Horizon scanning for novel and emerging in vitro mammalian cell mutagenicity test systems

The induction of gene mutation within a DNA sequence can result in an adverse impact, altering or preventing gene function. Therefore, in vitro evaluation of mutagenicity is an essential component of the toxicological screening process. A variety of mutagen screening tools are routinely used in genetic toxicology, which are based on selected reporter genes. These assays are however typically labour intensive and impractical for high throughput screening. Considering this, the IWGT (International Workshops on Genotoxicity Testing) sub-group on Novel & Emerging in vitro Mammalian Cell Mutagenicity Test Systems undertook a literature search to identify new approaches for mutation detection. This review therefore focused on identifying new approaches for mutation detection that have the potential for use as a future genotoxicity screening tool. A comprehensive literature review identified genome-wide loss-of-function screening tools, next generation sequencing (NGS) mutation characterisation and fluorescence-based mutation detection methods as having significant promise as an emerging in vitro mammalian cell mutagenicity test system. Each of the technologies considered was assessed for its capacity to report on a wide array of heritable mutagenic changes, necessary to cover the full spectrum of genetic events imparted by substances with a broad range of modes of action. Of the technologies evaluated, NGS techniques exhibited the greatest advantages for use in a genotoxicity testing setting. However, it is important to note that the emerging techniques identified could not facilitate routine mutagenicity testing in their current format and require substantial additional optimisation and tailoring before they could be utilised as an in vitro mammalian cell mutagenicity test system. Additionally, new mammalian cell mutation test systems must be able to accurately and reliably detect and quantify rare events; hence any new system would require careful validation. Nevertheless, with further development emerging technologies such as NGS could become important in establishing more predictive and high-throughput regulatory hazard screening tools of the future.