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100万例新诊断病例。太阳UVB（紫外线B）辐射是皮肤癌的主要病因;主要地，它导致皮肤表皮细胞中的DNA损伤，如果不修复，则可能导致启动细胞。这些启动的细胞主要在p53肿瘤抑制基因中具有突变，最终导致其克隆扩增和皮肤肿瘤的形成。防晒霜用于防止太阳UVB辐射;然而，由于皮肤癌的高发病率，继续努力开发有效的药物，可以对抗UVB引起的正常皮肤损伤，最终导致皮肤癌的化学预防。我们已完成的研究表明，水飞蓟宾是一种这样的代理，抑制UVB引起的皮肤损伤和预防皮肤癌的小鼠模型。我们还发现，水飞蓟宾降低UVB引起的环丁烷嘧啶二聚体（CPD）阳性细胞的DNA损伤，并进一步提高小鼠皮肤表皮细胞的p53蛋白水平，并选择性地增加慢性UVB暴露小鼠皮肤中的E2 F1蛋白水平。水飞蓟宾还增强了小鼠角化细胞JB 6细胞中p53的磷酸化和积累，以响应UVB。我们在p53-/-和野生型SKH-1无毛小鼠中的初步研究表明，水飞蓟宾通过以p53依赖的方式增强DNA修复，减少UVB诱导的皮肤CPD形成。基于这些已完成的新颖和创新的研究，其与水飞蓟宾的人类皮肤癌化学预防直接相关，本申请的主要焦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标。提出的中心假设是，水飞蓟宾通过增强DNA修复通过p53和E2 F1导致非黑色素瘤皮肤癌的化学预防减少UVB引起的DNA损伤。具体目标是：I）通过使用遗传学方法来定义和确定p53和E2 F1在响应于UVB的水飞蓟宾介导的表皮DNA修复和皮肤癌发生预防中的作用; II）定义和确定上游信号在响应于UVB的水飞蓟宾的p53和E2 F1介导的DNA修复机制中的作用;和III）检测和确定p53和E2 F1在响应UVB的水飞蓟宾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：本建议是高度相关的，在建立预防功效水飞蓟宾对UVB诱导的光损伤和光致癌与高度新颖的和有针对性的机制细节。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，我们相信本建议的结果将惠及“阳光下”的每一个人。 公共卫生相关性：化学预防是对抗皮肤癌的最有效措施，皮肤癌是美国癌症相关发病率的最大单一原因。来自阳光的UVB（紫外线B）辐射是皮肤癌的主要病因;主要地，它引起皮肤表皮细胞中的DNA损伤，如果不修复，最终导致它们的克隆扩增和皮肤肿瘤的形成。防晒霜对UVB辐射有部分保护作用;然而，由于皮肤癌的高发病率，人们继续努力寻找一种有效的药剂，可以对抗UVB引起的正常皮肤损伤，最终导致皮肤癌的化学预防。我们完成的研究表明，水飞蓟宾是一种这样的药剂，抑制UVB引起的皮肤损伤，并防止非黑色素瘤皮肤癌（NMSC）。水飞蓟宾已经在美国和世界范围内作为膳食补充剂被广泛消费，并在临床上用作保肝药。该化合物在动物研究和人体研究中均未显示出任何毒性。我们的研究结果将确定水飞蓟宾对UVB诱导的光损伤和光致癌作用的预防效果，并将为未来水飞蓟宾对人类非黑色素瘤皮肤癌生长和发展的化学预防临床试验奠定基础。

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'. PUBLIC HEALTH RELEVANCE: Chemoprevention is the most effective measure against skin cancer, which is the single largest cause of cancer-related incidences in the United States. UVB (ultraviolet B) radiation from the sunlight is the main etiologic factor for skin cancer; primarily, it causes DNA damages in skin epidermal cells which, if un-repaired, eventually lead to their clonal expansion and formation of skin tumors. Sunscreens have partial protective effect against UVB radiation; however, due to high incidence of skin cancer, the efforts continue for an effective agent 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 non-melanoma skin cancer (NMSC). Silibinin is already consumed extensively in the United States and world-wide as a dietary supplement and used in the clinic as a hepatoprotective agent. This compound has not shown any toxicity in animal studies as well as in humans. The outcomes of our proposed research will establish preventive efficacy of silibinin against UVB-induced photodamage and photocarcinogenesis, and will build the foundation for future chemoprevention clinical trial with silibinin against non-melanoma skin cancer growth and development in humans.