Prevention of PTEN deletion driven prostate cancer by selenium

描述（由申请人提供）：前列腺癌发生的化学预防是从根本上解决前列腺癌（PCa）问题的合理和必要的方法。以往的研究表明，补充硒（Se）可以预防或延缓人PCa。然而，NCI在2008年10月提前停止了硒和维生素E癌症预防试验（SELECT），因为未能证明硒蛋氨酸（SeMet）在北美男性中预防PCa的有效性，以及糖尿病风险轻微但无统计学意义的增加。由于硒蛋氨酸和其他硒形式之间的代谢和生物化学差异，硒蛋氨酸在SELECT研究中的失败应该也不能等同于所有硒形式对PCa预防无效。我们有令人信服的证据表明，每日口服补充甲基硒醇，甲基硒酸（MSeA）和硒-甲基硒代半胱氨酸（MSeC）的推定前体，抑制在体内生长的人前列腺癌异种移植物在无胸腺裸鼠，而硒蛋氨酸没有;和MSeA和MSeC抑制原发性癌的转基因小鼠前列腺腺癌（TRAMP）模型具有显着的生存效益。虽然这些体内数据表明这些第二代Se化合物（与SeMet相比）作为有前途的生物活性补充剂用于PCa预防并值得考虑用于未来的翻译研究，但TRAMP模型的固有局限性缓和了这些数据对人类可翻译性的价值。因此，在响应PA-07-362的R21提案中，我们假设MSeA作为第二代Se的代表，通过靶向Pten缺陷小鼠模型中的Akt信号通路抑制/阻止PCa从PIN进展为腺癌。提出了两个具体目标。目的1：确定MSeA在体内预防Pten缺失驱动的PCa发展的功效。我们将使用Cre-loxP技术产生前列腺特异性Pten缺失（Pten-/-）小鼠。野生型Pten+/+小鼠和Pten-/-小鼠将在7周龄（WOA）时用2个剂量的MSeA处理。在12 WOA和27 WOA时，每组处死10只小鼠。广泛的组织病理学调查将确定早期病变反应。组织样本将储存用于验证分子靶向（Aim 2）。将使用Pten-/-小鼠的另外的组群（n=20）来评估MSeA对其存活、PCa负荷（重量、数量）和转移的有益影响。目的2：检测MSeA的预防效果是否与抑制AKT信号通路有关。我们将通过免疫组织化学和蛋白质印迹法在前2个终点收集的前列腺组织中测量AKT磷酸化及其下游靶点，并将其与细胞增殖和细胞死亡指数以及总生存获益相关联。结果的影响：这些结果将提供关于Pten-/-模型在体内评估MSeA作为生物活性膳食补充剂的有用性的“原理验证数据”，并为未来的R 01/P01项目奠定基础，以开发这种和其他第二代Se用于分子途径靶向的PCa预防。 公共卫生相关性：硒和维生素E抗癌试验（SELECT）中的硒代蛋氨酸给整个硒抗癌研究领域带来了许多负面影响。这里提出的严格研究，使用临床相关的临床前模型和明智的硒剂选择，具有令人信服的机械原理和支持（与SeMet for SELECT的情况不同），对于产生相关数据以支持继续工作以实现第二代硒的全部健康益处以及改变科学家和公众对硒优点的看法和理解是必不可少的。

DESCRIPTION (provided by applicant): Chemoprevention of prostate carcinogenesis is a plausible and necessary approach to deal with the prostate cancer (PCa) problem at the root. Previous studies have suggested that supplementation of selenium (Se) may prevent or delay human PCa. However, the NCI stopped the Selenium and vitamin E Cancer prevention Trial (SELECT) in October 2008 ahead of schedule because of the failure to demonstrate an efficacy of selenomethionine (SeMet) for PCa prevention in North American men and a slight but non- statistically significant increase in diabetes risk. Because of the metabolic and biochemical differences between SeMet and other Se forms, the failure of SeMet in the SELECT study should and cannot be equated to all Se forms as ineffective for PCa prevention. We have compelling evidence that daily oral supplementation of putative precursors of methylselenol, methylseleninic acid (MSeA) and Se-methylselenocysteine (MSeC), inhibit the in vivo growth of human PCa xenograft in athymic nude mice whereas SeMet does not; and that MSeA and MSeC inhibit primary carcinogenesis in the transgenic adenocarcinoma mouse prostate (TRAMP) model with significant survival benefit. While these in vivo data suggest these second-generation Se compounds (vs. SeMet) as promising bioactive supplements for PCa prevention and merit consideration for future translational studies, inherent limitations of the TRAMP model temper the value of these data for human translatability. Therefore, in this R21 proposal in response to PA-07-362, we hypothesize that MSeA, as a representative of second-generation Se, inhibits/prevents PCa progression from PIN to adenocarcinoma through targeting Akt signaling pathway in a Pten-deficiency mouse model. Two specific aims are proposed. Aim 1: To determine the efficacy of MSeA in preventing Pten deletion-driven PCa development in vivo. We will generate prostate-specific Pten-deletion (Pten-/-) mice using Cre-loxP technique. The wild type Pten+/+ mice and Pten-/- mice will be treated with 2 dosages of MSeA at 7 weeks of age (WOA). At 12 WOA and 27 WOA, 10 mice of each group will be sacrificed. An extensive histopathology survey will determine the early lesion responses. Tissue samples will be banked for verifying molecular targeting (Aim2). Additional cohorts (n=20) of Pten-/- mice will be used to assess the beneficial impact of MSeA on their survival, PCa burden (weight, number) and metastasis. Aim 2: To test whether the preventive efficacy of MSeA is associated with a suppression of AKT signaling pathway. We will measure AKT phosphorylation and its downstream targets by immunohistochemistry and Western Blot in prostate tissues collected at the first 2 endpoints and correlate them to indices of cell proliferation and cell death and overall survival benefit. Impacts of the results: The results will provide "proof-of-principle data" regarding the usefulness of Pten-/- model for assessing MSeA as a bioactive dietary supplement in vivo and lay the ground work for future R01/P01 projects for developing this and other second-generation Se for molecular pathway-targeted PCa prevention. PUBLIC HEALTH RELEVANCE: The ill-reputed selenomethionine in the Selenium and vitamin E Cancer prevention Trial (SELECT) study has brought a lot of negative publicities on the whole research field of selenium-cancer prevention and treatment. Rigorous studies as proposed here that use a clinically relevant pre-clinical model and a judicious choice of selenium agents with compelling mechanistic rationale and support (unlike the case with SeMet for SELECT) are essential and necessary to produce relevant data to support continued work to realize the full health benefits of the second-generation selenium and change perceptions and understanding of scientists and the public alike on selenium's merits.