Zileuton as a chemopreventive agent for chronic myeloid leukemia

描述（由申请人提供）：本申请旨在开发一种通过靶向引发慢性粒细胞白血病（CML）的白血病干细胞（LSC）来预防CML的新策略。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（Alox 5）是LSC中的关键存活调节基因（Chen等人，Nature Genetics 41：783-792，2009），表明Alox 5用作预防CML的潜在靶基因。5-LO的已知功能是产生炎性白三烯，并且5-LO的酶活性可以被FDA批准的人抗炎药齐留通（Zyflo）抑制。因此，齐留通可能是一种有前途的CML化学预防剂;其潜在机制完全未知，可能与齐留通对Alox 5已知代谢功能或新功能或两者的影响有关。我们的初步研究还表明，齐留通抑制人类CML干细胞。由于CML来源于携带BCR-ABL癌基因的干细胞，我们的研究结果促使我们假设齐留通作用于负责LSC存活调节的Alox 5相关分子网络，并且是CML的潜在化学预防剂。验证这一假设具有临床意义，并将受益于：1）具有可检测的BCR-ABL转录本但未发展为CML的个体; 2）处于分子缓解期并希望或必须停止BCR-ABL激酶抑制剂的CML患者; 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Alox 5功能是产生白三烯，齐留通可能通过减少其产生来预防CML，这需要进行测试。我们的初步数据还揭示了Alox 5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抑制Alox 5功能。在这方面，我们的初步研究表明，P-选择素的缺失导致HIF 1a的上调，这增强了LSC中Alox 5的表达，并且Alox 5向β-连环蛋白发出信号。齐留通抑制LSC为CML提供了一种新的预防策略。对齐留通功能的深入研究有助于识别更多的Alox 5相关靶基因，以预防CML，并为修改现有药物对Alox 5和相关基因的活性提供理论基础。具体目标是：1）确定白三烯是否促进LSC的存活，齐留通是否通过减少白三烯产生抑制LSC，以及潜在的机制是什么; 2）确定齐留通在LSC中影响的细胞内途径; 3）确定齐留通是否类似地调节人CML干细胞中的Alox 5途径，并减少免疫功能低下小鼠中人CML细胞的植入。虽然我们专注于CML，但齐留通也是一种潜在的实体瘤化学预防剂，因为Alox 5与结肠、肺、胰腺、肝脏、食管、皮肤的致癌作用相关。

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.