New Therapeutic Targets in AML

描述(申请人提供)：尽管在了解急性髓系白血病(AML)的遗传原因方面取得了相当大的进展，但阿糖胞苷与蒽环类药物的联合使用已有40多年。尽管这些药物具有临床实用价值，但仍存在相当大的毒性，长期结果令人失望：AML患者的五年存活率不到20%。这项工作的重点是开发更好的治疗方法，治疗大约50%的急性髓系白血病(AML)病例，这些病例过度表达同源盒转录因子HOXA9和HOX辅助因子Meis1。HOXA9/Meis1基因失控是白血病发生的关键因素，也是判断预后不良的重要独立指标。我们的目标是更好地定义白血病中HOX放松调控的机制，以便确定关键的相互作用或酶活性，这些作用或酶活性可以作为治疗的靶点。这些靶点缺失的AML病例与混合系白血病基因MLL重排、组蛋白H3赖氨酸4特异性甲基转移酶(约占所有AML病例的10%)、核磷蛋白(NPM1)突变(导致其重新定位于细胞质(NPMc+)(约占AML病例的35%))或CDX2的过度表达密切相关，后者发生在90%的正常核型AML病例中。最常见的MLL重排是平衡易位，它将MLL与一系列核转位因子之一融合在一起。在其他情况下，MLL与使截短的MLL分子二聚化的易位伙伴融合。最后，MLL的部分串联复制(MLL-PTD)，由于编码氨基末端MLL的序列的复制，也解除了对HOX基因的表达调控。具有NPMc+的AML病例几乎从来没有MLL重排，但与MLL重排病例有相似的表达谱，并且与Flt3突变具有很强的协同性，这表明这些病例有最终共同的Hox去调控途径。我们发现MLL是通过与聚合酶相关因子复合体PAFC相互作用而被招募到HOX基因座的，在PAFC中，MLL通过其组蛋白H3赖氨酸4甲基转移酶活性来调节HOX基因的表达。此外，我们和其他人发现，常见的MLL融合蛋白将组蛋白H3赖氨酸79甲基转移酶DOT1L招募到目标位置，并且这种招募以及野生型MLL都是转化所必需的。该方案中的实验将为治疗靶向MLL-PAF轴或DOT1L治疗具有不同转化机制的白血病奠定基础。)

DESCRIPTION (provided by applicant): Although considerable progress has been made in understanding the genetic causes of acute myeloid leukemia (AML), the mainstay of chemotherapy, cytarabine in combination with anthracyclines, have been in use for more than 40 years. Despite their clinical utility, the drugs suffer from considerable toxicity and the long-term results are disappointing: the five-year survival rate for AML patients is less than 20%. The focus of this work is on developing better therapy for the approximately 50% of acute myeloid leukemia (AML) cases that over express the homeobox transcription factor HOXA9, along with the HOX cofactor MEIS1. HOXA9/MEIS1 deregulation has been shown to be pivotal for leukemogenesis as well as an important independent marker for adverse prognosis. Our goal is to better define mechanisms of HOX deregulation in leukemia in order to identify critical interactions or enzymatic activities that could be targeted therapeutically. AML cases with deregulation of these targets are strongly associated with rearrangement of the mixed lineage leukemia gene MLL, a histone H3 lysine 4 specific methyltransferase (involved in approximately 10% of all AML cases), mutation of nucleophosmin (NPM1), resulting in its re-localization to the cytoplasm (NPMc+)(approximately 35% of AML cases) or overexpression of CDX2, which occurs in as many as 90% of normal karyotype AML cases. The most common MLL rearrangements are balanced translocations that fuse MLL to one of a number of nuclear translocation factors. In other cases, MLL is fused to translocation partners that dimerize the truncated MLL molecule. Finally, partial tandem duplication of MLL (MLL-PTD), as a result of duplication of sequences encoding the amino terminal MLL, also deregulate HOX gene expression. AML cases with NPMc+ almost never have MLL rearrangements, but share similar expression profiles as MLL rearranged cases as well as strong cooperativity with FLT3 mutations suggesting these cases share final common pathways for HOX deregulation. We discovered that MLL is recruited to HOX loci through interaction with the polymerase associated factor complex, PAFc, where it regulates HOX gene expression through its histone H3 lysine 4 methyltransferase activity. In addition, we and others have found that common MLL fusion proteins recruit the histone H3 lysine 79 methyltransferase DOT1L to target loci and that this recruitment, along with wild type MLL, are all required for transformation. The experiments in this proposal will lay the groundwork for therapeutic targeting of the MLL-PAF axis or DOT1L in leukemias with varying mechanisms of transformation.)