HDAC8 Mediated Regulation of Acute Myeloid Leukemia Pathogenesis and Maintenance

描述（由申请人提供）：急性髓性白血病（AML）是成人中最常见的白血病类型，由于治疗抵抗和随后的复发，总体预后较差。白血病干细胞（LSCs）可以引发和维持AML，被认为是复发的潜在来源，因为它们不能通过标准化疗有效地消除。我们的长期目标是确定调节LSC产生和维持的分子机制，并确定新的基于机制的LSC靶向治疗。AML患者中最常见的染色体畸变之一是16号染色体倒置，这产生了编码CBF¿-SMMHC （CM）融合蛋白的融合基因CBFb-MYH11。本应用程序的目的是确定组蛋白去乙酰化酶8 （HDAC8）如何参与cm诱导的AML发病机制，确定HDAC8活性的分子机制，并评估同种异型选择性抑制剂（HDAC8i）靶向人类AML LSCs的功效。我们的中心假设是HDAC8活性通过inv（16）依赖性和独立机制解除调控，并且异常的HDAC8活性通过破坏p53乙酰化有助于AML LSC的转化和维持。因此，使用HDAC8i抑制HDAC8可能会重新激活p53并增强AML LSCs的靶向性。具体目的是：1)确定HDAC8如何促进inv（16）诱导的AML发病机制和LSC维持；2)确定HDAC8活性的潜在机制以及HDAC8亚型选择性药物抑制剂靶向非inv(16) AML LSCs的功效。在具体目标1中，我们将定义CM如何改变HDAC8和p53活性；使用我们的条件CM敲入小鼠，同时携带一个新的条件HDAC8缺失等位基因，确定HDAC8在CM诱导的LSC转化和维持中的作用；并验证来自inv(16)+患者的原发性AML LSCs的发现。在Specific Aim 2中，我们将确定非inv(16) AML LSCs中HDAC8表达与SOX4和HOXA9水平或p53状态之间的相关性；确定HDAC8过表达的功能后果，以及HOXA9/SOX4轴是否有助于HDAC8去调控；并评估HDAC8i对p53活性、LSC增殖和治疗耐药的影响。为了评估HDAC8的功能，我们产生了携带新的条件HDAC8缺失等位基因的小鼠。此外，我们将使用shrna介导的敲低和新型药理HDAC8i的组合。拟议的研究有望建立HDAC8失调的分子机制，以及在AML发病过程中HDAC8介导的翻译后p53失活的新机制。此外，这些研究将揭示HDAC8i的作用机制，以及HDAC8i是否可以重新激活p53并增强AML LSCs的消除。该结果将为靶向治疗提供新的理论基础和新的HDAC8亚型选择性药物抑制剂，并将对AML以及其他p53未突变的癌症类型具有转化意义。

DESCRIPTION (provided by applicant): Acute myeloid leukemia (AML) is the most common type of leukemia in adults and has poor overall outcome because of therapy resistance and subsequent relapse. Leukemia stem cells (LSCs) that can initiate and maintain AML are considered potential sources of relapse because they are not effectively eliminated by standard chemotherapy. Our long-term goals are to define the molecular mechanism(s) regulating LSC generation and maintenance, and to identify novel mechanism-based LSC targeted therapies. One of the most common chromosome aberrations found in AML patients is inversion of chromosome 16, which creates the fusion gene CBFb-MYH11 that encodes the CBF¿-SMMHC (CM) fusion protein. The objectives of this application are to define how histone deacetylase 8 (HDAC8) contributes to CM-induced AML pathogenesis, define the molecular mechanism(s) underlying HDAC8 activity and evaluate the efficacy of isoform-selective inhibitors (HDAC8i) in targeting human AML LSCs. Our central hypothesis is that HDAC8 activity is deregulated through both inv(16)-dependent and -independent mechanisms, and that aberrant HDAC8 activity contributes to AML LSC transformation and maintenance by disrupting p53 acetylation. Therefore, inhibiting HDAC8 by using HDAC8i may reactivate p53 and enhance targeting of AML LSCs. The specific aims are: 1) to define how HDAC8 contributes to inv(16)-induced AML pathogenesis and LSC maintenance, and 2) to determine the mechanism(s) underlying HDAC8 activity and the efficacy of HDAC8 isoform-selective pharmacological inhibitors in targeting non-inv(16) AML LSCs. In Specific Aim 1, we will define how CM alters HDAC8 and p53 activities; determine the role of HDAC8 in CM-induced LSC transformation and maintenance by using our conditional CM knock-in mice that also carry a new conditional Hdac8 deletion allele; and validate the findings in primary AML LSCs from inv(16)+ patients. In Specific Aim 2, we will determine the correlation between HDAC8 expression and levels of SOX4 and HOXA9 or p53 status in non-inv(16) AML LSCs; determine the functional consequences of HDAC8 overexpression and whether the HOXA9/SOX4 axis contributes to HDAC8 deregulation; and evaluate the effects of HDAC8i on p53 activity, LSC proliferation and resistance to therapy. To evaluate the function of HDAC8, we have generated mice carrying a new conditional Hdac8 deletion allele. In addition, we will use a combination of shRNA-mediated knockdown and novel pharmacological HDAC8i. The proposed studies are expected to establish molecular mechanism(s) underlying HDAC8 deregulation, as well as a novel HDAC8-mediated post-translational p53 inactivating mechanism in AML pathogenesis. In addition, these studies will reveal mechanisms of action and whether HDAC8i can reactivate p53 and enhance elimination of AML LSCs. The results will offer novel rationales and novel HDAC8 isoform-selective pharmacological inhibitors for targeted therapy, and will have translational implications for AML, as well as other cancer types in which p53 is not mutated.