Radiation sensitivity of human carcinoma cells transfected with small interfering RNA targeted against cyclooxygenase-2.
OBJECTIVE
Cyclooxygenase-2 (COX-2) is considered a potential target for cancer therapy, because COX-2 levels are elevated in the majority of human tumors compared with the normal tissues. COX-2 inhibitors inhibit tumor growth and enhance radiation response in vitro as well as in vivo. However, the precise role of COX-2 in radiation response is not clear. The purpose of the present study was to investigate the in vitro radiosensitivity of tumor cells as a function of COX-2 expression.


RESULTS
PC3 and HeLa cells express COX-2 protein constitutively. We silenced the COX-2 gene in these cells using small interfering RNA (siRNA). Transfection of PC3 cells with 100 nmol/L siRNA targeted against COX-2 resulted in reduction of COX-2 protein by 75% and inhibition of arachidonic acid-induced prostaglandin E2 synthesis by approximately 50% compared with the vehicle control. In HeLa cells, 100 nmol/L COX-2 siRNA inhibited COX-2 protein expression by 80%. Cell cycle analysis showed that transfection with COX-2 siRNA did not alter the cell cycle distribution. Radiosensitivity was determined by clonogenic cell survival assay. There was no significant difference in the radiosensitivity of cells in which COX-2 was silenced compared with the cells transfected vehicle or with negative control siRNAs (enhancement ratio = 1.1).


CONCLUSIONS
These data indicate that the in vitro radiosensitivity of tumor cells is minimally dependent on the cellular COX-2 status. Given that a number of potential mechanisms are attributed to COX-2 inhibitors for radiosensitization, specific intervention of COX-2 by RNA interference could help elucidate the precise role of COX-2 in cancer therapy and to optimize strategies for COX-2 inhibition.
Palayoor
Sanjeewani T
ST
Radiation Oncology Branch, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland 20892-1002, USA. Palayoor@mail.nih.gov
Arayankalayil
Moly J
MJ
Shoaibi
Azadeh
A
Coleman
C Norman
CN
D015153:Blotting, Western; D002277:Carcinoma / Q000532:radiotherapy*; D002453:Cell Cycle; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002470:Cell Survival; D051546:Cyclooxygenase 2 / Q000378:metabolism*; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D015232:Dinoprostone / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D020868:Gene Silencing; D006367:HeLa Cells; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D009578:Nitrobenzenes / Q000494:pharmacology; D011453:Prostaglandins / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000378:metabolism / Q000532:radiotherapy*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism*; D011836:Radiation Tolerance; D013449:Sulfonamides / Q000494:pharmacology; D014162:Transfection
D016861:Cyclooxygenase Inhibitors; D009578:Nitrobenzenes; D011453:Prostaglandins; D034741:RNA, Small Interfering; D013449:Sulfonamides; C080955:N-(2-cyclohexyloxy-4-nitrophenyl)methanesulfonamide; D051546:Cyclooxygenase 2; D015232:Dinoprostone