Identification of novel target genes for polycythemia vera (PV)

描述（由申请人提供）：JAK2V617F突变存在于大多数骨髓增生性肿瘤（mpn）中，包括真性红细胞增多症（PV）、原发性血小板增多症和原发性骨髓纤维化。类似于染色体阳性（Ph+）慢性髓性白血病（CML），这些费城染色体阴性（Ph-） mpn也来源于造血干细胞（hsc），有发展成血栓和急性白血病的风险。目前还没有治愈这些Ph- mpn的方法。最近JAK2V617F突变的发现促进了使用JAK2抑制剂来抑制JAK2V617F功能的靶向治疗的发展。尽管一些早期临床试验显示改善了患者的症状和生活质量，但这些JAK2抑制剂的长期有效性仍有待确定。人们已经开始担心这些药物的副作用。另一方面，研究表明，用JAK2抑制剂抑制JAK2V617F并不能根除pv启动细胞，这意味着用JAK2抑制剂抑制JAK2V617F的激酶活性不太可能治愈mpn，这与用BCR-ABL激酶抑制剂治疗Ph+ CML的情况类似，后者可以控制但不能治愈CML。开发治疗mpn的疗法需要深入研究JAK2V617F在这些疾病发生和维持中的分子基础，以识别新的有效靶基因。在本应用中，我们关注PV，这是与JAK2V617F相关的mpn的主要形式。我们观察到Ph+ CML和Ph- mpn涉及相同的HSC细胞群，具有相似的骨髓增生性表型，这表明CML和PV的发病细胞可能具有一些共同的调节机制。我的实验室一直在研究CML启动细胞或白血病干细胞（LSCs）在CML中的生物学和分子靶向，我们发现LSCs的生存和自我更新需要花生四烯酸5-脂氧合酶基因（Alox5），而Alox5对CML的发展至关重要（Chen等）。Alox5基因的缺失会损害白血病干细胞并预防慢性髓性白血病。Nature Genetics, 2009)。我们还发现，抑制Alox5功能可导致LSCs的根除并延长CML小鼠的生存期。我们的初步数据显示，JAK2V617F激活了Alox5，而Alox5基因的缺失会阻碍JAK2V617F诱导的小鼠PV的发展，这一点得到了Alox5抑制剂治疗后PV小鼠存活时间延长的支持。这些初步结果允许我们假设Alox5在JAK2V617F诱导的PV的发展中起着重要作用，并且是治疗PV的潜在靶基因。具体目的是：1)确定JAK2V617F激活Alox5的信号通路；2)检测Alox5通路的抑制是否抑制小鼠和人PV细胞。这些研究将为未来针对Alox5通路的PV临床试验奠定坚实的基础。

DESCRIPTION (provided by applicant): The JAK2V617F mutation is found in the majority of myeloproliferative neoplasms (MPNs) including polycythemia vera (PV), essential thrombocythemia and primary myelofibrosis. Similar to chromosome- positive (Ph+) chronic myeloid leukemia (CML), these Philadelphia chromosome-negative (Ph-) MPNs are also derived from hematopoietic stem cells (HSCs) and have a risk of developing thrombosis and acute leukemia. There are still no curative therapies for these Ph- MPNs. Recent discovery of the JAK2V617F mutation has promoted the development of targeted therapy using JAK2 inhibitors to inhibit the function of JAK2V617F. Although some early-stage clinical trials show improvement of symptoms and quality of life in patients, the long-term effectiveness of these JAK2 inhibitors remains to be determined. There are already some concerns for the side effects of these drugs. On the other hand, it has been shown that inhibition of JAK2V617F with a JAK2 inhibitor does not eradicate PV-initiating cells, implying that inhibition of the kinase activity o JAK2V617F with a JAK2 inhibitor is unlikely to cure MPNs, which is a situation similar to the treatment of Ph+ CML with BCR-ABL kinase inhibitors that control but do not cure CML. The development of a curative therapy for MPNs requires in-depth studies of the molecular basis of JAK2V617F in initiation and maintenance of these diseases for identifying new and effective target genes. In this application, we focus on PV, a major form of MPNs associated with JAK2V617F. We have observed that Ph+ CML and Ph- MPNs involve the same HSC cell population and have similar myeloproliferative phenotype, suggesting that the disease-initiating cells for CML and PV might share some common regulatory mechanisms. My laboratory has a history of studying the biology and molecular targeting of CML-initiating cells or leukemia stem cells (LSCs) in CML, and we show that the survival and self-renewal of LSCs require the arachidonate 5- lipoxygenase gene (Alox5) and that Alox5 is essential for CML development (Chen et al. Loss of the Alox5 gene impairs leukemia stem cells and prevents chronic myeloid leukemia. Nature Genetics 41:783-792, 2009). We also show that inhibition of Alox5 function leads to eradication of LSCs and prolonged survival of CML mice. Our preliminary data show that JAK2V617F activates Alox5 and loss of the Alox5 gene impedes the development of JAK2V617F-induced PV in mice, which is supported by prolonged survival of PV mice treated with an Alox5 inhibitor. These preliminary results allow us to hypothesize that Alox5 plays a significant role in the development of PV induced by JAK2V617F and is a potential target gene for the treatment of PV. The specific aims are: 1) To determine signaling pathways involved in Alox5 activation by JAK2V617F; and 2) To test whether inhibition of the Alox5 pathway suppresses mouse and human PV cells. These studies will build a solid foundation for future PV clinical trials by targeting the Alox5 pathway. PUBLIC HEALTH RELEVANCE: The JAK2V617F mutation is found in almost all patients with polycythemia vera (PV) that disrupts bone marrow functions and becomes leukemia. JAK2 inhibitors improve symptoms and quality of life but their long-term effectiveness remains to be determined. JAK2 inhibitors do not eradicate PV-initiating cells, and are unlikely to cure the disease. We have observed that JAK2V617F activates a novel gene called Alox5 and loss of this gene impedes the PV development in mice. Also, an Alox5 inhibitor prolongs survival of PV mice. These preliminary results indicate that Alox5 is a promising target gene for PV treatment. Our studies in this application will build a solid foundation for future PV clinical trials by targting the Alox5 pathway.