Role of Uridine Phosphorylase in Cancer Treatment

描述(申请人提供)：尿苷，一种对合成RNA和生物膜必不可少的嘧啶核苷，已被证明在调节正常组织和肿瘤组织中氟嘧啶的细胞毒性效应中发挥关键作用。在不同物种中，尿苷在血浆和组织中的浓度被严格控制在2-4 mM，尿苷稳态是通过尿苷磷酸化酶(UPase)的活性和细胞内转运机制来维持的。UPase负责尿苷的可逆磷酸化，并参与抗肿瘤药物5-氟尿嘧啶(5-FU)的细胞内激活。 在临床前研究和I-II期临床试验中，我们利用UPase的特异性抑制剂5-苄基丙烯酰胺(BAU)对UPase的抑制来提高血浆和正常组织中的尿苷浓度。UPase活性的调节导致正常组织和血浆中尿苷库的选择性增加，并显著降低了5-FU的宿主毒性。在过去的几年里，我们发现了正常细胞和肿瘤细胞在控制和调节尿苷水平方面的一系列差异，这些差异可以用来实现肿瘤中更具选择性的细胞毒性，更好地保护作为氟嘧啶毒性主要靶点的正常组织，并提高5-氟尿嘧啶的治疗指数。我们的建议侧重于UPase在调节正常组织和肿瘤组织细胞内尿苷水平中的作用，以及与正常组织相比，UPase在肿瘤中激活5-FU方面的功能评估，以及作为宿主毒性的中介，特别是在胃肠道组织水平上。为了实现这些目标：1)我们将利用最近开发的UPase基因敲除小鼠模型，评估UPase在血浆和组织尿苷水平的动态平衡调节中的作用；2)我们将分析UPase失活对5-FU及其新开发的前体药物抗肿瘤活性和由此产生的宿主毒性的影响。哺乳动物细胞中存在的第二种磷酸化活性，胸苷磷酸化酶(TPase)，已知有助于UPase的一些功能，从而限制尿苷稳态的破坏，并参与氟嘧啶的激活。因此，我们项目的第三个目标是建立第二个缺乏磷酸化活性的小鼠模型(UPase和TPase)，以确定UPase和TPase在调节尿苷稳态和氟嘧啶激活中的作用，重点关注这两种磷酸化酶的不同和可能互补的功能。

DESCRIPTION (provided by applicant): Uridine, a pyrimidine nucleoside essential for the synthesis of RNA and bio-membranes, has been shown to play a crucial role in modulating the cytotoxic effects of fluoropyrimidines in both normal and tumor tissues. The concentration of uridine in plasma and tissues is tightly regulated at 2-4 MM throughout different species, and uridine homeostasis is maintained by the activity of uridine phosphorylase (UPase) and by intracellular transport mechanisms. UPase is responsible for the reversible phosphorolysis of uridine into uracil, and it is involved in the intracellular activation of the antineoplastic agent 5-fluorouracil (5-FU). We have utilized, both in pre-clinical studies as well as in a Phase I-II clinical trial, inhibition of UPase by its specific inhibitor, 5-benzylacyclouridine (BAU), to elevate uridine concentration in plasma and normal tissues. Modulation of UPase activity resulted in the selective elevation of uridine pools in normal tissues and plasma and in a significant reduction of 5-FU host toxicity. During the past few years, we have uncovered a series of differences between normal and tumor cells in the control and regulation of uridine levels that can be exploited to achieve more selective cytotoxicity in tumors, better protection of normal tissues that are primary targets of fluoropyrimidine toxicity, and improve the therapeutic index of 5-fluorouracil. Our proposal focuses on the role of UPase in regulating the intracellular level of uridine in normal versus tumor tissue and on the assessment of the function of UPase in the activation of 5-FU in tumors compared to normal tissues and as a mediator of host toxicity, specifically at the gastrointestinal tissue level. To achieve these objectives: 1) we will evaluate the role of UPase in the homeostatic regulation of uridine levels in plasma and tissues, utilizing a recently developed UPase knockout murine model and 2) we will analyze the impact of UPase nullification on the activation of 5-FU and its newly developed pro-drugs for their antineoplastic activity and the resulting host toxicities. A second phosphorolytic activity present in mammalian cells, thymidine phosphorylase (TPase), is known to contribute to some of UPase functions, therefore limiting the disruption of uridine homeostasis and participating in the activation of fluoropyrimidines. Thus, a third objective of our project is to generate a second murine model lacking both phosphorolytic activities (UPase and TPase) to define the roles of UPase and TPase in the regulation of uridine homeostasis and fluoropyrimidine activation focusing on the different and possibly complementary functions of these two phosphorylases.