The mouse lymphoma assay (MLA) is a regulatory in vitro test deployed to evaluate the mutagenicity of a test substance via exposure of the thymidine kinase locus in L5178Y mouse lymphoma cells. As part of a proficiency study, we evaluated the mutagenicity of the total particulate matter (TPM) aerosol fraction derived from the mainstream smoke of 3R4F reference cigarettes (3R4F; University of Kentucky, USA). L5178Y tk^+/-clone 3.7.2C IVGT (PHE) cells were exposed to TPM derived from 3R4F under 4 h ± S9 and 24 h (-S9) treatment conditions using a study design compliant with the OECD guideline n° 476 and the recommendations of the International Workshop on Genotoxicity Testing (MLA Workgroup). On nine out of 10 independent test occasions, the TPM fraction induced biologically-relevant and concentration-dependent mutagenicity under the 4 h +S9 treatment condition. The lowest observed genotoxic effect level (LOGEL) range for this treatment condition was 30-60 µg/ml at relative total growth (RTG) values of 10-20%. TPM was also found to induce biologically-relevant mutagenicity in the absence of S9 with LOGELs between 12-30 µg/ml although the responses observed under these treatment conditions were less pronounced and occurred less frequently than in the presence of S9, and always arose at the cytotoxic limit of the assay. In conclusion, these data demonstrate the proficiency of the MLA at quantitating the mutagenicity induced by tobacco smoke-derived TPM.

References:
Organisation for Economic Co-operation and Development (OECD) Guideline for the Testing of Chemicals Protocol 476 (1997), In vitro Mammalian Cell Gene Mutation Assay.
Moore, M. et al., 2006, Environ. Mol. Mutagen. 47: 1-5.
Moore, M. et al., 2007, Mutat. Res. 627: 36-40.