Ashby J, Tinwell H, Glover P, Poorman-Allen P, Krehl R, Callander R D, Clive D
Zeneca Central Toxicology Laboratory, Cheshire, United Kingdom.
Environ Mol Mutagen. 1994;24(1):51-60. doi: 10.1002/em.2850240107.
The suspect human carcinogen, etoposide, is known to be genotoxic, producing both gene and chromosomal mutations, probably by virtue of its ability to inhibit topoisomerase II activity. The present paper describes assays conducted using the Salmonella assay, the mouse lymphoma tk+/- assay (gene and chromosomal mutation analysis and molecular analysis of tk-/- mutants) and the mouse bone marrow micronucleus assay. Nonreproducible, weak, dose-related increases in mutation frequency in strain TA98 (but not TA1538 or TA1537) of Salmonella typhimurium were observed. Etoposide was highly mutagenic at the heterozygous thymidine kinase (tk+/-) locus of L5178Y mouse lymphoma cells at concentrations below 0.1 micrograms/ml. Mostly small colony mutants were induced, consistent with the potent clastogenicity also observed. Molecular analysis of mutants indicated that 83% and 92% of large and small colony mutants, respectively, had lost the entire target gene sequence. Chromosomally aberrant L5178Y cells were approximately 2 to 600-fold more prevalent than small tk-/- mutant colonies. This suggests that the viable target for etoposide-mediated clastogenesis in the selective assay is approximately one-fifth of chromosome 11b, itself being approximately one-fortieth of the mouse genome. An unusually potent response was observed for etoposide in the mouse bone marrow micronucleus assay (63.1 +/- 18 MPE/1,000 PE 24 hours after an oral dose of 1 mg/kg). The minimum detectable dose level in the assay was between 0.01 and 0.1 mg/kg. At dose levels between 1 and 15 mg/kg, an inverse dose response was observed. This reduction in assay response was not due to the small concommitant decrease in the incidence of polychromatic erythrocytes, a conclusion based on studies with N-methyl-N-nitrosourea. Animals sampled 48 hours after dosing with etoposide (10 mg/kg) had no polychromatic erythrocytes in the bone marrow. These observations for the micronucleus assay await explanation. The chemical structure of etoposide is displayed and discussed within the context of such strong mutagenic activity being associated with a nonelectrophilic agent.
疑似人类致癌物依托泊苷已知具有遗传毒性，可能通过抑制拓扑异构酶II活性产生基因和染色体突变。本文描述了使用沙门氏菌试验、小鼠淋巴瘤tk+/-试验（tk-/-突变体的基因和染色体突变分析及分子分析）和小鼠骨髓微核试验进行的检测。在鼠伤寒沙门氏菌TA98菌株（而非TA1538或TA1537）中观察到与剂量相关的突变频率非重复性微弱增加。依托泊苷在浓度低于0.1微克/毫升时对L5178Y小鼠淋巴瘤细胞的杂合胸苷激酶（tk+/-）位点具有高度致突变性。诱导产生的大多是小集落突变体，这与观察到的强断裂剂作用一致。对突变体的分子分析表明，分别有83%和92%的大集落和小集落突变体失去了整个靶基因序列。染色体异常的L5178Y细胞比小的tk-/-突变体集落普遍约2至600倍。这表明在选择性试验中，依托泊苷介导的断裂作用的可行靶点约为11b染色体的五分之一，而11b染色体本身约为小鼠基因组的四十分之一。在小鼠骨髓微核试验中观察到依托泊苷有异常强烈的反应（口服剂量1毫克/千克后24小时，63.1 +/- 18个微核/1000个有核红细胞）。该试验中的最低可检测剂量水平在0.01至0.1毫克/千克之间。在1至15毫克/千克的剂量水平下，观察到剂量反应呈反比。试验反应的这种降低并非由于多染性红细胞发生率同时小幅下降，这是基于对N-甲基-N-亚硝基脲的研究得出的结论。用依托泊苷（10毫克/千克）给药48小时后取样的动物骨髓中没有多染性红细胞。微核试验的这些观察结果有待解释。依托泊苷的化学结构在与非亲电试剂相关的这种强诱变活性的背景下展示并进行了讨论。
