PREDICTION OF DRUG INTERACTIONS IN VIVO AND IN VITRO

本提案的总体目标是评估一个新的框架， 基于药物相互作用的抑制预测。 这个框架是 基于表征抑制剂对 使用人肝微粒体的特异性细胞色素P450亚型 准备工作 将检验两个假设：假设1： 任何药物-抑制剂体内相互作用的机制都可以解释 来自（i）特定细胞色素P450亚型的测定 负责药物主要代谢途径，和（ii） 测量每种亚型的体外抑制剂Ki。 假设 2：对于任何药物-抑制剂体内相互作用，Michaelis-Menton 模型可用于计算同种型特异性体内抑制 常数（Kiiv）。 这个常数提供了一个定量的估计， 预期抑制剂与任何 衬底 这些假设将用两类药物进行评估， 基于抑制的相互作用构成了关键的临床现实。 将追求以下具体目标：1（a）利用 人肝微粒体，如果华法林与 13种常用处方药是抑制 CYP2C9。 1（B）使用人肝微粒体确定是否存在临床 4种主要抗惊厥药和33种其他药物之间的相互作用是一种 结果抑制的具体亚型负责 抗惊厥药的主要部分清除率。 如果是， 测定这些亚型抑制的体外Ki， 将这些值与相应的Kiiv估计值进行比较， 文献资料 2（a）为了证明，对于亚型CYP 2C 9，（i） （S）-华法林和氟康唑之间的相互作用程度可能是 通过比值I/Kiiv定量预测，其中I是血浆 抑制剂浓度和（ii）对于2C 9获得相同的Kiiv， 当苯妥英用作底物时，氟康唑。 2（B） 证明，对于同种型3A 4，（i） （R）-华法林和氟康唑可通过 比率，I/Kiiv，和（ii）对于氟康唑，获得对于3A 4相同的Kiiv 当卡马西平用作底物时。 2（c）证明 具体目标2（a）和2（B）方法是抑制剂非依赖性的，a 第二种抑制剂将与每种同工酶的相同底物一起使用。 实验方法包括利用人肝库、可靠的 分析技术和一些健康受试者的人体研究。 如果提出的假设得到验证， 预测任何新药的抑制作用。

The overall objective of this proposal is to evaluate a new framework for the prediction of inhibition based drug interactions. This framework is based on the ability to characterize the effects of inhibitors on specific cytochrome P450 isoforms using human liver microsomal preparations. Two hypotheses will be tested: Hypothesis 1: The mechanism of any drug-inhibitor in vivo interaction can be accounted for from (i) a determination of the specific cytochrome P450 isoforms responsible for that drug's major route of metabolism and (ii) a measurement of the inhibitor in vitro Ki for each isoform. Hypothesis 2: For any drug-inhibitor in vivo interaction, the Michaelis-Menton model can be used to calculate an isoform specific in vivo inhibition constant (Kiiv). This constant provides a quantitative estimate of the magnitude of interaction to be expected between that inhibitor and any substrate. These hypotheses will be evaluated with two classes of drugs for which inhibition based interactions constitute a critical clinical reality. The following Specific Aims will be pursued: 1(a) To determine, using human liver microsomes, if the clinical interactions between warfarin and 13 commonly prescribed drugs are a consequence of the inhibition of CYP2C9. 1(b) To determine, using human liver microsomes, if the clinical interactions between 4 major anticonvulsants and 33 other drugs are a consequence of inhibition of the specific isoforms responsible for the major fractional clearances of the anticonvulsants. If they are, to determine the in vitro Ki's for the inhibition of these isoforms and to compare these values to the corresponding Kiiv's estimated from literature data. 2(a) To demonstrate, for isoform CYP2C9, that (i) the degree of interaction between (S)-warfarin and fluconazole can be predicted quantitatively by the ratio, I/Kiiv, where I is the plasma inhibitor concentration and (ii) the same Kiiv for 2C9 is obtained for fluconazole when phenytoin is used as the substrate. 2(b) To demonstrate, for isoform 3A4, that (i) the degree of interaction between (R)-warfarin and fluconazole can be predicted quantitatively by the ratio, I/Kiiv, and (ii) the same Kiiv for 3A4 is obtained for fluconazole when carbamazepine is used as the substrate. 2(c) To demonstrate that the approach of specific aims 2(a) and 2(b) is inhibitor independent, a second inhibitor will be used with the same substrates for each isozyme. The experimental approaches include the use of human liver bank, reliable analytical techniques and a number of human studies in healthy subjects. If the proposed hypotheses are validated it will become possible to predict inhibition based interactions for any new drug.