downloaded from http://ahajournals.org by on December 17, 2024 EVT indicates endovascular therapy; NET, neutrophil extracellular traps; and vWF, von Willebrand Factor. Created with BioRender.com.
TOPICAL REVIEW Stroke. 2024;55:2536–2546. DOI: 10.1161/STROKEAHA.124.045755 October 2024 2539 Yogendrakumar et al Emerging Adjuvant Thrombolytic Strategies typically contain large amounts of VWF. In mouse models of experimental stroke, recombinant human ADAMTS13 dose-dependently dissolved thrombolysis-resistant platelet- rich thrombi, resulting in rapid restoration of middle cerebral artery blood flow and reduced brain damage.26 Recombinant human ADAMTS13 is currently being inves- tigated in 2 phase 3 studies for thrombotic thrombocyto- penic purpura (NCT03393975 and NCT04683003) and in a phase 1 trial for sickle cell disease (NCT03997760). Future trials are required to investigate the efficacy of ADAMTS13 in the context of acute stroke. Antagonists of the VWF-GPIb interaction have also been shown to improve thrombolysis (Figure 2). In a high-shear mouse thrombosis model, the inhibition of the VWF-platelet GPIbα interaction resulted in the restora- tion of vessel patency by disaggregation of the exter- nal layer of the thrombus.42 A RNA aptamer targeting VWF, initially titled DTRI-031 and renamed BB-031, has been designed to inhibit VWF interactions with platelets and augment protein degradation processes targeted to VWF.43 Canine models simulating an acute ischemic stroke have shown promising results with BB-031.44 Recanalization, assessed 6 hours after a middle cerebral artery occlusion, occurred in 50% with the use of the aptamer and was associated with reductions in infarct volumes and no incidence of intracranial hemorrhage on follow-up imaging. A phase I human study of BB-031 was recently completed,45 and further investigations into this novel treatment option are ongoing (RAISE, NCT06226805; Table). Recently, microlyse, a novel thrombolytic agent that requires VWF binding for plas- minogen activation, was shown to overcome thromboly- sis resistance in experimental murine stroke models and could serve as an alternative strategy to target VWF-rich thrombi.46 Neutrophil Extracellular Traps NETs are Web-like scaffolds of DNA and histone proteins that are released by neutrophils in response to proinflam- matory triggers.47 NETs play an important role in immu- nity by trapping and killing various pathogens, but they are also involved in many pathological processes such as atherosclerosis, autoimmunity, and thrombosis.48 Within blood vessels, NETs promote further thrombus formation and are associated with ischemic stroke and poorer out- comes.25,49 NETs and extracellular DNA are a common structural component of ischemic stroke thrombi and are particularly abundant in platelet-rich zones.24,50,51 The degradation of NETs by DNase-1, a DNA-cleaving enzyme, shows promise as a novel approach to promot- ing arterial recanalization in ischemic stroke (Figure 2). Ex vivo analyses of the commercially available form of DNase-1, dornase alfa, have previously demonstrated a significant reduction in thrombus weight when dornase alfa is combined with alteplase on human stroke thrombi retrieved via thrombectomy.50–52 Furthermore, in animal models of stroke, treatment with DNase-1 significantly improved stroke outcomes without an increased bleeding Figure 2. Pharmacological mechanisms and targets for clot directed therapies. GP indicates glycoprotein. Downloaded from http://ahajournals.org by on December 17, 2024