利用骨形成蛋白2抑制骨肉瘤的分化疗法

Osteosarcoma can cause severe symptoms associated with impeded bone growth. Invasion of skeleton, such as spine and limbs, is commonly accompanied with complications such as neural deficits and pathological fracture, and thus requires surgical stabilization. Recombinant human bone morphogenetic proteins (BMP) have been recently approved to augment spinal fusion and recalcitrant long-bone non-unions for their equivalent or superior efficacy to autogenous bone graft in enhancing bony fusion. Nonetheless, the use of BMP-2 is contraindicated in surgery for bone tumors due to concerns that this anabolic growth factor may cause tumor proliferation. Recent evidence suggests that there is a small fraction of tumor-initiating cells present in a variety of cancers, including bone tumors. These cells express properties resembling stem cells (so-called cancer stem cells) that might be responsible for tumor growth, recurrence, and resistance to treatment. Our current investigations suggest that exposure of heterogeneous populations of cancer cells containing stem-like cells to BMPs can induce osteogenic differentiation of the stem-like cells and thereby reduce tumor growth and improve responsiveness to treatment. We hypothesize that BMP-2 induction reduces tumorigenic capacity of osteosarcoma while promoting osseous reunion of the intervened skeleton to facilitate surgical reconstruction after tumor resection. In particular, BMP-2 restricts the tumorigenecity of osteosarcoma by inducing "differentiation" of the osteosarco-stem cells that express high level of aldehyde dehydrogenase (ALDH), making them more susceptible to the affiliated therapies, restricting their expansion and plasticity. We propose to initiate our investigations by rigorously investigating differentiation pathways of BMP-2 treated ALDH bright cells and the consequent phenotypical expressions through their epigenetic profiling as well as by cross comparing those of other pluripotent cells. Followed by the in vitro studies, a canine model of spontaneous osteosarcoma will be utilized to assess the propensity of tumor recurrence and characterize the reconstituted tissues by BMP-2 induction in vivo through a sequential tissue extraction with specifically designed bone chambers. The primary goal of this translational research is to collect necessary information that will lead to the development of a new clinical strategy for possibly attenuating bone sarcoma expansion and enhancing bone union, particularly in skeletal reconstruction after tumor resection.

目前临床上禁止将骨形成蛋白2应用于骨肿瘤外科，主要的疑虑是其可能会导致癌症的生长与扩张。近年来的研究表明肿瘤的发生可能是由一小群肿瘤细胞所诱发，它们表现出许多类似干细胞的特性，支持肿瘤的生长、复发甚至阻抗癌症的治疗。申请人的研究团队发表了许多证据，指出将骨形成蛋白应用于由癌干细胞组成的非均质肿瘤，将可诱发这些癌干细胞的成骨分化，进而减缓肿瘤的生长以及增进其对治疗药物的反应。因此，我们希望通过本研究来进一步推动此科研成果到临床医学的转化。本研究拟将犬的骨肉瘤做为临床前先期测试的对象，来评估骨形成蛋白作为分化疗法的可行性，将达成（1）对骨形成蛋白诱发后，受肿瘤侵犯及手术切除骨骼新生组织的组成，及内含细胞的致癌能力的分析；（2）对接受骨形成蛋白进行重建的骨骼力学功能的测试等主要研究目标。

骨形成蛋白(BMP)是转化生长因子超家族的一员，在骨和软骨形成及损伤修复过程中起着十分重要的作用。目前有报道BMP-2, -4, 和 -7用于脊柱，长骨和自体移植骨的融合术，但临床上禁止BMP应用于骨肿瘤外科，担心其可能会导致癌症的生长与扩张。在本项目研究中，我们将3×105的143B骨肉瘤肿瘤细胞接种于BALB/C裸鼠上，成功建立了具有肺转移等特征的原位恶性骨肉瘤模型。通过对肿瘤和动物进行包括X射线，组织学以及肺部转移情况的分析，证明骨肉瘤模型与肿瘤临床特征相似。是理想的研究原发骨肉瘤的动物模型。在此基础上，项目组研究了BMP-2对荷瘤动物肿瘤的影响。我们发现在BMP-2治疗后，荷瘤小鼠中ALDHbr肿瘤干细胞受BMP-2成骨分化而减少，表达ki-67的肿瘤细胞生长受到抑制。另外X射线和Micro-ct扫描结果均表明BMP-2能够有效地抑制肿瘤细胞的侵袭和保持骨的完整性。同时研究肿瘤的转移能力也证明了BMP-2能够抑制骨肉瘤的肺转移。所有的研究结果表明：在我们建立的原位肿瘤模型上，BMP-2通过对骨肉瘤肿瘤干细胞的分化疗法，有效地抑制了肿瘤的生长与扩张，对受骨肿瘤侵袭的骨组织具有骨重建和骨保护作用。这为使用BMP-2及相关药物治疗恶性骨肉瘤提供了重要的理论基础，为临床治疗骨肉瘤提供了全新的思路和方法。