Fig. 1.

Approaches for in vivo carcinogenicity and mutagenicity testing. The gold standard for chemical cancer risk assessment involves exposing rodents to a test compound and assessing an increase in tumors relative to controls. While effective, the approach takes 2 y. Mutagenicity is one accepted surrogate for carcinogenicity risk which is more rapidly assessable. At present, TGR assays are the most validated in vivo mutagenesis measurement approach. A genetically modified strain carrying an artificial reporter gene is mutagen-exposed, necropsied, and the reporter is recovered from extracted DNA. Reporter DNA is then packaged into phage and transfected into bacteria for readout by counting total and mutation-bearing plaques following incubation at mutant-selectable temperature conditions. A simple mutant frequency can be determined within months, but the assay is complex. An ideal in vivo mutagenesis assay would be DNA sequencing-based and able to directly measure mutation abundance and spectrum in any tissue of any species without the need for genetic engineering or selection.