Komatsu T, Yamazaki H, Shimada N, Nakajima M, Yokoi T
Faculty of Pharmaceutical Sciences, Kanazawa University, Kanazawa, Japan.
Drug Metab Dispos. 2000 Dec;28(12):1457-63.
Tegafur, an anticancer prodrug, is bioactivated to 5-fluorouracil (5-FU) mainly by cytochrome P450 (P450) enzymes. The conversion from tegafur into 5-FU catalyzed by human liver microsomal P450 enzymes was investigated. In fourteen cDNA-expressed human P450 enzymes having measurable activities, CYP1A2, CYP2A6, CYP2E1, and CYP3A5 were highly active in catalyzing 5-FU formation at a tegafur concentration of 100 microM. Kinetic analysis revealed that CYP1A2 had the highest V(max)/K(m) value and that the V(max) value of CYP2A6 was high in 5-FU formation. In human liver microsomes, the activities of 5-FU formation from 10 microM, 100 microM, and 1 mM tegafur were significantly correlated with both coumarin 7-hydroxylation (r = 0.83, 0.86, and 0.74) and paclitaxel 6 alpha-hydroxylation (r = 0.77, 0.62, and 0.85) activities, respectively. Coumarin efficiently inhibited the 5-FU formation activities from 100 microM and 1 mM tegafur catalyzed by human liver microsomes that had high coumarin 7-hydroxylation activity. On the other hand, furafylline, fluvoxamine, and quercetin, as well as coumarin, showed inhibitory effects in liver microsomes that had high catalytic activities of 5-FU formation. The other P450 inhibitors examined showed weak or no inhibition in human liver microsomes. Polyclonal anti-CYP1A2 antibody, monoclonal anti-CYP2A6, and anti-CYP2C8 antibodies inhibited 5-FU formation activities to different extents in those two microsomal samples. These results suggest that CYP1A2, CYP2A6, and CYP2C8 have important roles in human liver microsomal 5-FU formation and that the involvement of these three P450 forms differs among individual humans.
替加氟是一种抗癌前体药物，主要通过细胞色素P450（P450）酶活化为5-氟尿嘧啶（5-FU）。研究了人肝微粒体P450酶催化替加氟向5-FU的转化。在14种具有可测量活性的cDNA表达的人P450酶中，CYP1A2、CYP2A6、CYP2E1和CYP3A5在替加氟浓度为100 microM时催化5-FU形成的活性很高。动力学分析表明，CYP1A2的V(max)/K(m)值最高，且CYP2A6在5-FU形成中的V(max)值较高。在人肝微粒体中，10 microM、100 microM和1 mM替加氟形成5-FU的活性分别与香豆素7-羟基化（r = 0.83、0.86和0.74）和紫杉醇6α-羟基化（r = 0.77、0.62和0.85）活性显著相关。香豆素有效抑制了人肝微粒体中由100 microM和1 mM替加氟催化的5-FU形成活性，这些人肝微粒体具有高香豆素7-羟基化活性。另一方面，呋拉茶碱、氟伏沙明、槲皮素以及香豆素在具有高5-FU形成催化活性的肝微粒体中显示出抑制作用。所检测的其他P450抑制剂在人肝微粒体中显示出微弱的抑制作用或无抑制作用。多克隆抗CYP1A2抗体、单克隆抗CYP2A6和抗CYP2C8抗体在这两个微粒体样品中对5-FU形成活性有不同程度的抑制作用。这些结果表明，CYP1A2、CYP2A6和CYP2C8在人肝微粒体5-FU形成中起重要作用，且这三种P450形式在个体之间的参与程度不同。
