Impact of impurity on kinetic estimates from transport and inhibition studies
Impact of impurity on kinetic estimates from transport and inhibition studies
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DOI：
10.1124/jpet.107.135863
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发表时间：
2008-07-01
影响因子：
3.5
通讯作者：
Polli, James E.
中科院分区：
文献类型：
--
作者：
Gonzalez, Pablo;Polli, James E.
尽管体外转运/抑制研究通常对不纯的候选药物进行，以筛选早期开发中的药代动力学特性，但缺乏关于可接受的杂质水平的定量指南。总体目标是建立杂质对转运和抑制研究影响的模型，并确定不影响测定结果的最大允许杂质水平。导出模型并进行模拟以评估杂质对底物性质 K-t 和 J(max) 以及抑制 K-i 的影响。使用肠道胆汁酸转运蛋白作为模型系统，用已知量的杂质对模拟结果进行实验挑战。对于底物吸收研究，甘氨胆酸盐作为底物，并被极强、强或中等杂质（即分别为牛磺石胆酸盐、鹅去氧胆酸盐或熊去氧胆酸盐）污染。对于抑制研究，牛磺胆酸盐和甘胆酸盐一起作为底物/抑制剂对，其中甘胆酸盐被牛磺石胆酸盐污染。模拟结果与实验观察结果高度一致。毫不奇怪，在抑制测定中，有效的杂质导致测试化合物看起来比测试化合物的真实效力更有效（即抑制K-i降低）。然而，运输场景中的结果令人惊讶地表明，有效的杂质并没有降低测试化合物的效力，而是增加了底物效力（即，降低了米氏底物 K-t）。一般来说，低于 2.5% 的杂质是一个合理的目标，前提是该杂质的效力比测试化合物强不到 10 倍。研究结果表明，当定量结构-活性关系分析无法解释转运或抑制研究中的高化合物效力时，需要仔细考虑可能的杂质效应。
Although in vitro transport/inhibition studies are commonly performed on impure drug candidates to screen for pharmacokinetic properties in early development, quantitative guidelines concerning acceptable impurity levels are lacking. The broad goal was to derive models for the effect of impurity on transport and inhibition studies and identify the maximum allowable impurity level that does not bias assay results. Models were derived, and simulations were performed to assess the impact of impurity on substrate properties K-t and J(max) and inhibition K-i. Simulation results were experimentally challenged with a known amount of impurity, using the intestinal bile acid transporter as a model system. For substrate uptake studies, glycocholate served as substrate and was contaminated with either a very strong, strong, or moderate impurity (i.e., taurolithocholate, chenodeoxycholate, or ursodeoxycholate, respectively). For inhibition studies, taurocholate and glycocholate together was the substrate/inhibitor pair, where glycocholate was contaminated with taurolithocholate. There was high agreement between simulation results and experimental observations. It is not surprising that, in the inhibition assay, potent impurity caused test compound to appear more potent than the true potency of the test compound (i.e., reduced inhibitory K-i). However, results in the transport scenario surprisingly indicated that potent impurity did not diminish test compound potency but, rather, increased substrate potency (i.e., reduced Michaelis-Menten substrate K-t). In general, less than 2.5% impurity is a reasonable target, provided the impurity is less than 10-fold more potent than test compound. Study results indicate that careful consideration of possible impurity effect is needed when quantitative structure-activity relationship analysis cannot explain high compound potency from transport or inhibition studies.