ALTERED HEPATIC DISPOSITION OF ANIONIC DRUGS-MECHANISMS

描述（由申请人提供）：阴离子药物继发于药物相互作用、化学暴露、疾病状态或遗传易感性的肝脏处置改变具有重要的治疗意义。全身暴露，因此药理学反应的大小和持续时间，可能受到药物肝脏转运变化的实质性影响。同样，肝转运的紊乱可影响全身、肠道，也许最重要的是肝毒性。这个正在进行的研究项目的长期目标是发展对肝脏转运改变如何影响阴离子药物及其衍生代谢物的整体肝胆配置的机制理解。结合相关体外表达系统（Sf9细胞，非洲爪蟾卵母细胞）的多实验方法；一种新型的三明治培养（SC）原代肝细胞模型，保留肝脏转运机制，提供胆道和基底外侧排泄的定量数据，并可通过RNAi下调转运蛋白；Mrp2缺失模型TR-大鼠离体灌注肝；一项人体体内研究将用于阐明模型阴离子底物肝脏转运改变的机制和后果。多个Mrp异构体有助于阴离子药物和肝脏代谢物的基底外侧排泄的假设将被测试，对这一过程有重要贡献的蛋白质将被鉴定，并将确定模型底物的运输动力学。据称，肝小管转运的“特异性”抑制剂可能与基底外侧转运蛋白相互作用，导致一种以前未被认识的药物-药物相互作用。这些抑制剂调节基底外侧排泄的能力，以及这种调节对肝胆处置的影响，将被探讨。将评估肝脏反应机制（基底外侧输出蛋白、其他小管转运蛋白和肝脏II期酶）补偿Mrp2功能受损的假设；核激素受体在这些代偿反应中的作用，以及这种代偿的动力学后果，将被定义。最后，人类SC肝细胞预测人类模型阴离子在肝胆配置的能力将通过一种新的临床方案进行评估，该方案允许对健康人类的胆道排泄进行定量。阐明肝脏转运的机制，并确定这些过程中改变的功能后果，是理解决定外源性药物系统性暴露（最终生物反应）的多种因素的重要一步，也是利用这些过程实现理想治疗结果的先决条件。

DESCRIPTION (provided by applicant): Altered hepatic disposition of anionic drugs secondary to drug interactions, chemical exposure, disease states or genetic predisposition has important therapeutic implications. Systemic exposure, and therefore the magnitude and duration of pharmacologic response, may be affected substantially by changes in hepatic translocation of drugs. Likewise, perturbations in hepatic transport can influence systemic, intestinal and, perhaps most importantly, hepatic toxicity. The long-term objective of this ongoing research program is to develop a mechanistic understanding of how alterations in hepatic transport influence overall hepatobiliary disposition of anionic drugs and derived metabolites. A multiexperimental approach incorporating relevant in vitro expression systems (Sf9 cells, Xenopus laevis oocytes); a novel sandwich-cultured (SC) primary hepatocyte model that retains hepatic transport mechanisms, provides quantitative data on biliary and basolateral excretion, and is amenable to transporter knockdown by RNAi; isolated perfused livers using TR- rats, a model of Mrp2 deficiency; and an in vivo human study will be employed to elucidate mechanisms and consequences of altered hepatic transport of model anionic substrates. The hypothesis that multiple Mrp isoforms contribute to basolateral excretion of anionic drugs and metabolites from the liver will be tested, proteins that contribute significantly to this process will be identified, and kinetics of transport will be determined for model substrates. Purportedly "specific" inhibitors of hepatic canalicular transport may interact with basolateral transport proteins, resulting in a previously unrecognized category of drug-drug interactions. The ability of these inhibitors to modulate basolateral excretion, and the consequences of such modulation on hepatobiliary disposition, will be explored. The hypothesis that hepatic response mechanisms (basolateral exporters, other canalicular transporters, and hepatic Phase II enzymes) compensate for impaired Mrp2 function will be evaluated; the role of nuclear hormone receptors in these compensatory responses, and the kinetic consequences of such compensation, will be defined. Finally, the ability of human SC hepatocytes to predict hepatobiliary disposition of a model anion in humans will be assessed with a novel clinical protocol that allows quantitation of biliary excretion in healthy humans. Elucidating mechanisms of hepatic transport, and identifying functional consequences of alterations in these processes, is an important step in understanding the multiplicity of factors that determine systemic exposure (and ultimately biologic response) to xenobiotics, and is prerequisite to exploiting these processes to achieve desirable therapeutic outcomes.