Endothelial membrane remodeling is obligate for anti-angiogenic radiosensitization during tumor radiosurgery

PLoS One. 2010 Aug 19;5(8):e12310. doi: 10.1371/journal.pone.0012310.


Background: While there is significant interest in combining anti-angiogenesis therapy with conventional anti-cancer treatment, clinical trials have as of yet yielded limited therapeutic gain, mainly because mechanisms of anti-angiogenic therapy remain to a large extent unknown. Currently, anti-angiogenic tumor therapy is conceptualized to either "normalize" dysfunctional tumor vasculature, or to prevent recruitment of circulating endothelial precursors into the tumor. An alternative biology, restricted to delivery of anti-angiogenics immediately prior to single dose radiotherapy (radiosurgery), is provided in the present study.

Methodology/principal findings: Genetic data indicate an acute wave of ceramide-mediated endothelial apoptosis, initiated by acid sphingomyelinase (ASMase), regulates tumor stem cell response to single dose radiotherapy, obligatory for tumor cure. Here we show VEGF prevented radiation-induced ASMase activation in cultured endothelium, occurring within minutes after radiation exposure, consequently repressing apoptosis, an event reversible with exogenous C(16)-ceramide. Anti-VEGFR2 acts conversely, enhancing ceramide generation and apoptosis. In vivo, MCA/129 fibrosarcoma tumors were implanted in asmase(+/+) mice or asmase(-/-) littermates and irradiated in the presence or absence of anti-VEGFR2 DC101 or anti-VEGF G6-31 antibodies. These anti-angiogenic agents, only if delivered immediately prior to single dose radiotherapy, de-repressed radiation-induced ASMase activation, synergistically increasing the endothelial apoptotic component of tumor response and tumor cure. Anti-angiogenic radiosensitization was abrogated in tumors implanted in asmase(-/-) mice that provide apoptosis-resistant vasculature, or in wild-type littermates pre-treated with anti-ceramide antibody, indicating that ceramide is necessary for this effect.

Conclusions/significance: These studies show that angiogenic factors fail to suppress apoptosis if ceramide remains elevated while anti-angiogenic therapies fail without ceramide elevation, defining a ceramide rheostat that determines outcome of single dose radiotherapy. Understanding the temporal sequencing of anti-angiogenic drugs and radiation enables optimized radiosensitization and design of innovative radiosurgery clinical trials.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Monoclonal / immunology
  • Antibodies, Monoclonal / pharmacology
  • Antibodies, Monoclonal / therapeutic use
  • Apoptosis / drug effects
  • Apoptosis / radiation effects
  • Cell Death / drug effects
  • Cell Death / radiation effects
  • Cell Line, Tumor
  • Cell Membrane / drug effects*
  • Cell Membrane / metabolism
  • Cell Membrane / radiation effects
  • Cell Survival / drug effects
  • Cell Survival / radiation effects
  • Ceramides / metabolism
  • Endothelial Cells / pathology*
  • Enzyme Activation / drug effects
  • Enzyme Activation / radiation effects
  • Fibroblast Growth Factor 2 / pharmacology
  • Humans
  • Mice
  • Neoplasms / blood supply*
  • Neoplasms / metabolism
  • Neoplasms / pathology*
  • Neoplasms / surgery
  • Neovascularization, Pathologic / drug therapy*
  • Radiation-Sensitizing Agents / pharmacology*
  • Radiation-Sensitizing Agents / therapeutic use
  • Radiosurgery*
  • Radiotherapy Dosage
  • Signal Transduction / drug effects
  • Signal Transduction / radiation effects
  • Sphingomyelin Phosphodiesterase / metabolism
  • Time Factors
  • Vascular Endothelial Growth Factor A / immunology
  • Vascular Endothelial Growth Factor A / pharmacology


  • Antibodies, Monoclonal
  • Ceramides
  • DC101 monoclonal antibody
  • Radiation-Sensitizing Agents
  • Vascular Endothelial Growth Factor A
  • Fibroblast Growth Factor 2
  • Sphingomyelin Phosphodiesterase