## Use of “Omic” Technology to Inform

the Risk Assessment Nancy McCarroll Health Effects Division/ Office of Pesticide Programs, U.S. Environmental Protection

Agency & Stephen Nesnow, Ph.D. National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental

Protection Agency May 24, 2011

# Introduction

• Goal: To set the stage for the 

## toxicogenomic investigations conducted by NHEERL, ORD • General background information: • Toxicogenomics • MOA/AOP • Case Study

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### IATA Strategy: Use of Computational and

Molecular Tools: Toxicogenomics

• Scientific field that examines apical endpoints from classical toxicology studies and combines them with information about gene, protein, and/or endogenous metabolite levels within particular cells, tissues, or organisms in response to a toxic substance. • “Omics” is the general term that is applied to other molecular profiling data generated from: • Genomics - global analysis of gene expression • Proteomics - global analysis of proteins ( i.e., gene product) • Metabolomics - global analysis of endogenous metabolites • Bioinformatics – Collection, interpretation & storage of data from the above areas of “omics” 3

### IATA Strategy: Use of Computational and

Molecular Tools: Toxicogenomics

• Ideally suited for MOA/AOP analysis (NAS, 2007) • Allows a more comprehensive understanding of the progression of an adverse effect starting with a molecular initiating event ( initial point of chemical biological interaction with the organism that initiates the AOP). • More mechanistic approach • Other events that occur along the pathway that lead to the adverse outcome are termed intermediate key events. • MOA analysis not limited to cancer risk assessment; can also be applied to non -cancer endpoints. 4

## Mode of Action Framework

• Hypothesis Based Weight of Evidence Approach



## International Framework  Introduced by USEPA & IPCS (1999, 2001)  ILSI and IPCS expands work (2003, 2006, 2008) 

###  IPCS continues works to update (ongoing) •Based on Bradford Hill Considerations for Causality (e.g., temporal & dose response concordance, biological plausibility, etc) •Distinguishes MoA vs Mechanism •Describes Human Relevance (Concordance) Analysis 5MOA Framework: Plausible Hypothesis Detailed Molecular Description 

## Mode vs. Mechanism Key event : • Critical • Measurable MoA: Not every step in the process, but the key events that are likely to “drive” the process. 6IATA Strategy: Use of Computational and

Molecular Tools: MOA Framework 

## • Begins with a brief description of the 

## postulated MOA • Provides data to support the key events 

## • Explains the sequence of key events that lead to the tumor response with respect to: 

## • Dose- response & • Temporal relationships • Analyzes alternative MOAs & human relevance 7

## Case Study: Propiconazole

• Reasons for Selection of Propiconazole as 

### the Model Compound: • Exceptionally rich database • Some information on a MoA, based on apical endpoint data • Belongs to a class of chemical (conazoles) 

### for which OPP has voluminous data.

• The regulatory status of this chemical in not 

### the focus of this effort. 8

## Case Study: Propiconazole • Conazole, antifungal pesticide 

## • Mechanism of antifungal activity: inhibition of CYP51 protein, ergosterol. 

## Steroid necessary for the fungal cell wall • Inhibits CYP isoforms • Induces liver tumors in male mice • Not mutagenic in conventional Genetic 

## Toxicology test battery 9Apical based MOA for Propiconazole

Increase Liver Tumors Increased Liver/body weight Induce Cyp2b protein and increased PROD activity Increase cell proliferation Hypertrophy

10Bradford Hill Considerations for Causal Relationships:

Propiconazole Mouse Oral Ingestion Studies

Key Event/ppm 1 day 4 day 14 day 4 wk 13 wk 100 wk Increased cell proliferation 850 X X 2500 X X

Increased PROD activity 850 X 2500 X

I ncreased liver hypertrophy 850 X 2500 X

Increased liver weight 2500 X

Adenomas & carcinomas 2500 X DOSE RESPONSE TEMPORAL ASSOCIATIONS

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