Characterizing the glioma cell of origin in vivo using MADM, a mouse genetic mosa

描述(申请人提供)：胶质瘤是最常见的恶性脑肿瘤类型。尽管癌症医学取得了广泛的进步，但这种毁灭性的疾病仍然无法治愈。最近有报道称，胶质瘤中含有大量的肿瘤干细胞，这些干细胞可以在培养中形成自我更新的肿瘤球体，并在移植到免疫抑制的小鼠体内后重新启动胶质瘤。靶向这些肿瘤干细胞是治疗胶质瘤的一个令人兴奋的前景。然而，开发这种治疗策略所需的关键信息，包括胶质瘤干细胞的发育来源，仍然未知。为了解决肿瘤细胞起源的问题，它需要使用允许分析早期癌前肿瘤细胞的胶质瘤动物模型。不幸的是，目前的小鼠模型不能为这类研究提供足够的体内分辨率。我们实验室基于一种新的遗传马赛克系统开发了一种新的小鼠脑胶质瘤模型，称为MADM(Mosaic Analysis with Double Markets，Zong等人细胞2005)。使用MADM，我们可以在正常的小鼠体内产生罕见的绿色荧光蛋白(GFP)标记的神经干细胞(NSCs)，这些细胞对两个关键的肿瘤抑制基因--p53和神经纤维瘤病1型(NF1)--是双空的。这种方法使我们能够在体内用单细胞分辨率分析胶质瘤形成的整个过程。我们的初步发现表明，尽管突变是在神经干细胞中产生的，但由此产生的胶质瘤细胞表现出许多少突胶质细胞前体(OPC)的细胞特征。在癌变之前，OPC是唯一在MADM小鼠中急剧过度扩张的细胞系。在胶质瘤肿块中，OPC也是维持活跃细胞分裂的主要细胞类型。当我们纯化这些OPC样脑胶质瘤细胞时，它们表现出显著的胶质瘤干细胞特征，包括形成可再生的肿瘤球体，分化为多个细胞系，以及移植到免疫抑制的小鼠体内后重新启动胶质瘤。基于这些初步结果，我们将检验以下假设：1)OPC是启动和更新胶质瘤形成的关键细胞类型；2)突变OPC可以去分化获得干细胞特性；3)靶向OPC或其干细胞特性将是胶质瘤的有效治疗策略。我们提出的研究将有助于我们对胶质瘤的发展过程有价值的基本了解。肿瘤起始细胞的鉴定应该为设计合理的治疗策略提供基础。从概念上讲，我们提出的工作探索了肿瘤起始的未知领域，并为完善小鼠模型以从机制上理解人类癌症提供了关键的基础。 公共卫生相关性：这项拨款中提出的研究旨在确定神经胶质瘤的癌症干细胞的来源，胶质瘤是一种目前无法治愈的疾病。对这些细胞的透彻了解应该能够通过靶向特定的细胞或基因来治疗胶质瘤来设计合理的治疗策略。因此，增强的特异性应该会导致更有效和毒性更低的药物，最终可能会提供治疗胶质瘤的方法。

DESCRIPTION (provided by applicant): Glioma is the most common type of malignant brain tumor. Despite widespread advances in cancer medicine, this devastating disease remains incurable. Recently, it was reported that gliomas contain a population of tumor stem cells that can form self renewable tumor spheres in culture and re- initiate gliomas after transplantation into immuno-suppressed mice. Targeting these tumor stem cells is an exciting prospect towards a glioma cure. However, critical information required to develop such therapeutic strategies, including the developmental origin of the glioma stem cells, remains unknown. To address the tumor cell of origin problem, it requires the use of glioma animal models that allow the analysis of early-stage pre-malignant tumor cells. Unfortunately, current mouse models cannot provide adequate in vivo resolution for such studies. Our laboratory has developed a new mouse glioma model based on a novel genetic mosaic system termed MADM (Mosaic Analysis with Double Markers, Zong et al Cell 2005). Using MADM, we can generate rare, green fluorescent protein (GFP)-labeled neural stem cells (NSCs) that are double null for two key tumor suppressor genes, p53 and Neurofibromatosis Type 1 (NF1), within an otherwise normal mouse. This approach allows us to analyze the entire course of gliomagenesis with single-cell resolution in vivo. Our preliminary findings show that, although the mutations are generated specifically in NSCs, resulting glioma cells manifest many cellular features of oligodendrocyte precursors (OPCs). Prior to malignancy, OPCs are the only cell lineage that drastically over-expands in the MADM mice. In the glioma tumor mass, OPCs are also the predominant cell type that maintains active cell divisions. When we purify these OPC-like glioma cells they manifest salient glioma stem cell features, including forming renewable tumor spheres, differentiating into multiple cell lineages, and reinitiating gliomas after being transplanted into immuno-suppressed mice. Based on these preliminary results, we will test the following hypothesis: 1) OPCs are the key cell type that initiates and renews gliomagenesis; 2) mutant OPCs can de-differentiate to acquire stem cell properties; and 3) targeting OPCs or their stem-cell characteristics will be effective treatment strategies for gliomas. Our proposed studies will lead to valuable basic understanding of the developmental process of gliomas. The identification of tumor-initiating cells should provide a basis for designing rationale treatment strategies for the cure. Conceptually, our proposed work explores the uncharted territory of tumor initiation, and provides critical groundwork for the refinement of mouse models for mechanistic understanding of human cancers. PUBLIC HEALTH RELEVANCE: Studies proposed in this grant aim at the identification of the origin of cancer stem cells for glioma, a currently incurable disease. A thorough understanding of these cells should enable the design of rationale therapeutic strategies by targeting specific cells or genes to treat gliomas. As a consequence, the enhanced specificity should lead to more effective and less toxic drugs, which could eventually provide a cure for gliomas.