The Role of the Stem Cell Niche in ALL

描述(由申请人提供)：肿瘤干细胞对癌症进展和复发的贡献被认为是实体和血液系统恶性肿瘤的重大临床挑战。要了解肿瘤干细胞存活和自我更新的机制，关键是要研究它们生长的微环境对它们的支持。骨髓微环境对调节细胞命运的贡献是血液系统恶性肿瘤以及随后的白血病干细胞(LSC)所特有的。在目前的研究中，我们研究了LSC与骨髓基质细胞(BMSC)的相互作用以及BMSC对维持LSC表型的作用机制。我们利用了一个独特的BCR；Abl+(Ph+)所有SUP-B15细胞，它们共同表达一组干细胞标记物、VE-钙粘蛋白和与B细胞系承诺相关的蛋白质。在与BMSC长期共培养(LTCC)后，SUP-B15肿瘤细胞表现出三系造血，形成解剖学上独特的三维耐化疗血球，干细胞标记物Oct-4表达增加，并持续高水平的低氧诱导因子-2a(HIF-2a)。SUP-B15细胞在NOD/SCID小鼠体内也重建了白血病，并在体内表现出分化。VE-钙粘附素的失稳增加了化疗诱导的LSCs的凋亡，这表明它在这一新的环境中发挥了重要作用。补充这些研究的是原始的、人类来源的、未鉴定的PRO/Pre-B ALL细胞，这些细胞与我们研究中使用的Ph+SUP-B15细胞株一致，表达高水平的VE-钙粘蛋白、Oct-4和HIF-2a。使用SUP-B15肿瘤细胞和患者来源样本的骨髓基质LTCC模型，我们将检验ALL的LSC表型是由骨髓微环境对VE-钙粘蛋白和Oct-4表达和稳定性的调节所支持的。我们的假设将通过完成以下特定目标来检验：(1)确定VE-钙粘蛋白对LSC表型的贡献以及VE-钙粘蛋白在LSC中的调控机制；(2)确定间质细胞调节肿瘤细胞OCT-4表达和活性的机制；(3)建立小鼠模型，从具有LSC表型的Ph+细胞亚群中鉴定启动白血病的关键因素。我们的长期目标是确定对白血病干细胞的骨髓利基支持至关重要的途径，这些途径可以通过靶向肿瘤本身或利基来破坏。因此，现有的治疗方法可能在靶向侵袭性Ph+白血病的干细胞成分方面具有更高的疗效。公共卫生相关性：国家癌症研究所报告说，急性淋巴细胞性白血病(ALL)是儿童中最常见的癌症，占15岁以下儿童癌症诊断的23%。在所有的肿瘤中，有一些亚型肿瘤的特点是复发风险高，预后差(Ph+ALL)，其中特别迫切地需要了解以干细胞表型为特征的细胞亚群对疾病进展的贡献。了解Ph+白血病干细胞受骨髓微环境保护的机制将增加我们设计新的治疗策略的能力，从而更有效地针对这一人群。

DESCRIPTION (provided by applicant): The contribution of tumor stem cells to progression and relapse of cancer is recognized as a significant clinical challenge in both solid and hematologic malignancies. Critical to understanding the mechanisms of tumor stem cell survival and self-renewal is investigation of their support by the microenvironments in which they thrive. Somewhat unique to hematopoietic malignancies, and subsequently leukemic stem cells (LSC), is an established appreciation of the contribution of the bone marrow microenvironment to regulation of cell fate. In the current study we investigate the interaction of LSC with bone marrow stromal cells (BMSC) and the mechanisms by which BMSC contribute to maintenance of the LSC phenotype. We utilize a unique population of Bcr;Abl+ (Ph+) ALL SUP-B15 cells that co-express a panel of stem cell markers, VE-cadherin, and proteins associated with commitment to the B-lineage. Following long-term co- culture (LTCC) with BMSC, SUP-B15 tumor cells demonstrate tri-lineage hematopoiesis, formed anatomically distinct three dimensional chemo-resistant hemospheres, had increased expression of the stem cell marker Oct-4, and had sustained, high levels of hypoxia inducible factor-2a (HIF-2a). SUP-B15 cells also reconstituted leukemia in NOD/SCID mice, as well as demonstrating differentiation in vivo. Destabilization of VE-cadherin increased chemotherapy-induced apoptosis of LSCs suggesting an important role for it in this novel setting. These studies are supplemented by inclusion of primary, human derived, de-identified pro/pre-B ALL cells that, consistent with the Ph+ SUP-B15 cell line utilized in our studies, express high levels of VE- cadherin, Oct-4 and HIF-2a. Using a model of LTCC of bone marrow stroma with SUP-B15 tumor cells and patient-derived samples we will test the working hypothesis that a LSC phenotype in ALL is supported by bone marrow microenvironment regulation of VE-cadherin and Oct-4 expression and stability. Our hypothesis will be tested by completion of the following specific aims: (1) To determine the contribution of VE-cadherin to LSC phenotype and the mechanism by which VE-cadherin is modulated in LSC, (2) To determine the mechanisms by which stromal cells regulate expression and activity of tumor cell Oct-4, and (3) To develop a murine model to identify the critical factors involved in initiating leukemia from sub-populations of Ph+ cells with a LSC phenotype. Our long-term goal is to identify pathways that are essential to bone marrow niche support of leukemic stem cells that are amenable to disruption, either through targeting the tumor itself, or the niche. Consequently, existing therapies may have enhanced efficacy in targeting the stem cell component of aggressive Ph+ leukemia. PUBLIC HEALTH RELEVANCE: The National Cancer Institute reports that acute lymphoblastic leukemia (ALL) is the most common cancer diagnosed in children and represents 23% of cancer diagnoses among children younger than 15 years. Within ALL there are sub-types of tumors that are characteristic of high risk for relapse and poor prognosis (Ph+ ALL) in which it is particularly urgent to understand the contribution of sub-populations of cells, characterized by a stem cell phenotype, to disease progression. Understanding the mechanisms by which the Ph+ leukemic stem cell is protected by the bone marrow microenvironment will increase our ability to design novel treatment strategies that are more effective in targeting this population.