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 Uterotrophic

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