Mitomycin C, 5-fluoruracil, colchicine and etoposide tested in the in vitro mammalian cell micronucleus test (MNvit) in the human lymphoblastoid cell line TK6 at Novartis in support of OECD draft Test Guideline 487

The following reference genotoxic agents were tested in the in vitro micronucleus test, at Novartis, Basel, Switzerland. Mitomycin C, 5-fluoruracil, colchicine and etoposide were tested in the human lymphoblastoid cell line TK6, with and without cytokinesis block (in the presence of cytochalasin B). This was done in support of the toxicity measures recommended in the draft OECD Test Guideline on In Vitro Mammalian Cell Micronucleus Test (MNvit) and was part of an international collaborative work. As toxicity measures, detecting cytostasis and cell death, relative cell counts (RCC), relative increase in cell counts (RICC), and relative population doubling (RPD) were used for treatments in the absence of cytokinesis block, and replication index (RI) or cytokinesis-blocked proliferation in the presence of cytokinesis block. All four reference agents were positive in the assay with and without cytokinesis block at concentrations giving approximately 50% toxicity or less as assessed by all of the toxicity measures used.Accordingly, the results of this work support the use of relative population doubling and relative increase in cell counts, as well as relative cell counts, as appropriate measures of toxicity for the non-cytokinesis-blocked in vitro micronucleus assay.