Combined effect of tumor necrosis factor-alpha and ionizing radiation on the induction of apoptosis in 5637 bladder carcinoma cells

Strahlenther Onkol. 2006 Aug;182(8):467-72. doi: 10.1007/s00066-006-1475-2.


Background and purpose: 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.

Material and 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.

Conclusion: 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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis* / drug effects
  • Apoptosis* / physiology
  • Apoptosis* / radiation effects
  • Cell Line, Tumor
  • Colony-Forming Units Assay
  • Combined Modality Therapy
  • Dose-Response Relationship, Drug
  • Dose-Response Relationship, Radiation
  • Humans
  • In Situ Nick-End Labeling
  • Radiotherapy Dosage
  • Time Factors
  • Treatment Outcome
  • Tumor Necrosis Factor-alpha / administration & dosage
  • Tumor Necrosis Factor-alpha / therapeutic use*
  • Tumor Stem Cell Assay
  • Urinary Bladder Neoplasms / drug therapy*
  • Urinary Bladder Neoplasms / pathology
  • Urinary Bladder Neoplasms / radiotherapy*


  • Tumor Necrosis Factor-alpha