title: Histone deacetylase inhibitors induce G2-checkpoint arrest and apoptosis in cisplatinum-resistant ovarian cancer cells associated with overexpression of the Bcl-2-related protein Bad.
abstract: Trichostatin A produces predominantly G(1) cell-cycle blockade and differentiation of the cisplatinum-sensitive A2780 ovarian cancer cell line. Given the propensity of ovarian tumors to become resistant to cisplatinum, often leading to cross-resistance to other agents, we have extended these observations by examining how the emergence of resistant phenotypes in A2780 cells affects the actions of histone deacetylase (HDAC) inhibitors. Trichostatin A exposure (100 ng/mL, 24 hours) induced ultrastructural differentiation of the "intrinsically" cisplatinum-resistant A2780-9M subline, with the reappearance of intercellular junctions and lumina containing primitive microvilli. Similar trichostatin A exposure in the acquired resistance A2780CP cells produced minimal differentiation consisting of occasional weak intercellular junctions. Independent of the differences in trichostatin A-induced differentiation, in both resistant sublines trichostatin A produced a similar reduction in cell viability, by >90%, within 5 days of treatment. Diminished viability in both A2780-9M and CP cells was associated with the absence of cell cycle arrest in G1, resulting in predominant G2-checkpoint arrest accompanied by a 10- to 20-fold increase in Annexin V binding and the reemergence of apoptosis. Similar cell cycle arrests and apoptosis were also observed using other HDAC inhibitors and in other resistant ovarian cancer cell lines (OVCAR-3 and SK-OV-3). Trichostatin A-induced apoptosis in resistant cells is in sharp contrast to its effects on the parental cisplatinum-sensitive A2780 and normal MRC-5 fibroblast cell lines (predominant cycle arrest in G1 with no detectable apoptosis). Western immunoblot analysis indicated trichostatin A triggers apoptosis in resistant ovarian cancer cells via p53-independent activation of the intrinsic "mitochondrial" pathway, commensurate with induction of the Bcl-2-related protein Bad. These results suggest cisplatinum resistance alters the effects of HDAC inhibition through a shift in cell cycle arrest from the G1 to the G2 checkpoint and reactivation of the intrinsic mitochondrial apoptotic cascade.
authors.affiliation: Department of Medicine, Laboratory for Molecular Oncology, LDS Hospital, Salt Lake City, Utah 84143, USA. ldkstrai@ihc.com
authors.forename: Kevin A
authors.initials: KA
authors.lastname: Strait
authors.forename: C Terry
authors.initials: CT
authors.lastname: Warnick
authors.forename: Clyde D
authors.initials: CD
authors.lastname: Ford
authors.forename: Bashar
authors.initials: B
authors.lastname: Dabbas
authors.forename: Elizabeth H
authors.initials: EH
authors.lastname: Hammond
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Ilstrup
mesh_terms: D017304:Annexin A5 / Q000737:chemistry / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis; D015153:Blotting, Western; D002352:Carrier Proteins / Q000096:biosynthesis*; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002470:Cell Survival; D002945:Cisplatin / Q000494:pharmacology*; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D005434:Flow Cytometry; D016193:G1 Phase; D016195:G2 Phase; D056572:Histone Deacetylase Inhibitors; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D007150:Immunohistochemistry; D008854:Microscopy, Electron; D008928:Mitochondria / Q000378:metabolism*; D008938:Mitosis; D010051:Ovarian Neoplasms / Q000188:drug therapy* / Q000378:metabolism*; D010641:Phenotype; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis*; D013997:Time Factors; D051025:bcl-Associated Death Protein
chemical_list: D017304:Annexin A5; D000970:Antineoplastic Agents; C494819:BAD protein, human; D002352:Carrier Proteins; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; D019253:Proto-Oncogene Proteins c-bcl-2; D051025:bcl-Associated Death Protein; C012589:trichostatin A; D002945:Cisplatin