Bone-targeted polymer therapeutics for nonunion fracture healing

每年有超过1500万美国人遭受骨折，其中5%导致骨不连。标准 骨不连的治疗是翻修手术：清创，然后自体移植和/或额外固定。 然而，翻修手术具有任何手术固有的风险，并且由于以下原因，高达60%的病例失败 潜在合并症。因此，治疗骨不连的新疗法是至关重要的，应予以重视。 通过无创输送或增加翻修手术成功率进行手术。总体而言， 数量和再生能力的关键尺寸的缺陷内的MSC。缺乏MSC会减少软骨， 骨形成、软骨痂重塑、矿化和关键成骨生长因子的表达 在胼胝体中。此外，长期的炎症有助于衰老相关的变化， 非工会发展。尽管有几种候选药物有望增强MSC的功能， 不愈合愈合，由于骨折生物分布不良的副作用阻碍了发展。因此 在向骨折部位输送强效再生药物方面存在关键的技术差距， 生物分布到非靶组织，以提高安全性和临床可转化性。为了克服这些障碍，我们 已经开发了一种GSK-3 β抑制剂AR28的靶向纳米颗粒（NP）递送系统， 上调再生Wnt/β-catenin通路。靶向通过掺入肽来实现， 特异性结合抗酒石酸酸性磷酸酶（TRAP5b），一种基质结合蛋白， 破骨细胞在整个愈合和骨不连。TRAP5b结合肽（TBP）靶向NP表现出 在传统股骨骨折处优先聚集。骨折局部β-连环蛋白的激活在很大程度上 与未处理的、游离药物的、非靶向的NP和乱序肽NP对照相比增加。加急 与对照组相比，用TBP-NPAR28处理的骨折中观察到愈伤组织形成更快 骨化最后，治疗骨折的最大失效扭矩是对照组的3 - 4倍。 治疗后几周。然而，该技术在临床相关情况下的潜力（例如， 成人和老年模型中的急性和已建立的骨折不愈合）对于进一步发展， 提出这个高风险高回报的提案假设TBP-NPAR 28将使药物递送到 促进老年和成年小鼠骨折不愈合的愈合，提出了以下目标： 目的1：评估TBP-NPAR 28预防成人和老年人骨不连的治疗效果 鼠模型。 目的2：评估TBP-NPAR 28在成人和老年完全确定的骨不连中的治疗效果 小鼠 这些目标的成功实现将大大提高我们针对药物的能力，以预防或 成人和老年骨折不愈合的愈合。

Of the more than 15 million Americans suffer from fractures each year, 5% result in nonunions. Standard nonunion management is revision surgery: debridement, followed by autograft, and/or additional fixation. However, revision surgery carries risks inherent to any surgery and fails in up to 60% of cases due to underlying comorbidities. Therefore, novel therapeutics for treating nonunions are critical and should obviate surgery through noninvasive delivery or increase revision surgery success. There is a reduction in overall number and regenerative capacity of MSCs within a critical sized defect. Deficient MSCs reduces cartilage and bone formation, soft callus remodeling, mineralization, and expression of critical osteogenic growth factors within the callus. Additionally, prolonged inflammation contributes to aging-related changes that underlie nonunion development. Despite the promise of several drug candidates for augmenting MSC function for nonunion healing, side effects due to poor fracture biodistribution have hampered development. Thus, a critical technological gap exists in delivery of potent, regenerative drugs to fracture sites while limiting biodistribution to off-target tissues to improve safety and clinical translatability. To address these hurdles, we have developed a fracture-targeted nanoparticle (NP)-based delivery system for the GSK-3β inhibitor AR28 to upregulate the regenerative Wnt/β-catenin pathway. Targeting is achieved by incorporation of a peptide that binds specifically to tartrate resistant acid phosphatase (TRAP5b), a matrix-bound protein deposited by osteoclasts throughout healing and at nonunions. TRAP5b-binding peptide (TBP) targeted NP exhibit preferential accumulation at conventional femur fractures. Fracture localized activation of β-catenin is greatly increased compared with untreated, free drug, untargeted NP, and scrambled peptide NP controls. Expedited callus formation was observed in fractures treated with TBP-NPAR28 versus controls with more rapid callus ossification. Finally, the maximum torque to failure of treated fractures was ~3-4-fold greater than controls 4 weeks after treatments. However, the potential of this technology within more clinically relevant situations (e.g., acute and established fracture nonunions in adult and aged models) is critical for further development, setting up this high-risk/high-reward proposal. With the hypothesis that TBP-NPAR28 will enable drug delivery to promote healing in fracture nonunions in aged and adult mice, the following aims are proposed: Aim 1: Assess the therapeutic effect of a TBP-NPAR28 for the prevention of nonunion in adult and aged murine models. Aim 2: Assess the therapeutic effect of TBP-NPAR28 in fully established nonunions in adult and aged mice. Successful completion of these Aims will significantly advance our ability to target drugs to prevent or enable healing of adult and aged nonunion fractures.