Understanding potential health risks is a significant challenge due to the large numbers of diverse chemicals with poorly characterized exposures and mechanisms of toxicities. showed promiscuous but distinctly different OP-1 patterns of EGT1442 activity whereas many of the EGT1442 pharmaceutical compounds showed promiscuous activity across GPCRs. Literature analysis confirmed >50% of the activities for the most potent chemical-assay pairs (54) but also revealed 10 missed interactions. Twenty-two chemicals with known estrogenic activity were correctly identified for the majority (77%) missing only the weaker interactions. In many cases novel findings for previously unreported chemical-target combinations clustered with known chemical-target interactions. Results from this large inventory of chemical-biological interactions can inform read-across methods as well as link potential targets to molecular initiating events in adverse outcome pathways for diverse toxicities. 1 Evaluating the safety and hazard of chemicals for potential human health and environmental effects is undergoing a major transformation.1 This 21st century toxicology paradigm has emerged from the limitations of the current paradigm in regard to cost time and throughput as well as the development of modern biological tools. These tools can probe chemical-biological interactions at fundamental levels focusing on the molecular and cellular pathways that are targets of chemical disruption.2 In this manner we can begin to understand mechanisms of chemical toxicity that may invoke disease or health effect end points. A more mechanistic understanding will help elucidate common pathways of toxicity and susceptibilities underlying human-relevant outcomes. Toxicity information is limited or absent for tens of thousands of compounds potentially entering the environment.1 3 4 Even for pharmaceuticals designed with a particular biological activity in mind there is little public information about unexpected toxicities or adverse responses that may be initiated by off-target binding to nuclear receptors G-protein-coupled receptors and receptor tyrosine kinases or by a myriad of events upstream or downstream to receptor engagement.5 6 Evaluating the untested chemicals through the current safety assessment paradigm is limited in throughput cost time and mechanistic revelation. As such high-throughput screening (HTS) of chemical-target interactions across chemicals including pharmaceuticals and chemicals of known and unknown toxicities through a broad range of biochemical assays will help describe the chemical-assay space for which there has been no information to date. Our broader hypothesis is that biochemical HTS when combined with the diverse assays within the ToxCast portfolio provides an anchor for predictive signatures and mechanistic pathways leading to toxicity. With further analysis these types of screens may help identify novel initial molecular events potentially associated with pathways of EGT1442 toxicity7 and inform systems modeling efforts aimed at characterizing adverse outcome pathways.8?16 EPA’s ToxCast project and the federal Tox21 collaboration are generating HTS data and building modeling approaches to identify and characterize biological pathways of toxicity.2 3 17 This approach employs a large structurally diverse chemical library to probe a wide spectrum of biological targets and cell-based activities which enables grouping and prioritizing of chemicals based on their activity profiles as well as EGT1442 deeper exploration of system biology relationships linking biological activities to toxicology. Further applications of this approach have the potential to enhance and refine structure metabolism or presumed mode of action-based read-across methods 18 as well as to identify potential targets for molecular initiating events in adverse outcome pathways for diverse toxicities. These approaches can be applied to testing prioritization hazard and safety assessment workflows design of green alternative chemicals or screening for adverse effects for drug development processes. ToxCast Phase I screened 310 unique compounds mainly food-use pesticides with rich data profiles in 467 biochemical or cell-based assays from 9 assay technologies.3 8 Despite the somewhat limited chemical diversity of EGT1442 this initial test library pesticidal compounds were found to have sufficiently rich bioactivity profiles and toxicity data. Some of these chemicals have known biological activities whereas most have limited toxicity data as.