Mitotic slippage in non-cancer cells induced by a microtubule disruptor, disorazole C1.

Background: Disorazoles are polyene macrodiolides isolated from a myxobacterium fermentation broth. Disorazole C1 was newly synthesized and found to depolymerize microtubules and cause mitotic arrest. Here we examined the cellular responses to disorazole C1 in both non-cancer and cancer cells and compared our results to vinblastine and taxol.

Results: In non-cancer cells, disorazole C1 induced a prolonged mitotic arrest, followed by mitotic slippage, as confirmed by live cell imaging and cell cycle analysis. This mitotic slippage was associated with cyclin B degradation, but did not require p53. Four assays for apoptosis, including western blotting for poly(ADP-ribose) polymerase cleavage, microscopic analyses for cytochrome C release and annexin V staining, and gel electrophoresis examination for DNA laddering, were conducted and demonstrated little induction of apoptosis in non-cancer cells treated with disorazole C1. On the contrary, we observed an activated apoptotic pathway in cancer cells, suggesting that normal and malignant cells respond differently to disorazole C1.

Conclusion: Our studies demonstrate that non-cancer cells undergo mitotic slippage in a cyclin B-dependent and p53-independent manner after prolonged mitotic arrest caused by disorazole C1. In contrast, cancer cells induce the apoptotic pathway after disorazole C1 treatment, indicating a possibly significant therapeutic window for this compound.