Angiogenic growth factor delivery for vascular regeneration in critical limb ischemia using acoustically-responsive scaffolds

摘要 促血管生成生长因子的临床应用可能会极大地影响严重肢体缺血的治疗 (CLI)一种以四肢动脉阻塞为特征的病症。对于CLI，40%的患者不符合条件 对于现有的治疗方法，即使有干预措施，6个月截肢的风险为25-40%， 年死亡率为20%。在CLI的临床前模型中，侧支血管形成和灌注 在施用血管生成生长因子后，在缺血肢体中观察到恢复。 然而，试图通过使用现场或全身的临床转化这些有希望的临床前结果， 注射血管生成生长因子仍然是一个挑战。通过注射递送生长因子 或使用传统的基于支架的方法不能提供对剂量、时间或空间的主动控制。 定位于侧支血管形成的预期部位。此外，在以下方面没有达成共识： 这些参数的范围，包括什么样的生长因子的组合，需要有效的 治疗性血管生成。因此，迫切需要开发一种安全有效的递送系统， 多种血管生成生长因子，概括了内源性生长因子信号传导的关键方面， 有助于确定这些关键参数。我们的长期目标是开发可植入的生物材料 对于再生分子的递送，其中递送可以在时空上以 外部监管，按需方式。调制机制是兆赫范围的超声， 临床上可转换，因为它可以无创应用，以亚毫米精度聚焦， 以时空限定的方式递送到体内深处的部位。本提案的目的是 开发一种可植入的支架，其中两种生长因子的释放剂量、顺序和定位 参与血管生成-碱性成纤维细胞生长因子（bFGF）和血小板衍生生长因子-BB（PDGF- BB）-非侵入性控制。该支架被称为声响应支架（ARS）， 用两种超声波敏感乳剂，每种乳剂都含有一种生长因子。推动这一理论的核心假设是 该项目是超声可以通过控制ARS内和周围的血管生成， bFGF和PDGF-BB的顺序释放。拟议研究的基本原理是， 研究bFGF和PDGF-BB的不同剂量和时空梯度如何影响 血管，其可用于治疗CLI的治疗性血管生成的转化。的 将通过三个具体目标来检验假设：1）增强ARS中生长因子的选择性释放; 2)使用ARS来证明bFGF的时空产生的梯度对血管生成的影响; 和3）证明使用ARS在鼠后肢缺血模型中恢复灌注。成功 完成拟议的研究是重要的，因为它将阐明如何微环境因素，如 因为生长因子剂量、时空分布和序列影响血管生成。

ABSTRACT The clinical use of pro-angiogenic growth factors could greatly impact the treatment of critical limb ischemia (CLI), a condition characterized by arterial blockages in the extremities. With CLI, 40% of patients are ineligible for available therapies and even with intervention, the 6-month risk of limb amputation is 25-40% with an annual mortality of 20%. In preclinical models of CLI, collateral blood vessel formation and perfusion restoration are observed in the ischemic limb following the administration of angiogenic growth factors. However, attempts at clinically translating these promising preclinical results, via the use of at-site or systemic injections of angiogenic growth factors, has remained a challenge. The delivery of growth factors via injection or using conventional scaffold-based approaches does not afford active control of the dose, timing, or spatial localization at the intended site of collateral vessel formation. Furthermore, no consensus exists regarding what range of these parameters, including what combination of growth factors, are required for effective therapeutic angiogenesis. Thus, there is an urgent need to develop a safe and effective delivery system for multiple angiogenic growth factors that recapitulates critical aspects of endogenous growth factor signaling and facilitates identification of these crucial parameters. Our long-term goal is to develop implantable biomaterials for the delivery of regenerative molecules, where delivery can be manipulated spatiotemporally in an externally-regulated, on-demand manner. The modulating mechanism is megahertz-range ultrasound, which is clinically translatable since it can be applied non-invasively, focused with sub-millimeter precision, and delivered in a spatiotemporally defined manner to sites deep within the body. The objective of this proposal is to develop an implantable scaffold where the released dose, sequence, and localization of two growth factors involved in angiogenesis - basic fibroblast growth factor (bFGF) and platelet derived growth factor-BB (PDGF- BB) - are non-invasively controlled. The scaffold, termed an acoustically-responsive scaffold (ARS), is doped with two ultrasound-sensitive emulsions that each contain a growth factor. The central hypothesis driving this project is that ultrasound can spatiotemporally pattern angiogenesis in and around an ARS by controlling the sequential release of bFGF and PDGF-BB. The rationale for the proposed research is that an ARS enables the study of how various doses and spatiotemporal gradients of bFGF and PDGF-BB affect the development of blood vessels, which can be used in the translation of therapeutic angiogenesis for the treatment of CLI. The hypothesis will be tested via three specific aims: 1) enhance selective release of growth factors from the ARS; 2) use an ARS to demonstrate the impact of spatiotemporally-generated gradients of bFGF on angiogenesis; and 3) demonstrate restoration of perfusion in a murine hind limb ischemia model using an ARS. Successful completion of the proposed research is significant since it will elucidate how microenvironmental factors – such as growth factor doses, spatiotemporal profiles, and sequence – affect angiogenesis.