Mechanism of BCL6-dependent stem cell maintenance in B cell lineage leukemia

B细胞系白血病中BCL6依赖性干细胞维持机制

• 批准号: 7979235
• 负责人: Markus Müschen
• 金额: $ 20.88万
• 依托单位: CHILDREN'S HOSPITAL OF LOS ANGELES
• 依托单位国家: 美国
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-07-01 至 2012-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7979235
• 关键词: Acute; Acute Lymphocytic Leukemia; Adjuvant; Adjuvant Therapy; Adverse effects; Affect; B-Cell Acute Lymphoblastic Leukemia; B-Cell Lymphomas; B-Lymphocytes; BCL6 gene; Biological Assay; Cancer Etiology; Cell Lineage; Cell Maintenance; Cell Survival; Cells; Child; Chronic Lymphocytic Leukemia; Chronic Myeloid Leukemia; Clinical Trials; Cytotoxic Chemotherapy; Derivation procedure; Diagnostic; Dose; Dose-Limiting; Drug resistance; Drug resistance pathway; Embryo; Frequencies; Funding; Gene Expression; Genes; Genetic; Goals; Human; In Vitro; Laboratories; Lymphoma; Maintenance; Malignant Neoplasms; Mediating; Mus; Myelogenous; NOD/SCID mouse; Oncogenes; Oncogenic; Pathway interactions; Patient Care; Patients; Peptides; Pharmaceutical Preparations; Phenotype; Play; Population; Process; Production; Program Development; Proliferating; Proto-Oncogenes; Recurrent disease; Regulation; Relapse; Reporter; Resistance; Role; Sampling; Schedule; Signal Transduction; Stem cells; Surface Antigens; Surrogate Markers; System; TP53 gene; Teenagers; Testing; Therapeutic; Toxic effect; Transcription Repressor/Corepressor; Transgenic Mice; Transgenic Organisms; Transplantation; Tyrosine Kinase Inhibitor; Validation; Work; Xenograft procedure; base; cell type; gain of function; gene repression; in vivo; inhibitor/antagonist; large cell Diffuse non-Hodgkin' s lymphoma; leukemia; leukemic stem cell; mouse model; novel; novel strategies; novel therapeutics; pre-clinical; preclinical study; prevent; programs; public health relevance; research study; response; self-renewal; senescence; stem; stem cell population

DESCRIPTION (provided by applicant): B cell lineage acute lymphoblastic leukemia (ALL) represents by far the most frequent type of malignancy in children and teenagers. Despite significant advances in ALL treatment, many patients still die because of drug- resistance or leukemia relapse. Since recent work implicated leukemia stem cells in both drug-resistance and relapse of the disease, current therapy approaches focus on leukemia stem cell eradication. In contrast to B cell lineage ALL, leukemia stem cells in myeloid lineage leukemia have been extensively characterized. Acute and chronic myeloid leukemias develop hierarchically from a phenotypically distinct stem cell population. However, recent work suggests that no such hierarchy exists in B cell lineage ALL, which precludes an unequivocal phenotypic definition of leukemia stem cells in ALL. Therefore, we propose to functionally characterize leukemia stem cells in B cell lineage ALL based on an operational definition, i.e. the ability to maintain stem cell self-renewal and overcome oncogene-induced senescence. Specifically, we will test the hypothesis that the BCL6 transcriptional repressor represents one of the critical factors in B cell lineage ALL to maintain a pool of functional leukemia stem cells. The BCL6 proto-oncogene is frequently translocated in diffuse large B cell lymphoma (DLBCL) and maintains self-renewal capacity of DLBCL cells by transcriptional repression of p53 in the lymphoma cells. However, an oncogenic function of BCL6 has not been described in other cell types so far. In preliminary studies for this proposal, we have discovered aberrant expression of BCL6 as a central component of a fundamentally novel pathway of leukemia stem cell maintenance: BCL6 prevents leukemia stem cell depletion through negative regulation of the Arf/p53/p21 pathway in B cell lineage ALL. Compared to leukemias from BCL6-/- mice, BCL6 is required for the reactivation of an early embryonic gene expression program, development of drug-resistance, leukemia cell colony formation and leukemia-initiation in serially transplanted NOD/SCID mice in B cell lineage but not myeloid lineage leukemia. A novel retro-inverso BCL6 peptide inhibitor (RI-BPI) strongly synergized with tyrosine kinase inhibitors in the treatment of B cell lineage ALL cells in vitro and in vivo. This proposal will test the hypothesis that BCL6-dependent self-renewal represents a critical requirement for stem cell maintenance in B cell lineage ALL. Based on the discovery of BCL6 as a key component of a fundamentally novel pathway of stem cell self-renewal in various subtypes of ALL, we propose three Aims to develop these findings towards application in patient care: (1) To test the hypothesis that aberrant expression of BCL6 in leukemia cells prevents Arf/p53-mediated senescence and promotes stem cell quiescence, (2) To identify transcriptional targets of BCL6 in primary human leukemia cells and their contribution to self-renewal signaling and (3) To validate BCL6-BPI as a therapy adjuvant for targeted eradication of leukemia stem cells. PUBLIC HEALTH RELEVANCE: Despite significant advances in the treatment of leukemia over the past four decades, the rate of long-term survival has reached a plateau and still large numbers of leukemia patients die, mostly because of relapse and drug-resistance, which was recently attributed to the persistence of leukemia stem cells. If a therapy succeeds in eradicating leukemia stem cells, de novo initiation of the disease (relapse) is no longer possible. Therapeutic progress in recent clinical trials has likely been stalled, partly because current cytotoxic therapy approaches target proliferating bulk leukemia cells rather than quiescent leukemia stem cells. We now discovered that BCL6, a factor known to play a central role in B cell lymphomas, also plays a key role in the maintenance of leukemia stem cells. Since leukemia stem cells represent the origin of relapse and drug-resistance in leukemia in many cases, the identification of BCL6 as a target for leukemia stem cell eradication holds great promise. BCL6 is a master regulatory factor that controls the production of many different important genes. BCL6 was not previously known to be involved in leukemias. In preliminary studies for this proposal, we have discovered aberrant expression of BCL6 as a central component of a fundamentally novel pathway of leukemia stem cell self-renewal and drug-resistance in a wide array of human leukemias, some of which are still difficult to treat. In these leukemias, drug-treatment results in aberrant production of BCL6 by the leukemia cells, which appears to allow leukemia stem cell to self-renew and become resistance against drug-treatment. Recently a drug has been developed that can attach to BCL6 and block its cancer-causing activities. We found that this BCL6 inhibitor, which is called RI-BPI, has strong synergistic activity when combined with conventional drug- treatment, which opens up a powerful new therapeutic strategy for leukemia stem cell eradication through targeted inhibition of BCL6. Based on the discovery of BCL6 as a key component of a novel pathway of drug-resistance and stem cell self-renewal in a wide array of leukemias, we propose three Aims to develop these findings towards application in patient care: (1) To test the hypothesis that aberrant expression of BCL6 in human leukemia cells promotes leukemia stem cell survival, (2) To determine the frequency and phenotype of BCL6-dependent leukemia stem cells in human B cell ALL and (3) To validate a the role of the BCL6 inhibitor RI-BPI as a therapy for targeted eradication of leukemia stem cells. Since RI-BPI is currently going through the process of approval for use in clinical trials, we expect to be able to test the power of this approach in clinical trials by the end of the funding period.

描述（由申请人提供）：B 细胞系急性淋巴细胞白血病 (ALL) 是迄今为止儿童和青少年中最常见的恶性肿瘤类型。尽管ALL治疗取得了重大进展，但许多患者仍然因耐药或白血病复发而死亡。由于最近的研究表明白血病干细胞与疾病的耐药性和复发有关，因此当前的治疗方法侧重于根除白血病干细胞。与 B 细胞系 ALL 不同，髓系白血病中的白血病干细胞已得到广泛表征。急性和慢性粒细胞白血病由表型不同的干细胞群分层发展。然而，最近的研究表明，B 细胞谱系 ALL 中不存在这样的层次结构，这排除了 ALL 中白血病干细胞的明确表型定义。因此，我们建议根据操作定义对 B 细胞系 ALL 中的白血病干细胞进行功能表征，即维持干细胞自我更新和克服癌基因诱导的衰老的能力。具体来说，我们将测试以下假设：BCL6 转录阻遏蛋白是 B 细胞谱系 ALL 中维持功能性白血病干细胞库的关键因素之一。 BCL6原癌基因在弥漫性大B细胞淋巴瘤（DLBCL）中经常易位，并通过淋巴瘤细胞中p53的转录抑制来维持DLBCL细胞的自我更新能力。然而，迄今为止，BCL6 在其他细胞类型中的致癌功能尚未被描述。在该提案的初步研究中，我们发现 BCL6 的异常表达是白血病干细胞维持的全新途径的核心组成部分：BCL6 通过 B 细胞谱系中 Arf/p53/p21 途径的负调节来防止白血病干细胞耗竭全部。与 BCL6-/- 小鼠的白血病相比，在 B 细胞系中连续移植的 NOD/SCID 小鼠中，BCL6 是早期胚胎基因表达程序重新激活、耐药性发展、白血病细胞集落形成和白血病启动所必需的，但不是髓系白血病。一种新型逆向 BCL6 肽抑制剂 (RI-BPI) 在体外和体内治疗 B 细胞谱系 ALL 细胞时与酪氨酸激酶抑制剂具有强烈协同作用。该提案将检验以下假设：BCL6 依赖性自我更新是 B 细胞谱系 ALL 干细胞维持的关键要求。 基于 BCL6 作为 ALL 各种亚型中干细胞自我更新的全新途径的关键组成部分的发现，我们提出了三个目标，以将这些发现应用于患者护理：(1) 检验以下假设： BCL6 在白血病细胞中的表达可防止 Arf/p53 介导的衰老并促进干细胞静止，(2) 鉴定原代人白血病细胞中 BCL6 的转录靶标及其对(3) 验证 BCL6-BPI 作为靶向根除白血病干细胞的治疗佐剂。 公共卫生相关性：尽管在过去四十年中白血病治疗取得了重大进展，但长期生存率已达到平台期，仍然有大量白血病患者死亡，主要是由于复发和耐药性，这是最近发现的归因于白血病干细胞的持续存在。如果治疗成功根除白血病干细胞，就不再可能从头引发疾病（复发）。最近的临床试验的治疗进展可能已陷入停滞，部分原因是当前的细胞毒性疗法针对的是增殖的大量白血病细胞，而不是静止的白血病干细胞。我们现在发现，BCL6（一种已知在 B 细胞淋巴瘤中发挥核心作用的因子）也在白血病干细胞的维持中发挥着关键作用。由于白血病干细胞在许多情况下代表了白血病复发和耐药的根源，因此将 BCL6 鉴定为白血病干细胞根除的靶点具有很大的前景。 BCL6 是控制许多不同重要基因产生的主要调控因子。此前并不知道 BCL6 与白血病有关。在该提案的初步研究中，我们发现 BCL6 的异常表达是多种人类白血病中白血病干细胞自我更新和耐药性的全新途径的核心组成部分，其中一些白血病仍然难以治疗。在这些白血病中，药物治疗导致白血病细胞异常产生 BCL6，这似乎使白血病干细胞能够自我更新并对药物治疗产生耐药性。最近开发出一种药物，可以附着在 BCL6 上并阻止其致癌活性。我们发现这种被称为RI-BPI的BCL6抑制剂与常规药物治疗结合时具有很强的协同活性，这为通过靶向抑制BCL6来根除白血病干细胞开辟了一种强大的新治疗策略。基于 BCL6 作为多种白血病耐药和干细胞自我更新新途径的关键组成部分的发现，我们提出了三个目标，以将这些发现应用于患者护理：(1) 测试人白血病细胞中BCL6的异常表达促进白血病干细胞存活的假设，（2）确定人B细胞中BCL6依赖性白血病干细胞的频率和表型ALL 和 (3) 验证 BCL6 抑制剂 RI-BPI 作为靶向根除白血病干细胞的疗法的作用。由于 RI-BPI 目前正在经历临床试验的批准过程，我们预计能够在资助期结束时在临床试验中测试这种方法的功效。