Apoptosis Induced by Glucocorticoids and MEK1/2 Inhibitors in Leukemia

描述(申请人提供)：这项提案的目标是建立临床前证据，证明糖皮质激素(如地塞米松)和MEK抑制剂(如PD184352)在诱导急性淋巴细胞白血病(ALL)细胞凋亡方面具有协同作用。糖皮质激素(GC)是包括ALL在内的许多淋巴系统恶性肿瘤化疗方案的常见成分。GC诱导的细胞凋亡涉及内在的线粒体依赖途径，但参与GC诱导细胞死亡的信号通路和下游靶分子尚不完全清楚。我们和其他人已经证明，BIM(BCL-2细胞死亡的相互作用介体)是一种促凋亡的BCL-2家族蛋白，在地塞米松诱导的所有细胞中都有上调，并在地塞米松诱导的细胞凋亡中发挥重要作用。此外，细胞外信号调节激酶(ERK)介导的存活/生长因子的磷酸化使BIM失活。因此，我们假设与Dex和MEK/ERK抑制剂联合治疗将通过BIM上调和激活促进所有细胞的凋亡，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抑制剂在各种细胞系中协同促进地塞米松的致死性。我们现在建议阐明MEK/ERK抑制增强BIM活性和干扰其他促和抗凋亡的bcl2家族成员以增强ALL细胞中Dex疗效的机制。其具体目的是：1)评价地塞米松联合治疗BIM依赖/非依赖途径的意义以及BIM在细胞凋亡中的磷酸化状态；2)确定地塞米松诱导BIM的分子机制；3)采用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潜在有效的方法来提高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)药物MEK抑制剂通过阻止BIM的磷酸化和降解进一步增强BIM的激活。从这项建议中获得的信息将为未来的尝试提供合理的基础，以提高地塞米松等糖皮质激素与临床相关的MEK抑制剂在治疗ALL和可能的其他血液系统恶性肿瘤中的活性。PHS 398/2590(Rev.11/07)PHS 398/2590(Rev.11/07)Page Continue Format Page Public Health Relationship：主要概念是我们有一种新颖且潜在有效的方法来增加糖皮质激素(GC)对急性淋巴细胞白血病(ALL)细胞的活性，这可能反映了以下事实：a)GC上调致死分子BIM；以及b)药理MEK/ERK抑制剂进一步增强BIM激活。在这项研究中，我们将建立MEK/ERK-BIM通路参与地塞米松(Dex)和MEK/ERK抑制剂协同作用的机制证据。从这项建议中获得的信息将为未来尝试改善糖皮质激素的活性提供合理的基础，例如在临床上相关的MEK抑制剂治疗ALL和可能的其他血液系统恶性肿瘤中使用地塞米松。

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. PHS 398/2590 (Rev. 11/07) Page Continuation Format Page PUBLIC HEALTH RELEVANCE: The main concept is that we have a novel and potentially effective way to increase glucocorticoids (GC) activity against acute lymphoblastic leukemia (ALL) cells, which may reflect the fact that a) GC up-regulate a pro-death molecule, BIM; and b) pharmacologic MEK/ERK inhibitors further potentiate BIM activation. In this proposal, we will establish the mechanistic evidence how MEK/ERK-BIM pathway involves the synergistic interaction of dexamethasone (Dex) and MEK/ERK inhibitors. Information derived from this proposal will provide a rational foundation for future attempts to improve the activity of glucocorticoids such as Dex with clinically relevant pharmacologic MEK inhibitors in the treatment of ALL and possibly other hematological malignancies.