Isothiocyanates as specific antagonists of human SXR

描述（由申请人提供）：药物不良反应（ADI）是美国主要的公共卫生问题。ADI和治疗效果失败的一个主要因素是遗传变异和/或环境诱导的肝脏和肠道药物处置的变化（包括饮食）。细胞色素P450 3A4 （CYP3A4）负责许多异种生物的肝脏和肠道代谢，包括药物化合物、一些致癌物质和几种重要的内源性类固醇。CYP3A4的组成和诱导表达受多种不同的转录因子/途径调控。CYP3A4活性最重要的决定因素是激素核受体，类固醇和异种受体（SXR，也称为孕激素x受体，PXR）。许多药物和非药物化学物质通过作为SXR配体诱导CYP3A4活性，并可引起显著的药物-药物相互作用并改变治疗效果。在初步研究膳食植物化学物质萝卜硫素（sulforaphane，一种在西兰花中发现的异硫氰酸盐）的化学预防作用的研究中，我们发现，萝卜硫素可导致人肝细胞中CYP3A4的显著下调。然后，我们在人源性肠细胞（LS-180）中验证了这种效应，然后证明SFN在低微摩尔浓度下作为配体结合SXR的有效拮抗剂。进一步的研究表明，这是一种物种（人类）特异性效应，与啮齿动物和人类之间已知的SXR配体差异一致。在这项资助中，我们建议：1)进一步阐明SFN阻断SXR功能的分子机制；2)评估SFN的结构类似物，以确定更有效和/或特异性的SXR拮抗剂；3)利用“人源化”SXR小鼠和其他体内方法建立人类反应的动物模型；4)进行一系列人类喂养研究，以确定西兰花芽中的SFN是否会降低人CYP3A4的基础表达和/或干扰利福平介导的CYP3A4的诱导，通过咪达唑仑清除率来测量。如果基础喂养研究确定了对CYP3A4的影响，则建议进行额外的喂养研究，以检查其他SFN类似物，并进一步表征影响的剂量和时间过程。这些结果可能会导致重要的新治疗和饮食方法的发展，从而减少药物不良反应。它们还可以帮助解释几十年来人们注意到的CYP3A4基因的巨大个体间差异。最后，它们可以帮助进一步阐明萝卜硫素的风险和益处，萝卜硫素是一种潜在的膳食植物化学物质，已被提议作为一种安全的“营养保健品”化合物来降低癌症风险。

DESCRIPTION (provided by applicant): Adverse drug interactions (ADI), are a major public health problem in the US. A major contributor to both ADI and failure of therapeutic efficacy is genetic variability and/or environmentally-induced (incl. diet) changes in hepatic and intestinal drug disposition. Cytochrome P450 3A4 (CYP3A4) is responsible for the hepatic and intestinal metabolism of numerous xenobiotics, including pharmaceutical compounds, some carcinogens, and several important endogenous steroids. Constitutive and inducible expression of CYP3A4 is regulated by a variety of different transcription factors/pathways. Among the most important determinants of CYP3A4 activity is the hormone nuclear receptor, Steroid and Xenobiotic Receptor (SXR; also known as the Pregnane X-receptor, PXR). Numerous drugs and non-drug chemicals induce CYP3A4 activity by acting as SXR ligands, and can cause significant adverse drug-drug interactions and alter therapeutic efficacy. In studies initially investigating the chemopreventive actions of the dietary phytochemical, sulforaphane (SFN; an isothiocyanate found in broccoli), we found that SFN causes remarkable 'down-regulation of CYP3A4 in human hepatocytes. We then verified this effect in human-derived intestinal cells (LS-180), and then demonstrated that SFN acts as an effective antagonist of ligand binding to SXR at low micromolar concentrations. Additional studies demonstrated that this is a species (human)-specific effect, consistent with known differences in SXR ligands between rodents and humans. In this grant we propose to: 1) further elucidate the molecular mechanisms by which SFN blocks SXR function; 2) evaluate structural analogs of SFN to identify more potent and/or specific SXR antagonists; 3) utilize 'humanized' SXR mice and other in vivo approaches to establish an animal model for human response, and 4) conduct a series of human feeding studies to determine if SFN in broccoli sprouts lowers basal expression of human CYP3A4 and/or interferes with rifampicin-mediated induction of CYP3A4, measured by midazolam clearance. If the basic feeding study identifies an effect on CYP3A4, additional feeding studies are proposed to examine other SFN analogs and further characterize the dose and time course of effects. These results may lead to the development of important new therapeutic and dietary approaches that could reduce adverse drug responses. They could also help explain the large inter-individual variability in CYP3A4 that has been noted for decades. Finally, they could help to further elucidate the risks and benefits of sulforaphane, a potential dietary phytochemical that has been proposed as a safe 'nutraceutical' compound to reduce cancer risk.