Zileuton as a chemopreventive agent for chronic myeloid leukemia

描述(申请人提供)：这项申请旨在开发一种新的策略，通过靶向启动慢性粒细胞白血病的白血病干细胞(LSCs)来预防慢性粒细胞白血病(CML)。这个想法是基于我们最近发表的发现，即花生四烯酸5-脂氧合酶(5-LO)基因(ALOX5)是LSCs中一个关键的生存调节基因(Chen等人。Natural Genetics 41：783-792,2009)，提示Alox5是预防慢性粒细胞白血病的潜在靶基因。5-LO的一个已知功能是产生炎性白三烯，5-LO的酶活性可以被FDA批准的人类抗炎药物齐留通(Zyflo)抑制。因此，齐留通可能是一种很有前途的CML化学预防药物；其潜在机制尚不清楚，可能与齐留通对Alox5的已知代谢功能或新功能的影响有关，或两者兼而有之。我们的初步研究还表明，齐留通可以抑制人类慢性粒细胞白血病干细胞。由于慢性粒细胞白血病来源于含有bcr-abl癌基因的干细胞，我们的发现提示我们假设齐留通作用于与ALOX5相关的分子网络，负责LSCs的生存调控，是一种潜在的CML化学预防药物。验证这一假说具有临床意义，将有利于：1)拥有可检测到的BCR-ABL转录本但尚未发展为CML的患者；2)处于分子缓解状态并希望或必须停止BCR-ABL激酶抑制剂的CML患者；以及3)接受骨髓移植但可能仍有残留白血病细胞的CML患者。从机制上讲，由于已知的ALOX5功能是产生白三烯，齐留通可能通过减少它们的产生来预防CML，这需要进行测试。我们的初步数据还揭示了Alox5的新功能，表明齐留通可能通过调节与白三烯产生无关的途径来抑制Alox5的功能。在这方面，我们在文中的初步研究表明，P-选择素的丢失导致HIF1a上调，从而增强LSC中ALOX5的表达，并且ALOX5向β-连环蛋白发出信号。齐留通对LSCs的抑制为慢性粒细胞白血病提供了一种新的预防策略。对Zileuton功能的深入研究有助于发现更多预防CML的Alox5相关靶基因，并为利用Alox5及其相关基因的活性来修饰现有药物提供理论依据。其具体目的是：1)确定白三烯是否促进LSCs的存活，齐留通是否通过减少白三烯的产生抑制LSCs及其潜在机制；2)确定Zileuton影响LSCs的细胞内途径；以及3)确定Zileuton是否类似地调节人CML干细胞中的Alox5途径，并减少免疫受损小鼠中人CML细胞的植入。虽然我们关注的是慢性粒细胞白血病，但齐留通也是一种潜在的实体肿瘤化学预防药物，因为ALOX5与结肠、肺、胰腺、肝脏、食道、皮肤的癌变有关。

DESCRIPTION (provided by applicant): This application aims to develop a novel strategy for preventing chronic myeloid leukemia (CML) by targeting leukemia stem cells (LSCs) that initiate CML. This idea is based on our recently published finding that the arachidonate 5-lipoxygenase (5-LO) gene (Alox5) is a key survival-regulatory gene in LSCs (Chen et al. Nature Genetics 41:783-792, 2009), suggesting that Alox5 serves as a potential target gene for preventing CML. A known function of 5-LO is to produce inflammatory leukotrienes, and enzymatic activity of 5-LO can be inhibited by an FDA-approved human anti-inflammatory drug Zileuton (Zyflo). Thus, Zileuton could be a promising chemopreventive agent for CML; the underlying mechanisms are totally unknown and could be related to the effects of Zileuton on the known metabolic function or novel functions of Alox5 or both. Our preliminary studies also show that Zileuton suppresses human CML stem cells. Because CML is derived from a stem cell harboring the BCR-ABL oncogene, our findings prompt us to hypothesize that Zileuton acts on an Alox5-related molecular network responsible for survival regulation of LSCs and is a potential chemopreventive agent for CML. Testing this hypothesis is of clinical significance and would benefit: 1) individuals who have detectable BCR-ABL transcripts but have not developed CML; 2) CML patients who are in molecular remission and hope or have to stop a BCR-ABL kinase inhibitor; and 3) CML patients who had bone marrow transplantation but may still have residual leukemia cells. Mechanistically, because the known Alox5 function is to produce leukotrienes, Zileuton may prevent CML by reducing their production, which needs to be tested. Our preliminary data also reveal novel functions of Alox5, suggesting that Zileuton may suppress Alox5 function through regulating pathways unrelated to production of leukotrienes. In this regard, our preliminary study in shows that loss of P-selectin causes upregulation of Hif1a which enhances Alox5 expression in LSCs and that Alox5 signals to beta-catenin. Inhibition of LSCs by Zileuton provides a novel preventive strategy for CML. In-depth study of Zileuton function helps to identify more Alox5-related target genes for preventing CML and provides a rationale for modifying existing drugs with activities on Alox5 and related genes. The specific aims are: 1) To determine whether leukotrienes promote the survival of LSCs, whether Zileuton suppresses LSCs through reducing leukotriene production and what the underlying mechanism is; 2) To determine the intracellular pathways affected by Zileuton in LSCs; and 3) To determine whether Zileuton similarly regulates the Alox5 pathway in human CML stem cells and reduces engraftment of human CML cells in immunocompromised mice. Although we focus on CML, Zileuton is also a potential chemopreventive agent for solid tumors as Alox5 is associated with carcinogenesis in the colon, lung, pancreas, liver, esophagus, skin.