Origins of Spontaneous Mutagenesis

描述(由申请人提供)： 大约一半的人类癌症没有记录在案的来源。人们通常认为，内源性因素，包括活性氧物种，是导致这些癌症的很大一部分原因。据推测，这类药物的作用机制是通过突变，而突变可能是由DNA损伤引起的。在没有已知环境暴露的非吸烟者的许多器官中，已经检测到显著水平的DNA修饰或损坏，这支持了这一假设。在大多数人类肿瘤中发现了原癌基因和抑癌基因的突变，这表明突变在肿瘤的发生中起着重要的作用。Laci和LacZ啮齿动物是唯一适用于体内诱变研究的全动物多器官系统。使用这样的系统，已经有可能确定体内任何器官的自发诱变率。由于这个系统中的突变是中性的，随着时间的推移，组织积累了新的突变，但以前的突变仍然存在。因此，只有在自发突变随着时间的推移大幅增加的器官中，尝试修改自发突变才是可行的。根据PI和其他机构实验室的报告，已经确定了几个这样的器官。在这项应用中，潜在的抑制物对两个这样的器官(结肠和膀胱)自发突变水平的影响将随着时间的推移而被监测。这些抑制剂是从据信可以防止或减少内源性DNA损伤的一类药物中挑选出来的。这些来源包括氧化剂、亲电剂和逃逸自由基。这些抑制剂包括抗氧化剂维生素E和C；自由基清除剂氨磷汀(一种已知的辐射保护剂)；N-乙酰半胱氨酸，一种潜在的自由基清除剂，它还可以提高谷胱甘肽的水平；以及1，2-二硫醇-3-硫氨酸，一种II相酶诱导剂。此外，年长和年轻动物的自发突变图谱将与氧化诱变剂博莱霉素的自发突变图谱进行比较，以确定氧化损伤是否是自发突变的主要因素。由于上述抑制剂的作用机制已被提出，本研究的结果将为进一步研究抑制的详细机制和自发诱变的起源提供基础。鉴于大量人类癌症可能归因于内源性来源，了解自发突变和识别抑制剂可能会对公共健康产生重要影响。

DESCRIPTION (provided by applicant): Approximately half of human cancer has no documented origin. It is often postulated that endogenous agents, including reactive oxygen species, are responsible for a significant fraction of these cancers. A presumed mechanism by which such agents act is via mutations, which in turn, may arise from DNA damage. Modified or damaged DNA has been detected at significant levels in a number of organs from nonsmokers with no known environmental exposures, lending support to this hypothesis. Mutations in proto-oncogenes and tumor suppressor genes have been found in a majority of human tumors, indicating that mutagenesis plays an important role in carcinogenesis. The lacI and lacZ rodents represent the only whole animal multi-organ systems applicable to the investigation of mutagenesis in vivo. Using such a system it has become possible to determine rates of spontaneous mutagenesis in any organ in vivo. As mutations in this system are neutral, the tissues accumulate new mutations over time, but previous mutations remain. Thus, only in organs where there is a substantial increase in spontaneous mutagenesis over time, is it practical to attempt to modify spontaneous mutagenesis. Based on reports from the lab of the PI and others, several such organs have been identified. In this application the effects of potential inhibitors on levels of spontaneous mutagenesis in two such organs (colon and bladder) will be monitored over time. The inhibitors have been chosen from classes of agents believed to prevent or reduce DNA damage from endogenous sources. These sources include oxidative agents, electrophiles, and flee radicals. The inhibitors include the antioxidant vitamins, E and C; the free radical scavenger amifostine (a known radioprotector); N-acetylcysteine, a potential radical scavenger which also enhances levels of glutathione; and 1,2-dithiole-3-thionine, a phase II enzyme inducer. In addition, the spontaneous mutation profile in older and younger animals will be compared with that of the oxidative mutagen, bleomycin, to determine whether oxidative damage is a major contributor to spontaneous mutagenesis. As mechanisms have been proposed by which the above inhibitors act, the results of this study will provide the basis for future studies on the detailed mechanisms of inhibition, and the origins of spontaneous mutagenesis. In view of the large numbers of human cancers likely attributable to endogenous sources, an understanding of spontaneous mutagenesis and the identification of inhibitory agents could have important public health consequences.