Targeting AML with PI3K/AKT inhibitors and BH3-mimetics

描述（由申请人提供）：迫切需要新的治疗策略来治疗难治性急性髓性白血病（AML）。凋亡调节蛋白Bcl-2家族以及PI3K/AKT/mTOR和MEK/ERK通路的失调在AML中经常发生，越来越多的证据表明，Bcl-2家族成员之间的相互作用，以及它们的相对丰度，在决定细胞命运中起着关键作用。我们现在提出了一种基于机制的抗白血病策略，结合PI3K/mTOR抑制剂和bh3模拟ABT-737/263，其中这三个重要的生存途径被协调破坏。该方法利用了我们最近的发现，在AML中，与其他肿瘤类型相比，PI3K/mTOR抑制剂与其他AKT通路拮抗剂不同，可以抑制AKT和ERK。在bh3模拟物存在的情况下，这将导致pro-（例如bh3）之间的关联发生重大变化。， Bim, Bak)和anti-(如。Mcl-1、Bcl-2/xL)凋亡蛋白，以及它们表达的扰动（如Mcl-1下调、Bim上调）。在Specific Aim #1中，我们将采用遗传策略（例如，Bim AKT或ERK磷酸化突变体，构成活性或激酶死亡的AKT或MEK突变体）来验证我们的假设，即协同作用除了源于Mcl-1下调外，还源于Mcl-1/Bcl- 2/xL抑制影响下释放上调的Bim（以及Bak）。在具体目标2中，我们将验证协同相互作用也会发生在原发性、遗传定义的AML标本中的假设，并且类似的机制将负责。我们还将验证PI3K/AKT通路突变的假设，特别是AKT的基础激活状态，可以预测这种易感性

DESCRIPTION (provided by applicant): New treatment strategies for refractory acute myelogenous leukemia (AML) are urgently needed. Dysregulation of the Bcl-2 family of apoptotic regulatory proteins and the PI3K/AKT/mTOR and MEK/ERK pathways occurs frequently in AML, and accumulating evidence indicates that interactions between Bcl-2 family members, in addition to their relative abundance, play key roles in determining cell fate. We now propose a mechanism-based anti-leukemic strategy combining PI3K/mTOR inhibitors with the BH3-mimetic ABT-737/263 in which these three important survival pathways are coordinately disrupted. This approach exploits our recent discovery that in AML, in contrast to other tumor types, PI3K/mTOR inhibitors, unlike other AKT pathway antagonists, inhibit both AKT and ERK. In the presence of BH3-mimetics, this leads to critical alterations in the association between pro-(e.g., Bim, Bak) and anti-(e.g., Mcl-1,Bcl-2/xL) apoptotic proteins, as well as perturbations in their expression (e.g., Mcl-1 down-regulation and Bim up-regulation). In Specific Aim #1, we will employ genetic strategies (e.g., Bim AKT or ERK phosphorylation mutants, constitutively active or kinase-dead AKT or MEK mutants) to test our hypothesis that synergism stems from, in addition to Mcl-1 down-regulation, unleashing of up-regulated Bim (as well as Bak) from the inhibitory influence of Mcl-1/Bcl- 2/xL. In Specific Aim 2, we will test the hypotheses that synergistic interactions will also occur in primary, genetically defined AML specimens, and that analogous mechanisms will be responsible. We will also test the hypothesis that PI3K/AKT pathway mutations, and particularly basal AKT activation status, can predict susceptibility to this strategy. In Specific Aim #3, we will test the hypothesis that PI3K/mTOR inhibitors and BH3-mimetics, which individually target primitive leukemia-initiating cells (e.g., CD34+/CD38-/CD123+), will interact synergistically to eradicate this classically resistant population. We will also characterize, for the first time, AKT and ERK activation in these cells. In Specific Aim #4, multiple in vivo systemic AML model systems will be employed to extrapolate in vitro findings to intact animals, and to determine whether similar mechanisms underlie anti-leukemic synergism. Fulfillment of these aims will provide the theoretical foundation needed to develop and implement a PI3K pathway inhibitor/BH3-mimetic anti-leukemic strategy, which represents the first to interrupt coordinately three mutually interactive leukemia-related pathways. It may also help to validate pharmacodynamic response determinants, and identify individual AML patients most likely to benefit from this strategy.