Targeting aberrant chromatin modifiers in clonal hematopoiesis and pre-leukemia.

骨髓恶性肿瘤，包括急性骨髓性白血病（AML）、骨髓增生性肿瘤（MPN）和骨髓增生异常综合征（MDS），是造血系统的恶性肿瘤，主要发生在老年人群中。最近的DNA测序研究和谱系追踪工作表明，这些疾病的基础突变出现在生命早期的造血干细胞中，并经历终身的克隆进化过程。在造血系统的老化过程中，内在和环境因素最终导致这些克隆的扩增和获得额外的突变事件，促进克隆进化和疾病发展。在血细胞中最常受年龄相关体细胞变异影响的基因是编码DNA甲基化修饰剂DNMT3A和TET2的基因。这些酶中的突变导致甲基胞嘧啶和羟甲基胞嘧啶在DNA中的分布偏斜，从而通过表观遗传重编程影响干细胞性、谱系同一性和细胞因子分泌。确切的分子机制，是至关重要的细胞内在的竞争优势，这些突变的前白血病细胞仍然知之甚少。因此，尚未建立预防克隆进化和最终血癌发展的治疗干预措施。来自我们小组的数据表明，在DNMT3A和TET2中携带突变的细胞选择性地易受MLL1（一种进化上保守的组蛋白甲基转移酶）的功能干扰。DNA甲基化修饰剂中的体细胞突变如何确切地导致这种对染色质作家的依赖性的问题将在本提案中得到解决。迄今为止，DNA甲基化和染色质生物学在很大程度上被认为是独立的表观遗传调控原则。我们的工作旨在将这些表观遗传实体连接到造血的克隆进化领域。除了对基本生物学原理的预期见解外，这项工作还具有潜在的治疗意义，因为靶向致癌MLL1复合物的小分子抑制剂最近已被开发并在早期临床试验中进行了测试。这些分子具有高度选择性，耐受性良好，并显示出治疗白血病患者的前景。在这个项目中，我们将测试这些新型化合物选择性损害DNMT3A和TET2突变造血细胞适应性的能力，并提供一个概念证明，靶向癌前克隆进化是可行的。我们希望这项工作将是治疗策略的发展，可能有助于防止恶性转化的高风险患者在未来的基础。

Myeloid malignancies, including Acute Myeloid Leukemia (AML), Myeloproliferative Neoplasms (MPN) and Myelodysplastic Syndromes (MDS) are malignancies of the hematopoietic system and occur predominantly in the older population. Recent DNA-sequencing studies and lineage-tracing efforts have demonstrated that founding mutations of these diseases arise in hematopoietic stem cells early in live and undergo a lifelong process of clonal evolution. During aging of the hematopoietic system, intrinsic and environmental factors eventually lead to expansion of these clones and acquisition of additional mutational events promoting clonal evolution and disease development. The genes most frequently affected by age-related somatic variants in blood cells are coding for the DNA-methylation modifiers DNMT3A and TET2. Mutations in these enzymes lead to skewing in the distribution of methylcytosine and hydroxy-methylcytosine across the DNA and thereby impact stemness, lineage-identity and cytokine secretion by epigenetic re-programming. The exact molecular mechanisms that are critical for the cell-intrinsic competitive advantage of these mutant pre-leukemic cells remains poorly understood to date. Therefore, therapeutic interventions to prevent clonal evolution and ultimately blood cancer development have yet not been established. Data from our group indicates, that cells harboring mutations in DNMT3A and TET2 are selectively vulnerable to functional perturbation of MLL1, an evolutionary conserved histone methyltransferase. The question of how exactly somatic mutations in DNA-methylation modifiers cause this dependency on a chromatin writer will be addressed in this proposal. To date, DNA methylation and chromatin biology are largely regarded as separate epigenetic regulatory principles. Our work aims to connect these epigenetic entities in the field of clonal evolution in hematopoiesis. Aside from the expected insights into basic biological principles, this work is of potential therapeutic relevance, since small molecule inhibitors targeting oncogenic MLL1 complexes have recently been developed and tested in early-phase clinical trials. Those molecules are highly selective, well tolerated and show promise for the treatment of patients with leukemia. In this project, we will test the ability of these novel compounds to selectively impair fitness of DNMT3A and TET2 mutant hematopoietic cells and provide a proof of concept that targeting of premalignant clonal evolution is feasible. We hope that this work will be the basis for the development of therapeutic strategies that may help to prevent malignant transformation in patient at high risk in the future.