title: Radiosensitizing effect of epothilone B on human epithelial cancer cells.
abstract: BACKGROUND
  A combined modality treatment employing radiation and chemotherapy plays a central role in the management of solid tumors. In our study, we examined the cytotoxic and radiosensitive effect of the microtubule stabilizer epothilone B on two human epithelial tumor cell lines in vitro and its influence on the microtubule assembly.
  
  
  METHODS
  Cancer cells were treated with epothilone B in proliferation assays and in combination with radiation in colony-forming assays. For the analysis of ionizing radiation-induced DNA damage and the influence of the drug on its repair a γH2AX foci assay was used. To determine the effect of epothilone B on the microtubule assembly in cells and on purified tubulin, immunofluorescence staining and tubulin polymerization assay, respectively, were conducted.
  
  
  RESULTS
  Epothilone B induced a concentration- and application-dependent antiproliferative effect on the cells, with IC(50) values in the low nanomolar range. Colony forming assays showed a synergistic radiosensitive effect on both cell lines which was dependent on incubation time and applied concentration of epothilone B. The γH2AX assays demonstrated that ionizing radiation combined with the drug resulted in a concentration-dependent increase in the number of double-strand breaks and suggested a reduction in DNA repair capacity. Epothilone B produced enhanced microtubule bundling and abnormal spindle formation as revealed by immunofluorescence microscopy and caused microtubule formation from purified tubulin.
  
  
  CONCLUSIONS
  The results of this study showed that epothilone B displays cytotoxic antitumor activity at low nanomolar concentrations and also enhances the radiation response in the tumor cells tested; this may be induced by a reduced DNA repair capacity triggered by epothilone B. It was also demonstrated that epothilone B in fact targets microtubules in a more effective manner than paclitaxel.
authors.affiliation: Department of Radiotherapy and Radiation Oncology, University of Rostock, Südring 75, Rostock, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Baumgart
authors.forename: G
authors.initials: G
authors.lastname: Klautke
authors.forename: S
authors.initials: S
authors.lastname: Kriesen
authors.forename: S A
authors.initials: SA
authors.lastname: Kuznetsov
authors.forename: D G
authors.initials: DG
authors.lastname: Weiss
authors.forename: R
authors.initials: R
authors.lastname: Fietkau
authors.forename: G
authors.initials: G
authors.lastname: Hildebrandt
authors.forename: K
authors.initials: K
authors.lastname: Manda
mesh_terms: D000970:Antineoplastic Agents / Q000008:administration & dosage; D045744:Cell Line, Tumor; D059248:Chemoradiotherapy / Q000379:methods; D003131:Combined Modality Therapy; D004305:Dose-Response Relationship, Drug; D034261:Epothilones / Q000008:administration & dosage*; D006801:Humans; D009375:Neoplasms, Glandular and Epithelial / Q000188:drug therapy* / Q000473:pathology / Q000532:radiotherapy*; D011829:Radiation Dosage; D011836:Radiation Tolerance / Q000187:drug effects* / Q000502:physiology*; D011838:Radiation-Sensitizing Agents / Q000008:administration & dosage
chemical_list: D000970:Antineoplastic Agents; D034261:Epothilones; D011838:Radiation-Sensitizing Agents; C093788:epothilone B