Morales-Ramírez Pedro, Vallarino-Kelly Teresita, Cruz-Vallejo Virginia
Instituto Nacional de Investigaciones Nucleares, Apartado Postal 18-1027, Mexico City, Mexico.
Cancer Chemother Pharmacol. 2017 May;79(5):843-853. doi: 10.1007/s00280-017-3290-0. Epub 2017 Mar 21.
This study analyzed the kinetics of in vivo micronucleus induction in normoblasts by determining the kinetics of difluorodeoxycytidine (dFdC)-induced micronucleated polychromatic erythrocytes (MN-PCEs) in the peripheral blood of mice. The kinetic indexes of MN-PCE induction of dFdC were correlated with the previously reported mechanisms DNA damage induction by this compound. In general, this study aimed to establish an in vivo approach for discerning the processes underlying micronucleus induction by antineoplastic agents or mutagens in general.
The frequencies of PCEs and MN-PCEs in the peripheral blood of mice were determined prior to treatment and after treatment using dFdC at doses of 95, 190, or 380 µmol/kg at 8 h intervals throughout a 72 h post-treatment.
The area beneath the curve (ABC) for MN-PCE induction as a function of time, which is an index of the total effect, indicated that the dose response was directly proportional and that the effect of dFdC on micronucleus induction was reduced compared with that of aneuploidogens and monofunctional and bifunctional alkylating agents but increased compared with that of promutagens, which is consistent with our previous results. The ABC showed a single peak with a small broadness index, which indicates that dFdC has a single mechanism or concomitant mechanisms for inducing DNA breaks. The time of the relative maximal induction (T ) indicated that dFdC requires more time to achieve MN-PCE induction compared with aneugens and monofunctional and bifunctional alkylating agents, although it requires a similar time to achieve MN-PCE induction as azacytidine, which is consistent with evidence showing that both agents must be incorporated into DNA for their action to be realized. The timing of maximal cytotoxicity observed with the lowest dFdC dose was correlated with the timing of the main genotoxic effect. However, early and late cytotoxic effects were detected, and these effects were independent of the genotoxic response.
A correlation analysis indicated that dFdC appears to induce MN-PCEs through only one mechanism or mechanisms that occur concomitantly, which could be explained by the previously reported concurrent inhibitory effects of dFdC on DNA polymerase alpha, polymerase epsilon, and/or topoisomerase. The timing of maximal cytotoxicity was correlated with the timing of maximal genotoxicity; however, an early cytotoxic effect that appeared to occur prior to the incorporation of dFdC into DNA was likely related to a previously reported inhibitory effect of dFdC on thymidylate synthase and/or ribonucleotide reductase.
本研究通过测定二氟脱氧胞苷（dFdC）诱导的小鼠外周血中微核多染性红细胞（MN-PCEs）的动力学，分析了正成红细胞体内微核诱导的动力学。dFdC诱导MN-PCEs的动力学指标与该化合物先前报道的DNA损伤诱导机制相关。总体而言，本研究旨在建立一种体内方法，以识别抗肿瘤药物或诱变剂一般诱导微核的潜在过程。
在治疗前以及使用剂量为95、190或380 μmol/kg的dFdC治疗后，以8小时的间隔在整个治疗后72小时内测定小鼠外周血中PCEs和MN-PCEs的频率。
作为时间函数的MN-PCE诱导曲线下面积（ABC），即总效应指标，表明剂量反应成正比，并且与非整倍体诱导剂、单功能和双功能烷化剂相比，dFdC对微核诱导的作用降低，但与促诱变剂相比增加，这与我们先前的结果一致。ABC显示出一个单峰，峰宽指数较小，这表明dFdC具有单一机制或诱导DNA断裂的伴随机制。相对最大诱导时间（T）表明，与非整倍体诱导剂、单功能和双功能烷化剂相比，dFdC诱导MN-PCEs需要更多时间，尽管它与阿扎胞苷诱导MN-PCEs所需时间相似，这与证据表明两种药物都必须掺入DNA才能实现其作用一致。观察到的最低dFdC剂量下最大细胞毒性的时间与主要遗传毒性效应的时间相关。然而，检测到了早期和晚期细胞毒性效应，并且这些效应与遗传毒性反应无关。
相关性分析表明，dFdC似乎仅通过一种或同时发生的机制诱导MN-PCEs，这可以用先前报道的dFdC对DNA聚合酶α、聚合酶ε和/或拓扑异构酶的同时抑制作用来解释。最大细胞毒性的时间与最大遗传毒性的时间相关；然而，在dFdC掺入DNA之前出现的早期细胞毒性效应可能与先前报道的dFdC对胸苷酸合成酶和/或核糖核苷酸还原酶的抑制作用有关。
