Taxane's Substituents at C3′ Affect Its Regioselective Metabolism: Different in Vitro Metabolism of Cephalomannine and Paclitaxel
Taxane's Substituents at C3′ Affect Its Regioselective Metabolism: Different in Vitro Metabolism of Cephalomannine and Paclitaxel
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DOI：
10.1124/dmd.107.018242
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发表时间：
2008-02
影响因子：
3.9
通讯作者：
Jiang-wei Zhang;Guangbo Ge;Yong Liu;Li-ming Wang;Xingbao Liu;Yan-Yan Zhang-Yan;Wei Li;Yu-qi He;Zheng-Tao Wang;Jie Sun;Hong-bin Xiao;Ling Yang
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文献类型：
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作者：
Jiang-wei Zhang;Guangbo Ge;Yong Liu;Li-ming Wang;Xingbao Liu;Yan-Yan Zhang-Yan;Wei Li;Yu-qi He;Zheng-Tao Wang;Jie Sun;Hong-bin Xiao;Ling Yang
为了研究紫杉烷在C3 ‘位置上的取代基如何影响其代谢，我们比较了头甘氨酸和紫杉醇的代谢，这是一对在C3 ’位置上略有不同的类似物。头甘氨酸与人肝微粒体在nadph生成系统中孵育后，采用液相色谱/串联质谱法检测两种单羟基化代谢物（M1和M2）。提出C4″（M1）和C6α (M2)作为可能的羟基化位点，并通过1H NMR对M1的结构进行了证实。重组人细胞色素P450 （P450）的化学抑制实验表明，4″-hydroxycephalomannine主要由CYP3A4产生，6α-hydroxycephalomannine主要由CYP2C8产生。在5个人类肝脏样本中，紫杉醇和头甘氨酸的总体生物转化率略有差异（184 pmol/min/mg vs 145 pmol/min/mg），但在C13侧链羟基化到C6α的代谢物的平均比例差异显著（15:85 vs. 64:36）。与紫杉醇相比，头甘氨酸的主要羟基化位点从C6α转移到C4″，主要代谢P450从CYP2C8转变为CYP3A4。在与大鼠或小型猪肝微粒体的孵育体系中，仅检测到4″-羟头甘氨酸，其形成受到CYP3A抑制剂的抑制。AutoDock的分子对接表明，头甘氨酸采用有利于4″-羟基化的取向，而紫杉醇采用有利于3 ' -对羟基化的取向。动力学研究表明，由于Vm增加，CYP3A4比紫杉醇更有效地催化头甘氨酸。我们的研究结果表明，相对较小的C3 '紫杉烷修饰对代谢有重大影响。
To investigate how taxane's substituents at C3′ affect its metabolism, we compared the metabolism of cephalomannine and paclitaxel, a pair of analogs that differ slightly at the C3′ position. After cephalomannine was incubated with human liver microsomes in an NADPH-generating system, two monohydroxylated metabolites (M1 and M2) were detected by liquid chromatography/tandem mass spectrometry. C4″ (M1) and C6α (M2) were proposed as the possible hydroxylation sites, and the structure of M1 was confirmed by 1H NMR. Chemical inhibition studies and assays with recombinant human cytochromes P450 (P450s) indicated that 4″-hydroxycephalomannine was generated predominantly by CYP3A4 and 6α-hydroxycephalomannine by CYP2C8. The overall biotransformation rate between paclitaxel and cephalomannine differed slightly (184 vs. 145 pmol/min/mg), but the average ratio of metabolites hydroxylated at the C13 side chain to C6α for paclitaxel and cephalomannine varied significantly (15:85 vs. 64:36) in five human liver samples. Compared with paclitaxel, the major hydroxylation site transferred from C6α to C4″, and the main metabolizing P450 changed from CYP2C8 to CYP3A4 for cephalomannine. In the incubation system with rat or minipig liver microsomes, only 4″-hydroxycephalomannine was detected, and its formation was inhibited by CYP3A inhibitors. Molecular docking by AutoDock suggested that cephalomannine adopted an orientation in favor of 4″-hydroxylation, whereas paclitaxel adopted an orientation favoring 3′-p-hydroxylation. Kinetic studies showed that CYP3A4 catalyzed cephalomannine more efficiently than paclitaxel due to an increased Vm. Our results demonstrate that relatively minor modification of taxane at C3′ has major consequence on the metabolism.