At the 7th IWGT, the following subgroups will be formed

1. A subgroup on the use of 3D models, led by Stefan Pfuhler, USA. The focus of the WG will be:

• Introduction to the concept of genetox testing in tissue models
• Status review of available genetox data generated in skin, liver and lung 3D tissue equivalents
• Validation status of the most developed 3D assays – the 3D skin micronucleus and comet assays
• Discuss test strategy fit and develop recommendations

2. A subgroup on emerging in vitro mammalian genotoxicity systems: endpoints and cell types, led by Bhaskar Gollapudi, USA. The group will critically assess emerging in vitro tools for measuring gene mutations in mammalian cell cultures, covering the following points:

• Basic algorithm for strategic placement of in vitro mutation assays
• Define basic principles of emerging assays
• Define current state of emerging assays
• Define research needs for the emerging assays to make them useful for regulatory applications
• In vitro models that can be used as surrogates for predicting in vivo response at the same locus
           > Higher throughput assays that are less laborious and less expensive
           > In vitro models to address mechanistic questions dealing with in vivo mutagenicity

• Focus groups will be:
           > Improving existing assays by applying new technologies
           > Mutation assays using cell lines from transgenic rodents
           > In vitro Pig-a mutation assays
           > Novel approaches to detect gene mutations in cell cultures

3. A subgroup will revisit the Salmonella mutagenicity (Ames) test, led by Rita Schoeny, USA, to discuss topics including these:

• Criteria for positive and negative responses; e.g. is there a place for alternatives to the 2x rule, such as Global Evaluation Factors or statistics?
• Criteria for acceptable assays and consideration of laboratory proficiency.
• Consideration of the five most widely used strains as well as what can be learned from use of others. Consideration of a data-based approach to defining a minimum strain set.
• How can strains best be maintained?
• Status of in silico SAR tools for prediction of mutagenicity in the Ames test. Would predictions change if positivity criteria change?

4. A subgroup will discuss aspects of risk assessment of aneugens, led by Francesco Marchetti, Canada, covering:

• Molecular mechanisms of chromosome segregations and differences between somatic and germ cells
• Utility of the Adverse Outcome Pathway approach to elucidate the mechanisms of aneuploidy
• Role of aneuploidy in carcinogenesis: initiation, promotion, or progression?
• Secondary effects of aneuploidy and their involvement in adverse health outcomes
• Aneuploidy in germ cells and hereditary diseases
• Implication of aneuploidy for human risk assessment

5. A subgroup, led by David Kirkland, UK, will discuss in vivo strategies:

• Can in vitro test outcome (mutagen, clastogen, aneugen) be used to suggest the appropriate in vivo test?
• Possibility to choose a single test instead of 2 tests to follow-up on an in vitro positive?
           > What can we learn from the historical database of overlapping TGR & comet results?
           > Can the comet assay substitute for the TGR, and in what circumstances?
• Are the OECD guideline default tissues (liver + site of contact) for the in vivo comet assay sufficient to detect expected positives?

           > How many tissues need to be tested in the comet assay to be predictive of (a) genotoxicity, (b) carcinogenicity?
           > Is there a need to include glandular stomach as well as duodenum for site-of-contact in the comet assay with orally dosed substances?
• What is “adequate exposure” and the proper route of exposure (i.p. vs oral or inhalation) for bone marrow MN test acceptability?
           > Are certain tissues or routes of exposure preferable, particularly for the in vivo MN test?
           > Is the i.p. route considered preferable to the normal route of human exposure (oral, inhalation, dermal) because it minimizes first pass metabolism in the liver?
           > Is demonstration of exposure in the plasma sufficient to ensure exposure of the bone marrow in a micronucleus test?
           > What is considered “insufficient” bone marrow exposure that might lead to a requirement to perform a site-of-contact comet assay instead of a bone marrow MN test?
• Are diet and drinking water as effective as gavage dosing for all in vivo tests?
• What is the state of validation of the MN assay in alternative tissues (i.e. liver, G.I. tract)?
• Where does the Pig-a assay fit into regulatory in vivo testing?

6. Finally, a plenary symposium, led by Carole Yauk, Canada, will discuss the state-of-the-science, current application and added-value of high- dimensional data in genetic toxicology testing including:

• Single-molecule sequencing
• Adductomics
• Whole genome transcriptional profiling
• High-content phenotype-based assays