Evaluation of the VitotoxTM test as a high-throughput genotoxicity assay

The VitotoxTM test is a high-throughput bacterial genotoxicity test based on the SOS DNA-repair system induced by genotoxic compounds. Two genetically engineered Salmonella typhimurium strains are used in this system, TA104recN2-4 (Genox strain), that contains the bacterial luciferase (lux) operon (luxCDABE) under transcriptional control of recN promoter, and TA104 pr1 (Cytox strain), that constitutively expresses lux operon.The performance of the VitotoxTM test was evaluated with 33 known Ames positive chemicals, 26 known Ames negatives and 18 drug candidates developed at Mitsubishi Pharma Corporation. Ten compounds had inconclusive results because they caused SOS-independent enhancement of light emission. Among 49 known chemicals with conclusive results, 89% of the Ames positive compounds were detected as positive (genotoxic) with the VitotoxTM test, and all of the Ames negative compounds were detected as negative. There was a 94% concordance between the Ames test results and the VitotoxTM test results.In a practical validation study using 18 drug candidates developed at Mitsubishi Pharma Corporation, 7 of 8 Ames positive compounds were detected as genotoxic and all of the Ames negative compounds gave negative results with the VitotoxTM test. The concordance between the VitotoxTM test results and the Ames test results for 18 drug candidates was 94% (17/18). Moreover, the VitotoxTM test required a smaller sample quantity than the Ames test to detect genotoxicity.The present results indicate that the VitotoxTM test is useful for rapid screening of large numbers of chemicals when only a small quantity of a chemical is available.