Shikonin and Nrf2 Chemoprevention

描述（由申请人提供）：雌激素是乳腺癌的致病因素。确定新的治疗方法，既能预防雌激素致癌，又没有明显的毒性，这一点仍然至关重要。解毒酶的诱导被认为是防止雌激素相关癌变的重要机制，因为它们有助于清除有毒的雌激素。解毒酶的水平由关键转录因子Nrf2决定，该因子与编码解毒酶的基因启动子中的抗氧化反应元件结合以增加转录。因此，化学预防的目标是增强Nrf2的功能。我们的初步研究表明，紫草素（一种从紫草植物中提取的生物活性物质）通过双重作用机制在乳腺癌预防中发挥了新的作用。紫草素抑制雌激素信号，诱导Nrf2表达。这种独特的化学预防活性抑制正常乳腺上皮细胞向恶性状态的转化，并阻止雌激素依赖性肿瘤的形成。基于这些发现，我们假设紫草素激活Nrf2功能，导致解毒酶表达增加。因此，这些酶将去除基因毒性雌激素，并减少DNA损伤。我们将通过确定1)雌激素和紫草素调节Nrf2和解毒酶表达的机制来验证这一假设；2)紫草素影响nrf2依赖性化学保护通路的能力；3) Nrf2基因敲除小鼠研究Nrf2在紫草素化学预防乳腺肿瘤发生中的作用。本研究结果表明，紫草素通过降低雌激素对Nrf2表达的抑制，以一种新颖的方式逆转雌激素的作用。这些研究表明，紫草素是一种新型的膳食剂，具有很大的乳腺癌预防潜力。

DESCRIPTION (provided by applicant): Estrogen is a causative factor for the development of breast cancer. It remains critically important to identify novel therapies that prevent estrogen carcinogenesis without significant toxicity. Induction of detoxifying enzymes is considered an important mechanism of protection against estrogen-associated carcinogenesis because they facilitate removal of toxic estrogens. The levels of detoxifying enzymes are determined by the key transcription factor Nrf2 factor that binds to the antioxidant response element in the promoters of genes encoding detoxification enzymes to increase transcription. Thus, a chemoprevention goal is to enhance Nrf2 function. Our preliminary studies show a novel role for shikonin (a bioactive agent extracted from the Shikon plant) in breast cancer prevention via a dual mechanism of action. Shikonin inhibits estrogen signaling and induces Nrf2 expression. This unique chemopreventive activity inhibits transformation from normal mammary epithelial to malignant states and prevents estrogen- dependent tumor formation. Based on these findings, we hypothesize that shikonin activates Nrf2 function leading to increased detoxifying enzyme expression. Consequently, these enzymes will remove genotoxic estrogen, and reduce DNA damage. We will test this hypothesis by determining 1) mechanisms of estrogen and shikonin in regulating expression of Nrf2 and detoxifying enzymes; 2) ability of shikonin to impact the Nrf2-dependent chemoprotection pathway; and 3) the role of Nrf2 in shikonin chemoprevention of mammary tumorigenesis using Nrf2 knockout mice. The results obtained from this proposal reveal that shikonin reverses the estrogen action in a novel way by reducing estrogen suppression of Nrf2 expression. These studies demonstrate that shikonin is a novel dietary agent with great potential as a breast cancer preventative.