Reduction of use of animals in regulatory genotoxicity testing: Identification and implementation opportunities-Report from an ECVAM workshop.

In vivo genetic toxicology tests measure direct DNA damage or the formation of gene or chromosomal mutations, and are used to predict the mutagenic and carcinogenic potential of compounds for regulatory purposes and/or to follow-up positive results from in vitro testing. These tests are widely used and consume large numbers of animals, with a foreseeable marked increase as a result of the EU chemicals legislation (REACH), which may require follow-up of any positive outcome in the in vitro standard battery with appropriate in vivo tests, regardless of the tonnage level of the chemical. A 2-day workshop with genotoxicity experts from academia, regulatory agencies and industry was hosted by the European Centre for the Validation of Alternative Methods (ECVAM) in Ranco, Italy from 24 to 25 June 2008. The objectives of the workshop were to discuss how to reduce the number of animals in standard genotoxicity tests, whether the application of smarter test strategies can lead to lower animal numbers, and how the possibilities for reduction can be promoted and implemented. The workshop agreed that there are many reduction options available that are scientifically credible and therefore ready for use. Most of these are compliant with regulatory guidelines, i.e. the use of one sex only, one administration and two sampling times versus two or three administrations and one sampling time for micronucleus (MN), chromosomal aberration (CA) and Comet assays; and the integration of the MN endpoint into repeat-dose toxicity studies. The omission of a concurrent positive control in routine CA and MN tests has been proven to be scientifically acceptable, although the OECD guidelines still require this; also the combination of acute MN and Comet assay studies are compliant with guidelines, except for sampling times. Based on the data presented at the workshop, the participants concluded that these options have not been sufficiently utilized to date. Key factors for this seem to be the uncertainty regarding regulatory compliance/acceptance, lack of awareness, and an in many cases unjustified uncertainty regarding the scientific acceptance of reduction options. The workshop therefore encourages the use and promotion of these options as well as the dissemination of data related to reduction opportunities by the scientific community in order to boost the acceptance level of these approaches. Furthermore, experimental proof is needed and under way to demonstrate the credibility of additional options for reduction of the number of animals, such as the integration of the Comet assay into repeat-dose toxicity studies.