Human Folylpolyglutamate Synthetase and Cancer Therapeutics

描述（由申请人提供）：叶酸聚谷氨酸合成酶是一种酶，可将天然存在的叶酸辅助因子和所有经典的叶酸抗代谢产物代谢为每个分子含有5-6个谷氨酸残基的形式。这些代谢物不会从细胞外排，因此，多谷氨酸化构成了一种代谢机制，在细胞中捕获叶酸。当使用抗叶酸治疗癌症时，临床医生劫持了这一机制，将酶抑制剂输送到肿瘤细胞，并将它们困在那里，在相当长的一段时间内与它们的靶标接触。本应用程序旨在研究决定细胞中存在多少叶酸聚谷氨酸合成酶活性的两种控制机制。小鼠酶被证明具有长链多谷氨酸的反馈，以适应小鼠叶酸代谢的特殊性。我们建议确定这种情况是否存在于人类酶中，以及这种反馈对用于癌症的抗叶酸药物（即甲氨蝶呤、雷替曲地和培美曲塞）的药理学影响。与这种假定反馈相关的酶学也将被探讨。fpgs基因转录表达的控制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。将确定这种沉默的机制，并确定白血病细胞绕过这种控制的机制。

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.