Prevention of UV-carcinogenesis through DNA repair-dependent immunomodulation

描述（由申请人提供）：拟议研究的目标是：(1)确定水飞蓟素（一种从水飞蓟（Silybum marianum L.）中提取的植物化学物质）改善紫外线（UV）辐射诱导的免疫抑制和DNA损伤的机制；(2)确定这些机制对水飞蓟素介导的皮肤癌预防的贡献。紫外线诱导的DNA损伤（以环丁烷嘧啶二聚体（CPDs）的形式）和免疫抑制已被证明与皮肤癌风险增加有关。我们已经证明，水飞蓟素局部治疗在体内小鼠模型中对紫外线诱导的免疫抑制和致癌都有显著的保护作用。已知紫外线照射会损害树突状细胞和效应T细胞的功能，但会诱导抑制性T细胞。此外，紫外线诱导的DNA损伤，主要是cpd的形成，是紫外线介导的免疫抑制的重要分子触发因素。我们已经证明水飞蓟素有能力增强紫外线暴露皮肤中CPD+细胞的清除或修复，并抑制uvb诱导的小鼠接触超敏反应的抑制。我们的初步数据进一步表明，水飞蓟素可以增强紫外线照射下树突状细胞中CPDs的去除，并恢复树突状细胞介导的活性，包括刺激T细胞。然而，水飞蓟素介导的紫外线诱导的免疫抑制在DNA修复缺陷的小鼠中被消除。总的来说，这些数据暗示水飞蓟素抑制紫外线诱导的免疫抑制的能力与其防止光致癌的能力之间的关键联系。我们的假设是水飞蓟素修复uvb诱导的DNA损伤是其对紫外线诱导的免疫抑制和光致癌作用的化学预防作用的关键。我们提出了四个相互关联的特异性目的，我们将使用转基因小鼠模型，包括核苷酸切除修复缺陷小鼠：(1)确定水飞蓟素是否通过恢复树突状细胞活性来抑制紫外线诱导的耐受性树突状细胞的发育；(2)确定水飞蓟素是否通过增强T细胞活化来抑制紫外线诱导的免疫抑制；(3)确定水飞蓟素是否抑制紫外线诱导的调节性T细胞的发育；(4)确定水飞蓟素对光致癌的抑制作用是否通过DNA修复介导。拟议的研究应该确定水飞蓟素在光致癌过程中纠正紫外线诱导的免疫抑制的机制。我们解决了一个主要的公共卫生问题，因为人类皮肤过度暴露于太阳紫外线辐射是美国黑色素瘤和非黑色素瘤皮肤癌发展的主要病因。使用水飞蓟素的新策略的发展可能有助于降低人类患皮肤癌的风险。

DESCRIPTION (provided by applicant): The goals of the proposed studies are to: (1) Identify the mechanisms by which silymarin, a phytochemical obtained from milk thistle (Silybum marianum L.), ameliorates ultraviolet (UV) radiation-induced immunosuppression and DNA damage; and (2) Determine the contribution of these mechanisms to silymarin-mediated prevention of skin cancer. Both UV-induced DNA damage, in the form of cyclobutane pyrimidine dimers (CPDs), and immune suppression have been shown to be associated with an increased risk of skin cancer. We have demonstrated that topical treatment with silymarin provides significant protection against both UV-induced immunosuppression and carcinogenesis in an in vivo mouse model. UV irradiation is known to impair the function of dendritic cells and effector T cells but induce suppressor T cells. Furthermore, UV-induced DNA damage, predominantly the formation of CPDs, is an important molecular trigger for UV-mediated immunosuppression. We have demonstrated that silymarin has the ability to enhance the removal or repair of CPD+ cells in UV-exposed skin, and inhibits UVB-induced suppression of the contact hypersensitivity response in mice. Our preliminary data further indicate that silymarin can enhance the removal of CPDs in UV-exposed dendritic cells and restore dendritic cell-mediated activities including stimulation of T cells. However, silymarin mediated inhibition of UV-induced immunosuppression is abolished in mice that have defect in DNA repair. Collectively, these data implicate key links between the ability of silymarin to inhibit UV-induced immunosuppression and its ability to prevent photocarcinogenesis. Our hypothesis is that the repair of UVB-induced DNA damage by silymarin is critical for its chemopreventive effects on UV-induced immunosuppression and photocarcinogenesis. We propose four inter-related Specific Aims in which we will use genetically modified mouse model, including nucleotide excision repair-deficient mice: (1) Determine whether silymarin inhibits the development of UV-induced tolerogenic dendritic cells through restoration of dendritic cell activity; (2) Determine whether silymarin- induced inhibition of UV-induced immunosuppression occurs through enhancement of T-cell activation, (3) Determine whether silymarin inhibits the development of UV-induced regulatory T cells; and (4) Determine whether silymarin inhibition of photocarcinogenesis is mediated through DNA repair. The proposed studies should identify the mechanisms by which silymarin acts to correct UV-induced immunosuppression in photocarcinogenesis. We address a major public health concern as overexposure of the human skin to solar UV radiation is the major etiologic factor for the development of melanoma and non-melanoma skin cancers in the United States. The development of new strategies using silymarin may help to reduce the risk of skin cancer in humans. PUBLIC HEALTH RELEVANCE: Chronic exposure of the skin to solar ultraviolet (UV) radiation induces multiple adverse effects including the risk of skin cancer development. In vitro and in vivo studies have indicated that silymarin, a plant flavonoid obtained from milk thistle, possesses potent anti-photocarcinogenic activity. In the current application, we will determine the molecular mechanism of prevention of photocarcinogenesis by silymarin. This study will also highlight that rapid repair of UVB-induced DNA damage by silymarin will result in the enhancement or restoration of immune system and that will lead to the prevention of UV-carcinogenesis. The generation of new knowledge will provide novel insights into the mechanisms by which silymarin can either correct, or compensate for, the UV-induced damage that triggers or promotes photocarcinogenesis.