Slow cycling brain tumor cancer stem cells

描述（申请人提供）：恶性胶质瘤是最常见的原发性脑肿瘤，占成人中枢神经系统癌症的大多数。恶性神经胶质瘤的发病率在世界范围内呈上升趋势，尤其是在老年人中。一般来说，恶性胶质瘤是不可治愈的肿瘤。传统的病理方法将恶性胶质瘤分为三级。II级低级别星形细胞瘤，患者平均生存期为5-15年。III级间变性星形细胞瘤，患者平均生存期为3年。多形性IV级胶质母细胞瘤（GBM）是最恶性和最常见的胶质瘤，尽管采用了最先进的成像技术、手术、放疗和化疗相结合的积极治疗，但平均生存时间不到1年。虽然经常观察到对治疗的短暂反应，但肿瘤复发几乎是不可避免的，并且通常发生在接受了强化细胞毒性治疗的组织中，这表明一个亚群的耐药细胞负责肿瘤的再生。癌症生物学领域最突出的主题之一是肿瘤启动细胞，其表型上模仿干细胞的基本特性，负责实体组织恶性肿瘤的起源和维持。肿瘤启动细胞（tic）可能表现出干细胞特征的观点在20世纪90年代首次得到证实，这是基于对急性髓性白血病的研究，此后又被与乳腺、前列腺、肺和间充质肿瘤相关的研究结果所加强。来源于人类胶质瘤组织的细胞在培养中产生神经球的能力表明，中枢神经系统肿瘤中存在具有神经干细胞特性（tNSCs）的肿瘤细胞，因为神经球的产生是神经干细胞存在的一个指标。此外，我们和同事的工作已经证明了tNSCs的分离、繁殖和连续移植，这些tNSCs表现出与神经干细胞非常相似的功能特性。重要的是，在植入tNSCs后，产生的肿瘤表现出人类多形性胶质母细胞瘤的典型体内特征；概述了原发性GBMs的形态、基因型和基因表达模式，以及具有广泛的迁移和浸润能力。这表明体外定义的脑肿瘤干细胞忠实地保留了人类多形性胶质母细胞瘤（hGBM）的关键体内特征。体细胞干细胞的一个决定性特征是由于细胞周期阻滞而不频繁的细胞分裂，这对于防止在生物体的生命周期中过早耗尽是必不可少的。众所周知，细胞周期阻滞可以保护细胞免受辐射和细胞毒性药物的伤害，因此，慢周期的tic将对传统的治疗方法产生抗性。根据这些观察结果，我们假设治疗后肿瘤再生是由一小群缓慢循环的化疗/耐照射tic开始的，这些tic表现出自我更新的基本干细胞特性。然后，tic产生一个独立的、短暂的快速分裂的后代细胞群，负责重新填充肿瘤的主体，就像体细胞干细胞产生一个快速分裂的前体细胞池来取代受损的组织一样。重要的是，该模型预测了神经胶质瘤患者的长期恢复需要消除tic。这一提议的基本假设是，hGBM肿瘤含有一群缓慢循环的细胞，这些细胞可以启动继发性肿瘤的形成，并且对常规治疗有抵抗力。具体目的是在体外和体内确定慢循环hGBM细胞的存在，表征照射和化疗对该亚群的影响，并研究这种耐药性的机制。这项研究的结果可能会确定相关的靶点，详细说明其耐药机制，并为药物开发开辟新的途径。公共卫生相关性：恶性胶质瘤是最常见的原发性脑肿瘤，占成人中枢神经系统癌症的大多数。它们在世界范围内不断增加，预后较差，无论治疗如何，大多数患者都死于这种疾病。我们正在使用通常用于研究正常成体干细胞的方法和技术，研究负责驱动长期肿瘤生长和对治疗的抵抗的细胞的作用。该项目将揭示脑肿瘤细胞的干细胞特征，并为如何调节癌细胞的行为提供见解。

DESCRIPTION (provided by applicant): Malignant gliomas are the most common primary brain tumour, accounting for the majority of cancers in the adult central nervous system. The incidence of malignant gliomas is increasing world-wide, particularly among the elderly. In general, malignant gliomas are not curable tumours. Traditional pathological approaches grade malignant gliomas into three grades of malignancy. Grade II low grade astrocytoma, with a mean patient survival of 5-15 years. Grade III anaplastic astrocytoma, with a mean patient survival of 3 years. Grade IV glioblastoma multiforme (GBM), the most malignant and common glioma, with a mean survival time of less than 1 year despite aggressive therapy that combines state-of- the-art imaging with surgery, radiotherapy and chemotherapy. Although a transient response to therapy is often observed, tumour recurrence is almost inevitable and usually occurs within tissue that has received intensive cytotoxic therapy, suggesting a sub-population of resistant cells are responsible for tumour regrowth. One of the most prominent topics in the field of cancer biology is that tumour-initiating cells, which phenotypically mimic the cardinal properties of stem cells, are responsible for the origin and maintenance of solid tissue malignancies. The idea that tumor-initiating cells (TICs) may exhibit stem cell characteristics was first confirmed in the 1990s, based on studies of acute myeloid leukaemia and has since been strengthened by findings related to breast, prostate, lung and mesenchymal tumours. The ability of cells derived from human glioma tissue to generate neurospheres in culture suggests the presence of tumour cells with neural stem cell properties (tNSCs) within CNS tumours, as neurosphere generation is one indicator of the presence of neural stem cells. Furthermore, work from ourselves and colleagues have demonstrated the isolation, propagation and serial transplantation of tNSCs that exhibit very similar functional properties as neural stem cells. Importantly, following implantation of tNSCs, the resulting tumours exhibit the classic in vivo features of human glioblastoma multiforme; recapitulating the morphology, genotype and gene expression patterns as primary GBMs, as well as having extensive migratory and infiltrative capacity. This indicates that the in vitro defined brain tumour stem cells faithfully preserve the key in vivo features of human glioblastoma multiforme (hGBM). One of the defining characteristics of somatic stem cells is their infrequent cell division due to cell cycle arrest, which is essential to prevent premature stem cell depletion over the lifetime of the organism. As it is well established that cell cycle arrest protects cells from irradiation and cytotoxic agents, it follows that the slow-cycling TICs will be resistant to conventional therapeutic approaches. In light of these observations, we hypothesise that post-therapy tumour regrowth is initiated from a small population of slow cycling chemo/irradiation-resistant TICs that exhibit the basic stem cell property of self-renewal. TICs then generate a separate and transient population of rapidly dividing progeny cells that are responsible for repopulating the tumour bulk, much like somatic stem cells generate a rapidly dividing pool of precursor cells to replace damaged tissue. Importantly, this model predicts that the elimination of the TICs is required for the long-term recovery of glioma patients. The underlying hypothesis of this proposal is that hGBM tumours contain a population of slow- cycling cells, which can initiate secondary tumour formation and are resistant to conventional treatment. The specific aims will establish the existence of slow cycling hGBM cells in vitro and in vivo, characterize the effects of irradiation and chemotherapy on this sub-population, and investigate the mechanisms underlying this resistance. The outcome of this study will likely define relevant targets, detail its mechanism of resistance and initiate a new avenue for drug development. PUBLIC HEALTH RELEVANCE: Malignant gliomas are the most common primary brain tumor, accounting for the majority of cancers in the adult central nervous system. They are increasing worldwide and carry a poor prognosis with most patients succumbing to their disease regardless of treatment. We are investigating the role of the cells responsible for driving long-term tumor growth and resistance to treatment using methods and techniques commonly used to study normal adult stem cells. The project should unveil the stem cell characteristics of brain tumor cells and provide insight in how to regulate the behavior of the cancer cells.