Objective      To investigate the inhibitory effect of metformin on prostate cancer development.       Methods      Lentivirus transfection was used to construct a LNCaP cell line with stable over-expression of interleukin 6 (IL-6)(LNCaP-IL-6)

and LNCaP cells transfected with normal lentivirus were used as control (LNCaP-ctr). Laser scanning confocal microscopy and ELISA were used to confirm IL-6 over-expression in the LNCaP cell line. The morphology of the cells was observed under an inverted microscope. The following experiments were carried out in the four groups: LNCaP-ctr group

LNCaP-ctr with metformin group

LNCaP-IL-6 group and LNCaP-IL-6 with metformin group. MTT assay was used to detect cell relative number

flow cytometry was used to analyze cell cycle

and wound healing assay was used to detect the invasive ability of LNCaP-IL-6. Western blotting was used to detect E-Cadherin and TWIST expression levels in LNCaP-ctr cells and LNCaP-IL-6 cells.       Results      Laser scanning confocal microscopy and ELISA confirmed that the LNCaP-IL-6 cells were successfully constructed

and the secretion level of IL-6 in LNCaP-IL-6 cells was 5 000 times more than that in LNCaP-ctr cells. MTT assay indicated that the relative number of LNCaP-IL-6 cells was 1.4 times as much as that of LNCaP-ctr cells

and was 1.6 times as much as  that in the LNCaP-IL-6 with metformin group after cultured for 5 d. Flow cytometry results indicated that LNCaP cell cycle was arrested at S phase. Morphology observation and Western blot analysis showed epithelia-mesenchymal transition in LNCaP-IL-6 cells. Wound healing assay proved that metformin inhibited LNCaP-IL-6 migration. Western blot  analysis  showed metformin could decrease TWIST expression and increase E-Cadherin expression.       Conclusion      Metformin reverses IL-6-induced EMT in LNCaP cells.