Dietary Cancer Prevention in DNA Repair Deficient Mice

描述（由申请人提供）：我们细胞中的基因组DNA不断受损和修复。这种损害是通过暴露于环境基因毒素（例如阳光的紫外线成分）而发生的，也是由于内源代谢物与 DNA 发生反应而自发发生的。 DNA 修复途径被破坏的遗传疾病揭示了不修复损伤的后果。即使没有明显暴露于环境基因毒素，人类的修复缺陷也会导致癌症风险大幅增加。因此，癌症的预防取决于识别内源性 DNA 损伤的来源以及避免或减轻损伤的方法。这些人类修复缺陷综合征的小鼠模型为识别这些来源提供了灵敏的工具。这项研究的长期目标是利用基因工程改造后缺乏 DNA 修复的小鼠来确定遗传毒性应激的饮食来源和预防癌症的营养干预措施。 ERCC1-XPF 是一种 DNA 链上大块损伤的核苷酸切除修复 (NER) 和二价 DNA 链间交联 (ICL) 修复所需的核酸内切酶。 ERCC1-XPF 亚型的小鼠实体瘤发生率非常高，这不能归因于它们的 NER 缺陷。因此，ERCC1-XPF 缺陷小鼠的肿瘤发生可归因于 ICL 修复缺陷，因此是自发 ICL 的结果。我们假设在这种 DNA 修复缺陷模型中促进自发性肿瘤的 ICL 损伤是由脂质过氧化 (LPO) 引起的。提出的实验将通过用富含多不饱和脂肪酸的饮食挑战 ERCC1-XPF 低等态小鼠来检验这一假设，多不饱和脂肪酸会促进内源性 LPO 的产生。该项目的具体目标是确定饮食中的多不饱和脂肪酸 (PUFA) 是否会促进癌症。膳食中的 PUFA 会被细胞膜同化，特别容易氧化，从而增加体内脂质过氧化 (LPO)。膜 PUFA 的 LPO 产生能够交联 DNA 的醛。我们假设 LPO 是自发 ICL 的来源，有助于修复缺陷小鼠的肿瘤发生。通过给予富含 PUFA 的饮食，将在 ERCC1-XPF 低等态小鼠中诱导 LPO。第二组动物将接受不含多不饱和脂肪酸的等热量饮食。我们预测，饲喂富含 PUFA 饮食的动物实体瘤的发病率会增加和/或发病较早。这些实验的结果将表明膳食脂肪是否会增加内源性 DNA 损伤的数量以及这种损伤是否会促进肿瘤发生。同样，结果将揭示避免饮食中的多不饱和脂肪酸是否会降低癌症风险。最后，这些实验将揭示 ERCC1-XPF 低等态小鼠是否是筛选可降低癌症风险的抗氧化剂的有用模型。

DESCRIPTION (provided by applicant): The genomic DNA in our cells is continuously damaged and repaired. The damage occurs via exposure to environmental genotoxins such as the UV component of sunlight and spontaneously due to endogenous metabolites that react with DNA. The consequences of not repairing the damage are revealed by genetic diseases in which DNA repair pathways are disrupted. Repair deficiency in humans can lead to a profound increase in the risk of cancer, even in the absence of obvious exposure to environmental genotoxins. Thus prevention of cancer is dependent upon identifying the sources of endogenous DNA damage and means to avoid or attenuate it. Mouse models of these human repair deficiency syndromes offer a sensitive tool for identifying these sources. The long term objective of this research is to use mice, genetically engineered to be deficient in DNA repair to identifying dietary sources of genotoxic stress and nutritional interventions that prevent cancer. ERCC1-XPF is an endonuclease required for nucleotide excision repair (NER) of bulky lesions on one strand of DNA and the repair of bivalent DNA interstrand crosslinks (ICL). Mice hypomorphic for ERCC1-XPF have a very high incidence of solid tumors, which cannot be attributed to their defect in NER. Thus tumorigenesis in ERCC1-XPF-deficient mice can be attributed to their defect in ICL repair, and therefore the consequence of spontaneous ICL. We hypothesize that the ICL damage that promotes spontaneous tumors in this DNA repair-deficient model is caused by lipid peroxidation (LPO). Experiments proposed will test this hypothesis by challenging the ERCC1-XPF hypomorphic mice with a diet rich in polyunsaturated fatty acids, which promote endogenous LPO. The specific aim of this project is to determine if dietary polyunsaturated fatty acids (PUFA) promote cancer. Dietary PUFA assimilate into cell membranes and are particularly vulnerable to oxidation, thus increase lipid peroxidation (LPO) in vivo. LPO of membrane PUFA produces aldehydes able to crosslink DNA. We hypothesize that LPO is a source of spontaneous ICL that contribute to tumorigenesis in the repair-deficient mice. LPO will be induced in ERCC1-XPF hypomorphic mice by administering a diet rich in PUFA. A second cohort of animals will receive an isocaloric diet depleted of PUFA. We predict that animals fed the PUFA-rich diet will have an increased incidence and/or earlier onset of solid tumors. The results from these experiments will indicate if dietary fats increase the amount of endogenous DNA damage and if this damage can promote tumorigenesis. Similarly, the results will reveal if avoiding dietary PUFA reduces cancer risk. Finally, these experiments will reveal if ERCC1-XPF hypomorphic mice are a useful model for screening anti-oxidants that may reduce cancer risk.