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December 1, 2014 

Fred Jenkins, Jr., Ph.D. 

Designated Federal Official 

FIFRA Scientific Advisory Panel Staff 

USEPA/OSCP (7201M) 

Environmental Protection Agency 

1200 Pennsylvania Ave., N.W. 

Washington, DC 20460–0001 

Dear Dr. Jenkins: 

RE: FIFRA SAP Meeting, Integrated Bioactivity and Exposure Ranking – A 

Computational Approach for the Prioritization and Screening of Chemicals in the 

Endocrine Disruptor Screening Program; Docket ID EPA–HQ–OPP–2014–0614. 

These comments are submitted on behalf of People for the Ethical Treatment of Animals, the 

Physicians Committee for Responsible Medicine, and the Humane Society of the United States – 

national animal protection and scientific advocacy organizations with a combined constituency 

of more than 13 million Americans who share the common goal of promoting reliable and 

relevant regulatory testing methods and strategies that protect human health and the environment 

while reducing, and ultimately eliminating, the use of animals. 

We appreciate the opportunity to comment on the white paper that is the subject of this FIFRA 

Science Advisory Panel (SAP) meeting, i.e., the Integrated Bioactivity and Exposure Ranking 

computational approach for use in prioritization and screening of in the Endocrine Disruptor 

Screening Program (EDSP). 

General Comments 

Our organizations are very impressed with and appreciative of the amount of work that the EPA 

has performed in developing and implementing computational and high throughput screening 

(HTS) tools to predict both chemical activity in the estrogen receptor (ER) and androgen receptor 

(AR) pathways and environmental exposure. We are excited about the progress that has been 

made and the strong likelihood that these tools may soon be ready to replace the uterotrophic and 

Hershberger EDSP Tier 1 in vivo assays, as well as the ER and AR receptor binding assays that, 

while considered to be in vitro assays, rely on the collection and use of animal tissues. 

There are two important improvements over the current EDSP encapsulated by the proposed 

approach: the evaluation and presentation of chemical activities as probabilities, and the 

inclusion of exposure estimates in prioritization (i.e. Integrated Bioactivity and Exposure 

Ranking (IBER). Such approaches to prioritizing and screening the universe of EDSP chemicals 

will lead to a better understanding of the potential endocrine activity of the broad spectrum of 

chemicals in the EDSP chemical universe as well as to a more efficient and more humane way to 

rapidly identify those substances that have the greatest potential of causing adverse effects in 
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human and wildlife populations, and ultimately result in the use of far fewer animals in testing 

under the EDSP. 

The ability of HTS screening to replace the mechanistic in vivo Tier 1 assays (i.e. the 

uterotrophic assay) is promising. The EPA should consider additional ways the information 

could be used to avoid in vivo testing. For example, as described in the white paper, the utility of 

the in vivo Tier 1 uterotrophic and Hershberger assays appears to be related to chemical 

activation and detoxification. Therefore, it may be possible in the near-term to skip Tier 1 

altogether and move on to further evaluation if it can be shown that detoxification is unlikely to 

play a role in high-IBER scoring chemicals. In addition, as the HTS assays improve and expand 

coverage and the IBER approach evolves, the true utility of other Tier 1 assays must continue to 

be reassessed. 

While we understand that the focus of the EDSP SAP meetings is on the adequacy and 

appropriateness of the science, there is often an accompanying lack of clarity with regards to 

policy – in this case a description of exactly how IBER results will be used to inform decisionmaking for purposes other than prioritization, such as informing additional Tier 1 and Tier 2 

testing. Because of the large animal numbers involved, particularly in Tier 2, consideration of 

how these methodologies will be used to inform future testing decisions is integral to this 

ongoing discussion. For example, does the EPA intend to require Tier 2 testing for high-ranking 

IBER chemicals, or would another level of intermediate testing be considered to further exclude 

chemical substances? Suggestions have been made for more nuanced tiering or integrated 

strategies, including addition of a “Tier 1.5”1

 or use of a strategy based on the OECD Conceptual 

Framework,2 which could provide a basis for applying IBER information, along with Other 

Scientifically Relevant Information (OSRI) to inform potential further testing. Can the EPA 

envision situations in which regulatory decisions could be made with IBER and Tier 1 assays, 

avoiding Tier 2 altogether? We urge the Agency to consider, and share with the public, how 

screening results from these methodologies could inform a more integrated approach to testing 

and assessment. 

Specific Comments 

1. Consideration of receptor-specific activity vs. potential “pseudo-receptor” activity (Table 

2.3 and 2.4, discussion on page 37) as well as representation of chemical activity as a 

probability (e.g. of agonist or antagonist activity) is particularly helpful in providing 

additional information regarding uncertainty and/or specificity of chemical behavior and 

provides a clear advantage of the HTS approach vs. conventional testing.

																																																								

1	Juberg,	D.R.,	Borghoff,	S.J.,	Becker,	R.A.,	Casey,	W.,	Hartung,	T.,	Holsapple,	M.P.,	Marty,	M.S.,	Mihaich,	E.M.,	Van	

Der	Kraak,	G.,	Wade,	M.G.,	Willett,	C.E.,	Andersen,	M.E.,	Borgert,	C.J.,	Coady,	K.K.,	Dourson,	M.L.,	Fowle	III,	J.R.,	

Gray,	L.E.,	Lamb,	J.C.,	Ortego,	L.S.,	Schug,	T.T.,	Toole,	C.M.,	Zorrilla,	L.M.,	Kroner,	O.L.,	Patterson,	J.,	Rinckel,	L.A.,	

and	Jones,	B.R.		(2014).		Lessons	learned,	challenges	and	opportunities:		The	U.S.	Endocrine	Disruptor	

Screening	Program.	ALTEX		31,	63‐78.	

2	Bishop,	P.L.	and	C.E.	Willett.	(2013).	The	Use	and	Acceptance	of	Other	Scientifically	Relevant	Information	

(OSRI)	in	the	U.S.	Environmental	Protection	Agency	(EPA)	Endocrine	Disruptor	Screening	Program.	Birth	

Defects	Res	B	Dev	Reprod	Toxicol.101(1):3‐22;	Juberg,	D.R.,	Gehen,	S.C.,	Coady,	K.K.,	LeBaron,	M.J.,	Kramer,	

V.J.,	Lu,	H.,	and	Marty,	M.S.		(2013).	Chlorpyrifos:	Weight	of	Evidence	Evaluation	of	Potential	Interaction	with	

the	Estrogen,	Androgen,	or	Thyroid	Pathway.		Regul.	Toxicol.	Pharmacol.		66,	249‐263.	
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2. With respect to the ER model’s concordance with results of reference chemicals run in 

the uterotrophic assay (p.50), the false negative and false positive rates of less than 10% 

are excellent. The two chemicals that were not predicted correctly appear to be activated 

or de-activated by metabolic processes not available in the HTS assays used. This 

underscores the need for more work on reliable methods that incorporate metabolism into 

the testing system. We urge the EPA to continue its investigation in this area and to make 

it a priority for future work.

3. On page 52, there is mention of a concordant mathematical relationship between in vitro

AUC values and the level of in vivo potency in the uterotrophic assay. We suggest that 

the EPA further investigate whether this relationship is maintained between the ER 

pathway model and higher-tier tests in order to facilitate avoidance of Tier 2 testing and 

move closer to using in vitro and in silico approaches for risk assessment. The 

development of metabolism and toxicokinetic models as described later in the paper are 

an important part of this goal, but lack of such models need not be a barrier to using the 

ER pathway model for quantitative prediction in appropriate cases. 

4. There appears to be a small error on pp. 58-59 with reference to Figure 2.8. From the 

sequence of figures, the figure number should probably be 2.16. 

5. We see real value in the prioritizing of chemicals for further testing by adding the 

exposure element to the model. On p. 59, 73 out of about 1,800 chemicals were predicted 

to have ER activity above the AUC cut-off designated for positive estrogen activity. This 

number was reduced to just six after applying IBER rankings (Fig. 6.5, p.97), 

highlighting this approach’s utility in focusing attention on only those chemicals with the 

most potential for adverse effects. 

6. Understanding that the work on the AR model is not as far along as that for the ER, we 

feel greater clarification is needed for the statements on p. 75: “The AR pathway analyses 

are currently underway and at this time, we propose that adequate confidence has been 

demonstrated only for the first goal (prioritization). Additional resolution of performance 

of the AR models and potential utility for contributing to the weight of evidence 

determination of AR bioactivity will likely be improved by adding additional reference 

chemicals.” As no timeframe is given in the white paper for the completion of the AR 

work, we question why results of the AR approach could not be used in the short term as 

part of a WOE, particularly if OSRI is available for a particular chemical that is 

concordant with those results. It is possible the information on AR bioactivity gathered 

thus far could be used to help inform decisions about List 2 chemicals and we hope it 

could be utilized for that purpose. 

7. We note the value of the current efforts in helping to identify and prioritize what 

additional exposure and biomonitoring data will be needed for better predictions of 

human exposure to chemicals (pp. 84-85). This will hopefully assist in directing and 

focusing monitoring efforts to provide more useful in the future. As the Agency is aware, 
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improved biomonitoring is a cornerstone of the 2007 National Academies Toxicity 

Testing in the 21st Century report. 

8. With respect to the work being described on the thyroid pathway (p. 99), we 

acknowledge the EPA as an international leader in attempts to model this pathway and 

develop useful assays but would also encourage Agency staff to stay engaged with the 

OECD and global efforts3 in order to maximize and speed progress in this area and 

enhance development of the model. 

9. We are pleased to see there are plans to model the various other pathways, e.g., 

steroidogenesis, cell stress, etc., and that the EPA will initiate systematic reviews and 

curation of the pubertal, AMA, and fish reproduction assays, and look forward to future 

presentations of these analyses at upcoming SAP meetings. 

We are truly excited by the enormous strides the EPA is making in developing and implementing 

21st century toxicology and risk assessment methods and the eventual effect this will have on 

both reducing the use of animals in regulatory testing and increasing the efficiency and accuracy 

of identifying chemicals of concern. 

Sincerely, 

Patricia L. Bishop, MS 

Research Scientist 

Regulatory Testing Division 

People for the Ethical Treatment of Animals 

Kristie Sullivan, MPH 

Director, Regulatory Testing Issues 

Physicians Committee for Responsible Medicine 

Catherine Willett, PhD 

Director, Regulatory Toxicology, Risk Assessment and Alternatives 

The Humane Society of the United States 

																																																								

3	Murk	AJ,	Rijntjes	E,	Blaauboer	BJ,	Clewell	R,	Crofton	KM,	Dingemans	MM,	Furlow	JD,	Kavlock	R,	Köhrle	J,	

Opitz	R,	Traas	T,	Visser	TJ,	Xia	M,	Gutleb	AC.		(2013).	Mechanism‐based	testing	strategy	using	in	vitro	

approaches	for	identification	of	thyroid	hormone	disrupting	chemicals.		Toxicology	in	Vitro	27	(2013)1320–

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