The aim of the present study was to investigate the anticancer effect of quercetin (QC) in the human lung cancer cell line A-549 and further study the mechanism of apoptosis induction by QC. Low differentiation potential A-549 human lung cancer cells were treated with QC at different doses and for different times, and the growth inhibitory rates were detected by MTT assay. Apoptosis induced by QC in A-549 cells was observed by Annexin V/PI double staining and flow cytometric assay. The relative tumor growth ratio of the treated/control tumors (T/C) (%) was chosen to represent the tumor growth inhibition of A-549 cell nude mouse xenografts by QC. Apoptosis of the nude mouse xenografts was observed by Annexin V/PI double staining and flow cytometric assay and DNA fragmentation assay. To further determine the molecular mechanism of apoptosis induced by QC, changes in the expression of bcl-2 and bax genes were detected by RT-PCR. Following incubation with QC, the cell growth of the low differentiation potential A-549 human lung cancer cells was dramatically inhibited in a dose-dependent manner. After the cells were exposed to QC for 24, 48 and 72 h, the IC50 value was 1.02±0.05, 1.41±0.20 and 1.14±0.19 µmol/l, respectively. Apoptosis in the A-549 cells induced by QC was noted. The apoptotic subpopulation of A-549 cells was approximately 12.96 and 24.58%, respectively, when cells were incubated with 1.2 µmol/l QC for 48 and 72 h. T/C (%) of A-549 nude mouse xenografts was 44.3, when the nude mice were treated with QC (8 mg/kg). Meanwhile, apoptosis induced by QC was observed in the A-549 nude mouse xenografts. Increased expression of the bax gene and decreased expression of the bc1-2 gene were noted using RT-PCR. Our results provide further evidence of the growth inhibition of the A-549 human lung adenocarcinoma cancer cell line by QC. This effect is associated with the induction of apoptosis in A-549 cells and the molecular mechanism may be related to the reduction in expression of the apoptosis-regulating gene bcl-2, and increase in expression of the apoptosis-regulating gene bax. These results were also confirmed in vivo.

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