Role of Uridine Phosphorylase in Cancer Treatment

描述（由申请方提供）：尿苷是一种合成RNA和生物膜所必需的嘧啶核苷，已显示在调节正常和肿瘤组织中氟嘧啶的细胞毒性作用方面发挥关键作用。在不同物种中，血浆和组织中尿苷的浓度在2-4 MM时受到严格调节，尿苷稳态由尿苷磷酸化酶（UPase）的活性和细胞内转运机制维持。UPase负责尿苷可逆磷酸化为尿嘧啶，并参与细胞内药物5-氟尿嘧啶（5-FU）的活化。 我们在临床前研究以及I-II期临床试验中均利用其特异性抑制剂5-苄基酰基尿苷（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池的选择性升高，并显著降低5-FU的宿主毒性。在过去的几年中，我们已经发现了正常细胞和肿瘤细胞在尿苷水平的控制和调节方面的一系列差异，这些差异可以用于实现肿瘤中更具选择性的细胞毒性，更好地保护作为氟尿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在调节细胞内水平的尿苷在正常与肿瘤组织中的作用，并在评估的功能，UPase在5-FU的激活肿瘤相比，正常组织和作为介体的宿主毒性，特别是在胃肠道组织水平。为实现这些目标：1）我们将利用最近开发的UPase敲除小鼠模型评估UPase在血浆和组织中尿苷水平的稳态调节中的作用，2）我们将分析UPase无效对5-FU及其新开发的前药活化的影响，以确定其抗肿瘤活性和由此产生的宿主毒性。哺乳动物细胞中存在的第二种磷酸化活性，胸苷磷酸化酶（TdR），已知有助于某些UPase功能，因此限制尿苷稳态的破坏并参与氟嘧啶的活化。因此，我们的项目的第三个目标是产生第二种缺乏磷酸化活性（UPase和TdR）的小鼠模型，以确定UPase和TdR在尿苷稳态和氟嘧啶活化调节中的作用，重点是这两种磷酸化酶的不同和可能的互补功能。

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.