[Growth inhibition of breast cancer cells in vitro and in vivo by siRNA targeting signal transducers and activators of transcription 3].

Objective: To observe the effect of signal transducers and activators of transcription 3 (STAT3) gene silence on the growth of breast cancer cell line MCF7 in vitro and in vivo and discuss the feasibility and effectiveness of STAT3 used as gene therapeutic target for breast cancer.
Methods: Human breast cancer cell line MCF7 cells were divided into 3 groups: mock control group, control group transfected with scrambled sequence siRNA, and experimental group transfectod with STAT3 siRNA. The STAT3 mRNA and protein levels were detected by semi-quantity RT-PCR and Western blotting, respectively. The cell proliferation and apoptosis were examined by MTT method and flow cytometry. MCF7 cells treated with STAT3-siRNA were transplanted subcutaneously in nude mice and their tumorgenic ability was observed. The STAT3 mRNA and protein levels of the samples from nude mice of different groups were detected by semi-quantity RT-PCR and Western blotting and compared.
Results: After treatment with STAT3-siRNA, STAT3 mRNA (0.327 ± 0.020 vs. 1.035 ± 0.050, 1.093 ± 0.018) and ptotein (0.153 ± 0.006 vs. 1.320 ± 0.033, 1.374 ± 0.022) levels in the MCF7 cells transfected with STAT3-siRNA were significantly lower than that in the two control groups (P < 0.05). MTT assay showed that after transfection of the STAT3-siRNA into MCF7 cells, cell proliferation was significantly reduced and the cell growth inhibition ratio in the STAT3-siRNA group was (44.00 ± 5.10)%, significantly higher than that in the control group (16.1 ± 1.05)% (P < 0.05). Flow cytometry results suggested that more apoptosis was observed in the STAT3-siRNA group. The apoptosis rate was (14.79 ± 0.22)%, much higher than that in the control group [(7.06 ± 0.71)%, (8.45 ± 0.43)%, P < 0.05]. The tumor growth in the experimental group was significantly slower than that in the two control groups. 0n the 22th day after transplantation, the tumor weight [(21.4 ± 10.6) mg vs. (88.6 ± 12.2) mg, (57.2 ± 21.9) mg] and volume [(41.15 ± 12.17) mm³ vs. (118.45 ± 24.68) mm³, (101.36 ± 21.90) mm³] in the experimental group were significantly lower than that in the two control groups (P < 0.05). The STAT3 mRNA and protein levels of the samples from nude mice in the experimental group were significantly lower than that in the two control groups.
Conclusion: siRNA targeting STAT3 can inhibit the proliferation of MCF7 cells in vitro and in vivo. STAT3 may become a novel therapeutic target for breast cancer.