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

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.

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

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.

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.

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.

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

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

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

Predictive Toxicogenomics Approaches Reveal Underlying Molecular Mechanisms of Nongenotoxic Carcinogenicity Nie 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.

A Gene Expression Biomarker Provides Early Prediction and Mechanistic Assessment of Hepatic Tumor Induction by Nongenotoxic Chemicals Fielden, 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!

Outcome of Interlaboratory Evaluation

Interlaboratory Evaluation of Genomic Signatures for Predicting Carcinogenicity in the Rat Fielden 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

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.