Karen Hamernik

Meeting report: Validation of toxicogenomics-based test systems: ECVAM-ICCVAM/NICEATM considerations for regulatory use

This is the report of the first workshop “Validation of Toxicogenomics-Based Test Systems” held 11–12 December 2003 in Ispra, Italy. The workshop was hosted by the European Centre for the Validation of Alternative Methods (ECVAM) and organized jointly by ECVAM, the U.S. Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM), and the National Toxicology Program (NTP) Interagency Center for the Evaluation of Alternative Toxicological Methods (NICEATM). The primary aim of the workshop was for participants to discuss and define principles applicable to the validation of toxicogenomics platforms as well as validation of specific toxicologic test methods that incorporate toxicogenomics technologies. The workshop was viewed as an opportunity for initiating a dialogue between technologic experts, regulators, and the principal validation bodies and for identifying those factors to which the validation process would be applicable. It was felt that to do so now, as the technology is evolving and associated challenges are identified, would be a basis for the future validation of the technology when it reaches the appropriate stage. Because of the complexity of the issue, different aspects of the validation of toxicogenomics-based test methods were covered. The three focus areas include a) biologic validation of toxicogenomics-based test methods for regulatory decision making, b) technical and bioinformatics aspects related to validation, and c) validation issues as they relate to regulatory acceptance and use of toxicogenomics-based test methods. In this report we summarize the discussions and describe in detail the recommendations for future direction and priorities.

Evaluation of the carcinogenic potential of pesticides. 2. Methidathion.

The carcinogen potential of methidathion, a dimethoxyorganic phosphorus pesticide and cholinesterase inhibitor, was evaluated by the Health Effects Division of the Office of Pesticide Programs using a consensus peer review process and the EPAs guidelines for risk assessment. Methidathion was categorized as a Group C (possible human) carcinogen based upon evidence of an increased incidence of benign and malignant hepatocellular tumors, alone and in combination, in a single study involving male Chr-CD-1 mice. The compound was not carcinogenic in female Chr-CD-1 mice in the same study or in Sprague-Dawley rats of either sex in a second study. Methidathion was not genotoxic in a variety of in vitro or in vivo tests designed to detect DNA damage, chromosome aberrations, gene mutations, and sister chromatid exchange. Although methidathion was identified as being structurally similar to two other organophosphate insecticides, prothidathion and lythidathion, no toxicological data were available on either of these agents for comparative purposes. The biological information on methidathion was reviewed by the agencys FIFRA Scientific Advisory Panel who agreed with the category C designation for methidathion. The data were not found to be sufficient to quantify human risk to methidathion.

Evaluation of the carcinogenic potential of pesticides: 1. Acifluorfen

The Health Effects Division of the Office of Pesticide Programs evaluates the carcinogenic properties of pesticides by a consensus peer review process in which all available biological information on a compound is evaluated according to EPAs guidelines for cancer risk assessment. In many cases, pesticides are also evaluated by an external group of accomplished scientists who comprise the Agencys Scientific Advisory Panel. The herbicide acifluorfen was evaluated by these processes and was classified as a Category B2 (probable human) carcinogen based upon evidence of an increased incidence of malignant, or combined benign and malignant, tumors in multiple experiments involving two different strains of mice. The compound produced benign and malignant liver tumors in male and female B6C3F1 mice and in female CD1 mice. Stomach papillomas were also observed in male and female B6C3F1 mice. Acifluorfen was mutagenic in bacteria and yeast, but not in mammalian cell systems. In addition, acifluorfen is structurally related to eight other diphenyl ether pesticides, all of which evoke liver tumours in mice or rats. The data were found to be sufficient to quantify human risk to acifluorfen.

Evaluation of the carcinogenic potential of pesticides: 3. Aliette

Aliette, a fungicide compound, was evaluated for carcinogenic potential by the Health Effects Division of the Office of Pesticide Programs using a consensus peer review process and EPAs guidelines for risk assessment. Aliette was categorized as a group C (possible human) carcinogen based upon evidence of an increased incidence of combined benign and malignant urinary bladder tumors in a single study involving male Charles River (CR) CD rats. The bladder tumors occurred only at the unusually high top dose level of aliette that was tested (40,000/30,000 ppm). The compound was not carcinogenic in female CR-CD rats in the same study, or in CD-1 mice of either sex in a second study. Monosodium phosphite, the main urinary metabolite of aliette, was also not carcinogenic in male or female CR-CD rats. Aliette was not demonstrated to be genotoxic. No structural analogues of aliette were identified. The mechanism of action for the production of bladder tumors was not identified; however, it did not appear to involve a genotoxic effect, a carcinogenic effect of metabolites, or the formation of renal stones. The data were not found to be sufficient to quantify human cancer risk from aliette.

General process for the risk assessment of pesticides that interact with or affect the endocrine system

The U.S. Environmental Protection Agencys Office of Pesticide Programs evaluates human health risk associated with exposure to pesticide chemicals. Chemical hazard and exposure assessment are components of the risk assessment process. For the risk assessment of single chemical conventional-type pesticides, there may be multiple exposure scenarios depending on the use pattern. Examples include acute and chronic dietary, and short-, intermediate-, and long-term occupational/residential exposures. For hazard assessment, available toxicity data and a weight-of the-evidence approach are used in the process of selecting appropriate toxicity endpoints for relevant exposure scenarios. The pesticide registration process requires that certain types of supporting toxicity data be submitted by the registrant depending in part on the chemical use pattern (e.g., food use). Types of toxicity data that might be submitted and used in hazard assessment include acute, subchronic, chronic, carcinogenicity, mutagenicity, metabolism, reproduction, developmental, neurotoxicity, and mechanistic studies. There may be data from multiple exposure routes (e.g., oral, dermal, inhalation) and from the scientific literature to consider. Dose-response information is also taken into account. In endpoint selection for a chemical, endocrine system-related effect(s) and dose-response relationship(s) are assessed in context of other types of effects, toxicities, and dose-response relationships noted. Endocrine system-related endpoints may include frank effects (e.g., endocrine organ hyperplasia or cancer) or precursor events (blood hormone level elevations). Endocrine system-related endpoints are generally treated like other cancer or non-cancer toxicity endpoints (e.g., hepatic cancer, neurotoxicity) in the risk assessment process. For chemicals with evidence of endocrine system interaction(s), an endocrine system-related effect may or may not be the most sensitive or relevant endpoint for a particular risk assessment exposure scenario. Some chemical examples will be presented. In the final risk assessment, hazard assessment information is integrated with exposure information. The assessment may be adjusted, at some point, for uncertainties in hazard or exposure data. An aggregate risk assessment, in which multiple sources or routes of exposure are considered, is typically performed for occupational and residential exposure scenarios. A cumulative risk assessment may be considered for groups of chemicals with a common mechanism of toxicity.