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Characterizing chlorotriazine effects in cancer-relevant high-throughput screening assays
Agnes L Karmaus1, Alex Charlton1
1Syngenta Crop Protection, LLC, Greensboro, NC, United States.
Introduction:
High-throughput screening (HTS) in vitro testing can be a powerful tool for evaluating chemicals across an abundance of mechanistic, targeted assay systems. This study reviewed HTS in vitro data for the systematic evaluation of endpoints relevant to carcinogenesis. To these means, we focused on assay endpoints from the ToxCast/Tox21 HTS program that have been mapped to Key Characteristics of Carcinogens (KCCs) to help focus our review on the ∼750 assay endpoints that have been previously identified as potentially informative for evaluating modes of action relevant to carcinogenesis.
Methods:
Data for ToxCast/Tox21 HTS assay endpoints were retrieved from the publicly accessible invitrodb v4.2 and reviewed for five chlorotriazine herbicides (atrazine, cyanazine, propazine, simazine, and terbuthylazine) to evaluate any indication of cancer-relevant bioactivity. More specifically, we present a workflow comprising the use of a focused assay endpoint inventory based on KCC attribution, integration of assay flags to identify robust bioactivity, and putting in vitro mechanistic insights into context with literature-based context for toxicokinetic considerations and in vivo evidence.
Results And Discussion:
There were common targets consistently identified as bioactive across the chemical class including induction of estrone levels and potential CAR/PXR activation. These findings were put in context by utilizing in vivo data and knowledge about atrazine to weigh the evidence. Though the ToxCast/Tox21 HTS mechanistic assays did not yield novel insights into chlorotriazine carcinogenicity, our workflow exemplifies how starting from mechanistic screening data and integrating apical endpoints can be conducted. By providing context to in vitro ToxCast/Tox21 data with toxicokinetics information and available in vivo study outcomes demonstrates how the HTS data and KCC framework can be applied to review a chemical class for carcinogenicity potential.
Insights
High-throughput screening (HTS) identified potential cancer-related bioactivity in chlorotriazine herbicides by analyzing ToxCast/Tox21 data. Integrating in vitro results with in vivo evidence provides a framework for assessing carcinogenicity.
Area of Science:
- Toxicology
- In vitro screening
- Chemical risk assessment
Background:
- High-throughput screening (HTS) in vitro testing offers a powerful method for evaluating numerous chemicals across diverse mechanistic assays.
- Carcinogenesis research benefits from systematic evaluation of HTS in vitro data for relevant endpoints.
- The ToxCast/Tox21 HTS program provides assay endpoints mapped to Key Characteristics of Carcinogens (KCCs), aiding in the identification of potential carcinogenicity mechanisms.
Purpose of the Study:
- To review HTS in vitro data from the ToxCast/Tox21 program for five chlorotriazine herbicides.
- To evaluate potential cancer-relevant bioactivity using KCC-mapped assay endpoints.
- To demonstrate a workflow integrating in vitro mechanistic data with toxicokinetic and in vivo evidence for carcinogenicity assessment.
Main Methods:
- Retrieved ToxCast/Tox21 HTS assay endpoint data from invitrodb v4.2 for five chlorotriazine herbicides.
- Focused the review on assay endpoints mapped to KCCs, identifying approximately 750 potentially informative assays.
- Integrated assay flags for robust bioactivity and contextualized in vitro findings with literature-based toxicokinetics and in vivo data.
Main Results:
- Common bioactive targets across the chlorotriazine herbicide class included induction of estrone levels and potential CAR/PXR activation.
- In vitro findings were contextualized using in vivo data and specific knowledge of atrazine.
- The HTS mechanistic assays did not reveal novel insights into chlorotriazine carcinogenicity but demonstrated workflow utility.
Conclusions:
- The developed workflow exemplifies integrating mechanistic screening data with apical endpoints for chemical class review.
- Contextualizing in vitro ToxCast/Tox21 data with toxicokinetics and in vivo outcomes is crucial for robust carcinogenicity assessment.
- The KCC framework, combined with HTS data and toxicokinetic information, provides a systematic approach to evaluating chemical carcinogenicity potential.
