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Transcriptional Biomarkers to Predict Female Mouse Lung Tumors in Rodent Cancer Bioassays - A 26 Chemical Set

ABSTRACT: The process for evaluating chemical safety is inefficient, costly, and animal intensive. There is growing consensus that the current process of safety testing needs to be significantly altered to improve efficiency and reduce the number of untested chemicals. In this study, the use of short-term gene expression profiles was evaluated for predicting the increased incidence of mouse lung tumors. Animals were exposed to a total of 26 diverse chemicals with matched vehicle controls over a period of three years. Upon completion, significant batch-related effects were observed. Adjustment for batch effects significantly improved the ability to predict increased lung tumor incidence. For the best statistical model, the estimated predictive accuracy under honest five-fold cross-validation was 79.3% with a sensitivity and specificity of 71.4 and 86.3%, respectively. A learning curve analysis demonstrated that gains in model performance reached a plateau at 25 chemicals, indicating that the size of the current data set was sufficient to provide a robust classifier. The classification results showed a small subset of chemicals contributed disproportionately to the misclassification rate. For these chemicals, the misclassification was more closely associated with genotoxicity status than efficacy in the original bioassay. Statistical models were also used to predict dose-response increases in tumor incidence for methylene chloride and naphthalene. The average posterior probabilities for the top models matched the results from the bioassay for methylene chloride. For naphthalene, the average posterior probabilities for the top models over-predicted the tumor response, but the variability in predictions were significantly higher. The study provides both a set of gene expression biomarkers for predicting chemically-induced mouse lung tumors as well as a broad assessment of important experimental and analysis criteria for developing microarray-based predictors of safety-related endpoints.

ORGANISM(S): Mus musculus

PROVIDER: GSE17933 | GEO | 2009/09/09

SECONDARY ACCESSION(S): PRJNA119871

REPOSITORIES: GEO

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Project description:The process for evaluating chemical safety is inefficient, costly, and animal intensive. There is growing consensus that the current process of safety testing needs to be significantly altered to improve efficiency and reduce the number of untested chemicals. In this study, the use of short-term gene expression profiles was evaluated for predicting the increased incidence of mouse lung tumors. Animals were exposed to a total of 26 diverse chemicals with matched vehicle controls over a period of three years. Upon completion, significant batch-related effects were observed. Adjustment for batch effects significantly improved the ability to predict increased lung tumor incidence. For the best statistical model, the estimated predictive accuracy under honest five-fold cross-validation was 79.3% with a sensitivity and specificity of 71.4 and 86.3%, respectively. A learning curve analysis demonstrated that gains in model performance reached a plateau at 25 chemicals, indicating that the size of the current data set was sufficient to provide a robust classifier. The classification results showed a small subset of chemicals contributed disproportionately to the misclassification rate. For these chemicals, the misclassification was more closely associated with genotoxicity status than efficacy in the original bioassay. Statistical models were also used to predict dose-response increases in tumor incidence for methylene chloride and naphthalene. The average posterior probabilities for the top models matched the results from the bioassay for methylene chloride. For naphthalene, the average posterior probabilities for the top models over-predicted the tumor response, but the variability in predictions were significantly higher. The study provides both a set of gene expression biomarkers for predicting chemically-induced mouse lung tumors as well as a broad assessment of important experimental and analysis criteria for developing microarray-based predictors of safety-related endpoints. Experiment Overall Design: Five-week-old female B6C3F1 mice were exposed for 13 weeks to 26 chemicals. The chemical and dose information are provided with the individual sample annotations. With each chemical treatment, a matched vehicle control group was run concurrently with the exposure. A subset of two chemicals, methylene chloride and naphthalene, were performed in a five-point dose response with a matched purified air control group. The concentrations for these exposures overlapped those in the original cancer bioassay. Gavage exposures were administered 5 days per week and feed exposures were provided 7 days per week. For inhalation exposures, mice were exposed 6 hr per day, 5 days per week. After 13 weeks, animals were euthanized and lungs were collected. The right lobe was used for microarray analysis. Microarray analysis was performed on the lungs of three to four mice per treatment group.

Project description:Two-year rodent bioassays play a central role in evaluating both the carcinogenic potential of a chemical and generating quantitative information on the dose-response behavior for chemical risk assessments. The bioassays involved are expensive and time-consuming, requiring nearly lifetime exposures (two years) in mice and rats and costing $2 to $4 million per chemical. Since there are approximately 80,000 chemicals registered for commercial use in the United States and 2,000 more are added each year, applying animal bioassays to all chemicals of concern is clearly impossible. To efficiently and economically identify carcinogens prior to widespread use and human exposure, alternatives to the two-year rodent bioassay must be developed. In this study, animals were exposed for 13 weeks to 10 chemicals that were positive for liver tumors in the two-year rodent bioassay, 14 chemicals that were negative for liver tumors, and two chemicals that produced an equivocal response. Matched vehicle control groups were run concurrently with each chemical treatment. Gene expression analysis was performed on the livers of the animals to assess the potential for identifying gene expression biomarkers and signaling pathways that can predict tumor formation in a two-year bioassay following a 13 week exposure. Five-week-old female B6C3F1 mice were exposed for 13 weeks to 26 chemicals. The chemical and dose information are provided with the individual sample annotations. With each chemical treatment, a matched vehicle control group was run concurrently with the exposure. A subset of five chemicals, methylene chloride, naphthalene, 1,2,3-trichloropropane, propylene glycol mono-t-butyl ether, and 1,4-dichlorobenzene, were performed in a five-point dose response with matched control groups. The concentrations for these exposures overlapped those in the original cancer bioassay. Gavage exposures were administered 5 days per week and feed exposures were provided 7 days per week. For inhalation exposures, mice were exposed 6 hr per day, 5 days per week. After 13 weeks, animals were euthanized and livers were collected. The right, caudate and median liver lobes were minced together and used for microarray analysis. Microarray analysis was performed on the livers of three to five mice per treatment group.

Project description:The primary goal of toxicology and safety testing is to identify agents that have the potential to cause adverse effects in humans. Unfortunately, many of these tests have not changed significantly in the past 30 years and most are inefficient, costly, and rely heavily on the use of animals. The rodent cancer bioassay is one of these safety tests and was originally established as a screen to identify potential carcinogens that would be further analyzed in human epidemiological studies. Today, the rodent cancer bioassay has evolved into the primary means to determine the carcinogenic potential of a chemical and generate quantitative information on dose-response behavior in chemical risk assessments. Due to the resource-intensive nature of these studies, each bioassay costs $2 to $4 million and takes over three years to complete. Over the past 30 years, only 1,468 chemicals have been tested in a rodent cancer bioassay. By comparison, approximately 9,000 chemicals are used by industry in quantities greater than 10,000 lbs and nearly 90,000 chemicals have been inventoried by the U.S. Environmental Protection Agency as part of the Toxic Substances Control Act. Given the disparity between the number of chemicals tested in a rodent cancer bioassay and the number of chemicals used by industry, a more efficient and economical system of identifying chemical carcinogens needs to be developed. Experiment Overall Design: Five-week old female B6C3F1 mice were exposed for 13 weeks in the following dose groups: 1) 1,5-Naphthalenediamine, CAS No. 2243-62-1, feed, 2000 ppm, positive lung carcinogen; 2) 2,3-Benzofuran, CAS No. 271-89-6, gavage, 240 mg/kg, positive lung carcinogen; 3) 2,2-Bis(bromomethyl)-1,3-propanediol, CAS No. 3296-90-0, feed, 1250 ppm, positive lung carcinogen; 4) N-Methylolacrylamide, CAS No. 924-42-5, gavage (water), 50 mg/kg, positive lung carcinogen; 5) 1,2-Dibromoethane, CAS No. 106-93-4, gavage (corn oil), 62 mg/kg, positive lung carcinogen; 6) Coumarin, CAS No. 91-64-5, gavage (corn oil), 200 mg/kg, positive lung carcinogen; 7) Benzene, CAS No. 71-43-2, gavage (corn oil), 100 mg/kg, positive lung carcinogen; 8) N-(1-naphthyl)ethylenediamine dihydrochloride, CAS No. 1465-25-4, feed, 2000 ppm, negative lung carcinogen; 9) Pentachloronitrobenzene, CAS No. 82-68-8, feed, 8187 ppm, negative lung carcinogen; 10) 4-Nitroanthranilic acid, CAS No. 619-17-0, feed, 10000 ppm, negative lung carcinogen; 11) 2-Chloromethylpyridine hydrochloride, CAS No. 6959-47-3, gavage (water), 250 mg/kg, negative lung carcinogen; 12) Diazinon, CAS No. 333-41-5, feed, 200 ppm, negative lung carcinogen; 13) Malathion, CAS No. 121-75-5, feed, 16000 ppm, negative lung carcinogen; 14) Corn oil control, gavage; 15) Water control, gavage; 16) Rodent diet control, feed. Feed animals were exposed 7 days/week and gavage animals were exposed 5 days/week (5 ml/kg). After 13 weeks, animals were euthanized and lungs were collected. The right lobe was used for microarray analysis. Microarray analysis was performed on the lungs of three to four mice per treatment group.

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Transcriptional Biomarkers to Predict Female Mouse Lung Tumors in Rodent Cancer Bioassays - A 26 Chemical Set

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