Radiosensitization via Targeting Cell Death

描述(申请人提供)：细胞的生存或死亡的命运是严格控制的。细胞凋亡是细胞死亡的主要机制之一，在许多癌症中都存在缺陷。照射后的实体瘤内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，利用溶酶体/空泡进行细胞降解，是细胞凋亡受阻时的备用死亡途径。我们的初步数据支持这一假设，即当细胞凋亡途径被阻断时，自噬是暴露在电离辐射下的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caspase3/7的情况下，我们发现自噬上调，并在超过50%的照射细胞中发生。因此，我们发现上调自噬可以增加癌细胞对辐射的敏感性。这一假说的核心是这样一个概念，即Bak/Bax或caspase3/7在辐射诱导的压力下负向调节自噬，并且在缺乏这些促凋亡蛋白的细胞中自噬被增强。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，或2)抑制Bak/Bax或caspase 3/7来诱导自噬，将增强辐射在癌症模型中的生物学效应。为了检验这一假说，本文提出了三个具体目标。具体目标1将确定Bak/Bax或caspase 3/7调节辐射诱导的自噬的机制。特异性目标2将确定抑制Bak/Bax或caspase3/7、诱导自噬途径和增强放射增敏是否是癌细胞的全球反应。具体目标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增强辐射反应。这项拟议的研究旨在了解辐射应激过程中细胞凋亡和自噬之间的分子相互作用，并确定在肿瘤模型中加强放射治疗的新靶点。这项研究的意义在于扩大我们对决定受辐射细胞命运的复杂分子信号的理解。这方面的知识将被用来提高癌症患者常规放射治疗的疗效。

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.