Delayed Radioprotection by Thiols

描述（由申请方提供）：本研究的目的是表征细胞暴露于非蛋白硫醇（NPT）后诱导的延迟辐射保护作用。潜在的假设是NPT暴露于细胞导致氧化还原敏感性核转录因子kappaB（NF kappaB）的激活和锰超氧化物歧化酶（MnSOD）基因表达的增强，随后是活性MnSOD蛋白的细胞内水平升高。MnSOD是一种抗氧化蛋白质，可以提供对电离辐射诱导的氧化自由基物种的保护。NPT在稍后时间诱导升高的MnSOD水平的能力导致延迟的辐射保护作用，其将在一般辐射保护中具有意义，并且特别是在肿瘤保护中具有意义。本研究的重点是四个临床批准的NPT，氨磷汀，美司钠，N-乙酰半胱氨酸（NAC），和卡托普利。这些NPT目前在临床上使用，并且它们在接受癌症治疗的患者的肿瘤中诱导延迟的辐射保护作用的潜力是一个尚未认识到的问题。提出了四个具体目标。目的1旨在检验以下假设：在一定剂量范围内的NPT将增强MnSOD基因表达，导致培养的肿瘤和非肿瘤细胞中活性MnSOD蛋白的细胞内水平升高，并伴有过氧化氢酶和谷胱甘肽过氧化物酶（GPx）活性增加。目的2将检验MnSOD活性升高将导致增强的辐射防护的假设，特别是在2戈伊下。目的3是集中在测试的假设，无论是单次或多次暴露于NPT的动物将导致MnSOD基因表达和蛋白质活性升高的正常和肿瘤组织，后者生长为肺肿瘤结节或实体瘤在动物的后腿。目的4将检验MnSOD活性升高将导致对所选正常和肿瘤组织的延迟辐射保护的假设，如通过定量存活测定所确定的，即，脾集落测定、肠小集落测定、肺集落测定和TCD 50测定。还将检验两个备选假设。MnSOD活性升高可导致与过氧化氢酶和GPx活性相关的抗氧化剂失衡，导致过氧化氢积聚和辐射致敏。第二，MnSOD水平升高而酶活性没有伴随增加，可能是由于MnSOD被过氧亚硝酸根（ONOO-）硝化所致。

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-).