Identification of novel target genes for polycythemia vera (PV)

说明(申请人提供)：JAK2V617F突变在大多数骨髓增生性肿瘤(MPN)中发现，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+)慢性髓系白血病(CML)类似，这些费城染色体阴性(Ph-)MPN也来自造血干细胞(HSCs)，并有发生血栓和急性白血病的风险。目前还没有针对这些Ph-MPN的根治疗法。最近发现的JAK2V617F突变促进了使用JAK2抑制剂抑制JAK2V617F功能的靶向治疗的发展。尽管一些早期临床试验显示患者的症状和生活质量有所改善，但这些JAK2抑制剂的长期有效性仍有待确定。这些药物的副作用已经引起了一些担忧。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MPNS，这类似于用控制但不能治愈CML的BCR-ABL激酶抑制剂治疗Ph+CML。开发MPNS的治疗方法需要深入研究JAK2V617F在这些疾病的启动和维持中的分子基础，以确定新的有效靶基因。在本应用程序中，我们关注的是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，具有相似的骨髓增殖表型，提示CML和PV的致病细胞可能具有某些共同的调控机制。我的实验室有研究慢性粒细胞白血病启动细胞或白血病干细胞(LSCs)的生物学和分子靶向的历史，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)，并且Alox5对CML的发展是必不可少的(Chen等人。Alox5基因的缺失会损害白血病干细胞，预防慢性髓系白血病。自然遗传学41：783-792,2009)。我们还表明，抑制ALOX5功能可以根除LSCs，延长CML小鼠的生存时间。我们的初步数据显示，JAK2V617F激活了ALOX5，ALOX5基因的缺失阻碍了JAK2V617F诱导的小鼠PV的发展，这一点得到了ALOX5抑制剂治疗的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的发生发展中起重要作用，是治疗PV的潜在靶基因。其具体目的是：1)确定JAK2V617F激活ALOX5的信号通路；以及2)测试抑制ALOX5通路是否抑制小鼠和人类PV细胞。这些研究将通过靶向Alox5途径为未来的光伏临床试验奠定坚实的基础。 公共卫生相关性：JAK2V617F突变几乎在所有真性红细胞增多症(PV)患者中发现，这种患者会破坏骨髓功能，并成为白血病。JAK2抑制剂可改善症状和生活质量，但其长期有效性仍有待确定。JAK2抑制剂不能根除PV启动细胞，也不太可能治愈这种疾病。我们观察到JAK2V617F激活了一种名为ALOX5的新基因，该基因的缺失阻碍了小鼠PV的发育。此外，ALOX5抑制剂可以延长PV小鼠的存活时间。这些初步结果表明，Alox5基因是一种很有前途的治疗PV的靶基因。我们在这一应用中的研究将为未来的光伏临床试验奠定坚实的基础，目标是Alox5途径。

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.