Potential therapeutic implications of targeting miR-150 in acute myeloid leukemia

描述（由申请人提供）：急性髓性白血病（AML）是一组遗传多样的造血系统恶性肿瘤，对治疗的反应各不相同。大约10%的AML涉及混合谱系白血病（MLL）基因的染色体重排，其具有超过60个融合伴侣。MLL重排的关键特征是产生由配偶体基因的5' MLL和3'序列组成的嵌合转录物（AML中80%涉及AF 9、AF 6、AF 10、ELL或ENL）。MLL相关白血病的预后很差。一组重要的癌基因，包括同源框A（HOXA）基因、MEIS 1、FLT 3、MYB和MYC，在MLL相关白血病中频繁上调，并且在携带MLL重排的白血病干细胞（LSC）的自我更新中起关键作用。然而，尚未开发出有效靶向这些基因的具有临床意义的疗法。因此，迫切需要更好地了解MLL相关白血病发病机制的分子机制，并在此基础上开发有效的治疗策略。MicroRNA（miRNA）是一类在转录后基因调控中起重要作用的非编码小RNA。最近，我们报道了miR-150在大多数AML病例中显著下调，并且其抑制对于MLL-AF 9介导的细胞转化和白血病发生是关键的; miR-150通过直接靶向FLT 3/MYB和间接靶向MYC/LIN 28/HOXA 9/MEIS 1，在MLL-fusion/MYC/LIN 28-miR-150-FLT 3/MYB/HOXA 9/MEIS 1信号传导回路中作为关键的肿瘤抑制剂看门人发挥作用（Jiang X.，等人Cancer Cell. 2012年）。假设：miR-150是MLL重排AML的发展和维持以及相关LSC自我更新所必需的。因此，miR-150表达/功能的恢复具有临床上适用于治疗这种类型的目前治疗抗性的肿瘤的显著潜力。 疾病具体目标：1）确定miR-150的抑制是否是MLL重排的AML的发展和维持所必需的; 2）确定miR-150的抑制是否是MLL重排的AML的LSC的自我更新所必需的;和3）确定miR-150的表达/功能的恢复（通过纳米颗粒递送）是否是治疗MLL重排的AML的有效新策略。研究设计：1）我们将使用小鼠骨髓移植（BMT）模型来确定miR-150的异位表达是否可以显著抑制MLL重排的AML的所有五种主要亚型（即，MLL-AF 9、-AF 6、-AF 10、-ELL和-ENL）。2)我们将进行竞争性再增殖和有限稀释试验，以确定miR-150的异位表达是否能显著抑制相关LSC的自我更新。3)我们将开发基于与miR-150寡核苷酸复合的FLT 3L（FLT 3配体）定向树枝状聚合物的新型靶向纳米颗粒，然后评估其在体外和体内靶向/治疗MLL重排AML的特异性和有效性。

DESCRIPTION (provided by applicant): Acute myeloid leukemia (AML) is a heterogeneous group of genetically diverse hematopoietic malignancies with variable responses to treatment. Around 10% of AMLs are involved in chromosomal rearrangements of the mixed lineage leukemia (MLL) gene with over 60 fusion partners. The critical feature of MLL-rearrangements is the generation of a chimeric transcript consisting of 5' MLL and 3' sequences of a partner gene (80% involving AF9, AF6, AF10, ELL or ENL in AML). The prognosis of MLL-associated leukemia is poor. A group of important oncogenes, including homeobox A (HOXA) genes, MEIS1, FLT3, MYB, and MYC, are frequently up-regulated in MLL-associated leukemias, and play a key role in the self-renewal of leukemia stem cells (LSCs) carrying MLL-rearrangements. However, clinically significant therapies have not been developed to effectively target these genes yet. Thus, better understanding of the molecular mechanisms underlying the pathogenesis of MLL-associated leukemia, and the development of effective therapeutic strategies based on such understanding, are urgently needed. MicroRNAs (miRNA) are a class of small, non- coding RNAs that play important roles in post-transcriptional gene regulation. Very recently, we reported that miR-150 is significantly down-regulated in most AML cases, and its repression is critical for MLL-AF9-mediated cell transformation and leukemogenesis; miR-150 functions as a pivotal tumor-suppressor gatekeeper in the MLL-fusion/MYC/LIN28⊣miR-150⊣FLT3/MYB/HOXA9/MEIS1 signaling circuit, through targeting FLT3/MYB directly and MYC/LIN28/HOXA9/MEIS1 indirectly (Jiang X., et al. Cancer Cell. 2012). Hypothesis: miR-150 is required for both development and maintenance of MLL-rearranged AMLs and for the self-renewal of the relevant LSCs. Therefore, the restoration of miR-150 expression/function holds significant potential to be clinically applicable to treat this type of presently therapy-resistant disease. Specific Aims: 1) To determine whether repression of miR-150 is required for both development and maintenance of MLL-rearranged AMLs; 2) To determine whether repression of miR-150 is required for the self- renewal of LSCs of MLL-rearranged AMLs; and 3) To determine whether restoration of the expression/function of miR-150 (delivered by nanoparticles) is an effective new strategy for treating MLL-rearranged AMLs. Study Design: 1) We will use mouse bone marrow transplantation (BMT) models to determine whether ectopic expression of miR-150 can significantly inhibit both development and maintenance of all five major sub- types of MLL-rearranged AMLs (i.e., MLL-AF9, -AF6, -AF10, -ELL and -ENL). 2) We will conduct both competitive repopulation and limiting dilution assays to determine whether ectopic expression of miR-150 can significantly inhibit the self-renewal of relevant LSCs. 3) We will develop novel targeted nanoparticles based on FLT3L (FLT3 ligand)-directed dendrimers complexed with miR-150 oligos, followed by assessment of their specificity and efficacy in targeting/treating MLL-rearranged AMLs both in vitro and in vivo.