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

描述（由申请人提供）：费城染色体阳性（Ph+） b细胞急性淋巴细胞白血病（B-ALL）是一种前体b淋巴细胞的恶性肿瘤，复发风险高，总生存率低，需要更好的治疗。在约85%的Ph+ B-ALL中，编码淋巴转录因子的Ikaros （IKZF1）基因发生失活突变，提示其在B-ALL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。在第一个目标中，将使用Ikzf1条件小鼠模型来描述ikaros失活突变在B-ALL发病机制和治疗反应差中的作用。初步研究表明，在ikzf1缺陷的B-ALL中，整合素信号的异常增加和局灶粘附激酶（FAK）的激活支持基质介导的生长和存活，并导致对BCR-ABL1酪氨酸激酶抑制剂（如达沙替尼）的基质依赖性耐药。在ikaros突变型B-ALL中抑制FAK是否会干扰白血病细胞存活并恢复对BCR-ABL1抑制剂的敏感性将被测试。随后，将采用一种全球性的方法来检查在B细胞前体分化过程中由Ikaros调节的信号和转录网络，并确定其中哪些促成了前体B细胞白血病表型。这将确定fak介导的生存途径的下游和平行的其他潜在药物靶点。最后，ikzf1缺陷的B-ALL似乎对糖皮质激素（GC）具有高度耐药，其机制将被研究，目的是确定GC耐药途径的关键节点，可以用于B-ALL的联合治疗。在第二个目标中，从小鼠B-ALL模型研究中获得的知识将被转化为人类B-ALL。来自Ph+ B-ALL人类患者的样本将筛选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白血病小鼠用于治疗研究。人类B-ALL对FAK抑制剂单独或与BCR- ABL1抑制剂联合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样品对ikzf1缺陷小鼠B-ALL中发现的信号和转录途径的激活情况。迄今为止，小鼠和人类ikaros缺陷B-ALL的特性非常相似，这表明该方法将确定治疗耐药、高风险人类B-ALL存活和增殖所需的额外药物靶点。总之，本申请中提出的研究将为ikaros突变型B-ALL的发病机制提供重要的新知识，并为使用FAK进行新型联合治疗来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.