The paradox of myeloid leukemia of Down syndrome

项目摘要 唐氏综合征（DS）患儿的急性髓性白血病（AML）和骨髓增生异常综合征（DS）是众所周知的统称 与DS相关的髓性白血病（ML-DS）。ML-DS患者的无事件生存率（EFS）较高 (89.9%）仅用基于阿糖胞苷（AraC）的方案治疗。相反，复发性ML-DS患者 尽管进行了包括股骨柄在内的挽救治疗， 细胞移植，强调需要提高我们对ML-DS生物学的理解， 治疗复发性疾病的患者。我们的研究已经确定ML-DS原始细胞明显更多 与来自无DS儿童的AML原始细胞相比，对AraC敏感。此外，增加的表达 染色体21定位的基因胱硫醚-β-合酶（CBS）与增强的AraC敏感性有关。 ML-DS细胞系的代谢组学分析显示，AraC-100细胞中胱硫醚和半胱氨酸水平降低。 与AraC敏感的ML-DS细胞系相比，具有较低的CBS活性，表明CBS活性降低， CBS活性降低在ML-DS的AraC抗性中起重要作用。其他代谢变化 继发于CBS过表达的H2S导致DS表型，包括H2S水平升高，H2S抑制 线粒体复合物IV活性，诱导线粒体功能障碍并降低氧化磷酸化 （OXPHOS）。据报道，具有获得性AraC抗性的非DS AML细胞具有增加的OXPHOS， 以OXPHOS为靶点可以克服对AraC的耐药性。因此，我们假设另一种机制 ML-DS原始细胞AraC敏感性增强与线粒体功能障碍有关， OXPHOS由于CBS过度表达。另一方面，难治性/复发性（R/R）ML-DS增加 OXPHOS由于CBS活性降低，导致对AraC的抗性。此外，表达反- 凋亡蛋白Bcl-2和Mcl-1也有助于AraC抗性。因此，OXPHOS，Mcl-1， Bcl-2可能是治疗R/R ML-DS的一种有希望的方法。我们对新型依米立酮ONC213的研究， 显示ONC213在非DS AML中有效抑制OXPHOS，并在两种非DS AML中下调Mcl-1， AML和ML-DS，并协同增强Bcl-2选择性抑制剂的抗白血病活性， venetoclax，在非DS AML和ML-DS细胞中。因此，ONC213和维奈托克的组合可 有效地根除AraC抗性ML-DS细胞。我们提出的研究将1）确定CBS在以下方面的作用： ML-DS细胞中的OXPHOS和AraC敏感性/抗性和2）使用ONC213与维奈托克组合作为 靶向AraC抗性R/R ML-DS细胞的方法。研究CBS过度表达与 和AraC敏感性将提高我们对ML-DS生物学的理解，这也可能导致 非DS AML患者的新疗法。开发R/R ML-DS的新治疗方法可能会改善结局 对于这种非常难治的患者

Project Summary Acute myeloid leukemia (AML) and myelodysplasia in children with Down syndrome (DS) are known collectively as myeloid leukemia associated with DS (ML-DS). ML-DS patients have high event-free survival (EFS) rates (89.9%) treated exclusively with cytarabine (AraC)-based protocols. In contrast, ML-DS patients with relapsed disease have extremely poor clinical outcomes with OS rates of <35%, despite salvage therapies including stem cell transplants, highlighting the need to improve our understanding of ML-DS biology and develop novel therapies for patients with relapsed disease. Our studies have identified that ML-DS blasts are significantly more sensitive to AraC compared to AML blasts from children without DS. Further, increased expression of chromosome 21-localized gene cystathionine-ß-synthase (CBS) is linked to the enhanced AraC sensitivities. Metabolomic profiling of ML-DS cell lines revealed reduced levels of cystathionine and cysteine in the AraC- resistant lines compared to the AraC-sensitive ML-DS cell line, indicating reduced CBS activity and suggesting that decreased CBS activity plays an important role in AraC resistance in ML-DS. Other metabolic changes secondary to CBS overexpression contribute to the DS phenotype including elevated levels of H2S, which inhibits mitochondrial Complex IV activity, induces mitochondrial dysfunction, and decreases oxidative phosphorylation (OXPHOS). It has been reported that non-DS AML cells with acquired AraC resistance have increased OXPHOS and targeting OXPHOS could overcome resistance to AraC. Hence, we hypothesize that another mechanism accounting for the enhanced AraC sensitivity of ML-DS blasts relates to mitochondrial dysfunction and decreased OXPHOS due to CBS overexpression. On the other hand, refractory/relapsed (R/R) ML-DS have increased OXPHOS due to decreased CBS activity, leading to resistance to AraC. Moreover, expression of the anti- apoptotic proteins Bcl-2 and Mcl-1 also contribute to AraC resistance. Thus, co-targeting of OXPHOS, Mcl-1, and Bcl-2 may represent a promising approach to treat R/R ML-DS. Our studies of the novel imipridone ONC213, revealed that ONC213 potently suppresses OXPHOS in non-DS AML and downregulates Mcl-1 in both non-DS AML and ML-DS, and synergistically enhances the antileukemic activity of the Bcl-2 selective inhibitor, venetoclax, in both non-DS AML and ML-DS cells. Hence, the combination of ONC213 and venetoclax may effectively eradicate AraC-resistant ML-DS cells. Our proposed studies will 1) determine the role of CBS in OXPHOS and AraC sensitivity/resistance in ML-DS cells and 2) use ONC213 in combination with venetoclax as an approach to target AraC-resistant R/R ML-DS cells. Studying the relationship between CBS overexpression and AraC sensitivity will improve our understanding of ML-DS biology, which may also lead to development of new treatments for non-DS AML patients. Developing new treatments for R/R ML-DS, may improve outcomes for this very therapy-resistant subgroup of patients.