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



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.



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.
Truman
Jean-Philip
JP
Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America.
García-Barros
Mónica
M
Kaag
Matthew
M
Hambardzumyan
Dolores
D
Stancevic
Branka
B
Chan
Michael
M
Fuks
Zvi
Z
Kolesnick
Richard
R
Haimovitz-Friedman
Adriana
A
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D016923:Cell Death / Q000187:drug effects / Q000528:radiation effects; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D002518:Ceramides / Q000378:metabolism; D042783:Endothelial Cells / Q000473:pathology*; D004789:Enzyme Activation / Q000187:drug effects / Q000528:radiation effects; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology; D006801:Humans; D051379:Mice; D009369:Neoplasms / Q000098:blood supply* / Q000378:metabolism / Q000473:pathology* / Q000601:surgery; D009389:Neovascularization, Pathologic / Q000188:drug therapy*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology* / Q000627:therapeutic use; D016634:Radiosurgery; D011879:Radiotherapy Dosage; D015398:Signal Transduction / Q000187:drug effects / Q000528:radiation effects; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism; D013997:Time Factors; D042461:Vascular Endothelial Growth Factor A / Q000276:immunology / Q000494:pharmacology
D000911:Antibodies, Monoclonal; D002518:Ceramides; C511761:DC101 monoclonal antibody; D011838:Radiation-Sensitizing Agents; D042461:Vascular Endothelial Growth Factor A; D016222:Fibroblast Growth Factor 2; D013108:Sphingomyelin Phosphodiesterase
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