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[Radiosensitization of nasopharyngeal carcinoma cell line CNE1 by inhibiting the expression of ATM/PI3K functional region].

BACKGROUND & OBJECTIVE
It is reported that ATM gene is closely correlated to cellular radiosensitivity in several malignant tumors. Suppression of ATM protein expression leads to cellular radiosensitization. This study was to determine whether this effect also exists in nasopharyngeal carcinoma (NPC) cell line CNE1 by inhibiting the expression of ATM protein through antisense RNA of ATM/PI3K region, which is the most important functional fragment of ATM gene.


METHODS
The recombinant pDOR-atm expressing antisense RNA of ATM/PI3K segment was constructed with retroviral vector pDOR. CNE1 cells were stably transfected with pDOR-atm by cationic liposome and named CNE1/pDOR-atm. Semi-quantitive RT-PCR was used to detect the level of ATM mRNA. Flow cytometry (FCM) was employed to analyze the percentage of positive cells and mean fluorescence density of protein expressing ATM. Cellular radiosensitivity was evaluated by colony survival assay (CSA) and linear-quadratic model in both CNE1/ pDOR-atm and control cells.


RESULTS
The level of ATM mRNA index (RI) was 0.23+/-0.02 in CNE1/pDOR-atm group, and 0.51+/-0.03 in control group (P<0.05). The percentage of positive cells and mean fluorescence density of proteins expressing ATM were 70.8% and 1.81+/-0.12 in CNE1/pDOR-atm group, while 99.3% and 4.51+/-0.18 in control group(P<0.01). The expression of ATM mRNA and protein was inhibited by antisense RNA. The alpha value (one function from linear-quadratic model) of CNE1/pDOR-atm group was 0.40 Gy(-1), while it was 0.36 Gy(-1) in control group. The radiosensitizing ratio of surviving fraction at 2 Gy (SF(2)) was 3.0, indicating that antisense RNA group was more radiosensitive to X-ray than the controls.


CONCLUSION
NPC cell line CNE1 could be radiosensitized by the down-regulation of ATM/PI3K expression.