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KIF11, a mitotic kinesin, is a component responsible for assembly and maintenance of mitotic spindle during mitosis. Tumor cells can upregulate KIF11. Inhibition of KIF11 results monopolar spindle formation, resulting in monoastral mitosis in cells. This activates the spindle assembly checkpoint, cells are arrested and prevented from entering cell cycle, resulting in cell death via apoptosis or necrosis, cell division with aneuploidy or mitotic slippage without division into tetraploid G1 phase. Methods We hypothesized that the effect of KIF11 inhibition on medulloblastoma (MB) is dependent of its p53 mutational status. Results Our findings on Hoechst staining demonstrated a small molecule inhibitor of KIF11 which induced apoptosis in p53-wildtype MB cells at 48h (p&amp;lt;0.0001), was able to trigger mitotic catastrophe (p = 0.0010) in p53-mutant MB cells at 24h and subsequent necrosis (p=0.0039) at 48h. KIF11 inhibitor exerted anti-proliferative effects on five MB cell lines at nanomolar concentration range, independent of its p53 mutational status. Cells treated with KIF11 inhibitor were arrested in G2/M phase. Apoptosis was observed on Annexin V flow cytometry 24h after treatment, followed by necrosis after 48h in p53-wildtype cells. In contrast, treated p53-mutant cells underwent necrosis at 24h. Differences in cell death mechanisms upon KIF11 inhibition was confirmed on immunoblotting by upregulated p53 expression and presence of cleaved-PARP and DNA-damage marker in p53-wildtype cells, indicative of apoptosis. While inhibition of KIF11 and increased p53 expression were observed only after 48h, cleaved-PARP expression was detected as early as 24h in p53-wildtype, suggesting KIF11-independent, cleaved-PARP-mediated cell death at 24h. In contrast, treated p53-mutant cells showed decreased p53 expression and absence of cleaved-PARP and DNA-damage marker after 24h. Conclusions Our results suggest that when mitotic arrest is induced, p53-mutant MB cells undergo mitotic catastrophe and necrosis while p53-wildtype MB cells predominantly undergo apoptosis.

EMBR-23. KIF11 DEPENDENCY ON P53 MUTATIONAL STATUS IN MEDULLOBLASTOMA