Mutational specificities of 1'-acetoxysafrole, N-benzoyloxy-N-methyl-4-aminoazobenzene, and ethyl methanesulfonate in human cells.

We have used an oriP-tk shuttle vector to determine the types of mutations induced in human cells by ethyl methanesulfonate (EMS), 1'-acetoxysafrole (AcOS), and N-benzoyloxy-N-methyl-4-aminoazobenzene (BzOMAB). Plasmid DNA was treated in vitro with mutagen and electroporated into human lymphoblastoid cells. After replication of the vector in human cells, plasmids were analyzed for mutations in the herpes simplex virus type 1 thymidine kinase gene. Ethyl methanesulfonate induced predominantly GC----AT transition mutations. Treatment of the shuttle vector with AcOS induced 5 of the 6 possible base substitution mutations, including GC----AT (32%) and AT----GC (14%) transition mutations, GC----TA (9%), GC----CG (18%), and AT----TA (14%) transversion mutations, as well as a low frequency (9%) of -1 frameshift mutations at GC base pairs. Replication in human cells of DNA modified with BzOMAB yielded a significant increase (17-fold) in the frequency of deletion mutations relative to solvent-treated DNA. A majority (94%) of the point mutations induced by BzOMAB occurred at GC base pairs and were predominantly GC----AT transitions (33%) and -1 frameshift (22%) mutations, with the remainder consisting mainly of transversions at GC base pairs (28%). The broad spectrum of base substitution mutations observed for AcOS and BzOMAB may indicate the frequent insertion of a variety of bases during replicative bypass of aralkylated bases in human cells.