The carcinogenicity of many drugs, such as antitumor agents, is a subject of growing concern. The newly developed pyrimidine nucleosides, 2'-fluoro-5-iodo-1-beta-D-arabinofuranosylcytosine (FIAC) and 2'-fluoro-1-beta-D-arabinofuranosyl-5-methyluracil (FMAU), have shown potent anti-herpes virus activity in tissue cultures, laboratory animals and man and an activity to inhibit the growth of certain tumor cell lines in vitro. Radioactivity of 14C-labeled FIAC and FMAU is incorporated into the DNA of normal and neoplastic mammalian tissues. However, we now report that FIAC and FMAU are inactive in a bacterial mutagenesis assay (Salmonella-microsome test) and in a mammalian cell mutagenesis assay employing V79 Chinese hamster cells in vitro. Both agents did not induce unscheduled DNA synthesis in primary Wistar rat hepatocytes in vitro.
