The p110 alpha and delta isoforms of PI3 kinase in hematopoiesis and leukemia

描述（由申请人提供）：急性髓性白血病（AML）每年影响25，000人中的1人，并且仅约40%的病例可治愈。治疗的主要方法是多药化疗和骨髓移植，这两种方法都有许多并发症和高死亡率。这主要归因于大多数抗白血病药物对造血干细胞（HSC）的毒性作用，经常导致血细胞减少。因此，关键是要确定哪些信号通路在白血病细胞中特别重要，而在HSC中不重要，以便设计出更特异、毒性更低的AML治疗方法。PI 3激酶（PI 3 K）通路在许多人类癌症（包括AML）中被病理激活。PI 3 K在造血过程中也可能是重要的，因为它被造血生长因子受体如促红细胞生成素受体、c-kit受体和fms样酪氨酸激酶3（FLT 3）激活。在造血细胞中，受体酪氨酸激酶通过PI 3 K的催化p110亚基（具有3种亚型（、、））发出信号，以激活靶激酶AKT的磷酸化。然而，PI 3 K及其特定亚基在正常和白血病干细胞功能中的作用知之甚少。我们推测，靶向PI 3 K的单个亚基可以实现最具选择性的抗白血病作用，同时具有最小的潜在不良影响。本研究将利用两种新的遗传学工具来研究PI 3 K亚基p110和p110在白血病细胞和正常HSC中的作用：（1）造血细胞中p110条件性缺失的小鼠和（2）p110种系缺失和p110条件性缺失的双突变小鼠。初步数据显示，HSC中p110的条件性缺失会导致红细胞生成受损，并轻微降低HSC的重建能力。由于AKT信号在p110缺失的骨髓中维持，我们假设p110，一种仅在造血细胞中表达的亚基，可以补充HSC中的p110。在特定目标1中，我们将分析p110和p110复合缺失对造血细胞中HSC功能和AKT信号传导的影响。初步数据表明，至少在一些白血病小鼠模型中，p110的缺失不足以阻止疾病进展。基于p110切除未能消除造血细胞中的AKT信号传导，我们假设可能需要消除p110和p110来抑制白血病细胞的生长。特定目标2将使用骨髓移植系统，使用逆转录病毒引入的突变酪氨酸激酶（包括BCR-ABL、FLT 3- ITD和JAK 2 V617 F），检查p110、p110或两者缺失后小鼠的白血病发生和进展。具体目标3将检查p110和p110在MLL-AF 9诱导的白血病中的白血病干细胞功能中的作用，这在治疗上特别难以靶向。总之，这些研究将为HSC中PI 3 K信号转导的作用和机制提供重要的见解，并为白血病中该途径的治疗靶向提供最佳策略。

DESCRIPTION (provided by applicant): Acute myeloid leukemia (AML) affects 1 in 25,000 people per year, and is curable in only about 40% of cases. The mainstay of treatment is multi-agent chemotherapy and bone marrow transplantation, both of which have many complications and high mortality. This is largely attributed to the toxic effects that most antileukemic drugs have on hematopoietic stem cells (HSC), frequently leading to cytopenias. Therefore, it is crucial to determine which signaling pathways are important specifically in leukemic cells but not in HSCs, to enable the design of more specific and less toxic treatments for AML. The PI3 kinase (PI3K) pathway is pathologically activated in many human cancers, including AML. PI3K may also be important during hematopoiesis, as it is activated by hematopoietic growth factor receptors, such as erythropoietin receptor, c-kit receptor, and fms-like tyrosine kinase 3 (FLT3). In hematopoietic cells, receptor tyrosine kinases signal through the catalytic p110 subunit of PI3K, which has 3 isoforms (, , ), to activate the phosphorylation of the target kinase AKT. However, the roles of PI3K and its specific subunits in normal and leukemic stem cell function are poorly understood. We hypothesize that targeting individual subunits of PI3K may achieve the most selective anti-leukemic effect with minimal potential adverse affects. This proposal will utilize two novel genetic tools to investigate the roles of the PI3K subunits p110 and p110, individually and together, in leukemic cells and in normal HSCs: (1) mice with conditional deletion of p110 in hematopoietic cells and (2) double mutant mice with germline deletion of p110 and conditional deletion of p110. Preliminary data reveal that conditional deletion of p110 in HSCs results in impaired erythropoiesis, and slightly reduced HSC repopulating ability. As AKT signaling is maintained in p110-deleted bone marrow, we hypothesize that p110, a subunit expressed exclusively in hematopoietic cells, can complement for p110 in HSCs. In Specific Aim 1, we will analyze the effects of compound loss of p110 and p110 on HSC function and on AKT signaling in hematopoietic cells. Preliminary data suggests that deletion of p110 is insufficient to halt disease progression in at least some murine models of leukemia. Based on the failure of p110 excision to abrogate AKT signaling in hematopoietic cells, we hypothesize that it may be necessary to eliminate both p110 and p110 to inhibit the growth of leukemic cells. Specific Aim 2 will examine leukemia initiation and progression in mice after loss of p110, p110, or both using the bone marrow transplant system with retrovirally introduced mutated tyrosine kinases, including BCR-ABL, FLT3- ITD, and JAK2V617F. Specific Aim 3 will examine the roles of p110 and p110 in leukemic stem cell function in MLL-AF9-induced leukemia, which has been particularly difficult to target therapeutically. Together, these studies will provide important insights into the role and mechanism of PI3K signal transduction in HSCs, and the best strategies for therapeutic targeting of this pathway in leukemia.