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Perspectives on Validation of High-Throughput Assays Supporting 21st Century Toxicity Testing
Citation:
JUDSON, R., R. J. KAVLOCK, M. T. MARTIN, D. REIF, K. A. HOUCK, T. B. KNUDSEN, A. M. RICHARD, R. R. TICE, M. WHELAN, M. XIA, R. HUANG, C. P. AUSTIN, G. P. DASTON, T. HARTUNG, J. R. FOWLE III, W. WOOGE, W. TONG, AND D. J. DIX. Perspectives on Validation of High-Throughput Assays Supporting 21st Century Toxicity Testing. Sonja von Aulock (ed.), ALTEX. Society ALTEX Edition, Kuesnacht, Switzerland, 30(1/13):51-66, (2013).
Impact/Purpose:
Toxicity testing for human health effects is undergoing a paradigm shift from classical laboratory animal studies to in vitro assays that primarily use human cells and focus on assessing perturbations to key biological pathways. This shift is due to two major factors: 1) the recognition that current testing methods, which are costly, time consuming, and often use large numbers of animals without always providing correspondingly large benefits, are not adequate to manage the increasing backlog of largely untested chemicals; 2) the frequent inability of current in vivo tests to provide clear mechanistic insight into toxicity pathways, an advantage offered by the new types of in vitro assays that are able to directly probe human genes, cells, and tissues.
Description:
In vitro high-throughput screening (HTS) assays are seeing increasing use in toxicity testing. HTS assays can simultaneously test many chemicals but have seen limited use in the regulatory arena, in part because of the need to undergo rigorous, time-consuming formal validation. Here we discuss streamlining the validation process, specifically for prioritization applications. By prioritization, we mean a process in which less complex, less expensive, and faster assays are used to prioritize which chemicals are subjected first to more complex, expensive, and slower guideline assays. Data from the HTS prioritization assays is intended to provide a priori evidence that certain chemicals have the potential to lead to the types of adverse effects that the guideline tests are assessing. The need for such prioritization approaches is driven by the fact that there are tens of thousands of chemicals to which people are exposed, but the yearly throughput of most guideline assays is small in comparison. The streamlined validation process would continue to ensure the reliability and relevance of assays for this application. We discuss the following practical guidelines: (1) follow current validation practice to the extent possible and practical; (2) make increased use of reference compounds to better demonstrate assay reliability and relevance; (3) de-emphasize the need for cross-laboratory testing; and (4) implement a web-based, transparent, and expedited peer review process. [Disclaimer: The views expressed in this paper are those of the authors and do not necessarily reflect the views or policies of the U.S. Environmental Protection Agency, the U.S. Food and Drug Administration, or the U.S. National Institutes of Health]
