Phenotypic screening of the ToxCast chemical library to classify toxic and therapeutic mechanisms

Abstract

Addressing the safety aspects of drugs and environmental chemicals has historically been undertaken through animal testing. However, the quantity of chemicals in need of assessment and the challenges of species extrapolation require the development of alternative approaches. Our approach, the US Environmental Protection Agency's ToxCast program, utilizes a large suite of in vitro and model organism assays to interrogate important chemical libraries and computationally analyze bioactivity profiles. Here we evaluated one component of the ToxCast program, the use of primary human cell systems, by screening for chemicals that disrupt physiologically important pathways. Chemical-response signatures for 87 endpoints covering molecular functions relevant to toxic and therapeutic pathways were generated in eight cell systems for 641 environmental chemicals and 135 reference pharmaceuticals and failed drugs. Computational clustering of the profiling data provided insights into the polypharmacology and potential off-target effects for many chemicals that have limited or no toxicity information. The endpoints measured can be closely linked to in vivo outcomes, such as the upregulation of tissue factor in endothelial cell systems by compounds linked to the risk of thrombosis in vivo. Our results demonstrate that assaying complex biological pathways in primary human cells can identify potential chemical targets, toxicological liabilities and mechanisms useful for elucidating adverse outcome pathways.

High-throughput identification of small molecules that affect human embryonic vascular development

“…2A). The library was screened at a single concentration (4.5 μM) according to previous studies using ECs (21)(22)(23)(24) and other cells (25,26), in a volume of 200 μL per well of EGM-2 medium containing 0.25% DMSO (vol/vol). To identify compounds that selectively target ECs, we screened the same library against human anterior cruciate ligament (ACL) cells.…”

Grouping of histone deacetylase inhibitors and other toxicants disturbing neural crest migration by transcriptional profiling

“…Then, the similarity of marker changes by an unknown compound could be used to infer the mode of action. The feasibility of this approach has been shown for a diverse set of markers and endpoints by a recent elegant study (Kleinstreuer et al, 2014): 84 endpoints were used for testing of mechanistically well character ized compounds. The patterns obtained from this where then used for grouping of several hundred environmental toxicants.…”

“…Such groups of up to 20 compounds have for instance been observed for the 148 compounds tested in the TG GATES project (Grinberg et al, 2014). Grouping along mechanistic markers has also been done for the ToxCast phase I chemicals (Kleinstreuer et al, 2014). Such information could guide biologically driven read across proce dures in hazard assessment (Bal Price et al, 2015a) to group compounds based on similarities of MoA.…”

Current approaches and future role of high content imaging in safety sciences and drug discovery

“…The profiles within a research institution or among different institutions could be gathered in computational database systems (Big Data) according to strict guidelines for data relevance and quality. Such efforts have already been initiated by toxCast (Kleinstreuer et al, 2014), the tox21 programs (Zang et al, 2013) and within the toxBank project of SeURAt-1 (toxbank.net). Once the database contains a critical number of compounds and read-out parameters (incl.…”