Department of Pharmaceutics, School of Pharmacy, University of Washington, Seattle, WA, USA.
Drug Metab Dispos. 2013 Aug;41(8):1566-74. doi: 10.1124/dmd.112.049940. Epub 2013 May 30.
The purpose of this study was to determine the impact of CYP3A5 expression on inhibitory potency (Ki or IC50 values) of CYP3A inhibitors, using recombinant CYP3A4 and CYP3A5 (rCYP3A4 and rCYP3A5) and CYP3A5 genotyped human liver microsomes (HLMs). IC50 ratios between rCYP3A4 and rCYP3A5 (rCYP3A5/rCYP3A4) of ketoconazole (KTZ) and itraconazole (ITZ) were 8.5 and 8.8 for midazolam (MDZ), 4.7 and 9.1 for testosterone (TST), 1.3 and 2.8 for terfenadine, and 0.6 and 1.7 for vincristine, respectively, suggesting substrate- and inhibitor-dependent selectivity of the two azoles. Due to the difference in the IC50 values for CYP3A4 and CYP3A5, nonconcordant expression of CYP3A4 and CYP3A5 protein can significantly affect the observed magnitude of CYP3A-mediated drug-drug interactions in humans. Indeed, the IC50 values of KTZ and ITZ for CYP3A-catalyzed MDZ and TST metabolism were significantly higher in HLMs with CYP3A5*1/1 and CYP3A51/3 genotypes than in HLMs with the CYP3A53/*3 genotype, showing CYP3A5 expression-dependent IC50 values. Moreover, when IC50 values of KTZ and ITZ for different HLMs were kinetically simulated based on CYP3A5 expression level and enzyme-specific IC50 values, a good correlation between the simulated and the experimentally measured IC50 values was observed. Further simulation analysis revealed that both the Ki ratio (for inhibitors) and Vmax/Km ratio (for substrates) between CYP3A4 and CYP3A5 were major factors for CYP3A5 expression-dependent IC50 values. In conclusion, the present study demonstrates that CYP3A5 genotype and expression level have a significant impact on inhibitory potency for CYP3A-catalyzed drug metabolism, but that the magnitude of its effect is inhibitor-substrate pair specific.
本研究旨在使用重组 CYP3A4 和 CYP3A5（rCYP3A4 和 rCYP3A5）和 CYP3A5 基因分型人肝微粒体（HLM）来确定 CYP3A5 表达对 CYP3A 抑制剂抑制效力（Ki 或 IC50 值）的影响。酮康唑（KTZ）和伊曲康唑（ITZ）对咪达唑仑（MDZ）的 rCYP3A4 和 rCYP3A5（rCYP3A5/rCYP3A4）IC50 比值分别为 8.5 和 8.8，睾酮（TST）为 4.7 和 9.1，特非那定（terfenadine）为 1.3 和 2.8，长春新碱（vincristine）为 0.6 和 1.7，表明这两种唑类药物具有底物和抑制剂依赖性选择性。由于 CYP3A4 和 CYP3A5 的 IC50 值不同，CYP3A4 和 CYP3A5 蛋白的非一致性表达可能会显著影响人类中 CYP3A 介导的药物相互作用的观察到的程度。事实上，在具有 CYP3A5*1/1 和 CYP3A51/3 基因型的 HLM 中，KTZ 和 ITZ 对 CYP3A 催化的 MDZ 和 TST 代谢的 IC50 值明显高于具有 CYP3A53/*3 基因型的 HLM，表现出 CYP3A5 表达依赖性的 IC50 值。此外，当基于 CYP3A5 表达水平和酶特异性 IC50 值对不同 HLM 中的 KTZ 和 ITZ 的 IC50 值进行动力学模拟时，观察到模拟值与实验测量的 IC50 值之间存在良好的相关性。进一步的模拟分析表明，CYP3A4 和 CYP3A5 之间的 Ki 比值（对于抑制剂）和 Vmax/Km 比值（对于底物）都是 CYP3A5 表达依赖性 IC50 值的主要因素。总之，本研究表明 CYP3A5 基因型和表达水平对 CYP3A 催化的药物代谢的抑制效力有显著影响，但影响的程度因抑制剂-底物对而异。
