Abstract

Background:

High-throughput screening of chemicals with in vitro reporter gene assays in Tox21 has produced a large database on cytotoxicity and specific modes of action. However, the validity of some of the reported activities is questionable due to the “cytotoxicity burst,” which refers to the supposition that many stress responses are activated in a nonspecific way at concentrations close to cell death.

Objectives:

We propose a pragmatic method to identify whether reporter gene activation is specific or cytotoxicity-triggered by comparing the measured effects with baseline toxicity.

Methods:

Baseline toxicity, also termed narcosis, is the minimal toxicity any chemical causes. Quantitative structure–activity relationships (QSARs) developed for baseline toxicity in mammalian reporter gene cell lines served as anchors to define the chemical-specific threshold for the cytotoxicity burst and to evaluate the degree of specificity of the reporter gene activation. Measured 10% effect concentrations were related to measured or QSAR-predicted 10% cytotoxicity concentrations yielding specificity ratios (SR). We applied this approach to our own experimental data and to $\sim \mathrm{8,000}$ chemicals that were tested in six of the high-throughput Tox21 reporter gene assays.

Results:

Confirmed baseline toxicants activated reporter gene activity around cytotoxic concentrations triggered by the cytotoxicity burst. In six Tox21 assays, 37%–87% of the active hits were presumably caused by the cytotoxicity burst ($\text{SR}<1$) and only 2%–14% were specific with $\text{SR}\ge 10$ against experimental cytotoxicity but 75%–97% were specific against baseline toxicity. This difference was caused by a large fraction of chemicals showing excess cytotoxicity.

Conclusions:

The specificity analysis for measured in vitro effects identified whether a cytotoxicity burst had likely occurred. The SR-analysis not only prevented false positives, but it may also serve as measure for relative effect potency and can be used for quantitative in vitro–in vivo extrapolation and risk assessment of chemicals. https://doi.org/10.1289/EHP6664

中文翻译：

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细胞毒性爆发？体外报告基因检测中区分 Tox21 的特异性和非特异性效应。

摘要

背景：

通过 Tox21体外报告基因检测对化学品进行高通量筛选，生成了有关细胞毒性和特定作用模式的大型数据库。然而，由于“细胞毒性爆发”，一些报道的活性的有效性值得怀疑，这是指许多应激反应在接近细胞死亡的浓度下以非特异性方式激活的假设。

目标：

我们提出了一种实用的方法，通过将测量的效果与基线毒性进行比较来确定报告基因激活是特异性的还是细胞毒性触发的。

方法：

基线毒性，也称为麻醉，是任何化学物质引起的最小毒性。为哺乳动物报告基因细胞系的基线毒性而开发的定量结构-活性关系（QSAR）作为锚来定义细胞毒性爆发的化学特异性阈值并评估报告基因激活的特异性程度。测量的 10% 效应浓度与测量的或 QSAR 预测的 10% 细胞毒性浓度相关，产生特异性比 (SR)。我们将这种方法应用于我们自己的实验数据并$～\mathrm{8,000}$在六种高通量 Tox21 报告基因检测中测试的化学物质。

结果：

已确认的基线毒物在细胞毒性爆发引发的细胞毒性浓度附近激活报告基因活性。在六次 Tox21 检测中，37%–87% 的活性命中可能是由细胞毒性爆发引起的（$\text{SR}<1$）并且只有 2%–14% 的具体内容是$\text{SR}\ge 10$对抗实验细胞毒性，但 75%–97% 对基线毒性具有特异性。这种差异是由大部分化学物质表现出过度的细胞毒性引起的。

结论：

对测量的体外效应的特异性分析确定是否可能发生细胞毒性爆发。SR 分析不仅可以防止假阳性，而且还可以作为相对效应效力的衡量标准，并可用于化学品的定量体外-体内外推和风险评估。https://doi.org/10.1289/EHP6664