Delayed Radioprotection by Thiols

描述(由申请人提供)：这项研究的目的是描述细胞暴露于非蛋白硫醇(NPT)后产生的延迟辐射防护效应。潜在的假设是，NPT暴露于细胞后，氧化还原敏感的核转录因子kappaB(NFkappaB)激活，锰超氧化物歧化酶(MnSOD)基因表达增强，细胞内活性MnSOD蛋白水平升高。锰超氧化物歧化酶是一种抗氧化性蛋白质，能抵抗电离辐射诱导的氧化自由基物种。NPT在以后诱导MnSOD水平升高的能力会导致延迟的辐射防护作用，这将在一般的辐射防护方面产生影响，特别是对肿瘤的防护。这项研究集中在四个临床批准的NPT，氨磷汀，美斯纳，乙酰半胱氨酸(NAC)和卡托普利。这些NPT目前正在临床上使用，它们在接受癌症治疗的患者的肿瘤中诱导延迟辐射防护作用的可能性是一个迄今未被认识到的问题。提出了四个具体目标。目的1旨在验证NPT在一定剂量范围内会增强MnSOD基因表达的假说，导致培养的肿瘤和非肿瘤细胞内活性MnSOD蛋白水平增加，同时过氧化氢酶和谷胱甘肽过氧化物酶(GPx)活性增加。目的2将验证这样一种假设，即提高MnSOD活性将导致辐射防护增强，特别是在2Gy射线照射下。目的3旨在验证这样一种假设，即动物单次或多次暴露于NPT会导致正常组织和肿瘤组织中MnSOD基因表达和蛋白活性的升高，后者生长为动物后腿的肺瘤结节或实体瘤。目的4将验证这样一种假设，即升高的MnSOD活性将导致对选定的正常组织和肿瘤组织的延迟辐射保护，这是通过定量生存分析确定的，即脾集落试验、肠道微集落试验、肺集落试验和TCD50试验。两个可供选择的假设也将得到检验。一次MnSOD活性升高可导致与过氧化氢酶和GPx活性有关的抗氧化失衡，导致过氧化氢积聚和辐射增敏。第二，过氧亚硝酸盐(ONOO-)硝化MnSOD可导致MnSOD水平的提高而不伴随酶活性的增加。

DESCRIPTION (provided by applicant): The goal of this investigation is the characterization of the delayed radioprotective effect induced following exposure of cells to non-protein thiols (NPT). The underlying hypothesis is that NPT exposure of cells results in activation of the redox sensitive nuclear transcription factor kappaB (NFkappaB) and enhancement in manganese superoxide dismutase (MnSOD) gene expression followed by elevated intracellular levels of active MnSOD protein. MnSOD is an anti-oxidant protein that can confer protection against oxidative radical species induced by ionizing radiation. The ability of NPT to induce at a later time elevated MnSOD levels results in a delayed radioprotective effect that will have implications in radioprotection in general, and tumor protection in particular. This study focuses on four clinically approved NPT, amifostine, mesna, Nacetylcysteine (NAC), and captopril. These NPT are currently in clinical use, and the potential for their induction of a delayed radioprotective effect in tumors of patients undergoing cancer treatment is a here-tofore unrecognized problem. Four specific aims are proposed. Aim 1 seeks to test the hypothesis that NPT over a range of doses will enhance MnSOD gene expression, leading to elevated intracellular levels of active MnSOD protein accompanied by increased catalase and glutathione peroxidase (GPx) activities in cultured tumor and non-tumor cells. Aim 2 will test the hypothesis that elevated MnSOD activity will result in enhanced radioprotection, especially at 2 Gy. Aim 3 is focused on testing the hypothesis that either single or multiple exposures of animals to NPT will result in elevated MnSOD gene expression and protein activity in both normal and tumor tissues, the latter grown as pulmonary tumor nodules or solid tumors in the hind legs of animals. Aim 4 will test the hypothesis that elevated MnSOD activity will result in delayed radioprotection to selected normal and tumor tissues as determined by quantitative survival assays, i.e., spleen colony assay, intestinal microcolony assay, lung colony assay, and the TCD50 assay. Two alternative hypotheses will also be tested. One elevated MnSOD activity can result in anti-oxidant imbalance relating to catalase and GPx activities, resulting in hydrogen peroxide buildup and radiation sensitization. Two, elevation in MnSOD level without a concomitant increase in enzymatic activity can result from nitration of MnSOD by peroxynitrite (ONOO-).