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TestSmart Endocrine Disruptors
February 25-26
Hyatt Fair Lakes Hotel
12777 Fair Lakes Circle
Fairfax, VA
Program Committee:
Richard A. Becker, American Chemistry Council
Alan M. Goldberg, Johns Hopkins University
Pamela J. Lein, Johns Hopkins University
Ellen K. Silbergeld, Johns Hopkins University
Gary Timm, US Environmental Protection Agency
James D. Yager, Johns Hopkins University
Proceedings for TestSmart -- Endocrine Disruptors
Progress in Implementing the U.S. Endocrine Disruptor Screening Program
Gary E. Timm
Office of Science Coordination and Policy, U.S. Environmental Protection Agency
U.S. Endocrine Disruptor - Screening Program
- Required by the Food Quality Protection Act of 1996
- Screen pesticides for estrogenic effects that may affect human health
- Use appropriate validated test systems or other scientifically relevant information
- EPA can require screening and testing of:
- Certain drinking water contaminants
- Other endocrine effects
- Other chemicals
Scope of EPA'S Endocrine Disruptor Screening Program
- Based on current science, the scope of the screening program includes:
- Estrogen, Androgen and Thyroid hormones
- Human health and ecological effects
- Broad range of chemicals and mixtures
The Universe of Chemicals
- Chemicals Under EPA's Purview
- 950 pesticide active ingredients
- 2500 "inerts" in 20,500 products
- 75,500 industrial chemicals on the TSCA inventory
- environmental contaminants (?)
- Chemicals Under Other's Purview
- cosmetics
- food additives
- nutritional supplements
Framework
- Initial Sorting
- Priority Setting
- Screening (Tier 1)
- Identifies substances for further testing
- Testing (Tier 2)
- Identifies adverse effects and establishes dose-response relationship for hazard assessment
Tier 1 Screening - Interaction with endocrine system.
- Screens should be
- inexpensive, quick, simple
- standardized and validated
- more sensitive than specific
- able to detect multiple endpoints
- readily interpretable
- Use information to
- make initial judgments
- direct and focus tier 2 tests
Modes of Action
- Hormone synthesis and clearance
- Hormone storage and release
- Hormone transport
- Receptor binding
- Altered post-receptor activation
Proposed Screen Battery (Tier 1)
- In vitro Screens
- ER Binding/Reporter Gene Assay
- AR Binding/Reporter Gene Assay
- Steroidogenesis Assay with minced testis
- In vivo Screens
- Rodent 3-day Uterotrophic Assay (sc)
- Rodent 20-day Pubertal Female Assay with Thyroid
- Rodent 5-7 day Hershberger Assay
- Frog Metamorphosis Assay
- Fish Reproduction Screening Assay
Alternate Screening Assays
- Rodent 20-day Pubertal Male Assay with Thyroid
- Placental aromatase
- 15-day Adult Male Assay
- Rodent in utero through Lactation Assay
Validation Process
- Method Development
- Pre-validation
- Demonstration of relevance
- Standardization of protocol
- Validation in multiple laboratories
- Scientific Peer Review
- Regulatory acceptance and implementation
Work to date: Tier 1 assays
| Detailed Review Paper | Pre-validation | Validation | |
| ER/AR binding | in progress | in progress | in progress |
| Uterotrophic* | completed | completed | completed |
| Hershberger* | completed | completed | |
| Pubertals | in progress | in progress | |
| Frog metamorphosis | in progress | in progress | |
| Fish repro screen* | in progress | in progress | |
| Steroidogenesis | in progress | ||
| Aromatase | in progress |
*OECD
Tier 2 Testing - Confirm and Characterize Endocrine Effects
- Tests should
- if found, determine if effects are a primary or secondary disturbance of endocrine function
- establish exposure/concentrations/timing and effects relationships
- be sensitive and specific
- assess relevant endpoints
- include life cycle of live-bearing and egg-laying species
- include a dose range for full characterization of effects
- be conducted in accordance with GLP
- be validated
Proposed Tier 2 Testing Battery
- Multigeneration reproduction and development studies
- Rodents
- Birds
- Frogs
- Fish
- Shrimp
Work to date: Tier 2 assays
| Detailed Review Paper | Pre-validation | Validation | |
| Mammalian 2-gen* | in progress | ||
| Avian 2-gen* | in progress | in progress | |
| Amphibian chronic* | |||
| Invertebrate chronic | in progress | in progress | |
| Fish chronic* | in progress | ||
| In utero/lactation | in progress |
*OECD
U.S. EPA Timeline
| 2000 | 2001 | 2002 | 2003 | 2004 | 2005 |
| Priority Setting | |||||
| Tier I Validation | |||||
| Tier II Validation | |||||
| Screening 1st chemicals | |||||
EPA Priorities
- Develop and validate Tier 1 "first generation" screens
- Develop QSAR pre-screening tools
- Develop and validate Tier 2 tests
- Identify and develop "second generation" screen technologies
Additional Priority Setting Tools
- AR receptor binding QSAR
- ER AR reporter gene assays
- QSARS for aromatase
- QSARs for steroidogenesis
Candidates for Second Generation Screens
- Cell based assay systems for aromatase
- Cell based assay systems for steroidogeneisis
- Gene expression assays for ER and AR to replace uterotrophic and Hershberger
- Additional mode of action based in vitro assays
Technology Challenge Program
- Purpose: To identify alternative screening technologies for development and validation
- Design:
- Solicit proposals
- Sponsor demonstration of promising technologies
- Award contract for further development of winners
Conclusions
- Only a small subset of the universe of chemicals will be tested in Tier 1 screens
- First generation Tier 1 assays will be a mixture of in vitro and in vivo assays
- A key goal of the EDSP is to move toward computer technology and mechanistic in vitro assays