Characterizing chlorotriazine effects in cancer-relevant high-throughput screening assays

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.