title: Mitotic spindle checkpoint inactivation by trichostatin a defines a mechanism for increasing cancer cell killing by microtubule-disrupting agents.
abstract: Microtubule-disrupting agents such as the taxanes comprise some of the most clinically useful chemotherapeutic agents and invoke the spindle checkpoint in proliferating cells. A robust spindle checkpoint in turn may forestall mitotic catastrophe, potentially providing a mechanism that permits cancer cells to survive transient exposure to these drugs. Previous reports on G2-M cell cycle progression by histone deacetylase inhibitors suggested a potential role in modulating the therapeutic efficacy of microtubule-disrupting agents. As both classes of agents are generally administered in clinical trials as pulse treatments, we investigated in human cancer cells the effects of brief treatments with the histone deacetylase inhibitor trichostatin A (TSA) alone or with nocodazole or paclitaxel (Taxol) on cell cycle progression and the spindle checkpoint. Treatment of synchronized cells with 200 ng/ml of TSA alone for eight hours to completely block class I and II HDACs did not interfere with progression into mitosis with chromosomal condensation as confirmed by MPM-2 expression. TSA treatment at this concentration surprisingly did not interfere with formation of the mitotic spindle or centrosomal separation, but instead led to missegregation of chromosomes, suggesting effects on the spindle checkpoint. Consistent with this hypothesis, TSA abrogated the phosphorylation and kinetochore localization of the mitotic checkpoint protein BubR1 and the phosphorylation of histone H3 after paclitaxel and nocodazole treatment. These effects in turn led to rapid cell death and considerably reduced clonogenic survival. These results together suggest that by inactivating the spindle checkpoint, TSA can potentiate the lethal effects of microtubule-disrupting drugs, a strategy that might be usefully exploited for optimizing anticancer therapy.
authors.affiliation: Department of Radiation Oncology, Philadelphia Veterans Affairs Medical Center and the University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Melissa
authors.initials: M
authors.lastname: Dowling
authors.forename: K Ranh
authors.initials: KR
authors.lastname: Voong
authors.forename: Mijin
authors.initials: M
authors.lastname: Kim
authors.forename: Michael K
authors.initials: MK
authors.lastname: Keutmann
authors.forename: Eleanor
authors.initials: E
authors.lastname: Harris
authors.forename: Gary D
authors.initials: GD
authors.lastname: Kao
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects*; D018385:Centrosome / Q000187:drug effects; D004359:Drug Therapy, Combination; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006367:HeLa Cells; D056572:Histone Deacetylase Inhibitors; D006657:Histones / Q000378:metabolism; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology*; D015151:Immunoblotting; D018386:Kinetochores / Q000187:drug effects / Q000378:metabolism; D008870:Microtubules / Q000187:drug effects*; D008938:Mitosis / Q000187:drug effects; D009369:Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D015739:Nocodazole / Q000494:pharmacology; D017239:Paclitaxel / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D008941:Spindle Apparatus / Q000187:drug effects*
chemical_list: D000970:Antineoplastic Agents; D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D056572:Histone Deacetylase Inhibitors; D006657:Histones; D006877:Hydroxamic Acids; C012589:trichostatin A; D011494:Protein Kinases; C584277:BUB1 protein, human; C090464:Bub1 spindle checkpoint protein; D017346:Protein Serine-Threonine Kinases; D017239:Paclitaxel; D015739:Nocodazole