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Evaluation of two high through-put (HTP) androgen receptor based assays: Utility of data for prioritization for further testing versus prediction of adverse effects.
Citation:
WILSON, V. S., J. F. Pregenzer, AND L. E. GRAY. Evaluation of two high through-put (HTP) androgen receptor based assays: Utility of data for prioritization for further testing versus prediction of adverse effects. Presented at Society of Toxicology 49th Annual meeting, Salt Lake City, UT, March 07 - 11, 2010.
Impact/Purpose:
This study examined the interaction of chemicals with the androgen receptor (AR) using in vitro cell-based transcriptional activation assays.
Description:
The androgen signaling pathway plays a critical role in sexual differentiation during development in mammals and is one of the better understood pathways in human development. Thus it was chosen as a model pathway to evaluate the potential of HTP in vitro assays as risk assessment tools. This study examined the interaction of chemicals with the androgen receptor (AR) using in vitro cell-based transcriptional activation assays. The chemicals identified as positive agonists or antagonists were then tested in competitive binding assays to confirm receptor interaction. An initial set of about sixty well-characterized compounds with varying affinities for the AR were tested. The in vitro results fromthese known compounds were compared to available data from in vivo Hershberger assays to evaluate the predictive capacity of the in vitro assays when compared to in vivo results. About fifty unknown chemicals were also tested in vitro and evaluated using the criteria developed. Results for chemicals with known activity in vitro and in vivo indicate that most with ED50s lower than 10-6 M were drugs or natural steroids. The pesticides and toxic substances known to have in vivo effects via the AR fell in the 10-4 to 10-6 M range. In the 10-4 to 10-6 M ED50 range, there Was no correlation between in vitro activity and the in vivo potency. An examination ofthe chemicals in this range . indicates that the limitations of the in vitro assays (failure to account for metabolic inactivation, activation, and half-life of a compound.) result in a high rate of "false positives" precluding their use for accurate prediction of in vivo effects. However, since there were no "false negatives" (in vitro versus in vivo) these in vitro receptor assays can be used to prioritize chemicals for additional in vitro or short-term in vivo screening for compounds that act via the AR signaling pathway in an HTP mode. Disclaimer: This abstract does not necessarily reflect EPA policy.