Molecular Determinants of Methotrexate in Acute Lymphoblastic Leukemia

描述（由申请人提供）：本研究项目旨在增加我们对甲氨蝶呤（MTX）的作用机制和耐药性的理解，甲氨蝶呤是急性淋巴细胞白血病（ALL）儿童治疗的通用成分。长期目标是将这些知识纳入基于新分子靶点的ALL试验设计中，并改善耐药表型患者的无事件生存期（EFS）。尽管抗叶酸剂MTX广泛用于ALL治疗，但关于耐药性的分子决定因素、临床应答的异质性、最佳剂量和方案仍存在重要的未回答问题。已证明MTX多聚谷氨酸盐（MTX-PG）的淋巴母细胞蓄积与临床结果相关。MTX-PG的代谢取决于血清MTX浓度、跨细胞膜转运，更重要的是叶酸-γ-聚谷氨酸合成酶（FPGS）的细胞系特异性表达。非随机易位是ALL克隆的特征，是临床结局的重要预测因子，并表征表现出显著FPGS表达异质性的ALL亚型。由于它们对基因转录和细胞周期控制的影响，非随机易位可能会改变药物代谢和耐药性。我们推测与非随机易位相关的分子机制通过改变淋巴母细胞FPGS表达导致MTX-PG代谢的差异。我们认为这些易位代表了白血病克隆中存在的分子“途径”，导致FPGS表达的异质性、MTX代谢的模式以及在儿童ALL亚型中观察到的对MTX的临床反应。此外，FPGS的单核苷酸多态性（SNPs）最近已被确定在一个种族多样性小组的个人。我们认为这些SNPs也导致了ALL中PFGS表达的异质性，并将研究它们的患病率和生理影响。此外，已经描述了导致体外抗叶酸剂抗性的药物诱导的突变。因此，我们还假设药物诱导的FPGS突变可以在ALL复发时检测到，并可能代表复发后耐药的新机制。更重要的是，由于这些遗传异常不存在于正常的造血细胞中，它们为ALL的基因治疗或其他分子方法提供了选择性靶点。

DESCRIPTION (provided by applicant): This research project aims to increase our understanding of the mechanisms of action and resistance to methotrexate (MTX), a universal component of therapies for children with acute lymphoblastic leukemia (ALL). The long-term objectives are to incorporate this knowledge in the design of ALL trials based on novel molecular targets and to improve event-free survival (EFS) for patients with resistant phenotypes. Even though the antifolate MTX is widely used in ALL therapies, important unanswered questions remain with respect to molecular determinants of drug resistance, heterogeneity of clinical response, optimal dose(s) and schedule(s). It has been demonstrated that lymphoblast accumulation of MTX polyglutamates (MTX-PGs) correlates with clinical outcome. Metabolism to MTX-PGs depends on serum MTX concentration, transport across the cell membrane, and more important the cell lineage-specific expression of Folyl-gamma-polyglutamate Synthetase (FPGS). Non-random translocations that characterize ALL clones are important predictors of clinical outcome and characterize ALL subtypes that exhibit significant heterogeneity of FPGS expression. Due to their effects on gene transcription and cell cycle control, non-random translocations may alter drug metabolism and resistance. We hypothesize that molecular mechanisms associated with non-random translocations lead to differences in metabolism to MTX-PGs by altering lymphoblast FPGS expression. We propose these translocations represent molecular "pathways" present in leukemic clones that result in the heterogeneity of FPGS expression, patterns of MTX metabolism, and clinical response to MTX seen in childhood ALL subtypes. In addition, single nucleotide polymorphisms (SNPs) of FPGS have been recently identified in an ethnically diverse panel of individuals. We propose these SNPs also contribute to the heterogeneity of PFGS expression in ALL, and their prevalence and physiologic impact will be investigated. In addition, drug-induced mutations leading to in vitro resistance to anti-folates have been described. Consequently, we also hypothesize that drug-induced mutations of FPGS can be detected at the time of relapse from ALL and may represent a novel mechanism of resistance after relapse. More important, because these genetic abnormalities are not present in normal hematopoietic cells, they offer selective targets for gene therapy or other molecular approaches in ALL.