Characterizing Chlorotriazine Effects in Cancer-Relevant High-Throughput Screening Assays

Agnes Karmaus^*Alex Charlton

• Syngenta Crop Protection, LLC, Greensboro, United States

High-throughput screening (HTS) in vitro testing can be a powerful tool for evaluating chemicals across an abundance of mechanistic, targeted assay systems. Herein, ToxCast/Tox21 HTS assay endpoints were reviewed for five chlorotriazine herbicides (atrazine, cyanazine, propazine, simazine, and terbuthylazine) to evaluate any indication of cancer-relevant bioactivity. To these means, we focused on assay endpoints from the 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. 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. More specifically, our workflow comprising the use of a focused ToxCast assay inventory based on KCC attribution, integration of assay flags to identify robust bioactivity, and providing context to in vitro ToxCast data with available in vivo study outcomes demonstrates how the ToxCast data and KCC framework can be applied to review a chemical class for carcinogenicity potential.