A Workflow to Investigate Exposure and Pharmacokinetic Influences on High-Throughput in Vitro Chemical Screening Based on Adverse Outcome Pathways

Abstract

BackgroundAdverse outcome pathways (AOPs) link adverse effects in individuals or populations to a molecular initiating event (MIE) that can be quantified using in vitro methods. Practical application of AOPs in chemical-specific risk assessment requires incorporation of knowledge on exposure, along with absorption, distribution, metabolism, and excretion (ADME) properties of chemicals.ObjectivesWe developed a conceptual workflow to examine exposure and ADME properties in relation to an MIE. The utility of this workflow was evaluated using a previously established AOP, acetylcholinesterase (AChE) inhibition.MethodsThirty chemicals found to inhibit human AChE in the ToxCast™ assay were examined with respect to their exposure, absorption potential, and ability to cross the blood–brain barrier (BBB). Structures of active chemicals were compared against structures of 1,029 inactive chemicals to detect possible parent compounds that might have active metabolites.ResultsApplication of the workflow screened 10 “low-priority” chemicals of 30 active chemicals. Fifty-two of the 1,029 inactive chemicals exhibited a similarity threshold of ≥ 75% with their nearest active neighbors. Of these 52 compounds, 30 were excluded due to poor absorption or distribution. The remaining 22 compounds may inhibit AChE in vivo either directly or as a result of metabolic activation.ConclusionsThe incorporation of exposure and ADME properties into the conceptual workflow eliminated 10 “low-priority” chemicals that may otherwise have undergone additional, resource-consuming analyses. Our workflow also increased confidence in interpretation of in vitro results by identifying possible “false negatives.”CitationPhillips MB, Leonard JA, Grulke CM, Chang DT, Edwards SW, Brooks R, Goldsmith MR, El-Masri H, Tan YM. 2016. A workflow to investigate exposure and pharmacokinetic influences on high-throughput in vitro chemical screening based on adverse outcome pathways. Environ Health Perspect 124:53–60; http://dx.doi.org/10.1289/ehp.1409450

Evaluating the Impact of Uncertainties in Clearance and Exposure When Prioritizing Chemicals Screened in High-Throughput Assays

“…The previous study 17 also identified 22 possible false negatives out of chemicals considered inactive in the same assay, based on their structural similarities to active chemicals. Since the analysis here required in vitro dose–response data, which is lacking for most inactive chemicals, only five of the 22 false negatives were carried over to the current study.…”

Drug Metabolism in Preclinical Drug Development: A Survey of the Discovery Process, Toxicology, and Computational Tools

“…Vinken et al , for example, developed AOPs describing the stepwise mechanistic association between the drug-implicated MIE of inhibition of the bile salt export pump and the organismal development cholestatic liver injury [108]. When combined with exposure and ADME assessments, the AOP framework has recently been demonstrated by Philips et al to identify drug metabolites and parent compounds that in fact engage in an MIE and therefore avoid unnecessary costs of comprehensive biological assessment [109]. Figure 3 outlines how the AOP concept might contribute to a preclinical drug metabolism assessment workflow, wherein predicted or experimentally established exogenous metabolites are screened for adverse outcomes according to the current knowledgebase.…”

Adverse Outcome Pathways--Organizing Toxicological Information to Improve Decision Making

“…In this tier, qualitative evaluation of ADME potential could aid in the identification of false positives, which are in vitro active chemicals that cannot reach the molecular target in vivo due to certain ADME characteristics (Phillips et al, 2015). For example, some chemicals (e.g., anthralin) can be sequestered in skin tissues; therefore, they are unlikely to enter the systemic circulation-and thus molecular targets in internal organs-when exposed via a dermal route.…”

“…For example, some chemicals (e.g., anthralin) can be sequestered in skin tissues; therefore, they are unlikely to enter the systemic circulation-and thus molecular targets in internal organs-when exposed via a dermal route. In addition, chemical structures or molecular descriptors could potentially be used to detect possible false negatives that are either inactive parents of active metabolites or in vivo active chemicals not detected in vitro (Phillips et al, 2015).…”