# Presentation: 181570

## Criteria for Screens— Review of the EDSTAC Recommendations

- Presentation to the EDMVS
- July 23, 2002

## Purpose of Tier 1

- To distinguish chemical substances that interact with the endocrine system from those that do not.
- Upon completion of Tier 1 EPA and stakeholders should be able to accept the assignment that a chemical has (1) either low or no potential for EAT activity, (2) or that it has such potential.

## EDSTAC Criteria for Screens

- Detect all known modes of action for the endocrine endpoints of concern
- Include sufficient diversity among endpoints, permitting weight-of-evidence conclusions
- Maximize sensitivity to minimize false negatives
- Include a sufficient range of taxonomic groups among the test organisms to represent differences in endocrine system and metabolism
- Relatively fast and efficient

## Advantages of In Vitro Assays

- Sensitivity to low concentrations
- High specificity of response
- Low cost
- Small amount of chemical required
- Assays can be automated for high throughput
- Results can be used in conjunction with QSAR models
- Can be used for complex mixtures
- Reduces or replaces animal use

## Advantages of In Vivo Assays

- Account for absorption, distribution, metabolism and excretion
- Evaluate a broad range of mechanisms
- Provide a comprehensive evaluation of the whole endocrine system as a unit
- Generally well-accepted methods in toxicity testing
- Some endpoints are toxicologically relevant and have been used in hazard assessment
- Give comparative perspective to other endpoints of toxicity

## Meeting the Screening Criteria

- Detect all known modes of action for the endocrine endpoints of concern
- Simple mechanistic screens do not exist for all modes of action, therefore it is necessary to include more complex multi-modal assays in tier
- Include sufficient diversity among endpoints, permitting weight-of-evidence conclusions
- Multiple endpoints in in vivo assays
- Redundancy among endpoints across assays

## Meeting the Screening Criteria

- Maximize sensitivity to minimize false negatives
- In vitro mechanistic screens are  highly sensitive
- Include a sufficient range of taxonomic groups among the test organisms to represent differences in endocrine system and metabolism
- Include in vivo assay for fish; fish have different hormones; opposite end of vertebrate phylogeny
- Relatively fast and efficient
- Maximize use of in vitro assays

## Screens vs. Biological Activity

|  | E | E- | A | A- | T | SSI | AI | 5a | HPG |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| ER Binding | X | X |  |  |  |  |  |  |  |
| AR Binding |  |  | X | X |  |  |  |  |  |
| Steroidogen |  |  |  |  |  | X |  |  |  |
| Aromatase |  |  |  |  |  |  | X |  |  |
| Uterotrophic | X | X |  |  |  |  |  |  |  |
| Pubertal fem | X | X |  |  | X | X | X |  | X |
| Hershberger |  |  | X | X |  |  |  |  | LH |
| Pubertal male | X |  |  | X | X | X |  | X | X |
| Adult male | X |  |  | X | X | X | (X) | X | X |
| Fish Reproductive | X | X | X | X | ? | X | X |  | X |
| Frog Thyroid |  |  |  |  | X |  |  |  |  |

## Weighing the Evidence

*In vitro* assays cannot be gatekeepers
*In vitro* assays that assess activity with and without metabolic activation are worth more than those without
- Results from *in vivo* assays have more weight than in vitro assays
- Results from apical *in vivo* assays are worth more than results from specific *in vivo* assays

## Conclusions

- No single assay can, at this time, meet all of the criteria for a Tier 1 screen;
- Therefore, a battery approach must be taken.
- The battery to be efficient should consist of both *in vitro* and *in vivo* assays.