KT-NB induces multipolar spindles. HeLa cells were treated with DMSO as a control (A) or 6.75 μg/ml of KT-NB (B) for 24 h. After incubation, cells were fixed and processed for immunofluorescence analysis. DAPI was used for DNA staining, while anti-tubulin shows the mitotic spindle. Merged images: (DAPI is blue, tubulin is red). (C) The percentage of mitotic cells with multipolar spindles was quantified in control and KT-NB treated cells (n > 100, three independent experiments). Scale bar: 5 μm.