The Future of Chemical Toxicity Testing in the U.S.

1. The Future of Chemical Toxicity Testing in the U.S. Toxicity Testing in the 21st Century June 21, 2010 David Jacobson-Kram, Ph.D., DABT Office of New Drugs, CDER, FDA

2. Risk Assessment: Pharmaceuticals vs. Environmental Contaminants • Pharmaceuticals are designed to have beneficial health effects, risk versus benefit weighed. Environmental contaminants present only risk to exposed individual. • Drugs are taken at pharmacologic doses, exposure to pollutants generally at subpharmacologic doses. • EPA performs quantitative risk assessments to determine safe or acceptable exposure levels, FDA either approves or does not approve a drug. Safety data provided in label.

3. FDA has data that can facilitate extrapolation to human toxicity Toxicity in cultured cells Toxicity in intact animals Toxicity in humans

4. A Proposed Vision on the Future of Carcinogenicity Testing • FDA is completely committed to the “3Rs”. • All ICH safety guidelines have 3R considerations as a top priority. • We are making progress in the short term and dramatic changes in the not too distant future. • Current focus is carcinogenicity studies.

5. The Perfect Carcinogenicity Test Would: • identify all materials that could potentially induce cancer in human beings. • have 100% sensitivity (no false negatives) and 100% specificity (no false positives). • rank carcinogens in order of potency. • identify target organs/tissues and types of tumors,e.g. small cell carcinoma of the lung vs. squamous cell carcinoma of the skin. • provide results rapidly and at low cost.

6. State of the art: 2-year carcinogenicity studies in rodents • Protracted, 2-year in-life, 3 month preliminary dose-range finding studies, 4 - 6 month post-life, 3+ years to get answer. • Expensive, depending on route of exposure, can cost from one to several million dollars. • Hazard assessment is imperfect. While most human carcinogens are identified by this assay, many false positives are suspected, especially those that induce tumors in only one species, one sex and/or one site. • Quantitative risk assessments tend to exaggerate risks to humans. • Many animals are required. Typically, 50+/sex/dose plus vehicle controls. More animals for TK • Positive data provide little or no mechanistic information about the material.

7. Near-term future of carcinogenicity testing • Carcinogenicity battery: • Negative genetox battery • Negative 6-month transgenic mouse • Lack of preneoplastic lesions and lack of hormonal perturbation in rat chronic study • Negative in silico prediction • Two year studies not required

8. How can the “omics” revolution help risk assessment for cancer • Shorten time required to determine if drug or a chemical is potentially carcinogenic • Lower cost of testing will allow more compounds to be tested • Improve extrapolation of animal data to humans • Improve extrapolation from experimental high dose to human exposure dose • Reduce animal usage • Provide insight into mechanisms of action

9. Research Objectives of the Carcinogenicity Working Group • Short Term Objectives: • Identify and evaluate the utility of genomic biomarkers to provide an early prediction of carcinogenicity, especially by non-genotoxic compounds • Develop an assay platform and test protocol to enable the early prediction and mechanistic assessment of carcinogens • Long Term Objectives: • Determine if genomic data combined with other sub-chronic/chronic toxicity endpoints can reduce the reliance on life-time rodent cancer bioassays • - see Jacobson-Kram (2008) Vet Pathol 45:707

10. Predictive Toxicogenomics Approaches Reveal Underlying Molecular Mechanisms of Nongenotoxic CarcinogenicityNie et al. Molec. Carc. 45:914, 2006 • Examined over 100 “paradigm compounds” to develop signature for nongenotoxic carcinogens. • Male rats given a single high dose (30 to 50% of published LD50) of each chemical and the livers were removed 24 hrs after dosing. • A training set consisting of 24 nongenotoxic carcinogens and 28 noncarcinogens was used to identify a six gene signature which identified nongenotoxic carcinogens with an accuracy of 88%. • This was the case whether or not the liver was the ultimate target organ.

11. A Gene Expression Biomarker Provides Early Prediction and Mechanistic Assessment of Hepatic Tumor Induction by Nongenotoxic ChemicalsFielden, et al.Tox. Sci. 99 90-100, 2007 • Rats treated for 5 days with one of 100 structurally and mechanistically diverse nongenotoxic hepatocarcinogens and nonhepatocarcinogens • Novel multigenebiomarker (i.e., signature) was derived to predict the likelihood of nongenotoxic chemicals to induce liver tumors in longer term studies • Independent validation of the signature on 47 test chemicals indicates an assay sensitivity and specificity of 86% and 81%, respectively • Not too bad!

12. Outcome of Interlaboratory Evaluation

13. Interlaboratory Evaluation of Genomic Signatures for Predicting Carcinogenicity in the RatFielden et al., Tox. Sci. 103:28, 2008 • Examined data from short term rat studies on over 150 compounds • Merged data sets indicated that the accuracy of the Fielden et al. and Nie et al. signatures was approximately 65% and 60%, respectively • Differences in study design and different microarray platforms resulted in reduced predictivity relative to internal validation estimates reported in the individual studies

14. Conclusions • Current tools for cancer hazard and risk assessment are imperfect. • In the near term reduce dependence on two-year carcinogenicity studies using “battery” approach. • In the longer term omics technology may provide faster and mechanistically-based risk assessments.