Bexarotene Induction of Differentiation in AML

描述（由申请人提供）：由于疾病的异质性，急性髓性白血病（AML）的靶向治疗很困难。全反式维甲酸（ATRA）是目前唯一已知的治疗急性髓性白血病的方法。宾夕法尼亚大学的临床医生最近证明，FDA批准的类维甲酸X受体（RXR）激动剂贝沙罗汀刺激了一部分复发性AML患者的白血病细胞分化，导致持续的临床反应。以下建议旨在描述贝沙罗汀在这组独特患者中诱导分化的机制，以进一步了解RXR刺激通路的扰动如何导致急性髓性白血病。将采用药物遗传学方法研究贝沙罗汀对AML细胞系和原代细胞的影响。在体外实验中，我们利用对贝沙罗酮诱导分化无反应和有反应的AML细胞系和原代细胞，首先通过RNA干扰应答性AML细胞中的RXR，并引入异源二聚化突变体Y402A，确定RXR激活和与其他核受体二聚化的作用。其次，我们将确定RXRa的组成上调或下调对谱系命运的影响，并确定在RXR和RAR激动剂刺激后，不可降解的RXRa S260A突变体的表达对谱系命运的影响。最后，我们将描述贝沙罗汀对骨髓转录因子CEBPe的新诱导作用，并确定患者的临床反应是否是由于该基因的表达或功能的恢复。这些研究将更深入地了解贝沙罗汀诱导分化的体外调控机制，从而进一步了解体内对贝沙罗汀反应性AML患者。

DESCRIPTION (provided by applicant): Targeted therapy of acute myeloid leukemias (AML) is difficult due to the heterogeneity of the disease. All- trans retinoic acid (ATRA) is currently the only known therapy to work in a subset of AML. Clinicians at the University of Pennsylvania recently demonstrated that the FDA approved retinoid X receptor (RXR) agonist bexarotene stimulated leukemic cell differentiation in a subset of patients with relapsed AML leading to sustained clinical responses. The following proposal aims to characterize the mechanism by which bexarotene induces differentiation in this unique set of patients to further the understanding of how perturbations in RXR stimulated pathways result in acute myeloid leukemias. A pharmacogenetic approach to study the effects of bexarotene on AML cell lines and primary cells will be used. Using AML cell lines and primary cells that have been characterized to be unresponsive and responsive to bexarotene induced differentiation in vitro, we will first define the contribution of RXR activation and dimerization with other nuclear receptors using RNA interference of RXR in responsive AML cells and introduction of the heterodimerization mutant Y402A. Second, we will determine the effects of constitutive up or down- regulation of RXRa on lineage fate and determine the consequence of expression of the non-degradable RXRa S260A mutant on lineage fate determination after stimulation with RXR and RAR agonists. Finally, we will characterize the novel induction of the myeloid transcription factor CEBPe by bexarotene and determine if clinical responses in patients are due to restoration of expression or function of this gene. These studies will provide a more thorough understanding of the regulatory mechanisms of bexarotene-induced differentiation in vitro to further the comprehension of bexarotene responsive AML patients in vivo.