title: Preclinical studies of vorinostat (suberoylanilide hydroxamic acid) combined with cytosine arabinoside and etoposide for treatment of acute leukemias.
abstract: OBJECTIVE
  Vorinostat [suberoylanilide hydroxamic acid (SAHA)] is a potent histone deacetylase inhibitor with promising clinical efficacy as an anticancer agent. In this preclinical study, we evaluated combining cytosine arabinoside [1-beta-D-arabinofuranosylcytosine (ara-C)] and/or etoposide with vorinostat for use in the treatment of acute leukemias.
  
  
  METHODS
  Cell survival was examined in vitro in HL-60 human myeloid leukemia cells and K562 myeloid blast crisis chronic myelogenous leukemia cells, using the 2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide inner salt and/or fluorescein diacetate/propidium iodide assays. Drug interactions were analyzed by the combination index method (CalcuSyn) and by a novel statistical method that we developed (SynStat). Cell cycle phase distribution was measured by flow cytometry.
  
  
  RESULTS
  Cytotoxic antagonism resulted when vorinostat was combined concomitantly with ara-C; however, when vorinostat was given first followed by a drug-free interval before ara-C treatment, this sequential combination was mostly synergistic. Etoposide combined with vorinostat was additive to synergistic, and the synergism became more pronounced when etoposide was given after vorinostat. Cell cycle analyses revealed that the sequence-dependent interaction of vorinostat and ara-C or etoposide reflected the arrest of cells in G1 or G2 phase during vorinostat treatment and recovery into S phase after removal of vorinostat.
  
  
  CONCLUSIONS
  These findings using two independent methods to assess drug combination effects provide a preclinical rationale for phase I trials of the sequential combination of vorinostat followed by ara-C and etoposide in patients with advanced or refractory leukemias. CalcuSyn findings were concordant with those of SynStat, validating the use of the latter in analyzing drug interactions.
authors.affiliation: Program in Experimental Therapeutics, University of Maryland Marlene and Stewart Greenebaum Cancer Center, and Division of Hematology and Oncology, Department of Medicine, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
authors.forename: Ken
authors.initials: K
authors.lastname: Shiozawa
authors.forename: Takeo
authors.initials: T
authors.lastname: Nakanishi
authors.forename: Ming
authors.initials: M
authors.lastname: Tan
authors.forename: Hong-Bin
authors.initials: HB
authors.lastname: Fang
authors.forename: Wen-chyi
authors.initials: WC
authors.lastname: Wang
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Edelman
authors.forename: David
authors.initials: D
authors.lastname: Carlton
authors.forename: Ivana
authors.initials: I
authors.lastname: Gojo
authors.forename: Edward A
authors.initials: EA
authors.lastname: Sausville
authors.forename: Douglas D
authors.initials: DD
authors.lastname: Ross
mesh_terms: D000208:Acute Disease; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D001752:Blast Crisis; D002470:Cell Survival / Q000187:drug effects; D003561:Cytarabine / Q000008:administration & dosage; D004353:Drug Evaluation, Preclinical; D004357:Drug Synergism; D005047:Etoposide / Q000008:administration & dosage; D016193:G1 Phase / Q000187:drug effects; D006801:Humans; D006877:Hydroxamic Acids / Q000008:administration & dosage; D007951:Leukemia, Myeloid / Q000188:drug therapy* / Q000473:pathology; D016196:S Phase / Q000187:drug effects; D014407:Tumor Cells, Cultured; D000077337:Vorinostat
chemical_list: D006877:Hydroxamic Acids; D003561:Cytarabine; D000077337:Vorinostat; D005047:Etoposide