Therapeutic Targeting of Oncogenic Stress in Cancer Treatment

描述(由申请人提供)：该项目的主要目标是为癌症治疗中的药物发现确定新的分子靶点。我们研究针对癌细胞的途径放松调控(与之相反。正常细胞)，但在大多数类型的癌症中是常见的，希望找出癌症的阿喀琉斯之踵。癌基因应激可导致P53的激活，P53可诱导细胞凋亡或细胞衰老，是肿瘤发生的重要屏障。只有当P53等DNA损伤反应通路被抑制时，细胞才会发展为癌症。我们已经确定了致癌激活过程中的一个关键事件，它导致了对P53功能的抑制。靶向这一途径可能会重建肿瘤发生的屏障，或增强化疗效果。这项提议是为了描述这一途径的机制细节，并为癌症的新治疗方法建立一个框架基础。TopBP1(DNA拓扑异构酶II2结合蛋白1)包含8个BRCA1-羧基末端(BRCT)基序，存在于参与DNA修复和细胞周期检查点控制的蛋白质中。它参与DNA复制、ATR激活和转录调控。TopBP1与促进生长和存活的作用一致，是E2F的靶标，其水平在G1/S过渡期和S期升高。我们的初步研究表明，TopBP1在癌症中经常过度表达，其过度表达与生存不良有关。更重要的是，我们实验室积累的数据表明TopBP1在控制两个关键转录因子E2F1和P53中发挥作用，特别是它们的促凋亡活性。PRb肿瘤抑制通路的缺失导致E2F活性过度，进而激活TopBP1的表达。TopBP1水平升高会抑制E2F1和P53依赖的细胞凋亡。这一事件可能会缩短TopBP1高水平癌症患者的生存时间。因此，我们假设TopBP1可以作为一种新的治疗靶点，在癌症治疗中同时增强E2F1和P53介导的细胞凋亡。为此，我们将进行体外和体内实验，以确定针对TopBP1途径的癌症治疗策略。目的1.阐明TopBP1与P53相互作用的机制及动态调节。目的2.探讨TopBP1与突变型P53相互作用的机制及生物学结果。目的3.靶向TopBP1的一个关键结构域，重新激活E2F1和P53，增强化疗敏感性。本项目完成后，我们将阐明TopBP1通路在癌细胞存活中的作用，并确定其分子细节和机制。我们还将确定TopBP1中用于药物开发的关键基序，并验证其目标效用。 与公共健康相关：正常细胞有一种内置的防御机制来阻止不受控制的生长。在癌症发展(致癌)过程中对生长和增殖的高需求产生了“致癌压力”，正常细胞通过激活肿瘤抑制基因如P53来做出适当的反应。不幸的是，这些防御机制在癌症中受到抑制。我们现在已经确定了这一抑制过程中的一个关键事件，并建议靶向该事件来重新激活自卫机制，从而治疗癌症。

DESCRIPTION (provided by applicant): The main goal of this project is to identify novel molecular targets for drug discovery in cancer therapy. We study the pathway deregulation that is specific to cancer cells (opposed to. normal cells), but common to most types of cancers in the hope to identify the Achilles' heel of cancer. Oncogenic stress can lead to activation of p53, which induces either apoptosis or cellular senescence and serves as an important barrier to tumorigenesis. Only when DNA damage response pathway such as p53 is inhibited, cells then develop into cancer. We have identified a key event during oncogenic activation that leads to inhibition of p53 function. Targeting this pathway might reconstitute the barrier to tumorigenesis or enhance chemotherapy efficacy. This proposal is to delineate the mechanistic details of this pathway and to establish a framework foundation for novel therapeutic approaches in cancer. TopBP1 (DNA topoisomerase II2 binding protein 1) contains eight BRCA1-carboxyl-terminal (BRCT) motifs, which are found in proteins involved in DNA repair and cell cycle checkpoint control. It is involved in DNA replication, ATR activation and transcriptional regulation. Consistent with a role in promoting growth and survival, TopBP1 is an E2F target, and its level rises at G1/S transition and S phase. Our preliminary studies demonstrate that TopBP1 is often overexpressed in cancer and its overexpression is associated with poor survival. More importantly, data accumulated in our lab demonstrate a role for TopBP1 in controlling two critical transcriptional factors E2F1 and p53, especially their pro-apoptotic activities. Loss of pRb tumor suppressor pathway leads to excessive E2F activities, which in turn activate TopBP1 expression. Elevated TopBP1 levels then cause inhibition of E2F1- and p53-dependent apoptosis. This event might contribute shorter patient survival in cancer harboring high levels of TopBP1. Thus, we hypothesize that TopBP1 could serve as a novel therapeutic target to potentiate both E2F1- and p53-mediated apoptosis in cancer therapy. To this end, we will carry out both in vitro and in vivo experiments to identify strategies in targeting the TopBP1 pathway for cancer therapy. Aim 1. Elucidate the mechanism and dynamic regulation of TopBP1 and p53 interaction. Aim 2. Investigate the mechanisms and biological outcomes of TopBP1 and mutant p53 interaction. Aim 3. Target a critical domain of TopBP1 to reactivate E2F1 and p53 and enhance chemosensitivity. Upon completion of this project, we will elucidate the TopBP1 pathway in cancer cell survival and define its molecular details and mechanisms. We will also identify the critical motif within TopBP1 for drug development and validate its target utility. PUBLIC HEALTH RELEVANCE: Normal cells have a built-in defense mechanism to halt the uncontrolled growth. The high demand for growth and proliferation during cancer development (oncogenesis) creates "oncogenic stress" to which normal cells properly respond by activation of tumor suppressor genes such as p53. Unfortunately, these defense mechanisms are inhibited in cancer. We have now identified a key event in this inhibition process and propose to target this event to reactivate self-defense mechanism in order to treat cancer.