Skin Cancer Chemoprevention by Silibinin: Mechanisms and Efficacy

描述（由申请人提供）：皮肤癌是最常见的恶性肿瘤，仅在美国每年就有超过100万的新病例被诊断出来。太阳紫外线（UVB）辐射是皮肤癌的主要病因；首先，它导致皮肤表皮细胞的DNA损伤，如果不修复，可能导致初始细胞。这些初始细胞主要在p53肿瘤抑制基因中携带突变，最终导致其克隆扩增和皮肤肿瘤的形成。防晒霜是用来防止太阳UVB辐射的；然而，由于皮肤癌的高发病率，人们继续努力开发有效的药物，以对抗uvb对正常皮肤造成的损害，最终实现皮肤癌的化学预防。我们已完成的研究表明水飞蓟宾是一种抑制uvb引起的皮肤损伤和预防小鼠皮肤癌的药物。我们还发现水飞菊素降低了UVB引起的环丁烷嘧啶二聚体（CPD）阳性细胞的DNA损伤，并进一步提高了小鼠皮肤表皮细胞中p53蛋白水平，选择性地增加了慢性UVB暴露小鼠皮肤中E2F1蛋白水平。水飞蓟宾还能在UVB作用下增强小鼠角化细胞JB6中p53的磷酸化和积累。我们对p53-/-和野生型SKH-1无毛小鼠的初步研究表明，水飞蓟宾通过p53依赖的方式增强DNA修复，减少了uvb诱导的皮肤CPD形成。基于这些已完成的与水飞蓟宾化学预防人类皮肤癌直接相关的新颖创新的研究，本应用的重点是进一步鉴定和建立水飞蓟宾预防皮肤癌功效的分子靶点。提出的中心假设是水飞菊素通过增强p53和E2F1的DNA修复来减少uvb引起的DNA损伤，从而导致非黑色素瘤皮肤癌的化学预防。具体目的是：1)通过遗传学方法确定和建立p53和E2F1在水飞滨素介导的表皮DNA修复和预防UVB皮肤癌变中的作用；II)定义并建立上游信号/s在p53-和e2f1介导的水飞脂素响应UVB的DNA修复机制中的作用；III)检查和定义p53和E2F1在水飞蓟宾响应UVB介导的核苷酸切除修复介导的DNA修复中的作用。人类健康相关性：本建议与建立水飞蓟宾对uvb诱导的光损伤和光癌变的预防作用高度相关，具有高度新颖和针对性的机制细节。总的来说，由于太阳辐射是最常见和不可避免的皮肤癌来源，我们相信目前建议的结果将使“阳光下”的每一个人受益。

DESCRIPTION (provided by applicant): Skin cancer is the most common malignancy with more than 1 million new cases diagnosed annually in the United States alone. Solar UVB (ultraviolet B) radiation is the main etiologic factor for skin cancer; primarily, it causes DNA damages in skin epidermal cells which, if un-repaired, potentially lead to initiated cells. These initiated cells harbor mutations primarily in p53 tumor suppressor gene that eventually lead to their clonal expansion and formation of skin tumors. Sunscreens are used to protect against solar UVB radiation; however, due to high incidence of skin cancer, additional efforts continue for developing effective agents that could act against UVB-caused damages in normal skin, eventually leading to skin cancer chemoprevention. Our completed studies suggest that silibinin is one such agent that suppresses UVB-caused skin damages and prevents skin cancer in mouse model. We have also found that silibinin lowers UVB-caused DNA damage in terms of cyclobutane pyrimidine dimmer (CPD) positive cells and further enhances p53 protein level in mouse skin epidermal cell, and selectively increases E2F1 protein level in chronic UVB exposed mouse skin. Silibinin also enhances phosphorylation and accumulation of p53 in mouse keratinocyte JB6 cells in response to UVB. Our preliminary studies in p53-/- and wild-type SKH-1 hairless mice showed a decrease in UVB-induced CPD formation in skin by silibinin through enhanced DNA repair in a p53-dependent manner. Based on these completed novel and innovative studies, which have direct relevance to human skin cancer chemoprevention by silibinin, the major focus of this application is to further identify and establish molecular targets of silibinin efficacy in preventing skin cancer. The central hypothesis proposed is that silibinin reduces UVB-caused DNA damage by enhancing DNA repair via p53 and E2F1 resulting in chemoprevention of non-melanoma skin cancer. Specific aims are: I) to define and establish the role of p53 and E2F1 in silibinin-mediated epidermal DNA repair and prevention of skin carcinogenesis in response to UVB by using genetic approaches; II) to define and establish the role of upstream signal/s in p53- and E2F1-mediated DNA repair mechanisms of silibinin in response to UVB; and III) to examine and define the role of p53 and E2F1 in nucleotide excision repair-mediated DNA repair by silibinin in response to UVB. Human Health Relevance: The present proposal is highly relevant in establishing the preventive efficacy of silibinin against UVB-induced photodamage and photocarcinogenesis with highly novel and targeted mechanistic details. Overall, since solar radiation is the most common and un- avoidable source of skin cancer, we believe that the outcomes of the present proposal will benefit each and every human being 'under the sun'.