The Microtubule Stabilizing Agent Discodermolide is a Potent Inducer of Accelerated Cell Senescence

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Abstract
Discodermolide is a microtubule stabilizing agent that suppresses dynamic instability and blocks cells in mitosis. Selection of A549 non-small cell lung carcinoma cells with increasing concentrations of discodermolide yielded a clone that proliferated in 8nM. When these cells were exposed to any concentration greater than 8nM, replication ceased and the cells developed a flattened, enlarged, granular morphology. Accelerated senescence was demonstrated by a functional β-galactosidase activity at pH 6. When parental A549 cells were treated with IC50-concentrations of doxorubicin, Taxol or discodermolide, the latter two drugs quickly produced aberrant mitosis. However, discodermolide, but not Taxol, also produced a large increase in senescence-associated β-galactosidase activity and altered levels of known senescence markers. Although some of these differences between Taxol and discodermolide were dose dependent, only discodermolide produced a doxorubicin-like induction of a senescence phenotype, including a senescence-associated β-galactosidase activity, upregulation of PAI-1 and p66Shc, and a strong, sustained, Erk1/2 activation. This research provides insights into the mechanism of action of discodermolide and provides the first demonstration of a microtubule stabilizing agent that inhibits tumor cell growth with a powerful induction of accelerated senescence.

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