Development of new small molecule targets for radiation protection

在“脏弹”爆炸后，或者一些不那么险恶但同样严重的核事故发生后，大多数随后的伤亡可以预期受到相对低剂量的辐射。因此，紧急服务将不得不治疗大量的受害者（包括受影响的公众、紧急救援人员和医务人员），其中由于“旁观者效应”造成的组织损伤是至关重要的。辐照后活性氧和活性氮（ROS和RNS）的产生是一种慢性现象，在接受剂量后几分钟内开始。我们最近从辐照后的大鼠组织中获得了证据，证明在低剂量剂量终止后几天内超氧自由基的持续产生。线粒体显然是产生超氧化物的位点，因为在辐照前组织中表达锰超氧化物歧化酶（MnSOD）可显著改善这一效应。此外，在内源性一氧化氮合酶（NOS）刺激后，辐射后组织中容易检测到过氧亚硝酸盐阴离子的产生，这表明这种强效氧化剂的二次生成是超氧化物水平升高的主要后果。在未辐照动物的对照组织中没有观察到这些影响。具体目的：1)确定在术后最初几个小时内产生初始超氧化物的线粒体位点（建议为mtNOS）

Following detonation of a "dirty bomb," or some less sinister but equally serious nuclear accident, the majority of the ensuing casualties can be anticipated to receive relatively low-dose exposures. Consequently, emergency services will have to treat large numbers of victims (including the affected public, emergency responders and medical staff) where developing tissue damage due to "bystander effects" is of paramount importance. Post-irradiation production of reactive oxygen and reactive nitrogen species (ROS and RNS) is a chronic phenomenon that starts within minutes of the dose being received. We have recently obtained evidence from post-irradiated rat tissue for sustained production of superoxide radical days after low-level doses have been terminated. The mitochondrion is clearly implicated as the site of superoxide production as manganese supeoxide dismutase (MnSOD) expression in the pre-irradiated tissue significantly ameliorates the effect. Furthermore, the readily detectable production of peroxynitrite anion in postirradiated tissue following the stimulation of endogenous nitric oxide synthase (NOS) indicates the secondary generation of this powerful oxidant to be a major consequence of the elevated superoxide level. None of these effects are observed in control tissue taken from unirradiated animals. Specific Aims: 1) Identify the mitochondrial site of the initial superoxide production (proposed to be mtNOS) in the first few hours following irradiation (the 'early process'); 2) Identify the mitochondrial sites damaged by ROS/RNS (proposed to be complex III) resulting in further (chronic) superoxide generation (the 'later process') and devise strategies for deactivating these centers; 3) Determine the relative importance of peroxynitrite and hydrogen peroxide production in post-irradiation damage to the electron-transport chain (ETC). Within the framework of these specific aims, it is proposed to develop and test putative drugs designed to prevent the formation of key ROS/RNS at the mitochondrial sites identified as responsible for their generation. In addition to efficacy, the possible toxicity of these compounds (at the level of the ETC) will be evaluated to facilitate improvements in the characteristics of further candidate drugs produced subsequently in iterative rounds of synthesis and testing.