DNA damaging agents can induce celll cycle arrest in different phases of mitosis

DNA damaging drugs often induce cell cycle arrest at G1 or G2, to allow the repair of damage, or apoptosis induction. Mitotic checkpoints have been also associated to DNA damage response, even if they are less well characterized. In this study we analyzed the progression through mitosis of the mismatch repair deficient (MMR-) HCT116 and HCT15 colon cancer cell lines and their MMR proficient (MMR+) counterparts, after treatment with the DNA polymerase inhibitor aphidicolin, the radiomimetic bleomycin and the Topoisomerase I (Topo) I inhibitor SN38. Cells were treated with the different drugs at concentrations and times suitable to detect DNA and chromosome damage, without abrogating mitosis. After fixation, cells were incubated with anti-α, -β or -γ tubulin antibodies and a secondary fluorescent antibody; DNA was counterstained with DAPI. The percentage of cells in the various phases of mitosis, abnormal mitoses (multipolar, with lagging chromosomes, etc.) and mitotic indexes were evaluated. Aphidicolin and bleomycin caused cell arrest mainly at the checkpoint between metaphase and anaphase, whereas SN38 induced cell accumulation at the end of mitosis, when tubulins are present only in the midbodies, just before the definitive cytodieresis. Since Aurora kinase B is essential in the control of cytodieresis, we plan to analyze the possible intervention of this kinase in tumor cell response to the drugs under study. Moreover, we are evaluating telomere damage that can be induced by Topo I inhibitors and may cause cell arrest at the end of mitosis