Induction of mutations in TK6 human lymphoblastoid cells by ethyl methanesulphonate, benzo[a]pyrene and benzidine

The experiments described were carried out as part of the UKEMS Third Collaborative Trial. The method used was essentially that described by Thilly et al., based on a cloning assay using microtitre test plates. The induction of mutations at both the thymidine kinase (tk) locus and the hypoxanthine guanine phosphoribosyl transferase (hprt) locus was determined following exposure to ethyl methanesulphonate (EMS), benzidine (BZD) and benzo[a]pyrene (B[a]P). EMS was tested in the absence of a metabolic activation system (S9 mix), BZD was tested in the presence and absence of S9 mix and B[a]P was tested only in the presence of S9 mix. Incubation with EMS or B[a]P caused the induction of mutations at both the tk and hprt loci. The effects of benzidine were not reproducible, although some individual data points at the tk locus were found to be significant.