# Increasing the Efficiency and Use of Resources for Tier 1 Screening

Lisa S. Ortego , PhD, DABT Bayer CropScience

# EPA White Paper Proposal

• EPA has proposed some considerations for increasing the efficiency of the Tier 1 battery

• Eliminate Uterotrophic and Hershberger Assays from Tier 1 Screening

• Rationale is that they were not positive for many, if any, substances in EPA’s analysis of the subset evaluated in their White Paper whereas the pubertals had more positive responses

• However, the Uterotrophic and Hershberger assays are among the most specific and extensively validated assays in the battery, having undergone testing and regulatory use before the rest of T1B

• Therefore, this recommendation may not be in the best interest of the scientific foundations of the T1B in determining the potential for specific endocrine activity

# Alternative Frameworks to T1B OECD and ECETOC

• The OECD Framework

• Places emphasis on data already in existence both in the public domain and previously

- generated industry data and incorporates testing at higher levels of biological organization with successive tiers



### • The European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC) Framework

• Aims to identify endocrine

- mediated adverse effects of risk assessment relevance that are confirmed/explained by an endocrine mode of action

• It integrates regulatory ecotoxicology / toxicology data and mechanistic screening studies

• Satisfies the accepted definitions of endocrine disruption (e.g. Weybridge , WHO/IPCS)

# Efforts to Stage Testing within Existing T1B

• Staging the T1B would allow assessment

- based decisions on which specific assays may or may not be needed

• For example, if a substance does not exhibit activity in the androgen receptor binding assay , the Hershberger assay, the aromatase, steroidogenesis or female pubertal assays, a case could be made that there’s no need to proceed with the fish, frog and male pubertal assays

• Such an assessment

- based approach for determining potential activity should be supplemented with analysis of other scientifically relevant information

# Other Staged Approaches

• A proposal similar in concept to staging was presented by Earl Gray at the recent Toxicology Excellence for Risk Assessment workshop

• In his presentation (based on Ankley and Gray, 2013) the fish short term reproduction assay and the male pubertal assay are reported to be sensitive and specific enough to stand alone as the initial studies in the battery

• For the 12 model compounds evaluated in the paper, there was typically at least one fish and one rat assay that indicated a positive finding with a high concordance

• The FSTRA and the male pubertal assays could be performed first

• If effects noted in either assays

– decide what other assays are needed to further characterize the potential effect observed

• If no effects observed, the chemical goes to a “hold” status, where no further endocrine screening is required at that time

# Other Staged Approaches ( con’t )

• FSTRA refinement

― Reproductive endpoint did not appear to be used

― Optional endpoints of steroid measurements were included

― The elimination of the quantitative reproduction endpoint could significantly shorten the time and labor required for performance of the assay

• Ankley and Gray focused on estrogen and androgen activity, but thyroid activity could also be covered by this approach

• A thyroid evaluation is included in the male pubertal assay or could be incorporated into the Hershberger assay

• Activity in mammalian thyroid evaluations appears share high concordance with that in amphibians (Pickford 2010 , OECD)

• Compared mammalian and amphibian thyroid responses in many chemicals across several modes of thyroid action

• Supports use of the thyroid evaluations in mammals as predictive of amphibian responses

# Advantages to Implementation of Battery Staging Concepts

• There are several highly credible proposals as described above that are alternatives to the EPA proposal to eliminate the U terotrophic and Hershberger assays

• These alternative proposals carry high potential for reducing the time, resources and animals needed to evaluate whether a compound has the potential for endocrine activity, and still maintain the scientific rigor and credibility of the T1B

• Any of these approaches could potentially reduce the testing required, speed decision making, and reduce animal use

• In this manner, rather than a requirement for all of the 11 assays in the battery, the EDSP could be transformed into an integrated, targeted testing and assessment program