Bcl-2选择性抑制剂ABT-199抗急性髓细胞白血病的机制研究

Acute myeloid leukemia (AML) remains a challenging disease to treat in both pediatric and adult populations. Resistance to anthracycline [e.g., daunorubicin (DNR)] and cytarabine (ara-C)-based chemotherapy is a major cause of treatment failure in this disease. Therefore, new therapies are urgently needed to overcome drug resistance, decrease relapse rate, and reduce short- and long-term adverse effects of treatment. Overexpression of anti-apoptotic Bcl-2 family proteins (Bcl-2, Bcl-xL, Mcl-1, etc.) has been shown to cause resistance to chemotherapy in many cancer types, including AML. While inhibitors of this family have been promising, inhibition of Bcl-xL has been associated with platelet death and subsequent thrombocytopenia. Fortunately, the recently developed ABT-199 is specific for Bcl-2, making it an attractive potential option for treatment of AML. Our preliminary studies found that AML cell lines harboring MLL fusion genes were especially sensitive to ABT-199 compared to those that did not. Further, the two acute promyelocytic leukemia (APL, FAB M3) cell lines tended to be more sensitive to ABT-199 compared to the other AML cell lines. Importantly, we found that primary AML samples with the APL phenotype are especially sensitive to single-agent ABT-199. Further, we found that ABT-199 inhibited the phosphorylation of tyrosine 15 of CDK1 (Cyclin-dependent kinase 1, a critical kinase in the G2 cell cycle checkpoint pathway) and induced apoptosis. We also demonstrated synergistic antileukemic cytotoxicities between a CHK1 selective inhibitor LY2603618 and ABT-199 against primary AML blasts. These results suggest that besides playing a critical role in the mitochondrial apoptotic pathway, Bcl-2 also plays an important role in the G2 cell cycle checkpoint pathway. We hypothesize that ABT-199 induces apoptosis in AML cells by targeting these functions of Bcl-2 in both pathways. In this study, we will thoroughly investigate the molecular mechanism by which ABT-199 induces apoptosis in AML cells by focusing on the effects of the mitochondrial apoptotic pathway and the G2 cell cycle checkpoint pathway on ABT-199-induced apoptosis. The results of this study will form a solid foundation for the clinical evaluation of ABT-199 for treating AML.

急性髓细胞白血病（Acute myeloid leukemia, AML）是一种常见的恶性血癌，许多患者仍死于耐药、复发或并发症。因此，引入抗癌新药来提高AML患者的治愈率具有特殊的重要性和迫切性。新型Bcl-2选择性抑制剂ABT-199 具有很好的治疗AML的临床应用前景，然而其作用机理尚不清楚。前期工作结果预示Bcl-2不仅在线粒体凋亡路径起重要作用，而且通过调节CDK1活性在G2细胞周期检验点路径中起重要作用。我们推测，ABT-199通过抑制Bcl-2的上述两种功能来杀伤AML细胞。我们将在此基础上系统、深入地研究：1）线粒体凋亡路径对ABT-199活性的影响；2）ATM/ATR-CHK1-CDK1信号通路在体外和体内对ABT-199活性的影响；3）Bcl-2调控CDK1活性的分子机制。本研究将为应用ABT-199单药或与其它药物联合治疗AML提供明确的理论基础和可靠的实验依据。

Bcl-2选择性抑制剂ABT-199 (Venetoclax)是治疗AML的潜力药物，但人们对其作用机制的研究尚不完整。课题组在2015到2018的四年间，按既定计划顺利完成所有研究内容，取得如下结果：1）明确Bim和Mcl-1在ABT-199抗AML活性中的重要作用，确定Mcl-1蛋白的表达是AML细胞对ABT-199不敏感的一个关键因素；2）证明将ABT-199与DNA损伤类常规化疗药物阿糖胞苷和柔红霉素联合应用能消除Mcl-1对ABT-199抗AML活性的抑制作用；3）证明抑制CHK1能通过下调Mcl-1表达以及增加ABT-199诱导的DNA损伤来增强ABT-199的抗AML活性。此外，我们还证明抑制CRM1蛋白、PI3K/Akt/mTOR和MEK/ERK信号通路均能通过调控Mcl-1来增强ABT-199的抗AML活性。在项目进行期间（2018年11月），ABT-199已经被FDA批准与地西他滨、阿扎胞苷或低剂量阿糖胞苷联合使用来治疗75岁及以上或者无法耐受常规化疗的AML患者。本项目的研究成果为ABT-199在AML治疗中的临床应用提供了实验与理论依据。

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