Ultrasound-Assisted Thrombolysis for Stroke Therapy

描述(申请人提供)：中风是美国第三大致死原因和致残原因。对于缺血性中风患者，溶栓药物重组组织型纤溶酶原激活剂(rt-PA)是唯一获得FDA批准的治疗方法。全身或外周应用rt-PA治疗卒中疗效有限，因为通过外周注射难以控制rt-PA向靶血栓的输送。通过导管将rt-PA直接注入血栓显示了希望，但到目前为止，它受到技术要求和可用专业知识的限制。此外，rt-PA还具有导致脑出血的显著风险。因此，为了提高rt-PA诱导的血栓溶解效果，减少rt-PA的用药量，我们在体外猪血栓模型上研究了rt-PA和120 kHz超声在溶栓中的协同作用。这些初步数据有力地支持了我们建议的中心假设，即超声主要通过机械机制促进血栓溶解。为了验证这一假说，我们建议调查三个特定的目标：在目标1中，我们将扩展超声介导的血栓形成机制的知识库。使用30 MHz主动空化探测器(或15 MHz被动...Constantin？)，我们将确定空化活性与暴露在脉冲超声下的加速溶栓之间的关系。热电偶测量脉冲超声静止期的凝块温度将阐明热效应对超声增强溶栓的贡献。作为AIM#2中的一种新方法，我们将研究由西北大学的McPherson和MacDonald开发的包裹气体和液体的亚微米级磷脂双层囊泡(Elip)将rt-PA输送到导致缺血性中风的血管内血栓附近的可能性。此外，通过将抗纤维蛋白抗体偶联到脂质体表面，ELIP可以靶向凝块。诊断超声(低MI)将用于体外鉴定t-PA脂质体并评估其靶向效率。脂质体破坏和药物输送的阈值将使用临床超声扫描仪(ATL HDI 5000)来确定。最后，在目标3中，我们将在猪出血性和缺血性中风模型中进行活体研究，以证明超声增强溶栓的有效性，并阐明治疗性超声波在存在回声造影剂的情况下对脑组织的潜在风险。我们预计，这些研究的成功完成将对我们开发一种超声辅助溶栓系统的长期目标做出重大贡献，该系统能够提供和加强脑血管的溶栓治疗，并在缺血性中风后迅速恢复灌流。

DESCRIPTION (provided by applicant):Stroke is the third leading cause of death and the leading cause of disability in the United States. For patients with ischemic stroke, the thrombolytic drug recombinant tissue plasminogen activator (rt-PA) is the only FDAapproved treatment. Systemic or peripheral administration of rt-PA has been used in the treatment of stroke with limited success as it is difficult to control delivery ofrt-PA to the target clot through a peripheral injection. Direct administration of rt-PA into the clot through a catheter shows promise, but to date has been limited by technical demands and availability of expertise in its administration. In addition, rt-PA has a significant risk to induce intracerebral hemorrhage. Therefore, to improve the efficacy of rt-PA-induced clot lysis and to reduce the administered rt-PA dose, we have investigated the synergistic effect of rt-PA and 120-KHz ultrasound on thrombolysis in an in vitro porcine clot model. These preliminary data strongly support the central hypothesis of our proposal that ultrasound enhances thrombolysis, primarily via mechanical mechanisms. To test this hypothesis we propose to investigate three Specific Aims: In Aim #1, we will expand the knowledge base of mechanisms of ultrasound-mediated thrombolysis.in a series of in vitro experiments with a porcine clot model. Using a 30-MHz active cavitation detector (or 15-MHz passive...Constantin?), we will determine the relationship between cavitational activity and accelerated thrombolysis from exposure to pulsed ultrasound. Thermocouple measurements of the clot temperature during the quiescent period of pulsed ultrasound will elucidate the contribution of thermal effects to ultrasound-enhanced thrombolysis. As a novel approach in Aim #2, we will investigate the potential of echogenic liposomes (ELIP), or submicron-sized phospholipid bilayer vesicles enclosing gas and fluid developed by McPherson and MacDonald at Northwestern University, to deliver rt-PA near the intravascular clot causing the ischemic stroke. Furthermore, ELIP can be targeted to clot by conjugating anti-fibrin antibodies to the liposome surface. Diagnostic ultrasound (low MI) will be used in vitro to identify the t-PA-loaded liposomes and to assess the targeting efficiency. The threshold of liposome destruction and drug delivery will be determined using a clinical ultrasound scanner (ATL HDI 5000). Lastly, in Aim #3, we will conduct in vivo studies in porcine hemorrhagic and ischemic stroke models to demonstrate the efficacy of ultrasound-enhanced thrombolysis and to clarify the potential risks for therapeutic ultrasound on brain tissue and in the presence of an echo contrast agent. We expect that successful completion of these studies will contribute significantly to our long-term goal to develop an ultrasound-assisted thrombolysis system that delivers and enhances thrombolytic therapy in the cerebral vasculature and rapidly restores perfusion after ischemic stroke.