Bexarotene Induction of Differentiation in AML

描述(申请人提供)：由于疾病的异质性，急性髓系白血病(AML)的靶向治疗是困难的。全反式维甲酸(ATRA)是目前已知的唯一对AML子集有效的疗法。宾夕法尼亚大学的临床医生最近证明，FDA批准的维甲酸X受体(RXR)激动剂贝沙罗汀可刺激部分复发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诱导这组独特患者分化的机制，以进一步了解RXR刺激通路的扰动如何导致急性髓系白血病。将使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。利用体外对贝沙罗汀诱导分化不敏感和敏感的AML细胞系和原代细胞，我们将首先利用RXR在反应性AML细胞中的RNA干扰和异源二聚突变体Y402a的引入，确定RXR激活和与其他核受体二聚化的贡献。其次，我们将确定RXRA结构性上调或下调对谱系命运的影响，并确定不可降解的RXRA S260A突变体在RXR和RAR激动剂刺激后表达对谱系命运的影响。最后，我们将表征贝沙罗汀对髓系转录因子CEBPE的新诱导，并确定患者的临床反应是否源于该基因表达或功能的恢复。这些研究将为更深入地了解贝沙罗汀诱导分化的调控机制，进一步了解贝沙罗汀在体内对AML患者的反应。

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.