Are all bacterial strains required by OECD mutagenicity test guideline TG471 needed?

The International Workshop on Genotoxicity Testing (IWGT) meets every four years to seek consensus on difficult or conflicting approaches to genotoxicity testing based upon experience, available data, and analysis techniques. At the 2017 IWGT meeting in Tokyo, one working group addressed the sensitivity and selectivity of the bacterial strains specified in the Organization for Economic Cooperation and Development (OECD) Test Guideline TG471 to recommend possible modification of the test guideline. Three questions were posed: (1) Although TA100 is derived from TA1535, does TA1535 detect any mutagens that are not detected by TA100? (2) Among the options of Salmonella TA1537, TA97 or TA97a, are these strains truly equivalent? (3) Because there is a choice to use one of either E. coli WP2 uvrA, E. coli WP2 uvrA pKM101, or Salmonella TA102, are these strains truly equivalent? To answer these questions, we analyzed published bacterial mutation data in multiple strains from large (>10,000 compound) databases from Leadscope and Lhasa Limited and anonymized data for 53 compounds tested in TA1535 and TA100 provided by a pharmaceutical company. Our analysis involved (1) defining criteria for determining selective responses when using different strains; (2) identifying compounds producing selective responses based upon author calls; (3) confirming selective responses by visually examining dose-response data and considering experimental conditions; (4) using statistical methods to quantify the responses; (5) performing limited additional direct-comparison testing; and (6) determining the chemical classes producing selective responses. We found that few mutagens would fail to be detected if the test battery did not include Salmonella strains TA1535 (8/1167), TA1537 (2/247), TA102 (4/46), and E. coli WP2 uvrA (2/21). Of the mutagens detected by the full TG471 strain battery, 93% were detected using only strains TA98 and TA100; consideration of results from in vitro genotoxicity assays that detect clastogenicity increased this to 99%.

[1]  K. Watanabe,et al.  Comparisons on chemically-induced mutagenicity among four bacterial strains, Salmonella typhimurium TA102 and TA2638, and Escherichia coli WP2/pKM101 and WP2 uvrA/pKM101: collaborative study I. , 1996, Mutation research.

[2]  E. Zeiger,et al.  The Ames Salmonella/microsome mutagenicity assay. , 2000, Mutation research.

[3]  Enhanced mutagenesis of Salmonella tester strains due to deletion of genes other than uvrB , 2007, Environmental and molecular mutagenesis.

[4]  Larry D. Claxton,et al.  The Salmonella Mutagenicity Assay: The Stethoscope of Genetic Toxicology for the 21st Century , 2010, Environmental health perspectives.

[5]  D M DeMarini,et al.  Influence of DNA repair on mutation spectra in Salmonella. , 2000, Mutation research.

[6]  J. T. Macgregor,et al.  The International Workshops on Genotoxicity Testing (IWGT): history and achievements. , 2007, Mutation research.

[7]  M. Shelby,et al.  Chlorambucil and bleomycin induce mutations in the specific-locus test in female mice. , 1996, Mutation research.

[8]  M. Cimino,et al.  Comparative overview of current international strategies and guidelines for genetic toxicology testing for regulatory purposes , 2006, Environmental and molecular mutagenesis.

[9]  R Daniel Benz,et al.  Next generation testing strategy for assessment of genomic damage: A conceptual framework and considerations , 2017, Environmental and molecular mutagenesis.

[10]  K. Mortelmans,et al.  The bacterial tryptophan reverse mutation assay with Escherichia coli WP2. , 2000, Mutation research.

[11]  B H Margolin,et al.  Strategies to reduce the cost of mutagenicity screening with the Salmonella assay. , 1985, Environmental mutagenesis.

[12]  T. Cebula,et al.  Salmonella typhimurium strain TA100 differentiates several classes of carcinogens and mutagens by base substitution specificity. , 1994, Carcinogenesis.

[13]  M. Garriott,et al.  The evaluation of methapyrilene for bacterial mutation with metabolic activation by Aroclor-induced, methapyrilene-induced and noninduced rat-liver S9. , 1993, Mutation research.

[14]  J. Ashby,et al.  Weak and unexpected mutagenicity to Salmonella of the rat hepatocarcinogen methapyrilene. , 1988, Environmental and molecular mutagenesis.

[15]  T Ohta,et al.  Recommendations for the performance of bacterial mutation assays. , 1994, Mutation research.

[16]  D. Gatehouse,et al.  Comparison of Salmonella typhimurium TA102 with Escherichia coli WP2 tester strains. , 1990, Mutagenesis.

[17]  M. O’Donovan.  The comparative responses of Salmonella typhimurium TA1537 and TA97a to a range of reference mutagens and novel compounds. , 1990, Mutagenesis.

[18]  K. Watanabe,et al.  Comparisons of chemically-induced mutation among four bacterial strains, Salmonella typhimurium TA102 and TA2638, and Escherichia coli WP2/pKM101 and WP2 uvrA/pKM101: collaborative study III and evaluation of the usefulness of these strains. , 1998, Mutation research.

[19]  B. Ames,et al.  A new Salmonella tester strain, TA97, for the detection of frameshift mutagens. A run of cytosines as a mutational hot-spot. , 1982, Mutation research.

[20]  E Zeiger,et al.  Chemicals mutagenic in Salmonella typhimurium strain TA1535 but not in TA100. , 1998, Mutation research.

[21]  R. Schaaper,et al.  The ΔuvrB mutations in the Ames strains of Salmonella span 15 to 119 genes , 2001 .

[22]  Overall evaluations of carcinogenicity: an updating of IARC Monographs volumes 1 to 42. , 1987, IARC monographs on the evaluation of carcinogenic risks to humans. Supplement.