Human Folylpolyglutamate Synthetase and Cancer Therapeutics

描述(申请人提供)：叶基多谷氨酸合成酶是一种代谢天然产生的叶酸辅助因子和所有经典叶酸抗代谢产物的酶，每个分子含有5-6个谷氨酸残基。这些代谢物不会从细胞外排出，因此，多聚谷氨酰胺构成了一种机制，以代谢方式将叶酸捕获到细胞中。当使用抗叶酸治疗癌症时，临床医生利用这一机制将酶抑制剂输送到肿瘤细胞并将其捕获在那里，在相当长的一段时间内与其靶标接触。这项申请建议研究两种控制机制，它们决定细胞中存在多少叶基多谷氨酸合成酶活性。小鼠的酶被证明具有与小鼠叶酸代谢的特殊性相适应的长链多谷氨酸的反馈作用。我们建议确定这是否存在于人类酶中，以及这种反馈对用于癌症的抗叶酸，即甲氨蝶呤、雷替曲德和培美曲塞的药理学的影响。与这一假定反馈相关的酶学也将被探索。Fpgs基因转录表达的调控也将在正常人类细胞和白血病细胞中进行研究。Fpgs基因在原始造血细胞中表达，然后在分化过程中沉默。这种沉默的机制将被确定，白血病细胞绕过这种控制的机制将被确定。 与公共健康相关：拨款申请提出了一些实验，这些实验将有助于理解人类叶基多谷氨酸合成酶是如何发挥其功能的，叶酸合成酶是一种限制用于癌症治疗的叶酸化合物及其类似物积累的酶。这种酶决定了单个人类肿瘤对抗叶酸药物甲氨蝶呤、雷公藤红素和培美曲塞以及5-氟尿嘧啶-亚叶酸钙联合治疗敏感或不敏感。所有这些药物目前都用于治疗人类癌症，因此，我们对限制药物效果的酶的任何了解的加强，都将有助于我们设计更合理的癌症药物治疗方法。

DESCRIPTION (provided by applicant): Folylpolyglutamate synthetase is an enzyme that metabolizes the naturally occurring folate cofactors and all classical folate antimetabolites to forms that contain 5-6 glutamic acid residues per molecule. These metabolites do not efflux from the cell, so that polyglutamation constitutes a mechanism to metabolically trap folates in the cell. When using antifolates in the treatment of cancer, the clinician is highjacking this mechanism to deliver enzyme inhibitors to the tumor cell and trap them there, in contact with their target for a substantial period of time. This application proposes to study the two control mechanisms that determine how much folylpolyglutamate synthetase activity exists in a cell. The mouse enzyme was shown to have a feedback by long chain polyglutamates that was adapted to the particularities of mouse folate metabolism. We propose to determine whether this exists with the human enzyme and the effects of such feedback on the pharmacology of the antifolates used in cancer, namely methotrexate, raltitredid and pemetrexed. The enzymology related to this putative feedback will also be explored. The control of expression of transcription of the fpgs gene will also be studied in normal human cells and leukemia cells. The fpgs gene is expressed in primitive hematopoietic cells, then silenced during differentiation. The mechanism of this silencing will be determined and the mechanism whereby leukemic cells circumvent this control will be determined. PUBLIC HEALTH RELEVANCE: The grant application proposes experiments that would lead to an understanding of how human folylpolyglutamate synthetase, an enzyme that limits the accumulation of folate compounds and analogs used for cancer therapy, carries out its functions. This enzyme determines whether individual human tumors are sensitive or insensitive to therapy with the antifolate drugs methotrexate, ralitrexid, and pemetrexed, and also the 5-fluoruracil- leucovorin combination. All of these drugs are currently used for treatment of human cancers, so any enhancement in our understanding of the enzyme that serves as a limitation for drug effects would help us design more rational cancer treatments with these drugs.