Bypassing Oncogene Addiction: Mechanisms of off-target resistance in CML

描述(申请人提供)：慢性髓系白血病(CML)的特征是髓系祖细胞过度增殖，并保持分化能力。自然的 慢性粒细胞白血病的病史包括进展到更具侵袭性的疾病原始危象阶段，此时终末分化受损，疾病表现出急性白血病的特征。就像许多其他已知的骨髓增生性疾病一样，慢性粒细胞白血病与激活的酪氨酸激酶有关。在慢性粒细胞白血病的病例中，9号和22号染色体之间的相互易位事件后产生的融合蛋白BCR-ABL是疾病的病因。目前对慢性粒细胞白血病的治疗包括使用酪氨酸激酶抑制剂(TKI)，这已被证明在大多数病例中导致深度临床缓解。然而，在三磷酸腺苷口袋中出现阻止TKI结合的耐药突变经常是疾病复发的原因。第二代和第三代TKI已经开发出来，它们共同保持了对所有导致耐药突变的活性。随着对这种“靶上”耐药机制的更好控制，未来的临床耐药将越来越多地是靶外耐药机制的结果，目前对此知之甚少。这项工作的目的是确定和验证CML靶外耐药的候选分子介体。在初步数据中，我们对CML患者的原始样本进行了分析，这些患者的临床特征是BCR-ABL非依赖型疾病，尽管BCR-ABL抑制，但持续的MAPK和JAK/STAT信号转导，我们已经确认存在激活的NRAS突变和EVI-1的过度表达。因此，我们假设激活的NRAS和EVI-1的过度表达可以协同地赋予对BCR-ABL TKI治疗的非靶点耐药性。在目标1中，我们将使用表达bcr-abl的细胞系和小鼠模型来评估这些病变单独和联合对bcr-abl TKI产生耐药性的能力。在目标2中，我们将评估这些突变的引入序列对分化和进展为原始细胞危象表型的影响。最后，在 目的3我们将评估这些损伤对关键信号通路状态的影响。它 预计这项工作将为“癌基因成瘾”的性质提供有价值的见解，“癌基因成瘾”是一种精致依赖于特定致癌病变活动的现象。此外，人们希望能够确定辅助治疗靶点，以改善慢性粒细胞白血病和其他与酪氨酸激酶病理性激活相关的恶性肿瘤患者的治疗结果。

DESCRIPTION (provided by applicant): Chronic myeloid leukemia (CML) is characterized by hyperproliferation of myeloid progenitors that retain the capacity for differentiation. The natural history of CML involves progression to a more aggressive disease blast crisis phase, where terminal differentiation is impaired, and the disease exhibits features of acute leukemia. Much like many of the other known myeloproliferative disorders, CML is associated with an activated tyrosine kinase. In the case of CML, the fusion protein, BCR-ABL, which is produced following a reciprocal chromosomal translocation event between chromosomes 9 and 22 is causative of the disease. Current treatment for CML involves the use of tyrosine kinase inhibitors (TKI), which have been shown to result in a deep clinical remission in the majority of cases. However, the emergence of resistance-conferring mutations preventing TKI binding in the ATP pocket is frequently responsible for disease relapse. Second and third generation TKIs have been developed which collectively retain activity against all resistance-conferring mutations. With improved control of this "on-target" resistance mechanism, clinical resistance in the future will increasingly be a consequence of off-target resistance mechanisms, which are presently poorly understood. The objective of this work is to identify and validate candidate molecular mediators of off-target resistance in CML. In preliminary data involving analysis of primary samples obtained from CML patients with clinical features of BCR-ABL-independent disease and persistent MAPK and JAK/STAT signaling despite BCR-ABL inhibition, we have identified the presence of activating NRAS mutations in conjunction with EVI-1 overexpression. We therefore hypothesize that activated NRAS and EVI-1 overexpression can cooperatively confer off-target resistance to BCR-ABL TKI treatment. In Aim 1 we will use BCR-ABL-expressing cell line and murine models to assess the ability of these lesions alone and in combination to confer resistance to BCR-ABL TKIs. In Aim 2 we will assess the impact of the sequence of introduction of these mutations on differentiation and progression to a blast crisis like phenotype. Finally, in Aim 3 we will assess the impact of these lesions upon the status of critical signaling pathways. It is anticipated that this work will provide valuable insights into the nature of "oncogene addiction", the phenomenon of exquisite reliance upon the activity of a particular oncogenic lesion. Additionally, it is hoped that adjunctive therapeutic targets will be identified that may improve treatment outcomes for patients with CML and other malignancies associated with pathologic activation of tyrosine kinases.