Role of p21 activated kinase in Leukemogenesis

描述（由申请人提供）：急性髓细胞白血病（AML）是一种侵袭性血液系统恶性肿瘤，其特征是预后不良。虽然近年来已经描述了AML治疗的化疗方案的逐步改进;但大多数AML患者复发，其中相当数量的患者死于这种疾病。虽然导致复发的确切机制尚不清楚，但缺乏白血病干细胞（LSC）的消除和获得耐药突变（如FLT 3受体患者中发现的耐药突变）可能是一些重要因素。在近30%的AML患者中观察到FLT 3的内部串联重复（ITD），并导致预后不良。同样，对Gleevec耐药的KIT激活环突变（例如KITD 816 V）仅与约50%的核心结合因子（CBF）-AML和95%的系统性肥大细胞增多症（SM）患者（骨髓增生性肿瘤（MPN）的一种形式）相关，并导致总体生存率较差。虽然已经进行了几项使用FLT 3和KIT抑制剂治疗上述适应症的临床试验，但没有一项显示出显著的长期临床疗效。因此，对于老年人，谁表现出这些疾病的发病率和死亡率最高，继续研究新的分子靶向和毒性较小的治疗是迫切需要的。最近，包括157例AML患者的四项独立临床研究表明，在高达50%的患者来源的BM细胞中，而不是在正常细胞中，粘着斑激酶（FAK）过表达。在这些患者中，有相当数量的人，FAK在Y397上过度磷酸化，这是其活化的关键残基。与FAK-细胞相比，FAK+ AML细胞显示出显著更高的迁移和对柔红霉素的抗性，并且FAK表达与高原始细胞计数、早期死亡和较短的存活率显著相关。除了FAK，最近一项利用112名AML患者的研究也表明，新诊断的AML患者中磷酸化（p）pStat 5的表达与总生存率低相关。值得注意的是，在100%携带KITD 816 V突变的肥大细胞增多症患者中观察到pStat 5的组成性激活。重要的是，在AML患者中观察到pStat 5和FLT 3 ITD突变之间存在强相关性。这些临床结果表明，FLT 3 ITD/KITD 814 V、FAK和Stat 5可能有助于AML和MPN的发生;然而，这些信号分子在AML或MPN发生或进展中的关系尚不清楚。重要的是，尽管Stat 5与几种涉及LSC的血液恶性肿瘤有关; Stat 5的激活在细胞质或细胞核中如何精确调节，以及在AML或MPN的背景下参与其核输入的信号分子是什么仍然是一个谜。我们将明确FAK及其下游效应子PAK 1和Stat 5在调控FLT 3 ITD/KITD 814 V诱导的转化中的作用。我们假设FAK通过FLT 3 ITD/KITD 814 V的过度活化和下游磷酸化以及Stat 5以PAK 1依赖性方式的核转位有助于FLT 3 ITD/KITD 814 V驱动的AML。

DESCRIPTION (provided by applicant): Acute myeloid leukemia (AML) is an aggressive hematologic malignancy characterized by poor prognosis. While incremental improvements in chemotherapy regimens have been described for AML treatment in recent years; majority of AML patients relapse and a significant number of them die of this disease. Although the precise mechanism(s) leading to relapse are poorly understood, lack of elimination of leukemia stem cells (LSCs) and the acquisition of drug resistance mutations such as those found in patients with FLT3 receptor may be some of the significant contributors. Internal tandem duplications (ITD) in FLT3 are observed in nearly 30% of all AML patients and confer poor prognosis. Likewise, KIT activation loop mutations (e.g. KITD816V), that are resistant to Gleevec, are exclusively associated with ~ 50% of core binding factor (CBF)-AMLs and 95% of systemic mastocytosis (SM) patients (a form of myeloproliferative neoplasm (MPN)) and confer poor overall survival. While several clinical trials have been conducted utilizing FLT3 and KIT inhibitors for above indications, none have shown significant long-term clinical efficacy. Thus, fo the elderly, who demonstrate the highest incidence of and mortality from these diseases, continued investigation for novel molecularly-targeted and less toxic therapies are desperately needed. Recently, four independent clinical studies comprising of 157 AML patients demonstrated overexpression of focal adhesion kinase (FAK) in up to 50% of patient derived BM cells but not in normal cells. In a significant number of these patients, FAK was hyper-phosphorylated on Y397, a critical residue for its activation. FAK+ AML cells displayed significantly higher migration and resistance to daunorubicin compared with FAK- cells and FAK expression significantly correlated with high blast cell counts, early death and shorter survival rate. In addition to FAK, a recent study utilizing 112 AML patients also showed that expression of phosphorylated (p) pStat5 in newly diagnosed AML patients is associated with poor overall survival. Remarkably, constitutive activation of pStat5 was seen in 100% of mastocytosis patients bearing the KITD816V mutation. Importantly, a strong correlation between the presence of pStat5 and FLT3ITD mutations was observed in AML patients. These clinical findings suggest that FLT3ITD/KITD814V, FAK and Stat5 are likely to contribute to the development of AML and MPNs; however, the relationship between these signaling molecules in the development or progression of AML or MPNs is poorly understood. Importantly, although Stat5 has been implicated in several hematologic malignancies involving LSCs; how precisely activation of Stat5 is regulated in the cytoplasm or in the nucleus and what are the signaling molecules involved in its nuclear import in the context of AML or MPN remains an enigma. We will define the role of FAK and its downstream effectors including PAK1 and Stat5 in regulating FLT3ITD/KITD814V induced transformation. We hypothesize that hyper-activation of FAK via FLT3ITD/KITD814V and downstream phosphorylation and nuclear translocation of Stat5 in a PAK1 dependent manner contributes to FLT3ITD/KITD814V driven AML.