MDM2抑制剂诱导携带FLT3-ITD突变的AML细胞凋亡过程中p53对CXCR4表达的调控作用

Acute Myelogeneous Leukemia (AML) carrying FLT3-ITD mutation accounts for 30% of total AML. Such sub-type of AML is proved to be a challenge for conventional therapy. We have confirmed that nearly 80% of newly diagnosed AML carry wt-p53, which renders MDM2 inhibitor great therapeutic potential for AML. Our previous study reported that FLT3-ITD was an indicator, other than wt-p53, for sensitivity to MDM2 inhibitor treatment. Our preliminary data showed that: 1) the expression of CXCR4 was significantly higher in FLT3-ITD AML blasts than FLT3-wt AML blasts; 2) MDM2 inhibitor treatment induced CXCR4 down-regulation that could be restored by the treatment of p53 siRNA; 3) down-regulation of CXCR4 by siRNA resulted in the repression of cell proliferation, indicating that decreased expression of CXCR4 was p53-dependent and critical to the apoptotic effect induced by MDM2 inhibitor on AML carrying FLT3-ITD. We are proposing focused investigation to obtain the direct evidence on the involvement of p53 in the regulation of CXCR4 expression by using gene knock-down or over-expressing techniques, and by the application of specific inhibitors. We anticipate that this study will lay a solid scientific foundation for the preferential usage of MDM2 inhibitor treatment on AML patients carrying FLT3-ITD mutation as an individualized targeted therapy.

急性髓系白血病（AML）中携带FLT3-ITD突变的亚群（占30%）是传统治疗的难点。我们发现80%初诊AML携带wt-p53，使MDM2抑制剂应用于治疗AML成为可能；并且证实FLT3-ITD是继wt-p53后预示AML对MDM2抑制剂敏感的分子标志物。预实验结果发现:1）CXCR4的表达在携带FLT3-ITD的AML中显著升高；2）MDM2抑制剂作用下CXCR4的表达下降，而p53的siRNA能够拮抗这种作用；3）下调CXCR4的表达能够抑制细胞增殖，高度提示CXCR4表达下调依赖于wt-p53，并且在MDM2抑制剂诱导FLT3-ITD AML凋亡中发挥重要作用。本研究拟进一步通过小分子干扰、基因转染、抑制剂实验等获得p53在MDM2抑制剂作用于FLT3-ITD AML细胞过程中参与调控CXCR4表达的直接证据，为MDM2抑制剂选择性用于治疗携带FLT3-ITD的AML提供科学依据。

AML的特点是恶性度高、缓解期短、复发率高，再次缓解的几率较一线治疗明显降低。诱导化疗毒性大，骨髓移植虽有望治愈AML，但具有很高的治疗相关死亡率，低毒有效的治疗方法有待探索。靶向治疗是研发热点。我们发现超过80%初诊AML携带wt-p53，p53基因异常（突变或17p LOH）是除核型和年龄外AML的独立预后因素。Mdm2抑制剂能阻止p53与Mdm2蛋白结合，重新激活wt-p53的功能，是治疗初诊AML的有效药物，同时对正常造血组织无毒。Flt3-ITD是AML预后不良的基因突变之一，携带Flt3-ITD的AML常伴随CXCR4表达升高，p53可能通过其他转录因子间接下调CXCR4的表达。NRP1是另一个与CXCR4表达呈负相关的受体蛋白，且受miR-9的直接调控。我们证实miR-9通过直接抑制NRP1的表达降低AML细胞的增殖。综上，Mdm2抑制剂联合miR-9/NRP1轴靶向治疗有可能是高效清除AML细胞、防止复发的新型治疗方案。

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