Long-term mitotic DNA damage promotes chromokinesin-mediated missegregation of polar chromosomes in cancer cells

DNA damage response (DDR) during interphase involves active signalling and repair to ensure genomic stability. However, how mitotic cells respond to DNA damage remains poorly understood. Supported by correlative live-/fixed-cell microscopy analysis we found that mitotic cells exposed to several cancer chemotherapy compounds acquire and signal DNA damage, regardless of how they interact with DNA. In-depth analysis upon long-term DNA damage during mitosis revealed a spindle assembly checkpoint (SAC)-dependent, but DDR-independent, mitotic delay. This delay was due to the presence of misaligned chromosomes that ultimately satisfy the SAC and missegregate, leading to micronuclei formation. Mechanistically, we show that long-term mitotic DNA damage specifically stabilizes kinetochore-microtubule attachments in cancer cells, causing the missegregation of polar chromosomes due to the action of arm-ejection forces by chromokinesins. Overall, these findings unveil that long-term therapeutic DNA damage regimens contribute to genomic instability through a surprising link between the stabilization of kinetochore-microtubule attachments and chromokinesin-mediated missegregation of polar chromosomes in cancer cells. ### Competing Interest Statement The authors have declared no competing interest.