The Role of Ubiquitin-Proteasome Pathway in Myeloma Bone Disease

多发性骨髓瘤仍然与高发病率和死亡率有关，主要是由于并发症 这是因为它对骨骼的影响。这些并发症部分反映了成骨细胞功能受损， 骨形成失败。目前可用的治疗方式不会增加已经很低的骨量， 骨髓瘤患者，并且迫切需要新的治疗范例，其增强新骨形成， 扭转骨质缺损尽管骨髓瘤中成骨细胞反应不足的机制仍然存在， Dickkopf 1（DKK 1）最近被发现。泛素-蛋白酶体（Ub-prot）途径的抑制 与小分子抑制剂如万珂的联合应用对骨髓瘤的临床管理产生了重大影响， 复发性、难治性疾病患者。我们最近有了一个令人兴奋的发现，除了他们的 蛋白酶体抑制剂（包括万珂）具有显著的抗肿瘤作用，也可在体外和体内增强骨形成。 啮齿类动物和正在进行的万珂在骨髓瘤患者中的临床试验数据支持这些发现。我们也 发现万珂是DKK 1表达的有效抑制剂。我们的假设是骨髓瘤中的蛋白酶体抑制 影响“种子”（肿瘤）和“土壤”（骨微环境），从而在骨移植中具有显著的有益效果。 骨髓瘤患者的治疗。这一假设是基于这样一个事实，即万珂通过抑制 蛋白酶体来阻断骨髓瘤细胞生长，并且还通过抑制DKK 1表达来恢复成骨细胞功能。 具体而言，我们提出：（i）种子和土壤对Ub-prot途径的抑制非常敏感;（ii） 两种情况下的确切机制可能不同，但E3 Ub连接酶β-TrCP似乎在中心参与;（iii） 万珂具有降低肿瘤负荷的潜力，同时逆转骨疾病，不像其他已知的 化疗方法。使用骨髓瘤骨病的小鼠5 TGM 1模型以及新的转基因 小鼠模型，再加上新的最先进的小动物成像模式，使我们能够纵向跟踪 肿瘤负荷（microPET）和骨细胞活性（microSPECT/CT）的动态，拟议的研究试图阐明 介导抑制Ub-prot通路在骨髓瘤中的有益作用的机制。具体目标是 (I)确定蛋白酶体抑制对Dkk 1和骨髓瘤相关骨病的影响（ii）确定蛋白酶体抑制对Dkk 1和骨髓瘤相关骨病的作用 Dkk 1在骨髓瘤骨病骨形成中的作用及其与蛋白酶体抑制的关系;（iii）定义 蛋白酶体抑制和肿瘤微环境中细胞中β-TrCP之间的关系（肿瘤细胞和 骨细胞）在骨髓瘤骨疾病中的作用。这些研究将进一步加深我们对这些机制的理解。 介导蛋白酶体抑制剂对肿瘤细胞和骨骼的影响，并提出了新的分子靶点，这些靶点可能作为开发治疗骨髓瘤骨病的靶向治疗剂的基础。

Multiple myeloma continues to be associated with high morbidity and mortality rates due mostly to complications resulting from its effects on the skeleton. These complications reflect, in part, an impairment of osteoblast function and failure of bone formation. Currently available treatment modalities do not increase the already low bone mass in myeloma patients, and there is a compelling need for new treatment paradigms that enhance new bone formation to reverse the bone deficit. Although the mechanism underlying this inadequate osteoblast response in myeloma remains unknown, Dickkopf 1 (DKK1) has recently been implicated. Inhibition of the ubiquitin-proteasome (Ub-prot) pathway with small molecule inhibitors such as Velcade is having a significant impact on clinical management of myeloma patients with relapsed, refractory disease. We have recently made the exciting discovery that, in addition to their profound anti-tumor effects, proteasome inhibitors, including Velcade, also enhance bone formation in vitro and in rodents and data emerging from on-going clinical trials of Velcade in myeloma patients support these findings. We also find that Velcade is a potent inhibitor of DKK1 expression. Our hypothesis is that proteasome inhibition in myeloma affects both 'seed' (tumor) and 'soil', (bone microenvironment), and thereby has outstanding beneficial effects in the treatment of myeloma patients. This hypothesis is based on the fact that Velcade works through inhibition of the proteasome to block myeloma cell growth and also to restore osteoblast function by inhibiting DKK1 expression. Specifically, we propose that (i) both seed and soil are exquisitely sensitive to inhibition of the Ub-prot pathway; (ii) the precise mechanism in either case may be different but the E3 Ub ligase beta-TrCP appears to be centrally involved; (iii) Velcade has the potential to reduce tumor burden and concomitantly reverse bone disease, unlike other known chemotherapeutic approaches. Using the murine 5TGM1 model of myeloma bone disease as well as novel transgenic mouse models, coupled with novel state-of-the-art small animal imaging modalities that allow us to longitudinally track dynamics of tumor burden (microPET) and bone cell activity (microSPECT/CT), the proposed studies seek to elucidate the mechanisms mediating the beneficial effects of inhibiting the Ub-prot pathway in myeloma. The Specific Aims are to (I) Determine the effects of proteasome inhibition on Dkk1 and related bone disease of myeloma (ii) Determine the role of Dkk1 in bone formation in myeloma bone disease and the relationship to proteasome inhibition; (iii) Define the relationship between proteasome inhibition and beta-TrCP in cells within the tumor microenvironment (tumor cells and bone cells) in myeloma bone disease. The proposed studies will further our understanding of the mechanisms mediating the impact of proteasome inhibitors on tumor cells and the skeleton and suggest new molecular targets which potentially would serve as the basis for development of targeted therapeutics to treat myeloma bone disease.