Impact of Environmental Chemicals on Key Transcription Regulators and Correlation to Toxicity End Points within EPA’s ToxCast Program

Exposure to environmental chemicals adds to the burden of disease in humans and wildlife to a degree that is difficult to estimate and, thus, mitigate. The ability to assess the impact of existing chemicals for which little to no toxicity data are available or to foresee such effects during early stages of chemical development and use, and before potential exposure occurs, is a pressing need. However, the capacity of the current toxicity evaluation approaches to meet this demand is limited by low throughput and high costs. In the context of EPA’s ToxCast project, we have evaluated a novel cellular biosensor system (Factorial) that enables rapid, high-content assessment of a compound’s impact on gene regulatory networks. The Factorial biosensors combined libraries of cis- and trans-regulated transcription factor reporter constructs with a highly homogeneous method of detection enabling simultaneous evaluation of multiplexed transcription factor activities. Here, we demonstrate the application of the technology toward determining bioactivity profiles by quantitatively evaluating the effects of 309 environmental chemicals on 25 nuclear receptors and 48 transcription factor response elements. We demonstrate coherent transcription factor activity across nuclear receptors and their response elements and that Nrf2 activity, a marker of oxidative stress, is highly correlated to the overall promiscuity of a chemical. Additionally, as part of the ToxCast program, we identify molecular targets that associate with in vivo end points and represent modes of action that can serve as potential toxicity pathway biomarkers and inputs for predictive modeling of in vivo toxicity.

环境化学物暴露会加剧人类与野生生物的疾病负担，且其影响程度难以估算，因此也难以采取有效的缓解措施。当前亟需能够评估现有（几乎无毒性数据或缺乏毒性数据）化学品的危害影响，或是在化学品开发与使用的早期阶段、潜在暴露发生前预判其效应的能力。然而，当前的毒性评估方法因通量低下、成本高昂，难以满足这一需求。
本研究依托美国环境保护署（Environmental Protection Agency, EPA）的ToxCast项目，对一种新型细胞生物传感器系统（Factorial）进行了评估。该系统可实现快速、高内涵的化合物基因调控网络影响检测。Factorial生物传感器将顺式与反式调控的转录因子报告基因构建体文库，与高度均一化的检测方法相结合，能够同时评估多重转录因子的活性。
本研究通过定量检测309种环境化学物对25种核受体与48个转录因子应答元件的作用，展示了该技术用于构建生物活性谱的应用。研究发现，核受体及其应答元件的转录因子活性呈现一致性；同时，作为氧化应激标志物的核因子红细胞2相关因子2（nuclear factor erythroid 2-related factor 2, Nrf2）的活性，与化学品的整体泛活性高度相关。
此外，作为ToxCast项目的组成部分，本研究还鉴定出了与体内终点相关的分子靶点，这些靶点所代表的作用模式可作为潜在的毒性通路生物标志物，以及用于体内毒性预测建模的输入参数。