Understanding and Targeting Chemotherapy Resistance in Acute Myeloid Leukemia

 描述（由申请人提供）：化疗耐药性是治疗急性髓性白血病（AML）患者最重要的临床挑战。大多数AML患者最初对化疗有反应，但超过一半的反应者会复发并最终死于疾病。传统上，化疗耐药性被假设为代表对具有白血病干细胞（LSC）特性的遗传上不同的克隆的选择。最近 数据和我们的初步结果（如下）表明，该模型的任何一部分都不完全正确。 相反，我们认为化疗耐药性可以并且经常是一种对化疗挑战的后天表观遗传反应，可能出现在任何白血病克隆中。在体外，我们已经模拟了化疗耐药性，并证明了DNA甲基化和组蛋白甲基化在用Ara-C治疗后迅速（在几天内）改变。具体而言，H3 K27 me 3增加，H3 K4 me 2减少。为了初步研究原代细胞中表观遗传变化的贡献，我们比较了140对AML细胞在诊断和复发时的遗传和DNA甲基化特征。重要的是，初步证据表明，至少20%的患者在复发时没有新的可检测的遗传异常。相比之下，当比较配对诊断与复发AML标本时，我们观察到影响特定途径的胞嘧啶甲基化的广泛和部分收敛的再分布， 基因背景。综合这些研究表明化疗耐药的表观遗传机制，但没有解决白血病干细胞的作用。为了解决这个问题，我们研究了阿糖胞苷（Ara-C）对NSG小鼠中异种移植的AML细胞的影响。重要的是，我们第一次证明了阿糖胞苷处理的AML细胞的有限稀释分析没有显示出SCID白血病起始细胞的富集。总的来说，这些数据使我们假设AML中的化疗耐药性是一种生物学复杂事件，包括但不能完全解释遗传病变，并且由固定和诱导的表观遗传因素组成。为了测试和探索这些想法，我们提出了3个具体目标：具体目标1）在体外AML细胞中鉴定和表征对Ara-C的表观遗传反应的候选机制。具体目的2）鉴定原发性AML患者样品中复发的表观遗传和遗传决定因素。3）确定白血病细胞群体中出现化学抗性特征的动力学和机制。

 DESCRIPTION (provided by applicant): Chemotherapy resistance is the most important clinical challenge in treating patients with acute myeloid leukemia (AML). The majority of patients with AML initially respond to chemotherapy but over half of responders will relapse and eventually die of disease. Traditionally, chemotherapy resistance is hypothesized to represent selection for a genetically distinct clone that has properties of leukemic stem cells (LSC). Recent data and our preliminary results (below) indicate that neither part of this model is fully correct. Rather, we propose that chemotherapy resistance can and frequently is an acquired epigenetic response to chemotherapeutic challenge that may arise in any leukemic clone. In vitro, we have modeled chemotherapy resistance and demonstrate that both DNA methylation and histone methylation are altered rapidly (within days) after treatment with Ara-C. Specifically, H3K27me3 is increased and H3K4me2 is decreased. In order to initially study the contribution of epigenetic changes in primary cells, we have compared the genetic and DNA methylation signature of 140 pairs of AML cells at diagnosis and relapse. Importantly, preliminary evidence suggests that at least 20% of patients have no new detectable genetic abnormalities at relapse. In contrast, when comparing paired diagnosis vs. relapse AML specimens we observe extensive and partially convergent redistribution of cytosine methylation affecting specific pathways, regardless of genetic background. Taken together these studies suggest an epigenetic mechanism of chemotherapy resistance but do not address the role of leukemic stem cells. To address this, we have studied the effect of cytosine arabinoside (Ara-C) on AML cells xenografted in NSG mice. Importantly, we demonstrate for the first time that limiting dilution analysis of Ara-C treatd AML cells does NOT show an enrichment in SCID-leukemia initiating cells. Collectively these data lead us to hypothesize that chemotherapy resistance in AML is a biologically complex event that includes but is not fully explained by genetic lesions and is composed of both fixed and inducible epigenetic elements. To test and explore these ideas, we propose 3 Specific Aims: Specific Aim 1) Identify and characterize candidate mechanisms of epigenetic response to Ara-C in AML cells in vitro. Specific Aim 2) Identify epigenetic and genetic determinants of relapse in primary AML patient samples. Specific Aim 3) Determine the dynamics and mechanism through which chemoresistant features emerge in leukemic cell populations.