Enhanced radiosensitization of p53 mutant cells by oleamide.
OBJECTIVE
Effect of oleamide, an endogenous fatty-acid primary amide, on tumor cells exposed to ionizing radiation (IR) has never before been explored.


METHODS
NCI H460, human lung cancer cells, and human astrocytoma cell lines, U87 and U251, were used. The cytotoxicity of oleamide alone or in combination with IR was determined by clonogenic survival assay, and induction of apoptosis was estimated by FACS analysis. Protein expressions were confirmed by Western blotting, and immunofluorescence analysis of Bax by use of confocal microscopy was also performed. The combined effect of IR and oleamide to suppress tumor growth was studied by use of xenografts in the thighs of nude mice.


RESULTS
Oleamide in combination with IR had a synergistic effect that decreased clonogenic survival of lung-carcinoma cell lines and also sensitized xenografts in nude mice. Enhanced induction of apoptosis of the cells by the combined treatment was mediated by loss of mitochondrial membrane potential, which resulted in the activation of caspase-8, caspase-9, and caspase-3 accompanied by cytochrome c release and Bid cleavage. The synergistic effects of the combined treatment were more enhanced in p53 mutant cells than in p53 wild-type cells. In p53 wild-type cells, both oleamide and radiation induced Bax translocation to mitochondria. On the other hand, in p53 mutant cells, radiation alone slightly induced Bax translocation to mitochondria, whereas oleamide induced a larger translocation.


CONCLUSIONS
Oleamide may exhibit synergistic radiosensitization in p53 mutant cells through p53-independent Bax translocation to mitochondria.
Laboratory of Radiation Effect, Korea Institute of Radiological and Medical Sciences, Seoul, Korea.
Yoon-Jin
YJ
Lee
Da Yeon
DY
Chung
Su-Jae
SJ
Lee
Gil
G
Ja Jhon
Yun-Sil
YS
Lee
D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D001254:Astrocytoma / Q000188:drug therapy / Q000532:radiotherapy; D045744:Cell Line, Tumor; D053938:DNA Fragmentation; D004354:Drug Screening Assays, Antitumor / Q000379:methods; D016158:Genes, p53; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000532:radiotherapy*; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D051336:Mitochondrial Membranes / Q000187:drug effects / Q000528:radiation effects; D009154:Mutation; D009829:Oleic Acids / Q000627:therapeutic use*; D017239:Paclitaxel / Q000627:therapeutic use; D010539:Permeability / Q000187:drug effects / Q000528:radiation effects; D011838:Radiation-Sensitizing Agents / Q000627:therapeutic use*; D014183:Transplantation, Heterologous; D051028:bcl-2-Associated X Protein / Q000378:metabolism
C494826:BAX protein, human; D009829:Oleic Acids; D011838:Radiation-Sensitizing Agents; D051028:bcl-2-Associated X Protein; C029407:oleylamide; D017239:Paclitaxel