Hilliard Cathy, Hill Rosina, Armstrong Michael, Fleckenstein Clint, Crowley Jessica, Freeland Elizabeth, Duffy Danielle, Galloway Sheila M
Merck Research Laboratories, Department of Genetic and Cellular Toxicology, West Point, PA 19486, USA.
Mutat Res. 2007 Mar 1;616(1-2):103-18. doi: 10.1016/j.mrfmmm.2006.11.013. Epub 2006 Dec 14.
Chromosome aberrations (Cabs) can be induced in vitro by non-DNA damaging compounds, often associated with cytotoxicity and DNA synthesis inhibition, and under conditions that would not be relevant in vivo. Such misleading positive results are reported both in Chinese hamster cell lines and in human peripheral blood lymphocytes (HL). We assessed the response of HL to compounds with varied genetic toxicity profiles, all of which induced Cabs in CHO cells Seven of 10 compounds were negative or equivocal in HL. Results in purified lymphocytes for four verified that the difference was not due to the presence of blood in cultures. Two compounds that were weakly positive in the Ames test and one that induced DNA adducts were negative or equivocal in the HL assay; their overall mutagenic potential in vivo is not clear. Of four Ames-negative compounds, three of which inhibited DNA synthesis in CHO cells, three were negative and one was equivocal in the HL assay. A potent Cab inducer, which also induced micronuclei in vivo (but was negative in the Ames test) was clearly positive in the HL assay. Two compounds were clearly positive in HL only when the mitotic indices (MI) were below 50% of control. These are genotoxic in other assays but our evidence suggests that Cab induction is related more to toxicity than to primary DNA damage. For this limited set of 10 compounds, HL were more likely than CHO cells to give negative or equivocal results. It is likely that more stringent checkpoint controls in human cells prevent damaged cells reaching mitosis, and may also influence the reported greater sensitivity to induction of aneuploidy and polyploidy of normal rodent compared with human cells. In the studies reported here, two strong inducers of polyploidy in CHO cells gave weaker increases in HL. Human lymphocytes have disadvantages as a routine screening assay (finding donors, known individual variability, increased time required and the inadequacy of the MI as a toxicity measure), but may be useful in follow-up testing to assess weight of evidence about genotoxic risk to humans, for compounds that are positive in the Chinese hamster cell Cabs assays.
染色体畸变（Cabs）可在体外由非DNA损伤化合物诱导产生，这些化合物通常与细胞毒性和DNA合成抑制有关，且在体内不相关的条件下也会出现。在中国仓鼠细胞系和人外周血淋巴细胞（HL）中均报道了此类误导性的阳性结果。我们评估了HL对具有不同遗传毒性特征的化合物的反应，所有这些化合物在CHO细胞中均诱导产生了Cabs。10种化合物中有7种在HL中呈阴性或结果不明确。对4种化合物在纯化淋巴细胞中的检测结果证实，差异并非由于培养物中存在血液所致。在Ames试验中呈弱阳性的2种化合物以及1种诱导DNA加合物的化合物在HL试验中呈阴性或结果不明确；它们在体内的总体致突变潜力尚不清楚。在4种Ames试验阴性的化合物中，其中3种在CHO细胞中抑制DNA合成，在HL试验中3种呈阴性，1种结果不明确。一种强效的Cabs诱导剂，在体内也诱导产生微核（但在Ames试验中呈阴性），在HL试验中明显呈阳性。只有当有丝分裂指数（MI）低于对照的50%时，2种化合物在HL中才明显呈阳性。这些化合物在其他试验中具有遗传毒性，但我们的证据表明，Cabs诱导与毒性的关系比与原发性DNA损伤的关系更大。对于这组有限的10种化合物，HL比CHO细胞更有可能给出阴性或不明确的结果。人类细胞中更严格的检查点控制可能会阻止受损细胞进入有丝分裂期，也可能会影响与人类细胞相比，正常啮齿动物对非整倍体和多倍体诱导更敏感的报道。在本文报道的研究中，2种在CHO细胞中强烈诱导多倍体的化合物在HL中的增加较弱。作为常规筛选试验，人淋巴细胞有诸多缺点（寻找供体、个体差异已知、所需时间增加以及MI作为毒性指标的不足），但对于在中国仓鼠细胞Cabs试验中呈阳性的化合物，在后续检测中评估对人类遗传毒性风险的证据权重时可能会有用。
