Irradiation promotes Akt-targeting therapeutic gene delivery to the tumor vasculature.
OBJECTIVE
To determine whether radiation-induced increases in nitric oxide (NO) production can influence tumor blood flow and improve delivery of Akt-targeting therapeutic DNA lipocomplexes to the tumor.


METHODS
The contribution of NO to the endothelial response to radiation was identified using NO synthase (NOS) inhibitors and endothelial NOS (eNOS)-deficient mice. Reporter-encoding plasmids complexed with cationic lipids were used to document the tumor vascular specificity and the efficacy of in vivo lipofection after irradiation. A dominant-negative Akt gene construct was used to evaluate the facilitating effects of radiotherapy on the therapeutic transgene delivery.


RESULTS
The abundance of eNOS protein was increased in both irradiated tumor microvessels and endothelial cells, leading to a stimulation of NO release and an associated increase in tumor blood flow. Transgene expression was subsequently improved in the irradiated vs. nonirradiated tumor vasculature. This effect was not apparent in eNOS-deficient mice and could not be reproduced in irradiated cultured endothelial cells. Finally, we combined low-dose radiotherapy with a dominant-negative Akt gene construct and documented synergistic antitumor effects.


CONCLUSIONS
This study offers a new rationale to combine radiotherapy with gene therapy, by directly exploiting the stimulatory effects of radiation on NO production by tumor endothelial cells. The preferential expression of the transgene in the tumor microvasculature underscores the potential of such an adjuvant strategy to limit the angiogenic response of irradiated tumors.
Sonveaux
Pierre
P
Unit of Pharmacology and Therapeutics, Université Catholique de Louvain Medical School, Brussels, Belgium.
Frérart
Françoise
F
Bouzin
Caroline
C
Brouet
Agnès
A
Dewever
Julie
J
Jordan
Bénédicte F
BF
Gallez
Bernard
B
Feron
Olivier
O
D000818:Animals; D003131:Combined Modality Therapy; D042783:Endothelial Cells / Q000378:metabolism / Q000528:radiation effects; D004730:Endothelium, Vascular / Q000502:physiology / Q000528:radiation effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018014:Gene Transfer Techniques; D015316:Genetic Therapy / Q000379:methods*; D049452:Green Fluorescent Proteins / Q000235:genetics; D008114:Liver Neoplasms, Experimental / Q000098:blood supply / Q000378:metabolism / Q000628:therapy; D008297:Male; D051379:Mice; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009369:Neoplasms / Q000098:blood supply* / Q000378:metabolism / Q000628:therapy*; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D052250:Nitric Oxide Synthase Type III / Q000172:deficiency / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics* / Q000378:metabolism; D011879:Radiotherapy Dosage; D014664:Vasodilation
D004791:Enzyme Inhibitors; D049452:Green Fluorescent Proteins; D009569:Nitric Oxide; C496314:NOS3 protein, human; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; D051057:Proto-Oncogene Proteins c-akt; D019331:NG-Nitroarginine Methyl Ester