title: Histone deacetylase inhibitors suppress thymidylate synthase gene expression and synergize with the fluoropyrimidines in colon cancer cells.
abstract: Despite recent therapeutic advances, the response rates to chemotherapy for patients with metastatic colon cancer remain at approximately 50% with the fluoropyrimidine, 5-fluorouracil (5-FU), continuing to serve as the foundation chemotherapeutic agent for the treatment of this disease. Previous studies have demonstrated that overexpression of thymidylate synthase (TS) is a key determinant of resistance to 5-FU-based chemotherapy. Therefore, there is a significant need to develop alternative therapeutic strategies to overcome TS-mediated resistance. In this study, we demonstrate that the histone deacetylase inhibitors (HDACi) vorinostat and LBH589 significantly downregulate TS gene expression in a panel of colon cancer cell lines. Downregulation of TS was independent of p53, p21 and HDAC2 expression and was achievable in vivo as demonstrated by mouse xenograft models. We provide evidence that HDACi treatment leads to a potent transcriptional repression of the TS gene. Combination of the fluoropyrimidines 5-FU or FUdR with both vorinostat and LBH589 enhanced cell cycle arrest and growth inhibition. Importantly, the downstream effects of TS inhibition were significantly enhanced by this combination including the inhibition of acute TS induction and the enhanced accumulation of the cytotoxic nucleotide intermediate dUTP. These data demonstrate that HDACi repress TS expression at the level of transcription and provides the first evidence suggesting a direct mechanistic link between TS downregulation and the synergistic interaction observed between HDACi and 5-FU. This study provides rationale for the continued clinical evaluation of HDACi in combination with 5-FU-based therapies as a strategy to overcome TS-mediated resistance.
authors.affiliation: Department of Pathology, Norris Comprehensive Cancer Center/University of Southern California, Keck School of Medicine, Los Angeles, CA 90033, USA.
authors.forename: William
authors.initials: W
authors.lastname: Fazzone
authors.forename: Peter M
authors.initials: PM
authors.lastname: Wilson
authors.forename: Melissa J
authors.initials: MJ
authors.lastname: Labonte
authors.forename: Heinz-Josef
authors.initials: HJ
authors.lastname: Lenz
authors.forename: Robert D
authors.initials: RD
authors.lastname: Ladner
mesh_terms: D001483:Base Sequence; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000201:enzymology / Q000473:pathology*; D017931:DNA Primers; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005434:Flow Cytometry; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D056572:Histone Deacetylase Inhibitors; D006801:Humans; D016133:Polymerase Chain Reaction; D011743:Pyrimidines / Q000494:pharmacology*; D013940:Thymidylate Synthase / Q000235:genetics*
chemical_list: D017931:DNA Primers; D004791:Enzyme Inhibitors; D056572:Histone Deacetylase Inhibitors; D011743:Pyrimidines; D013940:Thymidylate Synthase