Kumar G, Ray S, Walle T, Huang Y, Willingham M, Self S, Bhalla K
Department of Medicine, Medical University of South Carolina, Charleston 29425, USA.
Cancer Chemother Pharmacol. 1995;36(2):129-35. doi: 10.1007/BF00689197.
Taxol is metabolized by the liver microsomal cytochrome P450 enzyme system into its principal metabolite 6 alpha-hydroxytaxol (6HT). In the present in vitro studies 6HT was compared to taxol with respect to its effects on tubulin depolymerization, mitotic arrest, clonogenic survival and apoptosis in HL-60 cells. 6HT was generated by incubating taxol with human liver microsomes in a NADPH-generating system. HL-60 cells were incubated for 24 h with either taxol or 6HT, washed and placed in drug-free suspension or cultured for colony growth in agarose. For the suspension and colony culture growth of the cells, the IC50 concentrations of 6HT were 500 +/- 46 and 350 +/- 37 nM, while those of taxol were 3.2 +/- 0.2 and 2.8 +/- 0.5 nM, respectively. Immediately after a 24-h exposure of HL-60 cells to 50 nM taxol, electrophoresis of genomic DNA from HL-60 cells revealed an internucleosomal DNA fragmentation 'ladder'. In addition, 39% of the cells were arrested in mitosis and 16% showed the morphologic features of apoptosis. In contrast, an identical treatment with 6HT resulted in the mitotic arrest of only 2.8% of the cells, with 4.0% displaying apoptosis (P < 0.01); internucleosomal DNA fragmentation was not observed. 6HT was also significantly less effective than taxol in inhibiting the temperature-induced depolymerization of microtubules in a cell-free system. However, at equipotent concentrations, the effect of 6HT on tubulin depolymerization, mitotic arrest or apoptosis was similar to that of taxol. In addition, at concentrations of taxol or 6HT at or below their IC50, there was little tubulin depolymerization, mitotic arrest or apoptosis. The results presented here show that the biotransformation of taxol to 6HT substantially detoxifies taxol.
紫杉醇经肝脏微粒体细胞色素P450酶系统代谢为其主要代谢产物6α-羟基紫杉醇（6HT）。在目前的体外研究中，将6HT与紫杉醇在对HL-60细胞微管蛋白解聚、有丝分裂阻滞、克隆形成存活及凋亡的影响方面进行了比较。6HT是通过在NADPH生成系统中使紫杉醇与人肝微粒体孵育产生的。HL-60细胞分别用紫杉醇或6HT孵育24小时，洗涤后置于无药物的悬浮液中或在琼脂糖中培养以进行集落生长。对于细胞的悬浮培养和集落培养生长，6HT的IC50浓度分别为500±46和350±37 nM，而紫杉醇的IC50浓度分别为3.2±0.2和2.8±0.5 nM。HL-60细胞暴露于50 nM紫杉醇24小时后，HL-60细胞基因组DNA的电泳显示出核小体间DNA片段化“梯形条带”。此外，39%的细胞停滞于有丝分裂期，16%表现出凋亡的形态学特征。相比之下，用6HT进行相同处理仅导致2.8%的细胞发生有丝分裂阻滞，4.0%表现出凋亡（P<0.01）；未观察到核小体间DNA片段化。在无细胞系统中，6HT在抑制温度诱导的微管解聚方面也明显不如紫杉醇有效。然而，在等效浓度下，6HT对微管蛋白解聚、有丝分裂阻滞或凋亡的作用与紫杉醇相似。此外，在紫杉醇或6HT浓度等于或低于其IC50时，几乎没有微管蛋白解聚、有丝分裂阻滞或凋亡。此处给出的结果表明，紫杉醇向6HT的生物转化使紫杉醇大幅解毒。
