OBJECTIVE: To evaluate the synergistic inhibitory effects of Sijunzi decoction combined with gefitinib on non-small cell lung cancer PC9 cells by using the principle of intermediate effects

and to explore its effects on cell apoptosis and cell cycle.METHODS: CellTiter-Glo method was used to detect the effects of Sijunzi decoction and gefitinib on the proliferation of PC9 cells.Calcusyn software was used to evaluate the synergistic effects of the two drugs according to the principle of intermediate effects.The flow cytometry was used to detect the effects of the two drugs on apoptosis and cell cycle.RESULTS: Sijunzi decoction and gefitinib inhibited the proliferation of PC9 cells in a dose-dependent manner.When the two drugs were used in combination on PC9 cells

the IC

50

decreased from（0.75±0.26） μg/L to（0.10±0.02） μg/L

the difference was statistically significant compared with gefitinib alone（P

<

0.05）.The results of flow cytometry showed that after the combination of two drugs

the proportion of apoptosis increased significantly

and the percentage of cells in the G

2

/M phase was significantly different from that of the single drug（P

<

0.05）.CONCLUSIONS: Sijunzi decoction combined with gefitinib have synergistic inhibitory effect on non-small cell lung cancer PC9 cells

and the synergistic mechanism may be related to the induction of apoptosis and G

2

/M phase block.