急性髓细胞白血病（AML）是最常见的成人急性白血病, 许多患者死于耐药、复发或并发症。因此，引入抗癌新药来增强常规化疗药物的活性具有特殊的重要性和迫切性。在众多的抗癌新药中，组蛋白去乙酰化酶抑制剂（HDACI）尤其引人关注。我们发现HDACI通过抑制CHK1的表达，从而阻滞DNA修复及细胞周期检查点的激活，由此增强常规化疗药物引起的DNA双链断裂，并促进凋亡产生。并且发现，与CHK1的表达直接相关的主要是HDAC1、2和3。基于此本研究将首先确定CHK1在阿糖胞苷或柔红霉素引起的DNA双链断裂、细胞周期阻滞及细胞凋亡中的重要作用；并阐明HDAC1、2和3对CHK1转录调控的分子机理。这将为HDACI在AML的治疗中与常规化疗药物的联合应用提供明确的分子机制和理论依据；确定HDAC1、2和3为治疗AML的关键靶分子，并为新一代特异性更强、抗AML疗效更好的HDACI的设计提供理论基础。

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. Histone deacetylase (HDAC) inhibitors (HDACIs) are a promising new class of anti-cancer drugs, which induce differentiation, cell cycle arrest, and apoptosis in human leukemic cells,but less so in normal cells. Our previous studies demonstrated synergistic antileukemic cytotoxicities between HDACIs and ara-C in AML cell lines and diagnostic AML blasts. This was accompanied by cooperative induction of DNA double-strand breaks (DSBs) and apoptosis.However, the underlying molecular mechanisms remain largely unknown. Further, HDAC family members that are involved in the synergistic anti-leukemic activities with combined ara-C and HDACIs were not identified.As a logical extension of our previous studies, we will continue to explore the molecular mechanisms by which HDACIs enhance DNA damaging agent-induced DNA DSBs and apoptosis. The ability of HDACIs to enhance ara-C-induced DNA DSBs and apoptosis suggests that they may suppress the DNA damage response (DDR) in AML cells. The DDR represents a complex network of multiple signaling pathways involving cell cycle checkpoints, DNA repair, transcriptional programs, and apoptosis. In cancer treatment, the DDR occurs in response to DNA damaging agents (e.g., ara-C and DNR), representing an important mechanism limiting chemotherapeutic efficacy. We hypothesize that HDACIs enhance ara-C- or DNR-induced apoptosis in AML cells by suppressing the DDR. This hypothesis is strongly supported by our preliminary studies.We found that HDACIs suppresse the expression of CHK1, a critical gene in the DDR, in AML cell lines and primary AML patient samples. Our proposed studies will (1) determine the critical roles of CHK1 in ara-C- or DNR- induced DNA DSBs, cell cycle checkpoint activation, and apoptosis; and (2)identify the HDACs which regulate the expression of CHK1 in AML cells,determine the molecular mechanisms by which these HDACs regulate the expression of CHK1, and the roles of these HDACs in ara-C and DNR sensitivities. These results will be critical in establishing the molecular mechanisms underlying the synergistic anti-leukemic activities between HDACIs and standard chemotherapy drugs, and in designing the next generation HDACIs that show the best efficacies in treating AML with potentially reduced toxicity. Most importantly, our studies will establish a more efficacious therapy that combines HDACIs and standard chemotherapy drugs for treating AML.