DRUG METABOLISM IN CHILDHOOD CANCER

尽管在过去的20年里取得了巨大的进步，癌症仍然是主要的 美国1至15岁儿童的疾病死亡原因。 在 急性淋巴细胞白血病（ALL），最常见的儿童癌症，30% 的患者在当前治疗中失败，许多患者在当前治疗中失败， 许多治愈的患者经历了显著的发病率， 化疗 这次竞争性续约的长期目标是 通过了解如何开发更有效但毒性更小的治疗方法， 白血病细胞代谢并激活巯基嘌呤（MP），一种广泛的 使用抗白血病药物。 正常组织中的MP代谢高度 可变的，和甲基化的巯基嘌呤甲基转移酶（TPMT）是受 遗传多态性。 TPMT缺乏症作为一种遗传性疾病， 常染色体隐性遗传性状，和杂合子，有显着差异 红细胞中MP代谢模式，这影响MP对正常人的毒性 造血细胞 然而，还没有MP的体内研究 白血病细胞中的代谢或这与MP的抗白血病 方面的影响. 我们最近的研究表明， 抗代谢药（甲氨蝶呤）在ALL原始细胞中的作用在患者之间存在差异， 与白血病细胞的谱系和倍性（染色体数目）有关。 继续获得该补助金支持的研究将具有以下特点： MP在白血病细胞中的体内多态性代谢 儿童给予MP，并评估爆炸浓度的药效学 甲基巯基嘌呤核苷酸和硫鸟嘌呤核苷酸（TGN） MP的细胞毒性机制（例如，TGN掺入DNA， 抑制从头嘌呤合成）和ALL母细胞计数减少。 将在这些ALL原始细胞中测定多态性TPMT的活性， 在正常红细胞中，以评估其与mP代谢的关系， 方面的影响. 为了确定TPMT多态性的分子机制， 将从患有TPMT的儿童的正常白细胞中分离RNA和DNA- 缺陷和杂合基因型，从失活突变 将在编码TPMT的基因中被鉴定。 一旦失活突变 已经被定义（其中第一个，我们最近的特点），PCR- 将开发基于测试来确定TPMT基因型， 识别MP代谢异常和影响的患者。 作为第一 人类研究以检查MP在白血病细胞中的体内代谢， 它们将为我们提供重要的分子机制新见解 抗白血病反应的潜在个体间差异 巯基嘌呤

Despite great progress in the past 20 years, cancer remains the leading cause of death by disease in US children between 1 and 15 years of age. In acute lymphoblastic leukemia (ALL), the most common childhood cancer, 30% of patients fail current therapy, and many patients fail current therapy, and many patients who are cured experience significant morbidity from chemotherapy. The long-term objective of this competitive renewal is to develop more effective yet less toxic therapy, by understanding how leukemia cells metabolize and activate mercaptopurine (MP), an extensively used antileukemic agent. MP metabolism in normal tissues is highly variable,a nd methylation by thiopurine methyltransferase (TPMT) is subject to genetic polymorphism. Patients who inherit TPMT-deficiency as an autosomal recessive trait, and heterozygots, have significantly different patterns of MP metabolism in RBCs, which affects MP's toxicity to normal hematopoietic cells. However, there have been no in vivo studies of MP metabolism in leukemia cells or how this relates to MP's antileukemic effects. Our recent work established that metabolism of another antimetabolite (methotrexate) in ALL blasts differed among patients and was related to the lineage and ploidy (chromosomal number) of leukemia cells. The studies supported by the continuation of this grant will characterize the in vivo polymorphic metabolism of MP in leukemia cells isolated from children given Mp, and assess the pharmacodynamics of blast concentrations of methylmercaptopurine nucleotides and thioguanine nucleotides (TGN) on MP's mechanisms of cytotoxicity (e.., TGN incorporation into DNA, inhibition of de novo purine synthesis), and decrease in ALL blast count. The activity of polymorphic TPMT will be determined in these ALL blasts and in normal erythrocytes, to assess its relation to mP's metabolism and effects. To determine the molecular mechanisms of the TPMT polymorphism, RNA and DNA will be isolated from normal leukocytes of children with TPMT- deficiency and heterozygous genotypes, from which inactivating mutations will be identified in the gene encoding TPMT. Once inactivating mutations have been defined (the first of which we have recently characterized), PCR- based tests will be developed to determine TPMT genotype and prospectively identify patients with aberrant MP metabolism and effects. As the first human studies to examine the in vivo metabolism of MP in leukemia cells, they will provide important new insights on the molecular mechanisms underlying interindividual differences in antileukemic response to mercaptopurine.