Study on selective cancer chemotherapy targeting the deficiency of a purine metabolic enzyme

这项研究计划的广泛、长期目标是确定人类癌症中甲硫腺苷磷酸化酶（MTAP）缺乏症的患病率和临床特征，并开发和应用新的方法来特异性治疗MTAP阴性的癌症。在哺乳动物细胞中，甲硫腺苷（MTA）在多胺合成过程中产生。MTA在正常组织中不蓄积，但被MTAP迅速裂解为腺嘌呤和5 '-甲基硫代核糖1-磷酸（MTR-1-P）。腺嘌呤和MTR-1-P再循环为嘌呤核苷酸和甲硫氨酸。分别由于已知所有正常细胞或组织都含有MTAP，因此人类癌症中的MTAP缺陷将使我们能够开发肿瘤特异性化疗，其中在可以通过给予MTA作为嘌呤核苷酸或甲硫氨酸的来源来拯救MTAP阳性正常组织的条件下，用引起嘌呤核苷酸或甲硫氨酸耗尽的药物选择性杀死MTAP阴性癌细胞。为了检测MTAP阴性的原发性癌症，我们使用Taqman化学开发了定量PCR方法来检测MTAP基因的纯合缺失。该方法即使在含有30%正常细胞的样品中也能够诊断MTAP基因缺失。由于MTAP缺陷不仅仅是由于基因缺失，单克隆抗体已成功产生，并准备用于免疫组织化学。为了开发选择性治疗MTAP阴性癌症的新方法，我们使用L-丙氨酸核苷在动物模型中选择性治疗MTAP阴性肿瘤。

The broad, long-term objectives of this research proposal are to determine the prevalence and clinical characteristics of methylthioadenosine phosphorylase (MTAP) deficiency in human cancers and to develop and apply new methods for the specific treatment of MTAP-negative cancers.In mammalian cells, methylthioadenosine (MTA) is produced during the synthesis of the polyamines. MTA does not accumulate in normal tissues but is cleaved rapidly to adenine and 5'-methylthioribose 1-phosphate (MTR-1-P) by MTAP. The adenine and MTR-1-P are recycled to purine nucleotides and methionine. respectively. Since all normal cells or tissues are known to contain MTAP, MTAP deficiency in human cancers will enable us to develop tumor-specific chemotherapy, in which MTAP-negative cancer cells will be selectively killed with drugs causing the depletion of purine nucleotides or methionine, under conditions where MTAP-positive normal tissues can be rescued by giving MTA as the sources of purine nucleotides or methionine.In. order to detect MTAP-negative primary cancers, we have developed quantitative PCR assay to detect homozygous deletion of MTAP gene using Taqman chemistry. This method was able to diagnose MTAP gene deletion even in the samples containing 30 % normal cells. Since MTAP deficiency is not solely attributable to gene deletion, monoclonal antibodies has been generated successfully and are ready for immunohistochemistry. To develop new methods for the selective treatment of MTAP-negative cancers, we used L-alanosine to selectively treat MTAP-negative tumors in animal models.