title: Combined effect of tumor necrosis factor-alpha and ionizing radiation on the induction of apoptosis in 5637 bladder carcinoma cells.
abstract: OBJECTIVE
  Apoptosis can be induced by distinct but overlapping pathways. Ionizing radiation induces apoptosis by an "intrinsic", mitochondria-dependent pathway. Ligation of tumor necrosis factor-(TNF-)alpha, FAS (CD95) or TRAIL receptors are typical representatives of an extrinsic, death-receptor-mediated pathway. In this study the effect of irradiation, treatment with the cytokine TNF-alpha, or a combination of both on the induction of apoptosis and clonogenic survival of bladder carcinoma cells was investigated.
  
  
  METHODS
  5637 bladder carcinoma cells were treated with different concentrations of recombinant TNF-alpha (0-10 ng/ml), irradiated with single doses ranging from 0.5 to 10 Gy, or a combination of both modalities. Apoptotic cells were quantified by the TUNEL assay up to 96 h following treatment, clonogenic cell survival by a clonogenic assay. Synergistic effects of both modalities were evaluated using isobolographic analysis.
  
  
  RESULTS
  Irradiation of 5637 carcinoma cells resulted in a discontinuous dose dependence of the apoptotic fraction with a pronounced increase in the range of 0-2 Gy and a slighter increase at 2-10 Gy. The percentage of apoptotic carcinoma cells also increased continuously after treatment with lower concentrations of TNF-alpha reaching a plateau at concentrations of 5.0-10.0 ng/ml. Isobolographic analysis revealed a supraadditive interrelationship between irradiation and TNF-alpha in the range between 0.005 and 0.5 ng/ml, and an additive effect for TNF-alpha concentrations>0.5 ng/ml. The additive effects were confirmed in clonogenic survival assays with reduced survival fractions following combined TNF-alpha administration and irradiation.
  
  
  CONCLUSIONS
  The combination of two apoptosis-inducing modalities resulted in a synergistic effect on the induction of apoptosis in 5637 bladder carcinoma cells. Although a radiosensitizing effect still has to be proven in animal models, combined-modality treatment may increase the therapeutic effectiveness of irradiation in bladder cancer.
authors.affiliation: Department of Radiation Oncology, Friedrich Alexander University, Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Sammy A
authors.initials: SA
authors.lastname: Baierlein
authors.forename: Luitpold
authors.initials: L
authors.lastname: Distel
authors.forename: Renate
authors.initials: R
authors.lastname: Sieber
authors.forename: Christian
authors.initials: C
authors.lastname: Weiss
authors.forename: Claus
authors.initials: C
authors.lastname: Rödel
authors.forename: Rolf
authors.initials: R
authors.lastname: Sauer
authors.forename: Franz
authors.initials: F
authors.lastname: Rödel
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D045744:Cell Line, Tumor; D003114:Colony-Forming Units Assay; D003131:Combined Modality Therapy; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D020287:In Situ Nick-End Labeling; D011879:Radiotherapy Dosage; D013997:Time Factors; D016896:Treatment Outcome; D014409:Tumor Necrosis Factor-alpha / Q000008:administration & dosage / Q000627:therapeutic use*; D014410:Tumor Stem Cell Assay; D001749:Urinary Bladder Neoplasms / Q000188:drug therapy* / Q000473:pathology / Q000532:radiotherapy*
chemical_list: D014409:Tumor Necrosis Factor-alpha