Peloruside A, a microtubule-stabilizing agent, induces aneuploidy in ovarian cancer cells

To ensure proper chromosome segregation, mitosis is tightly regulated by the spindle assembly checkpoint (SAC). Low concentrations of microtubule-stabilizing agents can induce aneuploid populations of cells in the absence of G₂/M block, suggesting pertubation of the spindle checkpoint. We investigated the effects of peloruside A, a microtubule-stabilizing agent, on expression levels of several key cell cycle proteins, MAD2, BUBR1, p55CDC and cyclin B1. Synchronized 1A9 ovarian carcinoma cells were allowed to progress through the cell cycle in the presence or absence of peloruside A. Co-immunoprecipitation and Western blotting were used to probe the cell cycle kinetics of MAD2 and BUBR1 dissociation from p55CDC. Using confocal microscopy, we investigated whether premature dissociation of MAD2 and BUBR1 at low (40 nM) but not high (100 nM) concentrations of peloruside A was caused by defects in the attachment of chromosomes to the mitotic spindle. An increased frequency of polar chromosomes was observed at low concentrations of peloruside A, suggesting that an increased frequency of pseudo-metaphase cells, which are not detected by the spindle assembly checkpoint, may be underlying the induction of aneuploidy.