BONE REGENERATIVE EFFECTS OF ANTI-SCLEROSTIN ANTIBODY AFTER SPINAL CORD INJURY

描述 目前，美国有27万人患有脊髓损伤（SCI）。100%的功能完全性SCI患者会出现病灶下骨质疏松，这是SCI后骨折风险增加100倍的基础。目前的骨丢失治疗，包括双膦酸盐（一线药物治疗）和运动只能减缓SCI后的骨丢失，但不能再生病灶下的骨量。因此，需要SCI后的新型骨再生疗法。最近，已经开发了药理学“抗硬化蛋白”抗体（硬化蛋白-Ab），其通过否定内源性硬化蛋白（促进成骨细胞发育和骨形成的Wnt信号传导途径的负调节剂）产生深刻的骨合成代谢作用。硬化蛋白-Ab的有效性通过其仅用3周治疗就逆转大鼠中卵巢切除术诱导的1年骨损失的能力以及通过其完全防止后肢卸载后的骨损失的能力来证明。临床版本的Sclerostin-Ab（AMG 785）也已显示在单次治疗剂量的85天内使脊柱和髋关节BMD增加3-5%。重要的是，sclerostin在功能完全SCI后升高，表明它在SCI诱导的骨丢失中起作用;然而，没有研究评估SCI后Sclerostin-Ab的疗效。在将其推广到本人群的临床试验之前，必须在临床前模型中检查Sclerostin-Ab是否能够再生骨。 文献中几乎没有慢性SCI诱导的骨丢失模型。目前的模型利用脊髓横断或年轻（非脊椎成熟）啮齿动物，限制了其临床相关性。相反，我们已经开发了一个胸部中部挫伤SCI模型（利用脊椎成熟的雄性啮齿动物），表现出广泛的松质骨损失急性损伤后。需要进一步开发该模型以确定其是否表现出慢性皮质骨缺损，这是SCI后临床骨丢失的标志性特征。 对于该提议，我们将1）扩展我们目前的急性SCI骨丢失模型，以开发慢性SCI诱导的骨丢失的临床相关模型（解决现有模型的弱点）和2）确定硬化蛋白-Ab是否在该模型中再生骨。为了做到这一点，我们将评估：严重胸中部挫伤SCI（或假手术）后1个月、2个月和4个月的皮质骨和松质骨质量（通过CT）、骨转换（通过组织形态计量学）、骨强度（通过机械强度测试）和sclerostin表达，以确定SCI后皮质骨丢失峰值的时间。然后，我们将评估在该模型中峰值皮质骨丢失时施用硬化素-Ab是否使骨再生。为了支持这一提议，我们通过VA合作研发协议（CRADA）从安进公司获得了硬化蛋白抗体。我们的主要假设是：1）大鼠在SCI后将经历进行性骨丢失，其特征在于松质骨的早期丢失和皮质骨的延迟丢失，以及2）硬化蛋白-Ab将在慢性SCI诱导的骨丢失的啮齿动物模型中再生骨并改善骨强度。为了检验这些假设，将评价以下特定目的：目的1：表征严重胸中部挫伤SCI后成年雄性啮齿动物的急性和慢性骨缺损，以开发慢性SCI诱导的骨丢失的临床相关模型。 目标2：确定Sclerostin-Ab是否能够在表现出严重皮质骨和松质骨缺陷的慢性SCI啮齿动物模型中再生后肢骨矿物质特征和骨强度。 该提案将扩展我们的急性SCI模型，表现出严重的松质骨丢失，以开发一个临床相关的慢性SCI模型，表现出皮质骨和松质骨丢失（解决现有模型的弱点），并将提供有关Sclerostin-Ab在SCI后再生骨的能力的首次直接证据。这些发现将为未来的临床试验提供原理证明，旨在评估Sclerostin-Ab作为脊髓损伤退伍军人骨再生手段的有效性。

DESCRIPTION 270,000 individuals currently have a spinal cord injury (SCI) in the US. 100% of those with functionally- complete SCIs experience sublesional osteoporosis, underlying the 100-fold greater bone fracture risk after SCI. Current bone loss treatments, including bisphosphonates (a frontline pharmacologic treatment) and exercise only slow bone loss after SCI, but do not regenerate sublesional bone mass. As such, need exists for novel bone regenerative therapies following SCI. Recently, a pharmacologic "anti-sclerostin" antibody (Sclerostin-Ab) has been developed that produces profound osteoanabolic effects by negating endogenous sclerostin (a negative regulator of the Wnt-signaling pathway that promotes osteoblast development and bone formation). The effectiveness of Sclerostin-Ab is demonstrated by its ability to reverse 1-year of ovariectomy- induced bone loss in rats with only 3 weeks of treatment and by its ability to completely prevent bone loss subsequent to hind limb unloading. A clinical version of Sclerostin-Ab (AMG 785) has also been shown to increase spine and hip BMD by 3-5% within 85 days of a single treatment dose. Importantly, sclerostin is elevated after functionally-complete SCI, suggesting that it plays a role in SCI-induced bone loss; however, no study has evaluated the efficacy of Sclerostin-Ab after SCI. It is essential to examine whether Sclerostin-Ab is able to regenerate bone in a pre-clinical model before promoting it to clinical trials in thi population. Few models of chronic SCI-induced bone loss exist within the literature. The current models utilize spinal cord transection or young (non-skeletally mature) rodents, limiting their clinical relevance. In contrast, we have developed a mid-thoracic contusion SCI model (utilizing skeletally-mature male rodents) that exhibits extensive cancellous bone loss acutely after injury. Further development of this model is required to determine whether it exhibits the chronic cortical bone deficits that are a hallmark characteristic of clinical bone loss after SCI. For thi proposal, we will 1) expand upon our current acute SCI bone loss model in order to develop a clinically-relevant model of chronic SCI-induced bone loss (addressing the weaknesses of the existing models) and 2) determine whether Sclerostin-Ab regenerates bone in this model. In order to do so, we will assess: cortical and cancellous bone mass (via ¿CT), bone turnover (via histomorphometry), bone strength (via mechanical strength tests), and sclerostin expression at 1, 2, and 4 months after severe mid-thoracic contusion SCI (or Sham surgery) in order to determine the time of peak cortical bone loss after SCI. We will then evaluate whether Sclerostin-Ab regenerates bone when administered at the time of peak cortical bone loss in this model. In support of this proposal, we have obtained Sclerostin-Ab from Amgen through a VA Cooperative Research and Development Agreement (CRADA). Our primary hypotheses are that 1) rats will experience progressive bone loss after SCI that is characterized by the early loss of cancellous bone and a delayed loss of cortical bone and 2) Sclerostin-Ab will regenerate bone and improve bone strength in a rodent model of chronic SCI-induced bone loss. In order to test these hypotheses, the following Specific Aims will be evaluated: AIM 1: Characterize the acute and chronic bone deficits in skeletally-mature male rodents after severe mid- thoracic contusion SCI in order to develop a clinically-relevant model of chronic SCI-induced bone loss. AIM 2: Determine whether Sclerostin-Ab is capable of regenerating hind limb bone mineral characteristics and bone strength in a rodent model of chronic SCI that exhibits severe cortical and cancellous bone deficits. This proposal will expand upon our acute SCI model that exhibits severe cancellous bone loss in order to develop a clinically-relevant chronic SCI model that exhibits cortical and cancellous bone loss (addressing the weaknesses of the existing models) and will provide the first-ever direct evidence regarding the ability of Sclerostin-Ab to regenerat bone after SCI. These findings will provide proof-of-principle for future clinical trials intended o assess the efficacy of Sclerostin-Ab as a means of regenerating bone in Veterans with SCI.