Prevention of PTEN deletion driven prostate cancer by selenium

描述（由申请人提供）：前列腺癌的化学预防是一种从根本上解决前列腺癌（PCa）问题的可行和必要的方法。以前的研究表明，补充硒（Se）可以预防或延缓人类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），因为未能证明硒甲硫氨酸（SeMet）对北美男性前列腺癌的预防效果，以及糖尿病风险的轻微但无统计学意义的增加。由于SeMet与其他形式硒之间的代谢和生化差异，在SELECT研究中，SeMet的失败应该也不能等同于所有形式的硒对预防PCa无效。我们有令人信服的证据表明，每日口服甲基硒醇前体，甲基硒酸（MSeA）和硒甲基硒半胱氨酸（MSeC），可以抑制胸腺裸小鼠体内人PCa异种移植物的生长，而SeMet则没有；MSeA和MSeC在转基因腺癌小鼠前列腺（TRAMP）模型中抑制原发性癌变，具有显著的生存效益。虽然这些体内数据表明，这些第二代硒化合物（相对于SeMet）是预防前列腺癌的有希望的生物活性补充剂，值得在未来的转化研究中考虑，但TRAMP模型的固有局限性削弱了这些数据在人类可翻译性方面的价值。因此，在这项针对PA-07-362的R21提案中，我们假设MSeA作为第二代Se的代表，在pten缺乏小鼠模型中通过靶向Akt信号通路抑制/阻止PCa从PIN向腺癌的进展。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发展中的功效。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-/-小鼠在7周龄（WOA）时给予2剂MSeA。12 WOA和27 WOA时，每组处死10只小鼠。广泛的组织病理学检查将确定早期病变反应。组织样本将被储存以验证分子靶向（Aim2）。将使用额外的Pten-/-小鼠队列（n=20）来评估MSeA对其生存、PCa负担（体重、数量）和转移的有益影响。目的2：检测MSeA的预防作用是否与AKT信号通路的抑制有关。我们将在前两个终点收集的前列腺组织中通过免疫组织化学和Western Blot检测AKT磷酸化及其下游靶点，并将其与细胞增殖、细胞死亡和总体生存效益指标相关联。结果的影响：该结果将为Pten-/-模型在体内评估MSeA作为生物活性膳食补充剂的有效性提供“原理证明数据”，并为未来的R01/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PCa预防。

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.