Objective: To study the effect of nitidine chloride (NC) on expression of DNA polymerase δ catalytic subunit P125 in breast cancer cells (MCF-7 cells)

and investigate the mechanism of NC on inhibiting proliferation of breast cancer cells. Method: Different concentrations (0.075

0.15

0.3

0.60

1.20

4.80 mg·L-1) NC groups and blank group were established. Methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay was applied to evaluate the inhibitory rate of cells after treatment with different concentrations of NC. At the same time

the clone form assay was used to further verify the inhibitory effect of different concentrations of NC on MCF-7 cells proliferation

the effects of different concentrations of NC (0.50

1.00

2.00 mg·L-1) on mRNA expressions of DNA polymerase δ catalytic subunit gene POLD1

p53 and p21 were quantified by Real-time PCR. The protein expression of P125 was detected by Western blot

and the protein expressions of p53 and p21 were detected by enzyme linked immunosorbent assay (ELISA). Result: NC had obvious inhibitory effect on MCF-7 cells in a concentration-dependent manner. NC with concentrations of 0.075

0.15

0.3

0.60

1.20

2.40

4.80 mg·L-1 had an inhibitory rate of 0.16%

6.29%

19.56%

32.17%

44.46%

73.46%and 83.21%respectively on the cells. As compared with the blank group

NC had significant inhibitory effect on the formation of cell colonies (P<0.01)

in addition

the mRNA expression of POLD1 and the protein expression of P125 in various NC groups were significantly decreased (P<0.05)

the mRNA and protein expressions of p53 were significantly up-regulated (P<0.01)

but the mRNA and protein expressions of p21 were significantly up-regulated only in the high dose NC group (P<0.01). Conclusion: NC can significantly inhibit the proliferation of MCF-7

and one of the mechanisms may be associated with up-regulating the level of p53 expression and inhibiting the expression of P125.