ROLE OF INTESTINAL UGT IN DRUG DISPOSITION

描述（由申请方提供）：UGT的葡萄糖醛酸化是一个主要阶段 II代谢途径，广泛分布于体内，负责 许多药物、其他外源性物质和内源性底物的缀合。 葡萄糖醛酸化通常是一个解毒过程，尽管有值得注意的 例外.葡萄糖醛酸化还可指导 因此缀合物通常是主动转运的底物 进入尿液并在胆汁中排泄。胆汁排泄是 肠肝循环（EHC）的药物是葡萄糖醛酸化，它具有 表观清除率降低和肠道暴露增加的影响 毒品胆汁排泄被认为是增强肠道 细胞毒性药物如抗肿瘤剂伊立替康的毒性。先前 解决肠道毒性问题的方法， 代谢，胆汁排泄和EHC已经取得了一些成功，但预测 减少肠毒性的关系或方法通常仍然 难以捉摸药物引起的肠道毒性的一个关键组成部分， 在此之前没有被纳入该计划，是肠道的能力， 上皮细胞形成葡萄糖醛酸并将其排泄，从而提供 在细胞水平上对毒性的内在抵抗力。霉酚酸（MPA， 免疫抑制剂）和SN-38（抗肿瘤），是衍生自 分别依赖于葡萄糖醛酸化的前药MMF和伊立替康， 胆汁排泄用于消除。两者都是细胞毒性药物， 肠道毒性的发生率，表现为腹泻， 有效的治疗。 肠道UGT正在积极研究中，以表征其潜在作用 在保护免受外源毒素影响方面的作用以及识别和测量 UGT的特异性人类同种型的表达正从 许多实验室的努力。患者间变异性大， 人类中UGT的多态性也没有完全了解。一些实验室 基于定性RT-PCR鉴定UGT同种型的组织分布， 然而，这些措施并没有提供有关数量的信息， 这些酶的表达和功能能力。在此，我们建议 研究MPA和SN 38在人类和动物中的肠道毒性， 整合毒物代谢与肠UGT蛋白表达及其 直接催化底物形成葡糖苷酸。以下全球 假设将得到解决：肠道UGT在以下方面具有关键作用： 调节肠上皮细胞对药物的暴露，从而影响 其GI毒性。一系列细胞培养和人类的体外研究 组织，并在古恩和TR-大鼠模型中进行体内研究，将使用 MPA和SN-38葡萄糖醛酸化的特异性试验以及特异性Western 大鼠和人UGT同工酶的印迹，以确定 葡萄糖醛酸化和毒性。接受这些治疗的患者的转化研究 还将使用药物来评估人体肠道葡萄糖醛酸化 并检验局部组织特异性UGT可能调节 人体肠道毒性。

DESCRIPTION (provided by applicant): Glucuronidation by UGTs is a major Phase II metabolic pathway, widely distributed in the body, responsible for conjugation of numerous drugs, other xenobiotics and endogenous substrates. Glucuronidation is generally a detoxification process, though there are notable exceptions. Glucuronidation also directs the excretion and distribution of xenobiotics such that the conjugates are often substrates for active transport into the urine and excretion in bile. Biliary excretion is one step in the enterohepatic recycling (EHC) of drugs that are glucuronidated and it has the effects of reducing the apparent clearance and increasing intestinal exposure to drugs. Biliary excretion has been implicated as enhancing intestinal toxicity by cytotoxic drugs such as the antitumor agent irinotecan. Previous approaches to the problem of intestinal toxicity, with the integration of drug metabolism, biliary excretion and EHC have had some success, though predictive relationships or approaches to reduce intestinal toxicity are often still elusive. A critical component of drug-induced intestinal toxicity that has heretofore not been incorporated into the scheme, is the ability of intestinal epithelial cells to form glucuronides and excrete them, thus providing intrinsic resistance to toxicity at the cellular level. Mycophenolic acid (MPA, immunosuppressant) and SN-38 (antitumor), are active compounds derived from prodrugs MMF and irinotecan, respectively, that rely upon glucuronidation and biliary excretion for elimination. Both are cytotoxic drugs that have a high incidence of intestinal toxicity manifested by diarrhea that often limits effective therapy. Intestinal UGT is under active investigation to characterize its potential role in protection from exogenous toxins and methods to identify and measure expression of specific human isoforms of UGT are developing rapidly from the efforts of numerous labs. Large interpatient variability and potential polymorphisms of UGTs in humans are also not fully understood. Some labs have identified tissue distributions of UGT isoforms based upon qualitative RT-PCR, however, these measures do not provide information on the quantitative expression and functional capacity of these enzymes. Here we propose to investigate the intestinal toxicity of MPA and SN38, in humans and animals, by integrating toxicokinetics with protein expression of intestinal UGTs and their direct catalysis of substrates to form glucuronides. The following global hypothesis will be addressed: Intestinal UGTs have a critical role in modulating exposure of intestinal epithelial cells to drugs, thus influencing their of gi toxicity. A series of in vitro studies with cell culture and human tissues, and in vivo studies in Gunn and TR- rat models will be conducted using specific assays of MPA and SN-38 glucuronidation together with specific Western blots of rat and human UGT isozymes to determine the relationship between glucuronidation and toxicity. Translational studies to patients receiving these drugs will also be conducted to evaluate intestinal glucuronidation in humans and examine the hypothesis that local tissue specific UGTs may modulate intestinal toxicity in humans.