Workshop summary: Top concentration for in vitro mammalian cell genotoxicity assays; and report from working group on toxicity measures and top concentration for in vitro cytogenetics assays (chromosome aberrations and micronucleus)
Introduction:
This article summarizes the discussions and conclusions of the 5th International Workshop on Genotoxicity Testing (IWGT) regarding the selection of maximum concentrations for in vitro mammalian cell genotoxicity assays. The workshop reviewed the current top concentration recommended for these assays, which is 10 mM or 5 mg/ml, whichever is lower. The discussion focused on whether to reduce this limit and if so, whether the 1 mM limit proposed for human pharmaceuticals is appropriate for testing other chemicals.
Key Points:
* The article discusses the results of an evaluation conducted by ECVaM, which examined the published genotoxicity data for mammalian cell assays from the Gold Berkeley Carcinogenic Potency database. The evaluation found that only a small portion of chemicals that are rodent carcinogens and negative in the ames test but positive in the in vitro mammalian cell assays are positive only at concentrations above 1 mM.
* The article also discusses the rationale for the proposed revisions to the ICh guidelines for testing pharmaceuticals, which recommend a reduction in top concentration in the in vitro mammalian cell assays to 1 mM for pharmaceuticals. This recommendation is based on several factors, including human exposure levels and the fact that pharmacologically active concentrations for drugs and the optimal substrate concentrations for many enzymes, including P450s, are typically below 10 /h9262g/ml (20 /h9262M for molecular weight of 500).
* The article also discusses an alternative proposal to use a maximum concentration in mg/ml, instead of one based on molarity. This proposal is based on the maximum dose recommended by OECD for conducting chronic/subchronic in vivo toxicity studies, which is 1000 mg/kg/day.
* The in vitro cytogenetic assays working group discussed appropriate measures and level of cytotoxicity for in vitro cytogenetic assays. The group discussed acceptable measures and limits of toxicity and reviewed the results of an international trial comparing various measures of cytotoxicity.
Main Message:
The main message of the article is that there is reason to consider reducing the top concentration limit for in vitro mammalian cell genotoxicity assays and many attendees favored a reduction to 1 mM. however, there was not agreement on what the upper concentration limit should be, and several alternative proposals were put forward. The article also highlights the importance of appropriate measures and level of cytotoxicity for in vitro cytogenetic assays and the ongoing discussion around the best approach for determining the appropriate conditions for in vitro testing.
Citation
Galloway, Sheila, Elisabeth Lorge, Marilyn J. aardema, David Eastmond, Mick Fellows, Robert heflich, David Kirkland, et al. “Workshop Summary: Top Concentration for in Vitro Mammalian Cell Genotoxicity assays; and Report from Working Group on Toxicity Measures and Top Concentration for in Vitro Cytogenetics assays (Chromosome aberrations and Micronucleus).” Mutation Research/Genetic Toxicology and Environmental Mutagenesis 723, no. 2 (august 2011): 77–83. https://doi.org/10.1016/j.mrgentox.2011.01.003.
Galloway, Sheila, Elisabeth Lorge, Marilyn J. aardema, David Eastmond, Mick Fellows, Robert heflich, David Kirkland, et al. “Workshop Summary: Top Concentration for in Vitro Mammalian Cell Genotoxicity assays; and Report from Working Group on Toxicity Measures and Top Concentration for in Vitro Cytogenetics assays (Chromosome aberrations and Micronucleus).” Mutation Research/Genetic Toxicology and Environmental Mutagenesis 723, no. 2 (august 2011): 77–83. https://doi.org/10.1016/j.mrgentox.2011.01.003.
