Accumulation of mitotic cells was analyzed as described elsewhere. Briefly, cells were plated into a 24-well plate and, after 24-48 hours, coumarin-30 at different concentrations, 0.5 paclitaxel or nocodazole, or an equivalent concentration of DMSO were added for 12-24 hours. After incubation, cells were fixed with 4% formalin in PBS and stained with Hoechst 33342 or hematoxylin. The mitotic index was calculated in several fields of view, counting at least 300 cells.