Induction of mutations in mouse lymphoma L5178Y cells by ethylmethanesulphonate, benzidine and benzo[a]pyrene

As part of the third UKEMS collaborative trial, the induction of mutations in mouse lymphoma L5178Y cells was analysed by an agar cloning method. The method used was based on the published methods of Clive and co-workers and Amacher and co-workers. Mutations at the thymidine kinase (tk) locus were analysed following exposure to ethylmethanesulphonate (EMS) in the absence of S9 mix, benzo[a]pyrene (B[a]P) in the presence of S9 mix and benzidine (BZD) in the absence and presence of S9 mix. Mutations were induced under all these conditions and no difference was found between a 48-h and 72-h expression period. Small and large colonies on trifluorothymidine (TFT) selective plates were expanded and found to be stably resistant to TFT. The effects of varying the S9 level and the composition of the cofactor mix on the mutagenicity of BZD and B[a]P were also analysed. The ability of BZD to induce mutations at the hprt locus was investigated. No mutations were detected either in the presence or absence of S9 mix.