Shikonin and Nrf2 Chemoprevention

说明(申请人提供)：雌激素是导致乳腺癌发展的一个因素。找出既能预防雌激素致癌又不会有明显毒性的新疗法仍然至关重要。解毒酶的诱导被认为是防止雌激素相关致癌的重要机制，因为它们促进了有毒雌激素的清除。解毒酶的水平由关键转录因子Nrf2因子决定，该因子与解毒酶编码基因的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(一种从紫草属植物中提取的生物活性物质)通过双重作用机制在预防乳腺癌方面发挥了新的作用。紫草素抑制雌激素信号转导，诱导Nrf2表达。这种独特的化学预防活性可抑制从正常乳腺上皮向恶性状态的转化，并防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，这些酶将清除具有遗传毒性的雌激素，并减少DNA损伤。我们将通过确定1)雌激素和紫草素调节Nrf2表达和解毒酶的机制；2)紫草素影响依赖Nrf2的化学保护途径的能力；以及3)Nrf2在紫草素化学预防Nrf2基因敲除小鼠乳腺肿瘤发生中的作用来验证这一假说。结果表明，紫草素通过减少雌激素对Nrf2表达的抑制，以一种新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饮食制剂，具有很大的预防乳腺癌的潜力。

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.