Citation:

Gray, E. Quantification of the uncertainties in extrapolating from in vitro androgen receptor (AR) antagonism to key events in in vivo screening assays and adverse reproductive outcomes in F1 male rats. Society of Toxicology Annual Meeting 2016, Baltimore, MD, March 12 - 16, 2017.

Impact/Purpose:

the 2016 TSCA legislation calls for the use of validated HTS, in vitro, in vivo screening assays and tiered testing strategies to facilitate human health risk assessment and to reduce or replace animal use where possible. The current effort describes that the potency of chemicals with antiandrogenic activity to disrupt reproductive development in the male rat offspring can be predicted with reasonable certainty from a short-term screening assay, potentially reducing the resources required (time, animals, money, labor) to test chemicals for their ability to induce adverse developmental reproductive effects in utero.

Description:

There are multiple molecular initiating events (MIEs) that can disrupt male sexual differentiation including AR antagonism and inhibition of synthesis, and metabolism of fetal testosterone. Disruption of this event by pesticides like vinclozolin that act as AR antagonists and phthalate esters that inhibit fetal testosterone synthesis and alter testis gene expression, both reduce anogenital distance (AGD) and induce some common reproductive tract malformations in F1 male rat offspring. We are developing a quantitative network of adverse outcome pathways (AOPs) that includes multiple MIEs and key events linking anti-AR activities to permanent reproductive abnormalities. Here, our objective was to determine how precisely the EC50s from AR antagonism (the MIE) in vitro or ED50s from the in vivo Hershberger Assay (HA; reduced tissue growth a downstream key event in the AOP) predict the ED50s for reduced anogenital distance (AGD) in male rats after in utero exposure to AR antagonists. This effort combined in house data with published studies from the last 60 years on the effects of AR antagonists in the HA and on AGD and other malformations in male rat offspring. HA studies using castrate-, androgen-, stimulated- immature male rats that were dosed orally for 7 to 10 days, as well as developmental studies with oral exposure during sexual differentiation followed by a postnatal assessment of neonatal AGD and other effects were selected. The ED50s from the in vivo assays and the in vitro EC50s for AR antagonism were compared using regression models to determine the goodness-of fit and prediction intervals. In total, 250 studies were selected and included in the analysis, currently comprising 58 chemicals with data from at least two of the three assays. As reported in the literature, the ability to predict potency for key events and adverse developmental effects from the in vitro MIE displays considerable uncertainty with R2 values from in vitro to HA or AGD of about 25% and 5%, respectively. In contrast, there is less uncertainty in extrapolating from the HA to the in utero effects on neonatal AGD (R2 value of about 90%). In summary, the current results suggest that the key events measured in the HA can be extrapolated with reasonable certainty to predict the ED50s for the adverse effect of antiandrogenic chemicals on AGD. Ongoing efforts are adding additional key events and adverse outcomes to the analysis.

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