ELLEN MIHAICH, PH.D., DABTENVIRONMENTAL AND REGULATORY RESOURCES

ISRTP WORKSHOPDECEMBER 13, 2010

EDSP Test Guidelines and Guideline Modifications

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Courtesy of Tim Ward-ABC Laboratories

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890 Series In Vitro Screens

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Tier 1 Assay Guideline Purpose

Estrogen Receptor (ER) Binding Assay

USEPA 890.1250 An ER binding assay that utilizes rat uterine cytosol to examine the ability of a test chemical to bind with estrogen receptors

Estrogen Receptor Transcriptional Activation Assay

USEPA 890.1300OECD 455

An second type of ER binding assay that uses a human cell line to examine the ability of a test chemical to bind with estrogen receptors and alter gene transcription

Androgen Receptor (AR) Binding Assay

USEPA 890.1150 An AR binding assay that utilizes rat prostate cytosol to examine the ability of a test chemical to bind with androgen receptors

Aromatase Assay USEPA 890.1200 Aromatase is an enzyme complex responsible for estrogen biosynthesis that converts androgens into estrogens, estradiol, and estrone. The Aromatase in vitro assay uses a human recombinant form of the protein and focuses on this portion of the steroidogenic pathway to detect substances that inhibit aromatase activity.

Steroidogenesis Assay USEPA 890.1550 The Steroidogenesis in vitro assay utilizes the H295R human adrenocortical carcinoma cell line to detect interference with the body’s production of male and female steroid sex hormones (estrogen and testosterone).

890 Series In Vivo Screens

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Tier 1 Assay Guideline Purpose

Uterotrophic Assay USEPA 890.1600OECD 440

Ovariectomised or immature female rats are used to screen for estrogenic effects by measuring uterine weight changes.

Hershberger Assay USEPA 890.1400OECD 441

Designed to detect chemicals that are androgenic, anti-androgenic or inhibit 5α-reductase. Accessory sex gland weights, including several androgen-dependent tissues, are measured in castrated or immature male rats

Male Pubertal Assay USEPA 890.1500 Androgenic, anti-androgenic, and thyroid activity is screened in male rats during sexual maturation. Abnormalities associated with sex organs and puberty markers, as well as thyroid tissue are examined.

Female Pubertal Assay USEPA 890.1450 Estrogenic and thyroid activity is screened in female rats during sexual maturation. This assay examines abnormalities associated with sex organs and puberty markers, as well as thyroid tissue.

Fish Short-Term Reproduction Assay

USEPA 890.1350OECD 229

Screens for estrogenic and androgenic effects. The assay examines abnormalities associated with survival, reproductive behavior, secondary sex characteristics, histopathology, and fecundity (i.e., number of spawns, number of eggs/spawn, fertility, and development of offspring) of fish exposed to test chemicals.

Amphibian Metamorphosis Assay

USEPA 890.1100OECD 231

Involves the use of tadpoles to determine if chemicals affect the thyroid during metamorphosis and consequently result in developmental effects.

Test Order Restriction

Requirement to perform screens according to 890 series guideline

“…you may not deviate from an approved testing protocol unless you first consult with the Agency and obtain Agency approval of any planned deviation.”

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General and Specific Guideline Issues

• Primarily hitting the high points of some of the screens today

• For more information please see the Test Guideline comments sent by the EPF in the EPA docket:

EPA-HQ-OPP-2009-0634-0135

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General Guideline Issues

*No public review of guidelines prior to publication

• Very prescriptive and inflexible

• Test validity criteria too stringent

• Sensitivity and specificity issues

• Typographical errors

• No standard evaluation procedures

• No defined Weight of Evidence Procedures for the battery

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ER and AR Binding Assays

Shortcomings No metabolic capability Impacted by pH, denaturation, precipitates and

particulates Cannot distinguish agonists/antagonists

Validation and Guideline Issues Inconsistency in rat uterine cytosol preparation Inconsistency in cytosolic prostate gland preparation Numerous typographical errors

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ER Transcriptional Activation

Shortcomings No metabolic capability

Validation and Guideline Issues Only validated for ER agonists Limited validation and false positive rate high EPA’s recommendation for positive response

(PC10) deviates from peer review recommendation

EPA’s acceptable lower level of dynamic range of 4-fold induction raises issue of distinguishing from background noise

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Aromatase (Human Recombinant)

Shortcomings No metabolic capability Impacted by denaturation of protein

Validation and Guideline Issues Limited validation Numerous typographical errors

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Steroidogenesis (Human Cell Line)

• Shortcomings Cytotoxicity confounds results Presence of any detergent residue on glassware

can confound assay results

• Validation and Guideline Issues High variability between laboratories during

validation make the results difficult to interpret The guideline is poorly organized with no stated

purpose – more of a protocol than guidance Very small pipetting volumes could lead to errors Parallel evaluation of cytotoxicity needed.

Guideline permits up to 20% cytotoxicity while ICCVAM recommended only 10%

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Uterotrophic

• Shortcomings Route of administration and animal model

compared to relevance

• Validation and Guideline Issues While there are references to the anti-

estrogenic component of the study, there has been no validation of this and anti-estrogenicity should not be assessed

Dose route and animal model preferences not harmonized with OECD - environmental relevance and metabolism should be considered

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Hershberger

• Validation and Guideline Issues Wide inter-laboratory variation in the mean age at

which preputial separation occurs Clarity needed for the interpretation of study with and

without optional endpoints EPA recommends use of multivariate analyses of all

accessory sex organ weights in cases where only a single tissue gives a significant response; such post-hoc analyses are useful for hypothesis generation, but should not be used in hypothesis testing

Anesthetic agent and euthanizing method should be chosen carefully to avoid artifacts if performing optional steroid measurement

CV’s for control and high dose organ weights should be reported. Deviation of more than 3 could result in study rejection

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Pubertals

• Shortcomings High sensitivity but low specificity Apical endpoints provide only limited information

on the mode of action for potential endocrine-active chemicals

Significant inherent biological variability in the endpoints (puberty onset, estrous cycle, organ weights) complicates interpretation

• Validation and Guideline Issues Validation studies did not demonstrate a

negative response using a true negative control agent

Dose selection is critical to avoid non-specific outcomes

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Amphibian Metamorphosis

• Shortcomings Apical endpoints with unknown specificity Poorly soluble or unstable compounds difficult

to test Not a short screen

• Validation and Guideline Issues No known negative compounds Dose setting guidance needed Background levels of iodide in food and water

may make comparison between labs difficult Developmental staging

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Fish Short-Term Reproduction

• Shortcomings Multiple modes of action detected – apical

endpoints Medium sensitivity, low specificity Long and expensive “screen”

• Validation and Guideline Issues High variability observed in plasma sex steroids

suggests they are not particularly robust endpoints Statistical power of the fecundity endpoint is low Limited quantities of blood plasma may require

prioritization of most robust measurements, such as vitellogenin, rather than sex steroids

Dose setting is critical to avoid confusing systemic toxicity with genuine endocrine-mediated effects

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Sensitivity and Specificity

The Series 890.1350 TG (fish assay) states:

"It is recognized that some endpoints may be responsive to nonendocrine stresses in addition to endocrine-mediated pathways, particularly fecundity. Although reductions in fecundity indicate adverse organismal and, potentially, population level effects (i.e., reproductive toxicity), these cannot be definitively distinguished from direct endocrine-mediated effects by this assay when changes in other core endpoints are not present. Nevertheless, reductions in fecundity are considered a positive effect in this assay because they may be endocrine-mediated ..."

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Staging the Conduct of the Screens

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Summary

• The current US EPA EDSP falls short in meeting many of the attributes of an efficient and effective screening program. Many of the assays are not mechanistic, and some

have yet to be shown to meet the basic requirement of distinguishing an endocrine active substance from a negative control or differentiating potential endocrine-mediated responses from responses via other modes of action (e.g. hepatotoxicity) or systemic toxicity.

The prescriptive nature of the guidelines combined with typographical errors, overly conservative validity criteria, and inflexible test order requirements likely mandate protocol approval prior to conducting the tier 1 battery

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Summary-cont.

• A staged approach to the performance of the screens may improve the interpretability of the results, increasing the efficiency of the work and clarity of the results. Efficiency and clarity are essential because

interpretation of the entire battery is the determinant for proceeding to Tier 2.

• While staging the EDSP ESB may improve interpretation as to whether a substance may interact with components of the estrogen, androgen, and thyroid hormone systems, such activities cannot overcome inherent limitations of the tier 1 screens.

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• EPA EDSP ESB Test Guidelines can be accessed at http://www.epa.gov/ocspp/pubs/frs/publications/Test_Guidelines/series890.htm

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