At the laboratories of AstraZeneca, Alderley Park, UK the reference genotoxic agents etoposide (a topoisomerase II inhibitor), cadmium chloride (an inorganic carcinogen), colchicine (an aneugen that inhibits tubulin polymerisation), benzo[a]pyrene (a metabolism dependent reference genotoxin) and cyclophosphamide (a metabolism dependent reference genotoxin) were tested in the in vitro micronucleus assay (MNvit), using mouse lymphoma L5178Y cells, with and without cytokinesis block. Further, 2-aminoanthracene (a metabolism dependent weak clastogen) was tested in the MNvit, using TK6 cells, without cytokinesis block. This was done in support of the toxicity (cell death and cytostasis) measures recommended in the late 2007 version of the draft OECD Test
Guideline 487 for the testing of chemicals. All six reference agents were positive in the MNvit without cytokinesis block at concentrations giving approximately 50% toxicity or less as defined by draft Test
Guideline 487 recommended measures, relative population doublings and relative increase in cell counts. Furthermore, the five agents tested with cytokinesis block were positive in the MNvit at concentrations giving approximately 50% toxicity or less as assessed by replicative index. Accordingly, this work supports the premise that relative population doublings and relative increase in cell counts are appropriate measures of toxicity for the non-cytokinesis-blocked in vitro micronucleus assay.