Hans-Joerg Martus

Interlaboratory Evaluation of Genomic Signatures for Predicting Carcinogenicity in the Rat

The Critical Path Institute recently established the Predictive Safety Testing Consortium, a collaboration between several companies and the U.S. Food and Drug Administration, aimed at evaluating and qualifying biomarkers for a variety of toxicological endpoints. The Carcinogenicity Working Group of the Predictive Safety Testing Consortium has concentrated on sharing data to test the predictivity of two published hepatic gene expression signatures, including the signature by Fielden et al. (2007, Toxicol. Sci. 99, 90-100) for predicting nongenotoxic hepatocarcinogens, and the signature by Nie et al. (2006, Mol. Carcinog. 45, 914-933) for predicting nongenotoxic carcinogens. Although not a rigorous prospective validation exercise, the consortium approach created an opportunity to perform a meta-analysis to evaluate microarray data from short-term rat studies on over 150 compounds. Despite significant differences in study designs and microarray platforms between laboratories, the signatures proved to be relatively robust and more accurate than expected by chance. The accuracy of the Fielden et al. signature was between 63 and 69%, whereas the accuracy of the Nie et al. signature was between 55 and 64%. As expected, the predictivity was reduced relative to internal validation estimates reported under identical test conditions. Although the signatures were not deemed suitable for use in regulatory decision making, they were deemed worthwhile in the early assessment of drugs to aid decision making in drug development. These results have prompted additional efforts to rederive and evaluate a QPCR-based signature using these samples. When combined with a standardized test procedure and prospective interlaboratory validation, the accuracy and potential utility in preclinical applications can be ascertained.

Compilation and use of genetic toxicity historical control data.

The optimal use of historical control data for the interpretation of genotoxicity results was discussed at the 2009 International Workshop on Genotoxicity Testing (IWGT) in Basel, Switzerland. The historical control working group focused mainly on negative control data although positive control data were also considered to be important. Historical control data are typically used for comparison with the concurrent control data as part of the assay acceptance criteria. Historical control data are also important for providing evidence of the technical competence and familiarization of the assay at any given laboratory. Moreover, historical control data are increasingly being used to aid in the interpretation of genetic toxicity assay results. The objective of the working group was to provide generic advice for historical control data that could be applied to all assays rather than to give assay-specific recommendations. In brief, the recommendations include:

Derisking Drug-Induced Carcinogenicity for Novel Therapeutics

Assessing the carcinogenic potential of innovative drugs spanning diverse therapeutic modalities and target biology represents a major challenge during drug development. Novel modalities, such as cell and gene therapies that involve intrinsic genetic modification of the host genome, require distinct approaches for identification of cancer hazard. We emphasize the need for customized weight-of-evidence cancer risk assessments based on mode of action that balance multiple options for preclinical identification of cancer hazard with appropriate labeling of clinical products and risk management plans. We review how advances in molecular carcinogenesis can enhance mechanistic interpretation and preclinical indicators of neoplasia, and recommend that drug targets be systematically assessed for potential association with tumorigenic phenotypes via genetic models and cancer genome resources.

Summary of major conclusions from the 6th International Workshop on Genotoxicity Testing (IWGT), Foz do Iguaçu, Brazil.

a Novartis Institutes for BioMedical Research, Preclinical Safety, 4002 Basel, Switzerland b Public Interest Incorporated Foundation BioSafety Research Center, Iwata, Japan c National Institute of Health Sciences, Division of Genetics & Mutagenesis, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan d Federal Institute for Drugs and Medical Devices (BfArM), Bonn, Germany e Exponent, Inc., Center for Toxicology & Mechanistic Biology, Midland, MI 48640, USA f Pharmaceutical Sciences, Roche Innovation Center, F Hoffmann-La Roche AG, CH 4070 Basel, Switzerland g Office of Science Policy, Office of Research and Development, U.S. Environmental Protection Agency, Room 51134 RRB, 1200 Pennsylvania Avenue NW (8104R), Washington DC 20460-0001, USA h Safety Research Laboratories, Mitsubishi Tanabe Pharma Co., Chiba 292-0818, Japan i Kirkland Consulting, PO Box 79, Tadcaster LS24 0AS, UK

Evaluation of methyl methanesulfonate, 2,6-diaminotoluene and 5-fluorouracil: Part of the Japanese center for the validation of alternative methods (JaCVAM) international validation study of the in vivo rat alkaline comet assay

As a part of the Japanese Center for the Validation of Alternative Methods (JaCVAM)-initiative international validation study of the in vivo rat alkaline comet assay (comet assay), we examined methyl methanesulfonate, 2,6-diaminotoluene, and 5-fluorouracil under coded test conditions. Rats were treated orally with the maximum tolerated dose (MTD) and two additional descending doses of the respective compounds. In the MMS treated groups liver and stomach showed significantly elevated DNA damage at each dose level and a significant dose-response relationship. 2,6-diaminotoluene induced significantly elevated DNA damage in the liver at each dose and a statistically significant dose-response relationship whereas no DNA damage was obtained in the stomach. 5-fluorouracil did not induce DNA damage in either liver or stomach.

Setting Occupational Exposure Limits for Genotoxic Substances in the Pharmaceutical Industry.

In the pharmaceutical industry, genotoxic drug substances are developed for life-threatening indications such as cancer. Healthy employees handle these substances during research, development, and manufacturing; therefore, safe handling of genotoxic substances is essential. When an adequate preclinical dataset is available, a risk-based decision related to exposure controls for manufacturing is made following a determination of safe health-based limits, such as an occupational exposure limit (OEL). OELs are calculated for substances based on a threshold dose-response once a threshold is identified. In this review, we present examples of genotoxic mechanisms where thresholds can be demonstrated and OELs can be calculated, including a holistic toxicity assessment. We also propose a novel approach for inhalation Threshold of Toxicological Concern (TTC) limit for genotoxic substances in cases where the database is not adequate to determine a threshold.