The Role of Ubiquitin-Proteasome Pathway in Myeloma Bone Disease

多发性骨髓瘤仍然与高发病率和高死亡率有关，主要是由于并发症。 由于它对骨骼的影响而产生的。这些并发症部分地反映了成骨细胞功能的损害和 骨形成失败。目前可用的治疗方法不会增加本已很低的骨量 骨髓瘤患者，迫切需要新的治疗方案来促进新骨形成 扭转骨质疏松症。尽管骨髓瘤中这种不充分的成骨细胞反应的机制仍然 未知，Dickkopf 1(Dkk1)最近被牵连。抑制泛素-蛋白酶体(Ub-Prot)途径 使用像VELCADE这样的小分子抑制剂对骨髓瘤的临床治疗有重大影响 患有复发、难治性疾病的患者。我们最近有一个令人兴奋的发现，除了他们的 深刻的抗肿瘤作用，蛋白酶体抑制剂，包括VELCADE，在体外和体外也促进骨形成 啮齿动物和正在进行的骨髓瘤患者VELCADE临床试验的数据支持这些发现。我们也 发现VELCADE对Dkk1的表达有很强的抑制作用。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’，(骨骼微环境)，从而具有突出的有益效果 骨髓瘤患者的治疗。这一假说是基于这样一个事实，即VELCADE通过抑制 蛋白酶体通过抑制Dkk1的表达来阻止骨髓瘤细胞的生长，并恢复成骨细胞的功能。 具体地说，我们提出：(I)种子和土壤对Ub-prot途径的抑制都非常敏感；(Ii) 两种情况的确切机制可能不同，但E3Ub连接酶β-TrCP似乎是主要参与的；(Iii) 与其他已知的药物不同，VELCADE具有减轻肿瘤负担和逆转骨病的潜力 化疗方法。小鼠骨髓瘤性骨病5TGM1模型的建立及新型转基因 老鼠模型，加上新的最先进的小动物成像模式，使我们能够纵向跟踪 肿瘤负荷动态(MicroPET)和骨细胞活性(microSPECT/CT)，拟议的研究试图阐明 抑制骨髓瘤中Ub-prot通路有益作用的机制。具体目标是 (I)确定蛋白酶体抑制对Dkk1和骨髓瘤相关骨病的影响(Ii)确定其作用 Dkk1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 肿瘤微环境中细胞中蛋白酶体抑制与β-TrCP的关系 骨细胞)在骨髓瘤骨病中。拟议的研究将进一步加深我们对这些机制的理解 调节蛋白酶体抑制剂对肿瘤细胞和骨骼的影响，并提出新的分子靶点，这些靶点可能成为开发治疗骨髓瘤骨病的靶向疗法的基础。

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.