Apoptosis Induced by Glucocorticoids and MEK1/2 Inhibitors in Leukemia

描述（由申请人提供）：本申请的目标是建立糖皮质激素（如地塞米松（Dex））和MEK抑制剂（如PD184352）在诱导急性淋巴细胞白血病（ALL）细胞凋亡中的协同作用的临床前证据。糖皮质激素（GC）是许多淋巴细胞恶性肿瘤（包括ALL）化疗方案的常见成分。气相色谱诱导的细胞凋亡涉及内在的线粒体依赖通路，但气相色谱诱导细胞死亡的信号通路和下游靶分子尚不完全清楚。我们和其他人之前已经表明，BIM （BCL- 2细胞死亡的相互作用介质），一个促凋亡的BCL-2家族蛋白，在Dex处理下在ALL细胞中上调，并在Dex诱导的细胞凋亡中起重要作用。此外，生存/生长因子介导的细胞外信号调节激酶（ERK）介导的磷酸化使BIM失活。因此，我们假设Dex和MEK/ERK抑制剂共同处理会通过BIM上调和激活促进ALL细胞的凋亡，导致细胞死亡。值得注意的是，我们实验室的初步数据表明，MEK抑制剂在多种ALL细胞系中协同促进DEX致死性。我们现在提议阐明MEK/ERK抑制增强BIM活性并干扰其他促凋亡和抗凋亡BCL-2家族成员以增强Dex在ALL细胞中的疗效的机制。具体目的是：1)评估Dex和MEK抑制剂共同作用下BIM依赖/独立通路的意义以及BIM磷酸化在细胞凋亡中的状态；2)确定地塞米松诱导BIM的分子机制；3)建立ALL小鼠体内模型，为该策略的有效性奠定基础。主要的概念是，我们有一种新的和潜在有效的方法来增加GC对白血病细胞的活性，这可能反映了这样一个事实：a) GC上调BIM；b)药理学MEK抑制剂通过阻断BIM的磷酸化和降解进一步增强BIM的激活。从该建议中获得的信息将为未来尝试提高糖皮质激素（如地塞米松）与临床相关药理学MEK抑制剂在治疗ALL和其他可能的血液系统恶性肿瘤中的活性提供合理的基础。

DESCRIPTION (provided by applicant): The goal of this proposal is to establish pre-clinical evidence of synergism between glucocorticoids such as dexamethasone (Dex) and the MEK inhibitors such as PD184352 in the induction of apoptosis in acute lymphoblastic leukemia (ALL) cells. Glucocorticoids (GC) represent common components of many chemotherapeutic regimens for lymphoid malignancies including ALL. GC-induced apoptosis involves the intrinsic mitochondria-dependent pathway, but the signaling pathways and downstream target molecules involved in GC-induced cell death are not entirely clear. We and others have previously shown that BIM (BCL- 2 Interacting Mediator of cell death), a pro-apoptotic BCL-2 family protein, is up-regulated by Dex treatment in ALL cells and plays an essential role in Dex-induced apoptosis. Furthermore, BIM is inactivated by extracellular signal-regulated kinase (ERK)-mediated phosphorylation by survival/growth factors. We therefore hypothesize that co-treatment with Dex and MEK/ERK inhibitors will promote apoptosis in ALL cells through BIM up-regulation and activation, resulting in cell death. Significantly, preliminary data from our laboratory demonstrate that MEK inhibitors synergistically promote DEX lethality in a variety of ALL cell lines. We now propose to elucidate the mechanisms by which MEK/ERK inhibition enhances the activity of BIM and perturbs other pro- and anti-apoptotic BCL-2 family members to enhance Dex efficacy in ALL cells. The specific aims are to 1) evaluate the significance of BIM-dependent/-independent pathways and the BIM phosphorylation status in apoptosis with Dex and MEK inhibitors co-treatment; 2) determine the molecular mechanisms how BIM is induced by dexamethasone treatment; 3) employ in vivo murine models of ALL to establish a basis for the efficacy of the strategy. The main concept is that we have a novel and potentially effective way to increase GC activity against leukemia cells, which may reflect the fact that a) GCs up-regulate BIM; and b) pharmacologic MEK inhibitors further potentiate BIM activation by blocking BIM phosphorylation and degradation. Information derived from this proposal will provide a rational foundation for future attempts to improve the activity of glucocorticoids such as dexamethasone with clinically relevant pharmacologic MEK inhibitors in the treatment of ALL and possibly other hematological malignancies.