Aurora B inhibition promotes a hyper-polyploid state and continued endomitotic cycles in RB and p53 defective cells

Polyploidy is a common outcome of chemotherapies, but there is conflicting evidence as to whether this is a source of increased chemotherapy resistance and aggressive disease, or a benign or even favorable outcome. We have used Aurora B kinase (AURKB) inhibitors that efficiently promote polyploidy in many cell types to investigate the fate of polyploid cells. We demonstrate AURKB inhibitor treatment of cells that have loss of RB and p53 function causes them to become hyper-polyploid, undergoing continuous rounds of growth, replication and failed mitosis/cytokinesis (endomitosis), whereas RB and p53 functional cells will eventually exit the cell cycle. These hyper-polyploid cells (>4n DNA content) are viable and undergo continuous endomitotic cycles, but have lost the ability to form viable colonies in vitro or form tumours in vivo . Investigation of mitosis in these cells revealed that centrosome duplication remained coupled to DNA replication, with the hyper-polyploid cells containing high numbers of centrosome that were capable of supporting functional mitotic spindle poles, but these failed to progress to anaphase/telophase structures even when AURKB inhibitor was removed after 2-3 days. However, when AURKB inhibitor was removed after 1 day and cells had failed a single cytokinesis to become tetraploid, they retained long term colony forming ability. Collectively, these findings demonstrate that tetraploidy is well tolerated by tumour cells but higher ploidy states are incompatible with long term proliferative potential.