Radiosensitization via Targeting Cell Death

描述（由申请人提供）：细胞生存或死亡的命运受到严格调控。细胞凋亡是细胞死亡的主要机制之一，在许多癌症中存在缺陷。辐照后的实体瘤中有一小部分细胞发生凋亡。自噬是一种高度保守的自我消除机制，它利用溶酶体/液泡进行细胞降解，是细胞凋亡被阻断时的一种备用细胞死亡途径。我们的初步数据支持这样的假设：当凋亡途径被阻断时，自噬是电离辐射照射下肿瘤细胞的一种重要的替代细胞死亡机制。在缺乏促凋亡蛋白Bak/Bax或caspase 3/7的情况下，我们发现自噬上调，超过50%的辐照细胞发生自噬。因此，我们发现上调自噬会增加癌细胞的辐射敏感性。该假说的核心概念是Bak/Bax或caspase 3/7在辐射诱导的应激下负向调节自噬，并且在缺乏这些促凋亡蛋白的细胞中自噬增强。我们认为，通过1)mTOR抑制剂直接激活自噬信号或过度表达自噬蛋白来诱导自噬；2)抑制Bak/Bax或caspase 3/7，将增强辐射在癌症模型中的生物学效应。为了验证这一假设，提出了三个具体目标。Specific Aim 1将确定Bak/Bax或caspase 3/7调节辐射诱导的自噬的机制。特异性Aim 2将确定抑制Bak/Bax或caspase 3/7、诱导自噬途径和增强放射致敏是否在癌细胞中是一种全局反应。特异性Aim 3将确定是否通过抑制mTOR或过度表达自噬蛋白来诱导自噬信号传导增强辐射反应。本研究旨在了解辐射诱导应激过程中细胞凋亡和自噬之间的分子相互作用，并在癌症模型中寻找增强放疗的新靶点。这项研究的意义在于扩大了我们对决定辐照细胞命运的复杂分子信号传导的理解。这些知识将被探索，以提高正在用于癌症患者的传统放射治疗的疗效。

DESCRIPTION (provided by applicant): The fate of cell survival or death is a tightly regulated. Apoptosis, one of the major cell death mechanisms, is defective in many cancers. Apoptosis occurs in small fraction of cells within the irradiated solid tumors. Autophagy, a highly conserved self-elimination mechanism that utilizes lysosome/vacuoles for cellular degradation is a backup cell death pathway when apoptosis is blocked. Our preliminary data support the hypothesis that autophagy is an important alternative cell death mechanism in tumor cells exposed to ionizing radiation when the apoptotic pathway is blocked. In the absence of pro-apoptotic proteins, Bak/Bax or caspase 3/7, we found that autophagy is upregulated and occurred in over 50% of irradiated cells. As a consequence, we found that up-regulation autophagy confers increased radiation sensitivity of cancer cells. Central to this hypothesis is the concept that Bak/Bax or caspase 3/7 negatively regulate autophagy, upon radiation-induced stress and that autophagy is enhanced in cells lacking these pro-apoptotic proteins. We believe that induction of autophagy through 1) direct activation of autophagic signaling by mTOR inhibitors or overexpression of autophagic proteins; or 2) inhibition of Bak/Bax or caspase 3/7, will enhance the biological effects of radiation in cancer models. Three specific aims are proposed to test this hypothesis. Specific Aim 1 will identify mechanisms by which Bak/Bax or caspase 3/7 regulate radiation-induced autophagy. Specific Aim 2 will determine whether inhibition of Bak/Bax or caspase 3/7, induction of the autophagic pathway, and enhanced radiosensitization is a global response in cancer cells. Specific Aim 3 will determine whether induction of autophagic signaling by inhibition of mTOR or over expression of autophagic proteins enhances radiation response. The proposed study is to understand the molecular interaction between apoptosis and autophagy during radiation-induced stress and to identify novel targets for enhancing radiotherapy in cancer models. The significance of this study is to expand our understanding of the complex molecular signaling, which determines the fate of irradiated cells. This knowledge will be explored to improve the efficacy of conventional radiotherapy that is being used for cancer patients.