Role of IKAROS in the Biology and Therapy of High-Risk Precursor B-Cell Leukemia

描述(申请人提供)：费城染色体阳性(Ph+)B细胞急性淋巴细胞性白血病(B-ALL)是一种前体B淋巴细胞的恶性肿瘤，复发风险高，总体存活率低，需要更好的治疗方法。在~85%的Ph+B-ALL中，编码淋巴转录因子的Ikaros(IKZF1)基因的失活突变提示其在B-ALL的发病机制中具有肿瘤抑制作用。无论Ph染色体状态如何，Ikaros突变B-ALL的预后都很差，这表明Ikaros突变是化疗耐药的直接原因。然而，Ikaros在B-ALL发病机制和治疗中的生物学作用尚不清楚，这是我们目前研究的重点。在第一个目的中，将使用IKZF1条件小鼠模型来描述Ikaros失活突变在B-ALL治疗反应不良的发病机制中的作用。初步研究表明，在IKZF1缺陷的B-ALL中，整合素信号和粘着斑激酶(FAK)的激活异常增加，支持间质介导的生长和生存，并导致间质依赖性抵抗BCR-ABL1酪氨酸激酶抑制剂如达沙替尼。抑制Ikaros突变型B-ALL中的FAK是否会干扰白血病细胞的生存并恢复对bcr-abl1抑制剂的敏感性，将进行测试。随后，将采取一种全球性的方法来检查在B细胞前体分化过程中由Ikaros调控的信号和转录网络，并确定其中哪些与B细胞前体白血病的表型有关。这应该会确定更多的潜在药物靶点，既位于FAK介导的生存途径的下游，也与其平行。最后，IKZF1缺陷的B-ALL对糖皮质激素(GC)高度耐药，其机制将被研究，目的是找出GC耐药途径中的关键节点，可用于B-ALL的联合治疗。在第二个目标中，从B-ALL小鼠模型研究中获得的知识将被转化为人类B-ALL。来自人类Ph+B-ALL患者的样本将被筛选出IKZF1突变，并在免疫缺陷(NSG)小鼠中繁殖，以扩大白血病克隆并产生用于治疗研究的白血病小鼠。人类B-ALL对FAK抑制剂单独或与bcr-abl1抑制剂联合使用的反应将在体外和体内进行测试。还将评估IKZF1缺陷的Ph+或Ph-B-ALL样本在IKZF1缺陷的小鼠B-ALL中识别的信号和转录通路的激活情况。到目前为止，小鼠和人类的Ikaros缺陷B-ALL的特性非常相似，这表明这种方法将确定更多的可用药靶点，这些靶点是耐药、高风险的人类B-ALL生存和增殖所必需的。总之，本申请中提出的研究将提供有关Ikaros突变B-ALL发病机制的关键新知识，并为在新型联合疗法中使用FAK对抗这种疾病的临床研究奠定基础。

DESCRIPTION (provided by applicant): Philadelphia chromosome-positive (Ph+) B-cell acute lymphoblastic leukemia (B-ALL) is a malignancy of precursor B-lymphocytes with a high risk for relapse and poor overall survival for which better therapies are needed. Inactivating mutations in the Ikaros (IKZF1) gene encoding lymphoid transcription factors in ~85% of Ph+ B-ALL suggest its tumor-suppressor role in the pathogenesis of B-ALL. The poor prognosis of Ikaros- mutant B-ALL holds true irrespective of the Ph-chromosome status indicating that Ikaros mutations are directly responsible for resistance to chemotherapy. However, the biological role of Ikaros in the pathogenesis and therapy of B-ALL is not understood and is the focus of our current investigation. In the first Aim, an Ikzf1 conditional mouse model will be used to delineate the rol of Ikaros-inactivating mutations in the pathogenesis and poor response to treatment of B-ALL. Preliminary studies have shown that an aberrant increase in integrin signaling and activation of focal adhesion kinase (FAK) in Ikzf1-deficient B-ALL supports stromal-mediated growth and survival, and causes stromal-dependent resistance to BCR-ABL1 tyrosine kinase inhibitors such as dasatinib. Whether inhibition of FAK in Ikaros-mutant B-ALL interferes with leukemic cell survival and restores sensitivity to BCR-ABL1 inhibitors will be tested. Subsequently, a global approach will be taken to examine the signaling and transcriptional networks regulated by Ikaros during B cell precursor differentiation and determine which of these contribute to the precursor B-cell leukemic phenotype. This should identify additional potential drug targets, both downstream of and parallel to the FAK-mediated survival pathway. Finally, Ikzf1-deficient B- ALL appears to be highly resistant to glucocorticoids (GC), and the mechanism thereof will be investigated with the goal of identifying key nodes in the GC resistance pathway that can be exploited for combination therapy of B-ALL. In the second Aim, the knowledge gained from studies in the mouse models of B-ALL will be translated to human B-ALL. Samples from human patients with Ph+ B-ALL will be screened for IKZF1 mutations and propagated in immunodeficient (NSG) mice to expand the leukemic clone and generate leukemic mice for therapeutic studies. The response of human B-ALL to FAK inhibitors either alone or in combination with BCR- ABL1 inhibitors will be tested in vitro and in vivo. IKZF1-deficient Ph+ or Ph- B-ALL samples will also evaluated for activation of signaling and transcriptional pathways identified in Ikzf1-deficient mouse B-ALL. The strong similarities in the properties of mouse and human Ikaros-deficient B-ALL characterized to date suggest that this approach will identify additional druggable targets that are required for the survival and proliferation of therapy- resistant, high-risk human B-ALL. Together, the studies proposed in this application will provide critical new knowledge about the pathogenesis of Ikaros-mutant B-ALL, and set the stage for clinical studies using FAK in novel combination therapies to combat this disease.