Objective: To study the inhibitory effect and mechanism of ethyl acetate fraction(EFA) extracted from Daibaijie on A549 human lung cancer cell line in nude mice. Method: Xenotransplanted tumor models of A549 tumor cells in nude mice were established

and were randomly divided into model group

EFA high-dose

middle-dose and low-dose (200

100

50 mg·kg-1) groups

Xiaoaiping group and cyclophosphamide group. There were six mice in each group. Tumor weights were observed to calculate the inhibitory rate after three weeks of administration. The apoptosis rates were measured by terminal dexynucleotidyl transferase(TdT)-mediated dUTP nick end labeling (TUNEL) staining method and the protein expression levels of p53

B-cell lymphoma-2 (Bcl-2) and Bcl-2 associated X protein (Bax) were detected by immunhistochemical staining (IHC). Result: As compared with the model group

EFA can significantly inhibit the growth of A549 xenografts in a dose manner (P < 0.05

P < 0.01). TUNEL assay results showed that the apoptosis rate of tumor cells increased significantly after treatment with EFA. The immunohistochemical results showed that

as compared with model group

the protein expression level of Bcl-2 was decreased

while the expression levels of p53 and Bax were increased in nude mice after treatment with EFA. Conclusion: EFA has a significant inhibitory effect on human lung cancer A549 in nude mice. The mechanism may be related to up-regulating the expression of p53 and Bax protein

decreasing the expression of Bcl-2 protein

and inducing apoptosis of lung cancer cells.