PI3K Isoform Dependence in Adult Hematopoiesis and Myeloid Leukemia

 描述(申请人提供)：急性髓系白血病(AML)是一种毁灭性的疾病，每年约有19,000人被诊断出来，5年存活率只有24%。主要的治疗方法是多药联合化疗和骨髓移植，两者的发病率和死亡率都很高，主要是由于对造血干细胞(HSC)的毒性作用。为了能够设计出更特异的治疗方法，在白血病启动细胞(LIC)中确定治疗靶点是至关重要的，因为这一细胞群在 故态复萌和抵抗。PI3激酶(PI3K)是一种脂质和蛋白激酶，它传递生长因子和趋化因子信号，导致Ser/Thr激酶Akt的磷酸化和激活，调节新陈代谢、细胞周期、细胞凋亡和蛋白质合成。Akt的病理性磷酸化在AML患者样本中经常被报道，抑制PI3K/Akt通路在AML细胞系、患者样本和小鼠白血病模型中显示出有效性。这一途径是白血病和其他恶性肿瘤的一个有吸引力的治疗靶点。然而，PI3K信号在正常成人HSCs中的作用尚不清楚。这对于PI3K/Akt抑制剂在临床上的潜在毒性是一个重要的考虑。在造血细胞中，编码PI3K催化亚单位四种不同亚型(p110和)的基因被表达。这些异构体在正常细胞和癌细胞中具有独特的功能，但在某些情况下可能会相互替代。目前有两类PI3K抑制剂在临床开发中：一类是针对所有四种PI3K亚型的PAN-PI3K抑制剂，另一类是只针对一种或两种异构体的异构体选择性抑制剂。为了确定哪些PI3K亚型对造血是必需的，哪些在白血病细胞中更重要，我们产生了一系列的小鼠基因敲除，以单独研究每个亚型在成人HSCs中的作用。我们最近发现，RAS突变的髓系白血病依赖于PI3K的p110α亚型，并且p110α的药理抑制在治疗RAS突变的小鼠白血病模型中是有效的。然而，在缺乏p110α的情况下，HSC的正常功能仍可维持，使其成为安全的治疗靶点。目前尚不清楚PI3K是否是成人HSC功能所必需的，因为其他PI3K亚型可能补偿HSC中的p110α。此外，PI3K在LICs中的作用尚不清楚。我们现在已经建立了新的复合基因敲除小鼠模型，这将使成年HSCs中多个PI3K亚型的可诱导条件缺失成为可能。在特定的目标1中，我们将进一步描述PI3K亚型在HSC功能、自我更新、增殖和分化中的冗余作用。在特定的目标2中，我们将基因去除AML小鼠模型中的PI3K亚型，以确定PI3K在LIC功能中的作用。目前，选择最有可能对异构体选择性PI3K抑制剂治疗有反应的AML患者的标准尚未建立。为了解决这个问题，在特定的目标3中，我们将描述AML中PI3K依赖和PI3K亚型特异性的分子决定因素。

 DESCRIPTION (provided by applicant): Acute myeloid leukemia (AML) is a devastating disease that is diagnosed in about 19,000 people per year, with a 5-year survival of only 24%. The mainstay of treatment is multi-agent chemotherapy and bone marrow transplantation, both associated with high morbidity and mortality, largely due to toxic effects on hematopoietic stem cells (HSC). To enable the design of more specific treatments for AML, it is critical to identify therapeutic targets in leukemia-initiating cells (LICs), since this cell population is important in relapse and resistance. PI3 kinase (PI3K) is a lipid and protein kinase that transduces growth factor and chemokine signals, leading to phosphorylation and activation of the Ser/Thr kinase Akt, which regulates metabolism, the cell cycle, apoptosis, and protein synthesis. Pathologic phosphorylation of Akt is frequently reported in AML patient samples, and inhibition of the PI3K/Akt pathway has shown efficacy in AML cell lines, patient samples, and mouse leukemia models. This pathway is an attractive therapeutic target for leukemia and other malignancies. However, the role of PI3K signaling in normal adult HSCs is unclear. This is an important consideration for the potential toxicity of PI3K/Akt inhibitors in the clinic. In hematopoietic cels, genes encoding four different isoforms of the catalytic subunit of PI3K (p110  and ) are expressed. These isoforms have unique functions in normal and cancer cells, but may substitute for each other in some contexts. Two classes of PI3K inhibitors are currently in clinical development: pan-PI3K inhibitors, which target all four PI3K isoforms, and isoform-selective inhibitors, which favor only one or two isoforms. To determine which of the PI3K isoforms are essential for hematopoiesis, and which are more important in leukemic cells, we have generated a series of mouse knockouts to study the roles of each isoform individually in adult HSCs. We recently found that RAS- mutated myeloid leukemias are dependent on the p110alpha isoform of PI3K, and that pharmacologic inhibition of p110alpha is effective in treatment of murine models of RAS-mutated leukemia. However, normal HSC functions are maintained in the absence of p110alpha, making it a safe therapeutic target. It is still not known whether PI3K is essential for adult HSC function, as other PI3K isoforms may compensate for p110alpha in HSCs. Furthermore, the role of PI3K in LICs is unclear. We have now generated novel compound knockout mouse models, which will enable the inducible conditional deletion of multiple PI3K isoforms in adult HSCs. In Specific Aim 1, we will further characterize the redundant roles of the PI3K isoforms in HSC function, self-renewal, proliferation, and differentiation. In Specific Aim 2, we will genetically ablate PI3K isoforms in mouse models of AML, in order to determine the roles of PI3K in LIC function. At the moment, criteria for the selection of AML patients that are most likely to respond to isoform-selective PI3K inhibitor treatment have not been established. To address this issue, in Specific Aim 3, we will delineate the molecular determinants for PI3K dependence and PI3K isoform specificity in AML.