Identification of novel target genes for polycythemia vera (PV)

描述（由申请方提供）：JAK 2 V617 F突变见于大多数骨髓增生性肿瘤（MPN），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。与染色体阳性（Ph+）慢性髓性白血病（CML）类似，这些费城染色体阴性（Ph-）MPN也来源于造血干细胞（HSC），并且具有发展血栓形成和急性白血病的风险。对于这些Ph-MPN仍然没有治愈性疗法。最近JAK 2 V617 F突变的发现促进了使用JAK 2抑制剂来抑制JAK 2 V617 F功能的靶向治疗的发展。尽管一些早期临床试验显示患者的症状和生活质量有所改善，但这些JAK 2抑制剂的长期有效性仍有待确定。人们已经对这些药物的副作用感到担忧。另一方面，已经显示用JAK 2抑制剂抑制JAK 2 V617 F不会根除PV起始细胞，这意味着用JAK 2抑制剂抑制JAK 2 V617 F的激酶活性不太可能治愈MPN，这是与用控制但不治愈CML的BCR-ABL激酶抑制剂治疗Ph+ CML类似的情况。开发MPN的治愈性疗法需要深入研究JAK 2 V617 F在这些疾病的起始和维持中的分子基础，以鉴定新的有效靶基因。在本申请中，我们专注于PV，这是与JAK 2 V617 F相关的MPN的主要形式。我们已经观察到Ph+ CML和Ph-MPN涉及相同的HSC细胞群，并且具有相似的骨髓增殖表型，这表明CML和PV的疾病起始细胞可能具有一些共同的调节机制。我的实验室具有研究CML中CML起始细胞或白血病干细胞（LSC）的生物学和分子靶向的历史，并且我们表明LSC的存活和自我更新需要花生四烯酸5-脂氧合酶基因（Alox 5），并且Alox 5对于CML发展是必不可少的（Chen等人，Loss of the Alox 5 gene impairs leukemia stem cells and prevents chronic myeloid leukemia. Nature Genetics 41：783-792，2009）。我们还表明，抑制Alox 5功能导致LSC的根除和CML小鼠的存活期延长。我们的初步数据表明，JAK 2 V617 F激活Alox 5，Alox 5基因的缺失阻碍了小鼠中JAK 2 V617 F诱导的PV的发展，这得到了用Alox 5抑制剂治疗的PV小鼠的存活时间延长的支持。这些初步结果使我们能够假设Alox 5在JAK 2 V617 F诱导的PV的发展中起重要作用，并且是治疗PV的潜在靶基因。具体目标是：1）确定JAK 2 V617 F激活Alox 5所涉及的信号传导途径;和2）测试抑制Alox 5途径是否抑制小鼠和人PV细胞。这些研究将通过靶向Alox 5通路为未来的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.