Pre-B cell receptor signaling in acute lymphoblastic leukemia

描述(申请人提供)：急性淋巴细胞性白血病中的前B细胞受体信号。人类骨髓中的B细胞前体注定要死亡，除非他们通过成功组装的前B细胞受体的生存信号得到拯救。因此，前B细胞受体信号链的缺陷会严重阻碍人类早期B细胞的发育。同样，B细胞系急性淋巴细胞性白血病(ALL)细胞在B细胞发育的早期阶段被阻止。在这项建议中，我们检验了B细胞系的发育停滞主要反映了前B细胞受体功能异常的假设。B细胞系ALL是迄今为止儿童中最常见的恶性肿瘤，在成人中也很常见。尽管在过去的40年里取得了重大进展，但细胞毒治疗策略最近达到了一个平台期，儿童的治愈率为80%，成人的治愈率为55%。细胞毒药物治疗后复发、初始耐药和剂量限制毒性是目前治疗方法中最常见的并发症。因此，除了细胞毒药物治疗外，针对特定途径的治疗策略似乎有望进一步改善所有患者的治疗选择。在对148例前B细胞来源的人类ALL的初步研究中，我们发现所有携带E2A-Pbx1或MYC-基因重排的细胞-就像正常的前B细胞一样-高度选择表达功能性的前B细胞受体。与之形成鲜明对比的是，所有有其他细胞遗传学异常(如BCR-ABL1-或MLL-AF4)的细胞在几乎所有病例中都缺乏功能性前B细胞受体的表达。在一项原理验证实验中，我们研究了前B细胞受体在BCR-ABL1转基因小鼠前B细胞进行性转化过程中的功能：有趣的是，来自前B细胞受体的信号和致癌的BCR-ABL1激酶是相互排斥的，只有不表达功能上的前B细胞受体的前B细胞才允许被BCR-ABL1转化。与所有携带BCR-ABL1或MLL-AF4融合基因的细胞不同，前B细胞受体信号在E2A-Pbx1或MYC转化的ALL中是活跃的，因为这些细胞表现出强烈的钙信号以响应前B细胞受体的参与。基于这些发现，我们假设ALL可以根据前B细胞受体信号是启动(I型)还是抑制(II型)白血病生长而细分为两组。通过对原代人ALL异种移植和I型和II型ALL转基因小鼠模型的研究，我们在目标1中建议在这两个亚组中建立前B细胞受体信号的特征关键差异。在目标2中，我们建议确定前B细胞受体依赖的生存信号在I型ALL中的需求，作为药物抑制的潜在靶点。相反，我们在目标3中建议阐明II型ALL中前B细胞受体失活的机制，以及功能性前B细胞受体信号如何诱导II型ALL细胞凋亡。鉴于这一亚型ALL中的前B细胞受体信号有效地抑制了白血病的生长，我们在目标3中的目标是干扰这些失活机制，以恢复II型ALL细胞中前B细胞受体依赖的凋亡信号。所提出的对I型和II型的区分都类似于成熟B细胞淋巴瘤的分类，在这种分类中，可以根据B细胞受体表达的存在(即非霍奇金淋巴瘤)和不存在(即霍奇金淋巴瘤)来区分亚型。这项建议的中心目标是确定前B细胞受体信号在ALL恶性转化和克隆性进化中的作用，并针对其信号级联的单个组件，为ALL开发新的通路特异性治疗方法。公共卫生相关性：急性淋巴细胞性白血病中的前B细胞受体信号。B淋巴细胞不仅是人类免疫系统中产生抗体的细胞，也是大多数急性淋巴细胞性白血病(ALL)的起源细胞。ALL是迄今为止儿童中最常见的癌症类型，也是成人的常见病。多年来，ALL患者接受化疗，目前的治疗方案使儿童ALL患者的治愈率达到80%，成人ALL患者的治愈率达到55%。我们的目标是更好地了解人类ALL的生物学，即作为正常B淋巴细胞发育的灾难性异常。在正常的B淋巴细胞发育过程中，前B细胞受体是引导早期B淋巴细胞前体细胞成熟的关键信号单位。如果来自前B细胞受体的信号受到损害，例如在患有先天性免疫缺陷的患者中，B淋巴细胞前体就会像在所有细胞中一样，在原始阶段停止发育。因此，我们建议研究前B细胞受体信号单元的功能(1)作为一个潜在的靶点来干扰促进白血病生长的异常细胞信号和(2)恢复白血病细胞中正常的前B细胞受体信号。

DESCRIPTION (provided by applicant): Pre-B cell receptor signaling in acute lymphoblastic leukemia. B cell precursors in human bone marrow are destined to die unless they are rescued through survival signals from a successfully assembled pre-B cell receptor. For this reason, defects in components of the pre-B cell receptor signaling chain cause a severe block of early B cell development in humans. Likewise, B cell lineage acute lymphoblastic leukemia (ALL) cells are arrested at early stages of B cell development. In this proposal, we test the hypothesis that the developmental arrest in B cell lineage ALL predominantly reflects aberrant pre-B cell receptor function. B cell lineage ALL represents by far the most frequent malignancy in children and is also common in adults. Despite significant advances over the past four decades, cytotoxic treatment strategies have recently reached a plateau with cure rates at 80 percent for children and 55 percent for adults. Relapse after cytotoxic drug treatment, initial drug-resistance and dose-limiting toxicity are among the most frequent complications of current therapy approaches. For this reason, pathway-specific treatment strategies in addition to cytotoxic drug treatment seem promising to further improve therapy options for ALL patients. In preliminary studies for this proposal on 148 cases of pre-B cell-derived human ALL, we found that ALL cells carrying an E2A-PBX1- or MYC- gene rearrangement are -like normal pre-B cells- highly selected for the expression of a functional pre-B cell receptor. In striking contrast, ALL cells with other cytogenetic abnormalities (e.g. BCR-ABL1- or MLL-AF4) lack expression of a functional pre-B cell receptor in virtually all cases. In a proof-of-principle experiment, we studied pre-B cell receptor function during progressive leukemic transformation of pre-B cells in BCR-ABL1-transgenic mice: Interestingly, signaling from the pre-B cell receptor and the oncogenic BCR-ABL1 kinase are mutually exclusive and only "crippled" pre-B cells that fail to express a functional pre-B cell receptor are permissive to transformation by BCR-ABL1. As opposed to ALL cells with BCR-ABL1- or MLL-AF4-fusion gene, pre-B cell receptor signaling is active in E2A-PBX1- or MYC-transformed ALL, because these cells exhibit a vigorous Ca2+ signal in response to pre-B cell receptor engagement. Based on these findings, we hypothesize that ALL can be subdivided into two groups based on whether pre-B cell receptor signaling enables (Type I) or suppresses (Type II) leukemic growth. Studying primary human ALL xenografts and transgenic mouse models for Type I and Type II ALL, we propose in Aim 1 to establish characteristic key differences of pre-B cell receptor signaling in the two subgroups. In Aim 2, we propose to identify the requirements for pre-B cell receptor-dependent survival signaling in Type I ALL as potential targets for pharmacological inhibition. Conversely, we propose in Aim 3 to elucidate the mechanisms of pre-B cell receptor-inactivation in Type II ALL and how functional pre-B cell receptor signaling induces apoptosis in Type II ALL cells. Given that pre-B cell receptor signaling in this subgroup of ALL effectively suppresses leukemic growth, our goal in Aim 3 is to interfere with these inactivation mechanisms to restore pre-B cell receptor-dependent apoptosis-signaling in Type II ALL cells. The proposed discrimination between Type I and Type II ALL resembles the classification of mature B cell lymphoma, in which subgroups can be distinguished based on the presence (i.e. Non-Hodgkin's lymphoma) and absence (i.e. Hodgkin's lymphoma) of B cell receptor expression. The central goal of this proposal is to establish the role of pre-B cell receptor signaling during malignant transformation and clonal evolution of ALL and to target individual components of its signaling cascade for the development of novel pathway-specific therapy approaches for ALL. PUBLIC HEALTH RELEVANCE: Pre-B cell receptor signaling in acute lymphoblastic leukemia. B lymphocytes are not only the cells that produce antibodies as part of the human immune system, they are also the cell of origin in most cases of acute lymphoblastic leukemia (ALL). ALL represents by far the most frequent type of cancer in children and is also a common disease in adults. For many years, patients with ALL are treated with chemotherapy and current treatment protocols lead to cure rates of 80 percent for children and 55 percent for adult patients with ALL. Our goal is to better understand the biology of human ALL, namely as a catastrophic aberration of normal B lymphocyte development. During normal B lymphocyte development, the pre-B cell receptor represents a critical signaling unit that guides early B lymphocyte precursors on their path of maturation. If signaling from the pre-B cell receptor is compromised, as for instance in patients with innate immune defects, the B lymphocyte precursors are arrested in their development at a primitive stage -as in ALL cells. Therefore, we propose to investigate the function of the pre-B cell receptor signaling unit (1) as a potential target to disrupt aberrant cell signaling that promotes leukemic growth and (2) to restore normal pre-B cell receptor signaling in the leukemia cells.